FeCl3 coagulant production from waste pickle liquor using electrolysis

Abstract

Pickling is a typical method used in a cold milling plant to remove impurities from hot rolled coil by immersing the coil in strong acidic solution. The spent acidic solution or waste pickle liquor (WPL) requires certain waste treatment before it can be disposed to environment because of its metallic ion and acid content. WPL contains a number of metallic ions that can be utilized as ferric chloride coagulant. The purpose of this paper is to evaluate the kinetics of Fe²⁺ oxidation into FeCl₃ and the performance of the ferric chloride coagulant using the proposed electrolysis configuration. The electrolysis process was conducted in ambient condition with voltage 3 & 6 V, electrolysis time of 120 minutes, and addition of excess NaCl or HCl. The result shows that metal impurities in WPL and excess chlorine do not significantly affect the Fe²⁺ conversion. It can also be concluded that the optimum condition for electrolysis is using 6V of voltage, 90 minutes of electrolysis time, and excess chlorine at 0% stoichiometry which gave 60% conversion of Fe²⁺ in WPL. Due to the equilibrium between the Fe²⁺ dan Fe³⁺ which is formed during electrolysis process, the full conversion of Fe²⁺ is not possible yet, and the maximum conversion of Fe²⁺ is 60%. The presence of impurities in WPL is proven not affecting the Fe²⁺ conversion during the electrolysis process.