Investigation on the behavior of fly ash phosphate-based geopolymer stabilized acidic lead contaminated soil

The main binder on the market are cement-based materials and alkali-activated materials, which is incompatible with the acidic Pb2+ polluted soil. The fly ash phosphate-based geopolymer (APG) binder is acidic and has good performance in acidic environment and has superior S/S effect on Pb2+ polluted soil, but its applicability to acid Pb2+ polluted soil and optimal components has not been investigated. in this article, the APG binder was used to treat acid Pb2+ polluted soil, and the binder components were optimized based on different indexes. The impacted of the ADP content, liquid-solid ratio (L/S), curing time, and extract environment on the mechanical strength, EC, pH, and toxic leaching of APG treated acidic Pb2+ polluted soil were analyzed, and related mechanism was studied. Results show that the APG binder effect of S/S on acidic Pb2+ was excellent in different environments, and the APG treated acidic Pb2+ polluted soil has a good mechanical strength (> 350 kPa), the mechanical strength was impacted by the L/S and ADP concentration, when the APG binder was composed of 30 % ADP content and the 0.35 L/S, the APG treated acidic Pb2+ polluted soil yielded a maximum machanical strength of 1.93 MPa. The Pb2+ leaching was related to the extract environments, the Pb2+ leaching was minimum under deionized water and sulfuric-nitric acid environments (< 0.1 mg/L). Also, the Pb2+ was immobilized due to lead phosphate compound formation. Overall, the APG binder has good compatibility with acidic environment and great potential in treating acidic heavy metal contaminated soils, but further investigation on the durability of the APG binder is also needed.