Recycling of chromium electroplating sludge using combined calcination-hydrothermal treatment: A risk-reducing strategy for separation of Cr(III) from solid waste

Abstract

As a kind of hazardous solid waste, electroplating sludge that containing high contents of Cr(III) should be suitably treated to meet the landfill standard. Here we proposed a new way for harm minimization and Cr recovery of the sludge. By employing additional hydrothermal treatment instead of direct leaching after alkali oxidizing calcinations, it shows obvious increase in the Cr removal rate of the sludge. Moreover, the leaching risk of the calcination residue could be lowered down by the hydrothermal treatment. It firstly reveals that the hydrocalumite in the initial sludge will transformed to weak acid soluble CaFe dioxides after calcinations. And the doped Cr(III) in the dioxide will raise the leaching risk of the residue. The hydrothermal leaching enables the decomposition of the dioxide and release of the Cr (III) into the recovered solution of Cr. Furthermore, high purity hematite pigment could be obtained at the same time. This work provides a new insight for reevaluate the feasibility of the heat treatment for Cr containing sludge.