Phosphate with High Dolomite Content

Among the deleterious materials (Fc203, AI2O3, CaO, MgO) in phosphate rock, dolomite is the most troublesome. Dolomite causes higher consumption of sulfuric acids, reduces filtration capacity, and lowers the P2O5 recovery in fertilizer manufacturing. Therefore the MgO content is a very important index in evaluating the quality of the phosphate concentrate, hi Florida, the MgO in the final phosphate concentrate is usually required to be less than 1%. 

At present, gravitation separation and photometric sorting are mainly used for the treatment of phosphates with high dolomite concentration (Salter and Wyatt 1991). However, their effectiveness in many cases is Umited due to minimal density and reflectance differences between dolomite containing lumps 

X-ray excited steady-state luminescence has been checked as a distinctive feature for the phosphorites, Karatau (Gorobets et al. 1997a). Sedimentary apatite (francolite) is not luminescent under X-ray excitation and red Mn luminescence of dolomite was employed. As a result, concentration of MgO in the accepted fraction was lowered from 5.0% to 2.4%. The use of this method is limited because in many cases the X-ray luminescence of dolomite is very low or non-existent. Besides that, other minerals without luminescence come together with the accepted phosphate fraction, including sihceous shale, which is harmful for the following deep beneficiation. Thus new methods have to be developed for detection and content evaluation of dolomite in Florida phosphates on moving belt conveyors. 

Our study of sedimentary apatite from Israel proved that laser-induced time-resolved luminescence is a perspective tool for evaluation of sedimentary phosphate ores with high dolomite content (Gaft et al. 1993b). The idea was based on the fact that natural apatite contains several characteristic luminescence centers, which enables us to differentiate it from dolomite. The most widespread characteristic luminescence center in sedimentary apatite is uranyl (U02) with a typical vibrational green band luminescence under nitrogen laser excitation (Fig. 8.13a,b). Nevertheless, it appears that such luminescence is absent in phosphate rock samples from Florida, evidently because of extremely low uranium concentration (Fig. 8.13c,d). hi order to find potential liuninescence centers, ICP-MS analyses of Florida phosphates was accompHshed. From discovered REE, theoretically Dy + is the best candidate 

This metho dology was previously successfully used for express on-line analyses of phosphate ores. The commercial TRACER 2100 Laser Element Analyzer, a laser-induced breakdown spectroscopy instrument, was utilized for rapid analyses of phosphate ores at the mine site (Rosenwasser et al. 2001). Excellent calibrations were achieved for P and Mg with correlation coefficients significantly above 0.98. The instrument demonstrated strong potential of the LIBS for use in on-site, real-time or grading. LIBS apparatus was developed for ap- 

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Gaft M, Nagli L, Panczer G, Reisfeld R (2002) Laser-induced luminescence and breakdown spectroscopies evaluations of phosphates with high dolomite content. In Zhang P, El-Shall H, Somasundran P, Stana R (eds) Beneficiation of phosphates, fundamentals and technology. SME, Littleton, pp 145-152... 

Our study of sedimentary apatite from Israel proved that laser-induced time-resolved luminescence is a perspective tool for evaluation of sedimentary phosphate ores with high dolomite content (Gaft et al. 1993b). The idea was based on the fact that natural apatite contains several characteristic luminescence centers, which... 

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