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

为了从海水中高效、选择性地分离和回收锂，我们开展了以下工作：(1)开发了一种新型的λ型二氧化锰(λ-MnO_2)吸附剂，该吸附剂对钠有相当高的锂选择性；(2)对这种λ-MnO_2吸附剂的性能进行了评价；(3)用这种λ-MnO_2吸附剂制备了逐层吸附膜；(4)用膜渗透模块研究了海水中锂的选择性回收体系。作为本研究的结果，(1)成功研制了λ-MnO_2吸附剂，通过用盐酸或硝酸从尖晶石型锂锰氧化物中洗脱锂离子，实现了对锂离子的高选择性识别。这一结果被应用于一项日本专利。(2)我们用λ-MnO_2吸附剂实现了锂离子和钠离子的分离。在间歇法的情况下，锂/钠的选择性在800倍以上，在柱分离法的情况下，锂/钠的选择性在2300倍以上。这些选择性是世界上最好的(专利申请2002-46288)。(3)我们用纤维素滤纸交替地浸泡在λ-MnO_2吸附剂的悬浮水溶液中，即海藻酸钠的水溶液中，制备了几种逐层吸附膜。我们用扫描电子显微镜观察了这些膜的逐层结构。(4)利用这些逐层吸附膜，我们详细考察了一些实验条件对锂和钠在实验海水中的渗透速率的影响。我们评估了锂/钠的选择性随着膜的层叠次数的增加而大大提高。然而，与柱分离相比，无法实现锂的有效分离。

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.