Chemical Stabilization of Hexavalent Chromium in Industrial Sludge Using Ferrous Sulfate and Lime

Abstract

Industrial sludge containing hexavalent chromium presents serious environmental and public health risks due to the high toxicity, mobility, and carcinogenic nature of chromium compounds. Effective stabilization methods are therefore essential for reducing chromium leachability and ensuring safe sludge handling and disposal. The present study investigates the chemical stabilization of hexavalent chromium in industrial sludge using ferrous sulfate and lime under controlled treatment conditions. The research focuses on evaluating chromium reduction efficiency, stabilization performance, leaching behavior, and physicochemical changes associated with combined chemical treatment systems. Experimental analysis was conducted to examine the influence of ferrous sulfate dosage, lime concentration, pH, reaction time, moisture content, and curing conditions on chromium immobilization and sludge stabilization efficiency. Results demonstrate that ferrous sulfate effectively reduces hexavalent chromium to the less toxic trivalent chromium form through redox reactions, while lime treatment promotes precipitation and immobilization within stable hydroxide matrices. The study further reveals that optimized treatment conditions significantly reduce chromium mobility and improve sludge stability by enhancing alkaline conditions and promoting formation of insoluble chromium compounds. Increased curing time contributed to improved stabilization efficiency and reduced heavy metal leaching potential. Comparative assessment with untreated sludge confirms the advantages of combined ferrous sulfate and lime treatment, including improved environmental safety, lower contaminant mobility, and enhanced suitability for secure disposal or controlled reuse applications. In addition, the process demonstrated operational simplicity and adaptability for industrial sludge treatment systems.