Arsenic removal properties by electrolyzed and calcined manganese dioxide

As(V) removal properties of manganese dioxides which are commonly used for the removal of manganese in water treatment processes were evaluated in this paper. The following manganese dioxides were used: two types of powdered manganese dioxides powdered or electrolyzed MnO₂ (g-structure) and calcined MnO₂ (b-structure), and a granular MnO₂, which was prepared by coating MnO₂ onto a ceramic particle. The maximum arsenate adsorption capacity of the electrolyzed and calcined MnO₂ was 2.22 and 2.26 mg-As g^-1, respectively. The adsorption capacity of the granular MnO₂ was 0.543 mg-As g^-1 and this value corresponded to the MnO₂ content (23.2%) of the granular adsorbent. When an arsenate solution of 0.1 mg-As L^-1 was fed into the column (10 mm i.d.; 100 mm long) packed with the granular MnO₂ at SV = 20 h^-1, the column received 28.9 L of the feed solution (3,580 times the bed volume) before the breakthrough point (0.01 mg-As L^-1). The adsorption isotherms for the electrolyzed and granular MnO₂ were approximated by the modified Langmuir equations. On the other hand, the adsorption isotherm for the calcined MnO₂ was approximated by the Freundlich equation. Based on the adsorption isotherms, the As(V) adsorption amounts at 0.01 mg-As L^-1 of the equilibrium concentration were evaluated as follows: 1.27 mg-As g^-1 for the electrolyzed MnO₂, 1.20 mg-As g^-1 for the calcined one, and 0.29 mg-As g^-1 for the granular one. Since granular MnO₂ has been commonly used for the removal of manganese from water treatment systems, the process can be also applied to arsenate removal.