Effect of alkali-activation conditions on microstructure and heavy metal solidification of alkali-activated converter steel slag and municipal solid waste incineration fly ash

Abstract

Alkaline-activation technology was an effective means of disposing of low-activity and heavy-metal-containing industrial solid wastes. In this paper, alkali-activated converter steel slag and municipal solid waste incineration fly ash (MSWIFA) were prepared by modulating alkali-activation conditions. The effect of alkali-activation conditions on microstructure of C-(A)-S-H and leaching of lead and zinc, pore solution pH, and the correlation among them were revealed. The results showed that low modulus Na₂SiO₃ and highly Na₂O dosage facilitated the substitution of Al for Si in C-S-H gels and produced C-(A)-S-H exhibited a decreased Ca/Si ratio and an increased proportion of Q3 in Si-O-T chain. The leaching of lead was mainly dependent on Na₂SiO₃ modulus, and high Na₂SiO₃ modulus facilitated solidification of lead. The stabilization of zinc was largely affected by pore solution pH, leading to larger leaching in the matrix with high pore solution pH. Higher dosages of Na₂O significantly increased compressive strength but were detrimental to stabilization of lead and zinc. The study provided some guidance for selection of alkali-activation conditions for harmless treatment of steel slag and MSWIFA.