Method for preparing phosphoric acid and calcium chloride from low-grade phosphate ore by byproduct hydrochloric acid decomposition
By using a method of adding sodium chloride in stages and controlling pH at multiple levels, the solid-liquid separation and impurity removal problems in the hydrochloric acid decomposition process of medium and low grade phosphate rock were solved, achieving efficient separation and purification of phosphoric acid and calcium chloride, and improving resource utilization and product quality.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- KUNMING UNIV OF SCI & TECH
- Filing Date
- 2026-04-28
- Publication Date
- 2026-07-10
AI Technical Summary
The existing hydrochloric acid wet process for processing low- and medium-grade phosphate rock is prone to generating silica gel during acidolysis, making solid-liquid separation difficult. The separation effect of phosphoric acid and calcium chloride is not good, and the calcium chloride solution does not completely remove impurities, resulting in low resource utilization and limiting the large-scale application of the process.
The method employs a phased and quantitative addition of sodium chloride for defluorination, controls the acidolysis temperature and the final H+ concentration, uses multi-stage pH control for neutralization and impurity removal, and utilizes the difference in sodium chloride solubility for salt concentration and precipitation to achieve efficient separation and purification of phosphoric acid and calcium chloride.
It effectively inhibits silica gel formation, improves solid-liquid separation efficiency, thoroughly removes impurities such as iron, aluminum, and fluorine, enhances the purity of calcium chloride solution, realizes high-value utilization of resources, and strengthens the economic and environmental benefits of the process.
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Figure CN122355249A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of wet-process phosphoric acid and comprehensive resource utilization technology, and more specifically to a method for preparing phosphoric acid and calcium chloride by decomposing low-grade phosphate rock with by-product hydrochloric acid. Background Technology
[0002] Phosphoric acid, as an important basic chemical raw material, is currently mainly produced using the sulfuric acid wet process. However, this process has stringent requirements for raw materials, typically requiring high-grade phosphate rock with P2O5 content. This results in the ineffective utilization of a large amount of abundant medium- and low-grade phosphate rock (P2O5 10-30%). Furthermore, it causes significant pollution, with 4-5 tons of phosphogypsum inevitably produced as a byproduct for every ton of phosphoric acid produced. To address the dual pressures of ore depletion and solid waste pollution, the hydrochloric acid wet process has become an ideal alternative due to its efficient processing of medium- and low-grade and high-magnesium phosphate rock, and its production of highly soluble calcium chloride as a byproduct, completely eliminating the generation of phosphogypsum. While the existing hydrochloric acid wet process effectively alleviates the pressures of raw material adaptability and solid waste treatment, the difficulties in solid-liquid separation caused by silica gel formation during acidolysis, and the deep enrichment of metallic impurities such as iron, magnesium, and aluminum in the byproduct acidic calcium chloride wastewater, severely restrict the large-scale promotion and practical application of the hydrochloric acid wet process. Therefore, achieving efficient solid-liquid separation in the acidolysis process and deep purification and high-value utilization of the by-product calcium chloride have become key issues that urgently need to be addressed in this field.
[0003] Currently, the main technologies for decomposing low-grade phosphate rock with hydrochloric acid include traditional solvent extraction and crystallization-thermal decomposition methods. For example, patents CN101380062A disclose a method for producing feed-grade dicalcium phosphate from low-grade phosphate rock using hydrochloric acid, and CN101774556A discloses a method for preparing industrial-grade and food-grade phosphoric acid from low-grade phosphate rock using hydrochloric acid. These methods employ organic solvents to extract the acid hydrolysate to separate phosphoric acid and calcium chloride. While this achieves basic phosphorus-calcium separation, it often lacks efficient pretreatment methods for impurities such as fluorine, iron, and aluminum during the acid hydrolysis process. This leads to emulsification and phase separation difficulties in subsequent extraction processes. Furthermore, insufficient attention is paid to the deep purification and high-value utilization of the byproduct calcium chloride solution, limiting the overall economic benefits of the process. Techniques based on the thermal decomposition of intermediates, such as CN115043384A, disclose a method for producing calcium pyrophosphate by hydrochloric acid decomposition of phosphate rock. Although calcium pyrophosphate is obtained by adding sulfides to remove heavy metals and roasting via calcium chlorate intermediate, this method relies on a high-temperature roasting step of about 550°C, which not only consumes a lot of energy, but also the main target product is pyrophosphate for specific purposes rather than widely used industrial phosphoric acid. In addition, the recovery of calcium chloride is only an auxiliary process.
[0004] To address the problems in existing hydrochloric acid decomposition processes for medium- and low-grade phosphate rock, such as the easy generation of silica gel during acidolysis, insufficient defluorination, difficulty in solid-liquid separation, poor subsequent separation of phosphoric acid and calcium chloride, incomplete removal of impurities from calcium chloride solution, and low utilization rate of sodium chloride resources, there is an urgent need to develop a new method for processing medium- and low-grade phosphate rock that is rationally designed, has good defluorination effect, high impurity removal efficiency, and facilitates the recycling of by-products, so as to achieve efficient preparation of phosphoric acid and high-value utilization of calcium chloride products. Summary of the Invention
[0005] In view of this, the present invention provides a method for preparing phosphoric acid and calcium chloride by decomposing low-grade phosphate rock with by-product hydrochloric acid, in order to overcome the shortcomings of the prior art.
[0006] To achieve the above objectives, the present invention provides a method for preparing phosphoric acid and calcium chloride by decomposing low-grade phosphate rock with byproduct hydrochloric acid, the specific steps of which include:
[0007] (1) Acid hydrolysis: Medium and low grade phosphate rock is mixed with hydrochloric acid solution for acid hydrolysis reaction. The acid hydrolysis temperature, reaction time and acid hydrolysis endpoint H are controlled. + The concentration is adjusted to fully decompose the phosphorus-containing components in the phosphate rock, resulting in an acid hydrolysis slurry. During the acidolysis reaction, sodium chloride is added to the acidolysis system according to the predetermined stage and amount, so that the fluorosilicate in the acidolysis system is converted into sodium fluorosilicate precipitate, thereby achieving defluorination and inhibiting the formation of silica gel; after the acidolysis is completed, solid-liquid separation is performed to obtain an acidolysis solution containing phosphoric acid and calcium chloride; (2) Separation of acid hydrolysate: The acid hydrolysate is separated to obtain phosphoric acid solution and calcium chloride solution; (3) Neutralization and impurity removal: The calcium chloride solution is neutralized and impurities are removed by step-by-step pH control. By adjusting the pH value step by step, iron, aluminum, fluorine, magnesium and heavy metal ions are precipitated out in sequence. After filtration, the purified calcium chloride solution is obtained. (4) Concentration and salt precipitation and reuse: The purified calcium chloride solution is concentrated. The difference in solubility between sodium chloride and calcium chloride is used to make sodium chloride precipitate preferentially and then separated. The separated sodium chloride is returned to step (1) as a defluorination salt for recycling. The calcium chloride solution after separating sodium chloride is further concentrated and dried by crystallization to obtain calcium chloride product.
[0008] Preferably, in step (1), the P2O5 content in the medium-low grade phosphate rock is 15%~30% by mass, and the hydrochloric acid solution is industrial by-product hydrochloric acid with a mass concentration of 18%~25%; the parameters of the acid hydrolysis reaction are controlled as follows: acid hydrolysis temperature is 40~60℃, reaction time is 60~90min, and the acid hydrolysis endpoint H + The concentration is 0.5~1.0 mol / L.
[0009] The reaction equation for the acidolysis process is: Ca5F(PO4)3 + 10HCl → 3H3PO4 + 5CaCl2 + HF↑ Preferably, in step (1), the phased quantitative salt addition for defluorination includes at least two stages: adding sodium chloride in the first stage 10-15 minutes after the start of the acid hydrolysis reaction, and adding sodium chloride in the second stage when the acid hydrolysis reaction has proceeded for 15-25 minutes and the foam layer is stable.
[0010] More preferably, the molar amount of sodium chloride added in the first stage accounts for 40% to 60% of the total amount added, and the molar amount of sodium chloride added in the second stage accounts for 40% to 60% of the total amount added.
[0011] Preferably, the total amount of sodium chloride added is 1.05 to 1.30 times the theoretical molar amount of fluorine in the acid hydrolysis system.
[0012] Preferably, the sodium chloride is added in the form of a saturated sodium chloride solution.
[0013] Preferably, step (1) further includes adding sodium fluorosilicate seed crystals to the acid hydrolysis system before or at the same time as adding sodium chloride, so as to induce sodium fluorosilicate precipitation, further reduce colloidal silicon formation and improve solid-liquid separation performance.
[0014] The reaction equation for the defluorination process is H₂SiF₆ + 2NaCl → Na₂SiF₆↓ + 2HCl.
[0015] Preferably, in step (2), the separation of the acid hydrolysate is not strictly limited to a certain method. Any means that can effectively separate the phosphoric acid solution and the calcium chloride solution can be applied to the present invention. Preferably, the separation process is carried out by extraction and back-extraction.
[0016] Preferably, in step (3), the neutralizing agent used for neutralization and impurity removal is any one of lime milk, quicklime, limestone powder, and carbide slag. By controlling the addition rate of the neutralizing agent, the reaction temperature, the stirring intensity, and the final pH value, the selectivity of impurity removal can be improved and the loss of main salt can be reduced.
[0017] A stepped pH control system is implemented, employing either two-stage or three-stage pH control. Preferably, two-stage pH control specifically includes: Step 1: Add a neutralizing agent to the calcium chloride solution to adjust the pH value to 3.8~4.5, stir for 30~60 minutes at a temperature of 50℃~70℃, and filter to remove iron, aluminum and fluorine impurities; Step 2: Continue to add neutralizing agent to adjust the pH value to 8.5~9.5, stir for 30~40 minutes at a temperature of 50℃~70℃, and filter to remove magnesium and heavy metal ions.
[0018] Further optimized, an aging and settling time is set after each pH adjustment to promote the growth of precipitated particles, improve filtration performance, and reduce calcium chloride entrainment loss.
[0019] The equation for the first neutralization reaction is: 2FeCl3+3Ca(OH)2→2Fe(OH)3↓+3CaCl2; 2AlCl3+3Ca(OH)2→2Al(OH)3↓+3CaCl2; 2HF + Ca(OH)₂ → CaF₂↓ + 2H₂O; The equation for the second neutralization reaction is: MgCl2+Ca(OH)2→Mg(OH)2↓+CaCl2; MeCl2+Ca(OH)2→Me(OH)2↓+CaCl; Me represents heavy metals such as Cd, Pb, Cr, Hg, As, Cu, and Zn.
[0020] Preferably, in step (4), the calcium chloride solution is first concentrated to 45%~50% of the total mass to precipitate and separate sodium chloride; the calcium chloride solution after sodium chloride separation is further concentrated to 68%~72% of the total mass and then crystallized and dried. The precipitated sodium chloride is preferably returned to the upstream acid defluorination step after sedimentation, filtration or centrifugation. If necessary, it is washed, sieved, dissolved and purified or re-prepared before reuse to control the accumulation of impurities during the recycling process.
[0021] Preferably, in step (4), the crystallization drying is carried out in a fluidized bed dryer, and the hot air temperature is controlled at 250℃~300℃ to obtain an anhydrous calcium chloride product with high purity (spherical anhydrous calcium chloride with purity ≥94%).
[0022] As can be seen from the above technical solution, compared with the prior art, the beneficial effects achieved by the present invention include at least the following: 1. In the acid hydrolysis process, the present invention adopts a staged quantitative salt addition defluorination method, which enables fluorosilicates to be converted into sodium fluorosilicate precipitate in a timely manner, reduces the formation of colloidal silica, avoids excessive viscosity of acid hydrolysis slurry and filtration difficulties, and is conducive to improving the solid-liquid separation efficiency after acid hydrolysis.
[0023] 2. By synergistically controlling the addition stage, timing, and amount of sodium chloride, this invention can avoid problems such as local concentration fluctuations, uneven defluorination, and salt waste caused by adding salt all at once; if necessary, introducing sodium fluorosilicate seed crystals can further improve the precipitation effect.
[0024] 3. This invention adopts a stepwise pH control method, which removes iron, aluminum, fluorine, magnesium and heavy metal ions stepwise according to different precipitation conditions. Compared with the single-stage neutralization method, the removal of impurities is more thorough and the loss of main salt is lower, which is more conducive to obtaining a high-purity calcium chloride solution.
[0025] 4. The present invention preferably uses a calcium-based neutralizing agent for impurity removal, which is less likely to introduce new heterogeneous cations, helps to maintain the stability of the system composition, and reduces the adverse effects of exogenous impurities on the purity and crystallization behavior of calcium chloride products.
[0026] 5. This invention utilizes the sodium chloride precipitated during the back-end concentration process to return to the front-end defluorination process, realizing a closed-loop circulation between the front-end defluorination salt and the back-end precipitated salt, significantly reducing the amount of fresh sodium chloride replenishment and improving the system's salt utilization rate.
[0027] 6. This invention, through the synergistic effect of front-end defluorination and gum inhibition, mid-stage deep impurity removal, and back-end salt precipitation and recycling, can significantly improve the purity of calcium chloride solution and the quality of the final product, and enhance the resource utilization value of by-product streams.
[0028] 7. This invention directly utilizes medium- and low-grade phosphate rock and industrial by-product hydrochloric acid as raw materials, taking into account raw material adaptability, product quality and recycling efficiency, and has good prospects for industrial application. Attached Figure Description
[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.
[0030] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation
[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0032] Example 1 A method for preparing phosphoric acid and calcium chloride from low-grade phosphate rock by decomposing byproduct hydrochloric acid includes the following steps: (1) First, mix medium and low grade phosphate rock with P2O5 content of 10% with industrial by-product hydrochloric acid with concentration of 20% for acid hydrolysis treatment. The acid hydrolysis temperature is controlled at 50℃, the reaction time is 60 minutes, and the terminal H+ concentration of the acid hydrolysis solution is controlled at 0.8mol / L. Twelve minutes after the start of acidolysis, a first-stage sodium chloride solution, comprising 50% of the total sodium chloride addition, was added. A second-stage sodium chloride solution, comprising 50% of the total sodium chloride addition, was added after 20 minutes of acidolysis when the foam layer stabilized. The total amount of sodium chloride added was controlled to be 1.10 times the theoretical molar amount of fluorine in the acidolysis system. A small amount of sodium fluorosilicate seed crystals was also added simultaneously.
[0033] (2) First, the acid hydrolysate containing phosphoric acid and calcium chloride is subjected to multi-stage countercurrent extraction, wherein the extractant is tributyl phosphate (TBP) and the diluent is sulfonated kerosene. The ratio (O / A) is controlled at 4:1 and the number of stages is 6, to obtain an organic phase solution containing phosphoric acid and an aqueous phase solution containing calcium chloride respectively. The organic phase solution containing phosphoric acid is then back-extracted with pure water under the conditions of ratio (O / A) of 4:1 and temperature of 50°C to obtain a phosphoric acid solution with extremely low impurity content. (3) First, the aqueous solution containing calcium chloride is subjected to stepwise neutralization and impurity removal treatment. The neutralizing agent is lime milk. The first stage adjusts the pH value to 4.2 (temperature 60℃, stirring for 45 minutes), and the second stage adjusts the pH value to 9 (temperature 60℃, stirring for 45 minutes). After filtration, a purified calcium chloride solution is obtained. (4) The purified calcium chloride solution is subjected to multi-effect evaporation, and the first effect is concentrated to 48%. The sodium chloride that is separated and precipitated is recycled to the front-end defluorination. Then, it is further concentrated to 70% and dried in a fluidized bed dryer at 280°C to obtain anhydrous calcium chloride product.
[0034] Example 2 A method for preparing phosphoric acid and calcium chloride from low-grade phosphate rock by decomposing byproduct hydrochloric acid includes the following steps: (1) First, mix medium and low grade phosphate rock with a P2O5 content of 20% with industrial by-product hydrochloric acid with a concentration of 20% for acid hydrolysis treatment. The acid hydrolysis temperature is controlled at 45℃, the reaction time is 90 minutes, and the terminal H+ concentration of the acid hydrolysis solution is controlled at 0.6mol / L. Ten minutes after the start of acidolysis, a first-stage sodium chloride solution, comprising 40% of the total sodium chloride added, was added. The second-stage sodium chloride solution, comprising 60% of the total sodium chloride added, was added after 18 minutes of acidolysis when the foam layer stabilized. The total amount of sodium chloride added was controlled to be 1.20 times the theoretical molar amount of fluorine in the acidolysis system. After acidolysis, the solution was filtered to obtain the acidolysis solution.
[0035] (2) First, the acid hydrolysate containing phosphoric acid and calcium chloride is subjected to multi-stage countercurrent extraction, wherein the extractant is tributyl phosphate (TBP) and the diluent is sulfonated kerosene. The ratio (O / A) is controlled at 4:1 and the number of stages is 6, to obtain an organic phase solution containing phosphoric acid and an aqueous phase solution containing calcium chloride respectively. The organic phase solution containing phosphoric acid is then back-extracted with pure water under the conditions of ratio (O / A) of 4:1 and temperature of 50°C to obtain a phosphoric acid solution with extremely low impurity content. (3) First, the aqueous solution containing calcium chloride is subjected to stepwise neutralization and impurity removal treatment. The neutralizing agent is calcium hydroxide emulsion. The first stage adjusts the pH value to 4 (temperature 65℃, stirring for 40 minutes), and the second stage adjusts the pH value to 8.8 (temperature 65℃, stirring for 30 minutes). After filtration, a purified calcium chloride solution is obtained. (4) The purified calcium chloride solution is subjected to multi-effect evaporation, and the first effect is concentrated to 46%. The precipitated sodium chloride is separated and recycled for front-end defluorination. Then, it is further concentrated to 70% and dried in a fluidized bed dryer at 260°C to obtain anhydrous calcium chloride product.
[0036] Example 3 A method for preparing phosphoric acid and calcium chloride from low-grade phosphate rock by decomposing byproduct hydrochloric acid includes the following steps: (1) First, mix medium and low grade phosphate rock with P2O5 content of 30% with industrial by-product hydrochloric acid with concentration of 20% for acid hydrolysis treatment. The acid hydrolysis temperature is controlled at 60℃, the reaction time is 60 minutes, and the terminal H+ concentration of the acid hydrolysis solution is controlled at 1.0 mol / L. Fifteen minutes after the start of acidolysis, a first-stage sodium chloride solution, comprising 60% of the total sodium chloride added, was added. The second-stage sodium chloride solution, comprising 40% of the total sodium chloride added, was added after 25 minutes of acidolysis when the foam layer stabilized. The total amount of sodium chloride added was controlled to be 1.05 times the theoretical molar amount of fluorine in the acidolysis system. After acidolysis, the solution was filtered to obtain the acidolysis solution.
[0037] (2) First, the acid hydrolysate containing phosphoric acid and calcium chloride is subjected to multi-stage countercurrent extraction, wherein the extractant is tributyl phosphate (TBP) and the diluent is sulfonated kerosene. The ratio (O / A) is controlled at 4:1 and the number of stages is 6, to obtain an organic phase solution containing phosphoric acid and an aqueous phase solution containing calcium chloride respectively. The organic phase solution containing phosphoric acid is then back-extracted with pure water under the conditions of ratio (O / A) of 4:1 and temperature of 50°C to obtain a phosphoric acid solution with extremely low impurity content. (3) First, the aqueous solution containing calcium chloride is subjected to a stepwise neutralization and impurity removal treatment. The neutralizing agent is calcium carbide slag slurry. The first stage adjusts the pH to 4.5 (temperature 50℃, stirring for 60 minutes), and the second stage adjusts the pH to 9.5 (temperature 50℃, stirring for 40 minutes). After filtration, a purified calcium chloride solution is obtained. (4) The purified calcium chloride solution is subjected to multi-effect evaporation, and the first effect is concentrated to 50%. The sodium chloride precipitated is separated and recycled for front-end defluorination. Then, it is further concentrated to 70% and dried in a fluidized bed dryer at 280°C to obtain anhydrous calcium chloride product.
[0038] Comparative Example 1 Except for the fact that sodium chloride is not added in the acid hydrolysis process in step (1), the rest of the operation is basically the same as in Example 1.
[0039] The results showed that the system exhibited significant gelation during acid hydrolysis, with increased slurry viscosity, significantly prolonged filtration time, and poor filtrate clarity, indicating that silica gel formation was severe in the acid hydrolysis system without the addition of sodium chloride.
[0040] Comparative Example 2 Except for step (1), in which the sodium chloride used in Example 1 is added all at once after the acid hydrolysis begins, the other operations are basically the same as in Example 1, and the total amount of sodium chloride added remains the same.
[0041] The results showed that although the one-time salt addition method was better than the no-salt method, the filtration performance of the slurry after acid hydrolysis was still not as stable as that of the staged quantitative salt addition method. This indicates that the staged quantitative salt addition method has more advantages in inhibiting silica gel formation and improving solid-liquid separation.
[0042] Comparative Example 3 Except for step (3), which uses single-stage neutralization, i.e., directly adjusting the pH of the calcium chloride-containing aqueous phase to 9.0 in one step, the rest of the operation is basically the same as in Example 1.
[0043] The results showed that although single-stage neutralization could remove some impurities, the overall removal efficiency was lower than that of the step-by-step neutralization method, and the calcium chloride entrainment loss was relatively high. This indicates that the step-by-step pH control method is more conducive to achieving step-by-step selective removal of impurities.
[0044] Performance testing Medium- and low-grade phosphate rock were processed according to the methods of Examples 1-3 and Comparative Examples 1-3, respectively. The acid hydrolysis and solid-liquid separation effects, changes in aqueous phase impurities before and after neutralization and impurity removal, final products, and comprehensive results were tested. The results are shown in Tables 1-3.
[0045] Table 1. Effects of acid hydrolysis and solid-liquid separation
[0046] As shown in Table 1, in Examples 1-3, the acid hydrolysis system was relatively stable overall after the phased and quantitative addition of sodium chloride during the acid hydrolysis process, with good slurry flowability and high filtrate clarity. In contrast, Comparative Example 1, due to the absence of sodium chloride, showed significant gelation, resulting in a significantly prolonged filtration time. Although Comparative Example 2 added sodium chloride, the single-stage salt addition method resulted in lower effects on inhibiting gelation and improving filtration performance compared to Examples 1-3. These results indicate that phased and quantitative salt addition is beneficial for inhibiting silica gel formation and improving solid-liquid separation.
[0047] Table 2 Comparison of changes in impurities in the aqueous phase before and after neutralization and purification (unit: g / L)
[0048] As shown in Table 2, after using stepwise neutralization in Examples 1-3, the contents of Fe, Al, Mg, and other impurities all decreased significantly, while the loss of the effective component CaCl2 was relatively small. This indicates that stepwise neutralization is beneficial for achieving selective removal of impurities in stages while retaining the effective components. In contrast, Comparative Example 3, which used a single-stage neutralization method, also reduced impurities, but the impurity content after neutralization was significantly higher than in Examples 1-3, and the loss of CaCl2 was greater. This shows that stepwise neutralization has a greater advantage in terms of purification effect and component retention.
[0049] Table 3 Final Products and Overall Results
[0050] As shown in Table 3, the phosphoric acid products obtained in Examples 1-3 have high P2O5 content and low impurity levels, the anhydrous calcium chloride products have high purity, and the sodium chloride recovery rate is good, indicating that the method of the present invention has good product preparation effect and resource recycling effect. In contrast, Comparative Example 1 suffered from poor acid hydrolysis and solid-liquid separation, which affected subsequent processing and resulted in a significant decrease in the final product quality; Comparative Example 2 showed some improvement, but the overall effect was only average; Comparative Example 3 had a high P2O5 content in the phosphoric acid product, but insufficient neutralization and impurity removal resulted in an anhydrous calcium chloride purity lower than that of Examples 1-3.
[0051] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims
1. A method for preparing phosphoric acid and calcium chloride by decomposing low-grade phosphate rock with byproduct hydrochloric acid, characterized in that, The specific steps include: (1) Acid hydrolysis: Medium and low grade phosphate rock is mixed with hydrochloric acid solution for acid hydrolysis reaction. The acid hydrolysis temperature, reaction time and acid hydrolysis endpoint H are controlled. + After acid hydrolysis, solid-liquid separation is performed to obtain the acid hydrolysate. This also includes the phased and quantitative addition of salts for defluorination during the acidolysis reaction; (2) Separation of acid hydrolysate: The acid hydrolysate is separated to obtain phosphoric acid solution and calcium chloride solution; (3) Neutralization and impurity removal: The calcium chloride solution is neutralized and impurities are removed by step-by-step pH control, so that iron, aluminum, fluorine, magnesium and heavy metal ions are precipitated out in sequence, and the purified calcium chloride solution is obtained after filtration. (4) Concentration and salt precipitation and reuse: The purified calcium chloride solution is concentrated and the sodium chloride obtained is returned to step (1) as a defluorination salt for recycling; the calcium chloride solution after sodium chloride separation is further concentrated and dried by crystallization to obtain calcium chloride product.
2. The method for preparing phosphoric acid and calcium chloride by decomposing low-grade phosphate rock with byproduct hydrochloric acid according to claim 1, characterized in that, In step (1), the P2O5 content in the low-grade phosphate rock is 15%~30% by mass, and the hydrochloric acid solution has a mass concentration of 18%~25% by mass; the parameters of the acidolysis reaction are controlled as follows: acidolysis temperature is 40~60℃, reaction time is 60~90min, and the acidolysis endpoint H + The concentration is 0.5~1.0 mol / L.
3. The method for preparing phosphoric acid and calcium chloride by decomposing low-grade phosphate rock with byproduct hydrochloric acid according to claim 1, characterized in that, In step (1), the phased quantitative salt addition for defluorination includes at least two stages: the first stage sodium chloride is added 10-15 minutes after the start of the acid hydrolysis reaction, and the second stage sodium chloride is added when the acid hydrolysis reaction has proceeded for 15-25 minutes and the foam layer is stable.
4. The method for preparing phosphoric acid and calcium chloride by decomposing low-grade phosphate rock with byproduct hydrochloric acid according to claim 3, characterized in that, The amount of sodium chloride added in the first stage accounts for 40% to 60% of the total amount added, and the amount of sodium chloride added in the second stage accounts for 40% to 60% of the total amount added. The total amount added is 1.05 to 1.30 times the theoretical molar amount of fluorine in the acidolysis system.
5. The method for preparing phosphoric acid and calcium chloride by decomposing low-grade phosphate rock with byproduct hydrochloric acid according to claim 4, characterized in that, The sodium chloride is added in the form of a saturated sodium chloride solution.
6. The method for preparing phosphoric acid and calcium chloride by decomposing low-grade phosphate rock with byproduct hydrochloric acid according to claim 1, characterized in that, Step (1) also includes adding sodium fluorosilicate seed crystals to the acidolysis system before or at the same time as adding sodium chloride.
7. The method for preparing phosphoric acid and calcium chloride by decomposing low-grade phosphate rock with byproduct hydrochloric acid according to claim 1, characterized in that, In step (2), the separation of the acid hydrolysate is not strictly limited to a certain method; any means that can effectively separate the phosphoric acid solution and the calcium chloride solution is acceptable.
8. The method for preparing phosphoric acid and calcium chloride by decomposing low-grade phosphate rock with byproduct hydrochloric acid according to claim 1, characterized in that, In step (3), the neutralizing agent used for neutralization and impurity removal is any one of lime milk, quicklime, limestone powder, or carbide slag, and the pH value is controlled in stages, specifically including: Step 1: Add a neutralizing agent to the calcium chloride solution to adjust the pH value to 3.8~4.5, stir for 30~60 minutes at a temperature of 50℃~70℃, and filter to remove iron, aluminum and fluorine impurities; Step 2: Continue to add neutralizing agent to adjust the pH value to 8.5~9.5, stir for 30~40 minutes at a temperature of 50℃~70℃, and filter to remove magnesium and heavy metal ions.
9. The method for preparing phosphoric acid and calcium chloride by decomposing low-grade phosphate rock with byproduct hydrochloric acid according to claim 1, characterized in that, In step (4), the calcium chloride solution is first concentrated to 45% to 50% of the total mass to precipitate sodium chloride and separate it; after separating sodium chloride, the calcium chloride solution is further concentrated to 68% to 72% of the total mass and then crystallized and dried.
10. The method for preparing phosphoric acid and calcium chloride by decomposing low-grade phosphate rock with byproduct hydrochloric acid according to claim 1, characterized in that, In step (4), the crystallization drying is carried out in a fluidized bed dryer, and the hot air temperature is controlled at 250℃~300℃.