Removal and Recovery of Copper from Industrial Waste Streams: Design of an Electrochemical Cell

Abstract

Copper (Cu) exists in a variety of wastewater and process streams in a host of chemical, manufacturing, and commercial industries. These instances include complex streams from chemical-mechanical planarization (CMP) processes in the semiconductor industry, rinse streams from plating baths at electroplaters, and commercial discharge to surface waters requiring Cu concentrations to be well below 1 ppm. Conventionally, the removal of Cu from wastewater has followed two routes: (1) precipitation with an iron-based coagulant and (2) ion exchange (IX) to selectively removal lower concentrations of Cu.1 Coagulation approaches, while effective, produce a notable amount of sludge waste that must be disposed of properly. Recovery of specific metals from this sludge is also quite difficult, meaning that the value in the metals that are removed with the sludge would be lost. IX, while also a long-validated technology, needs to be used under highly specific conditions and often leads to unreliable separations, particularly during production upsets in upstream equipment.Electrochemical separations can alleviate many of the problems in existing wastewater treatment techniques. In particular, capacitive deionization (CDI) as an electrochemical separation route has seen significant development over the last decade, highlighting the ability for electrochemical cells to be used in new and useful ways.2 However, CDI often suffers from diminished separation lifetime and lack of high selectivity during the separation process, although gains in selectivity have been recently explored.3 In this talk, the use of a new electrochemical process will be reviewed for the selective removal and recovery of Cu.4 Use of asymmetric carbon electrodes in an electrochemical cell is found to provide localized conditions capable of effectively removing >95% of Cu from an influent stream while symmetric configurations offer much lower levels of Cu removal. Design of the carbon electrodes for fast Cu removal kinetics along with approaches to design of the electrochemical cell for high throughput will be reviewed. Electrode density, surface area, and spacing are found to impact the effectiveness of the resulting separation. Lifetime of this new separation process will also be reviewed with demonstrations of >20 hours of operation. Degradation mechanisms and the ability to mitigate loss of performance will be presented.