Sustainable operation of membrane distillation for enhancement of mineral recovery from hypersaline solutions

• DCMD was investigated as a replacement to natural evaporation.
• A novel application of DCMD for mineral resource recovery was tested.
• Hypersaline solutions were concentrated to greater than 350 g/L total solids.
• Membrane scaling was detected by a microscope at the onset of flux decline.
• Unique scale mitigation techniques were developed.

Membrane distillation (MD) is an emerging desalination technology that has the ability to desalinate hypersaline brines, including those used in mineral production. MD can potentially replace evaporation ponds in conventional mineral production processes because of its small footprint and ability to utilize industrial low-grade heat. In the current study MD was investigated for sustained water recovery and concentration of hypersaline brines. Direct contact MD (DCMD) experiments were performed with water from the Great Salt Lake (>150,000 mg/L total dissolved solids) as the feed stream and deionized water as the distillate stream. DCMD was able to concentrate the feed solution to twice its original concentration, achieving close to complete inorganic salt rejection. During experiments water flux declined to 80% of its initial value (from 11 to 2 L m−2 h−1). Real-time microscopy revealed that precipitation of salts on the membrane surface was the main contributor to the decline in water flux. The application of novel scale-mitigation techniques was highly effective in preventing scale formation on membrane surfaces, sustaining high water flux and salt rejection, and eliminating chemical consumption used for membrane cleaning. MD was compared to natural evaporation and was found to potentially replace 4047 m2 (1 acre) of evaporation ponds with approximately 24 m2 (259 ft2) of membrane area and to be nearly 170 times faster in concentrating hypersaline brines.

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