A Study of Deposition and Reaction of Cd (OH)2 on SiO2 Surface in Aqueous Solution
1995 Volume 1995 Issue 4 Pages 266-272
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1995 Volume 1995 Issue 4 Pages 266-272
SiO2 powder was allowed to react with Cd(OH)2 for 1 week and 2 months respectively, after adjustment to various pH's by adding some aliquots of KOH to the 0.005 M of Cd(NO3)2 solution containing SiO2 powder. Potentiometric titration curves for solutions with and without SiO2 powder were obtained by plotting pH of each test solution after the reaction as a function of the amount of K OH added. X-Ray diffraction and scanning electron microscopy were also performed for the reaction products. Formation of Cd(OH)2 and cadmium silicate occurred after 1 week and 2 months, respectively. Differe nce in the shape of potentiometric titration curves of the solutions with and without Si02 powder was f ound, which suggested that there was the difference between the state of Cd(OH)2 precipitated in the bulk of solution and that deposited onto the surface of the SiO2 powder after 1 week of reaction. The shape of the titration curve obtained after the reaction of 2 months reflects the formation of cadmium silicate. The formation of cadmium silicate was found to occur by the reaction of SiO2 powder with Cd(OH)2 in the pH region of near 8 where SiO2 powder was hardly dissolved. It is concluded that cadmium silicate is formed by the reaction consisting of deposition of Cd(OH)2 onto SiO2 powder surface by adding KOH and subsequent interfacial reaction between the deposited Cd(OH)2 and the substrate of SiO2 powder, and not by the reaction of the dissolved silicic acid with cadmium ion in the solution.
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