Study On Ecological Disposal And Water-salt Transport Process Of Dealkaline Bauxite Residue

Bauxite resdidue（BR）is a large amount of industrial waste generated during the production of aluminum oxide.It is difficult to comprehensively utilize due to its strong alkalinity,fine particles,and high salt content.Currently,the stockpile of bauxite residue may cause environmental pollution in the surrounding soil,atmosphere,and water,leading to ecological safety accidents.Ecological disposal is a promising way for large-scale disposal of bauxite residue.Based on the previous experimental results,titanium dioxide waste acid was used to regulate the alkalinity of bauxite residue.Through long-term p H monitoring experiments,the mechanisation of alkalinity regulation was studied using various microscopic characterization methods,and the parameters of scale-up dealkalization experiments were optimized.Pot experiments were conducted by adding river sand to improve its porosity,adding amendments including plant ash and decomposed edible fungi residue to increase nutrient content.Various indicators of plants,enzyme activity,and bacterial community abundance and species were determined to the feasibility of ecological reconstruction of dealkalized bauxite residue.Meanwhile,quantifying the contribution of various factors to promoting dealkalization bauxite residue pedogenesis.Water and salt transport studies were conducted for the optimal group of plant growth with differents amendments.The main conclusions are as follows:（1）The large amount of hydrogen ions generated by the hydrolysis of titanium dioxide waste acid faciliate to regulate the alkalinity of bauxite resdidue,and inhibits the p H rebound by consuming bound alkali.Adding hydrogen peroxide accelerates the hydrolysis process,effectively shortening the dealkalization time to 2 h.According to the enlarged experiment,m _BR:m _FS=10:1;When m _BR:v _H2O2=40:1,the main alkaline mineral[（NaAlSiO₄）₆·nH₂O]of bauxite redidue dissolved,and the pH reaches the ecological standard.（2）The addition of river sand and amendments improve the physicochemical properties and nutrients of dealkalized bauxite residue,reduce its bulk density and alkalinity,improve its porosity,field/saturated water capacity,and cation exchange capacity.And the change is greater as the proportion of amendments increases.（3）The dealkalized bauxite residue with addition of amendments can support plant growth.In the group of plant ash,the plant growth and biomass accumulation did not show significant changes with the increase of the addition ratio.When the addition ratio was 0.05%（M-0.05）,it was the best group for plant ash addition.However,the growth of plants in the group with the addition of decomposed edible fungi residue basically follows the rule of increasing with the addition ratio.When the addition ratio is 3%（B-3）,plant growth is optimal;The enzyme activities in the group with amendments were significantly higher than that of the RS group;The urease activity of the M-0.05 and B-3 groups increased by 29%and 56.67%respectively compared to the RS group,and the alkaline phosphatase activity increased by 43.3%and 188.11%respectively,β-The activity of glucosidase increased by 3.34%and 78.84%,respectively.The abundance and species of bacteria have changed,with the addition of plant ash groups,the abundance of Actinobacteria and Bacteroidetes decreased,while the abundance of Gemmatimonadetes and Chloroflexi increased;The abundance of Actinobacteria decreased significantly,while the abundance of Bacteroidetes,Gemmatimonadetes,and Chloroflexi increased in the group with the addition of mature bacterial rods;From the perspective of changes in the bacterial class,the application of improved materials reduced the abundance of Alphaproteobacteria and Bacteroidia classes,significantly increased the abundance of Gammaproteobacteria classes,and bacteria such as Chloroflexia,Longimimicrobia,Acidimimicrobia,Gemmatimonadetes,Subgroup＿6.（4）Multiple factors promote the formation of aggregates.When 0.05%（M-0.05）of plant ash is added,the proportion of decomposed edible fungi residue added is 3%（B-3）,and the proportion of matrix aggregates>0.5 mm is increased by 11.70%and 15.36%compared to the RS group,respectively.In the M-0.05 group,the contribution order of various factors to the formation of aggregate structure is plant>microorganism>physicochemical properties.In the B-3 group,the order is plant>physicochemical properties>microorganism.（5）The particles of dealkalized bauxite residue are extremely fine,making it difficult for water to penetrate.The addition of river sand and improved materials improved the water infiltration characteristics.Three water infiltration models were fitted,and Philip and Horton water infiltration models had the highest fitting degree,with R²=0.99.The water content and salt content increased with depth,indicating that the addition of river sand and improved materials was more conducive to the removal of soluble salts through leaching.