An Introduction to the Industrial Phosphates Industry
History and Background
The purification of phosphoric acid is closely linked to the evolution of phosphorus and phosphatic fertilizers By the end of the twentieth century, the industry had consolidated, with fewer corporations operating larger plants that sourced raw materials from limited locations However, in the next 50 years, there is potential for a shift towards smaller, local plants that utilize recycled materials Lessons learned from the global growth of the industry may prove valuable if it transitions to a more localized approach.
In his essay "Life’s Bottleneck," Isaac Asimov emphasized the irreplaceability of phosphorus, a vital element for life, which is being depleted through erosion, fertilizer runoff, and sewage The Global Phosphorus Research Initiative, established in 2008, highlighted the concept of Peak Phosphorus, sparking significant discussion on the topic Phosphorus, essential for the formation of DNA, RNA, and ATP, plays a crucial role in cellular energy transport and the overall health of plants and animals It naturally exists as phosphates, which undergo a biogeochemical cycle involving absorption by plants, consumption by animals, and eventual return to the soil through waste and decay This cycle is further influenced by water movement, leading to sedimentation and geological processes that alter the chemical composition of phosphorus, impacting its extraction and purification methods.
Phosphoric acid plays a crucial role in the purification and utilization of phosphate rock, which is mined and processed to create available phosphate for fertilizers This essential process enhances soil fertility by supplementing natural phosphate levels The phosphorus cycle, illustrated in Figure 7.1 of Chapter 7, highlights the significance of phosphoric acid in agricultural practices and its economic implications.
Ancient civilizations understood the advantages of fertilizing their land, although they lacked knowledge of the underlying mechanisms, including the significance of phosphates Historical texts, such as the book of Isaiah from around 700 BC, mention practices like trampling straw into dung heaps Similarly, the book of Luke, written approximately in 60 AD, includes a reference to a man enriching the soil around an unproductive fig tree with manure Additionally, Pliny the Elder, in his first-century work "Natural History," highlights these early agricultural practices.
AD, refers extensively to different manures, for different crops, including pigeon droppings and guano in general as well as the use of lime ash.
The discovery of phosphorus by Hennig Brandt in Hamburg, Germany, in 1669 is often regarded as a pivotal moment that transitioned alchemy into modern chemistry and marked the start of phosphorus's modern history Brandt, a trained glassmaker and soldier, utilized his wife's dowry to pursue alchemy, seeking the philosopher’s stone to convert base metals into gold through a process involving high-temperature heating of aged urine Despite the inefficiency of his method, which resulted in significant waste, Brandt produced a white, waxy substance that glowed in the dark, which he named "kalte feuer" or cold fire This discovery gained attention across Europe, and Brandt's legacy is captured in Joseph Wright's painting “The Alchymist in Search of the Philosopher’s Stone, Discovers Phosphorus,” housed in the Derby Museum and Art Gallery, alongside other notable works.
Johann Kunckel (1630–1702), the son of an alchemist at the Duke of Holstein's court, was a notable chemist who explored the properties of phosphorus He later served King Charles XI of Sweden, earning the titles of Baron von Lửwenstern and Counselor of Metals During a visit to Brandt, Kunckel promptly informed his friend Johann Daniel Krafft, a commercial agent from Dresden, who swiftly purchased Brandt's secret recipe for 200 thalers, equivalent to around $6000 today.
Krafft exhibited das kalte feuer at various European courts and was invited, for a fee of 1000 thalers, to show the phosphorus at the English court of King Charles
II in 1677 When Krafft arrived in London, he was contacted by Robert Boyle (1627–1691) and asked to give a demonstration to the Royal Society at Ranelagh House in London.
In September 1677, Krafft's initial demonstration of gummous and liquid noctilucas was not fully successful, prompting him to return a week later with a fresh piece of phosphorus the size of a pinhead Following the demonstration, Boyle deduced that the essential ingredient originated from humans, speculating it could be either urine or feces Subsequently, Boyle developed his own process with assistance from his team, documenting his findings in papers submitted to the Royal Society in 1680.
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The Industrial Phosphates Industry has roots tracing back to 1678 when Sir Robert Boyle collaborated with alchemist Johann Becher and young chemist Ambrose Godfrey Hanckwitz Together, they innovated a superior method for extracting phosphorus from urine and feces, achieving higher yields and purity than previous techniques Boyle meticulously documented his findings, which were published in the Royal Society, showcasing a clarity and style reminiscent of contemporary scientific literature This work not only established a solid foundation for future research but also solidified Boyle's reputation as "the father of modern chemistry."
Hanckwitz achieved remarkable success by producing highly pure phosphorus, which became a sought-after product across Europe This thriving business enabled him to acquire a laboratory located on Southampton Street in London In the early 1700s, the price of phosphorus was approximately £3 per ounce, equivalent to about $1500 today, translating to around $53 million per ton In his spare time, he managed to produce around 800 ounces annually.
FIGURE 1.1 “The Alchymist in Search of the Philosopher’s Stone, Discovers Phosphorus,” painted by Joseph Wright A.R.A of Derby (1734–1797) (author’s photograph).
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4 Phosphoric Acid: Purification, Uses, Technology, and Economics
The phosphorus process was based on urine until 1769, although Andreas Sigismund Marggraf (1709–1782) of Berlin improved the process through the use of red lead (Pb 3 O 4 ) and charcoal.
In Sweden, Carl Wilhelm Scheele and Johan Gottlieb Gahn made significant advancements in understanding bone composition by dissolving bone ash in sulfuric acid to create phosphoric acid Their method involved heating phosphoric acid with charcoal, which resulted in the release of phosphorus This marked the inception of the modern process for producing phosphoric acid.
In the late eighteenth century, France emerged as a hub for phosphorus manufacturing, led by chemist Bernard Pelletier, who utilized innovative processes to produce approximately 3,200 ounces of phosphorus annually At that time, the limited applications for phosphorus, primarily in lighting, theater, and flame-proofing, hindered the establishment of a robust chemical industry The first matches, created by Chancel in 1805, lacked phosphorus, while Dérosne and others introduced hazardous phosphorus matches around 1816 The invention of safer matches, known as Lucifers, occurred in 1831, evolving from earlier Prometheans that required dipping into flammable fluids The development of safety matches using red phosphorus by Bửttger in 1848 and patented by May in 1865 marked a significant advancement Prior to matches, igniting fires for cooking and heating involved a complex process of striking flint to light tinder, a challenging task in damp climates like England, where candles and lamps were essential for illumination.
In "A Tale of Two Cities," Charles Dickens illustrates the process of relighting a coach lamp, emphasizing the significance of the humble match as a transformative product in history The invention of the Lucifer match, as detailed by John Walker, created a substantial market for phosphorus, prompting its production to scale up industrially M.M Coignet from Lyon, France, enhanced the Pelletier process for producing bone ash by acidifying it with sulfuric acid to yield phosphoric acid, which was then converted into phosphorus.
Ca PO3( 4 2) +3H SO2 4→3CaSO4+2H PO3 4 (1.1)
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An Introduction to the Industrial Phosphates Industry 5
In the 1840s, France saw a significant increase in bone calcination, with kilns established across the country, exemplified by Figure 1.3 During this period, exports to England reached 4,500 kg, and prices plummeted to 21 shillings per pound, representing only 2% of the costs from the 1700s After completing his apprenticeship, Arthur Albright (1811–1900) relocated to join John.
Edmund Sturge Ltd., a manufacturing chemistry firm based in Birmingham, England, saw significant innovation when Albright joined as a partner in 1840 By 1844, he successfully convinced Sturge to produce phosphorus using bone ash sourced from South America Albright showcased their groundbreaking work at the Great Exhibition in London in 1851 and again in Paris in 1855.
During that period, key phosphorus producers included Coignet from Lyon, France, Zoeppritz from Freudenstadt, Germany, and Riemann from Nuremberg, along with smaller manufacturers in Russia and the United States Despite the phosphorus price dropping to 3 shillings per pound (approximately $300,000 per ton today), Albright and Sturge were still able to maintain profitability.
Chemistry and Process Overview
This section explores the chemistry of the phosphate industry, beginning with phosphate rock Key reaction equations for major phosphate products are outlined, serving as the foundation for understanding the cost structures associated with these products.
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Phosphoric acid plays a crucial role in various industrial applications, and understanding its purification processes, uses, and economic aspects is essential for effective plant design Subsequent chapters will delve into the chemistry of different phosphorus products and processes, providing detailed insights For an in-depth exploration of phosphorus chemistry and biochemistry, readers are encouraged to consult Corbridge [64].
The phosphate industry begins with phosphate rock, which is processed into approximately 30 million tons of phosphoric acid annually through a reaction with sulfuric acid About 90% of this phosphoric acid is transformed into fertilizers, primarily ammonium phosphates, and superphosphates, while a smaller portion is purified into various commercial grades, including food grade for food phosphates and higher purity grades for pharmaceuticals and semiconductors Additionally, a minority of phosphate rock is converted into elemental phosphorus, a process that demands significant electrical energy, and a small fraction is marketed as a low-cost fertilizer known as phosphate flour or direct application rock (DAR).
Phosphorus exists in several allotropes, including white (commonly known as yellow phosphorus due to its typical appearance), red, violet, and black Additionally, diphosphorus is another form of this essential element.
Phosphorus primarily exists in gaseous form, with global production focused on white phosphorus, totaling approximately 1,000,000 tons annually Red amorphous phosphorus (RAP), utilized in matches, ammunition, phosphor bronze, metal phosphides, and pigments, is produced by heating white phosphorus in a small agitated reactor at temperatures exceeding 250°C.
Phosphine (PH3) is a highly toxic and flammable gas produced through the reaction of metal phosphides with water, the treatment of RAP with water at approximately 250°C, or the alkaline hydrolysis of white phosphorus It serves as a precursor for catalysts and mining agents, and when reacted with formaldehyde and acids, it yields tetrakis(hydroxymethyl)phosphonium chloride (THPC) and sulfate (THPS), both utilized as flame retardants for cotton fabrics Key phosphorus derivatives include phosphorus trichloride (PCl3) and phosphorus pentasulfide (P4S10), along with the minor derivative phosphorus sesquisulfide (P4S3) These compounds are further processed into various phosphorus derivatives, such as glyphosate, an herbicide developed by Monsanto, and bisphosphonates for osteoporosis treatment Overall, the production of phosphorus derivatives is chemically complex and hazardous, though typically on a smaller scale compared to phosphate processes.
The relationship between phosphates and phosphorus is evident in thermal phosphoric acid and its derivatives Historically, before the advent of commercial solvent extraction purification, pure phosphoric acid was primarily obtained through the hydration of phosphorus pentoxide (P2O5), which is generated by burning phosphorus in specialized burners In certain regions, the economic viability of using thermal acid in fertilizers was established, and the production facilities for thermal acid can adjust its concentration based on specific requirements.
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27 A n I n tro d uc tio n t o t h e I n d u str ia l P h o sp h at es I n d u str y
Electricity Coke Silica Sulfuric acid Ammonia Potassium
Phosphorus We t process phosphoric acid
Phosphoric acid products (technical and food grade) Aluminum phosphates Monoaluminum phosphate (MALP)
Mono-, di-, tricalcium (MCP, DCP, TCP) Pyrophosphate, polyphosphate pigment Lithium phosphate
Di-, trimagnesium (DMP, TMP) Mono-, di-, tripotassium (MKP, DKP, TKP) Pyrophosphate, polyphosphate
Mono-, di-, trisodium (MSP, DSP, TSP) Chlorinated trisodium (TSP-chlor)
Di, tetrapyrophosphate (DSPP, TSPP) Polyphosphate (STPP)
Calcium phosphates Food, dental, pharmaceutical, catalyst, flow agent
Lithium phosphates Porcelain glaze, catalyst, batteries
Potassium phosphates Wide product range including antifreeze
Sodium phosphates Food, pharmaceutical, washing, water treatment
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Phosphoric acid (H₃PO₄) is typically commercially available at a concentration of 85% (61.6% P₂O₅), with variations ranging from 75% to 92% By reducing water content, concentrations can reach up to 116% H₃PO₄ (84% P₂O₅), and even higher levels, exceeding 118%, are achieved by adding solid phosphorus pentoxide, which is produced by burning phosphorus in dry air These polyphosphoric acids serve as drying agents and catalysts, offering logistical cost savings for small businesses that dilute concentrated forms for local sale Additionally, polyphosphoric acids can be produced by concentrating purified 85% H₃PO₄ to the desired grade, with concentrations typically starting at 105%, representing the eutectic mixture of orthophosphoric and pyrophosphoric acids Further details on polyphosphoric acid will be discussed in Chapter 3.
Phosphate rock, characterized by its apatite structure, is a complex mixture of elements that varies by mine location and within individual mines The primary components of commercial phosphate rock include calcium, phosphate, and fluoride Simplified chemical reactions illustrating the conversion of phosphorus and phosphoric acid using sulfuric acid are outlined in the following equations.
Ca PO F10 4 6 2 SiO2 C 1400 C CaSiO P CO CaF
Ca PO F4 H SO2 H O2 C CaSO H O H PO HF
In the phosphorus reaction, dried and ground rock is continuously mixed with coke and sand in a carbon-lined furnace, where temperatures reach between 1400°C and 1500°C due to graphite electrodes At these high temperatures, silica reacts with calcium in the rock, releasing phosphate and forming calcium silicate molten slag, while approximately 80% of the fluoride combines with calcium to create calcium fluoride The coke reduces the rock phosphate to diphosphorus vapor and carbon monoxide, with some silica forming silicon tetrafluoride gas (SiF4), which accounts for about 20% of the fluoride in the feed material In advanced plants, vapors and dust are processed through an electrostatic precipitator to minimize solid load, followed by a water condenser where phosphorus (P4) is condensed and stored underwater, with most silicon tetrafluoride dissolving in the solution.
Iron impurities in rock create iron phosphide (ferrophosphorus), which is melted, cooled, and solidified for sale to the steel industry The reactions involved in forming iron phosphide are detailed in Equations 1.8 and 1.9, along with the presence of other impurities in the rock.
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The industrial phosphates industry involves the processing of feed materials, which include sulfur, magnesium, and aluminum, alongside coke These components undergo similar reactions during production, leading to an approximate 8% loss of phosphorus content This reduction is accounted for when considering the phosphorus remaining in the calcium silicate slag.
The furnace burden in phosphorus production is determined by two key ratios: the silica/lime ratio (SiO2/CaO), typically between 0.8 and 1.0, and the phosphate/carbon ratio (P2O5/C), generally between 2.3 and 2.6 These ratios are influenced by the composition of rock and coke, the need for additional carbon to account for losses, and operational experience Electricity consumption ranges from 12.5 to 14 MWh per metric ton of phosphorus, constituting about 50% of the total production cost The condenser's vapor stream primarily contains carbon monoxide, along with hydrogen, phosphine, phosphorus particles, and other minor components In advanced plants, this stream can be utilized for drying rock or generating power, potentially reducing energy costs by nearly 20% when fully recycled The molten slag produced is waste, which has previously been used as road base but is now problematic due to radionuclide presence Simpler plants without precipitators depend on the condenser to remove dust, leading to emissions of burning carbon monoxide and hydrogen, as well as white fumes from phosphorus conversion, dispersing radioactive dust in the area.
In the phosphoric acid production process, ground rock and sulfuric acid are introduced into a reactor system, maintaining a temperature of 70°C–80°C to yield dihydrate calcium sulfate, commonly known as gypsum The reaction mass is continuously filtered, with the filter cake washed counter-currently, allowing the weak acid to be recycled back into the reactor for optimal solid and P2O5 content management The filter cake is then disposed of either in a gypsum stack or, if feasible, into nearby water bodies Although gypsum can be treated through washing and drying for plasterboard production, this method is often less economical than mining natural gypsum, as seen in Belgium and Japan Meanwhile, the resulting acid, with a concentration of approximately 30% P2O5, is stored for fertilizer use or further concentration.
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Phosphoric acid concentrators operate by utilizing low-pressure steam, typically sourced from dedicated boilers, on-site power plants, or heat recovery steam generators linked to sulfuric acid plants These facilities produce not only gypsum but also a complex phosphatic sludge during concentration and storage, along with fluoride-based waste To maximize the value of the phosphate, the sludge is converted into solid fertilizer products, while some plants process the fluoride waste into fluo-silicic acid (H2SiF6) for commercial use in aluminum production and water fluoridation.
Economics
The phosphate industry's economics are heavily influenced by the prices of key raw materials, including phosphate rock, sulfur, and electricity Additionally, the cost of ammonia, crucial for ammonia-based fertilizers, is closely tied to natural gas prices.
Phosphate rock is primarily supplied and priced by the industry, with energy costs and government taxation playing a role in price fluctuations In 2008, China implemented a 20% export tax on fertilizers to conserve its P2O5 resources, leading to a global spike in phosphate rock and sulfur prices Although prices eventually stabilized, they continue to correlate with fertilizer demand, which is influenced by food demand and population growth Ultimately, the price of phosphate rock is determined through negotiation between buyers and sellers, with P2O5 content being a key factor, and various organizations actively monitor and publish these prices.
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62 Phosphoric Acid: Purification, Uses, Technology, and Economics
Figure 1.24 shows phosphate rock prices from 1960 to 2012 plotted from The World Bank: Global Economic Monitor (GEM) Commodities.
Approximately 90% of sulfur is transformed into sulfuric acid, with around 65% sourced from oil, natural gas, and coal, referred to as recovered sulfur The global annual production of sulfuric acid reaches 200 million tons, with 65% used for producing phosphoric acid This supply of recovered sulfur is inelastic, being a fixed by-product of refineries and coal desulfurization, leading to demand-driven pricing, especially as the phosphate industry significantly influences market prices Sulfur and sulfuric acid prices are tracked across nine benchmarks, including Vancouver, the Middle East, and China, using International Commercial (INCO) terms like FOB and CFR, quoted in US dollars per metric ton for both spot and contract purchases Phosphoric acid producers often utilize sulfur to generate sulfuric acid, leveraging by-product steam for additional products and electricity, while some are strategically located near smelting plants to negotiate sulfuric acid prices without generating by-product steam Historically, the positioning of phosphorus plants has relied on proximity to local phosphate sources and coal, optimizing production advantages.
World phosphate rock price $/ton
FIGURE 1.24 World phosphate rock prices 1960–2012 data from World Bank GEM Commodities database.
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The industrial phosphates industry is significantly influenced by electricity prices, as seen in phosphorus plants established in Tennessee and the Western States As global electricity demands rise, prices tend to stabilize at a uniform level, often regulated by governments, while still allowing for individual agreements between buyers and sellers For cost comparisons, below-average prices in the United States are referenced Additionally, ammonia prices are closely tied to natural gas costs, creating competition among various industries for supply Organizations like Fertilizer Week and the National Agricultural Statistics Service of the US Department of Agriculture compile data on ammonia and fertilizer prices, highlighting the interconnected nature of these markets.
1.3.1 p roductIon c oStS of p hoSphoruS and p hoSphorIc a cId
The article provides a comparative analysis of the costs associated with producing phosphoric acid through the wet and thermal routes A typical product cost sheet outlines essential components, including raw materials ranked by importance, chemical services necessary for processing, and utilities like steam, water, and nitrogen Additionally, it covers direct labor costs for personnel involved in plant operations and maintenance, generally budgeted at 1%–5% of the plant's capital or replacement cost, along with indirect costs such as administrative overheads, depreciation, taxes, and insurance.
Table 1.6 displays a cost sheet for sulfuric acid as the majority of phosphoric acid enterprises include a sulfuric acid plant The wet process acid must be purified to compete
Sulfuric Acid Plant Cost Sheet
H 2 SO 4 330 Days/Year Usage/t H 2 SO 4 Price Unit $/t H 2 SO 4 %
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The cost analysis of purified phosphoric acid production reveals that the primary expense is the feed acid cost, significantly influenced by return acid credits, followed by maintenance, administration, and depreciation The impact of solvent extraction technology on overall costs is relatively minor Comparative cost sheets for various phosphoric acid plants indicate that thermal acid production is nearly double the cost of purified acid for equivalent P2O5 output, making thermal acid derivatives more expensive Historically, phosphorus manufacturing relied on local resources like rock, coal, and inexpensive electricity; however, rising electricity demand and fluctuating hydroelectric availability, as seen in early 21st century China, have forced producers to pay full commercial rates, limiting production capabilities Consequently, in developed economies, phosphorus plants must justify their existence by meeting market demands.
P 2 O 5 330 Days/Year Usage/t P 2 O 5 Price Unit $/t P 2 O 5 %
684 100% a Phosphate rock of 32% P 2 O 5 concentration, usage includes total losses (5%). b 98% H 2 SO 4 used, calculation based on 100% H 2 SO 4
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An Introduction to the Industrial Phosphates Industry 65
Phosphoric Acid Concentrator Plant Cost Sheet
P 2 O 5 330 Days/Year Usage/t P 2 O 5 Price Unit $/t P 2 O 5 %
718 100% a Based on 30% P 2 O 5 filter acid concentrating up to 59% P 2 O 5 and accounting for precipita- tion and processing losses.
Purified Phosphoric Acid Plant Cost Sheet
P 2 O 5 330 Days/Year Usage/t P 2 O 5 Price Unit $/t P 2 O 5 %
1060 100% a Based on 59% P 2 O 5 concentrated, low sulfate, acid feed, 2.5% losses. b Return acid credit is negotiated and ranges 0%–100% of the value of the feed acid, here it is 80%.
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66 Phosphoric Acid: Purification, Uses, Technology, and Economics
TABLE 1.10 Phosphorus Plant Cost Sheet
P 4 330 Days/Year Usage/t P 4 Price Unit $/t P 4 %
2720 100% a Based on 25% P 2 O 5 rock and 8% P 4 losses. b Rock price same as wet acid case based on P 2 O 5 content. c Silica requirement accounting for SiO 2 content of phosphate rock (25% SiO 2 ).
TABLE 1.11 Thermal Phosphoric Acid Plant Cost Sheet
P 2 O 5 330 Days/Year Usage/t P 2 O 5 Price Unit $/t P 2 O 5 %
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The industrial phosphates industry is experiencing a significant demand for phosphorus and its organic derivatives Currently, the United States has only one phosphorus furnace located in Idaho, while Europe has one in the Netherlands In contrast, the wet acid process for producing purified acid has proven to be economically viable, leading to the establishment of multiple purified acid plants globally.
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