The most common group of phosphorus-containing minerals is apatite. Apatite minerals are calcium phosphate compounds (5 calcium ions bonded to three phosphate ions) bonded to one of the F−, Cl− or OH− ions, commonly known as fluorapatite, chlorapatite and hydroxyapatite. Among these, fluorapatite (Ca5(PO4)3F) constitutes the largest amount of deposits of currently mined phosphate rocks. Phosphate rocks may contain some impurities, as well: of particular concern are cadmium and radionuclides including uranium and its decay products.
The application of phosphate-containing minerals can be categorized in two main streams: agricultural and nonagricultural. About 95% of all TP production around the world is utilized in the agricultural sector, mainly as fertilizers. Phosphorus and nitrogen are the two most important elements used in the inorganic fertilizers industry. In addition to fertilizers, P-containing minerals are also used in animal feed additives production.
In the nonagricultural sector, phosphorus is used in wide range of applications, from the food sector (as additives, i.e., polyphosphates) to actual industrial use, to preparation of household products. Soft drinks ingredients, detergents and cleansers, metal surface treatment and corrosion inhibition are just some examples of the many possible applications of this element. It is, however, important to emphasize that these constitute less than 5% of TP consumption in the world.
2.1. Current Phosphorus Production, Consumption and Resources
Phosphate rock as taken out of the ground, if it contains enough P to be considered as a usable source, is called ore. Ore is subjected to initial processing called beneficiation, which increases its purity: in a sedimentary phosphate ore, for example, beneficiation will remove much of the associated sand and clay. The resulting product is called phosphate rock (PR).
Traditionally, chemists used a weighting method for the determination of phosphorus content in fertilizers, in terms of P2O5. Nowadays, P content is still conventionally expressed in P2O5 equivalent: phosphate rock typically contains 30–32% P2O5 and, since P2O5 itself consists of 43.6% P, this range corresponds nominally to 13–14% P, by weight.
According to the International Fertilizer Association (IFA) [8
] data, world total PR production in 2014 was around 197 Mt PR. Assuming a nominal 30% P2
content, this would correspond to about 26 Mt P, with the biggest share produced in East Asia (42%, mainly in China), followed by North Africa (Morocco) and North America (US), with 21% and 14% respectively. Figure 2
illustrates regional shares of PR production in 2014. In the late 1980s, a peak in PR mining was observed, due to an excessive fertilizers’ use in the Soviet Union during those years, which was then followed by a considerable use decrease in the early 1990s (Figure 3
). The latter occurred due to reduction of inorganic fertilizer use by developed countries, due to new awareness of phosphorus harmful effects on the environment, and especially to reduced fertilizers demand following the dissolution of the Soviet Bloc [9
]. In the last decade, however, increased per-capita demand by developing countries due to dietary changes brought by increased generalized wealth, coupled with steady global population increase, has resulted in unprecedented levels of fertilizers production and consumption.
World total phosphate rock reserves in 2014 (Table 1
) were reported as 68,776 Mt (about 9000 Mt as P), of which 73% (50,000 Mt) just in Morocco and Western Sahara [11
]. China currently holds the second biggest global reserves at 3700 Mt PR, which however represent only 5.4% of the world total. Figure 4
shows the geographical distribution of phosphate rock reserves [11
]. Although total global phosphate resources are estimated at more than 300 billion tonnes, a great part of these are not available for extraction under current economic and technological conditions. For instance, deposits comparable to present Moroccan reserves have been detected in the continental shelves of the Atlantic and Pacific Oceans [12
]; however, at the moment there is no economically profitable method for ocean mining, and the exploitation of these deposits remains prohibitive for reasonable consideration.
North Africa, based on high production from its huge amount of reserves, has the highest export of phosphate worldwide, representing nearly 53% of all imports by other regions [8
]. North America, in spite of a high production rate and a still considerable amount of reserves, is highly dependent on imports, due to the declining internal availability of PR and the Country’s high consumption rate. Also, East Asian Countries, despite substantial amounts of PR production, have high consumption rates due to high population, which leads the region to import. Worldwide, however, Europe is the region most dependent on imports, which represent 86% of its total demand [8
] since local production is very low. The uneven global distribution of reserves, production control and population growth could therefore potentially induce critical and unprecedented international tensions, when the perception of the “announced” P crisis will hit the public.
2.2. Future Trends
Phosphate rock is a finite, irreplaceable, nonrenewable resource [13
]. The future trend of PR production and consumption and, consequently, the question of whether (and when) it will be totally depleted in the future, is currently one of the most controversial issues among researchers. As global population is expected to grow drastically, demand for phosphorus will increase due to the unavoidable need to produce more food. Nevertheless, there is still a huge amount of phosphate resources unexploited because of the lack of feasible and not over-expensive methods to extract them. Generally, there are two main views which address the issue of phosphorus scarcity [14
The first view claims that the rate of consumption will eventually regulate the rate of reserve depletion, leading to a fairly static reserve situation. Forecasting approaches based on this assumption are the “ratio of reserves to consumption” (R/C ratio) to estimate the “lifetime” of available reserves. This of course assumes that both numerator and denominator are static, both of which are highly unlikely assumptions. Nevertheless, applying the R/C ratio could be useful as a general indication of when concern about resources could be warranted.
Before 2010 the R/C ratio for global phosphorus was estimated at just over a century [15
]. However, in that year the International Fertilizer Development Center (IFDC) published revised estimates that were much larger than the previous [16
]. According to some researchers, this “expansion” of reserve estimates does not have a strongly proven basis [17
], nevertheless it has been accepted by most global institutions concerned. Accounting for the new estimates, the R/C ratio stands now at almost 300 years, a slightly reassuring figure. It might however be considered that any foreseen timeline for depletion, short of a very, very long time should be worrisome, and suggests that, at the very least, present wasteful use should be controlled, and actions for recovery researched and implemented.
Interestingly, the expanded estimate of global PR reserves is based largely on a paper published by the Morocco Phosphate Company, (OCP SA) [18
]. It is, however, also interesting to note that, in 2006, the president and CEO of the same company stated: “With the anticipated requirements for phosphate for agricultural and industrial uses, the world is likely to run out in the near future of low-cost recoverable phosphate rock
Another forecasting approach, with underlying assumptions similar to the former, consists of the application of the Hubbert Curve [13
]. This is based on the assumption that PR production will follow a Gaussian distribution, peaking when half of the reserves are consumed. This point is called “peak phosphorus”. Cordell et al. [20
] predicted that peak phosphorus would occur around year 2035. When the revised reserve numbers were included, the peak was extended only to around 2070. The peak phosphorus concept has been criticized from several points of view. Mew [21
], pointed out that the Hubbert Curve is intended to be applied to resources, such as oil, for which there are other feasible alternatives. Thus, the method may be considered to be useful for modeling production from an individual source (such as one country), for which other countries may serve as alternative sources. Its application to global production, whether for phosphorus or oil, has never been scientifically validated. Vaccari and Strigul [22
] show that the Hubbert curve worked when applied to USA PR production, but that the peak could not have been accurately “predicted” until after it had occurred! As Mew points out, these criticisms do not contradict the need to start a global discussion on how humanity could “use the finite resources of phosphate that exist, in the most efficient way possible
.” On the other side, the second approach criticizes the first one in some aspects. Primarily, it points out that this only considers PR proven reserves, and not other possible resources in estimating available phosphorus. Scholz and Wellmer [23
] point out that resources that are unexploitable under current economic and technological conditions may become available in the future. While this cannot be denied a priori
, it could also be said that, dealing with an irreplaceable and essential resource, it would be at least prudent to act on the basis of current conditions and available knowledge.
Both sides of the debate, however, recognize that phosphorus scarcity is not only dependent on just the rate of resources depletion. Other factors such as potential geopolitical instability of supplier countries, market price, time and effort it takes to extract phosphate rock, all of which lead PR to have highly variable value in the global society, are of great importance.
The historical trends of PR production should become clearer examining global production trends (Figure 3
), from which the per capita production illustrated in Figure 5
can be derived. Some of the interesting historical events that become evident from Figure 5
There was a large per-capita PR increase after World War II through the 1970s, which could be attributed to the “green revolution” of the time;
These high levels stabilized from 1975 to 1991 at an average of 30.1 kg PR per capita, per year;
This was followed by a 24% reduction for reasons described in Section 2.1
, to about 22.8 kg PR/cap/yr from 1993 to 2006;
In the last decade, the per capita consumption recovered to about 31.0 kg PR/cap/yr. This may be due to improved diet in historically undernourished regions, and due to an increased amount of meat in the diet of nations such as China that have experienced rapid economic development.
The world’s population has been increasing approximately according to a linear trend for the last 50 years, adding between 70 and 87 million people per year onto the globe. Since 1997, the rate has been more stable, between 77 and 81 million people per year. Nevertheless, the UN estimates the annual population growth rate to decline steadily from this point forward. If the current level of per capita PR production rate is applied to the median UN population projection, the current reserves would last until the year 2315. However, if population growth rate continues to stay similar to the current rate (as forecasted in the UN “high” population estimate), they would only last until 2170.
There are reasons to be concerned about the short-term vulnerability of phosphorus supply, as well. Some of the major producers have an R/C ratio of only a few decades (Table 1
). Specifically, two of the top three producers, China and the US, have an R/C ratio of less than 30 years. Thus, both can be expected to be running low of P in a similar time frame, when they will have to compete with each other for other sources, which are likely to include Morocco. Several investigators have looked at this situation on a country-by-country basis. Walan et al. [24
] predicts that “exports will depend heavily on Morocco in the future.” Cooper et al. [25
] predicted that “70% of global production is currently produced from reserves which will be depleted within 100 years
,” and that “Morocco, with nearly 77% of global reserves, will need to increase production by 700% by 2075 in order to meet most of this deficit
.” The situation looks dangerously similar to that in which the world found itself at the inception of the first oil crisis, with the difference that also China is now a major economic and military powerhouse.
The data indicate that a crisis in phosphorus resources is not yet imminent. Nevertheless, P scarcity, whether it occurs decades or in centuries from now, would be catastrophic for humanity. Although all future scenarios involve substantial assumptions, these could go either way: the catastrophe could be forestalled, or the situation could become even worse. This risk suggests that society should begin now to modify current wasteful practices concerning management of P resources, especially given that many of these practices result in environmental problems that affect us still today.