Study On Characteristic And Mechanism Of Red Mud And Phosphogysum Solidifying Heavy Metal Contaminated Soil

At present,the main way to deal with red mud and phosphogypsum at home and abroad is to store them in the open air.This method not only occupies a large amount of land resources but also pollutes the ecological environment,and has great potential safety hazards.How to realize the comprehensive utilization of red mud and phosphogypsum is an extremely urgent research topic.At present,a small number of studies have analyzed the feasibility of using red mud,phosphogypsum to make cement,roadbed landfill materials and other construction materials.Relevant research on the application of red mud and phosphogypsum in the restoration of heavy metal contaminated soil is rarely involved.The research on acid resistance and durability of red mud phosphogypsum solidified soil samples has paid little attention.In addition,the reaction mechanism and hydration products of red mud,phosphogypsum stabilizing agent and traditional cement stabilizing agent are significantly different.This article aims to provide a new way for the resource utilization of red mud and phosphogypsum,through a series of physical and mechanical samples,toxic leaching tests,durability studies and micro-tests,based on the physical,mechanical and leaching characteristics of solidified soil To determine the ratio of red mud phosphogypsum stabilizing agent,reveal the mechanism of red mud phosphogypsum stabilizing agent stabilizing composite heavy metals and its engineering properties and leaching change rules in different environments,and analyze the environmental effects of this stabilizing agent stabilizing sample in the environment Under durability.The main conclusions are shown as follows:(1)When red mud is added alone,the strength of the cured sample is low,and the addition of phosphogypsum significantly increases the strength of the cured sample.Compared with the red mud fly ash clean slurry sample,the red mud phosphogypsum clean slurry sample has a higher unconfined compressive strength,up to 2262.5 k Pa.Toxic leaching test results show that the red mud-phospho-gypsum-cement stabilizing agent has a good Stabilization/solidification effect on copper,lead,and zinc,but it is difficult to meet the Ministry of Ecology and Environment "Identification of Leaching Toxicity Identification Standard for Hazardous Waste"(GB5085.3-2007),the result analysis shows that the pH of the leaching solution of the red mud phosphogypsum solidified sample is acidic is the main reason.(2)The fixation of red mud and phosphogypsum stabilizing agent to heavy metals is mainly achieved by the adsorption of red mud and ettringite,the ion exchange of Ca or Al in ettringite and heavy metals,and the encapsulation of ettringite lattices to heavy metals.The addition of cement and quick lime significantly improves the effect of red mud-based stabilizing agent on Stabilization/solidification heavy metals.Among them,R4P1CA2.5 and R4P1PC2 have better strength and fixed heavy metal performance than other stabilizing agent combinations.Microscopic analysis of the above two cured samples,SEM and TGA results show that there are three different crystalline ettringite in R4P1CA2.5 and R4P1PC2.(3)When solidifying heavy metal contaminated soil,the unconfined compressive strength and pH of the leaching solution of RPPC and RPCA solidified soil increase with the stabilizing age and the amount of stabilizing agent,and the leaching concentration of heavy metal ions with stabilizing age and solidification The dosage of the agent increases and decreases.In laboratory tests,the physical and chemical indexes of RPCA solidified soil were lower than RPPC solidified soil;RPPC10 solidified soil was lower than PC10 solidified soil;RPPC15solidified soil was higher than PC10 solidified soil.(4)In the case of using different pH value leaching agents,the heavy metal leaching concentration of the PC10 solidified soil and the RPPC solidified soil has the same trend,and the results show that as the pH value increases,it first decreases and then increases.At pH = 2,the leaching concentration of heavy metals is the highest,and at pH = 8,the leaching concentration of heavy metals is the lowest.(5)Under the conditions of freeze-thaw cycle and dry-wet cycle,as the amount of stabilizing agent increases,the cumulative mass loss rate of RPPC cured soil and RPCA cured soil gradually decreases.The cumulative mass loss rate of RPPC solidified soil at the same dosage is less than that of RPCA solidified soil;the unconfined compressive strength decreases,and the decrease rate decreases with the increase of the stabilizing agent content.The limited compressive strength is greater than RPCA solidified soil.(6)Under the conditions of freeze-thaw cycle and dry-wet cycle,the pH of the leaching solution of RPPC solidified soil and RPCA solidified soil decreased.The leaching concentration was negatively correlated with the result of the pH value of the leaching solution,and the leaching concentration increased overall after the 10-stage circulation.When the dosage is the same,the leaching concentration of RPPC solidified soil as a whole is lower than that of RPCA solidified soil.(7)The microscopic test results show that the main components of red mud-phosphogypsum-cement cured soil are hematite(Ilmenite),ettringite(Ettringite),anhydrite(Anhydrite)and hydrated calcium silicate(CSH).RPPC solidified soil relies on the hydration product ettringite to achieve the Stabilization/solidification of heavy metals by filling pores,physical wrapping and chemical adsorption.