Abstract: Sulfate radical is contained in calcium slag,which is an important index influencing the quality of precipitated calcium carbonate (PCC) and it will increase the load to the impurity removing process during manufacturing PCC.Barium chromate spectrophotometry was adopted to determine sulfate radicals in calcium slag of phosphogypsum and a simple and rapid determination method with good selectivity has been established.At wavelenth of  410 nm,when the mass concentration of sulfate radicals is at  0.00~6.00 mg/mL and it has a linear relation with chromate radicals.Linear recession equation and the correlation coefficient are y=0.168 4x+0.003 2 and r=0.999 9 respectively.Relative standard deviation is less than 10%,and the standard sample recovery rates are at 96%~102%.This method is applied to the determination of sulfate radicals in calcium slag and has advantages of simplicity and strong feasibility, which can satisfy the determination requirements and can be used for real time monitor.

Key words: phosphogypsum, sulfate radical, barium chromate spectrophotometry