Traditionally the sulphate concentration in Cements is analyzed with wet chemical methods requiring long analysis time while the XRF technique with proper calibration is an available rapid reliable technique. However especially for blast furnace slag cements the XRF technique would analyse the total sulphur as sulphates, which actually would not be the case as part of the XRF determined sulphur would be sulphide sulphur from the slag.
The ratio of the two sulphur species would be important to know for optimizing the gypsum (acid soluble sulphates) in Portland Slag Cements. Hydration of Cements are a function of optimum levels of acid soluble sulphates and so for slag Cements and fly ash slag composite cements , the routine XRF analysis of sulphates (gypsum) would require a correction factor for the sulphide sulphur in slag component of the such Cements.
This paper discusses an innovative method developed on XRF to analyse & monitor sulphates (acid soluble sulphates) and sulphide sulphur. The principle used for the method based on the property of the different sulphur species to cause a peak shift, which can be used to separate both sulphur compounds, sulphate (SO42-) and sulphide (S2-) and determine their concentrations independently. Literature describes three methods for estimation sulphates and sulphides which are Satellite method, Overlap method and Ratio method. The present method is derived from combination of satellite and ratio method named as “ACC-Sulphide method”. This has enabled to analyse, monitor and control sulphur contributed from slag effectively for cement manufacturing works. This is possible by using both models of XRF (WD – XRF and ED-XRF)
The method primarily described in literature is for WDXRF however, “The method” was exercised at author’s laboratory and at various manufacturing units using WDX and EDX models of XRF, for successful estimation of sulphates and sulphides in Slag and Slag cements. The validation of method was done against BIS method of sulphate and sulphide estimation by wet chemical as per IS: 4032.