Application and mechanism of an ore-washing sludge in the remediation of chromium (III) and copper (II)-contaminated soils

Ore-washing sludge is a typical solid waste from metallurgical industry and needs proper treatment. For the first time, this kind of sludge was used as a stabilizer for heavy metal-contaminated kaolin. As a result, after Cu (3655 mg/kg) and Cr (430 mg/kg)-polluted kaolins were mixed with the stabilizer, only 7.98 ml/L of Cr and 8 mg/L of Cu were leached by the toxicity characteristic leaching procedure. These values were both lower than the limits for the leaching of chromium and copper (GB5085.3-2007). In a column leaching test, only 2.52 mg/L of Cr and 18.51 mg/L of Cu were detected in the leachate when the pH of the leaching solution was lower than 5.6. After the stabilizer was used in Cu/Cr stabilization, it showed solid phases of oxides, hydroxides, and layered double hydroxides. After detailed calculations, oxides in the stabilizer accounted for 54.82% of Cu and Cr stabilizations. Specifically, O-top sites in oxides played a main role in stabilizing Cu and Cr. Therefore, this work will help in the development of high-value-added utilization of solid waste, as well as the remediation of acidic and heavy metal-contaminated soils.