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Online Analysis of Phosphate Rock Slurry by Prompt Neutron Activation Technique


Project Summary

With the depletion of high grade phosphate deposits in Florida, it is necessary to develop new beneficiation processes or modify the current circuits for phosphate flotation. Greater process control over various streams seems to be inevitable in order to improve the processing efficiency. The on-line analysis of phosphate rock slurry for incorporating such process control is therefore required.

NMR and colorimetry methods have been evaluated for on-line analysis of phosphate rock slurries. These techniques yield information about P2O5 content, solids loading and acid insolubles, however a sampling system is involved in both of the techniques. Prompt neutron activation technique on the other hand, does not require sampling and is expected to yield more analytical information as compared to NMR and colorimetry methods.

In the present investigation, the analysis of phosphate rock slurry by prompt neutron activation technique has been studied. It was determined that Si, Ca and H can be analyzed using 252Cf neutron source. The technique was found to be insensitive to solids loading of the slurry, particle size distribution and the presence of flotation reagents in the system. The P2O5 content was calculated from the analysis of Ca due to the fact that most of the phosphate was present as fluorapatite (Ca5F(PO4)3) and dolomitic impurity was very low in all the samples tested. The accuracy of direct phosphorus analysis using 241Am/Be source was poor and magnesium failed to be detected in the present study, both due to interference from rare earth elements, particularly Gadolinium (Gd) associated with the Florida phosphate samples. Iron could be analyzed in the absence of steel background.

The standard deviation of P2O5 analysis by the probe was 0.48% and 0.80% for SiO2, which was directly proportional to 1/SQRT(T), T is the data acquisition time. The probe was found to be reliable also under industrial conditions.

The probe evaluated in this study was originally designed for borehole logging and not for phosphate rock slurry analysis. Hence, the performance of the probe can be improved considerably by using a stronger neutron source and a high resolution detector (e.g. Ge detector).