Effective disposal of hazardous waste from non-ferrous waste recycling through thermal treatment

Abstract

Hazardous wastes containing non-ferrous metals have significant value in recycling. However, the recycling process generates leaching residues (HWLR) with high levels of heavy metals, posing a risk to the environment. Based on the component characteristics of HWLR, silica residue (SR), and silicon tetrachloride cracking slag (STCS), the feasibility of co-thermal treatment for the efficient disposal of HWLR, SR and STCS was verified in this study. According to the SiO2–Na2O–CaO ternary system diagram, the melting point of the system decreases gradually with the appropriate increase in SiO2 content when the CaO/Na2O ratio in the system was determined to be about 2.33. When the theoretical liquid phase content of the mixed system of 100%, the thermal treatment temperature could be lowered to 1100 °C, which is significantly below the melting points of HWLR, SR, and STCS individually. The experimental results confirmed that thermal treatment at temperatures above 1000 °C effectively eliminated the leaching toxicity of Cu, Ni, Zn, Cr, Cd, and Pb in the mixed samples of HWLR, SR, and STCS, which can mainly be attributed to the formation of a glass network structure during the thermal treatment process. This study demonstrated that low-temperature melting treatments could efficiently and thoroughly solidify heavy metals in HWLR, SR, and STCS.