The possible use of Methanesulfonic Acid as a new Electrolyte for Silver Electrorefining

A. Dressler, M. Keil, T. Müller, M. Stelter

For the last 120 years the Möbius electrolysis in nitric acid system has been the most widely used technology for silver electrorefining in Europe. The Institute for Nonferrous Metallurgy and Purest Materials lately conducted several electrolysis experiments to examine the suitability of methanesulfonic acid (MSA) as an alternative electrolyte for silver refining.

The advantages of methanesulfonic acid are high silver solubility, high chemical and electrochemical stability, high electric conductivity, the avoidance of toxic gas formation and low costs. In the electrolysis tests temperature, silver concentration, free acid concentration, current density and the type of additives were varied. Basic electrolysis specifications were measured during the experiments and afterwards the deposited silver cathodes were chemically and optically examined.

The electrolysis tests showed that compact silver deposition is possible up to high current densities. By varying the process parameters relatively smooth surfaces even at high current densities could be produced. The results showed that low temperatures, a silver concentration in the range of 80 – 150 g/L and a relatively high free acid concentration improved the quality of the cathodes.

The tests proved that methanesulfonic acid is an interesting alternative to nitric acid for the electrorefining of silver, particularly if process stability, energy consumption and complexity of the cell design are considered.