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 am ount of seed present. A minimum degree of agitation is necessary to su spend the seed, but higher agitation rates are without further effect. Furthermore, the presence of seed extends the range of jarosite preci pitation to lower pH values and to lower temperatures than is the situ ation in the absence of seed. The presence of seed accelerates the ini tial precipitation rate at all pH values and temperatures and generall y eliminates any induction period. The activation energy for sodium ja rosite precipitation in the presence of seed is 106 kJ/mol. In the pre sence of sodium jarosite seed, the rate of sodium jarosite precipitati on is nearly independent of ferric ion concentrations > 0.03 M Fe3+ wh en the rate is expressed as a percentage of the initial Fe3+ concentra tion. A more pronounced ferric ion concentration dependence is noted i n 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 Na2S O4 concentrations. This dependence seems to be related mostly to the c hanging sodium ion concentration, as the rate is nearly independent of ZnSO4 concentrations up to 2.0 M in the presence or absence of seed.