(174bw) Sustainable, Efficient, and Robust Mxene-Based Emulsion Liquid Membranes for Heavy Metals Removal

Globally 1.8 billion people lack access to safe drinking water, and 842,000 people die every year due to unsafe water consumption¹. In addition, according to the United Nations, the world is set to face a 40 percent shortfall in water supply by 2030 consumption¹, and the global demand for water is projected to increase by 55% by 2050². Compared to existing methods of water purification, the membrane technology is more environmentally friendly, more efficient, and less expensive in terms of operating and capital costs. In particular, the emulsion liquid membrane (ELM) technology has the potential for the separation of toxic heavy metals even at very low concentrations^3-4. In ELMs, extraction and stripping occur simultaneously in one single step with no equilibrium limitation, high flux, and selective separation⁵. An ELM consists of an external phase, a membrane phase, and an internal phase. The internal phase plays an important role in stability and performance of the ELM system. Several inorganic acids at various concentrations have been used as the internal phase^6-11. However, the use of an acidic solution as the internal phase has several drawbacks such as the precipitation of metal salt at the oil-water interface, swelling, osmotic pressure buildup through the membrane phase, and leakage or membrane breakage. So far, there has not been any reported study on how the nature of the internal phase affects the morphology of globules in an ELM system.

We have studied the replacement of the acidic internal phase with two-dimensional (2D) nanomaterials. In this paper, we report results on the ELM stability, providing a better understanding of swelling, tendency to rupture, and separation performance in ELMs. We used kerosene, di(2-ethylhexyl) phosphoric ethyl hexyl) phosphoric acid (MEHPA), and Span 80 as the diluent, the carrier, and the surfactant, respectively. Graphene oxide, molybdenum disulfide and Ti₃C₂T_xMXene suspensions were used as the internal phase. MEHPA and the strippers were chosen based on conventional liquid–liquid extraction studies. In addition, process parameters such as the speed of mixing the two phases, concentrations of hydrogen ions in the internal and external phases, membrane-to-emulsion (M/E) ratio, and carrier, surfactant, and 2D nanomaterial concentrations were optimized to lower the level of mercury ions in water to below the level accepted by the U.S. Environmental Protection Agency.

Keywords: Emulsion Liquid Membrane, MXene, MEHPA, Mercury Ions, Wastewater Treatment

References

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