Study on the Fluoride Removal from Hot Spring Waste Water Using Si-Al-Mg Mixed Hydrous Oxide

Abstract

The mixed hydrous oxide is synthesized in a Si/Al/Mg mole ratio of 0.1/0.1/0.8, and its adsorption ability for fluoride ion is examined. The fluoride ion adsorption rate of the Si-Al-Mg mixed hydrous oxide is rapid and its adsorption amount reaches equilibrium after 8 hours at the fluoride test solution used. Logarithm plotting of the adsorption isotherm for fluoride ion almost corresponds to the Freundlich formula. The Si-Al-Mg mixed hydrous oxide has high affinity to fluoride ion, because the value of 1/n in the Freundlich formula shows 0.379. The changing the kind of acid used for the synthesis from nitric acid to hydrochloric acid will improve the selectivity of the Si-Al-Mg mixed hydrous oxide for fluoride ion. Although the adsorption rate for fluoride ion is decrease in the actual hot spring water, the Si-Al-Mg mixed hydrous oxide adsorbs fluoride ion under the waste water quality standards. Therefore, it can be expected that the Si-Al-Mg mixed hydrous oxide is used as a low-cost fluorine adsorbent.