World reserves of phosphate rock... a dynamic and unfolding story.

Abbreviations and Notes: P = phosphorus. Practically all of today’s inorganic P fertilizers are produced from PR. Phosphate rock is an imprecise term that describes naturally occurring geologic materials (minerals) that contain a relatively high concentration of P. The term PR is used to describe raw (unbenefi ciated) phosphate ores, but may also be applied to benefi ciated or concentrated products. Phosphate rock occurs in both sedimentary and igneous deposits across the world (Figure 1). Most (80 to 90%) of PR used to produce fertilizer is sedimentary in origin, and was deposited in ancient marine continental shelf environments. Sedimentary deposits, sometimes called phosphorites, occur throughout geologic time. Most PR is mined by open pit techniques, but a signifi cant amount of deposits in China, Russia and other countries are extracted by underground mining. Apatite, a calcium phosphate mineral, is the principle P bearing component of PR. The origin of the modern P fertilizer industry can be traced back to the mid-1800s when the fi rst patents were granted for treating “phosphoritic substances” such as apatite and bones with sulfuric acid to produce “superphosphate”. In 1842 patents were granted in England to both John Bennet Lawes and James Murray for the manufacture of P fertilizer by the process of acidulation. Although others, including Justus von Liebig, had been studying the process, Lawes and Murray have been credited as “the laymen who put the idea into permanent commercial practice” (Jacob, 1964). Practically all P fertilizers today are made by this “wet process” of treating PR with acid (e.g., sulfuric, nitric, or phosphoric) to produce phosphoric acid or triple superphosphate (TSP). Phosphoric acid is then used to produce both granular and fl uid P fertilizers. Phosphorus is essential for life, and the input of P fertilizer is critical to the production of suffi cient food, feed, fi ber, and fuel to support a growing world population. Considering these facts, and that PR is a fi nite and non-renewable natural resource, it is reasonable to question just how much PR there is in the world, and how long we can continue to extract it. This is a question that has generated considerable interest, discussion, and even some controversy. Following is a compressed narrative of some relevant history and current status of world PR supply.