Extraction of Indium from By-products of Zinc Metallurgy by Ultrasonic Waves

The extraction of indium from hard zinc slag is a relatively common method, but it is desired to further improve the leaching efficiency of indium. The leaching effect of indium from a hard zinc slag via ultrasonication was studied. We have found that the infiltration efficiency of indium can be improved by ultrasonic waves through its cavitation effect, mechanical effect, etc. The use of calcium hypochlorite instead of the chlorine used in the conventional method as an oxidant reduces corrosion of the equipment and does not pollute the environment. In this paper, HCl–CaCl2 and Ca(ClO)2 were employed as a leaching agent and oxidant, respectively. The effects of ultrasonic power, leaching time, initial acidity, reaction temperature, concentration of CaCl2, and amount of Ca(ClO)2 on the leaching rate of indium from zinc metallurgy by-products were investigated. The optimum conditions were as follows: ultrasonic power 700 W, reaction temperature 70 °C, leaching time 50 min with ultrasonication and 60 min without ultrasonication, HCl concentration 4.5 mol/L, CaCl2 concentration 150 g/L, and oxidizing agent concentration 35 g/L. Under the optimal conditions, the leaching rate of indium was 96.42% with ultrasonication and 94.8% without ultrasonication. The effect of the ultrasonic waves on the slag during hard zinc leaching was studied by scanning electron microscope.