消石灰中和法によるAs (III) およびAs (V) の沈殿除去反応について
1984 年 100 巻 1161 号 p. 1085-1091
詳細
1984 年 100 巻 1161 号 p. 1085-1091
The arsenious ions are removed from aqueous solutions with calcium hydroxide according to the following reaction:
2Ca2++2AsO2-+2OH-=Ca (AsO2) 2 Ca (OH) 2
The arsenic ions are removed according to the following reaction:
4Ca2++2AsO3-4+2OH-=Ca3(AsO4)2 Ca (OH)2
Consequently, the concentration of As (III) and As (V) in aqueous solutions will be controlled by the solubility product of Ca (AsO2)2·Ca (OH) 2or Ca3 (AsO4)2·Ca (OH) 2, namely, by pH and the concentration of calcium ion. It was found that, when the initial concentration of arsenic is less than 10 mg/l, As (III) and As (V) were remarkably removed from aqueous solutions by adding a large excess of calcium hydroxide. The concentration of arsenic, therefore, can be reduced nearly completely by using two steps of neutralization with calcium hydroxide. In the first neutralization arsenic is removed less than 10 mg/l, and then a large excess of calcium hydroxide is added to reduce the concentration of arsenic less than the government regulation (0.5mg/l) in the second neutralization. The residue from the second neutralization can be recycled as neutralizing agent to the first one.
