Preparation of microsized hematite powder from ferrous sulfate via microwave calcination

The preparation of microsized hematite powder from ferrous sulfate using microwave calcination was investigated based on the TG/DTG curves. The decomposition of industrial ferrous sulfate under air atmosphere was divided into three stages, and a ferrous sulfate sample added with 15% Fe_2O_3 could strongly absorb microwave energy. Therefore, preparing hematite powder from ferrous sulfate using microwave calcination was feasible. Hematite was obtained under the following optimized conditions: calcination temperature, 850 °C; microwave power, 650 W; and sample amount, 40 g. The obtained hematite satisfied the first-grade quality requirements. The total ferrum value was more than 58%, and the total sulfur and phosphorus contents were less than 0.5% and 0.2%, respectively. X-ray powder diffraction and scanning electron microscopy were used to characterize the structure and morphology of microsized hematite powder. The particles were non-spherical in shape, and the average particle size distribution was 10.45 μm. This work provides new potential applications for waste ferrous sulfate.

Decomposition of the mixed rare earth concentrate by microwave-assisted method

A novel process was proposed to strengthen the decomposition of the mixed rare earth concentrate by utilizing the microwave radiation.Mineralogical information on the mechanisms by which microwave heating improved the leaching behavior of rare earth elements（REEs）,and an interpretation of the interrelationship between mineralogy,decomposition process,and leaching process were provided in this study.The influences of the temperature,time of microwave heating and contents of NaO H（mass ratio of NaO H to mixed rare earth concentrate）on the decomposition of mixed rare earth concentrate were investigated.The results revealed that the temperature was the main factor affecting the decomposition process.The recovery of REEs by hydrochloric acid leaching reached 93.28% under the microwave heating conditions：140 oC,30 min and 35.35% NaO H.The BET specific surface area and SEM analysis indicated that the particles of mixed rare earth concentrate were non-hole,while the particles presented a porous structure after heating the concentrate by microwave radiation.For the microwave treated sample after water leaching,the BET specific surface area was 11.04 m^2/g,which was higher than the corresponding values（6.94 m^2/g）for the mixed rare earth concentrate.This result could be attributed to the phase changes of bastnaesite and monazite,and a number of cracks induced by thermal stress.The increase of BET specific surface area resulted in an increase of the recovery of REEs by promoting interaction within the system of acid leaching.