The demand for lithium has been steadily growing in recent years due to the boom of electric cars. High purity lithium is commonly used in the manufacture of battery grade lithium electrolyte. Sulfate residuals originating from acid leaching of lithium ores must be limited to below 20 mg·L⁻¹ during refining. There are methods to remove sulfate such as membrane processing and chemical precipitation using barium salts. However, membrane separation is unable to achieve the required purity while chemical precipitation often causes secondary contamination with barium and requires extra filtration processes that lead to increased processing costs. In this study, we developed a polymeric matrix entrapped with barium ions as a novel adsorbent to selectively adsorb sulfate in aqueous solutions. The adsorbent was prepared by dropwise injection method where alginate droplets were crosslinked with barium to form hydrogel microcapsules. In a typical scenario, the microcapsules had a diameter of 3 mm and contained 5 wt-% alginate. The microcapsules could successfully reduce sulfate concentration in a solution from 100 to 16 mg·L⁻¹, exceeding the removal target. However, the microcapsules were mechanically unstable in the presence of an excess amount of sulfate. Hence, calcium ions were added as a secondary cross-linking agent to improve the integrity of the microcapsules. The two-step Ca/Ba@alginate microcapsules showed an exceptional adsorption performance, reducing the sulfate concentration to as low as 0.02 mg·L⁻¹. Since the sulfate selective microcapsules can be easily removed from the aqueous system and do not result in secondary barium contamination, these Ca/Ba@alginate adsorbents will find applications in ultra-refining of lithium in industry.

近年来，由于电动汽车的蓬勃发展，对锂的需求一直稳定增长。高纯度锂通常用于制造电池级锂电解质。锂矿石酸浸产生的硫酸盐残留必须限制在20 mg·L ^-1以下在精炼过程中。存在去除硫酸盐的方法，例如膜处理和使用钡盐的化学沉淀。但是，膜分离无法达到所需的纯度，而化学沉淀通常会导致钡的二次污染，并且需要额外的过滤过程，从而导致加工成本增加。在这项研究中，我们开发了一种包埋有钡离子的聚合物基质作为一种新型吸附剂，可以选择性地吸附水溶液中的硫酸盐。通过滴注法制备吸附剂，其中藻酸盐滴与钡交联形成水凝胶微胶囊。在典型情况下，微胶囊的直径为3mm，并且包含5重量％的藻酸盐。微囊可以成功地将溶液中的硫酸盐浓度从100降低到16 mg·L^-1，超过去除目标。但是，在存在过量硫酸盐的情况下，微胶囊在机械上是不稳定的。因此，添加钙离子作为次级交联剂以改善微胶囊的完整性。两步式Ca / Ba @藻酸盐微胶囊显示出优异的吸附性能，将硫酸盐浓度降低至0.02 mg·L ^-1。由于硫酸盐选择性微胶囊可以很容易地从水系统中除去并且不会导致钡的二次污染，因此这些Ca / Ba @藻酸盐吸附剂将在工业锂的超精炼中得到应用。