Study On The Current Efficiency And Impurities Effect On The Electrowinning Of Gallium From The Enriched Mother Liquor Of Alumina Production

Gallium and its compounds are important materials for the semiconductor industry. As a rare element, the main pathway to obtain gallium is extracting it from the mother liquor of alumina production by some enrichment methods, such as ion exchange resin, followed by electrowinning gallium metal from the enriched gallium containing alkaline solution. However, the current efficiency of gallium electrowinning in the actual process is low due to the competition of the hydrogen evolution reaction and the presence of a large amount of impurities.In order to solve the above problems, a novel Cu/Ga electrode was developed which is suitable for the gallium electrowinning in alkaline solution. The effect of impurities from the mother liquor on the current efficiency was studied at the optimized electrowinning conditions. The main results are as following:(1) The effect of different cathode materials on gallium electrowinning were studies. The results shown that hydrogen evolution and gallium deposition were interfered each other when SUS304 stainless steel, nickel, copper, titanium, graphite, lead as the cathode. While the copper base gallium (Cu/Ga) electrode prepared by low temperature alloying method has high hydrogen evolution overpotential and low gallium deposition overpotential, which could effectively improve the current efficiency of gallium electrowinning.(2) The effect of current density, temperature, stirring speed, electrode distance and alkali concentration on the current efficiency of gallium electrowinning with Cu/Ga electrode was studies. The optimized electrowinning conditions were under 300 A·m-2 at 20? in 120 g·L-1 NaOH. The stirring speed and the electrode distance had little influence on current efficiency.(3) The effect of 7 kinds of impurities, V, Ca, Cu, Fe, Pb, Al, Si might come from the mother liquor on the current efficiency of gallium electrowinning was studied. Al and Si had little influence on current efficiency, the presence of Cu, Fe and Pb decreased the current efficiency, while V and Ca displayed significant influence. The current efficiency decreased obviously when 10 ppm of V existed, and the current efficiency reduced from 88.64% to 6.48% when 150 ppm of V existed. A possible explanation is the hydrogen evolution overpotential was decreased in the presence of V. On the contrary, the presence of Ca was beneficial to gallium electrowinning. The current efficiency increased from 88.64% to 95.46% with 50 ppm of Ca existed, which may be caused by the improvement of deposition of Ga on the electrode.(4) Two kinds of actual Ga-containing alkali samples (Ga 40 g·L-1, V 100 ppm) from the alumina plants in Guangxi province and Henan province were tested for gallium electrowinning with Cu/Ga electrode. It was found that the electrowinning process could not be performed with stainless steel electrode if without impurities removing pretreatment, while it could be carried out continuously with Cu/Ga electrode. The current efficiency were 48.54%(Ga 7g·L-1 after electrowinning) and 39.34%(Ga 2 g·L-1 after electrowinning), and the product purity were 99.32% and 96.61%, respectively.In summary, a novel Cu/Ga electrode is proposed in this thesis to electrodeposit Ga in the Ga-containing alkali solution with high current efficiency, which might provide a process to electrowin Ga from the enriched mother liquor of alumina production without further impurity removing pretreatment.