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

摘要

[Problem] To provide a scorodite-type iron-arsenic compound of good filterability which satisfies the release test standard (initial pH 5.8 to 6.3) according to the Japan Act (Notification No. 13 by the Ministry of the Environment in Japan) and which secures the excellent arsenic release-preventing effect even in an environment at a pH of around 3 and at a pH of around 7. [Means for Resolution] Scorodite-type iron-arsenic compound particles in which the particle surface layer part has an iron-rich layer having an Fe/As molar ratio of at least 1.24. The particles can be obtained in a reaction process of feeding an oxygen-containing gas to an aqueous solution containing an arsenic(V) ion and an iron(II) ion to precipitate a scorodite-type iron-arsenic compound crystal at a pH of at most 2, in which an oxidizing agent is further added to the liquid before the end of the reaction (treatment A). The particles may also be obtained according to a method comprising keeping a scorodite-type iron-arsenic compound particle of good crystallinity in contact with an iron ion-containing aqueous solution having a controlled pH of from 2 to 9 at 0 to 90°C (treatment B).