抄録
Adsorption gels were prepared from orange juice residue and brown seaweed (Konbu) which contain acidic polysaccharides, pectic acid and alginic acid, respectively, by means of saponification with calcium hydroxide followed by water washing and drying (gel A) and by crosslinking with epichlorohydrin(gel B), respectively, which greatly suppressed the leakage of water soluble components contained in these gels. Free acid type adsorption gel (gel C) was also prepared from the above-mentioned gel prepared from orange juice residue by washing with dilute hydrochloric acid. Big difference was observed between the gel A and the gels B and C in the adsorption behavior for ferric ion; that is, in the case of the adsorption on the gel A, it monotonously increased with increasing pH while, in the case of those on the gels B and C, it increased with increasing pH at low pH, but, it decreased with further increasing pH at pH higher than 2.5 ∼ 3. By using the gels A and B loaded with ferric ion, adsorption tests of arsenate and arsenite were carried out at 30 °C and compared with the conventional coprecipitation method with iron salt. It was found that arsenate was quantitatively adsorbed at low pH on the gels A (pH = 2 ∼ 5) and B (pH = 2 ∼ 3) while only 90 ∼ 80 % was removed at pH = 5 ∼ 6 by means of the coprecipitation method. In addition, several % of the coprecipitated arsenic was found to be dissolved in water while no leakage was detected from the gels. On the other hand, arsenite was effectively adsorbed under weakly basic condition.
On the basis of the above-mentioned adsorption tests using model arsenic solution, a field test of adsorptive removal of arsenic was carried out from the actual mine water at Horobetsu pyrite mine using the gels A and B. The mine water contains a large amount of iron the majority of which is ferrous ion in addition 10 mg / dm3 arsenic and pH is 1.8. To the sample of the mine water, magnesium oxide was added to adjust pH together with these gels which were unloaded with ferric ion. It was found that arsenic was nearly quantitatively removed by these gels over wide range of pH 4 ∼ 10 while considerable amount of arsenic, greater than 0.1 ml / dm3, was remained in the treated water in case these gels were not added, i.e. by the conventional coprecipitation method.
