Impact of Bioreactor Landfill Leachate Quality onAs, Cd, Pb and Zn Leaching from Mine Residues

In this paper, leaching of heavy metals (As, Cd, Pb and Zn) from two different metal rich wastes, namely mineral processing waste (W2) and waste derived fertilizer (W1) in batch extraction tests (TCLP, SPLP and deionized water) is presented. In addition, extraction tests using bioreactor MSW landfill leachates were also performed and results compared to the standardized tests. It was observed that the W1 (commercially available as Ironite) failed the TCLP tests, with Pb extract concentration (7.3 mg/L) higher than the TC limit. On the other hand, the W2 passed the TCLP test. Significant differences in arsenic leaching from W1 in the SPLP and deionized water extraction tests, compared to the TCLP tests reiterated the fact that TCLP underestimated the leachability of arsenic. Batch extraction tests using MSW landfill leachates were also performed. Landfill leachates were sampled from conventional (dry-tomb) and bioreactor facultative landfills. Leaching results indicated that TCLP overestimated Cd and Pb leaching in landfills. A comparison of all the batch extraction tests showed that leaching of heavy metals showed high pH dependency, with increased leaching in the acidic region (SPLP and deionized water tests). It was also observed that the dissolved organic carbon content and the volatile fatty acid content regulated the amount of heavy metals leached.