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Rapid determination of the SO_3 content in phosphogypsum samples by microwave digestion and flowinjection turbidimetry

The effects of digestion pressure,acid concentration and digestion time rock on dissolution rates of calcium sulfate were studied to obtain the optimal digestion conditions with phosphogypsum and phosphogypsum decomposition product( containing calcium sulfate and calcium sulfide) as raw materials. The results showed that the dissolution rate of calcium sulfate was 98. 3% under the conditions of digestion pressure of 0. 4 MPa,the amount of hydrochloric acid was 20 m L with content of 2 mol / L,and digestion time was 60 s. Under the optimal conditions,the SO_3 content of phosphogypsum and phosphogypsum decomposition products were obtained,and the results showed that the relative standard deviation of phosphogypsum samples results dissolved by hybrid microwave was less than 4% comparing with traditional digestion method,and standard addition recovery rate of the method was 101%. Based on above results,the SO_3 content of phosphogypsum in solid samples were measured by microwave digestion combined with flow-injection turbidimetry. The results showed that microwave digestion combined with flow-injection turbidimetry could achieve determination of the SO_3 content of phosphogypsum decomposition product rapidly,and the relative standard deviation was less than 5% comparing with the results determined by standard gravimetric method.