Treatment of Electroplating Wastes using New Generation Membrane Technology
This report was produced for the Urban Water Research Association of Australia, a now discontinued research program.
Report no. UWRAA 71
This project considers the potential for using charged Ultrafiltration (UF) or Nanofiltration (NF) membranes to process plating wastes. The application of principal interest is the separation of rinse tank waters to recover plating chemicals and produce a reusable rinse water. Charged UF and NF have been assessed since they have greater flux than Reverse Osmosis (RO) membranes and can provide selective separation of ions, potentially allowing removal of contaminants from the plating bath and rinse water circuit. This report deals mainly with chrome-plating wastes.
Charged UF membranes were shown to be able to retain divalent anions, such as chromates, to >60%. The retention was sensitive to the presence of other anions, and was able to be increased by treating the membranes with an anionic surfactant. On actual plating wastes rejections of up to 75% were achieved for chromates. However it was concluded that charged UF did not offer sufficient selectivity for practical applications.
Fourth in-film composite NF membranes were assessed. Under certain conditions these membranes showed potentially interesting separations. For example in laboratory trials, the XP20 membrane, operated at 500kPa on a diluted plating bath solution, was able to retain 80 to 85% of the desired species (CrO42+and SO42-), and show low retentions of contaminants (>0% rejection of Cl-,ca.25% for Zn2+ and 15% for Cu2+).
On-site trials were performed with 2 NF membranes on a plating waste containing Ni, Cu and Cr ions. Although single stage operation was unable to achieve the target permeate concentrations of >10ppm, this was achieved (for Ni and Cu) with two-stage processing. A permeate suitable for reuse was obtained.
Process calculations revealed that the currently available NF membranes were unlikely to provide benefits over RO membranes. This is because the limited rejection capability of the NF membranes requires 2 stage processing which offsets the advantage of higher flux than RO. Nevertheless it is strongly recommended that an on-going technical assessment of NF, and other relevant membrane technologies, be maintained in this rapidly developing field. The centre for Membrane Science and Technology has, through this project, the experience and contacts to further this application study.