original reaction equation in the study: »X(w)-OH + H2AsO3<1-> = »X(w)-O-AsOOH<1-> + H2O with log K = 2.8±0.1, formation constant in aqueous solution: AsO3<3-> + 2H<1+> = H2AsO3<1-> logK = 25.52 (Schecher, W. D.; McAvoy, D. C. MINEQL+, V. 4.5, Users Manual, Hallowell, ME, 1998)