As the global population continues to grow and developing countries emerge from poverty, freshwater is at risk of becoming one of the Earth’s most limited natural resources. In addition to water for drinking, sanitation and industry in human settlements, a significant proportion of the world’s agricultural production comes from irrigated crops grown in arid areas. With rivers like the Colorado, the Murray-Darling and the Yellow River no longer reaching the sea for long periods of time, the attraction of desalinating seawater as a new source of freshwater can only increase.
Desalination has serious drawbacks, however. In addition to high energy use (a topic covered in last year’sTop 10 Emerging Technologies), the process produces a reject-concentrated brine, which can have a serious impact on marine life when returned to the sea. Perhaps the most promising approach to solving this problem is to see the brine from desalination not as waste, but as a resource to be harvested for valuable materials. These include lithium, magnesium and uranium, as well as the more common sodium, calcium and potassium elements. Lithium and magnesium are valuable for use in high-performance batteries and lightweight alloys, for example, while rare earth elements used in electric motors and wind turbines – where potential shortages are already a strategic concern – may also be recovered.
New processes using catalyst-assisted chemistry raise the possibility of extracting these metals from reject desalination brine at a cost that may eventually become competitive with land-based mining of ores or lake deposits. This economic benefit may offset the overall cost of desalination, making it more viable on a large scale, in turn reducing the human pressures on freshwater ecosystems.
