Acid Materials Drive Alkaline Conversion And Pedogenesis Process In Combined Bauxite Residue

Bauxite residue is a highly alkaline waste generated in the dissolution of bauxite to produce alumina,and has high alkalinity and salinity,which not only occupies a lot of land,but also is easily eroded by wind to pollute the surrounding ecological environment.The disposal of bauxite residue has become a critical issue in restricting the sustainable development of alumina enterprises.Meanwhile,it is difficult to remove alkalinity of bauxite residue,and bauxite residue contains a variety of toxic metals,which resulting in the resource utilization rate is less than 2%.In recent years,the ecological disposal of mine rehabilitation has provided an idea for large-scale disposal of bauxite residue.In this study,the combined bauxite residue was taken as the research object,and the alkalinity release process and alkaline regulation of bauxite residue with the ferrous sulfate were systematically studied through titration analysis and various microscopic characterization methods.Meanwhile,a variety of acid organic materials including nitrohumic acid,citric acid and vinegar residue,which were used to improve the structure and nutrient content of bauxite residue.The physical and chemical propertise of bauxite residue were determined in plant growth,the pedogenesis mechanism of bauxite residue driven the ferrous sulfate combined acid organic material was discussed.Combined with the germination experiment,the improvement effect of the substrate in pedgenisis for bauxite residue was analyzed.Main results are as follows:（1）With the addition of ferrous sulfate from 1%to 5%,the p H and alkalinity of bauxite residue decreased from 10.6 and 44.1%to 8.14 and 27.7%,respectively.Bauxite residue contains a variety of basic mineral phases,whose long-term release affects the process of dealkalinity in bauxite residue.The acid neutralization capacity of bauxite residue decreased significantly after the addtion of ferrous sulfate,indicating that the addition of ferrous sulfate led to the reduction of alkaline mineral component in bauxite residue,and reacted with bauxite residue to form gypsum and amorphous Fe OOH/Fe CO₃.（2）The treatment of acid organic materials combined with ferrous sulfate improved the nutrient components during pedeogenesis of bauxite residue.Nitrohumic acid increased TOC and available nitrogen content of bauxite residue to 16.5 g kg^-1 and26.8 mg kg^-1,respectively.Citric acid increased available phosphorus content of bauxite residue to 9.6 mg kg^-1.Among the three organic materials,the improvement of citric acid and nitrohumic acid were the most significant for bauxite residue.（3）The addition of acid organic materials improved aggregate structure in the bauxite residue.The citric acid resulted in increases of silt clay and microaggregate components,the nitrohumic acid resulted in increase of macroaggregate component.The citric acid may be more involved in the formation of organo-mineral complex in the bauxite residue,and the nitrohumic acid and vinegar residue may be helpful to aggregation of small particles.The results showed that Ca,Fe and Mg were mainly involved in the formation of microaggregates,while Si and Al were more inclined to the formation of macroaggregates.（4）The germination rate of plants was used as the main evaluation indicator,the results of multi-index redundancy analysis showed that the physical structure of bauxite residue was negatively correlated with alkalinity,and positively correlated with nutrient content and multivalent elements（Ca,Fe,Al and Si）.The results of multi-index contribution rate study showed that compared with the nutrient content（TOC and available nitrogen）of bauxite residue,the improvement of physical structure is more conducive to germination and growth of plants.