Alkaline-thermal activated electrolytic manganese residue-based geopolymers for efficient immobilization of heavy metals

Heavy metals are significant components of industrial wastes and have caused severe environmental pollution and human health problem. Here, solid wastes such as electrolytic manganese residue (EMR), fly ash (FA) and metakaolin (MK) were used as raw materials to prepare EMR-FA-MK geopolymers for efficient immobilization of heavy metals like Pb2+ and Cd2+. The EMR-FA-MK geopolymers can effectively immobilize heavy metals owing to the ion exchange and the mechanism was studied. The effects of calcination temperature on the performances of geopolymers were investigated. The compressive strength of geopolymers after alkaline-thermal activation is improved, and reaches the maximum of 18.3 MPa with calcinated temperature of 600 degrees C. The loading of heavy metals also affects the mechanical properties of EMR-FA-MK geopolymers. Geopolymers with 0.5% heavy metals possess the highest compressive strength of 18.4 MPa after 28 d ambient curing. The leaching test indicates that EMR-FA-MK geopolymers have good immobilization effect on Pb2+ and Cd2+. The leaching concentration of Pb2+ and Cd2+ by the geopolymers are 0.444 mg/L and 0.032 mg/L, both far below the limits in Chinese national standards. Materials characterizations prove that the geopolymer reaction has fully occurred and calcium-silicate hydrate is generated, which could enhance the mechanical properties of the geopolymers. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

Heavy metals from industrial wastes are a significant source of environmental pollution and health problems. By using solid wastes to prepare geopolymers, heavy metals like Pb2+ and Cd2+ can be effectively immobilized. The study shows that geopolymers prepared under certain conditions have high compressive strength and good immobilization effect on heavy metals.