The effect of jarosite seed additio

The effect of jarosite seed additions on the rate of precipitation of ammonium jarosite and sodium jarosite was investigated over a wide range of conditions of relevance to the zinc industry. Jarosite seed additions significantly increase the rate of jarosite precipita- tion under all conditions, and the initial rate of precipitation seems to increase linearly with increasing concentrations of jarosite seed. The presence of jarosite seed also suppresses the induction period, which is commonly evident in the experiments done in the absence of seed. A minimum degree of slurry agitation is necessary to suspend the seed completely, but higher agitation rates are without additional benefit. The morphol- ogy of the jarosite precipitates is generally similar in both the presence and absence of seed; all the precipitates examined in this study consist of ‘cauliflower-like’ spheroidal masses composed of crudely formed crystals of ammonium jarosite or sodium jarosite. Increasing solution pH significantly increases both the rate and extent of jarosite precipitation. Consistently faster rates are observed in the presence of jarosite seed; a further advantage of seeding is that the pH range for jarosite precipitation is extended to lower pH values. Increasing temperatures also increase both the rate and extent of jarosite precipitation. Significantly higher rates are observed in the presence of 50 g/l of jarosite seed, and the addition of the seed extends the temperature range for jarosite precipitation to lower values. The apparent activation energy for the precipitation of sodium jarosite in the presence of sodium jarosite seed is 106 kJ/mol; the correspond- ing value in the absence of seed is - 100 kJ/mol.