Kinetic Aspects and Thermo chemical Analysis of Silver Cementation from Residual X Ray Fixer by Cementation on Zinc

Abstract

Silver cementation with zinc from residual X ray fixers was studied. The chemical analysis of XRF showed 5.16 g L-1 (Ag), 0.56 g L-1 (Al), 5.24 g L-1 (K), 7.02 g L-1 (Na) and 172.56 g L-1 (S). The process was thermodynamically simulated using Fact Sage software by constructing the potential-pH diagram at 298.15 K (25oC). This diagram showed that the 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 K (25°C) to 318.15 K (45°C)) 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, pH 6.0, 318 K (45°C) 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.