Immobilization capacity of element arsenic in alkali-activated slag-arsenic tailing system during self-healing process

The utilization of alkali-activated slag systems for encapsulating hazardous tailings to produce polymers can effectively reduce the leaching of hazardous elements. Nevertheless, the propensity of these polymers to develop cracks during service poses a risk of secondary release of hazardous elements. For this reason, this study focused on the development of polymer materials using calcium carbide residue (CCR), phosphogypsum (PG), ground granulated blast furnace slag (GGBS), superabsorbent polymers (SAP), and arsenic-containing tailings. The self-healing behavior of the alkali-activated slag system after cracking was analyzed, specifically targeting arsenic immobilization. Additionally, the crack width, crack area, and mechanical properties of the polymers was tested to evaluate their self-healing potential. The results revealed that the main healing products consisted of calcium silicate hydrate (C–S–H), ettringite (AFt), and calcite. These products covered the inner surfaces of the cracks, resulting in a reduction by 78.1–95.9% in arsenic leaching concentration after healing for 56 days. The incorporation of PG led to increased generation of AFt and facilitated secondary hydration reactions for self-healing. This enhanced crack closure and promoted strength recovery while simultaneously improving the pore structure of the crack walls. As a result, the leaching of arsenic from the cracked polymer was effectively inhibited. The mechanism of arsenic immobilization by polymers during self-healing process was as follows: i) adsorption of AsO₄³⁻ by C–S–H; ii) ion exchange of AFt with AsO₄³⁻; iii) physical encapsulation of mixed products including C–S–H, AFt, calcite, and swollen SAP.