Fertilizers are usually composed of phosphates and nitrates. The phosphorous, in general, originates from the phosphate rock. There is a wide variety of minerals which have an impact on the content and availability of phosphorous in phosphate rocks. X-ray diffraction (XRD) is a standard technique used to differentiate between the diverse mineral phases in the raw material. Using this method, the content of different minerals can be quantified according to their crystallographic structure.
Instrument
The Thermo Scientific™ ARL™ EQUINOX 100, which uses a custom-designed Cu (50 W) or Co (15 W) micro-focus tube with mirror optics, is completely portable and does not require an external water chiller due to low wattage consumption. Transportation of the unit between laboratories can be done without the need for special infrastructure.
Thanks to its unique curved position sensitive detector (CPS) that measures all diffraction peaks simultaneously and in real time, the ARL EQUINOX 100 can provide very fast data collection times when compared to other diffractometers, and is therefore ideally suited for both transmission and reflection measurements (Figure 1).
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Figure 1. ARL EQUINOX 100 X-ray diffractometer.
Experimental
A ball milled phosphate rock sample (3 minutes, 20 Hz) was measured in reflection mode. The sample analysis was carried out under Cu Kα (1.541874 Å) radiation for 10 minutes with the sample rotating during the analysis. Qualitative phase analysis was performed using a combination of MATCH! and COD database, while quantification using MAUD.
Results
A Rietveld refinement yielded the sample’s phase composition. It consists of 79% of fluoroapatite, 17% of quartz, and 4% of calcite (Figure 2) which corresponds to a very high phosphorous content (P2O5 ~ 26%).
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Figure 2. Rietveld fit of a phosphate rock sample.
Conclusion
Due to its ease and robustness, the ARL EQUINOX 100 is a suitable instrument to assess the quality of phosphate rocks using Rietveld’s method both in production plants and in the field. MATCH! and MAUD cover all requirements for quantification of phosphate related minerals.
This information has been sourced, reviewed and adapted from materials provided by Thermo Fisher Scientific - Elemental Analyzers.
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