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Arsenic dynamics in the rhizosphere and its sequestration on rice roots as affected by root oxidation

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Journal of Environmental Sciences 2014年第4期26卷 892-899页

作者： Weisong Pan Chuan Wu Shengguo Xue william hartley Institute of Environmental Engineering School of Metallurgical Science and Engineering Central South University College of Bioscience and Biotechnology Hunan Agricultural University Crop and Environment Sciences Department Harper Adams University

A pot experiment was conducted to investigate the effects of root oxidation on arsenic （As） dynamics in the rhizosphere and As sequestration on rice roots. There were significant differences （P 〈 0.05） in pH values between rhizosphere and non-rhizosphere soils, with pH 5.68-6.16 in the rhizosphere and 6.30-6.37 in non-rhizosphere soils as well as differences in redox potentials （P 〈 0.05）. Percentage arsenite was lower （4%-16%） in rhizosphere soil solutions from rice genotypes with higher radial oxygen loss （ROL） compared with genotypes with lower ROL （P 〈 0.05）. Arsenic concentrations in iron plaque and rice straw were significantly negatively correlated （R = -0.60, P 〈 0.05）. Genotypes with higher ROL （TD71 and Yinjingmanzhau） had significantly （P 〈 0.001） lower total As in rice grains （1.35 and 0.96 mg/kg, respectively） compared with genotypes with lower ROL （IAPAR9, 1.68 mg/kg; Nanyangzhan 2.24 mg/kg） in the As treatment, as well as lower inorganic As （P 〈 0.05）. The present study showed that genotypes with higher ROL could oxidize more arsenite in rhizosphere soils, and induce more Fe plaque formation, which subsequently sequestered more As. This reduced As uptake in aboveground plant tissues and also reduced inorganic As accumulation in rice grains. The study has contributed to further understanding the mechanisms whereby ROL influences As uptake and accumulation in rice.

关键词： arsenic iron plaque rhizosphere radial oxygen loss rice

The dynamic development of bacterial community following long-term weathering of bauxite residue

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Journal of Environmental Sciences 2020年第4期32卷 321-330页

作者： Hao Wu Li Chen Feng Zhu william hartley Yifan Zhang Shengguo Xue School of Metallurgy and Environment Central South UniversityChangsha 410083China Crop and Environment Sciences Department Harper Adams UniversityNewportShropshire TF108 NBUK

Bauxite residue is the industrial waste generated from alumina production and commonly deposited in *** sites are bare of vegetation due to the extreme high salinity and alkalinity,as well as lack of ***,long term weathering processes could improve residue properties to support the plant *** we investigate the development of bacterial communities and the geochemical drivers in bauxite residue,using Illumina high-throughput sequencing *** term weathering reduced the pH in bauxite residue and increased its nutrients *** bacterial community also significantly developed during long term weathering *** analysis revealed that natural weathering processes encouraged the populations of Proteobacteria,Chloroflexi,Acidobacteria and Planctomycetes,whereas reducing the populations of Firmicutes and *** analysis(RDA)indicated that total organic carbon(TOC)was the dominant factors affecting microbial *** results have demonstrated that natural weathering processes improved the soil development on the abandoned bauxite residue disposal areas,which also increased our understanding of the correlation between microbial variation and residue properties during natural weathering processes in Bauxite residue disposal areas.

关键词： Bauxite residue disposal areas Bacterial community Natural weathering processes Driving factors Soil formation

Changes in distribution and microstructure of bauxite residue aggregates following amendments addition

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Journal of Environmental Sciences 2019年第4期31卷 276-286页

作者： Shengguo Xue Yuzhen Ye Feng Zhu Qiongli Wang Jun Jiang william hartley School of Metallurgy and Environment Central South University Crop and Environment Sciences Department Harper Adams UniversityNewport

Bauxite residue is a highly alkaline byproduct which is routinely discarded at residue disposal areas. Improving soil formation process to revegetate the special degraded lands is a promising strategy for sustainable management of the refining industry. A laboratory incubation experiment was used to evaluate the effects of gypsum and vermicompost on stable aggregate formation of bauxite residue. Aggregate size distribution was quantified by fractal theory, whilst residue microstructure was determined by scanning electron microscopy and synchrotron-based X-ray micro-computed tomography. Amendments addition increased the content of macro-aggregates(> 250 μm) and enhanced aggregate stability of bauxite residue. Following gypsum and vermicompost addition, fractal dimension decreased from 2.84 to 2.77, which indicated a more homogeneous distribution of aggregate particles. Images from scanning electron microscopy and three-dimensional microstructure demonstrated that amendments stimulate the formation of improved structure in residue aggregates. Pore parameters including porosity, pore throat surface area, path length, and path tortuosity increased under amendment additions. Changes in aggregate size distribution and microstructure of bauxite residue indicated that additions of gypsum and vermicompost were beneficial to physical condition of bauxite residue which may enhance the ease of vegetation.

关键词： Bauxite residue Fractal characteristics Aggregate microstructure Substrate amendment Soil formation

Effect of arsenic on spatial pattern of radial oxygen loss and iron plaque formation in rice

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Transactions of Nonferrous Metals Society of China 2017年第2期27卷 413-419页

作者：吴川黄柳薛生国潘炜松邹奇 william hartley 莫竞瑜中南大学冶金与环境学院长沙410083 湖南农业大学生物科学技术学院长沙410128 Crop and Environment Sciences Department Harper Adams University

The effects of different arsenic （As） treatments on spatial pattern of radial oxygen loss （ROL）, iron （Fe） plaque formation and As accumulation in rice were investigated using three rice genotypes, planted under greenhouse conditions. Arsenic was applied to soil at 50 and 100 mg/kg, with untreated soil used as a control having an average As concentration of 8.5 mg/kg. It was demonstrated that the ratio of ROL in root tips to that at the root base slightly decreased with increasing As concentration, suggesting that the spatial ROL patterns in these groups may be shifted from the “tight” barrier towards the “partial” barrier form. Furthermore, increasing As concentration led to a increase in Fe plaque formation on root surfaces. In addition, root As concentrations of genotypes in 50 and 100 mg/kg As treatments were significantly higher than that of control treatment （P〈0.05）. Grain As concentration of genotype Nanyangzhan （with lower ROL） was significantly higher （P〈0.05） than that of genotype CNT87059-3 with higher ROL.

关键词： arsenic iron plaque rice spatial pattern of ROL

Variation on leaching behavior of caustic compounds in bauxite residue during dealkalization process

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Journal of Environmental Sciences 2020年第6期32卷 141-150页

作者： Yujun Wu Meng Li Feng Zhu william hartley Jiaxin Liao Wenhui An Shengguo Xue Jun Jiang School of Metallurgy and Environment Central South University932 Lushan South RoadChangsha410083China Crop and Environment Sciences Department Harper Adams UniversityNewportShropshireTF108NBUnited Kingdom Civil and Environmental Engineering Department The Hong Kong University of Science and TechnologyClear Water BayKowloonHong KongChina

Bauxite residue,a byproduct of alumina manufacture,is a serious environmental pollutant due to its high leaching contents of metals and caustic *** typical anions of CO3^2-,HCO3^-,Al(OH)4^- and OH-(represented caustic compounds) and metal ions(As,B,Mo and V) were selected to assess their leaching behavior under dealkalization process with different conditions including liquid/solid ratio(L/S ratio),temperature and leaching *** results revealed that washing process could remove the soluble composition in bauxite residue *** leaching concentrations of typical anions in bauxite residue decreased as follows:c(CO3^2-)> c(HCO3^-)> c[Al(OH)4-]> c(OH-).L/S ratio had a more significant effect on leaching behavior of OH-,whilst the leaching concentration of Al(OH)4-varied larger underleaching temperature and time *** the optimal leaching,the total alkaline,soluble Na concentrations,exchangeable Ca concentrations were 79.52,68.93,and 136.0 mmol/L,respectively,whilst the soluble and exchangeable content of As,B,Mo and V in bauxite residue changed ***,it should be noted that water leaching has released metal ions such as As,B,Mo and V in bauxite residue to the surrounding *** semiquantitative analysis of XRD revealed that water leaching increased the content of gismondine from 2.4% to 6.4%.The SEM images demonstrated the dissolution of caustic compounds on bauxite residue *** correlation analysis indicated that CO3^2- and HCO3^- could effectively reflect the alkalinity of bauxite residue,and may be regarded as critical de alkalization indicators to evaluate alkalinity removal in bauxite residue.

关键词： Bauxite residue Dealkalization Caustic compounds Soluble alkalinity Metal ions

Effect of amendments on the leaching behavior of alkaline anions and metal ions in bauxite residue

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Journal of Environmental Sciences 2019年第11期31卷 74-81页

作者： Tao Tian Jinaju Zhou Feng Zhu Yuzhen Ye Ying Guo william hartley Shengguo Xue School of Metallurgy and Environment Central South University Changsha 410083 China Crop and Environment Sciences Department Harper Adams University Newport Shropshire TF10 8NB UK

A column leaching experiment was used to investigate the efficacy of amendments on their ability to remove alkaline anions and metal ions from bauxite residue *** included,simulated acid rain (AR),phosphogypsum + vermicompost (PVC),phosphogypsum + vermicompost + simulated acid rain (PVA),and biosolids + microorganisms (BSM) together with controls (CK).Results indicated that amendment could effectively reduce the leachate pH and EC values,neutralize OH-,CO32-,HCO3-,and water soluble alkali,and suppress arsenic (As) *** analysis revealed significant linear correlations with pH and concentrations of OH-,CO32-,HCO3-,water-soluble alkali,and metal *** treatment showed optimum results with neutralizing anions (OH-,CO32-,and HCO3-),water soluble alkali,and removal of metal ions (Al,As,B,Mo,V,and Na),which was attributed to neutralization from the generation of small molecular organic acids and organic matter during microbial *** treatment reduced alkaline anions and metal ions based on neutralization reactions in bauxite residue leachate,which reduced the potential pollution effects from leachates on the soil surrounding bauxite residue disposal areas.

关键词： Bauxite residue leachate Amendments Alkaline anions Metal ions

Migration and distribution of saline ions in bauxite residue during water leaching

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Transactions of Nonferrous Metals Society of China 2018年第3期28卷 534-541页

作者： Xiang-feng KONG Xing-xing JIANG Sheng-guo XUE Ling HUANG william hartley Chuan WU Xiao-fei LI School of Metallurgy and Environment Central South UniversityChangsha 410083China Chinese National Engineering Research Center for Control&Treatment of Heavy Metal Pollution Central South UniversityChangsha 410083China

Bauxite residue,a highly saline solid waste produced from digestion of bauxite for alumina production,is hazardous to the environment and restricts vegetation establishment in bauxite residue disposal areas.A novel water leaching process proposed here was used to investigate the dynamic migration and vertical distribution of saline ions in bauxite *** results show that water leaching significantly reduced the salinity of bauxite residue,leaching both saline cations Na+,K+,Ca2+and anions CO32-,SO42-,HCO3-.Na+and K+migrated from 40-50 to 20-30 cm of the column,presenting a high migration *** migration capacity of Ca2+was lower and accumulated at 30-40 cm of the ***32-initially distributed at 20-30 cm of the column,subsequently transported to 30-40 cm of the column,and finally returned to 20-30 cm of the column along with ***42-was originally distributed at 40-50 cm,but finally migrated to 20-30 cm of the ***,HCO3-remained at the bottom of the column,and its migratory was less affected by evaporation.

关键词： bauxite residue salinity ion migration column stimulation water leaching

Improvements on physical conditions of bauxite residue following application of organic materials

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Journal of Environmental Sciences 2022年第6期34卷 198-208页

作者： Ying Guo Yuzhen Ye Feng Zhu Rui Xue Xianchao Zhang Mingxing Zhu william hartley Lin Guo Shengguo Xue School of Metallurgy and Environment Central South UniversityChangsha 410083China College of Environmental Sciences Sichuan Agricultural UniversityChengdu 611130China Agriculture and Environment Department Harper Adams UniversityNewportShropshireTF108NBUK Henan Institute of Geological Survey Zhengzhou 450001China

Soil formation and ecological rehabilitation is the most promising strategy to eliminate environmental risks of bauxite residue disposal areas. Its poor physical structure is nevertheless a major limitation to plant growth. Organic materials were demonstrated as effective ameliorants to improve the physical conditions of bauxite residue. In this study, three different organic materials including straw(5% W/W), humic acid(5% W/W), and humic acidacrylamide polymer(0.2% and 0.4%, W/W) were selected to evaluate their effects on physical conditions of bauxite residue pretreated by phosphogypsum following a 120-day incubation experiment. The proportion of 2-1 mm macro-aggregates, mean weight diameter(MWD) and geometric mean diameter(GWD) increased following organic materials addition, which indicated that organic materials could enhance aggregate stability. Compared with straw, and humic acid, humic acid-acrylamide polymer application had improved effects on the formation of water-stable aggregates in the residues. Furthermore, organic materials increased the total porosity, total pore volume and average pore diameter, and reduced the micropore content according to nitrogen gas adsorption(NA) and mercury intrusion porosimetry(MIP)analysis, whilst enhancing water retention of the residues based on water characteristic curves. Compared with traditional organic wastes, humic acid-acrylamide polymer could be regarded as a candidate according to the comprehensive consideration of the additive amount and the effects on physical conditions of bauxite residue. These findings could provide a novel application to both Ca-contained acid solid waste and high-molecular polymers on ecological rehabilitation at disposal areas.

关键词： Bauxite residue Soil formation Aggregates Pore characteristics Water retention

Leaching optimization and dissolution behavior of alkaline anions in bauxite residue

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Transactions of Nonferrous Metals Society of China 2018年第6期28卷 1248-1255页

作者： Xiao-fei LI Yu-zhen gE Sheng-guo XUE Jtm JIANG Chuan WU Xiang-feng KONG william hartley Yi-wei LI School of Metallurgy and Environment Central South UniversityChangsha 410083China Chinese National Engineering Research Center for Control ＆ Treatment of Heavy Metal Pollution Central South UniversityChangsha 410083China Crop and Environment Sciences Department Harper Adams UniversityNewportShropshireTF10 8NBUnited Kingdom

Bauxite residue is a highly alkaline waste containing soluble alkaline anions, which can cause environmental concerns. The optimal leaching conditions, distribution of alkaline anions, types of pivotal alkaline anions and their dissolution behaviors were investigated based on the combination of single factors-orthogonal experiments and leaching stage experiment. Using a two-stage leaching, 86% of the soluble alkaline anions（CO3^2-, HCO4^-,Al（OH）4^-, OH^-） were leached with a L/S ratio of 2 mL/g, at 30 ℃, over 23 h. During the first stage of leaching, approximately 88% of alkaline anions were leached from the dissolution of free alkali（Na OH, carbonate, bicarbonate, NaAl（OH）4） with the rest originating from the dissolution of alkaline minerals（calcite, cancrinite and hydrogarnet）. Supernatant alkalinity was 69.78 mmol/L with CO3^2- accounting for 75%. Furthermore, carbonate leaching was controlled by solid film diffusion using the Stumm Model with an apparent activation energy of 10.24 kJ/mol.

关键词： bauxite residue alkaline anions carbonate leaching optimization dissolution behavior