Purification of Wet-Process Phosphoric Acid by Hydrogen Peroxide Oxidation, Activated Carbon Adsorption and Electrooxidation

Abstract

In this work, three technologies are studied for the purification of phosphoric acid produced by the wet process: chemical oxidation with hydrogen peroxide, adsorption onto activated carbon, and electrochemical oxidation by boron-doped diamond anodes. The treatment of wet-process phosphoric acid by chemical oxidation with H2O2 as oxidizing agent can remove 75 % of the initial TOC as maximum, indicating that this wet-process phosphoric acid contains an important amount of organics that cannot be oxidized by hydrogen peroxide under the operation conditions used. High temperatures and hydrogen peroxide/TOC ratios close to 150 g H2O2/g TOC allow obtaining the best chemical oxidation results. The adsorption onto activated carbon can remove between 40 and 60 % of the initial TOC as maximum. Adsorption times of 2 hours and activated carbon/WPA ratios close to 12 g AC/Kg WTP assure both steady state and maximum adsorption of organics. The electrochemical process is the only technique by which complete mineralization of WPA organics can be achieved. Operating at 60 mA cm–2 and at room temperature, high current efficiencies are achieved which only seem to decrease by mass transport limitations.