Behavior analysis of pH, dissolved aluminum and fluoride species in acidified river environments rich in sulfate and fluoride

Abstract

In this study, the water quality of typical acidified rivers in Yamagata and Fukushima Pref., Japan (Matsu River, Ara River and Su River) were investigated. These rivers have been receiving an inflow of a treated acid mine drainage leaches or an acidic hot spring water. Effects of dissolved aluminum and fluoride species on the acidified river environments were studied by data analyses on the water quality and chemical equilibrium calculations using the aqueous speciation computer code of the program PHREEQC. The results showed that aluminum ion in river water inhibits a rise in pH (i.e. a pH buffering effect) by alkali consumption with the hydrolysis in processes of aluminum solid-phase formations. The chemical equilibrium calculations indicated that the aluminum solid phases forming in the rivers would be mainly basaluminite (Al4(OH)10SO4) and alunite (KAl3(SO4)2(OH)6) and generations of aluminum fluoride species such as AlF2+ and AlF2+ at the points with fluorine loadings such as the inflow of hot spring water. Moreover, it was suggested that generations of these aluminum fluoride species would be moderating the pH buffering effects with aluminum solid-phase formations by moderation of the hydrolysis of aluminum.