RESUMO
Toxicity characteristic leaching procedure (TCLP) is a prevalent way to evaluate the treatment effectiveness for Cr(â ¥)-bearing solid matrices (CBSM). But when a certain amount of residual reductants are present in the treated CBSM, Cr(â ¥) leaching concentration rebound phenomenon (CLCRP) occurs, which invalidates the TCLP. This study explores the microstructure of ferrous-reduced CBSM and proves that the residual Cr(â ¥), FexCr1-x(OH)3 precipitate and residual ferrous are separately distributed in a three-layer structure. In natural scenarios, the residual ferrous in the out-layer is firstly flushed away by rainfall and groundwater or oxidized by dissolved oxygen, resulting in the decrease of ferrous with time. Residual Cr(â ¥), due to being blocked by precipitate layer, is less flushed away. While in TCLP, all of released residual ferrous and Cr(â ¥) are in the leachate and react till one of them is almost exhausted, resulting in the underestimation of Cr(â ¥) leaching concentrations. The longer the samples experience the natural scenarios, the less of the residual ferrous, resulting in the decline of underestimation of Cr(â ¥) leaching concentrations with time. This study also provides a pretreatment which can effectively reduce the residual ferrous, achieving more accurate Cr(â ¥) leaching concentrations and eliminating CLCRP.