Influence Of Red Mud Based Granular Materials On Phosphorus Availability And Migration And Transformation In Soil

Red mud(RM)is a red residue discharged from aluminum industry,which is seriously harmful to environment.In order to promote the comprehensive utilization of red mud,based on the problems such as serious agricultural non-point source pollution,soil available phosphorus deficiency and insufficient phosphate mineral resources,the red mud based granular materials(RMG),prepared by roasting and activation,was applied as soil amendment in this study,in which the red mud was used as main raw material and a small amount of fly ash and cement was added.The study was carried out around the effect of RMG on the phosphorus availability and migration and transformation of soil,focusing on the effect of RMG on phosphorus availability in calcareous soil and analyzing the control effect of RMG on soil phosphorus loss under leaching state.In addition,the phosphorus-rich red mud based granular materials(PRMG)was applied to the soil to study the phosphorus release ability of PRMG.At the same time,the physical and chemical properties of the soil with red mud material were characterized.The effect of RMG on soil phosphorus availability was studied and the results indicated that,the addition of RMG increased the soil p H and CaCO₃content,further enhancing the adsorption and fixation of soil phosphorus and reducing the availability of soil phosphorus.The Olsen-P content in the soil with 10%RMG dosage was 42mg/kg after 60 days of culture,which was decreased by 61.3%compared to that in the control soil without RMG dosage.A dynamic equilibrium in the transformation of various inorganic phosphorus forms was proposed,in which Ca₂-P and Ca₈-P were gradually transformed into Ca₁₀-P,Ca₂-P was transformed into Al-P and Fe-P and furtherly transformed into O-P.The correlation between soil inorganic phosphorus and Olsen-P content was analyzed and the results indicated that:Ca₂-P was the most active phosphorus source,which directly affected the Olsen-P content and was considered as the most available phosphorus source for plants.Ca₈-P,Fe-P and Al-P were medium active phosphorus sources,which affected Olsen-P content through various transformations and could be used as reserve phosphorus sources for plants.O-P and Ca₁₀-P were stable phosphorus sources,which had a little contribution to Olsen-P content and were difficult to be used for plants.The study on the control effect of RMG on soil phosphorus loss indicated that,the addition of RMG increased the critical value of soil phosphorus leaching loss and showed good performance on phosphorus loss control form soil.The critical value of phosphorus leaching in the soil with 10%RMG dosage was 287 mg/kg,which was4.46 times compared with that in the original soil.The main forms of phosphorus in the leachate could be summarized as follows,at the initial stage of leaching,lots of fine and loose particles contained in the soil resulted in a high concentration of particulate phosphorus in the leachate.At the later stage of leaching,the main form of phosphorus in the leachate was stable and mainly existed as soluble reactive phosphorus.Increasing RMG dosage raised the p H in leachate and decreased the concentration of total phosphorus,indicating that the alkaline components in RMG promoted the adsorption and fixation of soil phosphorus.During this process,the Caand Fe components in RMG were dissolved and combined with phosphorus in soil to form a relatively stable phase.Moreover,a large amount of phosphorus was adsorbed on the RMG surface,thus further reducing the loss of phosphorus from soil.The study on the release effect of PRMG in soil demonstrated that,increasing temperature could significantly promote the release of phosphorus from PRMG into soil.Increasing soil moisture content could promote the resolution and migration of phosphorus from PRMG to soil.Phosphorus was released continuously after PRMG dosage,and TP content in soil was increased gradually with increasing PRMG dosage and prolonging culture time.The effect of PRMG on soil phosphorus availability was mainly manifested in the following two aspects.Firstly,PRMG released phosphorus into soil and increased soil Olsen-P content.Secondly,the release of alkaline components in PRMG improved the fixation role of soil phosphorus,and reduced Olsen-P content in the soil.The combined influence of these two aspects led to an optimum value of PRMG dosage,and the highest Olsen-P content was obtained in this study when the PRMG dosage in the soil was 6%.In conclusion,the red mud based granular material was applied to the soil in this study,and the results showed that RMG could effectively promote the adsorption and fixation of soil phosphorus and reduce the loss of soil phosphorus.In addition,after using the material to recover phosphorus from phosphorus contained wastewater,the obtained phosphorus-rich material had a good phosphorus release performance in soil.The influence rules of RMG on soil phosphorus availability and migration and transformation were clarified in this study,which could provide new ideas for red mud resource utilization and phosphorus resource recovery,and relevant research conclusions could provide a theoretical basis for the further application of materials.