Electrochemical Cell Design and Operation for Copper Recovery from Chemical Mechanical Polishing Slurries

Abstract

Copper (Cu) removal from chemical mechanical polishing (CMP) waste is critical to maintaining discharge compliance with local municipalities and the Environmental Protection Agency (EPA). Typical treatment of this waste stream has followed two conventions: either coagulant-based precipitation or ion exchange (IX).1 Many industries use iron-based coagulants for metal removal from wastewater to meet discharge compliance. However, the process is often cumbersome, requires long settling times and significant chemical utilization, and results in a sludge stream that must be shipped and disposed of properly, eliminating the possibility for metal recovery. Since the concentrations for Cu removal from CMP waste streams is normally low (<100 ppm), IX has generally been the preferred treatment method. Nevertheless, IX also has some negatives associated with the process. Hydrogen peroxide can and will damage the IX media, resulting in premature replacement. The industry has dealt with this impact by employing one-time use media, but this adjustment means that media is only used once before being shipped offsite for regeneration. This results in operational impacts due to the need for oversight of media replacement and also eliminates the ability for Cu to be recovered at the originating process site.In this talk, electrochemical methods to recover Cu from CMP wastewaters will be described. Electrochemical cell design and operation will be shown to provide Cu removal across wide ranges of concentration, and the depth of Cu separation (<2 ppm) and efficiency of the process will be discussed. The presence of hydrogen peroxide and its influence on the process will be evaluated. The removal and recovery of Cu will be shown in a complete cycle, demonstrating the ability to recover and reuse Cu directly at a process site. The impact of (1) pH, (2) chelator type, and (3) abrasive (SiO2) will also all be reviewed. Changes to the slurry, as analyzed pre- and post-electrochemical separation, will be characterized to determine possibilities for the reuse of the CMP slurry itself. Ultimately, the ability to design process systems using electrical input and minimal chemical additives to treat wastewater to municipal and EPA specifications while maximizing recycling efforts will be evaluated and presented.