Elimination of Cr(VI) from Electroplating Wastewater by Electrodialysis Following Chemical Precipitation

Abstract

In this work, the elimination of Cr(VI) from an electroplating wastewater in China was studied by chemical precipitation (CP), electrodialysis (ED), and their combination. The experimental results show that CP was effective as a rougher treatment for removing Cr(VI) from a high Cr(VI) wastewater, but not for a deep Cr(VI) elimination. ED alone failed to achieve a deep Cr(VI) elimination from a high Cr(VI) wastewater, although it was very effective for a medium Cr(VI) wastewater. The mechanism might be attributed to the sedimentation of chromatic ions as polychromates in the pores of ED membranes because of high Cr(VI) concentration in wastewater, which may block the pores and thus stop the transportation of the ions through the pores. It was found that the combined chemical precipitation and electrodialysis (CP + ED) process is an effective and economic process to treat high Cr(VI) electroplating wastewater. This process allows treated water to be completely recycled to electroplating lines, fewer environmental concerns, and lower reagent and operation costs.

Keywords:

• Electrodialysis
• Chemical precipitation
• Chromium ions
• Electroplating wastewater

Acknowledgments

The partial financial support to this work from the Consejo Nacional de Ciencia y Tecnología (CONACyT) of Mexico and the State of San Luis Potosi under grant FMSLP 2002‐55 are gratefully acknowledged.