Response of Typical Phytoremediation Species Vallisneria to Four Key Factors Under Eutrophic Water Conditions: A Review - Juniper Publishers

Ecology & Conservation Science: Open Access - Juniper Publishers

Abstract

In China, eutrophication is a major problem in watershed. Phytoremediation is a simple, cheap, and environmentally friendly method. As the main producer of aquatic ecosystems, submerged plants play an important role in phytoremediation. Vallisneria is a representative submerged plant, however, the growth of Vallisneria is mainly affected by many factors. In this article, it investigated four key factors, such as water depth, water movement, benthos and planting method and provided some theoretical support for the maintenance and restoration of submerged plants under ecological restoration.

Keywords: Water depth; Water movement; Benthos; Planting method; Vallisneria

Introduction

According to the Report on the State of the Ecology and Environment in China in 2017, among 109 lakes (reservoirs) whose nutritional status is monitored, 9 were under oligotrophic status, 67 were under mesotrophic status, 29 were under slight eutrophication, and 4 were under intermediate eutrophication. Excessive discharge of nitrogen (N) and phosphorus (P) is the main cause of surface water eutrophication [1,2] which leads to the deterioration of the ecological environment of lakes and rivers [3]. Eutrophication has led to the transformation of lakes from grass-dominated or algae-dominated to cyanobacteria-dominated, resulting in the destruction the ecological balance of the lake [4]. The high phosphorus concentration in the water body is considered to be a key factor in the outbreak of cyanobacteria. The outbreak of cyanobacteria not only reduces the light transmittance of the lake, but also secretes harmful allelochemicals, which leads to the reduction of species in the water ecosystem [5]. Phytoremediation is a simple, cheap, and environmentally friendly method to convert excess nutrients into valuable plant biomass [6], plays an important role in regulating lake functions and maintaining ecological balance [7]. As the main producer of aquatic ecosystem, submerged plants can release allelochemicals to inhibit the growth of cyanobacteria [8-10]，They also provide a habitat for fish, reduce the turbidity of water caused by phytoplankton [11], and provide natural substrates for the growth of bacteria, algae and other microorganisms, forming biofilms or epiphytic microbial communities [12], effectively inhibiting the formation of harmful algal blooms [13], Hence, submerged plants has been considered as one of the best options for improving the eutrophication of shallow lakes [14] and has been widely planted to restore the ecological environment of eutrophic water [15,16]. However, the growth of submerged plants is mainly affected by non-biological factors such as water depth, water movement, water temperature, nutrient content, etc. [17]. In addition, the biofilm on the surface of submerged plants will also affect the growth [18]. The combination of biofilm and plants can improve water quality [19]. Vallisneria is one of the submerged plants that exists widely in China and has good nitrogen and phosphorus removal ability [20]. Studies have shown that water depth, water movement, benthos have an important influence on the growth of Vallisneria.

The Effect of Water Depth

Water depth will affect the underwater light, turbidity, distribution of attachments on the surface of aquatic plants and the growth of submerged plants [21,22]. The low light intensity brought by the increase of water depth will result in the winter buds and biomass of Vallisneria decrease sharply [23]. The morphology and structure of the biofilm on the leaf surface, such as the growth of aerobic/anaerobic bacteria and algae on the leaf surface were also affected by water depth. The research of our group showed that water depth affected the biofilm of submerged plants and microbial population structure. Submerged plants were stressed in both shallow and deep water. Thus, the best planting depth was 0.9m-1.2m for vallisneria [24].

The Effect of Water Movement

There will be various changes in the biofilm-water interface under flowing water conditions, including bacterial density, changes in microbial activity through attachment or detachment and production of extracellular polymeric substance [25,26]. As the water flow increases, the thickness of the biofilm decreases, the morphology of the biofilm changes and the diversity of bacteria increases [27]. Water flow affects the biofilm by regulating the growth of aquatic plant leaves to provide an environment for microbial aggregation on the surface of the leaves. Furthermore, the flexibility of plant leaves reduces the rate of water flow and the shear force at the water leaf interface to make the formation of biofilms easier [28]. The research of our group showed that the combination of Vallisneria and its leaf biofilm played a significant role in the removal of total phosphorus from eutrophic water. In addition, the eutrophic water flow could induce the oxidative stress and antioxidant defense system response in plant leaves [29].

The Effect of Benthos

Benthos promote the circulation of nutrients in the water body through absorption and excretion, affecting the growth of submerged plants by preying on submerged plant biofilms [30] The biofilm on the surface of submerged plants plays an important role in the interaction between benthos and submerged plants. Excessive biofilm may have negative effects on submerged plants by reducing light conditions and nutrient utilization [31-33] Some studies have shown that snails can feed on the periphyton layers on the surface of submerged plants, improving the ability of submerged plants to absorb light and nutrients, promoting the growth of submerged plants by regulating the local water environment through metabolism. However, some studies have also shown that snails restrict the growth of submerged plants and cause damage [34]. The research of our group showed that the presence of snails was beneficial to the growth of submerged plants. The increase of snail density was beneficial to the growth of submerged plants when the density of snails was below the medium density condition. There has no significant effect on the growth of submerged plants when the snails change from medium density to high density [35].

The Effect of Planting Method

The planting method of Vallisneria should be determined according to the water conservancy, water quality and the characteristics of planting substrate. Traditional planting methods such as sowing method, cutting method, sinking method have their advantages and disadvantages. The survival rate of the cutting method was higher than that of the sinking method, the sowing method was the lowest, and there was no significant difference among the biomass of individual plants [36]. However, the cutting method requires a lot of manpower and material resources and the operation is difficult. The sowing method is simple but is restricted by environmental conditions and the survival rate is not high. The sinking method causes damage to plants and soil erosion reduces the survival rate of plants. The research of our group shows that the agar-based method effectively improved the photosynthesis of plants, reduced physical damage to plants, weakened the stress response of the antioxidant system and ultimately promoted plant growth. This study indicated that the agar-based method may improve plant performance over existing mud-sinking approaches, which may optimize the restoration of aquatic ecosystems [37].

Conclusion

This review indicated that the water depth, water movement, benthos and planting method could affect vallisneria growth status including shoot height, root height and total chlorophyll. Moreover, the amount of biofilm and the structure of microbial community on vallisneria leaves have also been significantly changed. For water depth, the optimal planting depth of vallisneria for ecological restoration was 0.9-1.2 m below the water surface. For water movement, the combination of periphyton biofilm and vallisneria played an important role in the removal of total phosphorus from flowing eutrophic water. For benthos, the presence of snails was beneficial to the growth of submerged plants. For planting method, the agar-based method promoted plant growth and photosynthesis more effectively than the existing mud-sinking approaches. These above findings provided a better understanding of submerged plants and their biofilms, demonstrating the potential use of biofilm-plant systems in watershed protection.

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PCR-RFLP Study of Candidate Genes for Egg Production in Layer Chicken - Juniper Publishers

 Archives of Animal & Poultry Sciences - Juniper Publishers

Abstract

Polymorphic variants of few candidate genes have been reported to be associated with production traits in layers. The objective of the present study was to genotype the long term selected pure-line layer population for Growth Hormone Receptor (GHR), Insulin Like Growth Factor -1 (IGF-1) and Prolactin (PRL) hormone gene and to observe their association with layer traits. Layer traits were recorded on 1082 pullets up to the age of 40 weeks under standard management conditions. Genotyping study was performed on 90 randomly selected pullets with reported PCR-RFLP markers for GHR, IGF-1 and PRL genes. The studied population revealed polymorphic pattern for GHR, IGF-1 and monomorphic for PRL. The frequency of Hind III ++ and Pst I ++ genotypes were high in comparison to Hind III - - and Pst I + - genotypes for GHR and IGF-1 gene respectively. Genotype-trait association analysis revealed a trend of association with means of some traits; however, the associations were not significant. The allelic and genotypic frequency of PRL gene at both promoter sites was 1.00 which confirmed the loss of broodiness in studied population. Results of this study indicated that direction of selection has supported the favourable alleles of GHR and IGF-1 genes in the studied layer population

Keywords: Candidate genes PCR−RFLP Egg production GHR; IGF−1 PRL

Introduction

Egg production in chicken is the result of many genes and gene interaction. Rapid understanding of genes and genome of chicken with various molecular markers have opened the opportunity to select for genes that are directly related to egg production traits. Candidate gene approach is one such method to genotype the layer stock for such genes which have significant contribution in genetic variability for egg production. Out of the many identified candidate genes polymorphism in layer chicken, only few have been reported to be significantly associated with egg production or, rate of lay. Most of the genotyping studies for reported SNPs or polymorphisms have largely been carried out with Polymerase Chain Reaction and Restriction Fragment Length Polymorphism (PCR- RFLP) type markers. The Growth Hormone, Growth Hormone Receptor and Insulin Like Growth Factor system (GH-GHR-IGFs) controls the number of follicles in the avian ovary that are recruited to the rapid growth phase [1] and a natural GHR mutation alters the ovulation rate [2]. It is also known that the GH-GHR-IGF-1 system has been modified as a result of selection for improved growth rate and egg production. Polymorphism studies have shown the association between GHR (growth hormone receptor) gene and egg production [3].

The chicken IGF-1(insulin like growth factor) polymorphism in the 5’ region [4] is associated with egg production. [5] reported positive association of ‘A’ allele of IGF-1 genotype with egg production in KNOCK chicken. Chicken prolactin hormone (PRL), a polypeptide, secreted by anterior pituitary is a physiological candidate gene for egg production. [6] reported the polymorphism in chicken prolactin promoter region, which was associated with egg production in different Chinese breeds. Presence of 24 bp indel in the same region was highly associated with egg production and a C/T 2402 SNP was involved in PRL transcriptional output. However, both sites showed monomorphic pattern in WL (white leghorn) chicken. Although, literature supports the association of egg production traits with reported polymorphisms of candidate genes, however, reports are unavailable on significant association of candidate genes with egg number in a long-term selected WL population.

In view of above, screening of existing breeding population for presence/absence of polymorphic variant genotypes for above genes and their association with layer traits is important to study the genetic variability at gene level. The IWH strain of WL hasbeen developed through long term selection programme with major emphasis on annual egg production. However, these stocks have not been analysed for the polymorphic status of reported candidate genes. The present investigation was initiated with the objective to genotype the IWH strain of WL population for GHR, IGF-1 and PRL genes and to analyse their association with egg production.

Material and Methods

Blood collection and DNA isolation

Pedigreed WLH pullets (n=90) were randomly taken from the IWH strain of pure line layers. The strain has undergone 29 generations of family selection [7] for part period and annual egg production in a closed flock at experimental layer farm of CARI, Izatnagar, UP. Performance of pullets for various economic layer traits was recorded up to 40 weeks of age under standard conditions of management. About 0.5-1ml of blood was collected from the jugular vein of each pullet at the age of 10 week by a sterile disposable heparinized syringe. The samples were transported in ice and subsequently stored at -20°C. Genomic DNA was isolated from the blood samples by Phenol: Chloroform extraction method. Quality and quantity of DNA was checked using Nano-Drop Spectrophotometer. The quality of genomic DNA was further checked by submarine agarose gel electrophoresis. Only intact DNA samples, devoid of smearing were utilized for present work

Polymerase chain reaction amplification of candidate genes

PCR primers:One set of reverse and forward primers specific to the gene of interest were used to amplify a region of chicken GHR and IGF-1genes while two sets were used for PRL. The set of primers were synthesized as per the published primer sequences (Table 1).

Setting up of PCR reaction: A total of 25μl reaction mixture was prepared by adding autoclaved triple distilled water 19.7l, 10 X PCR assay buffer (15 mM Mg++) 2.5l (1.5mM), forward and reverse Primer 0.5l (100 ng) each, dNTP mix 0.5l (0.5 mM), Taq DNA polymerase (3U /l ) 0.3 l(1.0 U) and Genomic DNA 1.0l (80-100 ng). The optimized reaction mixture that finally used for amplification for all the three genes was kept same except, the forward and reverse primers. All the above procedures were carried out on ice at 4ºC. Master mixture was mixed properly by vortexing followed by spinning. Finally, 24.0μl of master mixture was added to each PCR tube, containing 1.0μl of genomic DNA, followed by gentle mixing and spinning at 3000 rpm for 5-10 seconds. A negative control labelled ‘C’ containing all reaction components except template DNA was also used to check any contamination of DNA in the reaction components. Finally, the PCR tubes were kept in a pre-programmed thermo cycler (Bio-Rad make) for amplification of desired gene segments as per optimized reaction conditions. PCR products thus obtained were kept at 4ºC for further analysis.

Agarose gel electrophoresis: Horizontal submarine electrophoresis was performed on 2 % agarose gel (7.5μl of PCR product mixed with 1μl of gel loading dye) to check the amplified PCR products. Electrophoresis was conducted at constant voltage of 80 volt for 45 minutes at 37˚C using 1X TBE buffer. The mass ruler DNA ladder (100 bp) was used for size estimation of the DNA bands. The DNA fragments were stained with ethidium bromide and photographed using an ultraviolet (UV) trans-illuminator (BioRad, Gel Doc system) to visualize the bands.

Restriction Enzyme digestion: To identify the Restriction Fragment Length Polymorphism (RFLP), Hind III [8], Pst I [4] and Alu I [6] Restriction Enzymes (RE) were used to detect the polymorphism in GHR, IGF-1 and PRL genes respectively. A 154 bp PCR product was amplified from PRL gene, which was directly observed on 3 % agarose gel for presence or absence of 24 bp indel by horizontal submarine agarose gel electrophoresis. Therefore, restriction enzyme digestion was not needed for this gene. RE digested PCR products were analyzed on 6% PAGE (Poly Acrylamide Gel Electrophoresis) and visualized by silver staining.

Statistical Analysis

Genotypic frequencies of different PCR-RFLP patterns were estimated from the combination of various RFLP alleles generated based on presence or absence of one or more restriction sites. Different genotypes were identified based on different patterns. Gene frequencies were calculated from genotypic frequencies. The allele frequencies were calculated using standard methods [9].The Chi-square (χ2) test for goodness of fit was used to find out difference among various genotypes.

Association of allelic variation with egg production traits in WLH

The effects of IGF-1 and GHR genotypes on least squares means of layer traits were analysed using the GLM procedure (SAS, 6.12). The following model was used:

Yijkl = μ + Gi + Fj + Hk + eijkl

where Yijkl is an observation on the traits, μ is the overall sample population mean, Gi is the fixed effect associated with the ith genotype, Fj is the fixed effect associated with the jth dam , Hk is the fixed effect associated with kth hatch and eijkl is the random error.

Results

In the present investigation PCR-RFLP studies were carried out on some of the candidate genes to study the effects of polymorphism on layer traits in WLH birds. The restriction enzyme digestion of 730-bp product from the intron II of GHR gene revealed GHR-Hind III polymorphism with two types of restriction fragment pattern i.e., 410bp / 320bp for the HindIII (+ / +) genotype and 250bp / 160bp / 320 bp for the HindIII (- / -) genotype respectively (Figure 1). The HindIII++ genotype was at significantly higher frequency (0.966) as compared to HindIII- - (0.033) genotype, which was also true for the HindIII+ and HindIII- alleles in the population studied (Table 2). The 621- bp fragment from 5’-UTR (5’-untranslated region) of IGF-1 gene was restriction digested with PstI enzyme. Single polymorphism at PstI cutting site revealed two different restriction patterns i.e., 257bp and 364 bp for the PstI (+ /+) genotype and 257, 364 and 621 bp for the PstI (+ / -) genotype respectively (Figure 2). The PstI ++ genotype was at significantly higher frequency (0.944) than PstI+ - genotype (0.055). Similarly, frequency of PstI+ allele was significantly higher (0.972) than the frequency of PstI- allele (0.027).

The 439 bp fragment at the promoter region of chicken prolactin gene was amplified by using PRL I primer set. Restriction enzyme digestion of amplified product revealed monomorphic pattern at C- 2402 T site for Alu I enzyme (Figure 3). The fragments observed were of 160 bp, 144 bp, 81bp and 54bp in size. The PCRRFLP pattern revealed presence of CC genotype in the present population, which was like the results of [6] for WLH chickens. The results confirmed the transition of C to T at 2402 bp position as has been reported by [6]. Similarly, insertion of 24 bp at the promoter site -358 of chicken prolactin gene was observed in allthe hens with the second set of primer PRL II. As a result, the PCR product revealed 154 bp fragments on 3 % agarose gel.

Genotype trait association

Associations between genotypes of GHR and IGF-1 genes with layer traits were initially analysed using a linear model that included effects for the GHR genotype, the IGF-genotype, interaction between genotypes of the genes, the effects of dam, effects of sire and hatch. However, the interaction and sire effects were not found significant (P >0.05) on all the traits and were therefore, removed from the model. The effects of polymorphism on layer traits and the least squares means from the two different genotypes of GHR and IGF-1 genes have been presented in (Table 3,4) respectively. The mean values of different layer traits revealed differences among genotypes for both the genes, however no significant associations with genotypes were observed. However, few traits (BW 40, EW 40, EW 28, ASM, MOT 15, MOI 40 and ACL) showed the trend of association with IGF-1 and GHR genotypes at probability value greater than 05 percent but less than 20 percent level of significance.

Discussion

Genotyping studies for the reported polymorphisms in GHR gene have also been conducted by some earlier workers [3,8,10] in different exotic layer populations with the aim to find association of different genotypes with egg production and reproduction traits. The genotypes observed in present investigation for GHR gene were like the findings of [8,10]. GHR Hind III+ genotype was significantly associated with higher juvenile body weight [8] and a trend of association was found with age at first egg (P ≤ 0.14) and housing body weight (P ≤ 0.058). However, no significant association with other layer traits was reported by him. In the present study, similar trend of association with ASM (P≤ 0.11), ACL (P≤ 0.09), MOT 15 (P≤ 0.13) and MOI 40 (P ≤ 0.1935) were observed (Table 3), however the associations were not statistically significant at 5 % or at 1 %. The gene and genotype frequencies reported in present study were comparable to the results of [10] but the frequency of Hind III -/- was lower than the results of [10]. Both have reported comparatively higher frequencies for HindIII + allele as compared to HindIII – allele in their respective population, which has also been observed in the present study. [8] had observed that, there was a tendency for an increase in the frequency of Hind III + allele due to influence of selection (Table 5). Few other reports are available in literature [11,12] for identification of SNP in GHR gene but these SNPs belong to other regions of the gene than the present study.

IGF-1 gene has been reported to be associated with egg production [12] through regulating the growth and differentiation of follicles [13] in layer chickens. Genotyping for associated polymorphism at PstI site have been reported by some workers [4,5] in different exotic layer birds. The observed restriction fragment pattern for PstI + and PstI – allele was similar to the reported literature [4,5,10].

However, PstI - - genotype was not found in present investigation (Table 6). The observed frequency (0.972) for PstI + allele was higher than the frequency (0.83) reported by [4,5] (0.30) in two different layer chickens. [5] reported maximum frequency for PstI - allele in Korean native chicken contrary to the minimum frequency reported by [4] in WLH chickens. In the present study similar trend as reported by [4] was observed for PstI + allele. The allelic and genotypic frequencies for PRL gene at two different promoter sites were 1.00 in the population studied. The results were like the reports of [6] for WLH chicken. Due to monomorphic pattern, association analysis with production traits was not performed for these two genotypes. Presently reported higher frequency of Hind III ++ genotype indicated that direction of selection has supported the favourable allele, however, statistically significant differences were not observed in the least square means of two genotypes. This could have been due to some environmental effects or the background genome would have masked effects of genotypes. Further studies with larger sample size are suggested for the future. Higher frequency of PstI + allele of IGF-1 gene in WLH population has been reported to be significantly associated with egg weight [4]. The average egg weights were higher for the PstI ++ genotype than for PstI - - genotype [4], however; for the same trait, non- significant association was observed by [15].

The results of present investigation were comparable to the results of [4], however no significant association with egg weight was observed. Like the results of [4], a trend of association was observed for EW 28 (P≤ 0.06), EW 40 (P≤ 0.08) and BW 40 (P≤ 0.11) at higher levels of probabilities. [5] reported that Pst I ++ genotype was associated with higher egg production at the age of 50 week than PstI - - genotype. [10] have reported similar results for the association of IGF-1 polymorphism with 300- and 400-days egg production. The results of present investigation differed from the findings of [5,10] regarding absence of PstI - - genotype in the population studied. PstI - - genotype was reported to be associated with low egg production [5,10] and its frequency was reported to be higher in native chickens [5,10] than the WLH chickens. Higher frequency of PstI ++ genotype and the absence of PstI - - genotype in the population studied, indicate that the direction of selection for increased egg production has supported the favourable allele. Further studies with larger sample size, therefore, are suggested for the future.

The monomorphic patterns of PRL gene with both the primers sets confirm the loss of broodiness in the present layer population. The insertion of 24 bp (with primer pair PRL II) indel has been reported to be associated with lack of broodiness. [11] reported that insertion of 24 bp nucleotide sequence in the promoter region may inhibit a transcriptional factor-binding site for PRL and, therefore, decreases the expression of PRL, which contributes to non-broodiness in + / + hens. [6] reported that the frequency for II genotype in WL layers was 1.00 and the marker trait association analysis indicated that the 24 bp indel was associated with egg production (P < 0.01). Similarly, the C-2402 T AluI polymorphism has also been reported to show a frequency of 1.00 in WL population as compared to other native layers [6].

The present result with 1.00 frequencies for both the 24 bp indel and C-2402 T confirms the reports of previous workers [6,11] that WL population under selection for egg production has lost the broodiness character. From the present study, it may be conferred that direction of selection has stabilized the favourable alleles of selected gene candidates due to longer generations of selection [16]. The selected gene candidates would be of more use to explore the genetic variability in egg production traits of shortterm selected layer population or, native chicken.

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Assessing the geotechnical properties of soils treated with cement and nano-Silica additives - Juniper Publishers

JOJ Sciences  - Juniper Publishers

Abstract

One of the problematic soil types is fine-grained soils including CL, CH, ML, MH, which are found in construction projects in large amounts. The main problem with these soils in construction projects is their high ductility (inflation and shrinkage) and low strength, so the presence of these soils in the foundation of construction projects will cause hazards, indicating the necessity of utilization of improving methods. Studies conducted on geotechnical engineering effects of nanomaterials show the efficiency of these materials for soil treatment. by adding nanomaterials to the soil treated with cement, the strength of the base soil has been increased and the percentage of cement use has been significantly decreased, reducing the CO2 emissions into the environment, hence reducing the environmental pollution. The increase in soil strength is due to the high specific surface area of nanomaterials and cationic interactions with soil compounds. Research on nanomaterials and fine-grained soil treatment is very promising increasing our understanding of the relationship between nanotechnology and geotechnical engineering. In this research, the effects of nano-silica on the uniaxial compressive strength of fine-grained soils are investigated.

Keywords: Stabilization, Fine-grained soil, Nanotechnology, Uniaxial strength, Nano-silica

Introduction

Fine-grained soils CL, CH, ML, MH are considered as problematic soils present in almost every civil project, especially in roadbeds. Most of these soils are considered as inflatable soils [1-3]. Due to their water absorption ability, in addition to volume changes (so-called swelling), their strength is also significantly reduced, intensifying risks in the foundation of construction projects as well as in the road pavement beds. Therefore, various physical and chemical methods have been used to stabilize this type of soil. The advantages of using nanomaterials can be expressed in reducing environmental damages and gaining the desired strength for the problematic soils [1,4,5].

Additives used previously include lime, cement, bitumen, coal fly ash, etc. One of the basic requirements in construction projects is minimizing the environmental damages by choosing the most proper material, in addition to reducing project costs. Sometimes the land to be recovered covers a wide area such as highways, railways, dams, airports, etc so to overcome the requirements of the designs and to reduce environmental pollution, nano-products can be used as additives to problematic soils [1,6].

Various studies such as Kalkan et. al. [7,8], Taha [9,10], Taha and Taha [5], Arabani et.al [11], Mohammadi and Niazian [12], Changizi and Haddad [13-15] and Choobbasti et al. [16] have shown that the addition of small amounts of nanomaterials to the fine-grained problematic soils increases their strength significantly and minimizes soil swelling. The advantage of adding nanomaterials in comparison to other stabilizing materials such as lime and cement is that the small amount of nanomaterials can result in obtaining similar outcomes, presented in studies like Sobolev et al [17], Bahmani et al. [18,19], Choobbasti et.al [20,21], Choobbasti et al. [22]0.4, 0.8 and 1.2% by weight of the soil, Tsampali et al. [23] and Yao et al [24].

Nanotechnology

Nanotechnology is the manipulation of matter on an atomic, molecular, and supramolecular scale. A more generalized description of nanotechnology is defined as the manipulation of matter with at least one dimension sized from 1 to 100 nanometers. Nanotechnology in a simple definition allows the production of new materials or systems by considering the control of molecular and atomic levels, the controlled arrangement of nanostructures, and the achieving unique properties in the final system. This technology due to its rapid development and proper performance in various fields and the limitations in traditional materials (including bitumen, lime, cement, etc.) has become of great importance for improving soil engineering parameters by introducing the nanomaterials [25,26].

Utilizing the properties of materials at the nanoscale has become very promising in human life. The development of industry and urban planning on one hand and the importance of environmental sustainability on the other hand have challenged soil researchers to find a satisfactory solution for improving the soil engineering properties rather than using existing traditional materials such as cement and chemical mortar (sodium silicate, acrylate, and epoxy). These materials were both expensive and environmentally damaging, so their use has been limited. Therefore, by limited utilization of these materials, other substances with better performance and reduced consequences have been introduced by nanotechnology [27].

Stabilization theory with nanomaterials

The application of nanomaterials for problematic soils is one of the chemical stabilization methods of soils. The nanoparticles with unique characteristics like possessing very small size, high specific surface area, surface charges, and nanoporous can actively react with other soil particles. As a result, their usage even in small amounts in soil modifies soil engineering properties. Various nanomaterials are used for soil-improving purposes, including nano-silica, nano-alumina, nano-clay, nano-carbon, and nanoiron. In this research, the effects of nano-silica in fine-grained soil improvement are briefly discussed.

Effects of nano-silica on improving soil strength

The uniaxial compressive strength test is commonly performed for stabilized soils. Figure 1 shows the effects of a mixture of treated soil with cement and different percentages of nano-silica at 7, 14, and 28 days of curing time. The results indicate that the strength increases with more curing time and cement hydration process completion up to 28 days. Also, with the addition of nanosilica by 1.5% of soil dry weight to the cement-treated soil uniaxial compressive strength increases, it can be inferred that Nanosilica has made the cement-stabilized soil structure denser and more cohesive due to its high specific surface area, fine particles, and cation exchange. With the addition of more nano-silica, the soil strength decreases, which may be due to the agglomeration of nanomaterial particles where the soil particles are separated from each other and the cohesion and integrity of soil particles are reduced so the uniaxial strength of the soil is reduced. results of Bahmani et al., [18], Lei Lang et al., [28] and Thomas and Rangaswamy [29] works, presented in Figures 2 to 4, also confirm this.

Results

i. The addition of small amounts of nanomaterials to the fine-grained soil has significantly increased the strength of the samples. The difference between adding nanomaterials and other stabilizing materials such as lime, cement, etc. in obtaining similar results is on the small amount needed for nanomaterial in comparison to other stabilizers.

ii. As the curing time increases, the uniaxial compressive strength of the stabilized samples increases, since the soil reacts with the nanomaterials synthetically as time goes on the reactions are more complete and samples are better stabilized.

iii. Addition of nanomaterials to cement-treated soils has reduced the percentage of cement use, resulting in reduced environmental pollution.

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Research Progress of Gramineae Cellulose Synthase Gene in Cellulose Synthesis Regulation - Juniper Publishers

Horticulture & Arboriculture - Juniper Publishers

Abstract

Gramineae, such as Zea mays, Oryza sativa, Sorghum bicolor and Miscanthus, has a high cellulose content in the cell wall. Cellulose synthase gene (CesA) plays an important role in the process of plant growth and cell wall morphogenesis. In this paper, the related research results of CesAs in Gramineae was summarized, and the role of CesAs in regulating cellulose synthesis was analyzed.

Keywords: Gramineae; Cellulose; Cellulose synthase gene

Abbreviations: CesA: Cellulose Synthase; CesA: Cellulose Synthase Gene; CSC: Cellulose Synthase Complex; GT2: Glycosyltransferase 2; PCW: Primary Cell Wall; SCW: Secondary Cell Wall

Introduction

Gramineae have more than 500 genus and more than 8,000 species, which are widely distributed in different ecological environments around the world [1]. Gramineae include important grain or sugar crops such as Oryza sativa, Triticum aestivum, Zea mays and Saccharum officinarum, as well as important biomass ingredients crops such as Miscanthus and Panicum virgatum. Gramineae usually have a high cellulose content [2], and the stability and great ductility of cellulose make it an ideal raw material for manufacturing many fiber products [3,4].

Biosynthesis of Cellulose

Cellulose is one of the important components of the higher plants mature cell walls. As a structural polysaccharide, it accounts for 30-40% of the total cell wall polysaccharides [5]. The basic unit of cellulose is pyranoid D-glucose, which is connected by β-1,4 glucoside bonds and usually exists in the form of microfibrils, and its structure has a specific hydrogen bond structure between molecules [6]. Studies have shown that the pathway of cellulose biosynthesis is mainly divided into three steps (Figure 1), and CesA plays an important role in the program [7]. CesA is a membrane-bound transmembrane protein a member of the glycosyltransferase 2 (GT2) family that catalyzes the formation of β bonds between glycosylates. CesA is a hexagonal lotus shaped enzyme with a diameter of 25-30nm, it can be assembled into a Cellulose Synthase Complex (CSC) with a sixfold symmetrical rosette structure on the cell membrane [8]. The amount of CSC in plants is positively correlated with the final synthesis amount of cellulose. The number of rosette structures of the Arabidopsis mutant rsw1 is significantly less than that of the wild type, which caused β-1,4-glucan to accumulate in an amorphous form and the cellulose content is reduced [9].

Cellulose Synthase Gene (CesA)

The length of CesAs sequence is between 3.5~5.5 kb, containing approximately 9~13 introns and encoding 985~1,088 amino acid [10]. In 1982, Benziman [11]. cloned CesA in vitro bacteria for the first time [11]. In 1996, Peal et al. cloned the β-1,4- glucosidyltransferase gene encoding the catalytic CesA subunit from cotton for the first time by random sequencing and sequence analysis from a cDNA library [12]. Since the discovery of CesA in cotton, CesAs had been successively cloned in Arabidopsis thaliana [13], Oryza sativa [14], Zea mays [15], Populus trichocarpa [16], Boehmeria nivea [17] and Phyllostachys edulis [18]. In the studies of Gramineous CesAs, it was found that OsCesA4, 7,9 of rice were all involved in the formation of SCW, forming a complex regulatory network of SCW cellulose biosynthesis. These three CesA genes can be expressed cooperatively in rice seedling stage, young stem, immature panicle and root development, but relatively little expression in mature leaves [19]. The missense mutation of OsCesA7 caused the decrease of cellulose level and cell wall damage in S1-24 mutant rice; at the heading stage, compared with wild-type, S1-24 mutant rice has a lower mechanical strength and a relatively slower growth rate [20]; however, the expression of OsCesA7 could be directly up-regulated by regulating the MYB transcription factor OsMYB58/63 of rice [21]. When OsCesA9 has a missense mutation, it will cause plant dwarfing and extremely low fertility [22]. In Panicum virgatum L., PvCesA4 and PvCesA6 genes have different expression levels in different parts. After the overexpression and/or knockout of PvCesA4 and PvCesA6, the cellulose content of the transgenic plants decreased, while the xylan content increased. The increase of xylan content would lead to the decrease of crystallinity of cellulose, which would affect the synthesis of cellulose Therefore, the expression of CesAs had changed cell wall composition and cellulose crystallinity [23]. The CesAs of Miscanthus × giganteus has been reported. MgCesA10, MgCesA 11 and MgCesA 12 may participate in the formation of SCW and form an equal proportion of CSC. MgCesA5 and MgCesA6 are constitutively expressed genes that cooperate with MgCesA2, 3, 4, 7 and 8 to regulate the formation of PCW. However, except for MgCesA5, the expression of other CesA genes in leaves was reduced due to senescence. The expression of genes involved in the formation of Miscanthus × giganteus PCW varies depending on the location [24].

Different Regulation Levels of Gramineae CesA

Cellulose synthesis can be regulated at the transcriptional level by CesAs. The biggest difference between CesAs is the presence and location of introns in the coding sequence [13]. For example, wheat CesA1, 2 and 6 have 13 introns, while CesA4, 7 and 8 have 7, 12 and 9 introns respectively; CesA1, 2 and 6 participate in the formation of PCW, while CesA4, 7 and 8 participate in the formation of SCW [25]. This indicated that the number of introns of CesAs in the formation of wheat PCW was higher than that of CesAs in the formation of SCW. Previous studies have shown that genes containing introns have higher transcription levels [26]. This also indicates that transcription levels of CesAs participate in wheat PCW formation are higher than those of CesAs participate in SCW formation. In addition to the regulation of cellulose synthesis at the transcriptional level of CesAs, the post-transcriptional level of CesAs also affects the synthesis of cellulose. Daniel et al. found that the small RNA produced by HvCesA6 can selectively attenuate the expression of CesA gene, therefore, the expression of genes that affect cell wall formation can greatly influence the content of barley cellulose [27].

Conclusion

Cellulose is the most important component of plant cell walls, and cellulose synthase plays a key role in cellulose biosynthesis. In the studies of Gramineae CesAs, it was found that CesA gene family was involved in cell wall morphogenesis, forming a complex regulatory network of cellulose biosynthesis. Transcriptional or post-transcriptional regulation of CesA genes can change plant cell wall composition, change cellulose content and cellulose crystallinity, so as to provide a strong theoretical basis for the high value utilization of cellulosic feedstock crops.

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Magnetizing Reduction and Magnetic Separation Studies on Low-Grade Iron Ore of Chiniot, Punjab Province, Pakistan - Juniper Publishers

Mining Science & Technology - Juniper Publishers

Abstract

Magnetizing reduction is an important pre-treatment process used for low-grade iron ores which are difficult to upgrade by conventional beneficiation techniques. In present study, magnetizing reduction of a low-grade iron ore has been carried out followed by magnetic separation of iron minerals to produce iron concentrate. A potential process has been developed for magnetizing reduction of hematite into magnetite with domestic lignite coal. The experiments were carried out in Muffle furnace under controlled temperature conditions. The main process variables such as particle size of ore, ore to coal consumption ratio, reduction temperature and retention time were investigated to determine the extent of magnetizing reduction. In second step, reduced iron ore was subjected to low intensity magnetic separation to recover iron values in the magnetic concentrate. A single-factor variation method was applied in order to get the optimum conditions of the process. The results of bench scale experimental study showed that the maximum grade and recovery of iron concentrate was achieved at ore size of 90-95% minus 200 mesh, ore to coal consumption ratio of 1: 0.25, the reduction temperature of 700°C and the retention time of about 60 minutes. The ore containing 33.95% Fe was upgraded to a concentrate assaying 64.13% Fe with 83.70% recovery. The iron concentrate produced meets the specifications of metallurgical grade and is suitable for use as a feed for blast furnace and other direct reduction methods.

Keywords: Low-grade iron ore; Beneficiation; Magnetizing reduction; Low intensity magnetic separation; Iron concentrate; Hematite; Magnetite; Metallurgical grade; Recovery

Introduction

Conventionally iron and steel is produced by the reduction of high-grade iron ores in a blast furnace. About 80% of the world’s iron making is achieved through the blast furnace process and rest by different direct reduction (DR) processes. The role of high-quality iron ore and concentrate as a raw material is very critical to get the best quality iron and steel [1]. The high-grade iron ores or concentrate should contain at least 60% iron (Fe) content with maximum up to 7% silica (SiO₂) content [2]. The product of blast furnace is a pig iron which is then converted into steel by various techniques [3]. The quality of raw materials used in blast furnace plays an important role in steelmaking process.

The iron ores available at different areas of Pakistan are generally low-grade with high silica content. These ores as such cannot be utilized to produce iron and steel by conventional blast furnace technique or DRI processes. The first step in iron making involves the separation of iron minerals from low-grade iron ores. There are three basic methods for separation of iron minerals i.e., magnetic separation, froth flotation and gravity concentration [4]. The iron concentrate produced by any processing method is used for producing iron metal either by blast furnace or direct reduction methods [5]. The fine iron concentrate is to be palletized or sintered for both routes [6].

Magnetic separation is most used to separate natural magnetic iron ore (magnetite) from a variety of less magnetic or nonmagnetic material [7]. Magnetizing reduction is one of the most effective unit operations in the treatment of low-grade iron ores specially those which are poorly responsive to conventional beneficiation techniques such as froth flotation, gravity separation and magnetic separation [8,9]. It involves the conversion of feebly magnetic iron minerals in the ore to the strongly magnetic form by subjecting the ore to a reducing atmosphere at elevated temperatures. The resulting artificial magnetite is strongly magnetic and can be separated from the non-magnetic gangue by low-intensity magnetic separation. Many weakly magnetic minerals can be converted to more strongly magnetic compounds by magnetizing reduction processes [10-12].

Geological Survey of Pakistan (GSP) during regional survey in 1989 discovered iron ore deposits near Chiniot town and adjoining areas such as Rajoa, Chak Jhumra, Wad Syedan, Ghutti Syedan, Shaheen Abad, Sargodha and Sangla Hills etc. Subsequently, the Punjab Mineral Development Corporation (PUNJMIN) carried out detailed exploration in year 2005 to 2007. As a result of exploration work, anomalous zones containing iron ore and other associated metallic minerals have been confirmed in Chiniot with strong indications in Rajoa. The other metallic mineral resources including copper, gold, nickel, cobalt etc. are also found in the underlying sulphide zone associated with the iron ore. Around 150 million tons of good quality iron ore reserves had been identified in Chiniot. The field survey based on the cores recovered from several drill holes of the ore body has shown that the ore occurs in bands ranging from one meter to several meters in thickness. The Chiniot iron ore is predominantly oxide ore containing variable amount of hematite and magnetite as principal iron bearing minerals. The ore is massive, low to medium grade containing as low as 30 Fe₂O₃ to as high as 70 Fe₂O₃. The resources are buried under alluvium, aquifers and hosted in the subsurface volcanogenic rocks [13].

With ever rising steel prices, the local manufacturing of steel based on indigenous reserves of iron-ore is critical. The main problems in utilization of indigenous iron ore is up-gradation and beneficiation of available resources. Development of domestic technologies for utilization of indigenous iron ore will not only reduce the dependence of steel production on imported raw material, but it will also result in lowering the steel price. Present beneficiation studies are oriented towards exploring the possibilities of upgrading Chiniot iron ore to produce iron concentrate for utilization as a feed in conventional blast furnace or direct reduction method to produce iron and steel.

Materials and Methods

Sample Preparation

The core samples of seven drill holes of Chiniot iron ore weighing about 40kg were received for beneficiation studies. The drill cores were crushed in laboratory jaw crusher (set at 20mm) followed by roll crusher (set at 5mm) for size reduction. Riffling technique of sampling was used to prepare the head sample for chemical analysis. The head sample was pulverized to 100% minus 200 mesh (74µm) in disc pulverizer (Denver, USA). The crushed ore was split into 1kg samples and kept in plastic zipper bags for R& D work. These ore samples were ground in rod mill for magnetizing reduction and magnetic separation tests.

Chemical analysis of ore

The chemical analysis of head sample of iron ore originating from Chiniot area was carried out by standard wet analytical methods and atomic absorption spectrometer. Ore was fused with sodium carbonate and sample solution was made in dilute HCl. Silica, alumina, and sulphur were determined gravimetrically while iron was determined by oxidation reduction titration. Calcium and magnesium were determined by complexometric titration using standard solution of EDTA. Sodium and potassium were determined by flame photometer (PFP7, Jenway Limited, England). Loss on ignition (LOI) was determined at 1000^oC. The complete chemical analysis of head sample of Chiniot iron ore is shown in Table 1.

Magnetizing Reduction Tests

Magnetizing reduction tests were carried out on ground ore using locally available lignite to sub-bituminous coal used as reducing agent. The pulverized coal sample used has 2.45% moisture, 37.79% ash content, 35.20% fixed carbon, 24.56% volatile matter, 5.86% sulphur and its gross calorific value of coal was 6150 Btu/lb. Known weight and sizes of ground ore and coal were mixed in different composition. These were placed in porcelain crucibles (100ml capacity) and covered with lid. These were heated by gradually by raising the temperature with increment of 100°C per 30 min in electric (muffle) furnace to desired temperature and then maintaining it for magnetizing reduction of hematite into magnetite. The crucibles were removed after keeping them at different temperature for different time interval. Runs were conducted on 50g ore charged. The ore to coal ratio was studied from 1: 0.1 to 1: 0.30, the reduction temperature was ranged from 500 to 800°C, the residence time was varied between 30 min to 120 min and the particle size of ore was varied from 90-95% passing 100 mesh to 250 mesh.

Magnetic Separation Tests

The reduced ore (feed) was subjected to wet low intensity rotary drum magnetic separator (Sala, Italy) having permanent magnets for separation of magnetic minerals form associated gangue minerals. The drum dimensions were 200 mm dia × 100 mm width. The intensity of magnetic field (strength) was set at 1000 gauss. Tests were conducted at feed rate of 10-15 kg/hr, wash water flow rate of 20-25 l/hr and number of operations (passes) 2. The magnetic (concentrate) and non- magnetic (tailings) portions were collected separately, dewatered and oven dried. The dried concentrate and tailings were weighed and chemically analyzed for total iron content. The results of magnetic separation tests are given in Table 2. The flowsheet developed for the process is given in Figure 1. The images of the crushed sample, ground head sample, ground lignite coal and reduced magnetic concentrate are shown in Figure 2.

Results and Discussion

Chemical analysis

The chemical analysis of head sample (Table 1) indicates that ore contains 33.95% total Fe. The main impurity is silica being 36.25% which is more than the permissible limit required for iron and steel production. The level of other impurities is not very high except sodium oxide and potassium oxide. These impurities are present due to the occurrence of cerecite and feldspar in the ore. The iron mineralization varies from massive over 70% Fe₂O₃ through medium 50% Fe₂O₃ to low grade 30% Fe₂O₃. The iron minerals occur as hematite and magnetite. The hematite to magnetite ratio varied from 1. 3:1 to 2.0:1. The ore is hard, tough and compact. As hematite is a weekly paramagnetic mineral, while the other minerals present in the ore are diamagnetic in nature. It was decided, in this perspective, to convert hematite into magnetite followed by low intensity magnetic separation technique which has the potential to recover the iron values and reduce the siliceous gangue minerals effectively [14].

Effect of particle size of ore

The particle sizes worked at were almost 90-95% passing 100 mesh (150µm), 150 mesh (100µm), 200 mesh (75µm) and 250 mesh (65µm) for magnetizing reduction study keeping other factors constant. The results of beneficiation tests (Figure 3) showed that although some up-gradation has been affected at coarse size. However, the concentrates were high in silica content showing thereby that it is locked within iron oxide particles. It was thought essential to grind the ores to finer size. It was observed that the samples ground to 90-95% passing 200 mesh responded most favorably to magnetic separation. The magnetizing reduction followed by magnetic separation results showed that as the particle size of feed was reduced from 90-95% passing 100 mesh through 150 mesh to 200 mesh, the grade was improved gradually from 52.45% Fe through 58.90% Fe to 61.05% Fe with slight decrease in recovery of total iron content of concentrate from 87.12% through 85.03% to 84.72%. However, after that both grade (58.23%) and recovery (80.31%) were dropped sharply probably due to finer particle size of ore.

Effect of reduction temperature

Temperature has a significant effect on magnetizing reduction process. It plays an important role in the phase change of hematite and limonite during magnetizing reduction [15]. The iron ore samples of 90-95% passing 200 mesh size were subjected to magnetizing reduction with excess of coal (30%) at 500°C, 600°C, 700°C and 800°C for 60 min to study the effect temperature on the magnetizing reduction of iron ore. The reduced samples were separated, and magnetic fractions were subjected to chemical analysis to determine the iron content. The results obtained are shown in Figure 4. It is clear from this figure that iron grade and recovery in the magnetic fraction exhibits a gradual increase with rise in reduction temperature and reaches at maximum value 62.31% Fe with 82.75% recovery at the onset of reduction temperature of 700°C and then slowly declines. It is since as the temperature is raised between 200 to 700°C the carbon in the form of coal burns to produce carbon monoxide.

2 C(s) + O₂(g) → 2 CO(g)

The hot carbon monoxide is the reducing agent for the iron ore and reacts with the hematite iron oxide Fe₂O₃ (III) to produce magnetite iron oxide Fe₃O₄ (II) and carbon dioxide.

3 Fe₂O₃(s) + CO(g) → 2 Fe₃O₄(s) + CO₂(g)

The hot carbon dioxide formed in this process is re-reduced to carbon monoxide by further reaction with the coal.

C(s) + CO₂(g) → 2 CO (g)

As the temperature is further increased beyond 700°C, most of the coal is consumed away and some of freshly converted magnetite present on the surface is re-oxidized to hematite by air which lowers the recovery rate during magnetic separation [16].

Effect of reduction time

The effect of reduction time was investigated by varying it from 15 to 75 minutes with increment of 15 min and keeping other parameters constant at feed size of 90-95% passing 200 mesh size, the reduction temperature of 700°C and ore to coal ratio of 1: 0.30. It is obvious from the result (Figure 5) that iron grade and recovery in the magnetic fraction increases gradually in the beginning and then represents a sharp increase (63.45% Fe with 82.93%) at the onset of reduction time of 60min and then decreases with increase in reduction time. It is observed that when the reduction time was extended from 60min, the magnetic properties of the reduced ore were decreased (Figure 2). The prolonged reduction time results in excessive reduction and waste of energy resources. Also, when the reduction time is less than 60min, insufficient reduction occurs leading to lower metallurgical results [17].

Effect of coal consumption ratio

The effect of coal as reducing agent on the reduction of hematite to magnetite was investigated by varying the ratio of ore to coal from 1: 0.10 to 1: 0.30 in the charge at a temperature of 700°C for 60 min using the particle size of 90-95% minus 200 mesh size. The coal carbon burns as the temperature is increased and reducing gases such as carbon monoxide are formed that initiate the reduction of hematite into magnetite. As a result, this reaction, conversion of hematite into magnetite takes place [18,19]. The results obtained (Figure 6) show that the metallurgical performance (grade and recovery) of magnetizing reduction is improved and reaches its highest value of 64.13% Fe with 83.70% recovery as the ratio of coal in the ore was increased up to 1: 0.25 in the charge. Further increase seems to be insignificant as it does not improve the results.

Effect of Magnetic Separation

Low-intensity magnetic separators use magnetic fields between 1,000 and 3,000 gausses [20]. Low-intensity magnetic separation techniques are normally used on magnetite ore as an inexpensive and effective separation method. This method is used to capture only highly magnetic material, such as magnetite. High-intensity separators employ fields as strong as 20,000 gausses. This method is used to separate weakly magnetic iron minerals, such as hematite, ilmenite, rutile, siderite, chromite, wolframite, pyrrhotite, monazite from non-magnetic or less magnetic gangue material [21-25]. The preliminary direct low-intensity magnetic separation tests showed that ore contain mainly hematite as iron bearing mineral as only 25 to 35% of total iron (Fe) corresponding to magnetite was recovered by low-intensity magnetic separation. Between 30 to 35% of all the iron units being beneficiated are lost to tailings because hematite is only weakly magnetic.

The optimum conditions of magnetizing reduction parameters (Table 2) depict that when the crude ore grade is 33.95% Fe, the mass percent of pulverized coal as reducing agent is 25%, reduction temperature is 700℃, reduction time is 60 min and particle size is 90-95% passing 200 mesh # (0.074mm). The iron concentrate can be got after a low-intensity magnetic separation, whose grade is 64.13% Fe and recovery is 83.70%.

Metallurgical balance Calculation

The metallurgical balance (Table 3) shows that Chinot iron ore is amenable to beneficiation using low-intensity magnetic separation after magnetizing reduction technique. The magnetizing reduction trials of iron ore followed by magnetic separation has indicated that the ore has been concentrated to 64.13% Fe grade with 83.70% recovery starting from a crude ore assaying 33.95% Fe. The silica content is greatly affected by the magnetizing reduction treatment where it decreases from 36.25% in the ore to 4.38% in the magnetic portion. Magnetizing-reduction has been found an efficient technique for the recovery of values from this ore with acceptable recovery. The developed process is low energy consuming, cost effective and convenient.

Final concentrate analysis

The chemical analysis of final concentrate (Table 4) reveals that after beneficiation, iron content (Fe) has been increased significantly from 33.95% to 64.13% with decrease in amount of silica (SiO₂) from 36.25% to 4.38%. The prepared iron concentrate having iron and silica in this range is considered suitable for the preparation of iron and steel by Blast Furnace and alternative iron making processes such as SL/RN, Krupp-Renn, Midrex, Corex, Hyl, Romelt, Hismelt, Ausmelt, Dios etc. [26]. There is a quite variation in selection of feed for different processes. The reducing agents may be gas or solid or both fuels. The charge may be lumps, screen size, fines, pellets, sinter, agglomerate or briquettes. The quality of iron ore or concentrate is key parameter in the selection of process. Some rotary kiln processes such as (Krupp-Renn/ SL/RN) can use lower grade iron ores (Fe 50%) while other process require high grade iron ore having more than 65% Fe content such as Midrex process. The product of DR processes is sponge iron which is converted into steel [27].

The quality of high-grade iron ore or concentrate made from low grade ore has a significant effect on the efficiency and economy of blast furnace. The various impurities present in iron ore in the forms of silica, alumina, alkalis, phosphorus and sulphur behave differently during smelting and adversely affects the performance and economy of blast furnaces. The presence of phosphorus and sulphur increases surface cracking during steel processing. The acceptable levels of phosphorous (P) vary from 0.08 to 0.14%, while sulphur (S) is up to 0.06% in hot metal. High alkali (Na₂O & K₂O) contents lower the mechanical strength of coke and sinter, imbalance the furnace operation, reduce the furnace productivity and damage the lining. The desired levels of alkalis are 0.4% of hot metal. The increase in silica (SiO₂) content leads to the generation of more siliceous slag with high viscosity, consumes more limestone or dolomite. The desired level of silicon (Si) in the steel is 0.6%. High alumina (Al₂O₃) decreases the fluidity of slag, and more coke is required to increase the fluidity. It has been reported that reduction of the alumina content in iron ore by 1% improves blast furnace performance by 3%, reduces reduction degradation index (RDI) by 6 points, lowers the coke rate by 14 kg per ton of hot metal and increases sinter productivity by 10-15%. The high iron (Fe) content and low impurities contents in iron ore are highly desired in the blast furnace operations and economy. Different steel plants have varied quality requirements based on the techniques and process adopted. Specifications of a typical iron ores required by steel plants for iron making are as Fe 60-67%, SiO₂ 1-6%, and Al₂O₃ 3- 4%. The values of these constituents in the iron concentrate prepared from Chinot iron ore lies well within the acceptable limits [28,29].

Conclusion

The results of the experimental study showed that the quality of Chiniot iron ores can be greatly improved by subjecting to magnetizing reduction followed by magnetic separation technique. A great deal of impurities is removed, and the iron content is significantly increased. The ore concentrate obtained is high-grade material suitable for direct use as a feed to produce iron and steel in number of processes. The results reported show that it is possible to upgrade low grade iron ore of Chiniot area by magnetizing reduction followed by low intensity dry magnetic separation technique to produce iron concentrates of metallurgical grade with acceptable recovery. The SiO₂ content was reduced remarkably from 36.25% to 4.38%. The iron contents were upgraded significantly from 33.95% to 64.13% at recovery of 83.70%. The final concentrate produced meets all the specifications of the metallurgical grade iron concentrate and can be directly used to produce iron and steel after palletizing. The advantage of this technique is that it is easy to operate, less expensive and environment friendly.

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Fractures of the pelvis: Complications and Mortality in a Sub-Saharian Hospital - Juniper Publishers

Orthopedic & Orthoplastic Surgery - Juniper Publishers

Abstract

Objective: the aim of this work was to study the prognosis of pelvic fractures in the orthopedic-traumatology department of Idrissa Pouye General Hospital.

Materials and methods: We performed a retrospective, descriptive and monocentric study over a period of 13 years. We included in this study, hospitalized patients or not for fractures of the pelvis (151 cases). We estimated the prognosis of these fractures by assessing their mortality, their complications and their sequelae.

Results: One-third of the patients died (33.88%). Early complications were dominated by vascular lesions (14.80%). The correlation between the lesional type and the occurrence of vascular complications was statistically significant. However, there was no correlation between lesion site and urinary complications.

Conclusion: The prognosis of pelvic fractures is characterized by high early mortality in our country. This high rate of death is related to immediate complications and associated lesions responsible for polytrauma.

Keywords: Pelvis; Fracture; Urinary complications; Polytrauma

Introduction

Fractures of the pelvis are frequent, of variable severity, ranging from benign parcel fractures to major forms breaking the continuity of the pelvic ring, for which the mortality rate still remains high. Road traffic accidents are the largest contributors to these injuries [1-4]. The prognosis of these fractures can be vital from the outset because of the frequency of hemorrhagic shock, related to vascular lesions or bleeding of fractured bone slices, and to the risk of infection favored by the opening of the fracture and associated intra-pelvic visceral lesions (rectum, bladder, urethra). Functionally, the prognosis remains reserved because of the frequency of nerve sequelae, genitourinary and especially osteoarticular resulting from lesions not or insufficiently reduced and fixed. The goal of this work was to estimate the prognosis of pelvic fractures in the orthopedic-traumatology department of Idrissa Pouye General Hospital.

Material and Methods

We performed a retrospective, descriptive and monocentric study over a period of 13 years. We included in this study, hospitalized patients or not for fractures of the pelvis (151 cases). We also add lifeless body deposits with pelvic fractures (32 cases). Patients who had an isolated fracture of the acetabulum were not included in this study. The studied population consisted mostly of men (n = 125) with a sex ratio of 2.15. The average age was 33.87 years old ± 17.52. Pelvic fractures were more common in young adults (50.27%). The radiological data were assessed by Tile’s classification and type A lésions were predominant (63.38%). We estimated the prognosis of these fractures by assessing their mortality, their complications and their sequelae.

Results

Mortality

One-third of the patients died (33.88%; n = 62). The lifeless body deposits were the most common (17.49%). Among the patients arrived alive, mortality was higher within 24 hours (11.48%). It decreased gradually over the course of the days (Figure 1). Autopsy was performed in all cases of death and found 32.24% of deaths from severe polytrauma, 1.09% from pulmonary embolism and 0.54% from septicemia.

Among the severe polytraumatic patients who died:

a. a severe cranial trauma was noted in 10.38% of cases;

b. a thoracic contusion with hemothorax of great single or bilateral abundance was observed in 15.84% of cases;

c. Abdominal contusion was noted in 6.55% of cases, including 2.76% ruptures of the spleen, 3.82% liver fractures and 1.64% renal bruising;

d. pelvic vascular lesions were observed in 12.02% of cases;

e. and fractures of the lower limbs were also noted in 12.02% of cases including 5.46% open fractures.

Complications and sequelae

Early complications

They were dominated by vascular lesions (14.80%) followed by urinary lesions (7.64%). Of these, rupture of the membranous urethra was the most common (4.91%). Cutaneous opening was noted in 4.90% of patients (Table 1). Vascular complications were more common in type C lesions (7.65%). The correlation between the lesional type and the occurrence of vascular complications was statistically significant with a p-value= 0.0025 (Table 2). Lesions of the anterior arch were noted in all patients with urinary complications (7.65%). Isolated injury of the anterior arch was responsible for 3.27% urethral rupture and 1.64% of bladder rupture. Simultaneous injury of the anterior and posterior arches resulted in 1.64% urethral rupture and 1.09% of bladder rupture. The correlation between the site of injury and the occurrence of urinary complications was not significant with a p-value = 0.98% (Table 3).

Secondary complications

Massive pulmonary embolism was noted in 1.64% of patients. One case of sepsis was observed (0.54%).

Late complications and sequelae

The malunion was observed in 4.91% of patients. One patient had a shortening of a lower limb (0.54%). Sacroiliac pain was observed in 5.46% of patients, of which 1.64% had sacroiliac arthrodesis in the long run. Urethral stricture was noted in two patients (1.09%). A urethroplasty was performed in everyone.

Discussion

Mortality

One third of our patients died (33.88%). Overall pelvis trauma mortality is typically between 5 and 15%, but can reach 50% [5-8]. In france, Caillot et al. [9] reports a mortality rate of 19% in polytrauma victims with pelvic fractures (Table 4). This high frequency of mortality is explained by the fact that in our study we took into account the cases before their arrival at the emergency department. Indeed, we think that among the dead polytrauma, there are probably some who had a fracture of the pelvis that has been unknown. Lifeless body deposits are the most common (17.48%). This could be explained by the violence of traffic accidents encountered in the cities of Dakar and the poor conditions of pre-hospital care. Among patients who arrived alive, the mortality is higher within 24 hours (11.47%) and decreases gradually over the days. This rate is very high compared to that obtained by Caitlin et al. [10] (2%). In fact, in our surgical emergencies, the lack of qualified trauma equipment and staff present a real problem in the immediate care of pelvis trauma patients. In addition to this, the multi-disciplinary care of traumatized of pelvis is not promoted in our hospitals. This is also the cause of this high mortality in the first 24 hours.

Complications

The state of hemorrhagic shock is noted in 25.68% of patients. Our results are consistent with those of Ngongang et al. [2] and Ameziane et al. [1] which are respectively 20% and 28% of the announced patients in shock state. This very high frequency of hemodynamic instability is related to pelvic vascular lesions associated with fractures more often in unstable pelvic fractures and multiple extra-pelvic lesional associations. In Caillot’s work [9], 48% of patients were in hemorrhagic shock. This is related to the predominance of type C lesions (58%) in her study.

In our series, vascular complications are the most common among the associated pelvic lesions (14.80%), in the work of Ameziane et al. [1] and Traoré et al. [4], vascular lesions are predominant with 21% and 10% respectively (Table 5). This high frequency of vascular complications is related to the importance of vascularization of the pelvis. In addition, the vessels are in direct contact with the bone frame and they can be damaged in case of fracture of the pelvis following a violent trauma. We have had 7.65% urinary complications. Among them, urethral rupture is the most common lesion (4.91%) and it concerns only the membranous portion. In the series of Sy et al. [3] and Ngongang et al. [2], urinary lesions are the most common immediate complications with 34% and 17.15%, respectively. They are all dominated by urethral rupture (Table 5). The frequency of urinary complications is 11.40% in the Odzébéa and al. series with predominantly membranous urethra involvement. According to Le Guillou and Ferrière [11], rupture of the membranous urethra is the most frequent lesion of urinary complications that can reach 90%. This is explained by the high frequency of ruptures of the pelvis’s anterior arch. The predominance of rupture of the membranous urethra is due to the fact that it passes through the uro-genital diaphragm which, anatomically, is sharp like a razor blade.

Conclusion

The prognosis of pelvic fractures is characterized by high early mortality in our country. This high rate of death is related to immediate complications and associated lesions responsible for polytrauma. Thus, to improve the lesion prognosis of patients:

a. the pick-up of trauma victims at the accident site must be done with a medical ambulance.

b. and the management of severe pelvic fractures must be multidisciplinary in our hospitals.

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