Treatment method for wet purification of phosphoric acid pretreatment by-products

Abstract

The invention discloses a treatment method for wet purification of phosphoric acid pretreatment by-products, which comprises the following steps: treating white fertilizer slag through the steps of extraction and graining, crystal growing, filtering and washing in sequence, and dissolving and recycling available elements at the same time. In the extraction and graining step, a solution extraction agent is used for extracting the white fertilizer slag, a graining agent is used for graining the white fertilizer slag, and the recyclable elements comprise P, F and N. According to the method, the comprehensive utilization rate of phosphorus resources in the chemical process can be increased, in the white fertilizer slag purification process, intergranular phosphorus in semi-hydrated gypsum lattices and unreacted phosphorus in phosphorite are greatly reduced, the total P2O5 content in the white fertilizer slag is reduced to 0.1% or below, the recovery rate of P2O5 is increased to 99%, and the economic benefits of enterprises are increased.

Description

Technical Field

[0001] The invention belongs to the technical field of industrial by-product treatment, and in particular relates to a method for treating by-products of wet-process purified phosphoric acid pretreatment. Background Art

[0002] Industrial purified phosphoric acid is purified phosphoric acid, which is widely used in food processing, fertilizer manufacturing, fine chemicals and other industries. At present, with the improvement of global food quality and safety standards and the tightening of environmental protection regulations, the market demand for industrial purified phosphoric acid continues to grow. Technological progress has continuously improved the purification efficiency and purity of phosphoric acid, so a large number of by-products are produced during the purification process. In the wet phosphoric acid purification process, the first step is to pre-treat phosphoric acid, and produce it according to the process design of desulfurization, defluorination, dearsenicization, thickening, and filtration systems. Since it comes from phosphoric acid production, the by-product white fertilizer slag is acidic, and the main component is hemihydrate gypsum (CaSO4·1 / 2H2O), and there are also a certain amount of ammonium nitrogen, phosphate, fluoride and many other elements. If proper disposal measures are not taken, the storage of white fertilizer slag will pose great safety and environmental risks.

[0003] The patent with announcement number CN113772709A discloses a method for preparing anhydrous micron calcium sulfate using phosphogypsum, which is to add water, acid, nucleating agent and crystal form control agent to phosphogypsum and heat the reaction, and then filter and dry to obtain micron-grade anhydrous calcium sulfate, which has the advantages of stable crystal form and simple operation. However, the high acidity of the system is easy to corrode equipment, and the energy consumption is high, resulting in high product cost, which is not conducive to the high-quality development of enterprises.

[0004] The patent with announcement number CN114133276A discloses a method for resource processing of white fertilizer. The invention defluorinates white fertilizer by high-temperature calcination to obtain fluorine-containing gas and phosphorus-containing defluorinated white fertilizer slag; the temperature of the high-temperature calcination is 400-1200°C; the fluorine-containing gas is absorbed to obtain a fluorine-containing solution; the phosphorus-containing defluorinated white fertilizer slag is mixed with sulfuric acid for aging to obtain phosphate fertilizer. The patent adopts thermal calcination, which can make the fluorine in the white fertilizer escape in the gaseous form of a large amount of SiF4 and a small amount of HF, and absorb it into a fluorine-containing solution. The fluorine-containing solution can be used to prepare fluorine chemical products such as fluorosilicic acid or fluoride salts; at the same time, the fluorine-containing substances and phosphorus-containing substances in the white fertilizer can be separated to obtain phosphate fertilizer. However, this method requires high-temperature calcination, which has certain requirements on equipment investment and energy consumption, and increases the processing cost to a certain extent. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a method for treating by-products of wet purification of phosphoric acid pretreatment.

[0006] The present invention is achieved through the following technical solutions.

[0007] The invention provides a method for treating a by-product of wet purification phosphoric acid pretreatment, comprising treating white fertilizer residues in sequence through the steps of extraction and crystallization, crystal growth, filtration and washing, and simultaneously dissolving and recovering usable elements.

[0008] Preferably, in the extraction and crystallization step, a solution extractant is used to extract the white fertilizer slag, and a crystallization agent is used to crystallize the white fertilizer slag, and the recovered usable elements include at least one of P, F, and N.

[0009] Preferably, the extraction and crystallization step comprises: adding a solution extractant and a crystallizing agent to the white fertilizer residue, starting at a temperature of 80°C to 60°C, cooling by 10-15°C per hour, stirring at a speed of 300r / min to 500r / min for 1-3h, and increasing the speed by 30r / min per hour.

[0010] Preferably, the solution extractant includes at least one of phosphoric acid, sulfuric acid and citric acid.

[0011] Preferably, the liquid-to-solid ratio of the solution extractant to the white fertilizer slag is 3:1.

[0012] Preferably, the crystallizing agent in the crystallization step is at least one of II calcium sulfate and sodium silicate.

[0013] Preferably, the mass of the crystallizing agent is 1-5% of the mass of the white fertilizer slag.

[0014] Preferably, the crystal growing step comprises adding a crystallizing agent to the white fertilizer residue after extraction and crystallization, and stirring at a speed of 300 r / min to 100 r / min for 3-6 hours, with the speed decreasing by 30 r / min every hour.

[0015] Preferably, the filtering step comprises: transferring the slurry to a separation filter, washing, returning the washing liquid and the filtrate to the device of the original phosphoric acid extraction crystallization step, and washing the filter cake with lime water circulation until it is qualified.

[0016] Preferably, the washing step comprises: utilizing the tail washing system of the phosphoric acid pretreatment device to discharge the gaseous fluorine escaping from the extraction and crystallization steps after washing to meet the standards; washing silicon tetrafluoride with water to form 18% fluorosilicic acid and a small amount of silica gel, and returning the silica gel to the original phosphoric acid extraction and crystallization step device after filtration or filter press separation, and the fluorosilicic acid is transported to the storage tank by a pump.

[0017] The beneficial effects of the present invention are:

[0018] The method of the present invention can improve the comprehensive utilization rate of phosphorus resources in the chemical process. In the process of purifying white fertilizer slag, the intercrystalline phosphorus in the hemihydrate gypsum lattice and the unreacted phosphorus in the phosphate rock are greatly reduced, the total P2O5 content in the white fertilizer slag is reduced to below 0.1%, the recovery rate of P2O5 is increased to 99%, and the annual economic benefit created is 2 million yuan.

[0019] The method of the present invention improves the fluorine escape rate and the fluorine recovery ratio. Through special processes such as reaction and crystal transformation, the fluorine escape rate is improved, and the escaped silicon tetrafluoride enters the absorption tower for recovery, and is recovered into 18% concentration fluorosilicic acid for sale or made into other fluorine chemical products, thereby increasing the value.

[0020] The method of the present invention can also solve the environmental pollution caused by the stacking of by-products and achieve the dual goals of resource utilization and environmental protection. DETAILED DESCRIPTION

[0021] The technical solution of the present invention is further described below, but the scope of protection claimed is not limited to the description.

[0022] Embodiment 1:

[0023] A method for treating by-products of wet purification of phosphoric acid pretreatment comprises treating white fertilizer residue through extraction and crystallization, crystal growth, filtration and washing steps in sequence, converting hemihydrate gypsum (CaSO4·1 / 2H2O) contained in the white fertilizer residue into anhydrous microcrystalline calcium, and dissolving and recovering available elements at the same time.

[0024] In the extraction and crystallization step, a solution extractant is used to extract the white fertilizer slag, and a crystallization agent is used to crystallize the white fertilizer slag. The recovered usable elements include P, F, and N.

[0025] The extraction and crystallization step comprises: adding a solution extractant and a crystallizing agent to the white fertilizer residue, starting at a temperature of 80°C to 60°C, cooling by 12°C per hour, stirring at a speed of 300r / min to 500r / min for 1.5 hours, and increasing the speed by 30r / min per hour.

[0026] The solution extractant is 46% phosphoric acid and 80% sulfuric acid.

[0027] The liquid-to-solid ratio of the solution extractant to the white fertilizer slag is 3:1.

[0028] The crystallizing agent in the crystallization step is II calcium sulfate.

[0029] The mass of the crystallizing agent is 2% of the mass of the white fertilizer slag.

[0030] The crystal growing step includes adding a crystallizing agent to the white fertilizer residue after extraction and crystallization, and stirring at a speed of 300 r / min to 100 r / min for 3.5 hours, with the speed decreasing by 30 r / min every hour.

[0031] The above-mentioned crystallizing agents are all the same substance.

[0032] The filtering step comprises: transferring the slurry to a separation filter, undergoing three-stage countercurrent washing, returning the washing liquid and the filtrate to the device of the original phosphoric acid extraction crystallization step, and washing the filter cake with lime water circulation until it is qualified.

[0033] The washing step comprises: utilizing the tail washing system of the phosphoric acid pretreatment device to discharge the gaseous fluorine escaped from the extraction and crystallization steps after meeting the standards through secondary washing; washing silicon tetrafluoride with water to form 18% fluorosilicic acid and a small amount of silica gel, and returning the silica gel to the original phosphoric acid extraction and crystallization step device after filtering or filter pressing separation, and the fluorosilicic acid is transported to the storage tank through a pump.

[0034] The results of treating 100 kg of white fertilizer residue are shown in Table 1.

[0035] Table 1 White fertilizer residue purification test results

[0036]

[0037]

[0038] From the results in Table 1, it can be seen that the plasma content of P, F and other ions and the crystal water content values ​​dropped sharply, and the content of impurity metal ions such as P, F and other impurities decreased to 0.04% and 0.059%. This result shows that the phosphoric acid and sulfuric acid extractants work synergistically with calcium sulfate II to complete the purification of the phosphoric acid byproducts of the wet purification process, P can be recovered through the solution, and F and N can be recovered through the gas.

[0039] Embodiment 2:

[0040] A method for treating by-products of wet purification of phosphoric acid pretreatment comprises treating white fertilizer residue through extraction and crystallization, crystal growth, filtration and washing steps in sequence, converting hemihydrate gypsum (CaSO4·1 / 2H2O) contained in the white fertilizer residue into anhydrous microcrystalline calcium, and dissolving and recovering available elements at the same time.

[0041] In the extraction and crystallization step, a solution extractant is used to extract the white fertilizer slag, and a crystallization agent is used to crystallize the white fertilizer slag. The recovered usable elements include P, F, and N.

[0042] The extraction and crystallization step comprises: adding a solution extractant and a crystallization agent to the white fertilizer residue, starting at a temperature of 80°C to 60°C, lowering the temperature by 14°C per hour, stirring at a speed of 300r / min to 500r / min for 2.5h, and increasing the speed by 30r / min per hour.

[0043] The solution extractant is 80% sulfuric acid and 60% citric acid.

[0044] The liquid-to-solid ratio of the solution extractant to the white fertilizer slag is 3:1.

[0045] The crystallizing agents in the crystallization step are calcium sulfate and sodium silicate.

[0046] The mass of the crystallizing agent is 4% of the mass of the white fertilizer slag.

[0047] The crystal growing step includes adding a crystallizing agent to the white fertilizer residue after extraction and crystallization, and stirring at a speed of 300 r / min to 100 r / min for 5 hours, with the speed decreasing by 30 r / min every hour.

[0048] The above-mentioned crystallizing agents are all the same substance.

[0049] The filtering step comprises: transferring the slurry to a separation filter, undergoing three-stage countercurrent washing, returning the washing liquid and the filtrate to the device of the original phosphoric acid extraction crystallization step, and washing the filter cake with lime water circulation until it is qualified.

[0050] The washing step includes: using the tail washing system of the phosphoric acid pretreatment device to discharge the gaseous fluorine escaping from the extraction and crystallization steps after secondary washing to meet the standards; washing silicon tetrafluoride with water to form 18% fluorosilicic acid and a small amount of silica gel, and returning the silica gel to the original phosphoric acid extraction and crystallization step after filtering or filter pressing, and the fluorosilicic acid is pumped to the storage tank. The results of treating 100 kg of white fertilizer residue are shown in Table 2

[0051] Table 2 White fertilizer residue purification test results

[0052]

[0053] From the results in Table 2, it can be seen that with the increase in the dosage of the reagent, the ion content of P, F and the content of crystal water decreased sharply. Under the optimal conditions, the content of impurity metal ions such as P, F and others decreased to 0.05%-0.051%. This result fully demonstrates that the synergistic effect of sulfuric acid and citric acid extractants and the mixture of calcium sulfate and sodium silicate can complete the purification of the wet purification phosphoric acid byproducts. P can be recovered through the solution, and F and N can be recovered through the gas.

Claims

1. A method for treating byproducts of wet purification of phosphoric acid pretreatment, characterized in that: The invention comprises the process of treating white fertilizer residue through extraction, crystal growth, filtration and washing steps in sequence, and dissolving and recovering available elements at the same time.

2. The method for treating a by-product of wet purification of phosphoric acid pretreatment according to claim 1, characterized in that: In the extraction and crystallization step, a solution extractant is used to extract the white fertilizer slag, and a crystallization agent is used to crystallize the white fertilizer slag. The recovered usable elements include at least one of P, F, and N.

3. A method for treating a by-product of wet purification of phosphoric acid pretreatment according to claim 2, characterized in that: The extraction and crystallization step comprises: adding a solution extractant and a crystallizing agent to the white fertilizer residue, starting at a temperature of 80°C to 60°C, cooling by 10-15°C per hour, stirring at a speed of 300r / min to 500r / min for 1-3h, and increasing the speed by 30r / min per hour.

4. The method for treating a by-product of wet purification of phosphoric acid pretreatment according to claim 2, characterized in that: The solution extractant includes at least one of phosphoric acid, sulfuric acid and citric acid.

5. The method for treating a by-product of wet purification of phosphoric acid pretreatment according to claim 2, characterized in that: The liquid-to-solid ratio of the solution extractant to the white fertilizer slag is 3:

1.

6. The method for treating a by-product of wet purification of phosphoric acid pretreatment according to claim 2, characterized in that: The crystallizing agent in the crystallization step is at least one of calcium sulfate and sodium silicate.

7. The method for treating a by-product of wet purification of phosphoric acid pretreatment according to claim 2, characterized in that: The mass of the crystallizing agent is 1-5% of the mass of the white fertilizer slag.

8. The method for treating a by-product of wet purification of phosphoric acid pretreatment according to claim 1, characterized in that: The crystal growing step includes adding a crystallizing agent to the white fertilizer residue after extraction and crystallization, and stirring at a speed of 300 r / min to 100 r / min for 3-6 hours, with the speed decreasing by 30 r / min every hour.

9. The method for treating a by-product of wet purification of phosphoric acid pretreatment according to claim 1, characterized in that: The filtering step comprises: transferring the slurry to a separation filter, washing, returning the washing liquid and the filtrate to the device of the original phosphoric acid extraction crystallization step, and washing the filter cake with lime water in a cycle until it is qualified.

10. The method for treating byproducts of wet purification of phosphoric acid pretreatment according to claim 1, characterized in that: The washing step comprises: utilizing the tail washing system of the phosphoric acid pretreatment device to wash the gaseous fluorine escaped from the extraction and crystallization steps and discharge it after it meets the standards; washing silicon tetrafluoride with water to form 18% fluorosilicic acid and a small amount of silica gel, and returning the silica gel to the original phosphoric acid extraction and crystallization step device after filtering or filter pressing separation, and the fluorosilicic acid is transported to the storage tank by a pump.

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