Phosphorus is one of four plant macro-nutrients, along with nitrogen, potassium, and calcium. Because phosphorus plays a key role in photosynthesis, nutrient transport, and energy transfer, it is a very important ingredient in plant fertilizer. According to the web site, Agriculture Solutions, a plant with the proper amount of phosphorus will grow more vigorously and mature earlier than a plant with inadequate phosphorus. A plant with a phosphorus deficiency will exhibit stunted growth, lack of fruit or flowers, wilting, and leaves that may have a purple cast due to disruption of the photosynthetic process.
There is a large variety of minerals which influence the content and availability of phosphorus in phosphate rocks. One standard technique to distinguish between the different mineral phases in the raw material is X-ray diffraction (XRD). With this method it is possible to quantify the content of different minerals according to their crystallographic structure.
A study was conducted to demonstrate the use of an X-ray diffractometer to evaluate the quality of phosphate rocks using Rietveld’s method both in the field and in production plants. A ball milled phosphate rock sample (3 min, 20 Hz) was measured in reflection mode. The samples were analyzed under Cu Kα (1.541874 Å) radiation for 10 minutes with the sample rotating during the analysis. MATCH! combined with COD database was used for qualitative phase analysis, while MAUD was used for quantification. A Rietveld refinement yielded the phase composition of the sample. It contained 4% of calcite, 17% of quartz and 79% of fluoroapatite which corresponds to a quite high phosphorous content (P2O5 ~ 26 %).
For more information about the experiment and the XRD instrument used for the study, read the application note, Quantitative phase analysis of a phosphate rock sample for fertilizer production using ARL EQUINOX 100 X-ray diffractometer.
Phosphorus is also used to make calcium phosphate nutritional supplements for animals, and chemicals for use in industry. Most phosphorus is mined from phosphate rock using large-scale surface methods. According to the Minerals Education Coalition web site, extraction operations often supply feed to a nearby fertilizer-processing complex for the production of downstream concentrated fertilizer products. Opencast dragline or open-pit shovel/excavator mining methods are the most frequently used phosphate rock extraction and production techniques.
The USGS 2018 Mineral Commodity Summary for Phosphate Rock states that more than 95% of the phosphate rock mined in the United States was used to manufacture wet-process phosphoric acid and superphosphoric acid, which were used as intermediate feedstocks in the manufacture of granular and liquid ammonium phosphate fertilizers and animal feed supplements. Approximately 50% of the wet-process phosphoric acid produced was exported in the form of upgraded granular diammonium (DAP) and monoammonium phosphate (MAP) fertilizer, and merchant-grade phosphoric acid. The balance of the phosphate rock mined was for the manufacture of elemental phosphorus, which was used to produce phosphorus compounds for industrial applications.
Explore more aspects of mining, exploration, processing, and analysis in the Cement, Coal, and Minerals Learning Center.