THE LOADING CAPACITY OF SELECTED CATION-EXCHANGE RESINS AND ACTIVATED CARBONS FOR GOLD-THIOUREA COMPLEX

The loading capacities of several types of cation exchange resin and activated carbon for gold-thiourea complex has been evaluated. The maximum loading capacity after 96 hours at ambient temperature (22 degrees C) ranged from 189 to 243 kg Au/t for the cation exchange resins and 159 to 208 kg Au/t for the activated carbons. These values are higher than the capacity values reported by previous investigators. The capacity data were used to generate equilibrium loading isotherms based on the Langmuir and Freundlich modeled to determine the isotherm equilibrium constants. Some major problems associated with the thiourea system for gold recovery are discussed. They include (i) analytical procedure for the determination of thiourea in solution, (ii) autodecomposition of thiourea, (iii) stabilization of thiourea and (iv) flame AAS for determination of gold in thiourea solutions. The potassium iodate method was found to be better suited than the mercuric nitrate method for the determination of thiourea in solution. Autodecomposition of thiourea was slowed down considerably by the addition of reducing agents such as cysteine. An effective procedure for the use of flame AAS to determine gold in thiourea solutions is recommended.