Comparative assessment of Batch and semi-dynamic leaching studies for heavy metals release from solid waste base solidified soil

Abstract

This study aims to assess the potential leaching activity of heavy metals from contaminated soil solidified using a combination of industrial wastes (red mud, carbide slag, and phosphogypsum) and cement (RCP). Study on the leachability of solidified high concentration copper (RCP-Cu) and lead (RCP-Pb) contaminated soil under various leaching conditions. The desorption and diffusion behavior of RCP-Pb/Cu in acidic solutions were investigated through updated Batch and semi-dynamic leaching tests. Batch test results show that for leachates at pH of 2 and 3.2, copper/lead concentrations initially decrease but then increase with more leaching cycles. For distilled water leachates, the concentration, conductivity, and pH of the leachate gradually decrease with increasing leaching cycles. Moreover, stronger acidity leads to a smaller desorption distribution constant. Semi-dynamic leaching test reveal that when the leaching solution is weakly acidic (pH≥3.2), the samples exhibit excellent acid buffering, keeping the leachate pH around 12, with heavy metals cumulative leaching rate below 1 %. When the leaching solution is highly acidic (pH≤2), it accelerates the leaching of active ions and the dissolution of hydrated products, significantly increasing the leaching rate of RCP-Cu. As acidity increases, the diffusion coefficient rises, with RCP-Cu showing a higher diffusion coefficient than RCP-Pb. The batch leaching test shows higher leaching rates than the semi-dynamic test, suggesting it is a more conservative method for assessing environmental safety in engineering applications. Therefore, selecting the appropriate leaching evaluation method should be based on the specific project needs and goals.