The most obvious cause for physical scarcity of a non-renewable resource such as phosphate rock is complete depletion, when all of the resource has been extracted from the ground. The size of the resource also affects other potential drivers of scarcity, such as peak production. This section intends to establish how much phosphate rock is available for extraction today, or could become available in the future.
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Although finite, phosphorus is not a rare element. In fact, phosphorus is the eleventh most abundant element in the earth’s crust (Johnston and Steen, 2000), which contains more than a billion billion tonnes of phosphorus at a concentration of around 0.1% phosphorus (Emsley, 2001, Brinck, 1977). Under certain conditions, which involves both chemical and physical processes that rarely occur simultaneously, and over millions of years, the concentration of P-bearing minerals increases and physical reworking of P-rich sediments concentrates the phosphorus further, forming phosphorite deposits, or phosphate rock, which is mined for fertiliser production (Filippelli, 2011). In some cases, this rock can be mined to extract the phosphorus. Phosphate rock can be either sedimentary or igneous, but around 80% of the phosphate rock produced today comes from sedimentary rocks (Van Kauwenbergh, 2010). This phosphate rock ore typically contains 5 – 13% phosphorus (Cordell and White, 2011).
The mined phosphate rock ore usually undergoes a beneficiation process involving a combination of washing and screening processes to remove impurities and lower grade ores, and produce phosphate rock concentrate, which has an increased phosphorus content and has reached a marketable standard (Van Kauwenbergh, 2010, Edixhoven et al., 2013). The phosphorus content of the beneficiated concentrate is often expressed in terms of P2O5,
which contains 44% P, and commercial phosphate rock concentrates vary in grade from over 37% P2O5 (16% P) to less than 25% P2O5 (10.9% P) (Van Kauwenbergh, 2010). On average,
the phosphate rock produced in 2012 contained 30.6% P2O5, or 13.4% phosphorus (IFA,
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The mining and beneficiation process generates large quantities of unrecovered spoil, which contains around 20-30% of the mined phosphorus (Dawson and Hilton, 2011). However, as extraction technology improves, these large deposits of previously worthless rock may be transformed into valuable ore, as was the case with copper mining (West, 2011). Confusingly, both ores and concentrates are often referred to as simply ‘phosphate rock’, which can lead to errors being made.
Phosphate rock deposits are classified based on the economic viability of extraction, which depends on accessibility and quality of the mined rock, the extraction and processing costs, and the market price. The three broad classifications commonly used are reserves, base reserves, and resources, although for each of these there are often various subcategories such as measured, indicated, inferred and hypothetical. As shown below, the definitions of even these three broad terms are often unclear and inconsistent (Edixhoven et al., 2013). Reserves are defined by the United States Geological Survey (USGS) as “the part of the
identified resource which could be economically extracted or produced at the time of determination” (USGS, 2011). However, the economic assumptions that are used to define reserves, such as the $/tonne, are unclear and inconsistent between countries and companies (Cordell and White, 2011). The USGS produces a mineral commodity summaries report each year, which includes estimates of global phosphate rock reserves and annual production, and estimates for the individual countries with the largest reserves or production. The latest USGS report (January 2013) contained reserve and production estimates for 21 individual countries, and a combined estimate for all other countries. The USGS often appears to express reserves as ore (Edixhoven et al., 2013),
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while production is expressed as marketable concentrate (Jasinski, 2013). However, Moroccan reserves were increased in 2011 in line with the estimates from the IFDC, which reported reserves as concentrate, and not ore (Van Kauwenbergh, 2010). Therefore, it is assumed that USGS reserves are reported as concentrate.
Base Reserves are defined by the USGS as “the in-place, demonstrated portion of the total resource that is already economically available (reserves) or has a reasonable potential of becoming economically available within planning horizons beyond those that assume proven technology and current economics” (USGS, 2011). As with reserves, no actual price is specified. The USGS used to estimate the size of the reserve base within the mineral commodity summaries report. However, since the closure of the US Bureau of Mines (USBM) in 1996, the data upon which the latest reserve base estimates was based has not been updated and was considered too old to remain defensible, therefore reserve base estimates were discontinued in 2009 (USGS, 2010).
Resources are defined by the USGS as “a concentration of material in or on the Earth’s crust in such form and amount that economic extraction is currently or potentially feasible, which includes reserves and base reserves” (USGS, 2011). The IFDC defines resources as “phosphate rock of any grade, including reserves, that may be produced at some point in the future” (Van Kauwenbergh, 2010). However, this broad definition is criticised by Edixhoven et al. (2013) since it allows the possibility of any phosphate rock deposit being considered as a resource by not specifying a timescale or suggesting what the conditions of that future may be. The USGS quote a global phosphate rock resource
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figure within the mineral commodity summaries. However, it is not specified if this is phosphate rock concentrate or ore, so it is assumed to follow the same system used by the IFDC, being reported as ore. This can lead to confusion since reserves, which actually form part of the resource, are quoted as concentrate, while resources are quoted as ore, therefore the two are not directly comparable. Also, in general, resources have a lower phosphorus content and more impurities than reserves, which means that production of a tonne of phosphate rock from a resource would yield less elemental phosphorus compared to production of a tonne of phosphate rock from a current reserve deposit.
Reserve estimates are dynamic and can change for a number of reasons. They can increase with the discovery of new deposits and upgraded estimates of known deposits, or through a reclassification of base reserves or resources to economical reserves, which may occur as extraction and processing technology improve or the market price increases which makes previously uneconomic deposits become economically viable. Tilton (2003) suggests that when a company has more than 20 – 30 years left of reserves at current production rates then there is little incentive to invest significant sums of money in discovering additional reserves. However, as oil exploration programmes have explored most of the coastal basins around the world, it is believed that any large-scale discoveries of phosphate rock would have occurred already (UNIDO and IFDC, 1998).
Between 1996 and 2010, phosphate rock reserve estimates ranged between 11,000 and 18,000 Mt, with the 2010 estimate at 16,000 Mt. Before its discontinuation, the reserve base was estimated at 47,000 Mt (Jasinski, 2009). In January 2011 the USGS increased its reserves estimate to 65,000 Mt, more than a 4-fold increase (Jasinski, 2011), as shown in Figure 5.
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This change was largely influenced by a report produced by the International Fertilizer Development Centre (IFDC) in September 2010 which reviewed the literature surrounding phosphate rock reserves and resources and suggested that previous estimates had significantly underestimated the size of these deposits. The IFDC estimated that there remained approximately 60,000 Mt of reserves (as concentrate) and 290,000 Mt of resources (as ore in-situ) (Van Kauwenbergh, 2010). In particular, considerable revisions were made to Morocco’s estimated reserves, which were increased from the USGS 2010 estimate of 5,700 Mt to around 51,000 Mt. The increase to Morocco’s estimated reserves accounted for almost all of the increase to the global reserves estimate; in fact compared to the previous USGS estimate, the combined total of reserves held by all other countries actually decreased by around 10% in the IFDC report.
Figure 5: Historical U.S. Geological Survey phosphate rock reserve estimates. Data Source: Phosphate Rock, Mineral Commodity Summaries, USGS.
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The IFDC figures are not based on new discoveries but on data drawn from literature on global phosphate rock deposits, which has in itself become very limited since 1990 (Van Kauwenbergh, 2010). In order to estimate the size of Morocco’s phosphate rock reserves, the IFDC used reports from Gharbi (1998) and OCP (1989). Hence, the revisions are based on literature that was previously overlooked or unavailable to the USGS, and was therefore not included in its reserve estimates for Morocco. The revisions were not based on new discoveries or studies. It should be noted that within the IFDC report it cautions that it is not known if all of Morocco’s phosphate rock reserves are producible at today’s costs (Van Kauwenbergh, 2010), which raises questions as to whether some of the quoted reserves should instead be considered as base reserves or resources. This report was criticised by the Global Phosphorus Research Initiative (GPRI, 2010), and Edixhoven et al. (2013) concluded that “the IFDC report presents an inflated picture of global reserves”.
The dynamic nature of reserve estimates was demonstrated again in 2011, as 5,750 Mt of phosphate rock were found in Iraq (McPherson, 2011), and included within the USGS 2012 reserve estimates (Jasinski, 2012). This inclusion made Iraq the second largest country with phosphate rock reserves. However, these reserves were later removed in the USGS 2013 publication based on a report prepared jointly by the USGS and Iraqi Ministry of Industry and Minerals in 2012 (Jasinski, 2013), and it is likely that the reserves were downgraded to resources.
The latest USGS report (January 2013) estimates that globally there are 67,000 Mt of reserves and over 300,000 Mt over resources (Jasinski, 2013). At an average concentration of 13.4% P, this translates into around 9,000 Mt of P, or 9 x 109 tonnes of phosphorus in
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current reserves. This is much less than the 1 x 1018 tonnes of phosphorus estimated to be in the earth’s crust (Emsley, 2001). Therefore, despite being incredibly abundant, only a fraction of the total phosphorus is currently available because of the costs and energy required to recover it. This fact is recognised and well understood for water, but less so for phosphorus (Cordell & White 2011).
The size of the phosphate rock reserves has a big impact on the drivers for physical scarcity. In particular, the remaining reserves affect the timeframe until complete depletion based on constant extraction rates (Section 4.3.4) and the peak production analysis (Section 4.3.6). There is currently a lack of information on the size and quality of global phosphate rock reserves and resources which makes it difficult to determine the appropriate timeframe for increasing phosphorus security. There is also inconsistent terminology used within the reporting of reserves and resources, which further complicates the issue. The dynamic nature of reserves implies that more phosphorus will become available in the future, which suggests that scarcity is not a short-term issue, but alternatively, the current reserve figure may have been overestimated, which would result in scarcity occurring much sooner.