Synthesis of foamed geopolymers by substituting fly ash with tailing slurry for the highly efficient removal of heavy metal contaminants: Behavioral and mechanistic studies

Abstract

This study aimed to synthesize porous geopolymers from tailing slurry, a byproduct of bauxite mining, for use as potential materials for groundwater remediation. The effects of various factors, such as foaming agents, liquid-solid (L/S) ratio, and foam stabilizers, on the geopolymers’ pore structure and adsorption properties were investigated. Batch experiments and characterization methods were conducted to evaluate the adsorption capacity and mechanism of the geopolymers on binary heavy metals (Pb²⁺ and Cu²⁺). The results showed that adjusting the foaming behavior resulted in a porous geopolymer with porosity of 81.4%, connectivity of 17.2%, and water absorption rate of 122.9%. The presence of closed pores and capillaries hindered the removal performance of heavy metals. In contrast, optimizing foaming behavior could increase the adsorption capacity of Pb²⁺ from 7.49 mg/g to 24.95 mg/g by improving pore connectivity. The main removal mechanisms include physical sealing, chemical precipitation of heavy metal ions with —OH, and the formation of chemical bonds T (Si, Al)—O—M (Pb, Cu). Tailing slurry-based porous geopolymers (TPGs) demonstrated excellent heavy metal removal performance and exhibited great potential in remediating mine-polluted groundwater.