Abstract
Acid drainage from iron sulfide mine is neutralized by calcium carbonate or calcium hydroxide, after the oxidation of ferrous ions to ferric ions. And the precipitates formed, which mainly consist of ferric hydroxide and gypsum, are dumped to mill tailing dam. In order to utilize these precipitates, the separation of ferric hydroxide and gypsum by flotation method has been investigated. In the previous report, it was shown that synthetic mixture of ferric hydroxide and gypsum was satisfactorily separated each other in tne wide pH range by using dodecylammonium acetate (DAA) as a collector, where gypsum was floated and terric hydroxide remained in the solution.
This paper was concerned with the flotation separation of the precipitates formed by neutralizing an artificial acid mine water containing 1000mg/l of ferric ions and 6000mg/l of sulfate ions with calcium carbonate. It was indicated in the flotation tests of the precipitates without modifier by using DAA that the selectivity was affected by the rate of neutralization and that satisfactory results were obtained only when the aging process was introduced in the neutralization at pH 2.9. But it was found that starch acted as a selective flocculant as well as a depressor for ferric hydroxide and gave satisfying selectivity, even when rapid neutralization was adopted. These flotation products could be easily upgraded by washing with small volume of water or acidified saturated solution of gypsum.
