METHOD FOR THE PREPARATION OF CALCIUM MONOHYDROGEN PHOSPHATE

Abstract

This present invention disclosure relates to a method for the preparation of calcium monohydrogen phosphate comprising an etching in an aqueous medium, during a predetermined time period, of a phosphate source with an acid with formation of a pulp comprising an aqueous phase containing calcium phosphate in solution and a solid phase containing impurities, a first separation between said aqueous phase and said solid phase, during a predetermined time period, a neutralization of said aqueous phase at a sufficient pH to obtain a precipitation of said calcium monohydrogen phosphate, a second separation between said aqueous medium and said calcium monohydrogen phosphate, characterized in that said first separation of said step b) is carried out at a filtration rate of at least 0.1 ton of P.sub.2O.sub.5/P/m.sup.2/day.

Claims

1. A method for the preparation of calcium monohydrogen phosphate comprising the steps of: a) digesting in an aqueous medium, during a predetermined time period, a phosphate source by an acid with formation of a pulp comprising an aqueous phase containing calcium phosphate in solution and a solid phase containing impurities, b) separating said aqueous phase containing calcium phosphate in solution and said solid phase containing impurities, for a predetermined time period to provide a separated aqueous phase containing calcium phosphate in solution, c) neutralizing said separated aqueous phase containing calcium phosphate in solution at a sufficient pH to obtain a precipitation in an aqueous medium of insoluble calcium phosphate as aforementioned calcium monohydrogen phosphate, and d) separating said aqueous medium and said calcium monohydrogen phosphate, wherein step b) is carried out at a filtration rate of at least 0.1 ton of P.sub.2O.sub.5/P/m.sup.2/day, between 0.1 and 5 tons of P.sub.2O.sub.5/P/m.sup.2/day, between 0.15 and 3 tons of P.sub.2O.sub.5/P/m.sup.2/day, between 0.3 and 0.9 tons of P.sub.2O.sub.5/P/m.sup.2/day, or between 0.4 and 0.7 tons of P.sub.2O.sub.5/P/m.sup.2/day, said filtration rate being calculated according to the following equation: $\mathrm{Filtration}.Math..Math.\mathrm{rate}=\frac{Q_{P.Math..Math.2.Math.O.Math..Math.5}}{\sqrt{.Math..Math.P}.Math..Math..Math.T_f}$ where Q.sub.P205 corresponds to the quantity of P.sub.2O.sub.5 collected in the filtrate and is expressed in tons, is the filter surface area expressed in m.sup.2, P is the difference between the pressure at the filtrate outlet and the pressure applied to the pulp at the time of said first separation and is expressed in bar, and T.sub.f is the duration of said first separation and is expressed in day.

2. The method according to claim 1, wherein said predetermined time period of said step a) of digestion is greater than, less than or equal to that of the aforementioned first separation step b).

3. The method according to claim 1, wherein the aforementioned steps a) and b) are carried out in a predetermined duration of less than 2 hours, between 30 and 100 minutes, 30 and 70 minutes, or between 40 and 65 minutes.

4. The method according to claim 1, wherein said phosphate source and said acid are introduced into a first reactor comprising said aqueous medium simultaneously or successively, in order to carry out said step a) of digestion and wherein said pulp comprising said aqueous phase containing calcium phosphate in solution and said solid phase containing impurities is transferred from the first reactor to a separation means for carrying out said first separation referred to in the aforementioned step b).

5. The method according to claim 4, wherein said separation means is located between said first reactor and a second reactor.

6. The method according to claim 4, wherein said separation means is present in a second reactor into which said pulp comprising an aqueous phase containing calcium phosphate in solution and a solid phase containing impurities is introduced, to carry out said first separation referred to in the aforementioned step b).

7. The method according to claim 4, wherein said separation means is a filter selected from the group consisting of a rotary filter, a rotary filter with tilting cell, a press filter, a belt filter, a drum filter.

8. The method according to claim 1, wherein said acid is selected from the group consisting of hydrochloric acid (HCl), nitric acid, sulfuric acid, phosphoric acid and mixtures thereof.

9. The method according to claim 8, wherein said acid is an aqueous solution of acid having an acid concentration of less than or equal to 15% by weight.

10. The method according to claim 1, wherein steps a) and b) are carried out at a temperature of between 50 C. and 70 C. or equal to 60 C.

11. The method according to claim 1, wherein said phosphate source is selected from the group consisting of a phosphate rock, a phosphate ore, and secondary phosphate sources.

12. The method according to claim 1, wherein the neutralization step is carried out using a neutralization agent selected from the group consisting of calcium-based compounds.

13. The calcium monohydrogen phosphate obtained according to claim 1, wherein the calcium monohydrogen phosphate is suitable for producing phosphoric acid.

14. The calcium monohydrogen phosphate obtained according to claim 1, wherein the calcium monohydrogen phosphate has a purity level suitable for use in the food industry in the agricultural sector, or horticultural sector.

15. The method according to claim 11, wherein the secondary phosphate sources are selected from ash, sewage sludge, bone slurry, pig slurry, or mixtures thereof.

16. The method according to claim 12, wherein said calcium-based compounds are selected from the group consisting of calcium oxide, calcium hydroxide, calcium carbonate, and water-soluble calcium salts.

Description

EXAMPLE 1

[0073] We start from a phosphate ore having the characteristics of the following table 1:

TABLE-US-00001 Phosphate quantity 1000.0 g Humidity 1.93% 19.3 g CaO 48.90% 489.0 g P.sub.2O.sub.5 31.00% 310.0 g

[0074] A quantity of 120.8 g of demineralized water is introduced into a beaker and then a quantity of 75 g of phosphate from Table 1 is added to the demineralized water, under agitation, to form a mixture. The beaker is then covered with a watch glass and the mixture is brought to a temperature of 60 C.

[0075] 120.8 g of demineralised water is mixed with an aqueous solution of hydrochloric acid, which has a HCl concentration of 37%, in order to obtain 357.7 g of an aqueous solution of HCl at 12%. The latter is then added to the hot mixture of phosphate and demineralized water.

[0076] The digestion duration is measured from the time the dilute aqueous acid solution is added to the hot mixture containing phosphate and demineralized water.

[0077] The solution obtained after digestion is filtered, at a filtration temperature of 60 C., by means of a polyester fibre filter having a diameter of 90 mm and a thickness of 0.17 mm placed on a Buchner type equipment previously evacuated.

[0078] The filtration pressure used is 0.4 bar, which represents a driving pressure difference of 0.6 bar compared to the atmospheric pressure of 1 bar.

[0079] The filtration duration corresponds to the time required to obtain a wet cake from the pulp formed in the previous steps. After the filtration, the cake is subjected to a drying stage during which, the ambient air is sucked through the cake, the drying stage lasting 5 minutes. According to this first example of embodiment, the filtration duration is 5 minutes.

[0080] The weight of the wet cake obtained is then measured as well as the weight of the filtrate. The filtrates and the cake are then subjected to analysis.

[0081] The wet cake is then dried at a temperature of 60 C. and its weight, after drying, is also measured.

[0082] In this example, the digestion duration is 30 minutes and the filtration duration is 5 minutes, as shown in Table 2 below.

TABLE-US-00002 TABLE 2 Example 1 Starting phosphate quantity 75 grams Quantity of aqueous solution of HCl at 12% 357.7 grams Ore digestion temperature 60 C. Digestion duration 30 minutes Filtration temperature 60 C. Filtration duration 5 minutes Filtration rate 1.3 tons of P.sub.2O.sub.5/ m.sup.2/P/day

[0083] The P.sub.2O.sub.5 yield in the final product obtained at the end of the method after steps a and b is equal to 94.03%. The yield is calculated on the basis of the quantity of P.sub.2O.sub.5 present in the phosphate ore. It represents the percentage of P.sub.2O.sub.5 in the filtrate after the first separation step b in relation to this quantity.

EXAMPLE 2

[0084] This example is performed under the same operating conditions as described in example 1, with the exception of the digestion duration being 45 minutes and the filtration duration being 5.5 minutes, as shown in table 3 below.

TABLE-US-00003 TABLE 3 Example 2 Starting phosphate quantity 75 grams Quantity of aqueous solution of HCl at 12% 357.7 grams Ore digestion temperature 60 C. Digestion duration 45 minutes Filtration temperature 60 C. Filtration duration 5.5 minutes Filtration rate 1.1 ton of P.sub.2O.sub.5/ m.sup.2/P/day

[0085] The P.sub.2O.sub.5 yield after steps a and b of the method is 93.02%.

EXAMPLE 3

[0086] This example is performed under the same operating conditions as described in example 1, with the exception of the digestion duration being 60 minutes and the filtration duration being 4.75 minutes, as shown in Table 4 below.

TABLE-US-00004 TABLE 4 Example 3 Starting phosphate quantity 75 grams Quantity of aqueous solution of HCl at 12% 357.7 grams Ore digestion temperature 60 C. Digestion duration 60 minutes Filtration temperature 60 C. Filtration duration 4.75 minutes Filtration rate 1.3 ton of P.sub.2O.sub.5/ m.sup.2/P/day

[0087] The P.sub.2O.sub.5 yield in the product after steps a and b of the method is 93.16%.

EXAMPLE 4

[0088] This example is performed under the same operating conditions as described in example 1, with the exception of the digestion duration being 90 minutes and the filtration duration being 2.33 minutes, as shown in Table 5 below.

TABLE-US-00005 TABLE 5 Example 4 Starting phosphate quantity 75 grams Quantity of aqueous solution of HCl at 12% 357.7 grams Ore digestion temperature 60 C. Digestion duration 90 minutes Filtration temperature 60 C. Filtration duration 2.33 minutes Filtration rate 2.7 tons of P.sub.2O.sub.5/ m.sup.2/P/day

[0089] The P.sub.2O.sub.5 yield in the product obtained after steps a and b of the method is 91.96%.

EXAMPLE 5

[0090] This example is performed under the same operating conditions as described in example 1, with the exception of the digestion duration being 10.5 minutes and the filtration duration being 25 minutes, as shown in Table 6 below.

TABLE-US-00006 TABLE 6 Example 5 Starting phosphate quantity 75 grams Quantity of aqueous solution of HCl at 12% 357.7 grams Ore digestion temperature 60 C. Digestion duration 10.5 minutes Filtration temperature 60 C. Filtration duration 25 minutes Filtration rate 0.3 ton of P.sub.2O.sub.5/ m.sup.2/P/day

[0091] The P.sub.2O.sub.5 yield in the product obtained after steps a and b of the method is 96.33%.

EXAMPLE 6

[0092] This example is performed under the same operating conditions as those described in example 1, with the exception of the digestion duration being 15 minutes and the filtration duration being 13 minutes as shown in Table 7.

TABLE-US-00007 TABLE 7 Example 6 Starting phosphate quantity 75 grams Quantity of aqueous solution of HCl at 12% 357.7 grams Ore digestion temperature 60 C. Digestion duration 15 minutes Filtration temperature 60 C. Filtration duration 13 minutes Filtration rate 0.5 ton of P.sub.2O.sub.5/ m.sup.2/P/day

[0093] The P.sub.2O.sub.5 yield in the product obtained after steps a and b of the method is 96.19%.

EXAMPLE 7

[0094] This example is performed under the same operating conditions as described in example 1, with the exception of the digestion duration being 21.5 minutes and the filtration duration being 9 minutes, as shown in Table 8 below.

TABLE-US-00008 TABLE 8 Example 7 Starting phosphate quantity 75 grams Quantity of aqueous solution of HCl at 12% 357.7 grams Ore digestion temperature 60 C. Digestion duration 21.5 minutes Filtration temperature 60 C. Filtration duration 9 minutes Filtration rate 0.7 ton of P.sub.2O.sub.5/ m.sup.2/P/day

[0095] The P.sub.2O.sub.5 yield in the product obtained after steps a and b of the method is 96.09%.

EXAMPLE 8

[0096] This example is performed under the same operating conditions as described in example 1, with the exception of the digestion duration being 26.33 minutes and the filtration duration being 7.33 minutes, as shown in Table 9 below.

TABLE-US-00009 TABLE 9 Example 8 Starting phosphate quantity 75 grams Quantity of aqueous solution of HCl at 12% 357.7 grams Ore digestion temperature 60 C. Digestion duration 26.33 minutes Filtration temperature 60 C. Filtration duration 7.33 minutes Filtration rate 71.8 tons of P.sub.2O.sub.5/ m.sup.2/P/day

[0097] The P.sub.2O.sub.5 yield in the product obtained after steps a and b of the method is 95.85%.

[0098] It is understood that this invention is in no way limited to the embodiments described above and that many amendments may be made to it without going beyond the scope of the attached claims.