logK for Protolysis reaktion and background electrolyte complexation from [WDA00], site-type not clearly defined, assumed to be singly, R^2 = 0.971, residual mean of sum of squares = 1.002E-10, given sorption reaction: (>AlOH2<+1/2>)2 + HAsO4<2-> = (>AlO)2-AsO3, given mass action law: logK(As(V)) = [(>AlO)2As(OH)2]/[>AlOH<-/2>] * [HAsO4<2->]; acid dissociation constant pK3 = -12.52 for H3AsO4 [WGD92]