Procedia Engineering 46 ( 2012 ) 255 – 265

1877-7058 © 2012 The Authors. Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the Scientifi c Committee of SYMPHOS 2011doi: 10.1016/j.proeng.2012.09.471

1st International Symposium on Innovation and Technology in the Phosphate Industry [SYMPHOS 2011]

Manufacture of Aluminium Fluoride of High Density and Anhydrous Hydrofluoric Acid from Fluosilicic Acid

Alain Drevetona,*

AD Process Strategies Sarl, Rue Chaponnière 9, CH-1201 Geneva, Switzerland

Abstract

New process technologies are disclosed to manufacture aluminium fluoride of high density and anhydrous hydrofluoric acid starting from fluosilicic acid as raw material which is obtained during acidulation of phosphate rock in the manufacture of phosphatic fertilizers. An overview of the relevant process technologies used commercially to consume this fluosilicic acid is provided in this paper. The new process technologies which shall be implemented to satisfy market demand in fluorochemicals (production of aluminium fluoride of high density from fluosilicic acid and production of anhydrous hydrofluoric acid from fluosilicic acid) and overcome some technical issues as well are described.

© 2012 The Authors. Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the Selection and /or peer-review under responsibility of the scientific committee of SYMPHOS 2011.

Keywords: aluminium fluoride, hydrofluoric acid, fluorine technology, fluosilicic acid, fluorochemical, silicon tetrafluoride, sodium silicofluoride, suplphate of potassium, sodium sulphate

Nomenclature

AHF Anhydrous hydrofluoric acid ATH Alumina trihydrate, aluminium hydroxide DCP Dicalcium phosphate FSA Fluosilicic acid, fluorsilicic acid FSA1G FSA-based technology of the first generationFSA2G FSA-based technology of the second generation FSA3G FSA-based technology of the third generationHBD High bulk density, HD-AlF3

HFC Hydrofluorocarbon KSF Potassium silicofluoride, Potassium fluosilicate LBD Low bulk density, LD-AlF3

MGSF Magnesium silicofluoride, Magnesium fluosilicate MOP Muriate of Potassium, KCl PA Phosphric acid PR Phosphate rock, Rock SA Sulphuric acid SAC Sulphuric acid concentration

* Corresponding author. Tel.:+00 41 22 548 1249; fax:+00 41 22 545 7512. E-mail address: a.dreveton@adpro-stg.com

Available online at www.sciencedirect.com

© 2012 The Authors. Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the Scientifi c Committee of SYMPHOS 2011 Open access under CC BY-NC-ND license.

Open access under CC BY-NC-ND license.

256 Alain Dreveton / Procedia Engineering 46 ( 2012 ) 255 – 265

SSA Sodium sulphate anhydrous SSF Sodium silicofluoride, Sodium fluosilicate SOP Sulphate of Potassium STF Silicon tetrafluoride Symbols MMT Million metric tons

1. Fluorine raw material resources

Fluorochemicals are essentially produced from raw material fluorspar (Acid Grade Fluorspar: CaF2 > 97%). A small amount only (about 5%) is produced from phosphate rock, an alternative raw material containing fluorine for production of:

• Fluosilicic acid • Fluosilicates • Cryolite • Aluminium fluoride • Silicon tetrafluoride

1.1. Uses of Fluosilicic acid

Fluosilicic acid is used as water fluoridation agent of drinking water to prevent tooth decay in US, Canada, South Africa and Australia mainly. The US production of fluosilicic acid in 2010 estimated and reported by USGS (Miller, 2010) is 68’000 tons (FSA as 100% H2SiF6) mostly used for water fluoridation and manufacture of silicon tetrafluoride (STF = SiF4) up to 20’000 tons being a raw material for polysilicon produced by MEMC, an intermediate to high purity silicon for solar and chips applications. In this process, MEMC claimed that the capital cost of this process is reduced by 50 % compared to classical Siemens process and electric consumption for purification reduced by 20 folds. Other uses of FSA are in the tanning of animal skins, in ceramic and glass etching, in technical paints, in oil well acidizing, preservative of wood, hardening of masonry, remover of mould, remover of rust and stain in textiles, cleaning and sterilizing agent in industry, and in electro-refining of lead, etc. Very minor quantities of FSA are produced also from fluorspar processing.

Table 1: Uses of fluosilicic acid

COUNTRY COMPANY FLUOROCHEMICAL PRODUCT

YEARLY CAPACITY (TON)

US 4 Companies (Plants) Reporting FSA << 68’000

US PCS Phosphate Co. STF < 28’000

EU (BE) Prayon SSF/PSF 18’000 / 3’000

EU (HU) Bige Holdings Cryolite <<

EU (PL) TARNOBRZEG Ltd. Cryolite <<

EU (SE) Alufluor LD-AlF3 23’000

CN Several Producers LD-AlF3 Small

CN Wengfu AHF 20’000

IN Alufluoride LD-AlF3 5’000

IN Hindalco LD-AlF3 3’000

CN Several Plants SSF/PSF/MGSF /NH4F

--

CN Yunnan Three Circles Chemical Industry Co. SSF/PSF --

JO JPMC LD-AlF3 20’000

ID PT Petrokimia Gresik LD-AlF3 12’000

RU Phosagro /Ammophos LD-AlF3 / SSF 23’000

BY JSC Gomel Chem. Plant Cryolite / LD-AlF3 5’000/5’000

LT Eurochem / Lifosa LD-AlF3 17’000

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Aluminium fluoride is still the major product out of FSA with a production < 100’000 tons / annum against about 800’000 tons / annum mainly produced from fluorspar reported by (Reynolds, 2010) . See Table 2 below.

Table 2: World and China aluminium fluoride (AlF3) production and consumption per year (x 1’000 tons)

STF could grow significantly as its added value is higher than manufacturing AlF3 / AHF making projects even more attractive. Already five projects have been implemented in Asia (approx. 70’000 tons / annum STF) using the fluorspar process although it makes more sense to start from FSA.

Presently there is a supply shortage of FSA for water fluoridation in US and Canada and prices of FSA have risen significantly.

1.2. Fluorspar resources

China is dominating largely the fluorspar industry (59% of world fluorspar production) (Will, 2010)) and China is starting to face sourcing problems at present. China has changed its policy with tighter rules. Consequently fluorspar prices are rising. Europe has included fluorspar in a list of 14 minerals classified as “critical”. A raw material is labelled “critical” when the risks for supply shortage and their impacts on the economy are higher compared with most of the other raw materials

a) (b)

Fig. 1 : World production of fluorspar (a) 5.1 million tons (Will, 2010) and (b) 5.4 million tons (Miller, 2010). Reserves of fluorspar are reserves

that are economical to extract and recover according to USGS (Miller, 2010) are also reported.

According to (ResearchInChina, 2010), the fluorspar reserves in China (2009) reached 21 million tons, providing 9.3% of the world’s total, ranking at the third position, while the fluorite output recorded three million tons in the same year, contributing 58.8% to the world’s total, topping the global list. According to statistics of year 2009, the ratio of fluorite

258 Alain Dreveton / Procedia Engineering 46 ( 2012 ) 255 – 265

reserves to output in China was not more than seven, indicating that the fluorite resource in China is likely to run out within seven years provided that the recoverable reserves of fluorite will fail to increase.

China is deficient in fluorite resource and demand is growing for fluorite year after year at significant pace. In 2009, the apparent consumption of fluorite in China reached 2.8 million tons, up 8.2% from a year earlier; and the figure in H1 2010 hit 1.93 million metric tons (MMT). Concerning the consumption of fluorite, China ranks first around the globe, but lags far behind the developed countries in term of downstream consumption. A case to this is fluorine chemical industry, the demand of fluorite is 30% less in China than opposed to nearly 60% in developed countries.

Fig. 2 : Map of fluorspar reserves in China (HeQing, 2005, p. 5)

(a) (b)

Fig. 3: World HF production capacity is about 2 million tons in 2009 (a) and Fluorine Industry Segments: fluorocarbon production is the largest HF

segment followed by aluminium fluoride production (Will, 2010)

As long as fluorspar was cheap, there was no need for an alternative source of fluorine like FSA. Presently the price of fluorspar is about USD 350.-/ton FOB compared to FSA 100% that can be produced very cheaply, by operating a single absorber. The theoretical price of FSA would be USD 600.-/ton if fluorine F contained in FSA is assumed at the same value of F contained in fluorspar. At this price, it makes any business for fluorine attractive and it is adding appreciable value to the phosphate business. Especially for aluminium fluoride that is a bulk chemical, easily transportable requiring large

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amounts and competitive sources of fluorine. At the time of writing this paper, some Acid Grade Fluorspar from China reached USD 500.-/ton back to pre-recession highs.

• phosphate rock resources

The world population is expected to reach 9 billion of inhabitants in 50 years and productions / capacities are forecasted to increase by more than 50% maybe 70%. In the near future, fluosilicic acid uses will probably increase bearing in mind that environmental regulations are more stringent, technical hurdles for the technology are now resolved, technical expertise is available, communication between the industrial sectors concerned is improving constantly.

The phosphate rock reserves are assumed to be sufficient for more than a century; other base reserves less attractive will be considered at the end of the century only. (See below Fig. 4 Hubbert peak for phosphorus)

Table 3: Phosphate rock production and reserves according to USGS (Jasinski, 2011)

According to International Fertilizer Association (IFA, 2009), the world production of phosphate rock in 2009 was 162 million tons phosphate rock (49.7 million tons as P2O5) and the world production of phosphoric acid was 33.6 million tons expressed as P2O5 (48.6 million tons expressed as H3PO4)

Assuming that phosphate rock contains 2 to 5% fluorine (average approx. 3% F) an amount of 4.8 million tons of fluorine is available which is about twice the amount of F present in fluorspar. (Fluorspars are up to 48% F).

Fig. 4: Peak of phosphate rock [Hubbert peak] (Kauwenbergh, 2010)

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Assuming a recovery rate of 35% as a minimum as per data below (EFMA, 2000, p. 24) for dihydrate (DH) & Hemi-hydrate (HH) Phosphoric Acid processes: an amount of 1.7 million tons F could be recovered (2.0 million tons FSA 100%) corresponding to 1.4 million tons AHF about 70% of world production.

For higher accuracy of this assessment, the production of FSA should be defined for each production plant and calculated as a function of the rock used and technology used for manufacturing phosphoric acid if exact production is not known.

Table 4: Typical distribution of F in dihydrate and hemihydrate PA (phosphoric acid) processes

Dihydrate process (%) Hemihydrate process (%)

Acid 15 12

Gypsum 43 50

Reactor off gas 5 8

Flash cooler vapour 3 30

Concentrator vapour 35 -

As shown above (Table 1) fuosilicic acid finds its main application in the manufacture of low bulk density (LBD) aluminium fluoride being a large volume chemical which is mostly produced from fluorspar as high bulk density (HBD) aluminium fluoride. From fluosilicic acid a small amount only is produced. Aluminium fluoride is essentially used as a flux for smelting aluminium by volumetric addition to the cells of aluminium smelters in order to regenerate the cryolite bath. HBD aluminium fluoride is the preferred material due to its high density and good fluidity and none of this high density material is produced at present from FSA via intermediate HF which process is available, feasible and proven at this time.

Hereinafter are disclosed new process technologies for manufacturing anhydrous hydrofluoric acid (AHF) from fluosilicic acid (FSA) which AHF can be converted into (HBD) aluminium fluoride. This aluminium fluoride technology often referred to as the Dry/FSA Process which is a gas phase process using a fluidized bed reactor. An opportunity to invest in profitable projects does exist really. Additionally the manufacture of various downstream products of fluorine: refrigerants, fluoropolymers, etc and downstream products of silicon: silicon metal, silicon tetrafluoride, silicas may offer further interesting opportunities.

2. FSA-based Fluorine technologies

2.1. LBD-Aluminium fluoride from FSA [FSA1G]

FSA1G: FSA-based technology of the first generation (1G) is the: wet FSA process for production of AlF3 from FSA. This process has also an equivalent process of first generation starting with fluorspar which is the old wet HF/fluorspar process for production of aluminium fluoride and cryolite which is today totally abandoned.

The first process known for manufacturing (LBD) aluminium fluoride from fluosilicic acid was patented by Chemie-Linz, Austria (Weinrotter, 1963) about 50 years ago and many plants were built based on this technology or comparable technologies.

Chemistry:

H2SiF6 + Al2O3.3H2O 2 AlF3 + 3 SiO2 + 4H2O [1]

This process uses the direct neutralization of the fluosilicic acid with alumina hydroxide carried out in a stirred reactor. It is often referred to as the Wet/FSA Process . Although this technology tends to be abandoned due to the low density and low fluidity (flowability) of the product, the high capital cost of the plant and its environmental issues resolved partially only as neutralization of mother liquors may still be required, further developments of this process would revive this technology being still accepted by few players only. Improvements are available from us for material of construction and cost-effective design, improved crystallisation process, product granulation, etc.

This process requires very pure FSA. Quality of the FSA is often a limitation to use this process.

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Fig. 5: Flowsheet LBD-Aluminium fluoride from FSA. Wet FSA-based Process of first generation [FSA1G]

Plants (usual name) built with this technology: JPMC, Alufluor, Lifosa, Ammophos, Alcoa, Luzhai, Guixi, Dayukou, Wengfu, Achinsk, Péchiney Salindres, Lubon, DMCC, Alufluoride, Navin, Hindalco, SPIC, PT Petrokimia Gresik, AlQaim, Gomel, Trepca.

2.2. HBD-Aluminium Fluoride from FSA and AHF from FSA [FSA2G]

FSA2G: FSA-based technologies of the second generation (2G) known also as HF from FSA or dry process for AlF3 from FSA or fumed silica process by the fluorine route.

A process for manufacturing AHF from fluosilicic acid was disclosed first by Tennessee Corp., USA (Oakley, 1962) (Houston, 1962) maybe 50 years ago and further disclosed by Wellmann-Lord (Kelley & al., 1971), etc and more lately by (Flemmert, 1974) of Nynaes Petroleum, Sweden, and (Zawadzki, 1977) Lubon Works, Poland, the latter operated a small pilot plant for manufacturing diluted HF. In 2008 Wengfu, China commissioned a first commercial plant for AHF with the technology of Buss Chemtech AG, Switzerland based on know-how from Lubon Works.

Chemistry:

H2SiF6.SiF4(aq) + H2SO4 2 SiF4 + 2 HF(aq) + H2SO4 [2] 5 SiF4 + 2 H2O 2 H2SiF6 .SiF4 (aq) + SiO2 (s) [3] Al2O3.3H2O Al2O3 + 3 H2O [4] Al2O3 + 6 HF 2 AlF3 + 3 H2O [5]

The process is based on the decomposition of FSA by mixing strong fluosilicic acid with strong sulphuric in a stirred reactor and separating silicon tetrafluoride gas using sulphuric acid as dehydrating agent and extracting the anhydrous hydrofluoric acid into separation columns as per the principle shown on the flowsheet below. The evaporation can be realized with a single stage or two stages. Presently AD Process Strategies Sarl proposes an improved process of this technology to suit the water balance of the phosphoric acid (PA) plants, di-hydrate (DH) PA Process and especially hemi-hydrate (HH) PA process being not suitable to receive large amount of water at its goal is to produce strong phosphoric acid directly. Sulphuric acid containing water that is generated from this HF plant has to be re-circulated to the phosphoric acid plant. The sulphuric acid usage or recirculation which is normally 30 ton/ton AHF as 100% H2SO4 can be reduced to 15 ton/ton. Water contained in the acid recirculated is reduced from more than 10 ton/ton AHF down to 5 ton/ton.

The technology of second generation is proven, resolves environmental issues and is very profitable as raw material costs are low (low cost of fluorine, no cost for sulphur or sulphuric acid at all), the capital cost is reasonable. Moreover this technology is promising as it open markets to HBD aluminium fluoride and anhydrous hydrofluoric acid, both being large volume chemicals.

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This process is less sensitive to impurities contained in the FSA due the provision of AHF purification unit in the process.

Fig. 6: Simplified flowsheet AHF from FSA [FSA2G]

Fig. 7: Flowsheet HBD-Aluminium Fluoride from AHF [FSA2G]

An optional process is a process with hydrolysis of STF in the gas phase under high temperature to produce silica, Fumed silica as per the Nynaes process or silica as per the Reed process. Silicon tetrafluoride (STF) can be produced from this process as well.

Plants (usual name) built with this technology: Lubon, Grace, Wengfu for AHF

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2.3. HBD-Aluminium Fluoride and AHF from fluosilicates (from SSF or FSA) [FSA3G]

FSA3G: FSA-based technology of the third generation. This is the advanced process for stand-alone plants providing many alternatives for not recycling water and sulphuric acid to the phosphoric acid plant and alternatives for reusing the material streams available inside the process cycle.

When diluted sulphuric acid stream is not returned to the phosphoric acid plant or can not be re-circulated due to technical reasons or not and in particularly in the process of second generation mentioned above, AD Process Strategies Sarl proposes a new technology for stand-alone HF plants. The proposed process uses a fluosilicate as an intermediate (solid) raw material, which is transportable not like FSA and reaction of this fluosilicate with strong sulphuric acid. The silicon tetrafluoride and hydrofluoric acid so obtained are treated as per the state of art technique in a similar manner as mentioned above for the technology of second generation using absorption / desorption of HF in sulphuric acid. The diluted sulphuric acid stream resulting from this process can be pre-concentrated and recycled to the phosphoric acid plant or used in production of fertilizers like single superphosphate (SSP), dicalcium phosphate DCP, ammonium sulphate (AS), etc or concentrated and recycled to the HF reaction or purified for sale.

Fig. 8 : Block diagram for HFD Aluminium fluoride and AHF from SSF or FSA [FSA3G]. (in dark blue: main process cycle, in light blue: optional

process units). [Operation units: R-Reactor, S- Separator, A- Absorber, C- Crystallizer,..]

• Water balance for the various technologies

FSA1G Wastewater to be neutralised or recycled in cooling tower water loop.

FSA2G 30 to 15 tons sulphuric acid and 10 to 5 tons of water in spent acid per ton HF produced (or per 45 tons of PA produced expressed as P2O5) to be recycled.

FSA3G 5 to 0 tons of sulphuric acid and 5 to 0 tons of water in spent acid per ton HF produced to be recycled.

Chemistry: The process uses the chemical reaction of sulphuric acid / sodium fluosilicate in opposite direction under different conditions, in aqueous medium and low temperature (step 1) and in anhydrous medium and high temperature (step 2):

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• Step-1: Production of sodium fluosilicate (SFS) or silicofluoride (SSF) by one of these chemical reactions: (reaction 2 is the usual process to manufacture SSF)

H2SiF6(aq) + Na2SO4(s) Na2SiF6(s) + H2SO4(aq) [6a] H2SiF6(aq) + 2 NaCl(s) Na2SiF6(s) + 2 HCl(aq) [6b]

• Step-2: Decomposition of SSF by Sulphuric Acid and recycle of SiF4 creating a loop to generate additional FSA and SSF. (This reaction was tested; yield is not critical as the salt is recycled or can be purified as required)

Na2SiF6(s) + H2SO4 2 HF(g) + SiF4(g) + Na2SO4(s) [7] 3 SiF4 + 2 H2O 2 H2SiF6(aq.) + SiO2(s) [8]

• Step-3: The aluminum fluoride is produced between reaction of HF with alumina trihydrate in a fluidized bed reactor. This process is the same as for the fluorspar process or FSA process of second generation [FSA2G])

Al2O3.3H2O Al2O3 + 3 H2O [4] Al2O3 + 6 HF 2 AlF3 + 3 H2O [5]

• Step-4: Pre-concentration of sulphuric acid (A pilot unit is operating since more than 10 years concentrating sulphuric acid up to 85% in presence of fluorine) and recycle of this acid to the process or reused by other consumers.

Plants built with this technology: First prefeasibility study is underway. Acceptance for this technology of third generation is higher than for the technology of second generation.

Use of Potassium fluosilicate (PSF) instead of SSF for this Process still needs to be investigated. It provides the advantage of producing directly sulphate of potassium (SOP) which is a large volume fertilizer.

3. Extra- productions using third FSA generation technology [FSA3G]

Many alternatives are potentially available to use the materials present in streams internally recycled in this process that will definitely improve the benefits and economics of projects.

3.1. Production of Dicalcium Phosphate (DCP)

Production of DCP from HCl (and optionally from sulphuric acid and sodium chloride or sea water) for production of DCP (feed grade) as a production unit or as neutralization unit with separation of solids and recycling for production of DCP (fertilizer grade).

Dicalcium Phosphate dihydrate CaHPO4.2H2O, is produced by a wet process according to the following steps: Ca3(PO4)2 + 4 HCl Ca(H2PO4)2 + 2 CaCl2 [9] Ca(H2PO4)2 + Ca(OH)2 2 CaHPO4.2H2O + 2 H2O [10

- Reaction of phosphate rock with hydrochloric acid, main raw materials, from which a monocalcium phosphate liquor is obtained. • Purification of the remaining solution by means of the removal of the inert matters and undesirable compounds. • Production of dicalcium phosphate by means of calcium salts precipitation and product filtration.

• Drying of dicalcium phosphate at moderate temperature to keep its two water molecules.

3.2. Production of Sulphate of Potassium (SOP)

Production of SOP by the double salt decomposition, Glaserite process. In this process sodium sulphate is reacted with potassium chloride to yield potassium sulphate. This reaction occurs in two steps as follows:

4 Na2SO4 + 6 KCl = Na2SO4.3K2SO4 + 6 NaCl [11]

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2 KCl + Na2SO4.3K2SO4 = 2 NaCl + 4 K2SO4 [12] This process route is cheaper than the Mannheim process (thermal oven process) and it makes sense if the sulphate is

available and cheap.

3.3. Production of Silicon Tetrafluoride (STF)

STF product of reactions [2] [7] is dried, purified and compressed into pressure cylinders for transportation to the polysilicon plant, if required or better polysilicon plant is built at site.

3.4. Production of Sodium Sulphate (SSF)

Sodium sulphate product of reaction [7] can be purified using a crystallization process to obtain the quality required for the final applications of SSA in detergents, paper, glass, etc

3.5. Production of Silica

Byproduct silica can be used in the defluorination process of phosphoric acid or defluorination process of sulphuric acid, production of water glass, production of precipitated silica, production of zeolites, production of cements or used as soils conditioners.

4. Conclusion

Fluorine chemistry is basically a good solution for adding value to the phosphate downstream products. No doubt, economics are good as raw materials are available almost free of charge. It is only a matter to discuss how

good are the economics? What are the best options to be selected?

Presently as the costs of raw materials are escalating, environmental issues are every day of bigger concern, expertise is accessible, technologies are affordable in cost-effective manner and from us particularly, barriers between the various industrial sectors are not anymore a brake (between fluorine industry and other industrial sectors such as fertilizers, aluminium, cement, solar and polysilicon, etc), then great opportunities for cooperation are in front of us. Hoping in future cooperation.

These new fluorine technologies are real innovations for the fertilizer industry and surely they will be implemented progressively. More and more projects are under study and hopefully some projects might be realized in the near future.

References

[1] EFMA. (2000). Production of phosphoric acid, Best available techniques for pollution prevention and control in the European fertilizer industry, booklet No. 4 of 8.

[2] Flemmert, G. L. (1974). US3969485 Process for converting silicon-and-fluorine-containing waste gases into silicon dioxide and hydrgen fluoride. [3] HeQing. (2005). The situation and development of resource of fluorspar in China. Some thinking of fluorspar industry by CFIC. Fluorspar 2005. [4] Houston, T. T. (1962). US 3218125 Process of producing hydrgen fluoride from fluosilicic acid in a two-stage procedure. Tennessee Corp. [5] IFA. (2009). http://www.fertilizer.org/ifa/HomePage/STATISTICS/Production-and-trade. [6] Jasinski, S. M. (2011). Phosphate rock, U.S. Geological Survey, Mineral Commodity Summaries, January 2011. [7] Kauwenbergh, S. V. (2010). World phosphate rock reserves and resources. Center for Strategic and International Studies, September 22, 2010. IFDC. [8] Kelley, C., & al., A. G. (1971). U 3758674 Process for producing anhydrous HF. Wellman Power-Gas Inc. [9] Miller, M. (2010). Fluorspar. USGS. [10] Miller, M. (2010). Fluorspar, U.S. Geological Survey, Mineral Commodity Summaries, December 2010. USGS. [11] Oakley, L. C. (1962). US3218124 rocess of producing hydrogen fluoride a s a dry gas from clear fluosilicic acid-containing solutions. Tennessee

Corp. [12] ResearchInChina. (2010). Fluorspar report annoucement on ResearchInChina Website. ResearchInChina. [13] Reynolds, M. (2010). Aluminium Fluoride (AlF3) - A market striving towards equilibrium. Aluminium International Today , January,] February. [14] Weinrotter, F. (1963). Fluoride of aluminium as by-product of superphosphate manufacture. ISMA Technical Conference. Helsinki, Finland, 3-5

September 1963: IFA. [15] Will, R. (2010). China and the shift in the fluorochemical value chain. Fluorspar 2010. [16] Zawadzki, B. (1977). US4062930 Method of production of anhydrous hydrogen fluoride.