2020 Volume 53 Issue 10 Pages 585-591
In the process of desalination and salt production from seawater, a lot of bittern arises as by-products. The bittern contains various resources and is mostly unutilized. We focus on the syntheses of layered double hydroxides (LDH) from components of the bittern for economical use. The LDH is a clay mineral and has an anion exchange ability. In this study, syntheses of LDHs from the bittern and the anion exchange property are investigated in comparison with that from reagents of stoichiometric concentrations of LDHs. The simulated bittern was adjusted based on the actual composition of the bittern and was mixed with Al solutions. The precipitate of LDH obtained by adding drop-wise into sodium hydroxide solution by co-precipitation method in a high pH region and the powder sample was obtained by filtration from the slurry. The structure, ion concentration and anion exchange property of the LDHs, were analyzed by SEM, XRD and ICP. The precipitated LDH from the bittern was preferentially Mg-type hydrotalcite according to the results of the XRD measurements. The synthesis of Ca-type hydrocalumite can be also synthesized from the solution excluding the hydrotalcite at another higher pH region. In the syntheses, all LDHs had chloride ions as charged intercalants for keeping charge neutrality in the layer structures. The anion exchange property was investigated between Cl− and HPO42−. The exchange structures were checked by interlayer distance variation before and after the exchange operation. The anion exchange capacity of the hydrotalcite and hydrocalumite from the bittern was lower than that from the reagents prepared in stoichiometric concentrations. A recovery process of Mg and Ca ions from the bittern is proposed in this paper.
