Removal of cadmium from phosphoric acid in the presence of chloride ions using commercially available anion exchange resins

Abstract

The production of cadmium-free phosphoric acid is crucial for the manufacturing of environmentally friendly fertilizers. One of the most promising methods for purification of phosphoric acid is ion exchange/adsorption. The article presents studies on the adsorption of cadmium from a 40 % phosphoric acid solution in the presence of chloride ions with the use of commercially available anion exchange resins. Five borderline cases were examined in a batch system, as well as kinetic studies were performed. The effect of chloride (0.2–2.2 wt%) and cadmium (5–2500 mg/kg) concentration on adsorption with the use of two best resins was studied in depth. The Amberlite PWA5 resin was selected for column tests and for experiments with wet process phosphoric acid simulated solution (WPPA-SS) to prove the concept of practical application of the resin. The obtained results indicate that PWA5 has a number of advantages over the resins tested so far, e.g., the resin is characterized by high cadmium adsorption efficiency (89 % in batch experiments with WPPA-SS and 95.5 % in column tests), the resin effectively adsorbs cadmium in the presence of low chloride concentrations (0.2–0.5 wt%), and the column with this resin can work properly even at high flow rates (40 BV/h).