Extraction of rubidium from gold waste: Process optimization

The extraction of rubidium from gold waste from the Mouteh processing plant in Iran by a three-step process (acid washing, followed by salt roasting and water leaching) was optimized. The acid washing step for removal of impurities was found to be optimal at 85 °C and 5 h, using 5 M nitric acid. Factors effecting roasting operation were then optimized by a series of initial experiments, then using response surface methodology (RSM) based on a central composite design (CCD). Rb extraction of 90.95% was obtained with a mass ratio of GW/Na2SO4/CaCl2⋅ 2H2O of 1.00:0.11:0.45 at 910 °C for 30 min. Water leaching of the roasted mixture resulted in 97.14% Rb extraction under optimum conditions, viz. a liquid/solid ratio of 1.69 at 58.5 °C for 31.4 min. The proposed correlations using RSM showed good agreement with the experimental data.