Decomposition of sodium zincate in alkaline solution by dilution

The decomposition of sodium zincate, NaZn(OH)3, in the alkaline solution (Na2O–ZnO–H2O equilibrium system) containing 30–34% Na2O is complex because of the temperature dependence of the solid precipitate which occurred. In this paper, the sodium zincate decomposition in the alkali solution containing 32.43% Na2O and 22.93% ZnO is investigated by assessing the effects of temperature, dilution factor and time on the decomposition rate (R) of NaZn(OH)3. The results show that ZnO precipitates when the saturated NaZn(OH)3 solution at 100 °C is subjected to water dilution and subsequent cooling to 75, 50 and 25 °C. The decomposition kinetics at 75 °C can be described by the equation, R = 1 − e − 1.1 t 0.3 , where t is the reaction time. ZnO crystal obtained is rod-shaped and becomes coarser at higher temperatures and lower dilution times. The decomposition rate of NaZn(OH)3 increases with dilution temperature, stirring time and dilution factors. Sodium zincate decomposition and recycling of alkaline solution can be illustrated using the Na2O–ZnO–H2O equilibrium phase diagram, which are similar to those in alumina production. The results are beneficial to the extraction of zinc from its oxide ores leached with alkaline solution.