Zero-liquid discharge (ZLD) is an emerging wastewater management strategy that maximizes water recovery for reuse and produces a solid waste, thereby lowering the environmental impact of wastewater disposal. Evaporation ponds harvest solar energy as heat to passively evaporate water from brines for ZLD. However, large land areas are required due to low evaporation rates as direct utilization of solar energy for evaporation is limited by the transparency of water at visible and near-infrared wavelengths.

To address this, we are developing simple photo-thermal devices that convert sunlight into mid-infrared radiation where water is inherently a strong absorber, thereby achieving radiative heat localization at the water’s surface. This approach is passive and non-contact, which eliminates contamination risks and makes it uniquely suited for corrosive brines encountered in the ZLD process.

Forward osmosis (FO) is a promising technology for treating nontraditional water sources that are beyond the operating limits of state-of-the-art reverse osmosis (RO). FO uses a draw solution to drive water flux across a membrane in the first step (draw dilution), followed by separation of the draw from water (draw regeneration) to produce clean water. The technology has thus far had limited applicability due to the energetic requirements associated with draw regeneration.

To address this, we are using a new class of draw solutes, namely thermally responsive ionic liquids (ILs) that undergo phase separation upon heating with solar-thermal energy above their lower critical solution temperature (LCST). At a fundamental level, we are leveraging the unique characterization tools at the Advanced Light Source (ALS) to understand phase separation dynamics and its impact on radiative heat transfer in participating media. This project is funded by the DOE’s Solar Energy Technologies Office, and is in collaboration with Dr. Robert Kostecki’s group in ESDR and Dr. Jeff Urban’s group at The Molecular Foundry.

Critical materials are used in many products important to the U.S. economy and national security. For example, the demand for lithium is expected to increase significantly due to the rapid expansion of electric vehicles and grid-level energy storage markets that rely on lithium ion batteries (LIBs). Other critical materials include rare earth elements, which are essential for manufacturing high strength magnets used in electric vehicle motors and offshore wind turbine generators. Desalination brines and brines from other processes (e.g. geothermal power generation, oil and gas produced water, etc.) can serve as sources for these critical materials. We are developing electrochemical technologies with high selectivity and specificity to extract elements of value from different brine streams.