The lightweight aggregate ceramsite (LAC) was prepared from by-product sulfate salt slag (BPSS) of high-salt organic wastewater with fly ash. The BPSS fixation rate, leaching toxicity, morphological structures and potential environmental risks of heavy metals in LAC were investigated. BPSS can be fixed in LAC when the mass ratio of Fly ash: Kaolin: clay was 7:1:2, the addition of BPSS was 28%, the heating rate was 8°C min-1, and the calcination temperature was 1100°C. The characteristics of the LAC met the requirements for Chinese lightweight aggregate standards (GB/T17431.2-2010). The Total Organic Carbon (TOC) content of the aqueous leaching liquor in LAC was less than 0.5 mg·L-1. And the fixation rate of heavy metal was more than 99%, which meets the requirements of GB 5085.3-2007. The BPSS immobilization mechanisms were mainly related to the formation of new crystal phases, including Leucite (KAlSi2O6), Albite (Na2O·Al2O3·6SiO2), Potash Feldspar (K2O·Al2O3·6SiO2), Jadeite (NaAlSi2O6), Hauyne ([Na,Ca]8[Si,Al]12O24[SO4]2), Nosean (Na8Al6Si6O24SO4), and Sodalite (Na8Al6Si6O24[MnO4]2) by incorporation of heavy metals in high-temperature curing reaction. This work provides an effective method for the harmless treatment and recycling of by-product salt residues from high-salt organic wastewater.
Keywords: By-product sulfate salt; heavy metals; high-salt organic wastewater; immobilization; lightweight aggregate ceramsite.