Treatmentof Electroplating Wastes using New-Generation Membrane Technology

ReportNo WSAA 71

January 1994

SYNOPSIS

Thisproject considers the potential for using charged Ultrafiltration (UF) orNanofiltration (NF) membranes to process plating wastes. The application ofprincipal interest is the separation of rinse tank waters to recover platingchemicals and produce a reusable rinse water. Charged UF and NF have beenassessed since they have greater flux than Reverse Osmosis (RO) membranes andcan provide selective separation of ions, potentially allowing removal ofcontaminants from the plating bath and rinse water circuit. This report dealsmainly with chrome-plating wastes.

ChargedUF membranes were shown to be able to retain divalent anions, such as chromates,to >60%. Theretention was sensitive to the presence of other anions, and was able to beincreased by treating the membranes with an anionic surfactant. On actualplating wastes rejections of up to 75% were achieved for chromates. However itwas concluded that charged UF did not offer sufficient selectivity forpractical applications.

Fourthin-film composite NF membranes were assessed. Under certain conditions thesemembranes showed potentially interesting separations. For example in laboratorytrials, the XP20 membrane, operated at 500kPa on a diluted plating bathsolution, was able to retain 80 to 85% of the desired species (CrO₄²⁺and SO₄^2-), and show low retentions of contaminants (>0% rejection of Cl^-,ca.25% for Zn²⁺ and 15% for Cu²⁺).

On-sitetrials were performed with 2 NF membranes on a plating waste containing Ni, Cuand Cr ions. Although single stage operation was unable to achieve the targetpermeate concentrations of >10ppm, this wasachieved (for Ni and Cu) with two-stage processing. A permeate suitable forreuse was obtained.

Processcalculations revealed that the currently available NF membranes were unlikelyto provide benefits over RO membranes. This is because the limited rejectioncapability of the NF membranes requires 2 stage processing which offsets theadvantage of higher flux than RO. Nevertheless it is strongly recommended thatan on-going technical assessment of NF, and other relevant membranetechnologies, be maintained in this rapidly developing field. The centre for MembraneScience and Technology has, through this project, the experience and contactsto further this application study.

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