The effect of seeding on the rate of precipitation of ammonium jarosite and sodium jarosite

The beneficial effect of jarosite seed on the rate of precipitation of ammonium jarosite and sodium jarosite was confirmed, and it was shown that the initial rate of precipitation increases linearly with the amount of seed present. A minimum degree of agitation is necessary to suspend the seed, but higher agitation rates are without further effect. Furthermore, the presence of seed extends the range of jarosite precipitation to lower pH values and to lower temperatures than is the situation in the absence of seed. The presence of seed accelerates the initial precipitation rate at all pH values and temperatures and generally eliminates any induction period. The activation energy for sodium jarosite precipitation in the presence of seed is 106 kJ/mol. In the presence of sodium jarosite seed, the rate of sodium jarosite precipitation is nearly independent of ferric ion concentrations > 0.03 M Fe3+ when the rate is expressed as a percentage of the initial Fe3+ concentration. A more pronounced ferric ion concentration dependence is noted in the absence of seed. Increasing Na2SO4 concentrations cause the rate of sodium jarosite precipitation, in the presence or absence of seed, to increase to similar to 0.2 M Na2SO4 but to decrease at higher Na2SO4 concentrations. This dependence seems to be related mostly to the changing sodium ion concentration, as the rate is nearly independent of ZnSO4 concentrations up to 2.0 M in the presence or absence of seed.