FI87185C - OVERFLOWER FOR EXHAUST FLEARING OF FRAON PHOSPHATE - Google Patents

Description

1 87185

The present invention relates to a process for the removal of impurities from crude phosphate by dissolution. The present invention relates to a process for removing impurities from crude phosphate by dissolution.

Impurities in the crude phosphate, such as heavy metals, carbonates and silicates, can cause difficulties in phosphorus recovery processes.

In phosphate enrichment, side minerals such as carbonates and silicates lower the phosphorus content in the concentrate and thus reduce capacity in further processes. Attempts to reduce the amount of side-15 minerals, for example by foaming, often result in a decrease in intake.

In the preparation of phosphoric acid from crude phosphate by acidification with sulfuric acid, heavy metals dissolve for the most part and the remainder ends up in gypsum. Phosphoric acid must then be purified to meet the requirements of the various applications. There are also restrictions on the amounts of heavy metals in gypsum, especially when the gypsum ends up in the sea. Carbonates increase the consumption of sulfuric acid and thus also the amount of gypsum.

Magnesium and silicates can make it difficult to filter gypsum to form gel-like substances in phosphoric acid.

In phosphate fertilizers with nitrates, copper, together with chloride, can cause oxidation of the ammonium ion 30 in the fertilizer, called "cigar burning."

Various methods are known for removing heavy metals, especially cadmium, from crude phosphate.

EP-A-0 087 065 discloses such a process in which crude phosphate is dissolved in nitric acid in the presence of calcium ions at a pH of 0.2-3. Calcium nitrate is mainly used as the calcium ion source.

2 87185 DE 3332698 discloses a similar process for removing cadmium from a crude phosphate by dissolving the crude phosphate with an inorganic acid such as sulfuric acid, nitric acid or phosphoric acid in the presence of a chloride such as ammonium chloride, ferric chloride, or hydrochloric acid.

The disadvantage of both of the above methods is that part of the phosphate dissolves in the acid treatment step, which reduces the yield. The acid treatment also dissolves large amounts of metals, such as iron and aluminum, which do not need to be removed for fertilizer use, and in addition, these metals make it difficult to regenerate the solution.

The object of the invention is to provide a method for removing impurities from crude phosphate which avoids the disadvantages of the above methods.

According to the invention there is thus provided a process for removing impurities from a crude phosphate by dissolution, which process is characterized in that the dissolution is carried out in aqueous solution in the presence of an organic complexing agent using 1 to 6 carbon atoms, straight-chain or branched, saturated or unsaturated carboxylic -substituted with one or more hydroxyl, chloro or mercapto (-SH) groups or a mixture of two or more such carboxylic acids. A particularly preferred organic complexing agent is formic acid.

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Crude phosphate refers to phosphate concentrates containing phosphate ores and heavy metals. Examples are Moroccan, Taiba and Kovdor phosphate and Siilinjärvi concentrate, which are sedimentary or magmatic. The crude phosphate 35 is preferably ground so that 75% of the particles have a particle size of less than 75.

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The process of the invention can remove heavy metals such as cadmium, zinc, nickel, manganese, copper, lead and chromium from the crude phosphate. The process according to the invention can also remove side minerals, such as carbonates and silicates.

According to the invention, heavy metals can be removed from the crude phosphate by dissolving with the above-mentioned organic carboxylic acid so that the phosphorus remains mainly insoluble, with good yield, while carbonates and certain silicates are soluble in the side minerals. Preferred features of the organic carboxylic acid are that it is water soluble, that it has a pKa value greater than 2, that it forms soluble salts, that it has good complexing ability and that it has a low molecular weight.

Organic complexing agents can promote the dissolution of a particular metal over others by selecting an organic carboxylic acid that complexes that particular metal particularly well.

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According to the invention, in addition to the organic complexing agent, an inorganic complexing agent may also be present in the dissolution. Thus, it is possible to make combinations between organic and inorganic complexing agents, making it possible to combine the good properties of two or more complexing agents.

The inorganic complexing agent used according to the invention is preferably chloride ion. For example, ammonium chloride, calcium chloride or sodium chloride can be used as the chloride ion source.

According to the invention, it is advantageous not to dissolve the metals present in large quantities, such as iron and aluminum, whereby purification becomes more advantageous.

The dissolution according to the invention has the special feature compared to other dissolution methods that it so-called of the mixed granules, 35 4 87185 dissolves only a harmful side mineral, such as carbonate, leaving the valuable phosphorus untouched.

The dissolution can be effected in various ways, for example, by grinding the crude phosphate, which increases the reaction surface area, by delaying, which increases the reaction time, by a temperature which increases the reaction rate, and by the amount of solution which determines the amount dissolved.

The dissolution is usually carried out at a temperature of about 0 to 100 ° C, preferably about 20 to 90 ° C, with a residence time of preferably about 0.1 to 6 hours.

According to the invention, an amount of organic complexing agent or organic and inorganic complexing agent is added to the aqueous solution such that the pH is above 2, preferably between 2-5.

The solutions obtained from the leaching can be regenerated using known methods, for example by distillation, ion exchange, extraction, doping or electrolysis.

The invention is described in more detail below by means of examples.

25 Examples 1-6

Moroccan phosphate (25.0 g) was stirred with an aqueous solution (175.0 g) for 6 hours at 20 ° C. The aqueous solution contained 0.185 moles of organic complexing agent dissolved. The slurry was filtered and the dried concentrate was analyzed.

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The acidity of the solution was measured. The composition of the phosphate and the proportion of solute in this are shown in Table 1.

Table 1 Dissolution of Moroccan phosphate (20 ° C, 6 h) with organic complexing agents

Solubility of metals (wt%)

Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Phosphate Vinegar- Acrylic- Thio-Milk- Chlorine- 10 composition acid acid glycolic acid acetic acid _acid_acid_acid P2 ° 5% 30.5 *** 7.5 8.5 17.8 18.8 26.0

Ca% 35.0 3.4 9.0 14.1 20.5 24.9 30.1

Mg% 0.30 34.7 34.7 49.3 56.0 57.3 61.3

Fe% 0.16 2.5 5.0 57.5 2.5 10.0 *** 15 Mn ppm 14.5 36.2 38 ^ 4 76.5 67.7 68.2 71.3

Zn ppm 260 4.0 14.3 44.3 46.0 52.9 49.4

Cd ppm 18.3 24.1 23.9 35.2 55.6 53.6 65.9

Ni ppm 35.1 7.6 8.2 56.2 15.3 19.2 16.9

Cu ppm 23.0 *** 1.6 14.1 13.9 22.6 ***

Pb ppm 3.0 10.7 17.3 17.3 14.7 10.7 ***

Cr ppm 250 *** *** 4.2 2.5 20.5 4.8 20 pH 3.3 3.2 2.8 2.7 2.6 2.4 pKa 4.8 4.3 3, 6 3.8 3.9 2.9 *** _ no detectable dissolution 25 Examples 7-8

Moroccan phosphate (200 g) and water (400 g) were stirred at 80 ° C for 2 hours. The acidity of the aqueous solution (pH = 2) was adjusted with organic complexing agents. The slurry was filtered and the dried concentrate was analyzed. The phosphate composition and the proportion of solute in this are shown in Table 2.

Table 2

Dissolution of Moroccan phosphate (80 ° C for 2 h) with a mixture of organic complexing agents 6 87185 5 Solubility of metals (w / w)

Composition of Phosphate Example 7 Example 8 Formic- Citric & Acidic acid P205% 30.5 1.8 3.4 10 Ca% 35.0 4.1 9.0

Mg% 0.30 46.7 49.3

Fe% 0.16 *** *** Al% 0.27 *** ***

Mn ppm 14.5 63.0 57.2 15 Zn ppm 260 34.8 38.6

Cd ppm 18.3 39.4 31.1

Ni ppm 35.1 23.4 26.5

Cu ppm 23.0 23.8 22.8

Pb ppm 3.0 13.3 20.0 20 Cr ppm 250 *** 26.2 HCOOH g 197 152

CsHioOe g 50 25 *** no detectable dissolution

Examples 9-12

Moroccan phosphate (200 g) and water (400 g) were stirred at 80 ° C for 2 hours. The aqueous solution contained 0.684 moles of 30 Cl and the acidity (pH = 2) was adjusted with formic acid.

The slurry was filtered and the dried concentrate and filtrate were analyzed. The composition of the phosphate and the proportion of solute in this are shown in Table 3.

Table 3

Dissolution of Moroccan phosphate (80 ° C for 2 h) with formic acid and chloride 7 87185 5 Solubility of metals (w / w)

Example 9 Example 10 Example 11 Example 12

Phosphate HCOOH HCOOH / HCOOH / HCOOH / composition_NEUC1_CaCl2_NaCl_ P2Os% 31.4 1.7 1.7 0.7 1.1 10 Ca% 36.0 6.9 7.3 - 7.1

Mg% 0.24 36.6 38.3 41.4 37.0

Fe% 0.32 10.1 7.0 7.1 10.7 Al% 0.35 1.8 1.9 2.5 1.4

Mn ppm 105 17.5 20.0 21.0 19.1 15 Zn ppm 209 29.7 61.1 54.4 60.8

Cd ppm 13 25.5 61.3 59.6 60.8

Ni ppm 28 30.6 48.2 32.1 46.9

Cu ppm 23 9.1 39.9 60.2 54.6

Pb ppm 7.9 <6.0 7.2 16.2 <7.2 20 Cr ppm 169 6.7 6.7 4.7 8.4 V ppm 136 8.2 12.5 7.3 10.2 HCOOH g 135.6 133.6 78.1 110.3

Cl salt g 36.6 38.0 40.0 25

Examples 13-14

Taiba phosphate (200 g) and water (400 g) were stirred for 2 hours at 80 ° C. To the aqueous solution was added 0.684 moles of Cl and the acidity (pH = 2) was adjusted with formic acid. The slurry was filtered and the dried concentrate and filtrate were analyzed. The composition of the phosphate and the proportion of solute in this are shown in Table 4.

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Table 4

Dissolution of taiba phosphate (80 ° C for 2 h) with formic acid and formic acid and chloride 5 Solubility of metals (w / w)

Composition of Phosphate Example 13 Example 14 HCOOH HCOOH / _NaCl_ P = 0B% 35.6 34.6 1.8 2.1 10 Ca% 35.3 35.3 2.7 3.1

Mg ppm 256 256 32.6 33.6

Fe ppm 0.67 0.68 1.6 1.1 Al% 0.39 0.48 4.8 3.3

Mn ppm 201 203 52.3 54.4 15 Zn ppm 626 654 30.0 42.7

Cd ppm 94 96 7.7 17.1

Ni ppm 41 44 39.1 42.5

Cu ppm 58 65 30.0 38.0

Pb ppm 6.8 7.1 23.6 27.5 20 Cr ppm 184 182 <7.3 <7.6 V ppm 260,256 7.3 5.4

Si% 2.64 2.63 1.0 1.0 HCOOH g 133.6 110.3 NaCl g 40.0

Example 15

Covdor phosphate (200 g) and water (400 g) were stirred at 80 ° C for 2 hours. The acidity of the aqueous solution (pH = 2) was adjusted with an organic complexing agent. The slurry was filtered and the dried concentrate was analyzed. The composition of the phosphate and the proportion of solute in this are shown in Table 5.

Table 5

Dissolution of covdorphate phosphate (80 ° C for 2 h) with organic complexing agent 9 87185 5 Solubility of metals (wt%)

Phosphate Ant composition_acid_

Mg% 1.32 72.2

Fe% 0.189 14.4 10 Si% 0.560 48.6

Cu ppm 17.6 26.3 mass g 200 182.9 HCOOH g 133.6 15

Examples 16-17

Moroccan phosphate (50 g) and water (50 g) were stirred at 90 ° C for 2 hours. The acidity of the aqueous solution (pH = 2) was adjusted with an organic complexing agent. The slurry was filtered and the dried concentrate was analyzed and the dissolution was repeated in the same manner. The composition of the phosphate and the proportion of solute in this are shown in Table 6.

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Table 6

Dissolution of Moroccan phosphate (90 ° C for 2 h) with an organic complexing agent in multiples of 5 Solubility of metals (wt%)

Phosphate Example 16 Example 17 HCOOH HCOOH / repeat

Mg% 0.33 47.1 51.0 10 Fe% 0.18 9.9 10.8

Mn ppm 22.6 22.6 54.8

Zn ppm 212 39.4 46.1

Cd ppm 10.5 26.6 32.6

Ni ppm 40.7 64.8 78.0 15 Cr ppm 307 14.1 15.3 V ppm 177 17.5 19.0 mass g 46.3 44.1 HCOOH g 23.8 11.2 20

Examples 18-19

Siilinjärvi concentrate and water were mixed at 90 ° C. The acidity of the aqueous solution was monitored in the presence of an organic complexing agent. The slurry was filtered and the dried concentrate was weighed. The dissolution was repeated. Phosphate composition and analyzes are shown in Table 7.

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Table 7

Dissolution of phosphate precursor concentrate (90 ° C) by repeated organic complexing agent 5 Dissolution (w / w)

Phosphate Example 18 Example 19 Composition HCOOH HCOOH / repeat P2O5% 22.4 0.21 0.28 10 CO2% 17.6

Fe 2 O 3% 1.69 22.2 24.8 Al 2 O 3% 0.72

CaO% 43.8

MgO% 4.93 K20% 0.44

Na 2 O% 0.11

SiO 2% 3.50 mass (0 h) g 100 69.1 20 mass (1 h) g 62.5 mass (3.5 h) g 69.1 HCOOH g 65.3 37.5 H 2 O g 100 69.1 25 temperature ° C 90 90 dissolution time h 3.5 1.0 pH (H 2 O, 0 h) 8.7 (H 2 O, HCOOH 0.1 h) 2.1 2.0 (1.0 h) 2.0 30 ( 3.5 h) 2.5

Claims (6)

A process for removing impurities from rough phosphates by leaching, which contaminants may consist of heavy metals such as cadmium, zinc, nickel, manganese, copper, lead or chromium, or side minerals, such as carbonates or silicates, characterized in that the leaching is carried out in an aqueous solution in the presence of an organic complexing agent, using as an organic complexing agent a straight-chain or branched, saturated or unsaturated carboxylic acid having 1-6 carbon atoms, which may be substituted by one or more hydroxyl, chlorine or mercapto groups, or a mixture of two or more such carboxylic acids. Process according to claim 1, characterized in that formic acid is used as an organic complexing agent. Process according to claim 1 or 2, characterized in that the leaching is carried out at a temperature of about 0-100 ° C, preferably about 20-90 ° C, with the retention being about 0.1-6 hours. Method according to any of claims 1-3, characterized in that an inorganic complexing agent is further present in the leaching. 25 Process according to claim 4, characterized in that a chloride ion is used as an inorganic complexing agent. 6. A process according to claim 5, characterized in that ammonium chloride, calcium chloride or sodium chloride is used as the chloride ion source.