Insight into immobilization of Pb2+ in aqueous solution and contaminated soil using hydroxyapatite/attapulgite composite

Abstract Hydroxyapatite/attapulgite (HA/A) composite was prepared in this study and used for remediation of Pb2+ in aqueous solution and contaminated soil. The adsorption performance and mechanism of Pb2+ were investigated through adsorption kinetics, adsorption isotherms in batch experiments and characteristics identification of material by FTIR, XPS and XRD analysis. The results showed that HA/A possessed a good removal efficiency of Pb2+ from solution with adsorption capacity of higher than 400 mg/g with increasing of pH to 6. In addition, the kinetics features of Pb2+ adsorption by HA/A were modeled better by pseudo second-order model and the adsorption isotherms of Pb2+ onto HA/A were primely fitted by Langmuir isotherm, obtained a maximum adsorption amount of 421.94 mg/g at 25℃, indicating that chemisorption on the monolayer surface of HA/A took place. Furthermore, adsorption mechanism and reaction pathway of Pb2+ were interpreted based on characterization analysis of material and adsorption kinetics and isotherms. Finally, the HA/A was applied as a passivator to immobilization of lead in polluted soil. Community Bureau of Reference (BCR) sequential extraction procedure experiments for determination of Pb forms were conducted and the results revealed that the acid extractable form of Pb could be efficiently converted to reducible or residual fractions after addition of HA/A. Toxicity characteristic leaching procedure (TCLP) tests indicated that HA/A composite had significant immobilization performance on lead-contaminated soil with a reduce of 58.75% of the TCLP extracted lead content in soil after 60 days of passivation when the dosage of HA/A composite was 2%.