EARTH

[1901-09-08] Improvement of boron removal ability by adding Ca²⁺ to Mg-Al-NO₃^- LDH

○Kengo Yano¹, Mitsuaki Matsuoka¹, Norihiro Murayama¹ (1. kansai University)

Chairman：Naoki Hiroyoshi（Hokkaido University）

Keywords:Layered double hydroxide, Boron removal, Ion exchange

Layered double hydroxide (LDH) was synthesized by a co-precipitation method. LDH is represented as the following general formula; [M²⁺_1-xM³⁺_x(OH)₂]^x+･[A^n-_x/n･mH₂O]^x-. The removal of B from dilute aqueous solution by Mg-Ca-Al-NO₃^- LDH was investigated in this study. It is known that introducing Ca²⁺ in the Mg-Ca-Al LDHs can improve the removal ability of B in aqueous solution, though it may make the structure of LDH fragile partially during washing and removal operations. The Ca²⁺ molar ratio in the resulting Mg-Ca-Al-NO₃^- LDH decreased due to the partial elution of Ca²⁺ in LDH, compared with that of starting material in a co-precipitation process. B removal tests with the obtained products were performed using 1 ppm of B solution by a batch operation. The Ca²⁺ concentration in aqueous solution after a removal operation increased with an increase in shaking time. It was found that the Mg-Ca-Al-NO₃^- LDH had higher removal percentage than the Mg-Al-NO₃^- LDH or the Ca-Al-NO₃^- LDH, when Ca²⁺ was added to the LDH at the specific molar ratio in a co-precipitation process. To investigate the effect of partial disintegration of Mg-Ca-Al-NO₃^- LDH structure on the B removal ability, the amount of washing water was changed to wet cake of reaction products. The B removal was found to decrease with a decrease of the amount of washing water. On the other hand, the ratio of Ca²⁺ eluted from the product decreased with increasing the amount of washing water. It implied that the B removal ability was improved by the partial collapse of LDH structure during not washing process but B removal process. It was considered that the LDH structure became partly fragile due to the elution of Ca²⁺, suggesting that the sorption occurred in the removal operation. We will report more detailed results and mechanism considerations in our presentation.