FERTILIZER INDUSTRY. Fathi Habashi Department of Mining and'metallurgy Laval University, Quebec City Canada G1K 7P4 ABSTRACT

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1 SOLVENT EXTRACTION IN THE PHOSPHATE FERTILIZER INDUSTRY Fathi Habashi Department of Mining and'metallurgy Laval University, Quebec City Canada G1K 7P4 ABSTRACT The recovery of uranium from wet process phosphoric acid was applied on industrial scale in the 1940's by using octylpyrophosphoric acid as an extractant. Later, more efficient reagents were used, e.g., di(2-ethylhexyl) phosphoric acid and actylphenyl phosphoric acid. In the 1970's the rare earths in Kola phosphate were recovered in Finland and recently (1997) in Norway using HNO, as a leaching agent and di(2-ethylhexyl) phosphoric acid as solvent. It was demonstrated later on laboratory scale that both uranium and rare earths could be extracted from the rock by tributyl phosphate but at different ph values provided that the rock is leached with nitric or hydrochloric acids instead of the commonly used sulfuric. This new concept opens the way to the possibility of treating phosphate rock by in-situ, dump, or vat leaching for the recovery of phosphate values as well as uranium and the rare earths. Another solvent extraction process is used industrially for the purification of phosphoric acid using butyl and amyl alcohols. EPD Congress 1998 Edited by B. Mishra The Minerals, Metals &Materials Society,

2 INTRODUCTION Phosphate rock is the major source of phosphorus in nature. It exists mainly in the form of hydroxy and fluorapatite, Ca,,(PO,),(OH), and Ca,,j(PO,),F, respectively, or a mixture of both. About 100 million tons of rock are treated annually mainly for the production of fertilizers and a minor amount is used in the detergent and food industries [l Phosphate rock is of two types:,. Sedimentary. This represents about 90% of the world reserves and is characterized by containing about 100 ppm uranium and minor amounts of rare earths. An example of this type is in Florida,. North Africa, and the Middle East. Igneous. This represents the remaining 10% the world reserves arid is characterized.. by containing about 1 to 2% rare earths and negligeable amounts of uranium. An example of this type is in the Kola Peninsula and in Brazil. Phosphate rock also contains about 3% of fluorine, traces of cadmium, and the decay products of uranium of which radium is the most important because of its long half life of about' 1600 years. The problem with radium is. its disintegration to give radon gas which has a short half life of 3.8 days, and this in turn disintegrates to yield radioactive polonium which is a solid. Hence coming in contact with radium may result in deposition of radioactive decay products in the lungs because of the radon gas. There are two main routes for processing the rock depending on the final use: The route to fertilizers is based on the acidulation of the rock with either H,SO, or HNO, followed by ammoniation to produce ammonium phosphates. The product contains most of the impurities in the rock. The route to phosphorous compounds for other industries is based on: Purification of the solutions obtained by aciduating the rock, mainly by extaction with organic solvents. Reduction of phosphate rock in an electric furnace to get elemental phosphorus, which is then oxidized to P205 and this is then dissolved in water to form pure phosphoric acid.. The electric furnace process is energy intensive, polluting, and requires extensive maintenance. It is now being gradually displaced by the process based on acidification followed by purification. during the purification step, it is possible to recover ~iranium, rare earths, and fluorine, and reject radium, cadmium, and other undesirable components. Solvent extraction plays an important role during these processes.

3 Production of normal superphosphate SULFURIC ACID ROUTE The first fertilizer produced from phosphate rock was normal superphosphate. The ground rock was mixed with a limited amount of sulfuric acid and left to react slowly for few weeks to transform it into a water soluble phosphate available to the plants: Ca,, (PO4)$, + 7 H2S H,O -, 3Ca(H,PO4),.H2O + 7 (CaS04.2H20) + 2 HF normal supelphosphate Although the product had a low phosphorus content (18-20% P205), it was the major phosphate fertilizer produced for many years. Subsequent process improvements took place later when excess acid was deliberately added during mixing with the rock to accelerate the curing step; the excess acid was then neutralized by ammonia: Ca (H,PO4),.H,O + CaSO, + 2 NH, -, 2 CaHPO, + (NH,), SO4 + H20 Despite such improvements, the phosphate content of such products was relatively low which affected transportation charges. The emphasis today is to produce fertilizers containing high concentrations of nutrients. The production of phosphoric acid At present the principal route for treating the rock is by reaction with excess acid to liberate phosphoric acid and to reject the calcium as calcium sulfate, generally in the form of gypsum according to: The phosphoric acid is then concentrated by evaporation, and then neutralized with ammonia to produce mono or diammonium phosphates fertilizers, which typically contain 52 and 46% P20, respectively. Production of triple superphosphate With low grade phosphate rock, the phosphoric acid produced is reacted further with another batch of the rock to produce a product called triple superphosphate containing 40-48% p205. Problems associated with phosphoric acid production This route has the disadvantage of producing enormous quantities of gypsum contaminated with radioactive products. This requires a large space for disposal and

4 continuous monitoring to insure that the ground water is not contaminated with radium and fluorine compounds. Also there is always the environmental hazard due to the emanation of radon. Impurities in phosphoric acid There are two types of phosphoric acid produced by the sulfuric acid route: Black acid which is more common and its black color is due to the organic matter originally present in the rock. Green acid is free from organic matter and is produced from rock that was calcined in an oxidising atmosphere. Phosphoric acid contains all of uranium originally present in the rock, about one third of the lanthanides, appreciable amounts of sulfates, fluorides, and fluorosilicates as well as large amounts of metallic impurities such as iron, aluminum, calcium, magnesium, and sometimes appreciable amounts of vanadium. Toxic metallic impurities such as cadmium and arsenic may also be present. The presence of such impurities is undesirable because they lower the quality of the fertilizer produced from such acid, increase the acid viscosity, and cause formation of slow - settling sludge. They also cause a loss of ammonia due to the formation of insoluble metal ammonium phosphates when the acid is ammoniated. The recovery of fluorine is a step forwards for conservation of natural resources and for expansion of fluorine reserves, since the only other source is fluorspar. Fluorine can be removed and recovered quantitatively as sodium fluorosilicate, Na,SiF6, according to the reaction: 2 Na' + SiF2- + Na,SiF6 Purfication of phosphoric acid by organic solvents.. Organic solvents such as sec-butanol, iso-butanol, tributyl phosphate, or a mixture of tributyl phosphate and isopropyl alcohol, extract phosphoric acid leaving uranium and other impurities behind in the aqueous phase. Uranium can be recovered from the raffinate by precipitation with ammonia, and the alcohol recovered from the organic phase by distillation leaving the purified acid behind (Figure 1) [9,10]. NITRIC ACID ROUTE The use of nitric acid.instead of sulfuric acid for treating phosphate rock, has the following advantages [l 11: It eliminates the problems associated with gypsum. The acid is used both for dissolution of phosphate rock and for the addition of nitrate nutrient to the fertilizer product. Adoption of nitrophosphates has increased rapidly, especially in Europe. Such that today production of complex fertilizers produced by this route represents about 10% of the total fertilizer production. Two major processes are used:

5 Analysis D~stribut~on Techinical H3PO ( Defluorination 1 t 2xl50mL rec.butanol Extraction Organic phme (2 rtegesl containing "3" Solids: Filtration Phosphates of Al. Fe. Mg. I rare earths + I (11 gl NH40H Solution or'fe po-r (WmL) Precipitation Solution for production 1 of fertilizers (50 mlwith Uranium washings) concentrate ( ~ 1, ~ 2.Sg) 0 ~ ~ * Originally 7 ml. washings added. and volume diusted to 50 ml Figure 1 - Purification of phosphoric acid by organic solvents [9] Attack of the rock by nitric acid of 65-70% concentration to produce monocalcium phosphate and calcium nitrate: Ca,, (PO4)$, + 14 HNO, + 3 Ca(H2PO4), + 7 Ca(NO,), + 2 HF Dissolution of rock in nitric acid (50%-60% HNO,) to form phosphoric acid and calcium nitrate: Ca,, (P04),F HNO, -D 6 H3P Ca(NO,), + 2 HF

6 Phosphate Rock HN03 4 DIGESTION t Residue COOLING 1 I NH, P~~Cn'ITATION Ammonium Phosphate Removal of calcium nitrate Ammonium Nitrate Figure 2 - Treatment of phosphate rock by nitric acid Calcium nitrate must be removed because of its hygroscopic character. At least two methods are used: Crystallization This is the most important method and is used by Norsk Hydro and BASF. It involves cooling the solution to C; about 60% of the calcium nitrate crystallizes as tetrahydrate, Ca(NO,),-4H,O. Further cooling to -5 C will enhance the crystallization process up to 85 %. The remaining calcium in the solution is ammoniated according to the following equation: Calcium nitrate is usually converted to the carbonate which is easier to store Ca(NO,), + 2 NH, + CO, + H,O + 2 N&N03 + CaCO, The ammonium nitrate solution can be separated from the calcium carbonate by filtration (Figure 2).

7 Phosphate DIGESTION I FILTRATION * Residue Amy1 Alcohol r 1 AMMONIATION PRECIPITATION FILTRATION Alnmonium Phosphate Solvent extraction Ammonium Nitmte Figure 3 - ~xtractioi of nitrophosphate solution with tertiary amyl alcohol This process involves extracting the acid from the leach solution with tertiary amyl alcohol leaving behind calcium nitrate. The loaded organic phase is then ammoniated directly to precipitate ammonium phosphate as a high grade fertilizer and to regenerate the solvent for recycle. Calcium nitrate in the raffinate is then converted to ammonium nitrate. This process was developed by the Finnish Company Typpi Oy (Figure 3) [12]. Recovery of uranium and the lanthanides Uranium and the lanthanides can be recovered from the nitric acid leaching process without interfering with the production of fertilizers as follows : Crystallization of calcium nitrate route After the removal of calcium nitrate crystals, the solution now contains the phosphate values, uranium, the lanthanides, radium, and fluorine. It can be processed as follows : The solution is extracted with tributyl phosphate in two stages. In the first stage all of the uranium and about half of the lanthanides are extracted together with other impurities. The organic phase is then scrubbed with a limited amount of hot water to remove the impurities together with the lanthanides, leaving behind the uranium. Uranium is then stripped from the organic phase by hot water, and precipitated from the solution by ammonia. Uranium recovery is about 93 % (Figure 4).

8 Phosphate rock (Ba, Ca) SO. Water Hot water concentrate Ammonium Ln,O, phosphate concentrate Figure 4 - Recovery of uranium and the lanthanides from nitrophosphate solutions [ll] The raffinate is then adjusted to ph 1 by ammonia and the lanthanides are extracted with tributyl phosphate. They are then stripped with 0.05 M HNO,. This strip solution, combined with the scrub solution of uranium extraction is subjected to precipitation by oxalic acid. The oxalates are then washed and ignited to an oxide concentrate containing all the lanthanides in the phosphate rock. A modified route from the one mentioned above would be in combining the organic phases' from the first.and second stages, scrubbing to remove the lanthanides, then stripping to remove the uranium. In both cases, the solution can be defluorinated by adding a calculated amount of NaNO, followed by filtering off Na,SiF,, and radium can be removed by adding a dosed amount of barium nitrate followed by an equivalent amount of potassium sulfate to precipitate a barium calcium sulfate which is filtered off.

9 100 T Phosphate rock Leaching Gangue t Tertiary amyl alcohol + HN03 (0.05 M) Ammonium Raffinate nitrate solution Stripping Extraction /C\ Triburyl phosphate A Oxalic a c i d L Precipitation, TNf nitrate ~mminiu& C~(NO&~H~O 4 Ammonium Calcination Ammoniation calcination phosphate fertiliser (high grade) 1 Concentrate containing Ammonium Concentrate 13% Ln103 phosphate containing 87% CaO fertiliser - 0.8% U TRACE PIOS (low grade) t Figure 5 - Recovery of uranlum, the lanthanides, and ammonium phosphate using tertiary amyl alcohol [I21 Solvent extraction route A closer study of the amyl alcohol extraction process mentioned above, revealed the following [12]: Uranium was co-extracted with the alcohol while the lanthanides were not. Uranium could be recovered from the loaded alcohol by stripping with 50% ammonium nitrate, then precipitation with ammonia. After removing the uranium, the loaded alcohol could be ammoniated to produce nitrophosphate fertilizer without the need for separation of the intermediate phosphoric acid. The lanthanides were recovered from the raffinate by extraction with tributyl phosphate.

10 PHOSPHATE ROCK LEACHING IFILTRATION - RESIDUE B0ClZ RADIUM REMOVAL URANIUM EXTRACTION STRIPPING FILTRATION I I w URANIUM ~"i-7 1. LANTHANIDE RECOVERY FILTRATION AMMONIUM euneeuntc LANTHANIDE CONCENTRATE FILTRATION PURE CO SO4. 2H20 Figure 6 - Treatment of phosphate rock with hydrochloric acid [I31 t NH3 1 CONCENTRATE 100 k PHOSPHORIC EXTRACTION ACID STRIPPING TRlBUTYL PHOSPHATE Based on the data acquired, a process for the production of ammonium phosphate fertilizer and at the same time the recovery of uranium and the lanthanides was proposed (Figure 5). In this process the rock is solubilised in nitric acid and after separation of the insoluble silica gangue, the nitrophosphate solution is extracted with tertiary amyl alcohol. The alcohol is then washed with ammonium nitrate solution to remove the uranium, then treated with NH, to precipitate ammonium phosphate; it will then be ready for recycle. The raffinate containing the lanthanides and the bulk of impurities is extracted by uibutyl phosphate to recover the lanthanides.

11 HYDROCHLORIC ACID ROUTE Like nitric acid, hydrochloric acid will solubilize all the phosphate rock except siliceous gangue minerals [13]: Ca,, (PO,),F, + 20 HCl + 6 H3P CaC1, + 2 HF From an economic stand point, this process can only be used where hydrochloric acid is available as a by-product. Like nitric acid route, hydrochloric acid route has similar advantages, i.e., the absence of calcium sulfate disposal and the possible recovery of fluorides, uranium, and the lanthanides. Treatment of leach solution Two methods can be used for the recovery of phosphoric acid, uranium, and lanthanides. Extraction of phosphoric acid with isobutyl alcohol leaving calcium chloride with substantially all the impurities in the raffinate. The loaded organic phase is then stripped with water to produce pure phosphoric acid, while the solvent is recycled back to the extraction unit. Extraction of uranium with 5% solution of tributyl phosphate in hexane or Varsol followed by extraction of phosphoric acid by undiluted solvent (TBP) leaving behind most of the impurities together with calcium chloride and the lanthanides. The lanthanides can be precipitated from the raffinate by ammonia, and radioactivity-free gypsum by sulfuric acid to regenerate hydrochloric acid for recycle. Proposed process Based on these data the following process was proposed (Figure 6) : Phosphate rock is leached with the stoichiometric amount of HCl at 40'C, then filtered to remove the insoluble residue. Sodium chloride is added to the solution to precipitate sodium fluorosilicate which is removed by filtration. Barium chloride and sodium sulfate are added consecutively to remove radium by copprecipitation with barium sulfate. Uranium is extracted from solution by 5% tributyl phosphate in hexane or Varsol. The organic phase is stripped with ammonia to precipitate uranium and regenerate the tributyl phosphate for recycle. Phosphoric acid is then extracted by undiluted tributyl phosphate. The organic phase is scrubbed with a small amount of water to remove any chloride ion co-extracted. The organic phase contains all the phosphate values present in the rock. This can be recovered by precipitation with gaseous NH, and filtration to regenerate tributyl phosphate for recycle. The aqueous phase can be treated by NH, to precipitate the lanthanides. After filtration, H,SO, may be added to precipitate pure gypsum and regenerate hydrochloric acid for recycle.

12 line Figure 7 - In situ leaching of ores [22] IN SITU, DUMP, AND VAT LEACHING OF PHOSPHATE ROCK The work conducted at Lava1 [ was to propose to the phosphate industry, a technology widely used in the hydrometallurgy of nonferrous metals, namely, in situ, dump, and vat leaching. Applying in situ leaching technology, also known as solution mining, to extract phosphate values from the deposit without transportation of the rock, and to find ways to recover these values from solution as a concentrate suitable for shipping to processing plants or for export is new to the phosphate industry. In situ leaching, is used extensively for recovering copper, uranium, potash, and other salts (Figure 7). A similar technology is used for extracting sulfur from underground by the Frasch Process since the beginning of this century, and extensive testing has been carried out recently for the recovery of coal by underground gasification. Dump and vat leaching is used for copper, uranium and gold ores. These methods would be particularly suitable for phosphate deposits, involving excessive material handling and clay settling problems. When treating phosphate rock by these methods it will not be possible to use the common and the cheapest acid, H2S0,, because gypsum formed during leaching will block its passage. Therefore, HC1 and HNO, must be used. These acids, although expensive, have the advantage of solubilizing rapidly not only P20, content of the rock but also the uranium, the lanthanides, and the radium present, hence their recovery.or disposal (in case of radium) can be conducted. 212

13 BED VOLUMES BED VOLUME Figure 8 - Effect of acid concentration on column leaching of phosphate rock [14] Leaching When allowing HC1 or HNO, of different concentrations to percolate through a static bed of phosphate rock the following observations can be made: There is an optimal acid concentration for which the recovery of P205 is maximum. In the case of HC1 this maximum is at 10% and for HNO, at 20% as shown in Figure 8. The existence of this optimal concentration can be explained by the formation of moncalcium phosphate at low acid concentration according to: and phosphoric acid at high acid concentration according to: Phosphoric acid formed at the top of the bed reacts further with apatite on its descent to form dicalcium phosphate which is insoluble in water and therefore is retained in the bed : When conditions are favourable for the formation of monocalcium phosphate, recoveries of P,O, are more than 90%. A typical analysis of leach solutions of 10% HCl and 20% HNO, is shown in Table 1, from which the remarkable low concentration of fluorine in solution can be noted (wet process phosphoric acid contains g/l). This seems to be due to the nature of the leaching process (no agitation, ambient temperature, and percolating solution) which favours the formation of insoluble fluorine compounds, e.g., CaF, which are retained.in the bed.

14 -- Table 1 Analysis of phosphate rock leach solutions - ~ g/l 10% HCI route 20% HNO, route Recovery from leach solution Since P205 values in the leach solution are mainly in the form of monocalcium phosphate, crystallization in solar ponds was considered as a suitable route for recovery. On evaporating HC1 leach solution the double salt calcium chloride phosphate CaCI2.Ca(H2PO4),.2H20 (or CaC1HP04.H20) is obtained and from HNO, leach solution, the double salt Ca(N03), Ca(H2P04),.2H20 (or CaN0,H2P04.H20) known as nitrate phosphate. The double salts are soluble in water but are always contaminated by a small fraction (about 10%) of insoluble dicalcium phosphate, CaHPO, and CaHP04.2H,0. After separating the crystals, the mother solution contained mainly CaCl, or Ca(N03), depending on the acid used. Phosphate values The double salts can be decomposed at low temperature (200"-250 C) to form dicalcium phosphate and acid vapours as follows: CaC1H2P04.H20 + CaHPO, + HCI + H20 In this operation, the acid vapours can be condensed or washd with water for recovery, while the residue which typically analyzes 40% P205 can be marketed as a high grade phosphate product. Uranium and lanthanides Uranium and lanthanide can be extracted from the leach solutions prior to P205 recovery. Nitrate system. Uranium can first be extracted by a mixture of di-2-ethyltiexyl phosphoric acid (D2EHPA) and tributyl phosphate (TBP) in hexane. No lanthanides were coextracted. The concentration of the extractant in the organic please was critical since dilute solutions in hexane were less effective. The loaded organic phase was scrubbed with the least amount of distilled water to remove co-extracted impurities then the organic phase was stripped 214

15 10% HCI or 20% HNO, 1 extraction uranium I 1-b lanthanides 40% acid recovery condensation 60% acid recovery crystallization double salt decomposition 250 C regeneration v f CaHPO, product CaSO,. 2H,O 40% P,O, - - (rad~um-free) 'to dis~osal' Figure 9 - Proposed process for in-situ, dump, or vat leaching of phosphate rock [14] + filtration with 10% ammonium carbonate solution to form ammonium uranate precipitate. The organic phase therefore could be recycled to the extraction stage. The extraction of lanthanides was possible by TBP alone; 100% of lanthanides were removed in the organic phase and were stripped by dilute HNO, in two stages at aqueous organic ratio 111. The lanthanides in strip solution were precipitated by 12% oxalic acid, the precipitate was then calcined at 1200 C to yield a concentrate analyzing 12% Ln203 and 88% CaO. The weight of product represents 2% of the original weight of phosphate rock leached. Chloride system. Uranium can be extracted by a mixture of D2EHPA and TBP diluted with hexane. No lanthanides were co-extracted. The concentration of the extractant in the organic phase was also critical. Stripping of uranium and its recovery from strip solution was possible as in the HNO, system. The lanthanides were extracted from solution after the removal of uranium by D2EHPA diluted with toluene. Proposed process Based on these data the following process was proposed (Figure 9). Phosphate rock is leached with 10% HCl or 20% HNO, in situ, in dumps, or in vats to get a solution of monocalcium phosphate. The solution is then crystalized to get the double salts CaClH2P04-H20 or Ca(N03)H2P04.H20 depending on the acid used. The crystals are then separated and decomposed at C to get dicalcium phosphate product. In this operation, about 40% of the acid required for the leaching step is recovered for recycle. The remaining 60% can be regenerated by reaction of the mother liquor with H2S04:

16 CaCI, + H,SO, + 2 HCl + CaSO, Ca(NO,), + H,SO, + 2 HNO, + CaSO, To get a radioactivity-free gypsum, radium must be separated in an earlier step. this can be readily achieved by adding SO:' ion followed by a calculated amount of BaCl, solution and filtering off the precipitate formed. To recover uranium and the lanthanides, two solvent extraction steps should be incorporated before the crystallization step using the proper solvents. If in situ leaching used, then the cost of removing the overburden, mining, beneficiation, disposal of tailings and slimes are eliminated. On the other hand, the technology of in situ leaching must be mastered. Since this technology can be readily transferred from the metal industry, it is believed that the overall economics will be favourable. CONCLUSIONS To overcome the problems associated with the generation' of large amounts of radioactive gypsum, phosphate rock must be leached'with nitric or hydrochloric acids instead of sulfuric acid commonly used. This procedure has the following advantages : It permits the recovery of all the lanthanides which would otherwise be lost in the gypsum. The recovery of uranium could also be recovered without interferring with the manufacture of fertilizers. It permits the utilization of in situ, dump, or vat leaching technologies commonly used in hydrometallurgy for leaching copper, gold, and uranium ores, and known to be highly economical. It permits the removal of radium in a controlled way. Numerous organic solvents are available for the extraction of uranium and the lanthanides from the leach solutions as well as for obtaining purified phosphoric acid. References 1. F. Habashi, "Trends in Fertilizer Technology and its impact on the Environment", Materials & Society 9 (3), (1985). 2. F. Habashi, "Sulfur and the Fertilizer Industry", Arab Min. J. 5 (2), (1985). 3. F. Habashi, "The Recovery of Uranium from Phosphate Rock. Progress and Problems", Proc. Intern. Congr. Phosphom Compounds, pp , Institut Mondial du Phosphate, Paris, 1980 (Publ. 1981). 4: F. Habashi, "The Recovery of the Lanthanides from Phosphate Rock", J. Chern. Techn. & Biorechn. 35~. (I), 5-14 (1985). 5. M. Zailaf, "Recovery of Lanthanides from Phosphate Rock", M.S. Thesis, Lava1 University (1986).

17 F.T. Awadalla, "Recovery of Minor Elements from Phosphate Rock", Ph.D. nesis, Lava1 University (1987). F. Habashi and F.T. Awadalla, "The Removal of Fluorine from Wet Process Phosphoric Acid", Separation Sci. & Tech. 18 (3, (1983). F. Habashi, K. Naito, and F.T. Awadalla, "Crystallization of Impurities from Black Phosphoric Acid at High Temperature", J. Chem. Techn. & Biotechn. 33(A), (1983). F. Habashi and F.T. Awadalla, "The Recovery of Uranium During the Purification of Phosphoric Acid by Organic Solvents", Separation Sci. & Techn. 21(4), (1986). F.T. Awadalla, and F. Habashi, "The Removal of Radium During the Production of Nitrophosphate Fertilizer", Radiochimica Acta 38, (1985). F. Habashi, F.T. Awadalla, and M. Zailaf, "The Recovery of Uranium and the Lanthanides from Phosphate Rock. J. Chem. Techn. & Biotechn. 36, (1986). F. Habashi and F.T. Awadalla, "The Recovery of Uranium and Lanthanides During the Production of Nitrophosphate Fertilizers Using Tertiary Amy1 Alcohol", J. Chem. Techn. & Biotechn. 36, 1-6 (1986). F. Habashi, F.T. Awadalla, and Xinbao Yao, "The Hydrochloric Acid Route of Phosphate Rock", J. Chem. Techn. & Biotechn. 37, (1987). F. Habashi and F.T. Awadalla, "In-situ and Dump Leaching of Phosphate Rock", Ind. & Eng. Chem. Research 27, (1988). F.T. Awadalla and F. Habashi, "Extraction of Uranium and Lanthanides from the Systems Ca (NO,), - Ca (H2P04),- H,O and CaCl, - Ca (H2P04),- H2OW, Ind. & Eng. Research 28, (1989). F. Habashi, "A New Approach to Phosphate Processing", Phosphorus & Potassium NO. 193, (1994). F. Habashi, "New Horizons for the Phosphate Fertilizer Industry", Arab Min. J. 12 (I), (1994), Arabic Summary ibid. p. 26. F. Habashi, "Phosphate Fertilizer Industry Processing Technology", Ind. Minerals 3 18, (1994). F. Habashi, "A New Approach to the Processing of Phosphate Rock", Tema Tecnologia e Materiois (CETEM, Rio de Janeiro) 2 (3/4), 1-4 (1996). F. Habashi, "In-situ, Dump, and Vat Leaching of Phosphate Rock", pp in Process lntensflcarion Symposium, editors C.A. Pickles et al., Canadian Institute of Mining, Metallurgy, and Petroleum, Montreal 1996.

18 2 1. F. Habashi, "The Recovery of Uranium and Rare Earths from Phosphate Rock", pp in Proceedings 2gh Annual Meeting of Canadian Mineral Processors, CANMET, Ottawa F. Habashi, A Textbook of Hydrometallurgy, Lava1 University Bookstore, Cite Universitaire, Quebec City, Canada G1K 7P4