Hydration characteristics and pollutant solidification mechanism of full solid waste electrolytic manganese residue super sulfate cement

Abstract

In this study, electrolytic manganese residue (EMR) rich in soluble manganese, ammonia nitrogen, and sulfate was combined with carbide slag (CS) and granulated blast furnace slag (GBFS) to produce Full Solid Waste Electrolytic Manganese Residue Super Sulfate Cement (FWS-EMR-SSC). The compressive strength, hydration mechanism, microstructure, hydration kinetics, and pollutant solidification mechanism of FWS-EMR-SSC were investigated. The study revealed that the optimal ratio was 4% carbide slag, 40% EMR, and 56% GBFS, achieving a compressive strength of 38.34 MPa at 28 days. This was due to the release of OH- from carbide slag, causing EMR to dissolve large amounts of SO42- and Ca2+, while GBFS accelerated the release of Ca2+, Si2+, Al3+, leading to the formation of abundant AFt and C-(A)-S-H gel, providing strength to FWS-EMR-SSC. The heat release rate and cumulative heat of the FWS-EMR-SSC system were lower than Ordinary Portland Cement (OPC). Additionally, compared to OPC, the second exothermic peak rate was significantly reduced and delayed in the FWS-EMR-SSC system due to the exothermic release of gypsum, retarding effects, and pronounced generation of AFt. The simulation of FWS-EMR-SSC hydration kinetics using the Krstulović-Dabić model revealed that FWS-EMR-SSC underwent the NG-I-D process. Gypsum retarded the nucleation and crystal growth stages of NG, while AFt had a significant impact on the D diffusion stage. The C-(A)-S-H, AFt gel, and iron-manganese compounds (Fe2Mn(PO4)2(OH)2·(H2O)8, MnFe2O4) generated in the FWS-EMR-SSC system could undergo ion exchange and chemical precipitation with Mn2+. Meanwhile, NH3-N transformed into NH3 release, ensuring that the leaching toxicity of FWS-EMR-SSC met the Chinese standard limits of GB8978-1996 for wastewater discharge.