Recovery of Cr (VI) from tannery sludge and chrome-tanned leather shavings by Na2CO3 segmented calcination

Abstract Tannery sludge (Ts) and chrome-tanned leather shavings (CTLs) are regarded as hazardous wastes, which are produced considerably in industrial activities. It is urgent to develop an efficient and cost-effective method to treat these hazardous wastes and simultaneously recover their useful components. In this study, thermodynamic calculation and thermogravimetric characterization were used for analyzing the theoretical feasibility of calcinating Ts and CTLs and the factors affecting recovery of Cr in calcination process were investigated. The results showed that calcination environment, including Na2CO3 content, temperature, calcination time and organic compounds in materials, could greatly affect the recovery of Cr (Ⅵ) from Ts and CTLs. Meanwhile, the glassy chromate phase which formed in the calcination process could interfere with Cr (Ⅵ) release, resulting in decrease of recovery Cr. Thus, to overcome the existing negative effect in calcination process, a segmented calcination with Na2CO3 as a “catalyst” was developed and identified as a low-cost and simple process to effectively recover Cr (Ⅵ) from Ts and CTLs. The recovery of Cr (Ⅵ) from the Ts and CTLs increased by 12% and 38%, respectively, and the recovery of Cr (Ⅵ) from the mixed material reached 60%.