Reaction Between Ce4+ Ion And Thiourea In Aqueous Hcl Medium: An Electrochemical Study

Although thiourea is used as a reductant to inhibit Cl-2 production in the HCl leaching of rare earth roasted ores containing Ce(IV), no relevant reports provide theoretical support. Herein, an electrochemical test is designed to detect the intermediate and end products that may be generated during the reaction of Ce4+ ion and thiourea in HCl solution, and to reveal the influence laws of key conditions on the reduction peak potential of Ce4+ ion by cyclic voltammetry. The results show that Ce4+ ion is preferentially reduced by thiourea in aqueous HCl medium, which proves thiourea effectively inhibits Cl-2 production. Thiourea reacts with Ce4+ ion to produce the intermediate ([(SCN2H4)(2)](2+)) and the final products (SO4 (2-), NH3 and CO2) during the irreversible reaction, and the stoichiometric ratio of thiourea to Ce4+ ion is at most 1:8. In addition, the reduction peak potential of Ce4+ ion decreases with the increase of the ratio of F- to Ce4+ (0 similar to 2 mol mol(-1)) and temperature (25 similar to 40 degrees C), but it is independent of Ce4+ concentration (0.04 similar to 0.12 mol l(-1)). This work provides basic theoretical research for industrial application of thiourea and suggests a new route to find a cleaner reductant for avoiding Cl-2 generation in the recovery of rare earths.