Celestite, the most common strontium mineral, consists primarily of strontium sulfate. The second most common strontium mineral, strontianite, consists primarily of strontium carbonate. Reportedly, it is very difficult to concentrate strontium minerals to grades acceptable for producing chemical compounds. The two most common celestite-to-strontium carbonate conversion processes are the soda ash process and the calcining proc ess. Strontium metal is prod uced by the the rmal reduction of stron tium oxide with meta llic aluminum and the electrolysis of fused strontium chloride and ammonium or potassium chloride. Of the two strontium production processes, the soda ash method is a simpler process; however, the resulting product is of a lower gra de. The calcin ing method or black a sh method, produc es chemical-gra de strontium carb onate (SrCO3 ) which is at least 98% strontium carbonate; whereas, the soda ash method only produces technical-grade strontium carbonate >95% pure . Although the soda a sh method is a simple r process, the lower grade product c auses it to be the less preferred method of recovery. The black ash method is used by CPC.
The direct conversion of celestine (SrSO4 ) to strontium carbonate as well as its enrichment by hydrometallurgy were investigated. Hengyang was also conducted to investigate whether acid concentration affected the quality of strontium sulfate in celestine concentrates. Based on the results of a laboratory assay, it was determined that 98.04% SrSO4 was leached optimally under agitation. The ground sample of celestine concentrate was then leached by agitation for three hours after the dimensional analysis had determined the appropriate grinding time. To determine the optimal approach for the agitated leaching of strontium carbonate, different approaches were tested. Various factors, including temperature, return water, solid percentage, and sodium carbonate to strontium sulfate ratio, were studied. At 90°C, celestine completely converts into strontium carbonate with a solid percentage of 20% and a sodium carbonate to strontium sulfate ratio of 4:5. As part of the investigation into the possibility of producing strontium oxide, samples of celestine concentrate and strontium carbonate produced under optimal conditions were heated at 500 and 1000°C to determine which phase would form the oxidized phase. An X-ray analysis indicates that the oxidation phase forms at a temperature of more than 750°C.
