Carbon emission free preparation of calcium hydroxide with calcium carbide slag (CCS) through micro-bubble impurities removal

Abstract

Calcium hydroxide is a widely used bulk chemical, and traditional limestone calcination to prepare hydrated lime emits large amounts of CO2. Calcium carbide slag (CCS) is a waste residue with calcium hydroxide as the main component emitted by the PVC industry, which can be directly used to prepare calcium hydroxide. However, CCS has problems such as high impurity content, complex impurity occurrence state, and difficult separation. In this paper, the raw CCS and products under different separation conditions were prepared, and the presence state of main elements (Ca, Al, Si, Fe, C, Mg) in the CCS were studied by using XRD, XRF, XPS, SEM-EDS, and EPMA + SXES. According to the presence state of impurities, the microbubble strengthens in combination with agents used for deep directional separation of impurities in CCS, and DFT is used to calculate the surface binding energy between each component and agent in CCS. The results demonstrated that CaC2 and C wrap each other in CCS. Morphological and elemental chemical analyses of the dissociated residues revealed the existence of Si in the form of SiC and SiO2. Fe and C existed as particles of FeSi and carbon respectively. Al exists in the form of CaAl2O4 and Al2O3. Mg is loaded on the SiC in the form of Ca–Al–Mg mineral system. After the separation of microbubble equipment strengthens in combination with agents, the acid insoluble content can be reduced from 1.99% to 0.76%. At the same time, the yield can also reach 71.34%, and all indicators meet the standard indicators of industrial calcium hydroxide. The results can provide a new zero-carbon preparation pathway for calcium hydroxide.