Study of the mechanism of silver ions cementation onto copper from acidic sulphate solutions and the morphology of the silver deposit

Abstract

The mechanism of silver ion cementation with copper in acidic sulphate solutions has been investigated. It was found that oxygen present in solutions can strongly modify the mechanism of the process. In the first stage of the reaction, the Cu + ions appear in the solution independently of the presence or absence of oxygen. In deoxygenated solutions Cu + ions generated in the first stage can be transferred partially into the bulk of the solution. The migration of the reaction front results in a loosely adhering silver deposit. The reaction between Ag + and Cu + ions occurring in the bulk of the solution can be initiated in the deoxygenated solutions after reaching a certain value of the Cu +/Ag + concentration ratio. This reaction occurring in the bulk of the solution, parallel to the cementation reaction, consumes an additional amount of silver ions and produces a silver colloid in the deoxygenated solution. In oxygenated solutions saturated with oxygen the front of the reaction is located on the copper surface. As a result, tight and well-adherent silver deposit is formed. The morphology of the silver deposit is independent of the presence of oxygen in the solution. The tendency of silver deposition on already deposited silver cement was observed in the oxygenated solutions. This phenomenon is attributed to the fact that the surface area of anodic sites is more developed in the presence than in the absence of oxygen in the system due to the corrosion of copper. The anodic sites develop their surface into the bulk of the copper substrate and create cavities under the reaction surface.