A kinetic model that describes removal of chromium VI from rinsing waters of the metal finishing industry by electrochemical processes

A study was made to remove Chromium VI (Cr⁶⁺), present in large quantities in the rinsing waters from the plating industry, using electrochemical treatment. Large amount of Cr⁶⁺ are found. It was found that the reaction rate followed a variable kinetic order at concentrations up to 1700 mg Cr⁶⁺/L. It was also noticed that Cr⁶⁺ reduction depended on the ferrous ions (Fe²⁺) released at the anode, the cathode reactions and the acidic corrosion on electrodes. Iron salts produced electrode passivation and it caused a 50% increase in treatment time and power requirements. Eliminating the salt formation at the anode could reduce this effect. Using electrochemical processes it is possible to reuse treated waters in the rising stages of the plating industry owing to the fact that final Cr⁶⁺ concentration is less than 0.5 mg/L. Finally, a sludge characterization study revealed that residue generated in the process is not considered dangerous according to Mexican environmental protection standards.