Effect of different pHs and liquid-to-solid ratios on leaching behavior of heavy metals from landfill-mined-soil-like-fractions.

The potential reuse of landfill-mined-soil-like-fractions (LFMSF), a significant by-product of landfill mining (LFM), is restricted due to the leaching of heavy metals (HMs). In this context, the present study assesses the leaching behavior of six HMs, i.e., Cu, Ni, Zn, Cr, Pb, and Cd, from LFMSF under various pH levels (pH 2-13) and liquid-to-solid (L/S) ratios (1-20 L/kg), which are considered as the primary variables affecting the leaching of HMs at different environmental conditions. The pH-dependent leaching test according to USEPA Leaching Environmental Assessment Framework (LEAF) Method 1313 exhibited an amphoteric leaching behavior for Cu, Cr, Zn, and Pb, with minimal leaching at neutral pH levels and elevated leaching under acidic and alkaline pH conditions. The leaching behavior of Ni and Cd followed a cationic pattern characterized by a consistently declining concentration with increasing pH values. The pH-dependent leaching of all HMs was likely due to the dissolution and precipitation of their oxide, hydroxide, and sulfate compounds, along with the sorption and desorption processes. The leaching test at various L/S ratios by LEAF Method 1316 revealed that the increase in L/S ratios decreases the leached concentrations of HMs due to the dilution effect. The leached concentrations of Cu, Ni, and Pb were found to exceed the Ministry of Environment, Forest and Climate Change of India specified screening level groundwater quality standards across the entire pH levels and L/S ratios, suggesting that beneficial applications of LFMSF must be engineered.