Development of Selective Recovery System of Lithium From Seawater Using A Novel Layer-by-Layer Adsorption Membrane of MnO_2 Type Adsorbent

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For the purpose of efficient and selective separation and recovery of lithium from seawater, we have carried out : (1) Development of a novel λ type manganese dioxide (λ-MnO_2) adsorbent having quite high selectivity of lithium against sodium, (2) Performance evaluation of this λ-MnO_2 adsorbent, (3) Preparation of layer-by-layer adsorption membranes using this λ-MnO_2 adsorbent, and (4) Investigation of a selective recovery system of lithium from the seawater using membrane permeation module.As a result of this research, the followings were obtained.(1) We have successfully developed λ-MnO_2 adsorbent which high-selectively recognizes lithium ion by eluting lithium from spinel type lithium manganese dioxide with aqueous hydrochloric acid or aqueous nitric acid. This result was applied to a Japanese patent. (Patent pending 2002-46288, on February 22nd, 2002)(2) We have carried out the separation of lithium ion from sodium ion using the λ-MnO_2 adsorbent. We have obtained the selectivity of lithium/sodium of over 800 times in case of batchwise method, while 2300 times selectivity in case of column separation method. These selectivity are the best all over the world (Patent pending 2002-46288).(3) We have prepared some kinds of layer-by-layer adsorption membranes by alternately dipping a cellulose filter paper into a suspended aqueous solution of λ-MnO_2 adsorbent, an aqueous sodium alginate solution, in turn. We have observed the layer-by-layer structures of these membranes with a scanning electron microscope.(4) Using these layer-by-layer adsorption membranes, we have examined the effect of some experimental conditions on the membrane permeation rate of lithium and sodium in trial seawater in detail. We have evaluated that the lithium/sodium selectivity was greatly increased with increasing the lamination times of the membrane. However, we could not achieve effective separation of lithium compared with the column separation.