SILVER CEMENTATION WITH ZINC FROM RESIDUAL X RAY FIXER, EXPERIMENTAL AND THERMOCHEMICAL STUDY

摘要

Silver cementation with zinc from residual X ray fixers (XRF) was studied. The chemical analysis of XRF showed 5.16 g/l (Ag), 0.56 g/l (Al), 5.24 g/L (K), 7.02 g/L (Na) and 172.56 g/L (S). The cementation process in terms of solution pH was thermodynamically modeled using FactSage by constructing the potential-pH diagram at 298.15 K. This diagram showed that the cementation process leads to metallic silver together with residual unreacted zinc. The parameters experimentally evaluated were: pH (ranged from 3.0 to 7.0, temperature (ranged from 298.15 to 318.15 K) and the Ag:Zn weight ratio (1:1, 1:2, 1:3, 1:4 and 1:5). The maxim silver cementation (99.99% Ag) was obtained at 90 s of reaction, pH6.0, 318 K and Ag:Zn equal to 1:3. Silver cementation increases whit the Ag:Zn weight ratio, pH and temperature increases. The X-Ray and SEM-EDS results showed that the cementation product is formed by Ag and Zn.