In-situ investigation of melting characteristics of waste selective catalytic reduction catalysts during harmless melting treatment

Abstract

Selective catalytic reduction (SCR) catalyst waste is a hazardous solid waste that seriously threatens the environment and public health. In this study, a thermal melting technology is proposed for the treatment of waste SCR catalysts. The melting characteristics and mineral phase transformation of waste SCR catalysts blended with three different groups of additives were explored by heating stage microscopy, thermogravimetric analysis/differential scanning calorimetry (TG/DSC) analysis, thermodynamic simulation, and X-ray diffraction (XRD) analysis; heavy metal leaching toxicity was tested by inductively coupled plasma-atomic emission spectrometry (ICP-AES) analysis. The results indicated that the melting point of waste SCR catalysts can be effectively reduced with proper additives. The additive formula of 39.00% Fe2O3 (in weight), 6.50% CaO, 3.30% SiO2, and 1.20% Al2O3 achieves the optimal fluxing behavior, significantly decreasing the initial melting temperature from 1223 °C to 1169 °C. Furthermore, the whole heating process of waste SCR catalysts can be divided into three stages: the solid reaction stage, the sintering stage, and the primary melting stage. The leaching concentrations of V, As, Pb, and Se are significantly reduced, from 10.64, 1.054, 0.195, and 0.347 mg/L to 0.178, 0.025, 0.048, and 0.003 mg/L, respectively, much lower than the standard limits after melting treatment, showing the strong immobilization capacity of optimal additives for heavy metals in waste SCR catalysts. The results demonstrate the feasibility of harmless melting treatments for waste SCR catalysts with relatively low energy consumption, providing theoretical support for a novel method of disposing of hazardous waste SCR catalysts.