Selection of Salt, Metal, Radionuclide, and Other Valuable Material Recovery Approaches
Year Released: 2015
Type: White Paper
Funding Partner: Bureau of Reclamation
Total Investment: $183,128 (Cash: $124,964, In-Kind cash and service: $58,164)
Principal Investigator: Christopher Bellona, Ph.D., Clarkson University
Concentrate management is one of the most divisive aspects of desalination and often influences the feasibility of a desalination project. There is increased interest in RO concentrate minimization and zero liquid discharge (ZLD). One possible strategy to recover costs from desalination and ZLD implementation is the recovery of valuable constituents in concentrate streams. While a significant amount of research has been performed on constituent extraction, there is little consensus on its feasibility at a desalination facility.
Goals and Objectives
The goal of this project was to examine efforts aimed at recovering materials from aqueous solutions with the goal of recovering valuable compounds from desalination brine/concentrate streams. The objectives of this study were to:
- Review and summarize available literature on the extraction of metals, salts, and other valuable constituents,
- Organize information into searchable EndNote databases,
- Determine the feasibility of valuable material extraction from desalination brine/concentrate and
- Summarize relevant case studies where extraction was evaluated or performed.
The major goal of this project was to examine efforts aimed at recovering materials from aqueous solutions with the goal of recovering valuable compounds from desalination brine/concentrate streams. To this end, a comprehensive review was undertaken to summarize the literature pertaining to the extraction of metals, salts, and other valuable constituents from aqueous solutions. Based on the literature review, the feasibility of extracting materials in desalination brine/concentrate was evaluated and a preliminary cost assessment performed to evaluate the economics of extracting potentially viable compounds. Finally, various case studies on extraction in a variety of applications were compiled and summarized.
Findings and Conclusions
Currently, sodium chloride and magnesium compounds (magnesium hydroxide and magnesia) are the only compounds extracted from seawater at any appreciable extent. However, a significant amount of effort and research has been put into the development of processing schemes for the extraction of valuable constituents from desalination brine/concentrate over the past 40-years. With the exception of a planned process to produce calcium carbonate at a desalination facility in Southern California, only one documented case of valuable material extraction from desalination brine for economic gain was identified at the full-scale (sodium chloride is produced from SWRO brine in evaporation ponds in Israel).
Because the ocean is viewed as an inexhaustible resource, a significant amount of research has been performed to develop methods for extracting relatively high value trace metals. Particularly, technologies for the extraction of lithium, rubidium, and uranium have been continually refined over the past 30 years to improve extraction efficiency. Currently, such methods of extraction are inhibited by a number of factors including poor selectivity, low commodity pricing (with the exception of rubidium), relatively low aqueous concentrations, low demand (particularly for rubidium), and complex post-processing necessary to yield pure products. Many analysts believe that the extraction of constituents with concentrations less than boron (~26 mg/L in seawater) will likely never be feasible unless alternative resources become exhausted. While a number of publications have proposed the extraction of trace metals from desalination brine/concentrate, very few report on the feasibility of extraction at an appreciable scale.
Besides the previously discussed trace metals, preliminary screening of the major commodities in seawater desalination brine indicated that bromine, magnesium, and sodium chloride could potentially be extracted for economic gain. In addition, several researchers have concluded that chlorine and sodium hydroxide could also be produced from desalination brine for a profit. Preliminary cost analyses performed on several reported schemes for the production of the aforementioned commodities were developed to evaluate the economics of extraction. Preliminary cost analyses indicate that it is likely only economically feasible to produce magnesia (and potentially magnesium hydroxide) and potentially chlorine and sodium hydroxide from seawater desalination brine. The profitability of extracting chlorine and sodium hydroxide is strongly dependent upon the efficiency of the electrolytic cell, and more research is required to evaluate the efficiency of chlorine and sodium hydroxide production using purified desalination brine as feedstock.
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