Mechanochemical immobilization of lead smelting slag using quartz sand

Abstract

The lead smelting industry has produced a large amount of heavy metal-containing solid wastes, and lead leaching from these wastes under acidic conditions poses a great threat to the environment. In this study, lead slag was effectively stabilized by a mechanochemical reaction through a co-grinding operation with quartz sand (SiO2) in a planetary ball mill. The synthetic precipitation leaching procedure (SPLP) was used to examine the stabilization efficiency of lead slag by ball milling, and the results demonstrated that the lead immobilization for smelting slag with initial lead leaching concentration of 1503 mg/L could reach 99.99% under the conditions of 1000 rpm and 35:1 charge ratio when the ball milling time was 2 h, which was under the permitted concentration of lead according to the Chinese standards for hazardous wastes (<5 mg/L, GB5085.3-2007). Kinetic studies found that the rotation speed of the ball mill and the charge ratio between balls and powder were two key factors affecting stabilization efficiency. The stabilization rate increased with the rotation speed of the ball mill and the charge ratio, and fitted well with the Delogu Model. X-ray diffraction (XRD) characterization revealed that the characteristic peaks for both PbO and PbS disappeared after long-time grinding with SiO2. Mechanistic studies suggested that É centers (≡Si·) and non-bridging oxygen hole center radicals were generated due to the mechanical energy from ball milling with SiO2, which provide the possibility for the formation of Si–O–Pb and could effectively stabilize Pb species in the lead slag.