NL8001204A - PROCESS FOR PREPARING PHOSPHORIC ACID FROM PHOSPHATE STATES - Google Patents

Description

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Process for the preparation of phosphoric acid from phosphate rock.

The invention relates to a thermal treatment process and in particular to a thermal treatment of phosphate rock.

Calcium phosphate rock contains many contaminants, including organic compounds, for example humic acid. The organic impurities can cause severe foaming when the ore is treated with acid to form calcium sulfate and wet-process phosphoric acid and can also give rise to colored downstream products, for example, phosphoric acid and alkali metal phosphate salts. It is known to remove the organic materials by treatment with activated carbon or by applying oxidizing salts to the phosphoric acid or salts thereof or by calcining the ore. In the calcination, the ore is usually calcined to convert the organic materials to carbon dioxide leaving a calcined ore which is substantially free of organic carbon and suitable for conversion to downstream products; temperatures of 750 ° C or higher are useful for this annealing. The foaming can be eliminated by prolonged heating at temperatures above 650 ° C without the need for complete oxidation of the organic compounds (see Chem. Eng. Progress Vol. 58, 1962, pp. 91-93).

It has now been found that by thermal treatment of the ore at temperatures lower than those mentioned above, the organic compounds can be converted at least partly and usually almost completely into insoluble particulate carbon, which can be filtered off 800 1 2 04 2

a

with the calcium sulfate on subsequent acidification to form wet-process phosphoric acid.

The invention provides a process for preparing phosphoric acid phosphate rock, wherein phosphate rock is heated to form a heated ore and the heated ore is reacted with acid to form a calcium salt and phosphoric acid, characterized in that phosphate rock containing organic compounds is heated at 380-600 ° C to convert at least a portion of the organic compounds into carbon to form a heated ore containing carbon particles and the heated ore containing carbon particles is reacted with a mixture of sulfuric acid and phosphoric acid to form a solid fraction, comprising calcium sulfate and carbon particles, and wet-process phosphoric acid, and the acid is separated from this solid fraction. The phosphate rock is heated to a temperature sufficient to convert at least a portion of said impurities and preferably substantially all impurities into particulate carbon, but insufficient to cause combustion of all carbon 20 to an oxide of carbon so that the treated ore contains carbon particles. When the treated ore is reacted with the acid, a mixture is formed containing phosphoric acid, sulfuric acid, calcium sulfate simply as gypsum, carbon particles and usually a small amount of unaffected ore; the mixture can be filtered to leave a wet-process acid, which is free from carbon particles and which has a considerably reduced color, for example, yellow instead of the deep brown color of acid from some untreated ores.

The heating of the phosphate rock by the process of the invention may allow the reaction with the acid to proceed more satisfactorily with less or no foaming than if untreated ore is exposed to the attack, so that the acidification is carried out advantageously in substantially complete absence of any anti-foaming agent. The ore reaction can also be carried out at a higher filtration rate and ore attack rate than when ore calcined at 950 ° C is attacked. Furthermore, heating in the process of the invention reduces or eliminates the need for the application of activated carbon or oxidizing agents to the acid or its salts to reduce its color. Heating at a lower temperature also represents a considerable economic advantage.

The ore is heated to a temperature of not more than 600 ° C, that is, 380-600 ° C, such as 450-600 ° C, and in particular 450-550 ° C; temperatures of 380-500 ° C, for example, 380-480 ° C and especially 420-480 ° G, can be used, but the conversion rate of the organic materials to carbon is slower than at higher temperatures. The ore is usually heated at the given temperature for 0.01-10 hours, for example 0.1-10 hours, for example 0.5-2 hours for discontinuous processes, or 1 minute to 1 hour, for example 2-30 minutes for continuous processes, where the heating time is inversely proportional to the temperature used.

Although the usual annealing at 650 ° C or higher gives a significant amount of hydrogen fluoride in the gaseous effluent obtained upon heating, the heating at the lower temperature of the invention gives much less fluoride and often no fluoride at all in the effluent, so that the purification of this effluent is facilitated.

The heating treatment can be carried out under substantially anaerobic conditions with virtually no free oxygen (or other means capable of oxidizing the organic contaminants); thus, the ore can be externally heated in the absence of air, for example, in an oven with exclusion of air. However, the ore is advantageously heated in the absence of oxidizing agents (other than oxygen) which can oxidize the organic impurities; for example, the ore can be heated in the presence of air, such as in an oven, or heated, for example, by an oxidizing flame in an oven, to the required temperature. The heating can be carried out with too short of oxygen with respect to the amount required to convert the organic impurities to carbon, but preferably 800 1 2 04 4, at least the required amount and in particular a used in excess. The heating treatment is preferably carried out continuously, the ore, for example in the form of a continuous layer, continuously moving under a flame, or in a rotating drum 5 in counter-current with the hot combustion products of a flame or in a fluidized bed. Although the heating treatment can be carried out on an ore with large particles, the particles of the ore are preferably less than 5 mm and preferably the ore is ground first, for example to particles of 0.01-1 mm, for example at least 50% of the particles have a size of 0.0ΙΟ.5 mm and preferably less than 30% of the particles have a size of less than 0.1 mm.

The ore may contain 0.05-6%, for example, 0.05-1.0% or 0.5-6.0% organic matter (expressed as weight percent organic carbon) as well as conventional ore impurities.

The ore may thus contain 15-45 wt.%, For example 25-40 wt.%, 2- 5 wt.% 25-35 wt.% Or 30-40 wt.%, Or in particular 30-35 wt. > 25-55 wt.%, For example 45-55 or 50-55 wt.% CaO, 0.01-8 wt.%, For example 0.05-0.5 wt.% Or 0.5-5 wt. % 1 ^ 02 with 20 a total iron and aluminum content of, for example, less than 10 wt%, for example less than 4 wt% (expressed as and Α ^ Ο ^) and 1.0-7 wt%, for example 1- 3.5% by weight or 3.5-7% by weight of carbonate (expressed as (X ^). The invention is particularly suitable for the treatment of apatite phosphate ores, for example those which are digested with 27 % hydrochloric acid forms brown liquids, examples of such ores are from Zin in Israel, and Florida, however other ores, for example those from the Western United States or elsewhere, such as Tennessee, Tunisia, Jordan, and Morocco, may also The phosphate rock preferably contains 0.05-0.4% organic material or a weight ratio of organic material to from 0 * 01-0.1: 1; ores with a low organic matter content include those from Zin (Israel), Khouribga (Morocco), El Massa (Jordan), Algeria, Tunisia and Senegal.

The process of the invention is particularly suitable for the treatment of ores containing acid-soluble organic materials (as defined below). The term "acid-soluble organic materials" as used in this specification refers to organic compounds present in phosphate ore which have such character and are present in an amount that when digested the ore with a mixture of 56 % sulfuric acid and 20% thermal phosphoric acid (which mixture contains enough sulfuric acid to convert the calcium oxide content of the ore into calcium sulfate) to form a suspension in a liquid containing 25-30%, which is at least 600 ppm (e.g. 600-60,000 ppm) contains dissolved organic materials (expressed as total carbon), i.e. a weight ratio of dissolved organic materials (expressed as total carbon) to liquid of at least 0.002: 1, e.g. 0.002-0.2: 1 ; on the other hand, the content in the liquid of dissolved organic materials, expressed as oxidizable carbon, is at least 100 ppm, eg 100-10,000 ppm, ie a weight ratio of organic materials to 0.0003: 1, eg 0 , 0003-0.03: 1. These are those ores which give acids which contain the higher amounts of dissolved organic materials which can be most usefully improved by using the heating treatment of the invention to obtain treated ores from which acid contains smaller amounts. organic materials (e.g., 500 ppm or less total carbon or 50 ppm or less oxidisable carbon) can be prepared.

Ores that can be treated by the method of the invention include those in which the ores themselves contain a low content of organic materials, for example, 0.05-0.4% (total carbon), but these organic materials rials are acid soluble as defined above. Such ores are obtained, for example, from Zin in Israel, Algeria, Tunisia, Jordan and Senegal. According to another aspect of the invention, there is thus provided a process for the heat treatment of phosphate ore, wherein a phosphate ore containing 0.05-0.4% organic compounds (expressed as carbon) and acid-soluble in total organic materials, becomes 800 1 2 04

St 6 subjected to a heat treatment at 380-600 ° C to convert at least a portion of the organic compounds into carbon to form a heated ore containing carbon particles. Preferably the ore contains 30-40% and 5-55% 5 CaO.

Furthermore, it was found that when phosphate ores are exposed to a heating treatment at 650 ° C, a treated ore is obtained which, upon acidification with an inorganic acid, gives hydrogen sulfide in varying amounts depending on the ore and that when the ore is subjected to a heating treatment according to the method of the invention at a lower temperature, for example 380-600 ° C, the amount of the aggressive and toxic hydrogen sulfide formed on acidification can be reduced, which also applies to the iron content of the acid product. It is believed that this high temperature effect is caused by the conversion at the higher temperatures of acid-insoluble iron sulfide present in the ore into acid-soluble iron sulfide, which forms hydrogen sulfide and dissolved iron on acidification.

According to a special embodiment of the process according to the invention, there is thus provided a process for the preparation of phosphoric acid, in which phosphate rock, containing organic impurities and acid-insoluble, heat-labile iron sulfide, is heated at 380-600 ° C in order to obtain at least a convert part of said organic impurities into carbon particles, but insufficient to cause conversion of all the acid-insoluble sulfide into acid-soluble iron sulfide, the heating process resulting in a treated ore containing carbon particles and in acid insoluble iron sulfide, and the treated ore is reacted with the mixture of sulfuric acid and phosphoric acid to form a reaction mixture containing phosphoric acid, sulfuric acid, calcium sulfate, carbon particles and acid insoluble, heat-labile iron sulfide, and a solid fraction containing said carbon particles and acid insoluble Iron sulfide and calcium sulfate, usually as gypsum, separate from a wet process phosphoric acid. The terms "acid insoluble and acid soluble iron sulfide" refer to iron sulfides which are insoluble or soluble in a wet process phosphoric acid containing 28% and 0.5% SO2. The term "heat labile" iron sulfide, is used in

O

This description relates to the iron sulfide in the ore, which can be converted from acid insoluble to acid soluble when heated. The heating treatment is carried out at 380-600 ° C, for example 380-480 ° C, in particular 400-450 ° C or 450-550 ° C, and usually at a temperature below the phase-10 transition temperature in this ore before the conversion of acid insoluble in acid soluble iron sulfide. The heating conditions generally correspond to those described above.

The method comprising preventing hydrogen sulfide formation can be applied to any phosphate rock, such as those described above, but in particular to those containing heat-labile, acid-insoluble iron sulfide, for example in an amount of at least 100 ppm (preferably at least 500 ppm) sulfide (expressed in 20 parts by weight as S), such as 100-20,000, for example 500-10,000, such as 2000-5000 ppm or at least 200 ppm metal sulfide (expressed in parts by weight as FeS ^) such as 200-40,000, for example 1000-10,000 ppm. The heat-labile, acid-insoluble sulfide content of the unheated ore is obtained from the maximum value of hydrochloric acid-soluble sulfide, present in ores, heated at any temperature in the range of 100-1000 ° C.

Such ores are, for example, those from Zin, Youssoufia and especially Florida, the latter of which the preferred heating temperature is 450-550 ° C; ores from Tennessee, North Carolina, Idaho and the other Western States of the United States may also be treated in an analogous manner.

In another aspect, the invention provides a heated phosphate rock, containing carbon particles and acid-insoluble, heat-labile iron sulfide, of which at least 70%, for example at least 80%, such as 80-98% or at least 90% are acid insoluble and of which the remainder (if any) is soluble in acid 800 1 2 04 8. Preferably, the ore contains at least 500 ppm, for example 500-5000 ppm, of the acid-insoluble, heat-labile iron sulfide (expressed as S).

In the conversion of the heat-treated ore to wet process acid, regardless of whether the ore contains a significant amount of iron sulfides or not, the ore is treated with sulfuric acid and phosphoric acid to form the reaction mixture containing a liquid and a solid fraction. , a major amount of the solid fraction comprising calcium sulfate and a small amount of carbon particles (and optionally iron sulfide) and usually a small amount of unaffected ore. The amount of sulfuric acid is usually such that at least 90%, for example at least 95%, of the phosphate values in the ore are converted to wet-process phosphoric acid or is equivalent to at least 90% of the calcium oxide content of the ore and preferably 95-105%. The reaction of the treated ore with the mixture of phosphoric acid and sulfuric acid can be carried out at a low temperature and with a low concentration of sulfuric acid to form gypsum or at high temperatures, for example above 90 ° C, and with a high concentration of sulfuric acid to form of calcium sulfate hemi-hydrate or anhydrite. Suitably, the ore is mixed with sulfuric acid and weak recirculation phosphoric acid and a calcium sulfate recirculation slurry in wet process phosphoric acid to form the calcium sulfate slurry, a portion of which is recycled and the remainder separated, for example, by filtration , and the filter cake of the calcium sulfate (with carbon particles and possibly iron sulfide) is washed with water to obtain a filtrate of weak phosphoric acid, which is re-filtered to the step where the attack of the ore is carried out.

The invention is further illustrated but not limited by the following examples.

Examples I-III and Comparative Examples A-D.

Phosphate rock from Zin, Israel, had the following analysis: 32.0% 6.0 ^ CO2 '* S03' ^ S ^ ° 2 '4.0% F, 51% Ca (as CaO), 0.2% Mg , 0.3% Al (as Al ^), 0.2% 800 1 2 04 TV \ 9

Fe (as Fe 2 O ^), 0.9% Na (as ^ 2 0), 0.2% oxidizable organic material (expressed as C).

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

A layer of the above-mentioned ore was heated in an oven for 1 hour in the presence of air at a temperature as indicated below. The treated ore was examined after cooling. The ores, treated at 400-700 ° C, were dark and showed the presence of carbon particles.

To determine the effect of the heating to remove the organic materials from the ore, the ore (treated by heating or otherwise) (100 g) was gradually added to a mixture of concentrated chloro-15 hydrochloric acid (35%, 205 g) and water (75 g). The temperature of the mixture rose to 40-45 ° C and the mixture was then heated to boiling point for 1 hour. The degree of foaming obtained in the reaction of ore and acid was recorded. The reaction mixture was filtered hot to remove any carbon particles present, unreacted ore and a small amount of calcium salts, then cooled to room temperature and filtered again to yield crude phosphoric acid. The color of the crude acid was recorded and the results are shown below.

25 Table A

Preheat Color of Color of Acid Degree of Image Foam Temp. (° C) ore pressure _duct_ A (comp.) No sand color deep red-brown large 30 B (comp.) 200 sand color deep red-brown large X 400 pale black strong part II 450 medium black medium yellow III 500 black light green C (comp.) 700 gray light green small 35 D (comp.) 900 green light green small 800 1 2 04 f 10

Examples IV-VIII and Comparative Example D

In the same manner as in Examples I-III, phosphate rock from Zin, Israel, with the same analysis and particle size as described above, was heated at varying temperatures and for varying times. The treated ore was reacted with hydrochloric acid as described above and in separate experiments with a sulfuric acid-phosphoric acid mixture and the color of the liquid was recorded and the organic matter and P2 ° 5 content of the liquid was determined. The sulfuric acid-phosphoric acid mixture was a mixture of 200 g of 20% P2O5 thermal phosphoric acid and a sufficient amount of 56% sulfuric acid to combine with 98% of the calcium content of the phosphate rock used, the amount of which was that it contained 40 g. The specified amount of ore was mixed with stirring with 200 g of phosphoric acid at 60 ° C. When the foaming ceased, the sulfuric acid was added and the mixture was stirred at 70 ° C for 2 hours to obtain a slurry of gypsum in phosphoric acid. The suspension was filtered while hot and the filter 3. .

cake was washed three times with 50 cm of cold tap water. All 20 filtrates were combined to give the product acid, which was analyzed for total carbon and oxidizable carbon contents. The ore before and after the heating was also analyzed for F. The results are shown in Table B. The Zin ore contained before the heat treatment acid insoluble iron sulfide in an amount of 250 ppm (expressed as S). Examples IX-XVIII and Comparative Examples E-J.

In the same manner as in Examples IV-VIII, the same procedures for the heating of phosphate rock and for the reaction of the ore with hydrochloric acid or the sulfuric acid-phosphoric acid mixtures were performed with ores other than Zin. Details regarding the ores and the results obtained are given in Tables C-E below. In either case, the heating treatment was carried out for 1 hour unless otherwise indicated. When unheated Moroccan ore 35 was digested with the SO2 / HPO2 mixture, the liquid (after filtration) contained 27.8% 100-200 ppm total carbon and 15-20 800 1 2 04 11 ppm oxidizable carbon.

Examples XVII-XIX

The Zin ore as in Example IV was continuously subjected to a heating treatment in an inclined rotary annealer, with the ore slowly moving downward in the annealer in countercurrent with an air / burnt gas stream. The residence time was 20-30 minutes. The temperatures of the entering gas, of the solid at the exit point of the annealing device and of the effluent gas were measured. The heated ore was collected and treated with the sulfuric acid-phosphoric acid mixture as described in Example IV; the insoluble materials (including gypsum and carbon particles) were filtered off and the color of the product acid was recorded. The results indicated below were obtained.

Temperatures (° C) _

Emerging Incoming Effluent Acid image solid color gas_gas_product_ XVII 430 800 - orange yellow 20 XVIII 510 880 210 very light green XIX 520 890 200 very light green 800 1 2 04

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Table C

Phosphate rock analyzes

Source of the ore Morocco Jordan Florida _ (Khourigba) ___________% P205 31.5 33.9 31.3% CaO 51.2 52.8 45.1% Na20 0.7 0.57 0.6% MgO 0.8 0.29 0.75% Al2 O3 0.40 0.28 1.8% -Fe2 O3 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% organic 0.18 0.30 1.56

material like C.

% weight loss 1.3 1.2 0.8 when heated to

105 ° C

Particle size analysis (wt%)

Mesh No._Morocco_Jordan_Florida_

Greater than 1.2mm 63 (+14 mesh) 0.5mm-1.2mm 10 38 35 (+30 mesh) 0.25-0.5mm 7 24 39 (+60 mesh) 0.15-0 , 25 mm 15 27 23 (+100 mesh)

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Examples XX-XXII and comparative examples K-N

Florida ore with analysis as indicated above was heated at varying temperatures for 1 hour and then the treated ore was reacted with the sulfuric acid-phosphoric acid mixture as described in Example IV. A solid, comprising calcium sulfate, carbon particles, and iron sulfide, was separated from the reaction mixture leaving an acid product. The treated ore was treated with 14 wt% hydrochloric acid and analyzed for soluble iron and sulfide.

The results obtained are shown in the table below.

Example Temperature (° C) Analysis of ore _ ulf Sulfide (ppm)% soluble Fe 15 Comparative no heating 70 0.57

Ex. K

XX 400 110 0.73 XXI 500 220 0.76 XXII 600 980 0.94 20 Comparative 650 2180 1.12

Ex. L.

Comparative 750 3360 1.35

Ex, M

Comparative 900 110 1.36

25 Ex. N

800 1 2 04

Claims (18)

1. Process for preparing phosphoric acid from phosphate ore, wherein phosphate ore is heated to form a heated ore and the heated ore is reacted with acid to form a calcium salt and phosphoric acid, characterized in that phosphate ore containing organic compounds, is heated to 380-600 ° C to convert at least a portion of the organic compounds to carbon to form a heated ore containing carbon particles and the heated ore containing carbon particles to be reacted with a mixture of sulfuric acid and phosphoric acid to form a solid fraction, comprising calcium sulfate and carbon particles, and wet-process phosphoric acid, and the acid is separated from the solid fraction. 2. Process according to claim 1, characterized in that the phosphate rock is heated at 450-550 ° C. Process according to claim 1, characterized in that the phosphate rock is heated to 380-480 ° C. 4. Process according to claims 1-3, characterized in that the phosphate rock for heating is an ore, which gives a brown liquid with 27% hydrochloric acid. 5. Process according to claims 1-4, characterized in that the ore for heating is an ore containing 30-40%? 20 ^ and 45-55% CaO. 6. Process according to claims 1-5, characterized in that the ore for heating contains acid-soluble organic materials and a total of 0.05-0.4% organic compounds (expressed as carbon). 7. Process according to claims 1-6, characterized in that the ore comprises organic compounds and acid-insoluble, heat-labile iron sulfide and is heated at a temperature which is insufficient for all the acid-insoluble iron sulfide to be put in acid-soluble iron sulfide, and in the acidification of the treated ore a solid fraction, comprising calcium sulfate, carbon particles and acid-insoluble iron sulfide, is separated leaving purified wet-process phosphoric acid. 800 1 2 04 \. Process according to claim 7, characterized in that ore containing at least 500 ppm of acid insoluble iron sulfide (expressed as S) is heated. 9. A heat-treated phosphate ore, characterized in that it contains carbon particles and acid-insoluble, heat-labile iron sulfide. Ore according to claim 9, characterized in that it contains at least 500 ppm of said iron sulfide. Ore according to claims 9 or 10, characterized in that at least 80% of the iron sulfide is insoluble in acid and the rest, if present, is soluble in acid. 12. Process for the treatment by heating of phosphate ore, characterized in that phosphate ore containing a total of 0.05-0.4% organic compounds (expressed as carbon) and acid-soluble organic materials is heated to 380 -600 ° C to convert at least a portion of the organic compounds to carbon to form a heated ore containing carbon particles. Process according to claim 12, characterized in that the ore comprises 30-40% and 45-55% CaO. Process according to claims 12 or 13, characterized in that the ore is heated to 380-480 ° C. Method according to claims 12 or 13, 25, characterized in that the ore is heated to 450-550 ° C. Phosphoric acid prepared according to the method of claims 1-8. Treated ore prepared according to the method of claims 12-16. 18. Methods as described in the description and / or examples. 800 N 800 1 2 04 ï 4