Dowa Metals & Mining Co., Ltd.

Ryoichi Taguchi

Tetsuo Fujita

Hisashi Kubo

Provided is an arsenic-containing solid comprising 100 parts by mass of a scorodite-type iron-arsenic compound and at least 1 part by mass of an iron oxide compound added thereto, in which the scorodite-type iron-arsenic compound is produced by adding an oxidizing agent to an aqueous acidic solution that contains a 5-valent arsenic (V) ion and a 2-valent iron (II) ion, then promoting the precipitation of an iron-arsenic compound with stirring the liquid, and finishing the precipitation thereof within a range where the pH of the liquid is at most 1.2. The iron oxide compound includes goethite, hematite and their mixture, preferably having a BET specific surface area of at least 3 m/g, more preferably at least 20 m/g.

Arsenic-containing solid and method for producing it

A method of producing an iron-arsenic compound by adding an oxidizing agent to an aqueous solution containing arsenic ions and bivalent iron ions and allowing an iron-arsenic compound precipitation reaction to proceed under stirring of the solution, wherein the precipitation reaction is terminated at a solution pH in the range of 0 to 1. When the arsenic concentration of the pre-reaction solution is 25 g/L or greater, the reaction can be terminated at a solution pH in the range of &#x2212;0.45 to 1.2. The pH of the pre-reaction solution is preferably greater than 0 and not greater than 2.0. A ferrous sulfate is can be used as the source of the bivalent iron ions. Even when some amount of impurity elements is present in the arsenic-containing solution, the method is nevertheless capable of forming a scorodite compound excellent in crystallinity in the form of a compact compound barely swollen by moisture and the like, i.e., a niron-arsenic compound excellent in filterability.

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Akita, Japan

Ryoichi Taguchi