Effect of sodium silicate on the solubility of zinc oxide of the Na2O–ZnO–H2O equilibrium system

There is a competitive reaction of zinc and silica in the alkali leaching process of zinc oxide ore, leading to low zinc leaching rate. To increase leaching rate of zinc, the effect of sodium silicate on the solubility of zinc oxide of the Na2O–ZnO–SiO2–H2O equilibrium system is studied by adding Na2SiO3 and ZnO to NaOH solution. Results show that zinc oxide equilibrium concentration increases with temperature from 25 to 75 °C at the same molar ratio of Na2O to SiO2. The equilibrium concentration of zinc oxide initially increases and then declines with the increasing concentration of Na2O. This leads to the maximum ZnO concentration, which increases with temperature but decreases with the increasing dosage of sodium silicate. The precipitate of disodium zinc silicate (Na2(ZnSiO4)) generates due to the reaction of silicate SiO32 − and Zn(OH)42 − in the solution of Na2O–ZnO–H2O equilibrium system. High zinc leaching rate can be obtained when the Na2O concentration is lower than the values indicated by the “peak” points at higher molar ratios of Na2O to SiO2 and temperatures.

► Different ZnO solubility was measured at different molar ratio of Na2O to SiO2(1:1, 2:1 and 2.79:1);
► ZnO could also be dissolved into Na2SiO3 solution.
► SiO32 − can react with ZnO22 − in the sodium zincate solution and produce Na2ZnSiO4 precipitate.