Solvent extraction of rubidium from gold waste using conventional SX and new CFE methods

Solvent extraction (SX) of rubidium (Rb) from leaching filtrate of gold waste (GW) in Mouteh Processing Plant by 18-crown-6 (18C6) was studied. High potential of new column flotoextraction (CFE) method in extraction of Rb from dilute solutions was also demonstrated. First, the factors affecting SX of Rb from a synthetic rubidium sulfate solution (containing 100 mg·L−1 Rb) were identified. 0.05 mol·L−1 18C6 in kerosene, 0.02 mol·L−1 picric acid in aqueous phase, aqueous to organic (A/O) ratio of 1, pH 7 and mixing time of 15 min are the optimum values for affective factors. The three-stage precipitation with sodium carbonate, pH adjustment with sulfuric acid and two-stage evaporation and crystallization were conducted to purify the leaching from impurities such as Fe, Al, Mn, Ca and especially competing cations of K and Na. Almost complete extraction of Rb and K from final filtrate containing 0.08 mol·L−1 picric acid was performed using 0.2 mol·L−1 18C6 in kerosene. The Rb and K strippings of 99.12 % and 9.93 %, respectively, are obtained with 2 mol·L−1 nitric acid with A/O ratio of 2. Finally, the performance comparison of the CFE and SX methods in similar conditions shows increased extraction of K and Rb by 16 % and 5 %, respectively, using CFE method.