Permanent Stainless Steel Cathodes
Abstract
The use of permanent stainless steel cathodes in electrowinning, specifically with Solvent Extraction - Electrowinning (SX-EW) operations has now become the industry standard. These operations now vary in size from laboratory pilot plants (1 kg/day cathode copper), on site pilot plants (1 tpd cathode copper), medium size production plants (50 tpd) and up to large scale production plants (>200 tpd).
CMPS&F have been involved in the design, commissioning, operation and optimisation of a number of copper SX-EW projects around the world all of which have utilised permanent stainless steel cathodes. Each project has had its own specific electrowinning operation with varying physical and chemical limitations. In designing a system for permanent cathodes, it is necessary to ensure that optimum electrowinning conditions can be achieved and controlled. During commissioning and operation, the control of electrowinning conditions and maintenance of operational standards (ie housekeeping) are paramount. In resolving operational problems, and in optimisation, it is necessary to begin by reviewing the basic electrowinning principles. In all cases it must be remembered that permanent stainless steel cathodes are just that, permanent. They are designed to last the life of the project. As such any process parameter which can lead to damage of the cathode, either chemical or mechanical, must be strictly controlled from 'day one'.
In the following discussion the principles of using and maintaining permanent stainless steel cathodes are covered, along with what are considered the optimum conditions for electrowinning. Following this, some case studies are described to highlight some operational problems, and their resolution.