Precipitation of Fe_4(SO_4)(OH)_(10) and Hydronium Jarosite, (H_3O)Fe_3(SO_4)_2(OH)_6, in Ferric Sulphate-Sulphuric Acid Media

摘要

The factors affecting the precipitation of Fe_4(SO_4)(OH)_(10) and hydronium jarosite, (H_3O)Fe_3(SO_4)_2(OH)_6, in ferric sulphate-sulphuric acid media were systematically determined. Fe_4(SO_4)(OH)_(10) is readily precipitated at temperatures between 70 and 110 °C, but control of the Fe(SO_4)_(15) concentration in the 0.15 to 0.21 M range is required to yield single phase products. The precipitates made at pH values between 1.0 and 1.8 consist essentially of Fe_4(SO_4) (OH)_(10), but higher pH values cause the progressive precipitation of goethite. Concentrations of MgSO_4 or ZnSO_4 in the 0.0 to 0.4 M range have little effect on the precipitation of Fe_4(SO_4)(OH)_(10), but higher concentrations result in progressive goethite contamination. Fe_4(SO_4)(OH)_(10) seed additions >1 g/L significantly promote the rate of Fe_4(SO_4) (OH)_(10) precipitation. Hydronium jarosite precipitation increases with increasing retention time at temperature, and nearly complete reaction occurs within a few hours at 140 °C. Increasing hydronium jarosite seed additions accelerate the precipitation of hydronium jarosite and the effect is most evident for seed additions greater than 10 g/L. Only hydronium jarosite is precipitated at temperatures <180 °C and at pH values <1.9. Higher temperatures or pH values result in the co-precipitation of Fe(SO_4)(OH), Fe_2O_3 or goethite. Ferric sulphate concentrations in the 0.4 to 2.0 M Fe(SO_4)_(15) range and MgSO_4 or ZnSO_4 concentrations in the 0.0 to 0.8 M range yield single phase hydronium jarosite precipitates. However, higher concentrations of these salts result in the co-precipitation Fe_4(SO_4)(OH)_(10) and/or Fe_2O_3. Increasing Na_2SO_4 concentrations result in the preferential incorporation of Na relative to H_3O in the jarosite precipitates, but a nearly ideal solid solution series is formed.