Influence of pH, depth and humic acid on metal and metalloids recovery from municipal solid waste landfills

The recovery of metal(loid)s from municipal solid waste (MSW) samples <10 years old and >10 years old was investigated using a series of pH-dependence leaching batch tests ranging between pH 2 and 10. Further to this, the influences of various parameters, including depth, and humic acid (HA) concentrations on the recovery of metal(loid)s including Li, Al, Cr, Mn, Co, Ni, Cu, Zn, As, Cd, Pb, and Hg were investigated. The Visual MINTEQ geochemical software was then used to model the metal(loid)s release in the presence of different HA concentrations ranging from 28 mg/L to 100 mg/L, which can be found in landfill sites and pH ranging from 2 to 10. The results showed that the release amount of Li, Al, Cr, Mn, Co, Ni, Cu, Zn, As, Cd, Pb, and Hg are in the range of 0.03–0.14 mg/L, 0.65–83.33 mg/L, 0.01–0.19 mg/L, 0.18–18.17 mg/L, 0.01–0.09 mg/L, 0.06–0.38 mg/L, 0.12–5.2 mg/L, 0.14–11.57 mg/L, 0.02–0.10 mg/L, 0.00–26.17 mg/L, 0.03–25.17 mg/L, and 0.00–0.01 mg/L with deionised water as leachant at different pH. The release amount of HA was relatively increased from 0 to 2% in 48–55 m compared to 3–9 m in the MSW landfill. HA can promote the leaching rate of metals with an appropriate amount. Base on the study results, the optimal condition of leaching metals was pH 2, and HA 28 mg/L at less than 10 m depth. The high concentration of metals in landfill leachate may be enhanced to effectively recover metals as the critical challenge of recovering metals from leachate is the low concentration of metals. Thus, the information can be useful for economically feasible in the recovery of metals.