Yuzhen Ye

Bio: Yuzhen Ye is an academic researcher from Central South University. The author has contributed to research in topics: Bauxite & Humic acid. The author has an hindex of 6, co-authored 12 publications receiving 235 citations.

Industrial wastes applications for alkalinity regulation in bauxite residue: A comprehensive review

Abstract: Bauxite residue is a highly alkaline material generated from the production of alumina in which bauxite is dissolved in caustic soda. Approximately 4.4 billion tons of bauxite residues are either stockpiled or landfilled, creating environmental risks either from the generation of dust or migration of filtrates. High alkalinity is the critical factor restricting complete utilization of bauxite residues, whilst the application of alkaline regulation agents is costly and difficult to apply widely. For now, current industrial wastes, such as waste acid, ammonia nitrogen wastewater, waste gypsum and biomass, have become major problems restricting the development of the social economy. Regulation of bauxite residues alkalinity by industrial waste was proposed to achieve ‘waste control by waste’ with good economic and ecological benefits. This review will focus on the origin and transformation of alkalinity in bauxite residues using typical industrial waste. It will propose key research directions with an emphasis on alkaline regulation by industrial waste, whilst also providing a scientific reference point for their potential use as amendments to enhance soil formation and establish vegetation on bauxite residue disposal areas (BRDAs) following large-scale disposal.

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

Abstract: 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.

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

Abstract: 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−, CO32−, HCO3−, and water soluble alkali, and suppress arsenic (As) content. Correlation analysis revealed significant linear correlations with pH and concentrations of OH−, CO32−, HCO3−, water-soluble alkali, and metal ions. BSM 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 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.

Vermicompost and Gypsum Amendments Improve Aggregate Formation in Bauxite Residue

Abstract: Improving aggregate formation and stability of bauxite residue is essential for the development of a soil on the residue. Effects of gypsum and vermicompost on related chemical and physical conditions of bauxite residue were studied in a laboratory incubation experiment. Addition of gypsum at 2% and 4% w/w reduced pH and exchangeable sodium percentage, whilst increasing exchangeable calcium content. Addition of vermicompost reduced bulk density, whilst significantly increasing porosity and total organic carbon. Vermicompost had a positive effect on the formation and stabilization of water-stable aggregates in the residue, whilst gypsum was more beneficial to silt-sized microaggregate flocculation. Amendments also enhanced the erosion resistance of bauxite residue. Furthermore, wet sieving using the modified Le Bissonnais’ (LB) method revealed that in comparison to differential clay swelling and mechanical breakdown, slaking was the major disaggregation mechanism of residue aggregates. The combination of gypsum and vermicompost converted the residue from a sheet-like structure to a granular macroaggregated structure, whilst converting microaggregates from a grain to a granular or prismatic structure. The findings of this work suggest that application of gypsum and vermicompost to bauxite residue may directly influence aggregate size distribution and its micromorphology, resulting in the improvement of both aggregate stability and structure.

Phosphogypsum stabilization of bauxite residue: Conversion of its alkaline characteristics.

Abstract: 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 pH 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 Ca2 + in solid phase changed 112 mg/kg and 259 mg/kg, respectively. Ca2 + 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 macro-aggregates, whilst the content of Ca2 + 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.