Influence Mechanism of Impurity Silicon on Crystallization Process of Sodium Zincate Solution

Effect of impurity silicon on the crystallization process of sodium zincate solution was studied. Based on the crystal phase and thermodynamics analysis, the influence mechanism of impurity silicon on the structure of sodium zincate solution was obtained. The decomposition behavior of sodium zincate solution was analyzed. The effects of impurity silicon concentration, crystal seed and temperature on the crystallization process of sodium zincate solution were investigated. The results show that there is a critical silicon concentration. When the silicon concentration is higher than the critical silicon concentration, the impurity silicon inhibits the crystallization process; when the silicon concentration is lower than the critical one, the impurity silicon promotes the crystallization process. When zinc oxide is used as crystal seed, the critical silicon concentration at 35, 50, and 60 celcius are in the range of 0.20-0.40, 0.054-0.20 and 0-0.054 g/L, respectively; when zinc hydroxide is used as crystal seed, the critical silicon concentration is in the range of 0.20-0.40 g/L at 35 celcius. The critical silicon concentration decreases with increasing temperature. When silicon content is low, the phase is & epsilon;-Zn(OH)2 of polyhedron; when silicon content is high, the phase is & gamma;-Zn(OH)2 of nanorods and cuboids. Increasing the temperature can inhibit the formation of & gamma;-Zn(OH)2. The presence of silicon impurities may reorganize the structure of sodium zincate solution, and is conducive to the existence of zinc ions in the form of Zn(OH)+. The increase of temperature can reduce the influence of silicon impurities.