Conductive Spacers to Limit RO Membrane Scale Formation

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Mining extraction produces large quantities of wastewater, oftentimes with high salt concentrations. This brine must be treated before disposal into the environment. The technology of choice for salt-water separations is reverse osmosis (RO) membranes. However, RO membranes foul quickly under the high salinity conditions of mining wastewaters. The mining wastewaters of concern have high concentrations of calcium with excess sulfate. Under these conditions, a calcium sulfate (gypsum) scale composed of dense and sharp mineral precipitates form on the membrane surface. These scaling layers block trans-membrane water flow, reduce membrane ion selectivity, and can damage membrane surfaces. Electric fields have been shown to disrupt the formation of mineral scale. Positive applied electric potentials, for example, can prevent the deposition of Calcium ions on the membrane surface, thereby limiting the formation of gypsum. In preliminary research, electrically conductive membranes have shown promise for their ability to limit the formation of gypsum scale. Electrically conductive membranes, however, have only been fabricated at the lab scale and are far from commercial development. A simpler solution is to replace the polymeric spacers used in membrane modules with electrically conductive materials to which potentials can be applied. Our research will investigate the application of electric potentials to electrically conductive spacers as a means to reduce or limit mineral scale formation. We will investigate the impact of different applied potentials ranging between +0.5 V and 3.0 V, as well as different electrically conductive metal spacer materials (Al-Mg, stainless steel, and Cu) and metal spacer gauges.