Chemists have found a way to effectively desalinate water and extract lithium from brine using MOF membranes, as in living cells

    Lithium deficiency is one of the main reasons for the high cost of lithium-ion batteries, and as a result, the high cost of electric vehicles, where batteries are more than half the cost. If it weren’t for the difficulty with its production, we would live today in a completely different world, where alternative energy would probably be much more widespread, and people would gradually forget about burning hydrocarbons in transport. But the reality is that there are not so many rich deposits: they are located in Argentina, Bolivia, Chile, China, the USA, Russia and several other countries.



    World lithium reserves themselves are large. Only in Russia, 1 million tons of lithium, but here after the collapse of the USSR it is no longer mined: domestic enterprises import lithium-containing concentrate from Congo and China . Mining of lithium carbonate Li2 CO 3 involves the evaporation of brine in highly saline lakes (Chile, Bolivia, Argentina, USA) or acid processing, as is the case with Russian ore. After evaporation, the carbonate is chlorinated to obtain LiCl, electrolysis ($ 2LiCl \ {\ xrightarrow {\}} \ 2Li + Cl_ {2} \ uparrow $) and vacuum distillation. In total, about 35,000 tons of lithium per year are mined on world deposits .

    Fortunately, an increasing percentage of lithium-ion batteries are being recycled, so recycling now provides a noticeable percentage of all lithium that goes to manufacturing plants.

    But lithium is still not enough. Demand for lithium constantly exceeds supply - and is growing every year. Perhaps this problem can be solved in an extraordinary way. The fact is that the world's oceans contain giant lithium reserves (huge reserves of gold and other metals are also dissolved in it). The question is how to get these riches cheaply and efficiently. A new effective method for the extraction of lithium and other metals from sea water was proposedchemists from the University of Texas at Austin (USA), Monash University and the State Association of Scientific and Applied Research (both Australia).

    They proposed a process using metal-organic framework membranes (MOFs) that replicate the filtering mechanism — ion selectivity — of biological cell membranes in living organisms. This highly efficient metal ion is easily separated. For his discovery in living cells, the 2003 Nobel Prize in Chemistry was awarded. It can be used not only for the processing of sea water, but also for mountain ores.


    Schematic illustration of ion transfer through a ZIF-8 / GO / AAO membrane

    Another by-product after filtering metals in salt water is fresh, potable water. That is, the manufacturing process simultaneously produces valuable ore and fresh water. “The prospect of using MOF for sustainable filtration of water is incredibly interesting in terms of public utility, while the best way to extract lithium ions to meet global demand will help create new industries,” said Anita Hill, senior fellow at the National Association scientific and applied research.

    Effective desalination is the main task that the researchers set for themselves. “But this is only a small part of the potential potential of this phenomenon,” says Huanting Wang, professor at Monash University. - We will continue to investigate the selectivity of these membranes to lithium ions for practical use. Abundant amounts of lithium ions are present in seawater, so the discovery can be of great importance for the mining industry, where inefficient chemical methods are now used to extract lithium from rocks and brines. The global demand for lithium, which is needed for electronics and batteries, is very high. These membranes allow very efficient extraction of lithium ions from seawater. ”

    So in the future, the oceans can become a rich and easily accessible lithium resource. Perhaps, in addition to lithium, they will learn how to use membranes for filtering gold and other metals needed by industry.

    The scientific article was published on February 9, 2018 in the journal Science Advances (doi: 10.1126 / sciadv.aaq0066).

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