総説（特集）
坑廃水処理における水酸化物への共沈機構
キーワード:
Coprecipitation,
Surface complexation,
Surface precipitation,
Ferrihydrite,
Wastewater treatment
2020 年 54 巻 1 号 p. 5-14
詳細
2020 年 54 巻 1 号 p. 5-14
Mine drainage from approximately 100 abandoned/closed Japanese mines has been treated by neutralization over the last forty years. Coprecipitation is a main mechanism for removal of several toxic elements from mine drainage during the neutralization. In order to develop more efficient treatment methods, it is important to understand the coprecipitation mechanism quantitatively.
In many cases, coprecipitation can incorporate more toxic elements into the hydroxide than adsorption. In coprecipitation of arsenic to ferrihydrite, surface precipitation of low crystalline ferric arsenate was formed, as initial As/Fe molar ratio was increased. This surface precipitation enabled arsenic removal by ferrihydrite with high efficiency such as 1 mol-As / mol-Fe. On the other hand, in coprecipitation of chromate to ferrihydrite, structure of ferrihydrite was expanded due to inner-sphere surface complexation of chromate into inside of ferrihydrite, as initial Cr/Fe molar ratio was increased. These phenomena of surface precipitation and inner-sphere surface complexation will occur because surface complexation of arsenate or chromate is faster than ferrihydrite formation, and additional surface complexation of Fe3+ion onto them can be formed.
