ARSENIC SPECIATION IN IRON HYDROXIDE PRECIPITATES

In this study a special sequential extraction method is proposed to di scriminate between arsenic adsorbed and co-precipitated in precipitate s arising mainly from iron hydroxides or bound in low solubility miner al phases. Synthetic iron hydroxide precipitates were prepared to inve stigate the influence of the amount of arsenate, of the manganese addi tionally added and of the valence state of arsenic on the remobilisati on of arsenic. After preparing the precipitates with arsenate no arsen ic could be detected in the supernatant solution. About 82% (w/w) of t he arsenate is adsorbed to the precipitate and the remaining part can be dissolved by shaking with an oxalate buffer. A significant differen ce between the amount of arsenic added and the amount analysed in the two steps was not found. Consequently, compounds with a low solubility , such as scorodite, were not formed in the synthesized precipitates. The valence of the arsenic and addition of manganese influence signifi cantly the uptake of arsenic by iron hydroxides. Natural precipitate s amples from a percolate water of tin mill tailings were investigated u sing this method. (C) 1998 Elsevier Science B.V. All rights reserved.