Comparative Rates of Precipitation of Ammonium Jarosite and Sodium Jarosite in Ferric Sulphate – Sulphuric Acid Media

The comparative rates of precipitation of ammonium jarosite and sodium jarosite were determined in Fe(SO4)1.5-H2SO4 media. The apparent activation energy for the precipitation of ammonium jarosite and sodium jarosite is approximately the same; in the presence of 25 g/L of potassium jarosite seed having a surface area of 0.42 m2/g, the value is 87 kJ/mol. Over the temperature range from 70 to 100°C, the rate of ammonium jarosite precipitation is 9 greater (no seed) and 18 greater (25 g/L seed) than the rate of sodium jarosite precipitation. For (NH4)2SO4 or Na2SO4 concentrations ranging from 0.0125 to 0.7 M, the average rate of ammonium jarosite precipitation in the presence of 25 g/L of jarosite seed is 14 higher than that of sodium jarosite precipitation; in the absence of jarosite seed, the average rate of ammonium jarosite precipitation is 11 greater. For ZnSO4 concentrations ranging from 0.0 to 2.0 M, the average rate of ammonium jarosite precipitation in the presence of 25 g/L of potassium jarosite seed is 16 greater than that of sodium jarosite. For solutions containing 1.5 M ZnSO4 and 25 g/L of potassium jarosite seed, the average rate of ammonium jarosite precipitation is 19 greater than that of sodium jarosite precipitation. The rate of precipitation of both ammonium jarosite and sodium jarosite increases as the concentration of potassium jarosite seed increases from 0 to 50 g/L. At 100°C for solutions containing 1.50 M ZnSO4, the average rate of ammonium jarosite precipitation is 20 greater than that of sodium jarosite precipitation. The totality of the present data indicates that the rate of ammonium jarosite precipitation is about 15 greater than that of sodium jarosite precipitation.