Change in Lead–Zinc Waste Slag’s Physical and Chemical Properties and Heavy Metal Migration Characteristics Under Acid Soaking Environment

As a kind of industrial solid waste, lead–zinc waste slag can easily cause heavy metal migration in acid environments, resulting in safety risks. Along these lines, in this work, the waste slag of a lead–zinc mining area in western Qinling, Shaanxi, China, was selected as the experimental material. Seven groups of acid soaking solutions with different pH values were set up with three parallel samples in each group, and the acid soaking experiments were conducted for 100 days. During the experiment, the electrical conductivity, pH value, and heavy metal content of the solution, as well as the pore distribution and heavy metal content of the waste slag surface, were measured. The results showed that with pH = 4 and pH = 7 as the environmental limit values, the pH value, electrical conductivity (EC), and heavy metal contents in the solution changed to different types after the waste slag was soaked in the solution with a pH of less than 4 and the solution with a pH of 5–7. The release of heavy metals from waste slag exceeded the discharge standard in the environment with a pH of less than 4, and the pore structure of waste slag was obviously enhanced, especially in the soaking solution with an initial pH of 1. The maximum soaking amounts of Zn, Pb, and Cd were 2.584 mg/L, 1.28 mg/L, and 0.0169 mg/L, respectively, during the experiment, which did not meet the “Environmental quality standards for surface water” (GB 3838-2002) and could not be excreted as direct surface water. However, when the environmental pH was greater than 7, the heavy metals showed reverse adsorption. This result indicated that when the acid soaking solution entered the alkaline range, the heavy metal content in the solution was less, which can basically meet the discharge standard. However, the pores of waste slag continued to expand. Our work provides valuable insights into the treatment of waste slag and environmental protection in lead-zinc mining areas containing sulfur.