Phosphate Rock: An Industry in Transition

By Dilip Kumar and Deepak Kumar

Phosphate Rock: An Industry in Transition takes an interdisciplinary approach to dealing with the phosphate rock chain and its exploration, extraction, processing, fertilizer making, and storage and transportation. The book treats the subject from a global perspective, giving readers insights into what is happening in the emerging economies of the world and possible solutions to problems. It also provides all the parameters necessary to evaluate economic viability of undertaking a mining venture, taking into consideration demands of sustainable mining – social responsibly, environmental pollution control measures, community development, and precautions necessary for ensuring health and safety in the hazardous conditions of mining operations.

In recent years, supply chain management has grown in importance as it forms tighter links in integration of key business processes from initial extraction of raw phosphate rock to end customers through different stages of process techniques. The book surveys the changes in technology, including many game-changing innovations that could transform mining.

• Presents a purposive classification of resources, status of global phosphate rock reserves, and their life-indices
• Covers mining conditions and possibilities of improvement in methods of exploration and environmental impact
• Includes economic considerations for resource assessment, mining, quality control and supply problems

• Language: English
• Publisher: Elsevier Science
• Release date: Apr 13, 2023
• ISBN: 9780323959834

Dilip Kumar

Dilip Kumar has worked in many countries including Germany, Algeria, India, and Canada as Chief Engineer at Central Mine Planning and Design Institute (CMPDI), Ranchi, India. He worked in coal and mineral mining industry for 25 years. Dr. Kumar’s research interests include both coal and phosphate rock mining and processing, steel metallurgy, mineral processing, mine economics, and mine management with special reference to integration of supply chain.

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Chapter One: Introduction

Abstract

Phosphorous is an irreplaceable nutrient for all living beings on earth. Yet, this nonrenewable resource is available in limited quantities. Phosphate mineral deposits of the apatite group are the main sources of phosphate rock. Phosphorous circulates through water, earth’s crust, and living organism as part of the phosphorous cycle. Phosphate deposits are classified into igneous and sedimentary formation. It is mainly used in fertilizer industry. In addition to apatite, phosphate rock contains impurities. Raw phosphate ores are beneficiated to meet the industry requirements. There are many losses in the process of using phosphorous which requires various remedial measures to match the world’s increasing consumption intensity of phosphorous.

Keywords

Apatite; Calcareous; DAP; Insular; MAP; Metamorphic; Nexus; Phosphorite; P2O5; TSP

1.1. Phosphate rock

In 1669, the German alchemist Hennig Brandt was the first to discover phosphorous (P). The phosphorus required for industrial processes is traditionally obtained by mining phosphate rock (PR). This consists mainly of apatite: Ca5(PO4)3X, (X = OH, F, Cl). Apatite is a calcium phosphate mineral group that includes chlorapatite Ca5(PO4)3Cl, hydroxyapatite Ca5(PO4)3OH, and fluorapatite Ca5(PO4)3F. There are about 200 arrays of phosphate minerals, of which the apatite group are the minable ones. In the natural form, Ca can be replaced by Sr, Pb, Ba, Na, Cd, Mg, Mn, and Fe, while P can be substituted by PO4, Si, SO4, As, CO3, V, etc (Sudarsanan et al., 1972).

The names and compositions of selected phosphate minerals are presented in Table 1.1. Fluorapatite, also called as apatite, is largely plentiful. It exists virtually in all igneous rocks, normally containing 0.1%–1% by volume, though in some cases it may be considerably elevated. Apatite occurs in both thermally and regionally metamorphosed rocks and reflects the phosphorus composition of the original rock. In sedimentary rocks, apatite occurs as a detrital mineral and as a primary chemical precipitate. Some extensive sedimentary deposits contain up to 80% apatite and are locally interbedded with limestone. Such deposits, called phosphorites, are commonly exploited as phosphate ore. Much of the phosphate in these deposits is formed directly from P-rich aqueous solutions via diagenetic and biochemical processes in the sediments, although significant phosphorus deposits can originate from skeletons and guano. Apatite minerals also form the hard parts of many living organisms. Hydroxylapatite makes up 65%–70% of mammal bones, the remainder being mostly organic compounds (Turek & Buckwatler, 1994). The apatite crystal structure is very accommodating, allowing the incorporation of nearly half of the elements in the periodic table. Thus, apatite serves as a repository for minor and trace elements in rocks (Hughes et al., 2002).

The heavy-metal phosphate minerals—monazite, xenotime, and rhabdophane are widely distributed as microcrystals in crystalline and sedimentary rocks. Monazite occurs as an accessory mineral in granitic rocks and as large crystals in pegmatites. Because monazite and xenotime are resistant to weathering (Oelkers & Poitrasson, 2002), they can be concentrated in stream and beach sands. Together with apatite, they are a major source of rare earth elements (REEs) uranium and thorium. As such, they play a significant role in U–Th–Pb dating of rocks and minerals (Parrish, 1990). These minerals have served as thorium and uranium ores and their solubility controls to a large degree the REE signature of natural waters (Johannesson et al., 1995; Köhler et al., 2005). The low solubility and slow dissolution rates of the anhydrous heavy-metal phosphates have led many to propose their use in radioactive waste storage (Sales et al., 1983).

Table 1.1

REE, rare earth element.

Modified from Oelkers et al. (2008), Derhy et al. (2020).

There are extensive discrepancies regarding origin, structure, mineralogical composition, and quality of PR. Phosphate deposits are classified as follows:

• Sedimentary

• Igneous

• Insular

Sedimentary deposits amount to 80% of the world's phosphate production. Phosphate ores can also be classified (Abouzeid, 2008) based on their major gangue minerals such as the following:

• Siliceous ores containing quartz, chalcedony, or different forms of silica

• Clayey ores containing mainly contain clays and hydrous iron and aluminum silicates or oxides as gangue materials

• Calcareous ores of sedimentary origin containing calcite and/or dolomite as the major impurities with small amounts of silica

• Phosphate ores with rich organic matter content

• Phosphate ores having numerous gangue minerals

• Igneous and metamorphic phosphate ores including main gangue materials like sulfides, magnetite, carbonates (calcite, dolomite, siderite, and ankerite), nepheline syenite, pyroxenite, foskorite, etc.

Fig. 1.1 shows a map of the PR deposits currently in operation, those that have been exploited in the recent past, and those that have proven to be potentially economic.

Figure 1.1  World phosphate rock resources. Source: IFDC.

Sedimentary deposits (often called phosphorites) are the most important phosphorus raw material sources. Sedimentary PRs have been formed throughout the geological time scale. Most of them were apparently formed in offshore marine conditions on continental shelves. Sedimentary deposits exhibit a wide range of chemical compositions and great variations in physical form. The most desirable sedimentary PRs contain distinct phosphate particles that can be separated from the unwanted gangue minerals. They are much more widespread than the igneous ones and usually of higher content. Sedimentary deposits are defined in certain phosphate-bearing regions and countries, such as the United States of America (Florida, North Carolina, Tennessee, Idaho, Montana, Utah, Wyoming, etc.), Northern and Western African countries (Morocco, Tunisia, Algeria, Western Sahara, Togo, etc.), the Middle East (Jordan, Israel), China, Vietnam, Australia, Russia, etc.

The most important countries producing PR of igneous origin are Russia, South Africa, Zambia, Zimbabwe, Brazil, Finland, and Sweden. Igneous phosphate ores are often of low grade.

1.2. Phosphorous (P) cycle

Phosphorous, mainly in the form of phosphate ions (PO4 ³- and HPO4 ²-), is an essential nutrient of both plants and animals. Phosphorous circulates through water, earth's crust, and living organism in the phosphorous cycle. In this cycle, phosphorous moves slowly from phosphate deposits on land and in shallow ocean sediments to living organisms, and then back to the land and ocean. Bacteria are less important here than in the nitrogen cycle. Unlike carbon and nitrogen, phosphorous does not circulate in the atmosphere because at earth's ambient temperature and pressure, phosphorous and its compounds do not exist in the gaseous state.

Phosphorous released by the slow breakdown, or weathering, of PR deposits is dissolved in the soil water and then taken up by plant roots. Wind can also carry the phosphate particles to long distances. Most soils contain little phosphorous because phosphate compounds are only slightly soluble in water and found in few kinds of rocks. Thus, phosphorous is the limiting factor for plant growth in many (but not all) soils and aquatic ecosystems.

Animals get phosphorous by eating producers or animals that have eaten producers. Animal wastes and the decay of dead animals and producers return much of this phosphorous to the soil, to streams, and eventually to the ocean bottom as deposits of PR. Some phosphate returns to the land as guano, phosphate-rich manure, typically of fish-eating birds such as pelicans and cormorants. This return is small, though, compared with the phosphate transferred from the land to the oceans each year by natural processes and human activities.

Phosphorous returns to the land mainly through slow geological process over millions of years as it may push up and expose the seafloor. Weathering then slowly releases phosphorous from the exposed rocks and continues the cycle. The cycle of phosphorous is fascinating and puzzling and it repeats itself.

Humans intervene in the phosphorous cycle chiefly in two ways: First, we mine large quantities of PR for use in commercial inorganic fertilizers and detergents. Second, we add excess phosphorous to aquatic ecosystems in runoff of animal wastes from livestock feedlots, runoff of commercial phosphate fertilizers from cropland, and discharge of municipal sewage. Too much of this nutrient causes explosive growth of cyanobacteria, algae, and aquatic plants, disrupting life in aquatic ecosystems.

The modern terrestrial phosphorous cycle is dominated by agriculture and human activity. The natural riverine load of phosphorous has doubled due to increased use of fertilizers, deforestation and soil loss, and sewage sources. This has led to eutrophication of lakes and coastal areas, and will continue to have an impact for several thousand years based on forward modeling of human activities (Filippelli, 2008).

Phosphorus moves through the lithosphere, hydrosphere, and biosphere in what is called the phosphorus cycle (see Fig. 1.2). Unlike other biochemical cycles such as for nitrogen and coal, the atmosphere does not play a significant role in the phosphorus cycle, since production of phosphine gas only occurs in specialized, local conditions (Ruttenberg, 2003). The cycle begins with a volcanic activity or an uplift of phosphorus rich sediments, which makes the phosphate minerals exposed to physical erosion and chemical weathering. Although the PR is poorly soluble, this results in a release of dissolved phosphorus in both organic and inorganic forms that is transported out to soils, rivers, and seas. On land, plants take up phosphorus from the soil in the form of various phosphate ions. The phosphorus is returned to the soil by decomposition of dead plants and animals or from animal feces.

Figure 1.2  Phosphorous (P) cycle.

Much of the phosphorus ends up in lakes and oceans where it is taken up by photosynthetic organisms. Unfortunately, because of human activity and reduced return of phosphorus to the fields in the form of human excrement, increasingly more of the phosphorus has ended up in the oceans. Death and decomposition of marine organisms return some phosphorus to the water. Phosphorus-rich shells and other hard parts fall to the ocean floor and become a part of the marine sediments. After 10–100 million years, movement of crustal plates uplift the seafloor and the phosphates become exposed to erosion and weathering once again (Smil, 2000). The PR deposits usually only occur during some special conditions in some specific areas as a result of the phosphorus cycle. PR deposits can mainly be found in regions outside the old shield area and in old folded mountain areas. A large amount of PR was also created during specific periods when the conditions were particularly favorable for the formation of these deposits (Ruttenberg, 2003).

These geological deposits of phosphate are called PR and are found all over the world. They can be divided into two main categories: sedimentary and igneous PR deposits. The latter are often low in grade and expensive to recover. Sedimentary deposits are more plentiful than the igneous rock deposits. The majority of today's global PR production is used in agricultural products and/or applications, mainly in fertilizers (Cisse & Mrabet, 2004). In addition, phosphorus is omnipresent in all living organisms and accounts for around 2%–4% of the dry weight of most cells (Karl, 2000). It is the second most abundant mineral in the human body, only surpassed by calcium. It is mostly found in bones and teeth (biomineral hydroxyapatite). Moreover, it is a key player in fundamental biochemical reactions (Westheimer, 1987) involving genetic material (DNA, RNA) and energy transfer within the cell through the molecule adenosine triphosphate, and in structural support of organisms provided by membranes (phospholipids).

As phosphorus occupies a prominent role in modern life, the world phosphate reserves of high grade are being depleted currently due to increasing demand (Steen, 1998). Thus, it is felt necessary to understand the current situation and the future forecasting of phosphate production and reserves, which will be described in Chapter 2. Furthermore, the depletion of phosphate reserves in combination with the fact that phosphorus is a nonrenewable resource has led to the development of numerous techniques to recover phosphorus from various waste streams (Cordell et al., 2009). An extensive overview will be given as to the existing variety of full-scale P-recovery techniques that may allow to increase the future availability of phosphorus.

1.3. Usages

Phosphorus is an irreplaceable nutrient, utilized for its life-giving capabilities to all life on Earth. Phosphorus is critical to carrying out a variety of cellular and biological processes that help plants, animals, and even humans to grow strong and healthy. As such, phosphorus is a key ingredient in fertilizers and animal feeds. Phosphorus is mined all over the world in the form of PR and processed into all the products that keep our world running. It is a key component in crop production, livestock feed, and even in consumer products.

Most PR produced are utilized for fertilizers and chemically changed into more useable forms. Phosphate rocks are upgraded to meet the market specifications for use as raw material for the production of fertilizers, phosphoric acid, and animal feed and many other phosphate compounds (Abouzeid, 2008). Naturally occurring phosphate mineral deposits are not usually used as mined. Igneous ores are often low in grade but through beneficiation processes can provide PR with required concentration.

The most common P fertilizers in the world are currently diammonium phosphate, monoammonium phosphate, and triple superphosphate. A large amount of P is traded as phosphoric acid, of which 80–85% is used in the production of various P fertilizers. The properties of common phosphate fertilizers are indicated Table 1.2.

Phosphorus is generally found in mineral forms, as phosphates, which is most often insoluble. Phosphorus is a nonmetal of the nitrogen group and is essential for all life on our planet. Elemental phosphorus has been known for about 350 years and exists in two major allotropes, namely white and red phosphorus. These allotropes have a great diversity of physical properties and chemical reactivity. The most common form is white phosphorus or tetra phosphorus (P4), which has a tetrahedral structure and is highly reactive with air, while red phosphorus exists as polymeric chains (Pn) and is more stable (Pfitzner et al., 2004). White phosphorus transforms to red phosphorus when exposed to sunlight, or by heating it in anoxic conditions to 250°C. However, phosphorus is never found as a free element due to its high reactivity. It is widely distributed in many minerals, mainly phosphates (Desmidt et al.,