THE EFFECT OF SILICA , pH AND TEMPERATURE ON PYRITE PRECIPITATION

The effect of silica on pyrite precipitation was studied in order to contribute to lhe investigation to the genesis ofbanded iron formations (BIF) . Batch precipitation experiments were canied out in the presence and absence of silica. Pyrite was obtained by lhe reaction between ferrous and sultíde ions in aqueous solution. The influence of time (O to 500h), temperature (65 e 80°C) and silica concentration (O a I OOOmg/L) on the amount of solid formed and also on the solids morphology was investigated. The solid reaction product was characterized with respect to lhe presence of crystalline phases and size. ln pH 6 and temperature of 65°C, pyrite formation was favored both in pure system and in lhe presence of silica. The presence of 80mg/L of silica in pH 7 and temperature of 80°C also favored the pyrite precipitation in comparison of pure system. However, in Iower pH, 6, lhe opposite effect was observed. The sulfur soluble in solution thus indicates that in pH 7 and temperature of 80°C, high silica concentrations (500 e lOOOmg/L) could mask lhe silica effect. For lhe whole concen!ration range evaluated, it was not observed change on lhe morphology of pyrite particles formcd .