Release characteristics of heavy metals in high-sulfur coal gangue: Influencing factors and kinetic behavior

Abstract

High-sulfur coal gangue (HS-CG) is extremely unstable in the environment, releasing acid mine drainage with high concentrations of harmful heavy metals (HMs). The effects of HS-CG particle size, leaching solution pH, Fe3+ and acidophilic microorganisms on the release of HMs from the HS-CG and their kinetic behavior were studied using static leaching tests. The results showed that the smaller the particle size of HS-CG and the more acidic the leaching solution, the greater the release of HMs. As the chemical catalyst, the external addition of 300 mg/L Fe3+ can make the leaching amount of Fe, Mn, Cu, Zn, Ni, Cr reached 10,224.93, 93.88, 52.25, 11.56, 7.55, 2.97 mg/kg respectively, and the release of HMs was 1.36–2.60 times of the tests without the addition of iron. However, the concentration of Fe3+ above 800 mg/L promoted the production of jarosite on the surface of HS-CG, which led to decrease in the release of HMs. The HMs forms in HS-CG were different, while the effect of microorganisms on the leaching of Zn (54.99%) and Mn (52.35%) in the higher acid soluble fraction was more obvious, their leaching amount reached 87.21 and 107.58 mg/kg respectively. The kinetic analysis indicated that the rate-controlling step was mainly redox reaction at first, and then gradually controlled by the diffusion of ash layer. So, the kinetic equation controlled jointly by two rate-controlling stages has been proposed to describe the dissolution of HS-CG. This work help develop pertinent strategies for mine area remediation via controlling the HMs generation path.