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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.  相似文献
2.
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.  相似文献
3.
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 leachates. Treatments 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~-, CO_3~(2-), HCO_3~-, and water soluble alkali, and suppress arsenic(As)content. Correlation analysis revealed significant linear correlations with pH and concentrations of OH~-, CO_3~(2-), HCO_3~-, water-soluble alkali, and metal ions. BSM treatment showed optimum results with neutralizing anions(OH~-, CO_3~(2-), and HCO_3~-), 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 metabolism. BSM 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.  相似文献
4.
Bauxite residue is the industrial waste generated from alumina production and commonly deposited in impoundments. These sites are bare of vegetation due to the extreme high salinity and alkalinity, as well as lack of nutrients. However, long term weathering processes could improve residue properties to support the plant establishment. Here we investigate the development of bacterial communities and the geochemical drivers in bauxite residue, using Illumina high-throughput sequencing technology. Long term weathering reduced the pH in bauxite residue and increased its nutrients content. The bacterial community also significantly developed during long term weathering processes. Taxonomic analysis revealed that natural weathering processes encouraged the populations of Proteobacteria, Chloroflexi, Acidobacteria and Planctomycetes, whereas reducing the populations of Firmicutes and Actinobacteria. Redundancy analysis (RDA) indicated that total organic carbon (TOC) was the dominant factors affecting microbial structure. The 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.  相似文献
5.
Biomass fermentation provides a potential route toward the ecological disposal for the bauxite residue (BR) with high alkalinity issues.However,how to accelerate the remedia-tion of the alkaline problem with a long-term durability is still a big challenge.Herein,we investigated the acceleration of the decomposition of straw toward organic acid species via a pyrolysis strategy as well as the pH stability during long-term dry-wet aging for the treated BR.The pH of pyrolytic BR at 300 ℃ is stabilized at around 8.90 after 70 days' dry-wet aging.During the aging,the main Ca-contained alkaline minerals of calcite and cancrinite are dis-solved and the content of exchangeable Na+ is reduced.This pyrolysis process can decom-pose straw quickly and produce more organic matters that are easily degraded to fulvic and humic acid as evidenced by 3D fluorescence spectrum analysis.Compared to the fermen-tation with straw under natural conditions,the alkalinity regulation of BR after pyrolysis is featured with shorter period and lower pH as well as long-term pH stability.Therefore,the synergistic pyrolysis of BR with straw provides an alternative method to address the alkaline issues,which is conducive to promoting the soil formation of BR.  相似文献
6.
Bauxite residue, a byproduct of alumina manufacture, is a serious environmental pollutant due to its high leaching contents of metals and caustic compounds. Four typical anions of CO32−, 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 time. The results revealed that washing process could remove the soluble composition in bauxite residue effectively. The leaching concentrations of typical anions in bauxite residue decreased as follows: c(CO32−) > 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 treatment. Under 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 slightly. However, it should be noted that water leaching has released metal ions such as As, B, Mo and V in bauxite residue to the surrounding environment. The 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 surface. The correlation analysis indicated that CO32− and HCO3 could effectively reflect the alkalinity of bauxite residue, and may be regarded as critical dealkalization indicators to evaluate alkalinity removal in bauxite residue.  相似文献
7.
Reduction of the high alkalinity of bauxite residue is a key problem to solve to make it suitable for plant growth and comprehensive utilization. In this study, phosphogypsum, a waste product from the phosphate fertilizer industry, was used to drive the alkaline transformation of the bauxite residue. Under optimal water washing conditions(liquid/solid ratio of 2 mL/g, 30°C, 24 hr), the impact of quantity added, reaction time and reaction mechanism during phosphogypsum application were investigated. Phosphogypsum addition effectively lowered p H levels and reduced the soluble alkalinity by 92.2%. It was found that the concentration of soluble Na and Ca ions in the supernatant increased gradually, whilst the exchangeable Na+and Ca~(2+)in solid phase changed 112 mg/kg and 259 mg/kg, respectively. Ca~(2+)became the dominant element in the solid phase(phosphogypsum addition of 2%, liquid/solid ratio of 2 mL/g, 30°C, 12 hr). X-ray diffraction data indicated that cancrinite and hydrogarnet were the primary alkaline minerals. SEM images suggested that phosphogypsum could promote the formation of stable macroaggregates, whilst the content of Ca~(2+)increased from 5.6% to 18.2% and Na reduced from 6.8% to 2.4%. Treatment with phosphogypsum could significantly promote the transformation of alkalinity cations by neutralization, precipitation and replacement reactions.This research provided a feasible method to promote soil formation of bauxite residue by phosphogypsum amendment.  相似文献
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