The Versatile Apatite Mineral Group
05.20.2014 Apatite refers to a group of phosphate minerals which includes fluorapatite, chlorapatite, hydroxylapatite, carbonate-rich apatite, and francolite, the most common of which is fluorapatite. The word apatite is derived from the Greek word for deceit, “apate” because apatite can be mistaken for many other minerals. It is usually green, but can also be blue, yellow, purple, or brown. Apatite is the main source of phosphorous, an important nutrient required by plants. As such, apatite is the key ingredient in phosphate fertilizers. Most of the phosphorus used in fertilizer comes from phosphate rock, which is mined almost exclusively for this application. According to the U.S. Geological Survey Mineral Commodity Summaries, February 2014, more than 95% of the phosphate rock mined in the U.S. is used as intermediate feedstocks in the manufacture of granular and liquid ammonium phosphate fertilizers and animal feed supplements. An article on Columbia University’s Earth Institute website explains that worldwide supply of high-grade phosphate ore is diminishing due to an increasing population that is consuming more meat and dairy products, while the costs to mine, process, store, and transport phosphate is rising. While most experts believe we’ll never run out of phosphate rock, possible solutions to making phosphorus resources more sustainable are being evaluated. Apatite is also a biological mineral with important applications in the chemical and pharmaceutical industries. For example, a special form of apatite found in bone may find use for bone grafting materials and other orthopedic or dental applications. Apatite has a high fluoride content and is a source of fluoride additives used in the United States. In the geological world, apatite is used for fission track dating, a technique that determines the age of a mineral sample by its uranium content. Apatite contains many minor and trace elements and can be used as an ore for rare earth elements. The largest apatite deposits are found in sedimentary rocks, but apatite also occurs in igneous and metamorphic rock. In sedimentary beds of phosphate rock, apatite occurs as a white or brownish earthy mass which must be detected by chemical tests. Because there is such a large range in composition of the various apatites, eight elements must be monitored (P, Al, Si, Na, K, Ca, Fe and Ti) for routine process control. The analysis must not only be highly accurate but very fast as well. These requirements make the analysis ideal for wavelength dispersive X-ray fluorescence (WDXRF). WDXRF analysis is a stable fast analytical technique which requires very little sample preparation. Elemental analysis techniques such as ICP or AA require the samples to be digested and diluted into an aqueous solution for analysis. In contrary, samples in WDXRF simply can be analyzed as loose powder, pressed pellet, lithium borate fusion or even in a liquid solution. See study results of a WDXRF instrument used to analyze apatite samples, including typical calibration ranges and results for each of the eight elements.
Leave a Reply