Evaluation of the affinity of some toxic elements to schwertmannite in natural streams contaminated with acid mine drainage

Nagano, Tetsushi  ; Yanase, Nobuyuki; Hanzawa, Yukiko  ; Takada, Morio*; Mitamura, Hisayoshi; Sato, Tsutomu*; Naganawa, Hirochika  

Schwertmannite is a poorly-crystalline ferric sulphate mineral that secondarily forms in acid mine drainages (AMD) as a result of the oxidative weathering of pyrite (FeS2), and is known to work as a naturally-occurring scavenger of some toxic elements in AMD-contaminated streams due to its high fixation potentials. In this study, to examine the feasibility of using schwertmannite in water purification technique, we evaluate the affinity of some selected elements to schwertmannite using two parameters: (1) conventional apparent solid-liquid partition coefficients between schwertmannite and stream waters, and (2) newly introduced parameters that correspond to ratios of ions fixed by schwertmannite to those existing as dissolved phases. As a result, both of the two parameters revealed that schwertmannite has high fixation potential for fluvial transport of various toxic anions such as V, Cr, As, Mo and Sb in AMD-contaminated streams, and that it could be used for purification of waters contaminated with these toxic anions.