Preparation method of feed-grade calcium phosphate

Abstract

The invention relates to the technical field of phosphorus chemical industry, in particular to a preparation method of feed-grade calcium phosphate, which comprises the following steps: A) heating raffinate acid to 60-120 DEG C; b) mixing the heated raffinate acid with an oxidizing agent, and carrying out oxidation reaction at 90-100 DEG C; c) mixing the product solution obtained in the step B) with CaCO3 slurry to obtain feed-grade calcium phosphate slurry; and D) drying the feed-grade calcium phosphate slurry to obtain the feed-grade calcium phosphate. According to the method, volatile organic solvents and organic matters in the raffinate acid are oxidized by using the oxidizing agent, and volatile organic matters in the raffinate acid are removed, so that the problems of generation site and product peculiar smell in the process of preparing feed-grade calcium phosphate from the raffinate acid are solved, and the 0-grade odorless standard requirement specified by Emission Standard of Odor Pollutants (GB14554-93) is met.

Description

Technical Field

[0001] The invention relates to the technical field of phosphorus chemical industry, and in particular to a method for preparing feed-grade calcium phosphate. Background Art

[0002] Solvent extraction is a method of purifying phosphoric acid, which is low in energy consumption and cost, and is now gradually replacing thermal phosphoric acid, which is energy-intensive. Raffinate acid is a byproduct of wet phosphoric acid purification with solvents, and about half of the phosphoric acid in the feed acid remains in the raffinate acid.

[0003] Due to the high impurity content of raffinate acid, the industry uses raffinate acid for heating and steaming to volatilize volatile organic matter, and then combines it with a large amount of raw acid with low impurity content to produce compound fertilizers and fertilizer-grade monoammonium phosphate.

[0004] When using raffinate to prepare feed-grade calcium phosphate, since raffinate contains organic solvents and other volatile organic matter, organic solvents evaporate during the preparation and drying process of feed-grade calcium phosphate slurry, which causes odors to easily appear on the production site and in the product. Summary of the invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a method for preparing feed-grade calcium phosphate salt, decompose the solvent and organic matter in the raffinate acid into CO2 and water, and effectively eliminate the on-site odor and product odor in the production process of feed-grade calcium phosphate salt.

[0006] The present invention provides a method for preparing feed-grade calcium phosphate, comprising the following steps:

[0007] A) heating the raffinate to 60-120°C;

[0008] B) mixing the heated raffinate with an oxidant and performing an oxidation reaction at 90 to 100° C.;

[0009] C) mixing the product solution obtained in step B) with CaCO slurry to obtain feed-grade calcium phosphate slurry;

[0010] D) drying the feed-grade calcium phosphate slurry to obtain feed-grade calcium phosphate.

[0011] Preferably, in step A), the mass content of P2O5 in the raffinate is 20% to 54%, and the mass content of Mg 2+ The mass content of Fe is less than 1%, 2+ The mass content of N<3000ppm, the mass content of Al<2000ppm, the mass content of TBP>10ppm, and the mass content of TOC>50ppm;

[0012] The pH value of the raffinate acid is <1.

[0013] Preferably, in step A), the raffinate is heated to 95-100° C.;

[0014] The heating method is direct heating or using a partition heat exchange device to increase the temperature of the raffinate acid.

[0015] Preferably, in step B), the oxidant is at least one of peroxide and superoxide;

[0016] The oxidant accounts for 0.5% to 5% of the mass of the heated raffinate.

[0017] Preferably, in step B), the oxidant is hydrogen peroxide.

[0018] Preferably, in step B), the mixing time is not less than 30 minutes.

[0019] Preferably, in step B), after the heated raffinate acid is mixed with the oxidant, the oxidation reaction time is not less than 30 minutes.

[0020] Preferably, in step C), the mass ratio of P2O5 in the product solution obtained in step B) to the Ca element in the CaCO3 slurry is 3 to 4:1.

[0021] Preferably, in step D), the drying method is atomization drying or return material granulation drying; the outlet temperature of the atomization drying or return material granulation drying equipment is 70-105°C.

[0022] Preferably, in step D), after the drying, the step further comprises: cooling;

[0023] The temperature of the product after cooling is less than 60°C;

[0024] The tail gas generated by the drying is washed with an alkaline detergent and then discharged; the pH value of the alkaline detergent is 7-14.

[0025] The present invention uses an oxidant to oxidize the residual organic solvent in the raffinate acid, decomposes the organic solvent in the raffinate acid into CO2 and H2O, effectively eliminates solvent volatilization, and no volatile organic matter is generated at the treatment site; effectively utilizes Fe in the raffinate acid 2+Metal ions such as ions are used as oxidation catalysts to reduce the amount of oxidants and improve oxidation efficiency. The removal rate of volatile organic solvents in the raffinate acid can reach 100%, and the total TOC removal rate can exceed 80%. After oxidation, the raffinate acid can effectively remove odors from the source, effectively prevent the solvents in the calcium phosphate pulping and slurry drying stages from volatilizing due to heat, effectively solve the problem of organic solvent residues in the product, and thoroughly improve the production environment. The site and products meet the 0-level odorless standard requirements specified in the "Emission Standards for Malodorous Pollutants" (GB14554-93). Compared with the existing raffinate acid heating volatilization of organic solvents or raffinate acid combined with fresh acid to prepare compound fertilizers and fertilizer-grade monoammonium phosphate, it can reduce the mixed acid and heating volatilization solvent operation units, and eradicate the volatile organic solvents in the raffinate acid use process from the source. DETAILED DESCRIPTION

[0026] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] The present invention provides a method for preparing feed-grade calcium phosphate, comprising the following steps:

[0028] A) heating the raffinate to 60-120°C;

[0029] B) mixing the heated raffinate with an oxidant and performing an oxidation reaction at 90 to 100° C.;

[0030] C) mixing the product solution obtained in step B) with CaCO slurry to obtain feed-grade calcium phosphate slurry;

[0031] D) drying the feed-grade calcium phosphate slurry to obtain feed-grade calcium phosphate.

[0032] Regarding step A):

[0033] Heat the raffinate to 60-120°C.

[0034] The mass content of P2O5 in the raffinate is 20% to 54%, and the mass content of Mg 2+ The mass content of Fe is less than 1%, 2+ The mass content of Al is less than 3000ppm. 3+ The mass content of is less than 2000ppm, the mass content of organic solvent (TBP) is greater than 10ppm, and the mass content of total organic carbon (TOC) is greater than 50ppm.

[0035] For example, in the raffinate, the mass content of P2O5 is 20% to 30%, and the mass content of Mg 2+ The mass content of Fe is 0.3% to 1%, 2+ The mass content is 2000~3000ppm, Al 3+ The mass content of B2 is 1000-2000ppm, the mass content of TBP is 10-100ppm, and the mass content of TOC is 50-250ppm.

[0036] Specifically, in the raffinate, the mass content of P2O5 is 22.66%, and the mass content of Mg 2+ The mass content of Fe is 0.59%, 2+ The mass content of Al is 2205ppm, 3+ The mass content of is 1226ppm, the mass content of organic solvent TBP is 58ppm, and the mass content of TOC is 188ppm.

[0037] The pH value of the raffinate acid is <1.

[0038] In certain embodiments of the present invention, the raffinate is heated to 80-100°C, 90-100°C or 95-100°C; specifically 60°C, 80°C, 100°C.

[0039] The heating method may be direct heating or using a partition heat exchange device to increase the temperature of the raffinate acid.

[0040] Regarding step B):

[0041] The heated raffinate acid is mixed with an oxidant and an oxidation reaction is carried out at 90-100°C.

[0042] The oxidant is at least one of peroxide and superoxide, such as hydrogen peroxide, with a mass concentration of 27.5% to 70%, preferably 27.5%. The oxidant accounts for 0.5% to 5% of the mass of the heated raffinate, such as 0.5% to 3%, specifically 0.99%, 1.65%, 2.03%, 0.67%, 1.01%, 1.99%, 0.49%, 1.11%, 2.01%.

[0043] The mixing time is not less than 30 minutes, such as 1 to 2 hours, specifically 1 hour.

[0044] The mixing is carried out in a tubular mixer.

[0045] The oxidation reaction is carried out in an oxidation reaction tank.

[0046] After the heated raffinate acid is mixed with the oxidant, the oxidation reaction time is not less than 30 minutes, such as 1 to 2 hours, specifically 1.5 hours.

[0047] Regarding step C):

[0048] The product solution obtained in step B) is mixed with CaCO3 slurry to obtain feed-grade calcium phosphate slurry.

[0049] The CaCO3 slurry is prepared by mixing CaCO3 with water. The mass concentration of the CaCO3 slurry is 25% to 65%. In order to meet the transportability of the CaCO3 slurry and increase the solid content of the calcium phosphate slurry after the reaction of the raffinate acid and the CaCO3 slurry, preferably, the mass concentration of the CaCO3 slurry is 50% to 60%, such as 60%.

[0050] The mass ratio of P2O5 in the product solution obtained in step B) to the Ca element in the CaCO3 slurry is 3 to 4:1, such as 3.65 to 3.95:1, specifically 3.8:1.

[0051] The mixing is carried out in a pulping reaction tank.

[0052] Regarding step D):

[0053] The feed-grade calcium phosphate salt slurry is dried to obtain feed-grade calcium phosphate salt.

[0054] The drying method is atomization drying or return material granulation drying. The outlet temperature of the atomization drying or return material granulation drying equipment is 70-105°C, for example, 105°C.

[0055] After the drying, the process further includes: cooling, such as natural cooling. The temperature of the product after the cooling is less than 60° C., such as 56° C. The product is packaged after the cooling.

[0056] The tail gas generated by the drying is washed with an alkaline detergent before being discharged. To avoid nozzle blockage caused by tail gas washing atomization, the pH value of the alkaline washing water is controlled to be 7 to 14, preferably 12 to 13. The alkaline detergent is a Na2CO3 aqueous solution or a NaOH aqueous solution.

[0057] The present invention has no particular limitation on the sources of the raw materials used above, and they can be generally commercially available.

[0058] The invention provides a method for preparing feed-grade calcium phosphate salt by removing volatile organic matter from raffinate acid.

[0059] The present invention uses an oxidant to oxidize volatile organic solvents and organic matter in the raffinate acid, removes volatile organic matter in the raffinate acid, and the raffinate acid without the volatile organic solvent is directly used for the first time to prepare feed-grade calcium phosphate salts (monocalcium phosphate (MCP), monocalcium phosphate (MDCP)), shortens the process, and fundamentally eliminates the odor on site and in products.

[0060] In the prior art, solvent extraction is used to purify wet-process phosphoric acid. The selected solvents include alcohols, esters, ethers or mixtures of the above solvents. The solvents are volatile and have a flash point of 50 to 145°C. Traditional raffinate acid deodorization (organic solvent / organic matter) uses the method of heating the raffinate acid to a temperature greater than the flash point to volatilize the organic solvent in the raffinate acid. This method does not completely volatilize the organic solvent in the raffinate acid (especially the organic matter brought into the wet-process phosphoric acid), and cannot improve the surrounding environment and completely eliminate the odor.

[0061] The present invention is based on the Fe contained in the raffinate. 2+ , in Fe 2+ Under the catalysis of Fe 2+ +H2O2→Fe 3+ +(OH) - +OH·), it is the presence of hydroxyl radicals that makes H2O2 more oxidizing. Therefore, persistent organic matter, especially aromatic compounds and some heterocyclic compounds that are difficult to oxidize with common reagents, are all degraded by non-selective oxidation. 2+ Through the coordinated coupling effect, alcohols, esters, ethers or mixtures of the above solvents are oxidized and degraded to generate CO2 and H2O, and the organic solvents and organic matter in the raffinate acid are completely removed, effectively solving the odor in the raffinate acid. The product does not affect the surrounding environment and the operating environment is clean. The odor-free raffinate acid is directly used to prepare feed-grade calcium phosphate salts. This is the first time in the industry that the on-site odor in the pulping and drying process can be completely avoided, so that the hygiene indicators of the raffinate acid for preparing feed-grade calcium phosphate salts meet the standards.

[0062] Compared with the traditional method of heating and volatilizing solvents, the present invention uses an oxidation method to degrade volatile organic solvents and organic matter in the raffinate acid, thereby saving energy and reducing consumption, being beneficial to improving the production operation environment and reducing secondary pollutants.

[0063] In order to further illustrate the present invention, a method for preparing a feed-grade calcium phosphate salt provided by the present invention is described in detail below in conjunction with examples, but it should not be construed as limiting the scope of protection of the present invention.

[0064] In the embodiments and comparative examples, the mass content of P2O5 in the raffinate is 22.66%, and the mass content of Mg 2+ The mass content of Fe is 0.59%, 2+ The mass content of Al is 2205ppm, 3+ The mass content of 1226ppm, the mass content of organic solvent (TBP) is 58ppm, and the mass content of TOC is 188ppm. The pH value of the raffinate acid is <1.

[0065] Comparative Examples 1 to 4 and Examples 1 to 9

[0066] Preparation method of calcium phosphate salt:

[0067] 1) The partition heat exchange equipment is used to heat the raffinate acid to the experimental set temperature (i.e., oxidation reaction temperature), the temperature range is 45-100°C (see Table 1).

[0068] 2) The heated raffinate acid and the oxidant (hydrogen peroxide, mass concentration of 27.5%) are mixed in a tubular mixer in proportion (the mixing time is 1 hour), and the percentage of the added amount of hydrogen peroxide to the mass of the heated raffinate acid is shown in Table 1; then, an oxidation reaction is carried out in an oxidation reaction tank (the reaction temperature is shown in Table 1).

[0069] 3) Mixing the product solution obtained in step 2) with CaCO3 slurry in a slurrying reaction tank to obtain feed-grade calcium phosphate slurry; the CaCO3 slurry is obtained by adding CaCO3 to water and mixing evenly. The mass concentration of the CaCO3 slurry is 60%.

[0070] The mass ratio of P2O5 in the product solution obtained in step 2) to the Ca element in the CaCO3 slurry is 3.8:1.

[0071] 4) After the feed-grade calcium phosphate slurry is atomized and dried (the outlet temperature of the atomization and drying equipment is 105° C.), it is naturally cooled to 56° C. to obtain feed-grade calcium phosphate.

[0072] The tail gas generated by the drying is washed with an alkaline detergent (Na2CO3 aqueous solution) and then discharged. The pH value of the alkaline detergent is 12-13.

[0073] The parameters and effect data of each embodiment and comparative example are shown in Table 1. In Table 1, temperature: the temperature of the raffinate after heating in step 1); hydrogen peroxide / raffinate: the percentage of the amount of hydrogen peroxide added in step 2) to the mass of the raffinate after heating; reaction time: the time of the oxidation reaction in step 2); TOC: the mass content of TOC in the oxidized raffinate obtained in step 2); TBP: the mass content of TBP in the oxidized raffinate obtained in step 2).

[0074] Table 1 Parameters and effect data of various embodiments and comparative examples

[0075]

[0076] From Comparative Examples 1 to 2 in Table 1, it can be seen that the TOC and TBP removal by heating and boiling the raffinate acid without adding hydrogen peroxide is low in the TOC and TBP removal rate, and the TOC and TBP removal rate increases with increasing temperature.

[0077] From Comparative Examples 3 to 4 in Table 1, it can be seen that the temperature of the raffinate after heating is 45° C., the percentage of the added amount of hydrogen peroxide to the mass of the raffinate after heating is 2.02% and 3.01%, respectively, the TOC removal rates are 53.45% and 74.14%, respectively; the TBP removal rates are 54.26% and 59.04%, respectively.

[0078] From Examples 1 to 3 in Table 1, it can be seen that the temperature of the raffinate after heating is 60°C, the amount of hydrogen peroxide increases from 0.99% of the mass of the heated raffinate to 1.65% and 2.03%, and the TOC removal rates are 50%, 70.21%, and 80.85%, respectively; the TBP removal rates are 84.48%, 100%, and 100%, respectively.

[0079] From Examples 4 to 6 in Table 1, it can be seen that the temperature of the raffinate after heating is 80°C, the amount of hydrogen peroxide increases from 0.67% of the mass of the heated raffinate to 1.01% and 1.99%, and the TOC removal rates are 42.55%, 80.85%, and 84.04%, respectively; the TBP removal rates are 99.31%, 100%, and 100%, respectively.

[0080] From Examples 7 to 9 in Table 1, it can be seen that when the temperature of the raffinate after heating is 100° C., the amount of hydrogen peroxide increases from 0.49% to 1.11% and 2.01% of the mass of the raffinate after heating, and the TOC removal rates are 65.43%, 85.64% and 90.43%, respectively; the TBP removal rates are all 100%.

[0081] Comparative Example 5

[0082] The existing Fenton conditions are used to control the oxidation pH value and temperature, and an oxidant is added to degrade the organic matter in the raffinate acid.

[0083] The difference from Example 1 is:

[0084] There is no step 1);

[0085] Step 2) is:

[0086] 2-1) adjusting the pH value of the raffinate to 3-4 using sodium hydroxide; adjusting the pH value of the raffinate from less than 1 to 3-4, precipitating a neutralized precipitate, and filtering and separating;

[0087] 2-2) Hydrogen peroxide (hydrogen peroxide, mass concentration is 27.5%) is added to 0.99% of the mass of the raffinate obtained in step 2-1), and the raffinate and hydrogen peroxide are fully mixed in a tubular mixer according to the proportion, and the Fenton room temperature oxidation conditions are adopted, and the residence time in the oxidation reaction tank is 1 hour.

[0088] The other steps are the same as those in Example 1 to obtain calcium phosphate.

[0089] Due to the filtration and separation of the neutralization precipitate in step 2) of Comparative Example 5, a part of the organic solvent floating in the raffinate acid was adsorbed by the neutralization precipitate, resulting in the TOC of the raw material raffinate acid used in Comparative Example 5 being reduced from 188 to 150 ppm, and the TBP content being reduced from 58 ppm to 9 ppm.

[0090] The parameters and effect data of Example 1 and Comparative Example 5 are shown in Table 2.

[0091] Table 2 Effect data of Example 1 and Comparative Example 5

[0092]

[0093] As can be seen from Table 2, step 2) of comparative example 5 adopts traditional Feton conditions. Under the condition that other steps are the same, it can be seen that traditional Fenton conditions cannot effectively remove TOC and TBP in the raffinate acid. The TOC removal rate of the raffinate acid is 29.33%, and the TBP removal rate is 44.44%. The removal rates of TOC and TBP are lower than those in Example 1.

[0094] In Example 5 and Example 8, by increasing the oxidation temperature, the removal effect of TOC and TBP can be further improved under the condition of substantially the same amount of oxidant as that of Comparative Example 5. The comparative examples and examples fully illustrate that the present invention can significantly reduce TOC and TBP by increasing the oxidation temperature and acidity, and the removal effect is better than that of the traditional Fenton method.

[0095] The calcium phosphate products prepared in Examples 3, 6, 9 and Comparative Example 1 were tested using the National Standard for Calcium Dihydrogen Phosphate (GB22548-2017), and the production site and product odor detection used the Emission Standard for Malodor Pollutants (GB14554-93). The test results are shown in Table 3. In Table 3, the contents (%) involved in the indicator column are all mass contents.

[0096] Table 3 Test results of calcium phosphate products prepared in Examples 3, 6, 9 and Comparative Example 1

[0097]

[0098]

[0099] As can be seen from Table 3, the calcium phosphate salt prepared in Comparative Example 1 has a TBP residue of 0.5 ppm and a TOC residue of 3 ppm. The product prepared in Comparative Example 1 has a noticeable odor and cannot meet the "Emission Standards for Odor Pollutants" (GB14554-93).

[0100] The applicant also found in the experiment that in Comparative Example 5, the pH value of the raffinate was adjusted to 3-4 using sodium hydroxide, which consumed the hydrogen phosphate ions in the raffinate, resulting in low reaction activity. The water-soluble P and Ca contents in the prepared calcium phosphate product could not meet the requirements (the standard requires total phosphorus (P) ≥ 22%, water-soluble phosphorus (P) ≥ 20%, and calcium (Ca) ≥ 13%), and could not meet the "National Standard for Monocalcium Phosphate" (GB22548-2017).

[0101] The experimental results show that the preparation site and product of the embodiment of the present invention meet the 0-level odorless standard requirements specified in the "Emission Standard of Malodorous Pollutants" (GB14554-93). Compared with the existing method of heating raffinate acid to volatilize organic solvents or using raffinate acid with fresh acid to prepare compound fertilizers and fertilizer-grade monoammonium phosphate, the mixed acid and heated volatilized solvent operation units can be reduced, and the volatile organic solvents present in the use of raffinate acid can be eradicated from the root.

[0102] The description of the above embodiments is only used to help understand the method of the present invention and its core idea. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing feed-grade calcium phosphate, comprising the following steps: A) heating the raffinate to 60-120°C; B) mixing the heated raffinate with an oxidant and performing an oxidation reaction at 90 to 100° C.; C) mixing the product solution obtained in step B) with CaCO slurry to obtain feed-grade calcium phosphate slurry; D) drying the feed-grade calcium phosphate slurry to obtain feed-grade calcium phosphate.

2. The preparation method according to claim 1, characterized in that: In step A), the mass content of P2O5 in the raffinate is 20% to 54%, and the mass content of Mg 2+ The mass content of Fe is less than 1%, 2+ The mass content of N<3000ppm, the mass content of Al<2000ppm, the mass content of TBP>10ppm, and the mass content of TOC>50ppm; The pH value of the raffinate acid is <1.

3. The preparation method according to claim 1, characterized in that: In step A), the raffinate is heated to 95-100° C.; The heating method is direct heating or using a partition heat exchange device to increase the temperature of the raffinate acid.

4. The preparation method according to claim 1, characterized in that: In step B), the oxidant comprises at least one of peroxide and superoxide; The oxidant accounts for 0.5% to 5% of the mass of the heated raffinate.

5. The preparation method according to claim 1, characterized in that: In step B), the oxidant is hydrogen peroxide.

6. The preparation method according to claim 1, characterized in that: In step B), the mixing time is not less than 30 minutes.

7. The preparation method according to claim 1, characterized in that: In step B), after the heated raffinate acid is mixed with the oxidant, the oxidation reaction time is not less than 30 minutes.

8. The preparation method according to claim 1, characterized in that: In step C), the mass ratio of P2O5 in the product solution obtained in step B) to the Ca element in the CaCO3 slurry is 3 to 4:

1.

9. The preparation method according to claim 1, characterized in that: In step D), the drying method is atomization drying or return material granulation drying; the outlet temperature of the atomization drying or return material granulation drying equipment is 70-105°C.

10. The preparation method according to claim 1, characterized in that: In step D), after the drying, the step further comprises: cooling; The temperature of the product after cooling is less than 60°C; The tail gas generated by the drying is washed with an alkaline detergent and then discharged; the pH value of the alkaline detergent is 7-14.

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