Passivation Of Modified Attapulgite To Heavy Metal Lead In Rare Earth Tailings Soil

Currently,soil pollution with persistent and potentially toxic heavy metals is ubiquitous worldwide.Especially in the mining and processing of mines,the unreasonable treatment of wastes rich in heavy metals has caused serious pollution to the mining area and the surrounding soil.The extensive mining of ionic rare earth mines in southern Gannan,the unreasonable disposal of tailings waste residues has resulted in excessive heavy metal content in the surrounding environment of the mining area,and the self-buffering capacity and purification and repair capacity of the ecosystem are extremely low,which has posed a serious threat to the lives and health of local residents.Accordingly,in this study,natural and organic modified attapulgite（APT）was used as the passivating agent.The chemical composition,functional groups,surface characteristics,etc.of the two passivating agents were analyzed using XRF,SEM,FTIR,XRD and other chemical analysis methods.For analysis.The selected research object is an abandoned rare earth tailings soil in Dingnan County,Ganzhou.The effects of natural and organic modified attapulgite on the pH value of the soil and the form of lead occurrence in the soil were studied by passivation repair experiments,and the passivation behavior of heavy metals was analyzed..Subsequent studies on the adsorption characteristics and thermodynamics of heavy metal lead in passivated soils revealed the mechanism of heavy metal lead adsorption.It provides theoretical support for the development of high-efficiency soil passivation remediation agents,and has important theoretical and practical significance for promoting the remediation of heavy metal lead pollution in mine tailings soil.The research results are as follows:（1）The organically modified attapulgite was prepared by acid activation treatment and high-speed shearing method.The main chemical components of attapulgite are SiO₂,Al₂O₃,MgO and Fe₂O₃,other minor components are K₂O and CaO,and contain a small amount of Na₂O,P₂O₅ and SO₃,and the specific surface area is 400 m²/g.Through characterization,it was found that the acid activation treatment can remove impurities such as water and carbonates in the APT structure,and the through holes increase the specific surface area and reveal the organic active groups.Organically modified grafted mercapto,hydroxyl,etc.with the inner surface.The specific surface area of the modified attapulgite rod increases,more adsorption sites appear on the inner surface of the channel,and the ion exchange capacity and complexing ability are greatly improved,so that the modified attapulgite rod has a significant curing advantage.（2）After applying two passivating agents to the tailings soil through the passivation experiment,the pH value of the tailings soil increased and was close to 7,and the physical and chemical properties of the soil were improved;compared with natural attapulgite,it was found that It exhibits stronger passivation ability,which lowers the acid extractable content from 25.69 mg/kg to 7.42 mg/kg.It also promotes the conversion of Pb from the acid-extracted state to the residue state,and the mobility in the soil decreases by less than 1.91,which greatly reduces the bioavailability.The modified attapulgite has a good fixing effect on Pb,the content of TCLP extracted state is reduced by 65.70%compared with the control group,and the environmental ecological risk of soil contaminated by heavy metals is effectively controlled.After applying different treatment passivating agents,the relationship between the extraction state of heavy metal lead acid and the extraction state of TCLP is negatively correlated with pH,so controlling pH is also a common method for passivation repair.（3）Through static adsorption experiments,it was found that the soil with natural and modified attapulgite passivating agents showed strong adsorption and removal capacity for heavy metal ions Pb²⁺,and the adsorption capacity of thiolated soil for Pb²⁺was more significant.The removal amount of Pb²⁺by both passivating agents increases with the increase of the dosage,pH value,dosage,reaction time,heavy metal ion concentration and temperature,but in order to avoid Pb²⁺in the form of hydroxide precipitation Removal and comprehensive consideration of the use cost and removal efficiency of the passivating agent.At room temperature,the optimal removal conditions when the initial concentration of Pb²⁺is 40 mg/L are as follows:the natural passivator soil and the modified passivator soil are added to Pb²⁺.The dosage is 0.4 g and 0.8 g,respectively,the latter removal rate is greater;the initial pH of Pb²⁺solution is 6.0 and 5.0,respectively,the latter is more suitable for acid soil environment;the reaction equilibrium time is 180 min and 360 min,respectively,the latter adsorption The amount is greater.The removal of Pb²⁺by the two kinds of passive soils is consistent with the pseudo second-order kinetic equation and the Freundlich model,indicating that the removal process is dominated by chemical adsorption reaction,and the surface of the material is composed of multiple layers of uneven crystal structure.Among the thermodynamic parameters of Pb²⁺adsorption,ΔG<0,ΔH andΔS are all greater than 0,indicating that the removal process is a spontaneous process of endothermic and entropy increase.The maximum removal of Pb²⁺by natural passivated soil and thiolated soil at room temperature was 927 mg/kg and 1007 mg/kg,respectively.The removal mechanism is mainly ion exchange of Ca²⁺,Mg²⁺and Pb²⁺,followed by adsorption and surface precipitation.In addition,the removal of Pb²⁺by the modified attapulgite grafted with mercapto groups also has a complex reaction mechanism between chemical groups such as-SH and-OH and heavy metal ions.