Method for preparing crude rare earth by multi-stage leaching and decomposition of Zhijin rare earth-containing phosphorite with high-pressure nitric acid

Abstract

The invention discloses a method for preparing crude rare earth by multi-stage leaching and decomposition of Zhijin rare earth-containing phosphorite through high-pressure nitric acid, elements in the Zhijin phosphorite are gradually dissolved and separated through the leaching effect of multi-stage nitric acid, and then secondary leaching is realized through the acoustic cavitation effect of an ultrasonic device, so that the leaching rate of rare earth elements in a filter cake is increased; a crude rare earth enriched product is obtained; according to the method, the rare earth leaching efficiency of the Zhijin phosphorite is improved to 99%, and meanwhile, the by-product fertilizer of the nitrophosphate fertilizer device is utilized.

Description

Technical Field

[0001] The invention relates to the technical field of rare earth recovery, in particular to a method for preparing crude rare earth by using high-pressure nitric acid multi-stage leaching to decompose Zhijin rare earth-containing phosphate ore. Background Art

[0002] Rare earths are a strategic resource that supports modern science and technology. Due to their excellent optical, electromagnetic and other physical properties, rare earths can be combined with other materials to form a wide variety of new materials with different properties. Their most significant function is to greatly improve the quality and performance of other products. For example, they can greatly improve the tactical performance of steel, aluminum alloys, magnesium alloys and titanium alloys used to manufacture tanks, aircraft and missiles. Moreover, rare earths are also lubricants for many high-tech industries such as electronics, lasers, nuclear industry, and superconductivity. Their irreplaceable nature is reflected in the empowerment of underlying technologies in high-end manufacturing, clean energy, national defense and military industry, information technology and other fields, as well as their geopolitical weight in the global supply chain game. Currently, there are two main methods for the recovery and production of rare earths: acid leaching and alkali fusion.

[0003] The existing acid leaching method for extracting rare earths from rare earth-containing phosphate rock has the following defects: 1) The traditional nitric acid single-stage leaching process is insufficiently efficient in leaching rare earth elements encapsulated in the phosphate rock lattice, with a leaching rate generally below 65%, resulting in a large amount of rare earth remaining in the acid hydrolysis slag; 2) The pH control accuracy in the neutralization reaction stage is poor, with a fluctuation range exceeding ±0.5, resulting in a co-precipitation loss rate of rare earth and calcium and magnesium impurities as high as 12-15%; 3) The decalcification process needs to be repeated 3-4 times to reduce the calcium ion concentration to below 0.5 g / L, resulting in a process flow extension of more than 40%. Based on the above shortcomings, how to provide a rare earth extraction method that combines multi-stage nitric acid synergistic leaching, precise pH control, deep decalcification and co-production of gypsum, and waste liquid recycling has become a technical problem that needs to be solved urgently. Summary of the Invention

[0004] In view of the shortcomings of the above-mentioned technology in that the leaching rate of rare earth elements in Zhijin phosphate ore is low and the effect is poor, the present invention provides a method for producing crude rare earths by decomposing Zhijin rare earth-containing phosphate ore with high-pressure nitric acid in multi-stage leaching.

[0005] To achieve the above object, the present invention provides a method for producing crude rare earths by decomposing Zhijin rare earth-containing phosphate ore using high-pressure nitric acid in multi-stage leaching, which is characterized by comprising the following steps:

[0006] S1, obtaining phosphate rock, and processing it through crushing and calcining to obtain calcined ore and release waste gas containing CO2;

[0007] S2, after the calcined ore is cooled, the calcined ore is mixed with a dilute nitric acid solution in a certain proportion, placed in a high-pressure reactor, and then a certain concentration of lime milk is added to cause a secondary neutralization reaction under specific temperature and pH conditions, followed by filtration and washing to obtain phosphate concentrate, demagnesium removal filtrate, and demagnesium removal washing solution;

[0008] S3, mixing the phosphate concentrate with a certain concentration of nitric acid and washing acid and adding the mixture into an acid hydrolysis tank for acid hydrolysis, and filtering and separating the mixture to obtain an acid hydrolysis solution, an acid hydrolysis residue, and an acid hydrolysis washing solution;

[0009] S4, performing freeze crystallization on the acid hydrolyzed solution, and filtering and washing again through a double drum filter to obtain a crystallization mother liquor, washing acid, and calcium nitrate crystals;

[0010] S5, adding sulfuric acid or ammonium sulfate solution and washing solution to the mixed crystallization mother liquor for deep decalcification, and filtering to obtain a deep decalcified filtrate and a decalcified filter cake;

[0011] S6, adding ammonia water to the deep decalcified filtrate for neutralization reaction, then adding washing water for filtering and washing to obtain filter cake, neutralization washing liquid and neutralization filtrate, finally adding repulping water and washing water for repulping and washing, and finally filtering through an ultrasonic device to obtain a crude rare earth concentrate and repulping filtrate.

[0012] Preferably, in S1, the phosphate rock is crushed into phosphate rock powder with a particle size of less than or equal to 0.3 mm by a crusher, and the phosphate rock powder is then fed into a calcining kiln and calcined at a calcination temperature of 900-1150° C. for 2 hours to generate calcined ore.

[0013] Preferably, in S2, a nitric acid solution with a mass concentration of 17% is added to a high-pressure reactor and mixed with the calcined ore. Under the conditions of a reaction temperature of 45-50°C and a pressure of 20KPa, the mixture is reacted in tank A with a pH of 1.5-1.8, tank B with a pH of 1.2-1.5, tank C with a pH of 1.2-1.5, tank D with a pH of 1.0-1.2, and tank E with a pH of 1.0-1.2 for 0.5h, followed by secondary neutralization, and lime milk with a concentration of 25-30% is added for a secondary reaction. The mixture is reacted at a reaction temperature of 45-50°C and a pH of 5.0-6.0 for 1h, and then the impurities attached to the phosphate rock are washed with wash water to produce phosphate concentrate, demagnesium removal filtrate and demagnesium removal washing solution.

[0014] Preferably, the demagnesium washing solution is used to dilute nitric acid with a mass concentration of 65% to a nitric acid solution with a mass concentration of 14-18%, and the lime milk with a mass concentration of 25-30% is prepared from calcium hydroxide and the demagnesium washing solution.

[0015] Preferably, in S3, a nitric acid solution with a mass concentration of 50-55% is added to the acidolysis tank and stirred with the phosphate concentrate to cause an acidolysis reaction. The reaction temperature is 60-65°C for 1.5-2h, and the acidolysis liquid-solid ratio is 1:1-1:1.5. After the reaction is completed, washing water is added, and the acidolysis liquid, acidolysis residue and acidolysis washing liquid are separated by a filter press, and the filtration time is 96min.

[0016] Preferably, in S4, the acid hydrolyzed liquid is placed in a low-temperature reactor for freeze crystallization, and then the acid hydrolyzed liquid after freeze crystallization is sent to a double-drum filter, nitric acid with a mass concentration of 50-55% and a temperature of 5-10°C and washing water with a temperature of 5-8°C are added for centrifugal filtration to separate the crystallization mother liquor, washing acid and calcium nitrate crystals.

[0017] Preferably, in S5, sulfuric acid and washing solution with a mass concentration of 40-45% are added to the sulfuric acid-resistant reactor to deeply decalcify the crystallization mother liquor, and the reaction is carried out at 58-62° C. for 6 hours. The deeply decalcified crystallization mother liquor is passed through a vacuum belt filter for solid-liquid separation to obtain a deeply decalcified filtrate and a decalcified filter cake.

[0018] Preferably, the decalcified filter cake is washed with water to obtain a washed filter cake and a first wash liquid, and water is added for a second washing to obtain gypsum and a second wash liquid. The first wash liquid and the second wash liquid are used to prepare a sulfuric acid solution with a mass concentration of 40-45% with sulfuric acid with a mass concentration of 98% and used for deep decalcification with the crystallization mother liquor.

[0019] Preferably, in S6, the deep decalcified filtrate and ammonia water are placed in a neutralization reactor, and a neutralization reaction is carried out at 90-95° C. for 2-3 hours. The deep decalcified filtrate after the neutralization reaction is then added to a repulping stirring tank, and washing water is added for filtration and washing to obtain a filter cake, a neutralization washing liquid and a neutralization filtrate. Finally, repulping water and washing water are added to the filter cake for repulping treatment, and the filter cake is treated with an ultrasonic device at 20-40 kHz and a power of 500-1000 W for 1 hour to separate and obtain a crude rare earth concentrate and a repulping filtrate.

[0020] The beneficial effects of the present invention are as follows: compared with the prior art, the present invention provides a method for preparing crude rare earths by decomposing Zhijin rare earth-containing phosphate ore through high-pressure nitric acid multi-stage leaching, adopts a high-pressure nitric acid leaching method in combination with a multi-stage leaching process to purify and extract rare earth elements, gradually dissolves and separates the elements in the Zhijin phosphate ore through the leaching action of the multi-stage nitric acid, removes impurities through acid hydrolysis, freeze crystallization, deep decalcification steps, and then realizes secondary leaching through the acoustic cavitation effect of an ultrasonic device, thereby increasing the leaching rate of rare earth elements in the filter cake and obtaining a crude rare earth concentrate; the present invention increases the rare earth leaching efficiency of the Zhijin phosphate ore to 99%, and at the same time utilizes the by-product fertilizer of the nitric acid phosphate fertilizer device. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a flow chart of the method for producing crude rare earths by decomposing Zhijin rare earth-containing phosphate ore through high-pressure nitric acid multi-stage leaching according to the present invention;

[0022] Figure 2 This is a first process flow chart of the present invention;

[0023] Figure 3 This is a second process flow chart of the present invention. DETAILED DESCRIPTION

[0024] In order to more clearly illustrate the present invention, the present invention will be further described below with reference to the accompanying drawings.

[0025] In the following description, example details are provided to provide a deeper understanding of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. It should be understood that the specific embodiments are only used to illustrate the present invention and are not intended to limit the present invention.

[0026] It should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of the stated features, integers, steps, operations, elements or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components or combinations thereof.

[0027] See also Figure 1 The method of producing crude rare earths from Zhijin rare earth-containing phosphate ore by multi-stage leaching and decomposition with high-pressure nitric acid includes the following steps: obtaining phosphate ore, and subjecting it to crushing, screening, and calcining to obtain calcined ore and CO2-containing waste gas; mixing the calcined ore with a dilute nitric acid solution in a certain proportion, placing it in a high-pressure reactor to cause a demagnesization reaction, then adding a certain concentration of lime milk and causing a neutralization reaction under specific temperature and pH conditions, and then filtering and washing to obtain phosphate concentrate, demagnesization filtrate, and demagnesization washing liquid; mixing the phosphate concentrate with a certain concentration of nitric acid and adding it to an acidolysis tank for acidolysis, adding washing water to separate the acidolysis liquid, acidolysis residue, and acidolysis washing liquid; and in step S3, adding a nitric acid solution with a mass concentration of 50% and the phosphate concentrate to the acidolysis tank and stirring them to cause an acidolysis reaction. The reaction temperature is 60-65° C. for 2 hours, and the acidolysis liquid-to-solid ratio is 1:1-1:1.5. After the reaction is completed, washing water is added, and the acidolysis liquid, acidolysis residue and acidolysis washing liquid are separated by centrifugation for 96 minutes; low-temperature nitric acid and low-temperature washing water are added to the acidolysis liquid for freeze crystallization treatment, and the liquid is centrifuged and filtered again to obtain a crystallization mother liquor, washing acid and calcium nitrate crystals; sulfuric acid solution and washing liquid are added to mix the crystallization mother liquor for deep decalcification, and the liquid is filtered to obtain a decalcified filtrate and a decalcified filter cake; ammonia water is added to neutralize the decalcified filtrate, and then washing water is added for filtering and washing to obtain a filter cake, a neutralization washing liquid and a neutralization filtrate, and finally repulping water and washing water are added for repulping and washing, and finally a crude rare earth concentrate and a repulping filtrate are filtered and separated by an ultrasonic device.

[0028] Before calcination, the phosphate rock needs to be crushed by a jaw crusher or a hammer crusher. The crushed phosphate rock can react more thoroughly in the subsequent calcination or acid hydrolysis process, thereby effectively separating the substances in the phosphate rock and crushing the phosphate rock to a size of less than or equal to 0.3mm. Then, it is screened through a filter with a mesh diameter of less than 0.3mm to ensure that the phosphate rock particle size does not exceed 0.3mm. The screened phosphate rock powder is added to the calcination kiln and calcined for 2 hours at a calcination temperature of 900-1150℃ to generate calcined ore and release CO2-containing waste gas.

[0029] In this embodiment, a nitric acid solution with a mass concentration of 17% is added to a high-pressure reactor and mixed with the calcined ore to cause a first reaction. Under the conditions of a pressure of 20 MPa and a reaction temperature of 45-50° C., the reaction is carried out for 0.5 h in tank A with a pH of 1.5-1.8, tank B with a pH of 1.2-1.5, tank C with a pH of 1.2-1.5, tank D with a pH of 1.0-1.2, and tank E with a pH of 1.0-1.2, respectively, for a total reaction time of 3 h. The nitric acid under high pressure can fully dissolve the impurity metal oxides such as calcium and magnesium in the calcined ore, releasing phosphorus and rare earth Elements are then subjected to secondary neutralization, and lime milk with a concentration of 25-30% is added for secondary reaction. The reaction temperature is 45-50°C and the pH value is 5.0-6.0, and the reaction time is 1 hour. In this step, the efficient removal of magnesium from the calcined ore and the maximum retention of rare earth elements are achieved through lime milk combined with pH multi-stage gradient control and selective precipitation; wherein the magnesium removal washing liquid is returned to dilute nitric acid with a mass concentration of 65% to a nitric acid solution with a mass concentration of 14-18%, and the lime milk with a mass concentration of 25-30% is prepared from calcium hydroxide and the magnesium removal washing liquid.

[0030] In this embodiment, a nitric acid solution with a mass concentration of 50-55% is added to the acidolysis tank and stirred with the phosphate concentrate to cause an acidolysis reaction. The reaction temperature is 60-65°C for 1.5-2h, and the acidolysis liquid-to-solid ratio is 1:1-1:1.5. After the reaction is completed, wash water is added, and the acidolysis liquid, acidolysis residue and acidolysis washing liquid are separated by a filter press, and the filtration time is 96min.

[0031] In this embodiment, the acid hydrolyzed liquid is placed in a low-temperature reactor for freeze crystallization, and then the acid hydrolyzed liquid after freeze crystallization is sent to a double-drum filter, and low-temperature nitric acid with a mass concentration of 50-55% and a temperature of 5-10°C and low-temperature wash water with a temperature of 5-8°C are added for centrifugal filtration to separate the crystallization mother liquor, washing acid and calcium nitrate crystals.

[0032] In this embodiment, sulfuric acid with a mass concentration of 40-45% and a washing liquid are added to a sulfuric acid-resistant reactor to deeply decalcify the crystallization mother liquor, and the reaction is carried out at 58-62° C. for 6 hours. The deeply decalcified crystallization mother liquor is passed through a vacuum belt filter for solid-liquid separation to obtain a deeply decalcified filtrate and a decalcified filter cake; wherein, the decalcified filter cake is washed with water to obtain a washed filter cake and a first washing liquid, and a second water washing is added to obtain gypsum and a second washing liquid. The first washing liquid and the second washing liquid are used to prepare a sulfuric acid solution with a mass concentration of 40-45% with sulfuric acid with a mass concentration of 98% and used for deep decalcification with the crystallization mother liquor, thereby fully utilizing the solution.

[0033] In this embodiment, the neutralization reaction of ammonia water and decalcified filtrate is carried out in a neutralization reactor, and the residual nitric acid in the decalcified filtrate is deeply neutralized by ammonia water, so that rare earth ions are precipitated in the form of hydroxides; after being treated with an ultrasonic device at 20-40 kHz and a power of 500-1000 W for 2-3 hours, a crude rare earth concentrate and a re-pulped filter wash liquid are separated by the acoustic cavitation effect. The ultrasonic wave generated by the ultrasonic device in the liquid can enhance the permeability of the wash water to the filter cake, deeply wash the residual impurities and unprecipitated rare earths remaining in the filter cake, play a role in physical separation, and improve the leaching rate of rare earth elements in the filter cake.

[0034] See also Figure 2-Figure 3 , in Example 1:

[0035] Calcination: 1170g of phosphate rock was obtained, crushed to a particle size of 0.3mm or less, and then placed in a calcining furnace and calcined at 900°C for 2 hours to obtain 951g of calcined ore and release 219g of waste gas containing CO2;

[0036] Magnesium removal: The calcined ore was placed in a high-pressure reactor, and 951 g of water and 3131 g of 17% nitric acid were added in the same proportion. A multi-stage leaching treatment was carried out at a pressure of 20 MPa and 45°C. The leaching was carried out in tank A with a pH of 1.8, tank B with a pH of 1.5, tank C with a pH of 1.4, tank D with a pH of 1.2, and tank E with a pH of 1.0. Each reaction was carried out for 0.5 hours to complete the multi-stage leaching treatment. Then, 45 g of lime milk with a mass concentration of 30% was added and the reaction was carried out at 50°C for 1 hour to adjust the pH value of the calcined ore to 5.9. 4773 g of calcined ore was produced.

[0037] Acid hydrolysis: 4773g of calcined ore was rinsed with 2340g of washing water for 120 minutes to obtain 1057g of phosphate concentrate, 3669g of demagnesiumization filtrate and 2344g of demagnesiumization filtrate. The demagnesiumization filtrate can be used to prepare lime milk and dilute nitric acid; the phosphate concentrate was placed in an acid hydrolysis tank, 1678g of nitric acid with a mass concentration of 50% was added, and the mixture was stirred continuously for 2h at 65°C to allow the nitric acid to separate impurities in the phosphate concentrate, producing 2293g of a mixture of phosphate concentrate, nitric acid and impurities. At this time, the mixture was added to a centrifuge, and 428g of washing water was added for centrifugal filtration for 90 minutes to obtain 1864g of acid hydrolysis solution, 486g of acid hydrolysis washing solution and 365g of acid hydrolysis slag;

[0038] Freeze crystallization: 1864 g of the acid hydrolyzed slurry after freeze crystallization was mixed with 438 g of 50% nitric acid at 10°C and 16 g of wash water in a double drum filter and centrifuged for 6 hours. Washing and filtration yielded 996 g of crystallization mother liquor, 711 g of wash acid, and 319 g of calcium nitrate crystals.

[0039] Deep decalcification: 996 g of crystallization mother liquor and 248 g of sulfuric acid with a mass concentration of 45% were added to a sulfuric acid-resistant reactor. 248 g of sulfuric acid was continuously added at 58 ° C for 1 hour, and the mixture was stirred continuously for 6 hours for the fourth leaching treatment to generate 1221 g of crystallization mother liquor containing sulfuric acid, which was then pressed through a filter press for 9 minutes to separate 1000 g of deep decalcification filtrate and 211 g of decalcified filter cake.

[0040] Enrichment of rare earth: add 1023g of ammonia water and 1000g of deep decalcification filtrate and stir at 95°C for 2h, control the pH value of the deep decalcification filtrate to 6.0, and obtain 1906g of ammonia-containing deep decalcification filtrate, which is then added to a centrifuge, and 454g of wash water is added for centrifugal treatment to obtain a mixture with a total weight of 1327g and containing 375g of filter cake, and then add 1000g of repulping water and 446g of wash water in an ultrasonic tank, and leach for 1h by an ultrasonic device at 20kHz and a power of 1000W, finally obtaining 330g of crude rare earth enriched material with a total liquid-solid ratio of 1:4, containing 86.7g of rare earth and 1418g of repulping filtrate.

[0041] Example 2:

[0042] The difference between Example 2 and Example 1 is that: in Example 2, in the demagnesium step, the reaction is carried out in a demagnesium reaction tank with a pH of 1.5 at 45° C. in a normal atmospheric pressure environment for 3 hours; in the rare earth enrichment step, the stirring treatment is carried out in a stirring tank for 1 hour, and other conditions remain unchanged.

[0043] Example 3:

[0044] The difference between Example 3 and Example 1 is that the operating frequency of the ultrasonic device is 40 kHz, the power is 1000 W, and other conditions remain unchanged.

[0045] Comparative Example 1:

[0046] The difference between Comparative Example 1 and Example 1 is that the reaction is not carried out in a high-pressure reactor, and other conditions remain unchanged.

[0047] Comparative Example 2:

[0048] The difference between Comparative Example 2 and Example 1 is that in the demagnesium step, the reaction is carried out in a demagnesium reaction tank with a pH of 1.2, and other conditions remain unchanged.

[0049] Comparative Example 3:

[0050] The difference between Comparative Example 3 and Example 1 is that in the rare earth enrichment step, Comparative Example 3 does not undergo ultrasonic treatment, and other conditions remain unchanged.

[0051] Table 1

[0052]

[0053] Table 1 is a reference table of Examples 1-3 and Comparative Examples 1-3 under different pressures, pH concentrations, and ultrasonic leaching frequencies. As can be seen from Table 1, in the demagnesiation step of Example 1, the calcined ore is leached five times in sequence in AE tanks with different pH values ​​under a pressure of 20 MPa, and under the leaching action of the ultrasonic device, the final crude rare earth concentrate and the weight of rare earth elements obtained are much higher than those of Comparative Examples 1-3. The five leachings can effectively decompose impurities and metal oxides in the calcined ore, thereby improving the purity of rare earth elements in the phosphate concentrate. Under the action of the final ultrasonic device, the leaching rate of rare earth elements is further improved by the acoustic cavitation effect, thereby improving the purity of rare earth elements in the separated crude rare earth concentrate. Therefore, under the conditions of high pressure, multi-stage leaching, and ultrasonic leaching, Example 1 has a much higher rare earth element leaching rate than Comparative Examples 1-3. Similarly, the differences between Examples 2 and 3 and Example 1 are that Example 2 In the demagnesium step, the reaction was carried out at 45° C. in a demagnesium reaction tank with a pH of 1.5 for 3 h in a normal atmospheric pressure environment; in the rare earth enrichment step, the stirring treatment was carried out in a stirred tank for 1 h. The operating frequency of the ultrasonic device in Example 3 was 40 kHz and the power was 1000 W. The final rare earth element leaching rate was also similar to that in Example 1, proving that as long as high-pressure multi-stage leaching and ultrasonic device treatment are carried out, a higher rare earth element leaching rate can be obtained under reasonable control of pressure, pH value, number of leaching times and working parameters of the ultrasonic device. This shows that the present method has strong adaptability and flexibility, and the process parameters can be adjusted according to actual conditions to achieve the best rare earth element extraction effect. At the same time, from the comparison of the results of Examples 1-3, it can be seen that although Examples 2 and 3 differ from Example 1 in some process conditions, the final rare earth element leaching rates obtained are similar, further proving the stability and reliability of the present method.

[0054] The advantages of the present invention are:

[0055] 1. The present invention gradually dissolves and separates the elements in the Zhijin phosphate ore through the leaching action of multi-stage nitric acid, adopts a high-pressure nitric acid leaching method, combines a multi-stage leaching process, and uses an ultrasonic device to assist in secondary leaching of the solid residue, thereby generally improving the leaching rate of rare earth elements and obtaining a crude rare earth concentrate.

[0056] The above disclosures are only several specific embodiments of the present invention, but the present invention is not limited thereto. Any changes that can be conceived by those skilled in the art should fall within the scope of protection of the present invention.

Claims

1. A method for producing crude rare earths by multi-stage leaching and decomposing Zhijin rare earth-containing phosphate ore using high-pressure nitric acid, characterized in that: The following steps are involved: S1, obtaining phosphate rock, and processing it through crushing and calcining to obtain calcined ore and release waste gas containing CO2; S2, after the calcined ore is cooled, the calcined ore is mixed with a dilute nitric acid solution in a certain proportion, placed in a high-pressure reactor, and then a certain concentration of lime milk is added to cause a secondary neutralization reaction under specific temperature and pH conditions, followed by filtration and washing to obtain phosphate concentrate, demagnesium removal filtrate, and demagnesium removal washing solution; S3, mixing the phosphate concentrate with a certain concentration of nitric acid and washing acid and adding the mixture into an acid hydrolysis tank for acid hydrolysis, and filtering and separating the mixture to obtain an acid hydrolysis solution, an acid hydrolysis residue, and an acid hydrolysis washing solution; S4, performing freeze crystallization on the acid hydrolyzed solution, and filtering and washing again through a double drum filter to obtain a crystallization mother liquor, washing acid, and calcium nitrate crystals; S5, adding sulfuric acid or ammonium sulfate solution and washing solution to the mixed crystallization mother liquor for deep decalcification, and filtering to obtain a deep decalcified filtrate and a decalcified filter cake; S6, adding ammonia water to the deep decalcified filtrate for neutralization reaction, then adding washing water for filtering and washing to obtain filter cake, neutralization washing liquid and neutralization filtrate, finally adding repulping water and washing water for repulping and washing, and finally filtering through an ultrasonic device to obtain a crude rare earth concentrate and repulping filtrate.

2. The method for producing crude rare earths by multi-stage leaching and decomposing Zhijin rare earth-containing phosphate ore using high-pressure nitric acid according to claim 1, characterized in that: In S1, the phosphate rock is crushed into phosphate rock powder with a particle size of less than or equal to 0.3 mm by a crusher, and then the phosphate rock powder is sent to a calcining kiln and calcined at a calcination temperature of 900-1150°C for 2 hours to generate calcined ore.

3. The method for producing crude rare earths by multi-stage leaching and decomposing Zhijin rare earth-containing phosphate ore using high-pressure nitric acid according to claim 1, characterized in that: In S2, a nitric acid solution with a mass concentration of 17% is added to a high-pressure reactor and mixed with the calcined ore. Under the conditions of a reaction temperature of 45-50°C and a pressure of 20KPa, the mixture is reacted in tank A with a pH of 1.5-1.8, tank B with a pH of 1.2-1.5, tank C with a pH of 1.2-1.5, tank D with a pH of 1.0-1.2, and tank E with a pH of 1.0-1.2 for 0.5h, followed by secondary neutralization. Lime milk with a concentration of 25-30% is added for secondary reaction. The mixture is reacted at a reaction temperature of 45-50°C and a pH of 5.0-6.0 for 1h. Impurities attached to the phosphate rock are then washed with washing water to generate phosphate concentrate, demagnesium removal filtrate and demagnesium removal washing solution.

4. The method for producing crude rare earths by multi-stage leaching and decomposing Zhijin rare earth-containing phosphate ore using high-pressure nitric acid according to claim 3, characterized in that: in, The demagnesium washing solution is used to dilute nitric acid with a mass concentration of 65% to a nitric acid solution with a mass concentration of 14-18%. The lime milk with a mass concentration of 25-30% is prepared from calcium hydroxide and the demagnesium washing solution.

5. The method for producing crude rare earths by multi-stage leaching and decomposing Zhijin rare earth-containing phosphate ore using high-pressure nitric acid according to claim 1, characterized in that: In S3, a nitric acid solution with a mass concentration of 50-55% is added to the acidolysis tank and stirred with the phosphate concentrate to cause an acidolysis reaction. The reaction temperature is 60-65°C for 1.5-2h, and the acidolysis liquid-solid ratio is 1:1-1:1.

5. After the reaction is completed, washing water is added, and the acidolysis liquid, acidolysis residue and acidolysis washing liquid are separated by a filter press. The filtration time is 96min.

6. The method for producing crude rare earths by multi-stage leaching and decomposing Zhijin rare earth-containing phosphate ore using high-pressure nitric acid according to claim 1, characterized in that: In S4, the acid hydrolyzed liquid is placed in a low-temperature reactor for freeze crystallization, and then the acid hydrolyzed liquid after freeze crystallization is sent to a double-drum filter, nitric acid with a mass concentration of 50-55% and a temperature of 5-10°C and washing water with a temperature of 5-8°C are added to perform centrifugal filtration to separate the crystallization mother liquor, washing acid and calcium nitrate crystals.

7. The method for producing crude rare earths by multi-stage leaching and decomposing Zhijin rare earth-containing phosphate ore using high-pressure nitric acid according to claim 1, characterized in that: In S5, sulfuric acid with a mass concentration of 40-45% and a washing solution are added to a sulfuric acid-resistant reactor to deeply decalcify the crystallization mother liquor, and the reaction is carried out at 58-62° C. for 6 hours. The deeply decalcified crystallization mother liquor is passed through a vacuum belt filter for solid-liquid separation to obtain a deeply decalcified filtrate and a decalcified filter cake.

8. The method for producing crude rare earths by multi-stage leaching and decomposing Zhijin rare earth-containing phosphate ore using high-pressure nitric acid according to claim 7, characterized in that: in, The decalcified filter cake is washed with water to obtain a washed filter cake and a first wash liquid. The second water washing is performed to obtain gypsum and a second wash liquid. The first wash liquid and the second wash liquid are used to prepare a sulfuric acid solution with a mass concentration of 40-45% with sulfuric acid with a mass concentration of 98% and used for deep decalcification with the crystallization mother liquor.

9. The method for producing crude rare earths by multi-stage leaching and decomposing Zhijin rare earth-containing phosphate ore using high-pressure nitric acid according to claim 1, characterized in that: In S6, the deep decalcified filtrate and ammonia water are placed in a neutralization reactor, and a neutralization reaction is carried out at 90-95°C for 2-3 hours. The deep decalcified filtrate after the neutralization reaction is then added to a repulping stirring tank, and washing water is added for filtration and washing to obtain a filter cake, a neutralization washing liquid and a neutralization filtrate. Finally, repulping water and washing water are added to the filter cake for repulping treatment, and the filter cake is treated with an ultrasonic device at 20-40kHz and a power of 500-1000W for 1 hour to separate and obtain a crude rare earth concentrate and a repulping filtrate.

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