Abstract: 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 m2/g, more preferably at least 20 m2/g.

Abstract: To provide a recovery agent for recovering arsenic, fluorine, lead, and selenium from a solution containing environmentally hazardous substances including arsenic and fluorine. A porous iron oxide having a particle size of 10 to 100 ?m and a specific surface area of 50 m2/g or larger determined by three-point BET method is introduced into a solution containing the environmentally hazardous substances. Alternatively, a solution containing the environmentally hazardous substances is passed through a column filled with the porous iron oxide. Thus, the environmentally hazardous substances are recovered from the solution.

Abstract: 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 m2/g, more preferably at least 20 m2/g.