GB2069987A - Heat treating phosphate rock - Google Patents

Abstract

Phosphate rock is heat treated at 380-600 DEG C to convert the organics to filterable carbon and the rock converted to wet process phosphoric acid of reduced colour and with reduced foaming. The acid may be converted into fertilizers, calcium or alkali metal salts or may be purified to recover its acid or uranium contents. Super phosphates or triple superphosphates may also be made. Rocks having high acid soluble organics but low total organics, and rocks containing a high content of acid insoluble heat labile iron sulphide are especially suitable.

Description

SPECIFICATION Rock treatment process This invention relates to a thermal treatment process, in particular a thermal treatment of phosphate rock.

Calcium phosphate rock contains many impurities, among which are organic compounds e.g.

humic acid. The organic impurities can cause severe foaming when the rock is treated with acid to form calcium sulphate and wet process phosphoric acid and also gives rise to coloured downstream products e.g. phosphoric acid and alkali phosphate salts. It is known to remove the organics by active carbon treatment or use of oxidising salts on the phosphoric acid or salts therefrom or by calcination of the rock.

In the calcination, the rock is usually burnt to convert the organics to carbon dioxide to leave a calcined rock substantially free of organic carbon, and suitable for conversion to down stream products; temperatures of 7500C or above are useful for this calcination. The foaming characteristics can be removed by prolonged heating at temperatures above 6500C without necessarily complete oxidation of the organic compounds (see Chem. Eng. Progress Vol. 58 1962 pages 91-93).

We have found that by thermal treatment of the rock at lower temperatures than described above, the organic compounds can be at least partly, and usually substantially converted into insoluble particulate carbon, which can be filtered with the calcium sulphate in the subsequent acidification to form wet process phosphoric acid.

The present invention provides a process for treating phosphate rock wherein phosphate rock comprising organic compounds is heated at 380--600"C to convert at least some of the organic compounds to carbon to produce a heated rock comprising carbon particles. Preferably said heated rock comprising carbon particles is reacted with a mixture of sulphuric acid and phosphoric acid to form a solid fraction comprising calcium sulphate and carbon particles and wet process phosphoric acid, and the acid is separated from said solid fraction. The phosphate rock is heated at a temperature sufficient to convert at least some of the said impurities and preferably substantially all of them, to particulate carbon but insufficient to cause burning of all the carbon to an oxide of carbon so that the treated rock contains carbon particles.When the treated rock is reacted with the acid there is formed a mixture comprising phosphoric acid, sulphuric acid, calcium sulphate usually as gypsum, carbon particles and usually a little unattacked rock; the mixture may be filtered to leave a wet process acid free of carbon particles, and of significantly reduced colour e.g. yellow rather than the deep brown of acid from some untreated rocks.

The heating of the phosphate rock by the present process may enable the reaction with the acid to proceed more satisfactorily, with less or no foaming than if untreated rock is attacked so that the acidification is advantageously carried out in the substantial absence of any anti-foaming agent. The reaction with rock may also be carried out with a faster filtration rate and rate of attack of the rock than if rock calcined at 9500C is attacked. Furthermore the heating in the present process reduces or eliminates the need for use of active carbon or oxidizing agents on the acid or salts therefrom to reduce their colour. The lower temperature heating also represents a significant economic advantage.

The rock is heated at a temperature of at most 6000C i.e. 380--6000C, such as 450-6000C and especially 51 0-5900C or 450--5500C e.g. 460-5400C; temperatures of 380-5000C e.g.

380-4800C and especially 380--4400C or 420-4800C may be used but the rate of conversion of the organics to carbon is slower than at higher temperatures. The rock is usually heated at the given temperature for 0.01-10 e.g. 0.1-10 hours and preferably less than 2 hours e.g. 0.6-2 hours for batch processes or 1 niin-1 hour e.g. 2-40 minutes for continuous processes inversely depending on the temperature. The time and temperature are chosen so that preferably at least 30% of the organic compounds are converted to carbon and especially at least 80% of the organics.Particular useful combinations are 40 mins to 2 hours at 450--5500C for Florida or Zin or Oron rock for batch processes or 1 5 mins to 2 hours e.g. to 1 hour at 450-5500C for continuous processes, while for Moroccan (e.g.

Khourigba white Youssoufia) rocks 30 mins to 2 hours at 380--4400C for batch processes or 1 5 mins to 2 hours e.g. 1 5 mins to 1 hour at 380--440"C for continuous processes are preferred. 380-4400C is also advantageous for rocks from Syria, Senegal, Algeria, Jordan while 560--5900C is useful for black Youssoufia rock.

Preferably when the rock is heated in the 460--5400C region it is not of Egyptian origin if the heating is at 490--5100C nor of Russian if it is at 490--5400C and not of Florida origin if the heating is at 490--5400C unless the heat treatment is a continuous rather than batch wise operation. When the rock is heated at 510590 C, it is preferably not of Utah or Morocco origin if the heating is at 540--5600C or of Russian origin if the heating is at 510--5400C and when the heating is at 4400--460" the rock is preferably not of Utah or Morocco origin.In the cases of the Egyptian, Russian, Florida, Utah and Moroccan rocks, the above temperatures may be used in continuously operated process. A mixture of rocks may be used.

While conventional calcination at 650"C or above gives a significant amount of hydrogen fluoride in any gaseous effluent from the heating, the heating at the lower temperature of this invention gives much less fluoride, often substantially no fluoride in the effluent rendering easier the purification of that effluent. The heating treatment may be carried out under essentially anaerobic conditions with essentially no free oxygen (or other agent capable of oxidizing the organic impurities); thus the rock may be externally heated in the absence of air e.g. in an oven with exclusion of air.However, advantageously the rock is heated in the presence of a gas comprising molecular oxygen e.g. air or combustion gases comprising air, and in the absence of added organic compounds and in the absence of oxidants (apart from oxygen) capable of oxydizing the organic impurities; added Chlorine and/or hydrogen chloride are preferably absent from the gas. The rock may be heated e.g. by an oxidizing flame in a kiln to the requisite temperature. The heating may be carried out with a defiency of oxygen relative to the amount needed to convert the organic impurities to carbon, but preferably at least the required amount and especially an excess is used. The conditions are usually sufficient to give a heated rock comprising carbon particles and substantially no acid soluble organics (as hereinafter defined) and often substantially no other organic compounds.

The heat treatment is preferably continuous so that the rock is passed continuously through at least one heated zone at 380 -600 C in order to convert at least some of the organic compounds to carbon and a heated rock comprising carbon particles is withdrawn and usually allowed to cool.

The heating is usually carried out at 380-6000C without subsequently raising the temperature higher than 6000 C; the temperature of the rock is then reduced. Preferably a rotary kiln is used with co-or countercurrent flow of rock and hot gases e.g. the hot combustion products of a flame, or the rock may be mixed with fuel and the fuel burnt and rock heated at the same time during passage of rock and fuel through a calciner. Alternatively a fluidised bed of rock and hot gases may be used or the rock in a layer may be passed continuously under a flame or through an externally heated zone. Ring ovens or tunnel ovens may also be used.While the heat treatment may be carried out on a large particulate rock the rock is preferably at less than 5 mm size, and preferably is ground first e.g. to a size of 0.1-1 mm e.g. with at least 50% of 0.01-0.5 mm and preferably with less than 30% of less than 0.1 mm.

The rock may contain 0.56% e.g. 0.05-1.0% or 0.5-6.0% or 1.06% organic material (expressed by weight as organic carbon) as well as conventional rock impurities. The rock may thus contain (by weight) 15-45% P205 e.g. 25-40% P205, 25-35% or 30-40% or especially 30-35% P205, 25-55% e.g. 45-55 or 50-55% Ca expressed as CaO, 0,01-8% e.g. 0.05-0.5% or 0.55% Fe203 with a total iron and aluminium content of e.g. less than 10% e.g. less than 4% by weight (expressed as Fe203 and Al2O3) and 1.07% e.g. 1-3.5% or 3.5-7% carbonate (expressed as CO2).The invention is particularly suitable for treating apatite phosphate rocks e.g. those which on digestion with 27% hydrochloric acid form brown liquids; examples of such rocks are those from Zin in Israel, and Florida. However other rocks e.g. those from the US Western States e.g. Idaho, or elsewhere such as North Carolina, Tennessee, Tunisia, Jordan, Morocco (e.g. Youssoufia), Algeria, Senegal, Kola, Nauru or Oceania may also be treated. The phosphate rock preferably contains 0.05-0.4% organics, or a weight ratio oforganics to P205 of0.001-0.1 :1, rocks with a low organic content such as those from Zin (Israel), Khouribga (Morocco), El Massa (Jordan), Algeria, Tunisia, Senegal or Oron (Israel).The process is particularly suitable for treating rocks which contain acid soluble organics (as hereinafter defined). The term "acid soluble organics" as used in this specification means organic compounds found in phosphate rock, which are of such a nature and in such an amount, that on digestion of the rock with a mixture of 56% sulphuric acid and 20% thermal phosphoric acid, (said mixture containing enough sulphuric acid to convert the calcium oxide content of the rock into calcium sulphate), to form a suspension in a liquid containing 25-30% P205, contains at least 600 ppm (e.g. 600-60,000 ppm) dissolved organics (expressed as total carbon) i.e. a weight ratio of dissolved organics (expressed as total carbon) to P205 in the liquid of at least 0.002:1 e.g. 0.002-0.2:1; alternatively the liquid content of dissolved organics expressed as oxidizable carbon is at least 100 ppm e.g. 100-10,000 ppm i.e. a weight ratio of organics to P205 of 0.0003:1 e.g. 0.0003-0.03:1. It is these rocks which give acids containing the higher amounts of dissolved organics which can be most usefully improved by the heat treatment of the invention in order to give treated rocks from which acid containing smaller amounts of organics (e.g. 500 ppm or less total carbon or 50 ppm or less oxidizable carbon) can be made.

Among rocks which may be treated by the process of this invention are those where the rocks themselves have a low organics content e.g. 0.05-0.4% (total carbon), but these organics are acid soluble as hereinbefore defined. Such rocks are obtained for example from Zin in Israel, Algeria, Tunisia, Jordan and Senegal. Thus in another aspect the present invention provides a process for heat treating phosphate rock, wherein a phosphate rock comprising a total of 0.05-0.4% organic compounds (expressed as carbon) and acid soluble organics is heat treated at 380 -600 C to convert at least some organic compounds to carbon to form a heated rock comprising carbon particles. Preferably the rock comprises 30-40% P 205 and 45-55% Ca expressed as CaO.

Furthermore we have found with phosphate rocks that heat treatment of the rock at 650 C gives a treated rock that on acidification with a mineral acid gives hydrogen sulphide in different amounts depending on the rock, and that when the rock is heat treated by the process of this invention at a lower temperature e.g. 380-6000C, the amount of the offensive and poisonous hydrogen sulphide produces on acidification may be reduced as may be iron content of the product acid. We believe this high temperature effect is due to conversion at the higher temperatures of acid insoluble iron sulphide present in the rock into acid soluble iron sulphide, which on acidification forms hydrogen sulphide and dissolved iron. The low temperature also may reduce the arsenic content of the product acid over that obtained from high temperature calcined rocks.

Hence in a particular embodiment of the present invention, there is provided a process for preparing phosphoric acid wherein phosphate rock containing organic impurities and acid insoluble heat labile iron sulphide is heated at 380-6000C to convert at least some of said organic impurities to carbon particles but insufficient to cause conversion of all of the said insoluble sulphide into acid soluble iron sulphide, the heating process giving a treated rock containing carbon particles and acid insoluble iron sulphide.Preferably the treated rock is reacted with a mixture of sulphuric and phosphoric acids to form a reaction mixture comprising phosphoric acid, sulphuric acid, calcium sulphate, carbon particles and acid insoluble heat labile iron sulphide and there is separated a solid fraction comprising said carbon particles and acid insoluble iron sulphide and calcium sulphate, usually as gypsum, from a wet process phosphoric acid. The terms acid insoluble and acid soluble iron sulphide means those iron sulphides which are insoluble or soluble in a wet process phosphoric acid containing 28% P205 and 0.5 SO3. The term "heat labile" iron sulphide in this specification means the iron sulphide in the rock which can be changed from acid insoluble to acid soluble on heating.The heat treatment is carried out at 3800C to 6000C e.g. 380-4800C especially 400--4500C or 450-5500C and usually at a temperature being the phase transition temperature in that rock for the conversion of acid insoluble to acid soluble iron sulphide. The heating conditions are generally otherwise as described above and again the process is preferably performed continuously. The process involving avoidance of the production of hydrogen sulphide may be applied to any phosphate rock such as those described above but particularly those which contain heat labile acid insoluble iron sulphide, e.g. in an amouint of at least 100 ppm (preferably at least 500 ppm) sulphide (expressed by weight as S) such as 100--20,000 e.g.

500-10,000 such as 2000-5000 ppm or at least 200 ppm metal sulphide (expressed by weight as FeS2) such as 200-40,000 such as 1,000-10,000 ppm. The content of heat labile acid insoluble sulphide of the unheated rock is obtained from the maximum level of hydrochloric acid soluble sulphide found in rocks heated to any temperatures in the 100-1 0000C range. Such rocks are for example those from Zin, Youssoufia, Senegal, Christmas Island, and especially Florida, for the last of which the preferred heating temperature is 450550C C; rocks from Tennessee, N. Carolina, Idaho and the other US Western States may also be similarly treated.

In another aspect the present invention provides a heated phosphate rock comprising carbon particles and acid insoluble heat labile iron sulphide at least 70% e.g. at least 8C% such as 8098% or at least 90% of which is acid insoluble and the rest if any is acid soluble. Preferably the rock contains at least 500 ppm e.g. 500-5000 ppm of said acid insoluble heat labile iron sulphide (expressed as S).

The heat treated rock comprising carbon particles (whether or not it contains iron sulphides) may be reacted with at least one of phosphoric acid and sulphuric acids to form a calcium phosphate fertilizer. Reaction with phosphoric acid gives a triple superphosphate fertilizer while reaction with sulphuric acid gives a superphosphate fertilizer comprising calcium dihydrogen phosphate and calcium sulphate. Preferably the amount of acid is at least 80% e.g. 80-120% of the amount needed to react with the calcium in the rock to form calcium dihydrogen phosphate when the acid is phosphoric acid or of the amount needed to form the mixture of calcium dihydrogen phosphate and calcium sulphate (and substantially no free phosphoric acid) when the acid is sulphuric acid.Preferably the rock has been heated at 460-5400C and is not of Morocco or Utah origin unless the heating has been at 380-4400C, or 560-6000C or unless the rock is reacted with sulphuric acid or a mixture thereof with phosphoric acid, or unless the rock has been heated as part of a continuous operation. In one embodiment the rock comprising carbon particles is reacted with phosphoric or sulphuric acid but not a mixture of both. The calcium phosphate fertilizer may be mixed with ammonium nitrate or phosphate in solution or in solid form, and optionally potassium chloride to form compound fertilizers after blending or granulation.

The procedures adopted for preparing the calcium phosphate fertilizers and producing the NPK fertilizers therefrom may be as described with calcium phosphate rock in Waggaman, "Phosphoric Acid, Phosphates and Phosphatic Fertilizers" Hafner Publishing Co. 2nd Ed. 1969, pages 238-307, Van Wazer, Phosphorus and its Compounds Interscience Publ. New York Vol.111961 pp 1076-1144 and Hignett and Slack in J. Ag. and Food Chem. Vol. 5, No. 11, page 81 5 et seq., the disclosure of each of which is hereby incorporated by reference.

The heat treated rock may also be reacted with a mineral acid comprising hydrochloric, nitric or sulphuric acids, to produce a mixture of a calcium salt thereof phosphoric acid and carbon particles, and a solid fraction comprising said particles is separated from said mixture. Preferably the rock is heated at 380-5900C especially when the acid is solely hydrochidoric acid and indeed the rock is preferably not of Florida or Morocco origin unless the heating has been at 380-5900C or unless the heating process has been as part of a continuous operation. The rock is preferably reacted with an amount of acid equivalent to at least 90% of the calcium content of the rock in order to convert the phosphate values in the rock to phosphoric acid. Though hydrochloric may be used as attack acid, preferably an acid comprising nitric or sulphuric acid is used, because then the separated solid fraction also comprises calcium nitrate or sulphate respectively, thereby reducing the calcium content of the liquid left after separation. A process for reacting phosphate rock with hydrochloric acid, the process operation of which may be used in the present case is described in USP 2880063 and 3072461, the disclosures of which are hereby incorporated by reference. The reaction of phosphate rock with nitric acid may be carried out with process operations as described in Canadian Pat. 672008 and USP 3363978 the disclosures of which are hereby incorporated by reference.

In the conversion of the heat treated rock to the wet process acid, whether that rock contains a significant amount of iron sulphides or not, the rock is treated with sulphuric acid and phosphoric acid, to produce said reaction mixture containing a liquid and a solid fraction in which a major amount of the solid fraction comprises calcium sulphate and a minor amount of carbon particles (and if appropriate iron sulphide) and usually a little unattacked rock.The amount of sulphuric acid is usually such as to convert at least 90% e.g. at least 95% of the phosphate values in the rock into wet process phosphoric acid or is equivalent to at least 90% of the Calcium oxide content of the rock preferably 95105%. The reaction of the treated rock with the mixture of phosphoric and sulphuric acids may be carried out at low temperature and with a low concentration of sulphuric acid to form gypsum or at high temperatures e.g.

above 900C and with a high concentration of sulphuric acid to form calcium sulphate hemi hydrate or anhydrite. Conveniently the rock is mixed with sulphuric acid and recycle weak phosphoric acid and a recycle suspension of calcium sulphate in wet process phosphoric acid to form the suspension of calcium sulphate a portion of which is recycled and the rest is separated e.g. by filtration and the filter cake of the calcium sulphate (with carbon particles and possibly iron sulphide) is washed with water to give a filtrate of weak phosphoric acid, which is recycled to the stage of attack on the rock.The crude wet process acid made after treatment with mineral acid and separation of solids may be used as such, especially when calcium sulphate has been separated, or may be further treated, often after concentration e.g. to 4060% P2Qs in the case of acid from a sulphuric/phosphoric acid mixture attack.

Further details of the process operations involved in reacting phosphate rock with a mixture of sulphuric and phosphoric acids are given in Waggaman (see above pages 174-209).

The crude wet process phosphoric acid made after treatment of the heat treated rock with the mineral acid and separation of the solid fraction with or without concentration may be treated with a water immiscible organic solvent to produce an organic phase and an aqueous phase, with acid recovered from at least one of said phases. The heat treatment process of the invention decreases the production of emulsions at this stage and increases the rate of separation of the phases over those obtained if rock heat treatment is not performed. Preferably unless the rock has been heated continuously as described above, then the rock has been heated at 380590OC when the acid is solely hydrochloric and said organic phase comprises dissolved phosphoric acid.The solvent may be one in which phosphoric acid is not substantially soluble or which is not capable of extracting phosphoric acid out of aqueous phosphoric acid of the given concentration so that the solvent extracts impurities leaving the bulk of the phosphoric acid in the aqueous phase. The impurities may be simply contaminants in the acid to be removed e.g. iron, or maybe valuable in their own right as with uranium. Examples of solvents to remove iron from the acid usually without concentration are long chain amines, alcohols, ethers, esters and ketones from dilute phosphoric acid.Examples of solvents to remove uranium from the acid usually without concentration are tri alkyl phosphine oxides e.g. trioctyl phosphine oxide, di-alkyl phosphates e.g. di (2-ethylhexyl) phosphate or especially mixtures thereof, or alternatively mono alkyl pyro phosphates such as mono octyl pyrophosphate and/or dialkyl pyrophosphates or alternatively monoalkylphenyl phosphates and/or di alkyl phenyl phosphate and especially mixtures thereof such as mono and di octylphenylphosphoric acids, in each case each alkyl usually contains 6-12 carbon atoms.When using the phosphine oxide and/or diester as extractant the uranium in the acid needs to be oxidized to the hexavalent state, and therefore the iron present in the acid is inevitably also oxidized; application of the heat process of the invention often reduces the iron content of the acid over the value obtained from a high temperature calcined rock and hence less oxidant may be needed to oxidize the uranium. A product comprising uranium may be recovered from the organic phase e.g. by re-extraction into aqueous acid and eventual conversion to uranium oxide. The process operations of extracting uranium into an organic phase out of wet process phosphoric acid are described further in Ind. Eng.

Chem, Process Design and Development, 1972 11, Vol. 1 pp 122-8 and 1974, 13 No. 3 pp 286-91 and Ind. Eng. Chem. 1957,49, 628-38, the disclosures of which are hereby incorpsorated by reference.

The water immiscible organic solvent may be one which preferentially extracts phosphoric acid leaving the majority of the impurities behind in the aqueous raffinate phase, which is separated from the organic phase containing purified phosphoric acid and phosphoric acid is recovered from the organic phase as phosphoric acid or a phosphate salt thereof, e.g. by contact with water or aqueous phase and optionally heating. Examples of suitable solvents are alcohols, ethers, organic esters and ketones among which those of 4-9 carbon atoms are preferred e.g. butanol, amyl alcohols, isopropyl ether and methyl isobutyl ketone; other esters such as trialkyl phosphates e.g. tributyl phosphate may also be used. This solvent extraction process is highly desirable when the attack mineral acid is hydrochloric acid or nitric acid because it separates the phosphoric acid from the calcium salts of the crude reaction mixture. The phosphate values in the extract may be obtained by evaporation or preferably by contacting the extract with water and/or base.The higher carbon content solvents are usually used with the acids after concentration to e.g. 50-60% P205. Further details of process operations for the purification of wet process phosphoric acid by extraction of acid into an organic phase and subsequent release which may be used in the present invention are given in USPs 1929442,2880063, 3072461,3318661, 3363978, 3388967, 3410656, 3556739,4127640, Canadian Pat. 672008 British Pats.1112033, 11 99042, the disclosures of which are hereby incorporated by reference.

The wet process acid left after separation of the solid fraction comprising carbon particles, and especially when it comprises calcium nitrate or sulphate may also be treated with or without after concentration to e.g. 40-60% P205 with at least one nitrogenous compound comprising ammonia to form at least one ammonium phosphate salt, e.g. mono and/or di ammonium phosphate for fertilizer use. Often the ammonia is mixed with ammonium nitrate or nitric acid is added first or was the attack acid and use of the heat treated rock of the invention enables one to use less nitrate than if untreated rock is used, because the latter and hence the acid from it contains organic compounds and these react with the nitrate.The production of the ammonium phosphate from the nitric based phosphoric acid may be as described in the Tennessee Valley Authority article "New Developments in Fertilizer Technology" Fifth demonstration, October 6ih/7th 1964, page 56, the disclosure of which is hereby incorporated by reference. The corresponding production from a sulphuric acid based phosphoric acid may be as described in J. Ag. and Food Chemistry Vol. 5 page 258, the disclosure of which is herein incorporated by reference.

The wet process acid left after separation of the solid fraction comprising carbon particles and, especially when that fraction also comprises calcium sulphate, may also be treated with an alkali to form at least one phosphate salt, which is separated from any solids such as heavy metal hydroxides and phosphates also formed. The alkali may be a hydroxide, carbonate or bicarbonate of sodium or potassium. The reaction of base and acid may be carried to a metal:P atom ratio of 1:1,2:1 or 3:1 or preferably 1.67:1, the latter for subsequent heat treatment to form alkali metal tripoly phosphate. The rock heat treatment process enables one to reduce and may be eliminate the amount of oxidant needed to decolourize the acid or phosphate salt liquor and hence the tripoly phosphate.The process operations of conversion of wet process acid with alkali to alkaki metal phosphate salts and optional subsequent production of alkali metal tripoly phosphates e.g. at 200-6000C may be as described in Van Wazer pages 1 21 3-121 9 of Vol II and 642-8 of Vol I the disclosure of which is herein incorporated by reference.

Particularly when the attack acid is hydrochloric acid but also in the case of nitric and sulphuric acid as well, the wet process acid after separation of the solid fraction may be treated sequentially with one or more than one e.g. 2-4 portions of an alkaline earth metal base e.g. a hydroxide or carbonate or calcium or magnesium to precipitate a number of fractions of alkaline earth metal (e.g. calcium) hydrogen phosphate, suitable for animal feedstuff use which may be separated from the mother liquor which contains calcium chloride or nitrate or water depending on the attack acid. The process operations of reaction of the acidified rock with calcium hydroxide may be as described in Chemical Engineering, November 1 955 pages 370-373, the disclosure of which is hereby incorporated by reference.The invention is illustrated in the following Examples.

EXAMPLES 1-3 AND COMPARATIVE EXAMPLES A-D Phosphate rock from Zin, Israel, had the following analysis 32.0% P205; 6.0% CO2; 2.0% SO3; 1.5% SiO2; 4.0% F; 51% Ca (as CaO); 0.2% mg 0.3% Al (asAl2O3); 0.2% Fe (as Fe203); 0.9% Na (as Na2O); 0.2% oxidizable organic material (expressed as C).

It had a particle size distribution of 6.5% greater than 0.5 mm; 27.3% between 0.25 and 0.5 mm; 38.9% between 0.15 and 0.25 mm; 27.3% less than 0.15 mm.

A layer of the above rock, was heated in an oven for 1 hour in the presence of air at a temperature specified below. The treated rock was inspected when cold. The rocks treated at 400-7000C were dark and showed the presence of carbon particles.

As an estimation of the effect of the heating to remove the organics from the rock, the rock (heat treated or otherwise) (100 g) was added gradually to a mixture of concentrated hydrochloric acid (35%, 205 g) and water (75 g). The temperature of the mixture rose to 40-450C and the mixture was then heated for 1 hour at the boiling point. The degree of foaming obtained in the reaction of rock and acid was noted. The reaction mixture was filtered hot to remove any carbon particles, unreacted rock and some calcium salts, then cooled to room temperature and refiltered to give a crude phosphoric acid.

The colour of the crude acid was noted and the results were as follows TABLE 1

Temp. of Colour of Degree of Example heating "C Rock Product Colour of acid foaming A (Comp) None Sandy deep red brown large B (Comp) 200 , ,, ,, " large 1 400 Pale black Strong yellow 2 450 Medium black Medium yellow 3 500 Black pale green C (Comp) 700 Grey " ., small D (Comp) 900 Green tr ,, small EXAMPLES 4-8 AND COMPARATIVE EXAMPLE D In the same manner as in Ex. 1-3, phosphate rock from Zin, Israel of the same analysis and particle size as before was heated at various temperatures and for various times. The treated rock was reacted with hydrochloric acid as before and in separate experiments with a sulphuric/phosphoric acid mixture and the colour of the liquid noted and organic and P205 content of the liquid obtained. The sulphuric/phosphoric acid was 3 mixture of 200 g of 20% P205 thermal phosphoric acid and enough 56% sulphuric acid to combine with 98% of the calcium content of the phosphate rock used, the amount of which was such as to contain 40 g P205.The specified amount of rock was mixed with stirring with 200 g of phosphoric acid at 600C. When foaming ceased the sulphuic add was added and the mixture stirred for 2 hrs at 700 C to give a suspension of gypsum in phosphoric acid. The suspension was filtered hot and the filter cake washed three times with 50 cc cold tap water. All the filtrates were combined to give the product acid which was analyzed for P205, total carbon and oxidizable carbon contents. The rock before and after the heating was also analysed for F. The results were as follows.

(see Table 2). The Zin rock before heat treatment contained acid insoluble iron sulphide in amount of 250 ppm (expressed as S).

EXAMPLES 9-18. COMPARATIVE EXAMPLE E-J In the same manner as in Ex. 4-8, the same procedures of heating phosphate rock, and reacting the rock with hydrochloric or the sulphuric/phosphoric acid mixtures were carried out with rocks other from Zin. Details of the rocks, and the results obtained are given in the Tables 3-5 below. In each case the heat treatment was for 1 hour, unless stated otherwise. When the unheated Moroccan rock was digested with the H2SO4/H3PO4 mixture, the liquid (after filtration) contained 27.8% P205, 100-200 ppm total carbon and 16--20 ppm oxidizable carbon.

EXAMPLE 17-19 The Zin rock as in Example 4 was continuously heat treated in an inclined rotary calciner in which the rock travelled slowly down the calciner against a stream of air/burnt gas. The residence time was 20-30 minutes. The temperatures of the entry gas, solid at the point of leaving the calciner and effluent gas were measured. The heat treated rock was collected and treated with the sulphuric/phosphoric acid mixture as in Example 4; the insolubles (comprising gypsum and carbon particles) were filtered and the colour of the product acid noted. The results were as follows.

Temperatures C Example Solids exit Entry Gas Effluent Gas Colour of product acid 17 430 800 - orange yellow 18 510 880 210 Very pale green 19 520 890 200 Very pale green TABLE 2

H2SO4/H3PO4 HCl acidulation acidulation Heat treatment on Rock %F in Colour of Degree Colour of Example Temp. C Time (mins) rock acid produced of Foaming acid produced E Uncalcined - 3.8 Strong red-brown large Reddish-brown 4 400 15 - " Light reddish-brown 5 400 60 3.8 Yellow some Yellow 6 500 15 - " Pale yellow 7 " 30 3.9 Yellow-green small # 8 " 60 3.8 Pale-green small Very pale green The filtered liquid from the H3PO4/H3SO4 acidulations in Comparative Example E and Example 8 were analyzed for % P2O5, total carbon and oxidizable carbon.The results were as follow; % P2O5 Example E 27.9%, Example 8 29.9%, ppm total carbon Example E, 1280 Example 8, 370, ppm oxidizable carbon Example E, 650, Example 8 non found.

TABLE 3 Phosphate Rock Analyses

Morocco Source of Rock (Khourigba) Jordan Florida %P2O5 31.5 33.9 31.3 % CaO 51.2 52.8 45.1 % Na2O 0.7 0.57 0.6 % MgO 0.8 0.29 0.75 %AL3O2 0.40 0.28 1.8 $Fe2O3 0.21 0.09 2.4 % SiO2 2.4 2.37 5.9 % SO3 2.1 1.37 3.3 % CO2 6.4 4.46 3.6 % F 4.0 3.88 3.8 % Cl 0.03 0.06 0.005 % organics as C 0.18 0.30 1.56 % loss in weight on heating at 1050C 1.1 1.2 0.8 Particle Size Analysis % by Weight

Mesh No. Morocco Jordan Florida Greater than 1.2 mm 63 - | - (+14 mesh) 0.5 mm-1.2 mm 10 38 35 (+30 mesh) 0.25 - 0.5 mm 7 24 | 39 (+60 mesh) 0.15 - 0.25 mm 15 27 23 (+100 mesh) Less than 0.15 mm 5 11 3 (-100 mesh) TABLE 4

Hydrochloric Acid acidulation of given rock Morocco Jordan Heat Treatment Morocco Degree of Jordan Degree of Temperature C Example Colour of Acid Foaming Example Colour of Acid Foaming Untreated E Strong yellow Much G Pale yellow some 400 9 Strong yellow medium 11 - 500 10 Yellow moderate 12 pale yellow small with green tinge 900 F Yellow negligible Similar degrees of foaming occurred when the rocks were treated with the phosphoric/ sulphuric acid mixture as in Example 4.

TABLE 5 Results on Floride Rock

HCl Acidulation H2SO6/H3PO4 acidulation Heat treatment Degree of Degree of Example Temp. C Time Colour of Acid Foaming Colour of Acid Foaming H Uncalcined Dark-reddish brown. Large - 13 400 1 hr. " " Light brown-yellow small 14 500 1 hr. Orange-brown. medium Very pale brown- small yellow 15 500 2 hrs. Pale yellow small - 16 600 1 hr. Yellow-green small - J 900 1 hr. Orange-yellow none Very pale green, small almost colouriess EXAMPLE 20-22 AND COMPARATIVE EXAMPLES K-N Florida rock, of analysis as given above was heated for 1 hour at various temperatures and then the treated rock reacted with the sulphuric/phosphoric acid mixture as in Example 4. A solid comprising calcium sulphate, carbon particles and iron sulphide was separated from the reaction mixture, to leave a product acid. The treated rock was treated with 14% w/w hydrochloric acid and analyzed for soluble iron and sulphide.

Analysis of Rock Temperature Example "C sulphide ppm % Soluble Fe Comp. Un-heat- 70 0.57 Ex. K. treated 20 400 110 0.73 21 500 220 0.76 22 600 980 0.94 Comp. 650 2180 1.12 Ex. L.

Comp. 750 3360 1.35 Ex. M Comp. 900 110 1.36 Ex. N.

EXAMPLE 23 AND COMPARATIVE EXAMPLE P The acids of Example 8 (1 hr heat treatment of rock at 5000 C) and Comparative Example E (uncalcined rock) were separately mixed at 350C in a 3:2 weight ratio with separate solutions of 0.5 M di (2-ethyl hexyl) phosphoric acid and 0.15 M trioctyl phosphine oxide in petroleum ether of boiling point 1 00-1 200C and the phases allowed to separate. The phases separated immediately with the acid of Example 8 into an aqueous acid phase and an organic phase, which was separated and its uranium content recovered therefrom by treatment with aqueous phosphoric acid containing ferrous ions (Ex.

23). With the acid of Comparative Example E, mixing of the acid and petroleum ether solutions gave an emulsion which cleared over 5 minutes to give the organic and aqueous phases (Comparative Example P).

EXAMPLES 24-26 Rock of analyses as shown in Ex. 38 hereafter was treated for 1 hour at 5000C as described in Ex.

1. Wet process phosphoric acids were made from this rock and also from the unheat treated rock by reaction with a sulphuric/phosphoric mixture (as in Ex. 4) and separation of a solid fraction comprising gypsum, carbon particles and unattacked rock. Similarly wet process acids were made from rocks of analysis given in Ex. 1 and 27 hereafter. Also wet process acids made in Ex. 42-44 hereafter from heat treated rocks were taken. Each acid was concentrated and oxidized by boiling, with air passed through it to reduce the Fe II content. Each of the 6 acids, which contained an amount of P205 in the 24-29% P2O5 range was mixed with stirring at 350C in a 1:1 volume ratio with a solution in petroleum ether (b.p.

100-1 200C) of 0.5 M di (2 ethyl hexyl) phosphoric acid and 0.15 trioctyl phosphine oxide. After 5 mins stirring, the mixtures were allowed to stand. Within 40 seconds each of those derived from wet process acids from the heat treated rocks separated into an organic phase comprising uranium and an aqueous acid phase. With each of the mixtures from acids from unheat treated rock there was a substantial amount of interfacial solid debris and an interfacial emulsion, which took 10-30 mins to break before leaving an organic phase comprising uranium and an aqueous acid phase. In each case, the two phases were separated and uranium recovered from the organic phase by extraction with aqueous phosphoric acid containing ferrous iron.

EXAMPLES 27-38 AND COMPARATIVE EXAMPLES O--U In these Examples the following rocks with the given analyses were used. The Florida II rock was from a different mine from that of the Florida rock used in Ex. 1 3-1 6.

Youssoufia black (dried Youssoufia Florida II 1 500021 hr.) White Senegal %P2O5 30.9 29.9 31.0 35.8 %CaO 46.0 49.8 51.0 50.1 %SO3 1.4 2.0 1.2 0.33 %C02 4.3 6.7 6.1 1.7 %SiO2 3.4 4.1 %F 3.7 3.9 4.1 3.9 %CI 0.001 0.024 ppm < 100 %Na20 0.7 0.63 0.85 0.18 %MgO 0.7 0.61 0.29 500 ppm %Al2O3 0.9 0.32 0.17 0.53 %K20 0.2 0.028 < 0.1 %Fe2O3* 1.1 0.15 0.13 1.1 Organic Carbon % C 0.5 1.3 0.15 1.08 In each of the Examples below the rock was heated as follows. The rock as a layer in a silica tray was heated in a muffle oven vented to the atmosphere maintained at a fixed temperature for 1 hour.The treated rock was then reacted with the sulphuric/phosphoric mixture of Ex. 4 and separately with 14% w/w hydrochloric as in Ex. 20-22 and also with 70% phosphoric acid with separation of the insoluble solids comprising carbon particles.

Florida II Rock Colour of acid Acid labile Acid soluble after HCI treatment Example Temperature C sulphide ppm iron % Fe of rock.

Q Untreated 8 0.67 dark brown 27 500 230 0.95 lemon green 28 600 1030 1.10 lemon green R 750 3280 1.31 lemon green Black Youssoufia Rock S Untreated - - dark brown 29 400 260 0.11 lemon green 30 500 220 0.11 lemon green 31 600 120 0.11 lemon green 32 580 - - lemon green White Youssoufia Rock T Untreated 0.11 blue green 33 400 160 0.12 lemon green 34 450 - - lemon green 35 500 220 0.11 lemon green 36 550 215 lemon green 37 600 220 0.12 lemon green Acid labile Acid soluble Colour of acid Example Temperature C sulphide ppm iron % Fe after HCI treatment Senegal Rock U Untreated - - brown 38 500 - - lemon green EXAMPLES 39-41 In these examples the Florida rock used in Ex. 13-1 6 was used in Ex. 39 while for Ex. 40, the Florida II rock of Ex. 27 and 28 was used and in Vex. 41. Moroccan rock as used in Ex. 9 and 10.

For Ex. 39, the Florida rock of Ex. 13-16 was heat treated in air in an oven for 1 hour at 550 C to give a grey rock containing carbon particles. This was treated with the sulphuric/phosphoric acid mixture of Ex. 4 and a solid fraction comprising gypsum and carbon particles was separated to leave a wet process acid which was a light green colour, compared to the dark brown colour from the unheat treated rock.

For Ex. 40, the Florida II rock of Ex. 27 and 28 was continuously heat treated in the manner described in Ex. 1 7-19 with a solid exit temperature of 500 C and entry and effluent gas temperatures of 7900C and 1 900C respectively with an average retention time of 20-30 mins. The heated rock was treated with the sulphuric/phosphoric mixture as in Ex. 4 and insolubles comprising gypsum and carbon particles were separated therefrom to leave a wet rocess phosphoric acid of light green colour, compared to the dark brown colour from the unheat treated rock.

For Ex. 41 the Moroccan rock was continuously heat treated in the manner described in Ex.

1 7-19 with a solid exit temperature of 3900C and entry and effluent gas temperatures of 760OC and 1 300C with an average retention time of 20-30 mins. The heat treated rock comprising carbon particles were separated therefrom to leave a wet process phosphoric acid of light green colqur, from insolubles. The acid was a medium yellow colour compared to the strong yellow colour of acid from the unheat treated rock.

EXAMPLE 42 Phosphate rock, of analysis, as shown in Ex. 1, was heat treated continuously as in Ex. 1 9 and the heat treated rock converted continuously with a mixture of sulphuric and phosphoric acids in the presence of gypsum slurry into a wet process phosphoric acid with separation of a solid fraction comprising gypsum, carbon particles and unattacked rock. The reaction was carried out in a single stage stirred tank reactor by a conventional method and use of an amount of sulphuric acid which was 102% of the calcium content in the rock. The product phosphoric acid contained 2830% P205 and no detectable oxidizable carbon.No antifoam agent was needed in the attack vessel, compared to the addition of 0.6% oleic acid (based on the weight of P 206 in the rock when the rock was used. The rate of filtration of the gypsum slurry was also significantly faster than when unheat treated rock was used.

EXAMPLE 43 AND 44 In the same way as in Ex. 42 Florida II rock heat treated at 5000C continuously according to Ex.

40 and Moroccan (Khouribga) rock heat treated continuously according to Ex. 41 were continuously converted into wet process acid. The product phosphoric acids contained 2830% P206 and no detectable oxidizable carbon. No antifoam agents were needed in the attack vessel compared to the addition of 1.0% or 0.6% respectively oleic acid (based on weight of P205 in the rock) when unheat treated rock was used. The rates of filtration of the gypsum slurry were also significantly faster than when unheat treated rock was used.

EXAMPLE 45 The wet process phosphoric acid made in Ex. 42 was purified by solvent extraction. It was concentrated to an acid of 54.7% P,O,! i 1.51% SO, 0.32% Fe, 0.24% Mg and 0.07% Al and less than 50 ppm oxidizable carbon. This acid was purified in a system comprising 2 stage countercurrent extraction with methyl isobutyl ketone to give an extract and aqueous raffinate, followed by 4 countercuttent scrubbing stages on the extract using product purified acid as scrub liquor to give a purified extract and used aqueous scrub liquor which was recycled to the extraction and 2 stage countercurrent release with water to give a substantially acid free solvent layer recycled to the extraction and a purified acid containing 41.2% P205, 0.50% S03 40 ppm Fe, 6 ppm Mg and 1 ppm Al 0.4 ppm As, which was a pale yellow colour. The purification procedure was as described in USP 3914382 with a 65:35 split of P205 between the P205 in the product acid and in the raffinate. The colour of the purified acid could be improved if needed by treatment with 1% active carbon, compared to the need for 5% active carbon with a corresponding process based on unheat treated rock. No phase separation problems e.g.

formation of long lasting emulsions at the solvent/water interface occured while significant problems occured with the process based on unheat treated rock.

EXAMPLE 46-48 The wet process phosphoric acids made in Examples 42 and 44 were each converted into sodium phosphates and hence sodium tripoly phosphate. Each acid was treated to reduce its sulphate and fluorine impurity contents and reacted with sodium carbonate to a NA:P ratio of 5:3 with filtration of precipitated solids to leave an aqueous solution of mixed sodium hydrogen phosphates of Na:P ratio 5:3, which was dried and calcined for 1 hour to give sodium tripoly phosphate. The salt from the acid of Ex. 42 was white, of less colour than that of the salt made from unheat treated rocks. The colour may be improved by treatment of the 5:3 Na:P liquors with up to 0.5% active carbon, compared to use of 5% or more with the product from the corresponding unheat treated rock. The salts from the acids of Ex. 43 and 44 were white.

EXAMPLE 49-51 Rocks prepared as in Ex. 1 9, 40 and 41 were reacted wth 17% hydrochloric acid to form reaction mixtures comprising calcium chloride, carbon particles, phosphoric acid, residual hydrochloric acid and unattacked rock. Each reaction mixture was defluorinated by treatment with a portion of an aqueous calcium hydroxide suspension (equivalent to the F content and some of the acid), and then separation of the solids and then addition of a large amount of the calcium hydroxide suspension (equivalent to most of the acid content for making dicalcium hydrogen phosphate) was added with separation of the solid dicalcium hydrogen phosphate suitable for animal feeds.Finally the rest of the acid was reacted with a final portion of the calcium hydroxide suspension to give a final fraction of dicalcium hydrogen phosphate which was separated from mother liquor which comprises calcium chioride. The amounts of calcium hydroxide suspension added in the three steps were 20%, 70% and 10% of the total amount respectively.

EXAMPLE 52, 54 Each reaction mixture comprising calcium chloride, carbon particles phosphoric acid residual hydrochloric acid, unattacked rock, as made in Ex. 49-51 was filtered to remove a solid fraction comprising the rock and carbon particles and to leave an acid liquor. 5 parts by volume of this liquor were extracted with 10 parts by volume of mixture of 8 parts by volume amyl alcohol and 2 parts of 35% hydrochloric acid to give an organic phase comprising purified phosphoric acid and hydrochloric acid and an aqueous acid phase which were separated. The phases separated quickly with no interface problems.The organic phase was mixed with 2.5 parts by volume of water to release the acids to give an organic phase of reduced acid content and an aqueous phase mixture of hydrochloric and phosphoric acids; the phases were separated again with no interface problems. The aqueous phase mixture was heated to evaporate hydrochloric acid to leave purified wet process phosphoric acid.

EXAMPLE 55, 56 In the same manner as in Ex. 45, the wet process acids of Ex. 43 and 44 were concentrated and were purified by solvent extraction with methylisobutyl ketone and release with water to give purified aqueous phosphoric acids. The concentrated wet process acid derived from Ex. 43 containing 51.9% P20, 1.8% SO3 1.36% Fe, 0.9% Mg 1.0% Al was purified to give an acid of 42.7% P205, 0.54%, SO3, 185 ppm Fe 9 ppm Mg and 12 ppm Al and a raffinate of 41.3% P20s, 2.7% SO3, 2.8% Fe, 2.0% Mg and 1.9% Al, with a 68:32 split between purified acid and raffinate.The concentrated wet process acid derived from Ex. 44 contained 56.0% P205, 1.3% SO3, 0.23% Fe and 0.6% Mg and was purified to give an acid of 40.5% P20s, 0.7% SO3, 28 ppm Fe and 10 ppm Mg and a raffinate of 40% P20s, 1.7% SO3, 0.6% Fe and 1.4% Mg with a 70:30 split between purified acid and raffinate. In neither case were there problems due to production of emulsions at the liquid/liquid interface.

EXAMPLE 57-59 Rocks prepared as in Ex. 1 9, 40 and 41 were reacted with 24.2 parts by weight of 58% nitric acid per 10.8 parts by weight of heat treated Moroccan rocks (and corresponding amounts for the other 2 rocks) which gave in each case an aqueous mixture of calcium nitrate, carbon particles, unattacked rock, phosphoric acid and residual nitric acid. Each mixture was filtered to remove the carbon particles and rock and cooled to OOC and a solid fraction comprising calcium nitrate was separated from the aqueous acid solution, which contained nitric and phosphoric acids and calcium nitrate. Each aqueous acid solution was treated with 2.55 parts of anhydrous ammonia added continuously.The mixture obtained which contained ammonium nitrate and phosphate and calcium nitrate was evaporated to give a melt containing 0.55% water, which could be used as such as a fertilizer. The melt in each case was mixed with 5.8 parts of potassium chloride and the mixture granulated to give a compound fertilizer of N:P:K assay 17:17:17.

EXAMPLES 60-62 The wet process acids obtained in Ex. 42-44 were each concentrated to a 54% P205 content acid. Each concentrated acid was treated by bubbling anhydrous ammonia through it to an N:P atom ratio of 1.35:1. The temperature rose to 11 50C and water was added to keep the slurry obtained free flowing (about 20% free water). The hot slurry was distributed over a bed of recycled ammonium phosphate product fine particles and the ammoniation was completed with anhydrous ammonia to an N:P ratio of about 1.8:1; the recycle ratio was 2.5 parts recycled to 1 part removed as product. The product at 850C was passed to a drier and a cooler and then granulated to give an ammonium phosphate of assay 18:47:0, suitable as a fertilizer.

EXAMPLE 63-65 The wet process acids obtained in Ex. 42-44 were each concentrated to 50% P205 content acid.

50 parts of each concentrated acid was mixed with 1 2.5 parts of water and passed into a vessel containing ammonium phosphate slurry. 8 parts of anhydrous ammonia were added to give a mixture of N:P ratio 1.3:1. Water was evaporated to leave an 80% slurry of ammonium phosphate. The slurry could be granulated by mixing with recycle solid product and granulated to form a granular ammonium phosphate fertilizer. The slurry with solid potassium chloride and an 80% solution of ammonium nitrate and granulated to give an N:P:K compound fertilizer.

EXAMPLE 66-68 6.2 parts of each concentrated acid of 50% P2O5 content used in Ex. 63-5 was mixed with 7 parts of a 95% ammonium nitrate solution and then into the mixture was passed 0.8 parts anhydrous ammonia. The heat of reaction evaporated water to leave a concentrated solution with 5% water, which was fed to an evaporator to produce a dry melt. Each melt was mixed with 7.8 parts of potassium chloride and the mixture granulated to form 20 parts of a compound fertilizer of N:P:K assay 15:1 5:21.

EXAMPLE 69-71 6.parts of the heat treated rocks of Ex. 41 (and corresponding amounts of the heat treated rocks of Ex. 1 9 and 40) were each ground to give a powder, of which 80% passed through a 1 50 micron sieve.

Each powder was mixed with 4.8 parts of 72% sulphuric acid to give a slurry which was passed continuously through a curing chamber to give a solid product, which was broken up and stored in a heap for 1 week to complete the reaction to form superphosphate. Each superphosphate could be used as such as a fertilizer. Each superphosphate was mixed with solid potassium chloride and an 80% aqueous solution of ammonium nitrate in the weight proportions of 48:17:36, followed by granulation, cooling and drying to give a free flowing fertilizer of assay N:P:K of 10.5:10.5:10.5.

EXAMPLE 72-74 In the same way as in Ex. 69-71,4.1 parts of the heat treated rock of Ex. 41 (and corresponding amounts of the heat treated rocks of Ex. 1 9 and 41) were ground and mixed with 6-8 parts of wet process phosphoric acid containing 50% P205 and the product made as in Ex. 67-69. Each triple superphosphate obtained could be used as such as a fertilizer. Each triple superphosphate was mixed with potassium chloride and an aqueous solution of ammonium nitrate in proportions of 30:25:54 and the mixture converted as before into a free flowing compound fertilizer of assay N:P:K 15:15:1 5.

Claims (47)

1. A process for heat treating phosphate rock, wherein calcium phosphate rock containing organic compounds is heat treated at 380-6000C to convert at least some of said organic compounds to carbon to form a heated rock comprising carbon particles.

2. A process according to claim 1, wherein the rock is heated by being passed continuously through at least one heated zone at 380-6000C and heated rock is withdrawn therefrom.

3. A process according to claim 1 or 2, wherein the rock is heated at 380--4800C.

4. A process according to claim 1 or 2, wherein the rock is heated at 460-540 C.

5. A process according to claim 4 wherein the rock is not of Florida or Egyptian origin if the heating is at 490-510 C or of Russian origin if the heating is at 490-5400C.

6. A process according to claim 1 or 2, wherein the rock is heated at 510-5900C and is not of Utah or Morocco origin if the heating is at 540-5600C or of Russian origin if the heating is at 510-5400C.

7. A process according to any one of claims 1-6 wherein said rock comprises a total of 0.050.4% organic compounds (expressed as carbon) and acid soluble organics.

8. A process according to any one of claims 1-7 wherein said rock comprises 3040% P205 and 4555% calcium (expressed as CaO).

9. A process according to any one of claims 1-8 wherein the phosphate rock before heating is one which gives a brown liquid with 27% hydrochloric acid.

10. A process according to any one of claims ? 1-9 wherein the origin of said rock is Idaho. North Carolina, Tennessee in the United States of America or Tunisia, Jordan, Algeria, Senegal, Youssaufia in Morocco, Kola, Nauru, Oceania orZin in Israel.

11. A process according to claim 2, 7 or 8, wherein Florida rock is heated in a continuous operation for 15 minutes to 1 hour at 450-5500C.

12. A process according to claim 2 or 8, wherein Moroccan rock is heated in a continuous operation for 15 minutes to 1 hour at 380-4400C.

13. A process according to any one of claims 1-12, wherein the rock comprises organic compounds and acid insoluble heat labile ion sulphide and is heated at a temperature insufficient to convert all said acid insoluble iron sulphide into acid soluble iron sulphide and a heated rock comprising phosphate rock, carbon particles and acid insoluble iron sulphide is produced.

14. A process according to claim 13, wherein the rock before heating comprises at least 500 ppm acid insoluble iron sulphide (expressed as S).

15. A heat treated calcium phosphate rock prepared by a process as claimed in any one of claims 1-14.

16. A heat treated calcium phosphate rock comprising carbon particles.

17. A rock according to claim 16, which comprises also acid insoluble heat labile iron sulphide.

18. A rock according to claim 17, which comprises at least 500 ppm of said iron sulphide.

19. A rock according to claim 1 7 or 1 8, wherein at least 80% of the iron sulphide is acid insoluble and the rest if any is acid soluble.

20. A process for preparing phosphates from phosphate rock, wherein phosphate rock comprising carbon particles as claimed in any one of claims 14 8 is reacted with at least one of phosphoric and sulphuric acids to form a calcium phosphate fertilizer.

21. A process according to claim 20, wherein the rock is not of Morocco or Utah origin unless the rock has been heated as part of a continuous process, or has been heated at 380-4400C or 460--5400C or 560--6000C or unless the rock has been reacted with sulphuric acid or a mixture thereof with phosphoric acid.

22. A process according to claim 20 or 21, wherein the rock has been heated at 460--5400C.

23. A process according to claim 21 or 22, wherein the rock and its heating are as defined in claim 2,11 or 12.

24. A process according to any one of claims 20-23, wherein the rock comprising carbon particles is reacted with an amount of phosphoric acid which is 80120% of that amount needed to react with the rock to form calcium dihydrogen phosphate or with an amount of sulphuric acid which is 80120% of the amount needed to react with the rock to form a mixture of calcium sulphate and calcium dihydrogen phosphate.

25. A process for preparing phosphoric acid from phosphate rock, wherein calcium phosphate rock comprising carbon particles prepared by heating phosphate rock at 380--6000C or as claimed in any one of claims 1 5-19 is reacted with a mineral acid, which comprises hydrochloric, nitric or sulphuric acids to produce a mixture of a calcium salt thereof, phosphoric acid and carbon particles and a solid fraction comprising said particles is separated from said mixture.

26. A process according to claim 25, wherein the phosphate rock has been heated continuously as defined in claim 2.

27. A process according to claim 25 or 26, wherein the phosphate rock is heated at 380-5900C when the acid is solely hydrochloric acid.

28. A process according to claim 25, 26 or 27, wherein the rock comprising carbon particles is reacted with an amount of acid equivalent to at least 90% of the calcium content of the rock.

29. A process according to claim 28, wherein the rock is from Florida or Morocco and has been heated at 380--5500C.

30. A process according to claim 25, 26, 28 or 29, wherein the acid is at least one of nitric and sulphuric acids.

31. A process according to claim 30, wherein the rock comprising carbon particles is reacted with a mixture of sulphuric acid and phosphoric acid to form a solid fraction comprising calcium sulphate and carbon particles, and wet process phosphoric acid, and the acid is separated from said solid fraction.

32. A process according to any one of claims 25-31 wherein when said heated rock comprises said insoluble heat labile iron sulphide, the solid fraction comprises said carbon particles and said acid insoluble iron sulphide, the solid fraction comprises said carbon particles and said acid insoluble iron sulphide.

33. A process according to any one of claims 25-32 wherein after separation of said solid fraction, the phosphoric acid is treated with a water immiscible organic solvent to produce an organic phase and an aqueous phase, and acid is recovered from at least one of said phases.

34. A process according to claim 33, wherein the phosphoric acid contains uranium and with or without prior concentration of the acid after separation of the solid fraction is extracted with a solvent to remove at least some of said uranium into the organic phase, from which a product comprising uranium is recovered.

35. A process according to claim 22 or 34, wherein the phosphoric acid with or without concentration after the separation of the solid fraction is extracted with a water immiscibie organic solvent to give an organic phase comprising purified phosphoric acid and an aqueous affinate layer, which are separated, and phosphoric acid is recovered from said organic phase as phosphoric acid or a salt thereof.

36. A process according to any one of claims 25-34 wherein after separation of said solid fraction and with or without concentration of the acid, said phosphoric acid is treated with at least one nitrogenous compound comprising ammonia to form at least one ammonium phosphate salt.

37. A process according to any one of claims 25-34, wherein after separation ot said solid fraction, said phosphoric acid is treated with an alkali to form at least one alkali metal phosphate salt, which is separated from any solids also formed.

38. A process according to any one of claims 25-34, wherein after separation of the solid fraction, the wet process acid, which has been derived from hydrochloric or nitric acid attack is mixed with calcium hydroxide and precipitated calcium, hydrogen phosphate is separated.

39. A process according to any one of claims 31-38, wherein the rock has been heated by being passed continuously through at least one heated zone at 380--6000C and heated rock is removed from said zone or zones.

40. A calcium phosphate fertilizer prepared by a process as claimed in any one of claims 20-24.

41. A liquid mixture comprising a calcium salt and phosphoric acid prepared by a process as claimed in any one of claims 25-30 or 39.

42. Wet process phosphoric acid prepared by a process as claimed in any one of claims 30-32 or 39.

43. Purified wet process phosphoric acid ca e salt thereof prepared by a process as claimed in claims 33 or 35 or 39.

44. A product comprising uranium obtained by a process as claimed in claim 34 or 39.

45. An ammonium phosphate prepared by a process as claimed in claim 36 or 39.

46. An alkali metal phosphate prepared by a process as in claim 37 or 39.

47. A calcium hydrogen phosphate prepared by a process as claimed in 35 or 39.