SCORODITE-TYPE IRON-ARSENIC COMPOUND PARTICLES, PRODUCTION METHOD, AND ARSENIC-CONTAINING SOLID

摘要

Provided is a scorodite-type iron-arsenic compound having good filtration performance that satisfies the criteria for elution tests (initial pH of 5.8 to 6.3) in accordance with Japanese laws and ordinances (Ministry of the Environment Bulletin No. 13) and that realizes an excellent arsenic elution-preventing effect, even under an environment of approximately pH 3 or approximately pH 7. There is an iron-rich layer having an Fe/As molar ratio of 1.24 or greater at the particle surface layer part of the scorodite-type iron-arsenic compound particles. Such particles can be obtained by further adding, before the reaction is complete, an oxidizer to a reaction process whereby an oxygen-containing gas is fed to an aqueous solution containing pentavalent arsenic ions and bivalent iron ions as scorodite-type iron-arsenic compound crystals are caused to precipitate under a pH of 2 or less (treatment A). Moreover, these particles can also be obtained by bringing scorodite iron-arsenic compound particles having good crystallinity into contact with an iron ion-containing aqueous solution at 0 to 90°C that has been brought to a pH of 2 to 9 (treatment B).