Hexavalent Chromium (Cr⁶⁺) Removal from Wastewater through Electrolysis: Influence of Al³⁺, Fe³⁺, and Mg²⁺ Ion Additives on Treatment Efficiency

S A Thilini N Jayasinghe¹A A Gayan D Amarasooriya²Tomonori Kawakami³Vasan Sivalingam⁴Gamunu Samarakoon^5*

• ¹Faculty of Applied Sciences, Uva Wellassa University, Badulla, Sri Lanka
• ²Faculty of Applied Sciences,, Uva Wellassa University, Badulla, Sri Lanka
• ³Faculty of Engineering, Toyama Prefectural University, Toyama, Japan
• ⁴Sweco Norge AS, Porsgrunn, Norway
• ⁵Department of Process, Energy and Environmental Technology, Faculty of Technology, Natural Sciences and Maritime Sciences, University of South-Eastern Norway, Porsgrun, Norway

A type of batch electrolysis system comprising a platinum anode and stainlesssteel cathode was investigated for the removal of hexavalent chromium (Cr 6+ ) from the synthetic wastewater. Electrochemical treatment was conducted at a constant current of 0.25 A with NaCl of 1 g/L as the supporting electrolyte. The highest Cr⁶⁺ removal efficiencies achieved were at 100 mg/L metal ion dosing and an initial Cr⁶⁺ concentration of 5 mg/L, yielding removal rates of 56.80% for Fe 3+ , 49.62% for Al 3+ , and 30.05% for Mg 2+ . Removal was attributed to the in-situ formation of metal hydroxides (Al(OH)3, Fe(OH)3, Mg(OH)2), which subsequently enhanced the reduction and immobilization of Cr 6+ through co-precipitation and electrostatic adsorption. Further increase in Cr 6+ removal efficiency was inhibited at higher initial Cr 6+ concentrations due to the saturation of hydroxides, which also exhibited competitive behaviour toward ion adsorption. These results confirm the significant role of multivalent cation additives in increasing the remediation of Cr 6+ in the electrochemical system, thus lending support to the theory behind the development of scalable additive-assisted electrochemical water treatment techniques.