original reaction equation in the study: »X(w)-OH + HAsO4<2-> = »X(w)-O-AsO3<2-> + H2O with log K = 6.2±0.8, formation constant in aqueous solution: AsO4<3-> + H<1+> = HAsO4<2-> logK = 11.60 (Schecher, W. D.; McAvoy, D. C. MINEQL+, V. 4.5, Users Manual, Hallowell, ME, 1998)