Cutting-edge technology for the selective separation of monovalent salts from seawater brine
Noura Ahmed Chehab*, Nikolay Voutchkov, Mohammed Qasem Alsindi
ENOWA Water/NEOM, Saudi Arabia
*Corresponding author
https://doi.org/10.5004/po2024109
ABSTRACT
ENOWA Water is the water utility of NEOM. NEOM is an independent economic zone located in the Northwest of Saudi Arabia. NEOM depends on the designation to produce drinking water. Desalination, however, necessitates the production of brine, which is considered a valuable by-product by NEOM. Traditionally, brine is produced as a byproduct of desalination processes and is typically released into the sea. The emphasis, however, is gradually turning toward environmentally sustainable alternatives. This project proposes a revolutionary technology for brine valorization, with the goal of extracting individual minerals from brine without the typically practiced split of the desalination brine into two separate streams of monovalent and polyvalent minerals. In the presented process developed by the ENOWA Water Innovation Center (WIC) first. Selective SWRO membranes are used to separate a particular mineral targeted for extraction directly from seawater. After that, the target mineral is crystallized by a membrane-based crystallization technology that substitutes traditional thermal evaporation processes with brine concentration and membrane crystallization technologies. The use of the selective RO (Reverse Osmosis) membrane developed by the WIC research team, combined with the downstream membrane crystallization technology we have developed with industry partners that is based on forward osmosis (FO) principles can be used for the selective extraction of a wide spectrum of minerals from seawater or brackish water brine. The selective membrane separation process involves the transfer of the target mineral with fresh water on the permeate side of the SWRO membrane by applying active ingredient in the membrane layer, which creates a passage for this mineral and rejects other salts. Then, the target mineral, which is contained in the second stage of the BWRO system downstream of the SWRO membranes, is crystalized on the surface of FO membranes driving the water out of the brine by osmotic pressure difference created by draw solution with higher osmotic pressure than the target mineral. In this article, potassium chloride selective SWRO membrane system combined with FO membrane crystallization system with magnesium chloride draw solution are presented to illustrate the process described above. The results from the testing of the potassium selective membrane separation process are presented and evaluated based on the outcomes from the operation of WIC’s brine valorization demonstration plant facility in Duba, Saudi Arabia. The potassium chloride extracted from the source seawater using the process described above has purity of 95% or more. The purity of the extracted mineral allows potassium chloride to be used directly as liquid fertilizer for agricultural applications. The potassium chloride selective system allows to recover over 90% of the potassium chloride naturally contained in the source seawater. The key advantages of this potassium selective membranes are the ease of installation, low membrane and energy costs and producing a high value product without the need for costly system for separation of monovalent and bivalent minerals first. Most existing and likely future plants already utilize a two-pass process configuration, so no SWRO and BWRO capital investment would be needed to pursue this use of this brine mining system at existing reverse osmosis desalination plants. In addition, the final product is a low-volume, high-value “chemical feedstock” that will generate an additional revenue stream for the SWRO plant. Moreover, the membrane crystallizer unit has three distinct advantages. Initially, the smooth-surfaced membrane prevents scaling and encourages the formation of small crystals, which eventually detach and amass in a collection basin. Second, an osmotically assisted reverse osmosis (OARO) system reconcentrates the diluted draw solution internally, allowing it to be reused for crystallization. Finally, the system shows the ability to extract commercially valuable minerals from seawater by employing FO. Energy associated with membrane crystallization is an order of magnitude lower than that needed for thermal evaporation and crystallization. This novel technology of brine processing helps to a more sustainable and ecologically friendly desalination processes by boosting water recovery, improving energy efficiency, and recovering valuable minerals from brine.
Keywords: Selective membrane; Membrane crystallizer; Brine mining; Zero liquid discharge (ZLD); Water desalination
