A production method for enriching phosphate rock and preparing calcium nitrate and magnesium carbonate by a two-step ammonium method

Abstract

The present invention relates to the technical field of the phosphate rock industry, and particularly to a production method for enriching phosphate rock by a two-step ammonium method and preparing calcium nitrate and magnesium carbonate. The present application discloses a production method for enriching phosphate rock by a two-step ammonium method and preparing calcium nitrate and magnesium carbonate, comprising the following steps: calcination, cooling, magnesium removal reaction, magnesium removal liquid filtration, magnesium removal filtrate concentration, calcium nitrate cooling crystallization, calcium nitrate centrifugal separation, ammonium solution treatment, filtration after ammonium solution treatment, primary calcium removal, secondary calcium removal, and carbonization. The production method described in the present application has the advantages of low treatment cost, thorough separation of calcium and magnesium, and the products meeting the industrial grade standards.

Description

Technical Field

[0001] The present invention relates to the technical field of the phosphate rock industry, and particularly to a production method for enriching phosphate rock by a two-step ammonium method and preparing calcium nitrate and magnesium carbonate. Background Art

[0002] The natural phosphate rock in Guizhou, such as the phosphate rock in the Weng'an and Fuquan phosphate ore areas, is a marine sedimentary phosphorite. The phosphorus-containing mineral is collophanite, and the associated minerals are mainly dolomite, and also contain a small amount of calcite, quartz, clay minerals, etc. Due to the associated gangue such as dolomite, the grade of the natural phosphate rock is not high, and the content of phosphorus pentoxide is about 25%. If such natural phosphate rock is directly used, it will increase the production cost of the downstream. Usually, the method is to beneficiate the raw phosphate rock at a lower cost to obtain concentrate. The current beneficiation method is foam flotation. Through bubble foam, the phosphate concentrate and dolomite gangue float or sink respectively to achieve the separation of the phosphate concentrate and dolomite. Although the raw ore can obtain high-grade phosphate concentrate through foam flotation, it will inevitably produce phosphate rock mainly composed of dolomite, which is difficult to utilize and can only be stockpiled.

[0003] Currently, the decomposition of traditional phosphate rock mainly uses strong inorganic acids to decompose phosphate rock to obtain phosphoric acid. Among them, the process of decomposing phosphate rock with sulfuric acid (sulfuric acid method) is relatively mature, but the biggest problem of the sulfuric acid method is the problem of phosphogypsum. Although the research efforts and economic investment in the treatment of phosphogypsum have been continuously increased in recent years, due to the bottleneck restriction of technical and economic conditions, it is impossible to completely solve and consume a large amount of the stockpiled phosphogypsum. In addition to the sulfuric acid method, there are also other options such as the hydrochloric acid method and the nitric acid method that can decompose phosphate rock to produce acid. These methods do not produce gypsum naturally, so they have good advantages in terms of solid waste discharge.

[0004] Regarding the separation and utilization of calcium and magnesium in phosphate rock, most of the domestic research is still in the laboratory research or semi-industrial stage, and no industrialization results have been seen so far. Various researches mainly focus on the stacking treatment of waste, the production of compound fertilizers, etc., or adopt secondary flotation to recover phosphorus from tailings again. Although it alleviates the problem of the stockpiling of phosphate tailings to a certain extent, it does not solve the comprehensive utilization problem of phosphate rock resources, especially the problem of eliminating the generation of tailings from the source.

[0005] Patents related to the beneficiation of phosphate rock and the utilization of phosphate tailings disclose corresponding contents; for example, Patent CN102674407A uses means such as calcination, digestion, carbonization, and pyrolysis to treat phosphate tailings to make magnesium oxide; Patent CN102534254A uses high-temperature calcination of phosphate tailings, then adds ferrosilicon and fluorite as raw materials, and finally reduces to obtain metallic magnesium; CN102923739A calcines phosphate rock or phosphate tailings at high temperature, digests, carbonizes and filters, and adds hydrofluoric acid to the filtrate to obtain products such as magnesium fluoride and calcium carbonate.

[0006] In summary, although there are many reports on the separation of magnesium and calcium from phosphate rock, the biggest problem in the existing processes is that a carbonization process is required for calcium separation. The process is complex, the treatment cost is relatively high, and the carbonization process has high requirements and is prone to simultaneously generate magnesium carbonate and calcium carbonate, greatly reducing the recovery rates, purity, and whiteness of calcium and magnesium. Summary of the Invention

[0007] In order to overcome the deficiencies of the prior art, the present invention provides a production method for enriching phosphate rock by a two-step ammonium solution method and preparing calcium nitrate and magnesium carbonate. This production method has the advantages of low treatment cost, thorough separation of calcium and magnesium, and the products meeting industrial-grade standards.

[0008] The technical solution adopted by the present invention to solve its technical problems is as follows:

[0009] A production method for enriching phosphate rock by a two-step ammonium solution method and preparing calcium nitrate and magnesium carbonate, comprising the following steps:

[0010] S1. Calcination

[0011] Calcine the phosphate rock at 700 - 950 °C.

[0012] S2. Cooling

[0013] After the calcination of the phosphate rock is completed, cool it to obtain calcined phosphate rock for standby.

[0014] S3. Demagnesium reaction

[0015] Add the calcined phosphate rock to the ammonium solution for demagnesium reaction. The calcium in the calcined phosphate rock and the magnesium in the ammonium solution are controlled at a molar ratio of 1:1.1 - 1.5.

[0016] Among them, the calcined phosphate rock includes calcium oxide and magnesium oxide; the ammonium solution includes magnesium nitrate.

[0017] S4. Filtration of the demagnesium solution

[0018] After the demagnesium reaction is completed, filter to obtain filter residue and demagnesium filtrate.

[0019] S5. Concentration of the demagnesium filtrate

[0020] Concentrate the demagnesium filtrate to obtain a concentrated slurry.

[0021] S6. Cooling crystallization of calcium nitrate

[0022] Perform cooling crystallization treatment on the concentrated slurry.

[0023] S7. Centrifugal separation of calcium nitrate

[0024] After crystallization, centrifuge the slurry after freeze crystallization to separate out calcium nitrate tetrahydrate crystals and filtrate.

[0025] S8. Ammonium decomposition treatment

[0026] The filter residue obtained in step S4 is subjected to an ammonium decomposition reaction with excessive ammonium nitrate;

[0027] S9. Filtration after ammonium decomposition

[0028] After the ammonium decomposition ends, filtration and separation are carried out to obtain phosphate concentrate filter cake and ammonium decomposition filtrate;

[0029] S10. Primary decalcification

[0030] The ammonium decomposition filtrate obtained in step S9 reacts with excessive ammonium carbonate. After the reaction ends, filtration is carried out to obtain a primary filter cake and a primary decalcification solution; the primary filter cake is dried to obtain calcium carbonate by-product;

[0031] S11. Secondary decalcification

[0032] The primary decalcification solution obtained in step S10 reacts with a decalcifying agent. After the reaction ends, filtration is carried out to obtain a secondary filter cake and a secondary decalcification solution;

[0033] S12. Carbonization

[0034] The secondary decalcification solution obtained in step S11 is subjected to a carbonization reaction with ammonium carbonate. After the reaction ends, filtration is carried out, and the filter cake is dried to obtain magnesium carbonate by-product.

[0035] The following will explain and illustrate in detail the steps and technical principles involved in the production method for enriching phosphate rock and preparing calcium nitrate and magnesium carbonate by the two-step ammonium decomposition method

[0036] In step S1, the phosphate rock is calcined at 700 - 950 °C. After calcination, the carbonate minerals in the phosphate rock decompose into calcium oxide and magnesium oxide, and the collophanite apatite does not decompose at this temperature. The following reaction occurs: CaCO3·MgCO3 = CaO + MgO + 2CO2

[0037] In step S2, the calcined phosphate rock is cooled to below 100 °C and reserved for use.

[0038] In step S3 for magnesium removal, the cooled calcined phosphate rock is added to the ammonium decomposition solution,

[0039] At this time, calcium oxide and magnesium oxide are digested by water to become calcium hydroxide and magnesium hydroxide.

[0040] The following reactions occur: CaO + H2O = Ca(OH)2, MgO + H2O = Mg(OH)2. Calcium hydroxide reacts with magnesium nitrate in the ammonium decomposition solution to form calcium nitrate and magnesium hydroxide: Ca(OH)2 + Mg(NO3)2 = Mg(OH)2 + Ca(NO3)2.

[0041] In the demagnification stage, the addition amounts of the ammonium decomposition solution and the calcined phosphate rock must be controlled, that is, the molar ratio of calcium (calcium oxide in the calcined phosphate rock) to magnesium (magnesium nitrate in the ammonium decomposition solution) is 1.1 - 1.5. Otherwise, the demagnification fails. Through the demagnification stage, the ammonium decomposition solution contains soluble calcium and magnesium, namely calcium nitrate and magnesium nitrate. Through this reaction, the soluble magnesium in the ammonium decomposition solution is converted into insoluble magnesium, namely magnesium hydroxide, and an equal amount of magnesium nitrate is generated, thereby realizing the demagnification of the ammonium decomposition solution. During the demagnification reaction process, the temperature is controlled at 90 - 100 °C.

[0042] Among them, the ammonium decomposition solution can be the ammonium decomposition filtrate obtained in step S9 or a self-prepared solution containing magnesium nitrate, and the weight content of magnesium nitrate is 1 - 20%.

[0043] In step S4, after the demagnification reaction, soluble calcium nitrate exists in the solution, and the insoluble solid is phosphate rock and magnesium hydroxide; filtration is carried out to separate solid substances such as calcium nitrate and phosphate rock.

[0044] In step S5, the concentration of the filtered pure calcium nitrate solution is relatively low and needs to be further concentrated. It is evaporated and concentrated into a concentrated slurry. When the supernatant density of the concentrated slurry reaches 1.1 - 1.5 g / cm 3 then, the concentrated slurry is sent to a cooling crystallizer.

[0045] In step S6, the concentrated slurry from the concentrator is fed into a freezing crystallizer, the crystallization temperature is controlled at 0 - 5 °C, and the crystallization time is 4 - 8 h. After crystallization is completed, it is sent to a centrifuge for separation.

[0046] In step S7, the slurry after freezing crystallization is pumped into a centrifuge to separate out the crystal calcium nitrate tetrahydrate, and the filtrate can be returned to the demagnification section for continuous recycling.

[0047] In step S8, the above-mentioned filter residue after demagnification, mainly containing phosphate rock, is added with excessive ammonium nitrate for ammonium decomposition, and gaseous ammonia escapes when heated to boiling (reaction temperature 90 - 100 °C). Under this condition, magnesium hydroxide in the filter residue reacts with ammonium nitrate to generate magnesium nitrate, and the reaction formula is as follows: Mg(OH)2 + 2NH4NO3 = Mg(NO3)2 + 2NH3 + 2H2O. The added ammonium nitrate is in excess to ensure complete ammonium decomposition reaction. At this time, calcium hydroxide in the demagnification residue will also react with ammonium nitrate: Ca(OH)2 + 2NH4NO3 = Ca(NO3)2 + 2NH3 + 2H2O. The generated gaseous ammonia is absorbed by water spraying, and the absorption liquid is recycled. After the concentration of the absorption liquid reaches 10% - 20%, it is pumped to the subsequent carbonization process for use.

[0048] In step S9, after ammonium decomposition is completed, filtration and separation are carried out. The filter residue is phosphate concentrate, and the ammonium decomposition filtrate is a solution containing calcium and magnesium. Part of this filtrate is sent for primary decalcification, and part is sent for demagnification.

[0049] In step S10, the ammonium decomposition filtrate contains magnesium nitrate and a small amount of calcium nitrate. Decalcification is required to obtain a pure magnesium nitrate solution. Ammonium carbonate (obtained by reacting the carbon dioxide obtained from the calcination in step S1 and the ammonia gas obtained from the ammonium decomposition treatment in step S8) is used for the first decalcification; when no new precipitate is produced, it can be judged that the reaction is over and no new ammonium carbonate needs to be added;

[0050] Utilizing the insolubility of calcium carbonate, the soluble calcium ions in the calcium-magnesium mixed solution are transformed into insoluble calcium carbonate precipitates, while the magnesium ions remain soluble. Then, this part of the calcium component is separated by filtration operation to reduce the calcium content in the solution. In this way, most of the calcium ions can be removed.

[0051] Filtration of the first decalcification liquid: After the first decalcification, the formed precipitate is calcium carbonate. After filtration and separation, the filter residue is dried to obtain the calcium carbonate by-product, and the filtrate is the magnesium nitrate solution with a very low calcium content;

[0052] In step S11, although the calcium content in magnesium nitrate is greatly reduced through the first decalcification, there are still a small amount of calcium ions, which do not meet the requirements of industrial-grade magnesium carbonate products. Deep decalcification is required. For the decalcification liquid after the first decalcification, oxalic acid is used as the decalcifying agent for the second decalcification. Through the precipitation reaction, the remaining soluble calcium ions form insoluble calcium oxalate; when no new precipitate is produced, it can be judged that the reaction is over and no new oxalic acid (analytical pure grade oxalic acid solution) needs to be added;

[0053] Filtration of the second decalcification liquid: The solution from the second decalcification reactor is sent to a filter press for solid-liquid separation. The filter residue is calcium oxalate, and the filtrate is a pure magnesium nitrate solution.

[0054] In step S12, the filtrate obtained after filtration in the second decalcification is the calcium-free magnesium nitrate solution. Ammonium carbonate recovered is added for carbonization reaction. The carbonization reaction temperature is controlled at 30 - 40 °C. After the reaction ends (until no new product is generated), (basic) magnesium carbonate precipitates. The recovered ammonium carbonate is the ammonia water obtained by absorbing the ammonia gas generated in the ammonium decomposition treatment in step S8 with water and the carbon dioxide gas generated in the calcination stage in step S1. After the ammonia water and carbon dioxide are combined, ammonium carbonate is formed. Magnesium carbonate can be used as a refractory material, a heat insulation material for boilers and pipelines, and an additive for food, medicine, cosmetics, rubber, ink, etc.

[0055] Filtration of the carbonized liquid: The magnesium carbonate precipitated in the carbonization reaction has very low solubility and precipitates in the form of a precipitate. The precipitate can be separated by filtration. The precipitate is dried to obtain the product magnesium carbonate. The main component of the filtrate is ammonium nitrate, which is returned to the ammonium decomposition process for use.

[0056] Drying: If the water content of the magnesium carbonate obtained by filtration needs to be reduced, it can be dried to obtain the dry finished product.

[0057] Regeneration: The filter residue filtered after secondary decalcification, with the main component being calcium oxalate, can be regenerated, recycled, and reused to reduce the decalcification cost. The regeneration is carried out by treating with sulfuric acid, and calcium oxalate is converted into calcium sulfate.

[0058] Filtration: After regeneration, calcium oxalate is converted into calcium sulfate, which exists in the form of a precipitate, releasing oxalic acid. The calcium sulfate filter residue is removed by filtration, and the filtrate is oxalic acid, which is returned for recycling.

[0059] The beneficial effects of the present invention are as follows:

[0060] 1. After the phosphate rock raw ore is calcined at high temperature, the gangue dolomite contained in the raw ore is thermally decomposed into calcium oxide and magnesium oxide. At this time, the phosphate rock itself does not decompose. Then, calcium oxide and magnesium oxide are combined with water to be converted into calcium hydroxide and magnesium hydroxide, and calcium hydroxide and magnesium hydroxide react with ammonium nitrate through double decomposition reaction to generate soluble calcium nitrate and magnesium nitrate, while releasing ammonia gas; the solution dissolving calcium nitrate and magnesium nitrate and the insoluble solid phosphate concentrate are separated by filtration to achieve the separation of phosphate rock and gangue minerals. The carbon dioxide released during calcination and the ammonia gas released during ammonolysis are collected and introduced into the calcium nitrate solution to form calcium carbonate precipitate, which is filtered to obtain a high-whiteness calcium carbonate product for external sale, and the filtrate is recycled. Similarly, carbon dioxide and ammonia gas are introduced into the magnesium nitrate solution to obtain a pure magnesium carbonate product;

[0061] 2. The obtained by-products of calcium carbonate, magnesium carbonate and calcium nitrate tetrahydrate crystals have high purity and do not need to be further processed and can be directly utilized. Brief Description of the Drawings

[0062] The present invention will be further described below in conjunction with the drawings and embodiments.

[0063] Figure 1 is the process flow chart of a production method for enriching phosphate rock and preparing calcium nitrate and magnesium carbonate by a two-step ammonium solution method described in the present application. Detailed Embodiments

[0064] For the convenience of those skilled in the art to understand, the present invention will be further described below in conjunction with embodiments. The content mentioned in the embodiments does not limit the present invention.

[0065] As used herein, the term "and / or" includes all combinations of any and one or more of the associated listed items. The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. As used herein, the singular forms "a", "an", "one" and "the" are also intended to include the plural forms unless the context clearly indicates otherwise. Further understanding, when "comprising" is used in this specification, it specifies the stated features, integers, steps, operations, elements and / or components, but does not exclude the existence or addition of one or more other features, integers, steps, operations, elements, components and / or their combinations.

[0066] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this invention belongs. Further understanding is that terms, such as those defined in a commonly used dictionary, are interpreted to be consistent with their meaning in the context of the relevant field and are not in an idealized or overly formal sense, unless explicitly defined as such here.

[0067] The exemplary inventions described herein may suitably lack any one or more of the element limitations that are not specifically disclosed herein. Accordingly, terms such as "comprising", "including", "containing", etc. should be understood broadly and non - restrictively. Additionally, the term expressions used herein are used for description without limitation, and it is not intended that these term expressions, which do not include any equivalent features, only describe a part of their features, but various modifications are possible within the scope of the present invention according to the rights. Therefore, although the present invention has been specifically disclosed through preferred embodiments and optional features, modifications to the present invention as embodied herein may be recorded by those skilled in the art, and such modifications and variations will be considered within the scope of the present invention.

[0068] The raw materials or reagents used in the examples and comparative examples of the present invention are all purchased from mainstream manufacturers in the market. For those without indicating the manufacturer or concentration, they are all raw materials or reagents of analytical pure grade that can be obtained conventionally, and there is no special limitation as long as they can play the expected role. The equipment such as reaction kettles and rotary evaporators used in this example are all purchased from major manufacturers in the market, and there is no special limitation as long as they can play the expected role. For those not indicating specific techniques or conditions in this example, they are carried out according to the techniques or conditions described in the literature in this field or according to the product specifications.

[0069] Example 1

[0070] A production method for enriching phosphate rock and preparing calcium nitrate and magnesium carbonate by a two - step ammonium solution method, comprising the following steps:

[0071] Calcination: 100 grams of phosphate rock is calcined at 700 °C for 5 h.

[0072] The composition of the original ore used is as follows:

[0073]

[0074] Cooling: The calcined phosphate rock becomes calcined phosphate, and after being taken out from the calcination furnace, it is air - cooled to 80 °, and 85 grams of cold calcined phosphate rock is obtained.

[0075] Demagnesium reaction: The cooled calcined phosphate rock is added to the ammonium decomposition solution, and the addition amounts of the ammonium decomposition solution and the calcined phosphate rock are controlled, i.e., the molar ratio of calcium to magnesium is 1:1.1. Through the demagnesium stage, the ammonium decomposition solution containing soluble calcium and magnesium, namely calcium nitrate and magnesium nitrate, is transformed into insoluble magnesium, i.e., magnesium hydroxide, and an equal amount of magnesium nitrate is generated, thereby realizing the demagnesium of the ammonium decomposition solution. The temperature of the demagnesium reaction is 90 °C and the time is 8 h.

[0076] Filtration of the demagnesium solution: After the demagnesium reaction, soluble calcium nitrate exists in the solution, and the insoluble solids are phosphate rock and magnesium hydroxide. Filtration is carried out to separate solid substances such as calcium nitrate and phosphate rock.

[0077] Concentration of the demagnesium filtrate: The concentration of the pure calcium nitrate solution after filtration is relatively low and needs to be further concentrated. It is evaporated and concentrated into a concentrated slurry, and the concentration is carried out by the method of vacuum concentration. After detection, when the density of the supernatant of the concentrated slurry reaches 1.1 g / cm 3 it is sent to the cooling crystallizer.

[0078] Cooling crystallization of calcium nitrate: The concentrated slurry from the concentrator is sent to the freezing crystallizer. The temperature for the cooling crystallization treatment is 0 - 5 °C, the crystallization time is controlled for 4 h, and after cooling to room temperature, it is sent to the centrifuge for separation.

[0079] Centrifugal separation of calcium nitrate: The slurry after freezing crystallization is pumped into the centrifuge. The filter cake obtained after separation is dried, and calcium nitrate tetrahydrate crystals are obtained after drying; the filtrate is returned to the demagnesium section for continuous recycling.

[0080] Ammonium decomposition treatment: The filter residue after demagnesium above, mainly containing phosphate rock, is added with excessive ammonium nitrate for ammonium decomposition, and gaseous ammonia escapes when heated to boiling. Under these conditions, magnesium hydroxide in the filter residue reacts with ammonium nitrate to form magnesium nitrate. The ammonium decomposition is carried out at room temperature for 6 h;

[0081] Filtration of the ammonium decomposition solution: After the ammonium decomposition is completed, filtration separation is carried out. The filter residue is phosphate concentrate, and the filtrate is a solution containing calcium and magnesium. Part of this filtrate is sent for primary decalcification, and part is sent for demagnesium.

[0082] Primary decalcification: At 30 °C, ammonium carbonate (recovered carbon dioxide and ammonia) is used for primary decalcification. Utilizing the insolubility of calcium carbonate, the soluble calcium ions in the calcium and magnesium mixed solution are transformed into insoluble calcium carbonate precipitates.

[0083] Filtration of the primary decalcification solution: After primary decalcification, the formed precipitate is calcium carbonate. After filtration separation, the filter residue is dried to obtain calcium carbonate by-product.

[0084] Secondary decalcification: For the decalcification solution after primary decalcification, excessive oxalic acid is added as the decalcifying agent, and the remaining soluble calcium ions form insoluble calcium oxalate through a precipitation reaction (at 30 °C).

[0085] Secondary decalcification liquid filtration: The solution from the secondary decalcification reactor is sent to a filter press for solid-liquid separation. The filter residue is calcium oxalate, and the filtrate is a pure magnesium nitrate solution.

[0086] Carbonization: The filtrate obtained after secondary decalcification and filtration is a calcium-free magnesium nitrate solution. At 30°C, the recycled ammonium carbonate is added for carbonization reaction, and (basic) magnesium carbonate precipitates out.

[0087] Carbonized liquid filtration: The magnesium carbonate precipitated during the carbonization reaction has very low solubility and precipitates in the form of a precipitate. The precipitate can be separated by filtration, and the product magnesium carbonate is obtained after drying the precipitate.

[0088] The calcium nitrate tetrahydrate obtained after centrifugal separation of calcium nitrate has the following impurity test results:

[0089]

[0090] The magnesium carbonate obtained after carbonization has the following impurity test results:

[0091] MgO Ca K Na Al Mn P Pb S Si 40.70％ 0.18％ 0.02％ 0.05％ 0.0037％ 0.0001％ 0.0004 0.0001％ 0.10％ 0.054％

[0092] The calcium carbonate by-product obtained after primary decalcification has the following impurity test results:

[0093]

[0094]

[0095] Example 2

[0096] A production method for enriching phosphate rock by a two-step ammonium solution method and preparing calcium nitrate and magnesium carbonate, comprising the following steps:

[0097] Calcination: Take 500 grams of phosphate rock and calcine it at 900°C for 2 hours.

[0098] The composition of the original ore used is as follows:

[0099]

[0100] Cooling: After the calcined phosphate rock is taken out of the calcination furnace, it is air-cooled to 50°, and 410 grams of cold calcined phosphate rock is obtained.

[0101] Demagnesium reaction: The cooled calcined phosphate rock is added to the ammonium solution, and the addition amount of the ammonium solution and the addition amount of the calcined phosphate rock are controlled, that is, the molar ratio of calcium to magnesium is 1:1.5. The temperature of the demagnesium reaction is 95°C and the time is 8 hours.

[0102] Demagnesium liquid filtration: After the demagnesium reaction, soluble calcium nitrate exists in the solution, and the insoluble solid is phosphate rock and magnesium hydroxide. Filtration is carried out to separate solid substances such as calcium nitrate and phosphate rock.

[0103] Concentration of demagnesium filtrate: The concentration of the purified calcium nitrate solution after filtration is relatively low and needs to be further concentrated. It is evaporated and concentrated into a concentrated slurry, and concentrated by means of vacuum concentration. After detection, when the density of the supernatant of the concentrated slurry reaches 1.5 g / cm 3 it is sent to the cooling crystallizer.

[0104] Cooling crystallization of calcium nitrate: The concentrated slurry from the concentrator is fed into the freezing crystallizer. The temperature for the cooling crystallization treatment is 0 - 5 °C, the crystallization time is controlled at 6 h, and after cooling to room temperature, it is sent to the centrifuge for separation.

[0105] Centrifugal separation of calcium nitrate: The slurry after freezing crystallization is pumped into the centrifuge. The filter cake obtained after separation is dried, and calcium nitrate tetrahydrate crystals are obtained after drying; the filtrate is returned to the demagnesium section for continuous recycling.

[0106] Ammonium decomposition treatment: The above-mentioned demagnesium filter residue is added with excessive ammonium nitrate for ammonium decomposition and heated to boiling to obtain a magnesium nitrate solution. After the ammonium decomposition is completed, filtration and separation are carried out. The filter residue is phosphoric acid concentrate, and the filtrate is a solution containing calcium and magnesium. The ammonium decomposition is carried out at room temperature for 7 h;

[0107] Primary calcium removal: At 35 °C, ammonium carbonate (recovered carbon dioxide and ammonia) is used for primary calcium removal. Utilizing the insolubility of calcium carbonate, the soluble calcium ions in the calcium-magnesium mixed solution are converted into insoluble calcium carbonate precipitates. After primary calcium removal, the formed precipitate is calcium carbonate. After filtration and separation, the filter residue is dried to obtain calcium carbonate by-product.

[0108] Secondary calcium removal: For the decalcified solution after primary calcium removal, oxalic acid is added as the calcium remover, and the remaining soluble calcium ions form insoluble calcium oxalate through a precipitation reaction (at 35 °C). The solution after secondary calcium removal is sent to a filter press for solid-liquid separation. The filter residue is calcium oxalate, and the filtrate is a pure magnesium nitrate solution.

[0109] Carbonization: The filtrate obtained after filtration in secondary calcium removal, which is a calcium-free magnesium nitrate solution, is added with recovered ammonium carbonate for carbonization reaction (at 35 °C), and (basic) magnesium carbonate precipitates out.

[0110] Filtration of carbonized liquid: The magnesium carbonate precipitated in the carbonization reaction has very low solubility and precipitates in the form of a precipitate. The precipitate can be separated by filtration, and the precipitate is dried to obtain the product magnesium carbonate.

[0111] Drying: The magnesium carbonate is dried by 150 °C air flow to obtain the finished product.

[0112] The test results of impurities of calcium nitrate tetrahydrate obtained after centrifugal separation of calcium nitrate are as follows:

[0113]

[0114] The magnesium carbonate obtained after carbonization has the following impurity test results:

[0115] MgO CaO Na P <![CDATA[SO4 2- > K Al Fe Mn 40.50％ 0.50％ 0.45％ 0.37％ 0.12％ 0.05％ 0.01％ 0.01％ 0.04％

[0116] The calcium carbonate by-product obtained after the first decalcification has the following impurity test results:

[0117] Test Items CaCO3 MgO <![CDATA[Na2O]]> <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> Results (%) 96.11 0.97 0.102 0.026 0.538 0.10

[0118] Example 3

[0119] A production method for enriching phosphate rock and preparing calcium nitrate and magnesium carbonate by a two-step ammonium solution method, comprising the following steps:

[0120] Calcination: Take 1000 grams of phosphate rock and calcine it at 800 °C for 3 h.

[0121] The composition of the original ore used is as follows:

[0122]

[0123] Cooling: After the calcined phosphate rock is taken out of the calcination furnace, it is air-cooled to 50 ° to obtain 826 grams of cold calcined phosphate rock.

[0124] Demagnesium reaction: The cooled calcined phosphate rock is added to the ammonium solution, and the addition amounts of the ammonium solution and the calcined phosphate rock are controlled, that is, the molar ratio of calcium to magnesium is 1:1.5. The temperature of the demagnesium reaction is 100 °C and the time is 8 h;

[0125] Demagnesium liquid filtration: After the demagnesium reaction, soluble calcium nitrate exists in the solution, and the insoluble solid is phosphate rock and magnesium hydroxide. Filtration is carried out to separate solid substances such as calcium nitrate and phosphate rock.

[0126] Concentration of the demagnesium filtrate: The concentration of the pure calcium nitrate solution after filtration is relatively low and needs to be further concentrated. It is evaporated and concentrated into a concentrated slurry and sent to a cooling crystallizer.

[0127] Cooling crystallization of calcium nitrate: The concentrated slurry from the concentrator is sent to a freezing crystallizer, and the temperature for the cooling crystallization treatment is 0 - 5 °C. The crystallization time is controlled for 8 h, and after cooling to room temperature, it is sent to a centrifuge for separation.

[0128] Centrifugal separation of calcium nitrate: The slurry after freezing crystallization is pumped into a centrifuge, and the filter cake obtained after separation is dried to obtain calcium nitrate tetrahydrate crystals; the filtrate is returned to the demagnesium section for continuous recycling.

[0129] Ammonium solution treatment: The above-mentioned filter residue after demagnesium is added with excessive ammonium nitrate for ammonium solution treatment and heated to boiling to obtain a magnesium nitrate solution. After the ammonium solution treatment is completed, filtration and separation are carried out. The filter residue is phosphate concentrate, and the filtrate is a solution containing calcium and magnesium. The ammonium solution treatment is carried out at room temperature for 8 h;

[0130] Primary decalcification: At 40°C, ammonium carbonate (recovered carbon dioxide and ammonia) is used for primary decalcification. Utilizing the insolubility of calcium carbonate, the soluble calcium ions in the calcium-magnesium mixed solution are transformed into insoluble calcium carbonate precipitate. After primary decalcification, the formed precipitate is calcium carbonate. After filtration and separation, the filter residue is dried to obtain the calcium carbonate by-product.

[0131] Secondary decalcification: For the decalcified solution after primary decalcification, oxalic acid is added as the decalcifying agent, and the remaining soluble calcium ions form insoluble calcium oxalate through a precipitation reaction (at 40°C). The solution after secondary decalcification is sent to a filter press for solid-liquid separation. The filter residue is calcium oxalate, and the filtrate is a pure magnesium nitrate solution.

[0132] Carbonization: The filtrate obtained after filtration in secondary decalcification, which is a calcium-free magnesium nitrate solution, is added with recovered ammonium carbonate for carbonization reaction (at 40°C), and (basic) magnesium carbonate precipitates out.

[0133] Filtration of carbonized solution: The magnesium carbonate precipitated out in the carbonization reaction has very low solubility and precipitates in the form of a precipitate. The precipitate can be separated by filtration, and the precipitate is dried to obtain the product magnesium carbonate.

[0134] Drying: The magnesium carbonate is dried by 150°C air flow to obtain the finished product.

[0135] The calcium nitrate tetrahydrate obtained after centrifugal separation of calcium nitrate has the following impurity test results:

[0136]

[0137] The magnesium carbonate obtained after carbonization has the following impurity test results:

[0138] MgO CaO Na P <![CDATA[SO4 2- > K Al Fe Mn 40.2％ 0.6％ 0.39％ 0.28％ 0.15％ 0.11％ 0.03％ 0.04％ 0.03％

[0139] The calcium carbonate by-product obtained after primary decalcification has the following impurity test results:

[0140] Test Items CaCO3 MgO <![CDATA[Na2O]]> <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[Fe2O3]]> Results (%) 95.64 0.68 0.032 0.135 0.785 0.12

[0141] The above embodiments are preferred implementation schemes of the present invention. In addition, the present invention can also be implemented in other ways. Any obvious substitution without departing from the concept of the present invention is within the protection scope of the present invention.

Claims

1. A production method for enriching phosphate rock and preparing calcium nitrate and magnesium carbonate by a two-step ammonium method, characterized in that, It includes the following steps: S1. Calcination Calcine the phosphate rock at 700 - 950 °C; S2. Cooling Cool the phosphate rock after calcination to obtain calcined phosphate rock for standby; S3. Demagnesium reaction Add the calcined phosphate rock into the ammonium solution for demagnesium reaction. The temperature of the demagnesium reaction is 90 - 100 °C. The calcium in the calcined phosphate rock and the magnesium in the ammonium solution are controlled at a molar ratio of 1:1.1 - 1.5; Among them, the calcined phosphate rock includes calcium oxide and magnesium oxide; the ammonium solution includes magnesium nitrate; S4. Filtration of demagnesium solution After the demagnesium reaction, filter to obtain filter residue and demagnesium filtrate; S5. Concentration of demagnesium filtrate Concentrate the demagnesium filtrate to obtain concentrated slurry; S6. Cooling crystallization of calcium nitrate Perform cooling crystallization treatment on the concentrated slurry. The temperature of the cooling crystallization treatment is 0 - 5 °C, and the crystallization time is controlled at 4 - 8 h; S7. Centrifugal separation of calcium nitrate After crystallization, perform centrifugal separation on the slurry after freezing crystallization to separate out calcium nitrate tetrahydrate crystals and filtrate; S8. Ammonium decomposition treatment Perform ammonium decomposition reaction on the filter residue obtained in step S4 and excessive ammonium nitrate, absorb the ammonia gas generated by the ammonium decomposition reaction with water to obtain ammonia water; then react the ammonia water with the carbon dioxide generated in step S1 to obtain ammonium carbonate; S9. Filtration after ammonium decomposition After ammonium decomposition, perform filtration separation to obtain phosphate concentrate filter cake and ammonium decomposition filtrate; S10. Primary decalcification React the ammonium decomposition filtrate obtained in step S9 with excessive ammonium carbonate to convert the soluble calcium ions in the ammonium decomposition filtrate into insoluble calcium carbonate precipitate, while the magnesium ions remain soluble. After the reaction, filter to obtain primary filter cake and primary decalcification liquid; dry the primary filter cake to obtain calcium carbonate by - product; S11. Secondary decalcification React the primary decalcification liquid obtained in step S10 with a decalcifying agent. After the reaction, filter to obtain secondary filter cake and secondary decalcification liquid. Regenerate the obtained secondary filter cake. The regeneration treatment is to treat the secondary filter cake with sulfuric acid. The decalcifying agent is oxalic acid; S12. Carbonization Perform carbonization reaction on the secondary decalcification liquid obtained in step S11 and ammonium carbonate. After the reaction, filter and dry the filter cake to obtain magnesium carbonate by - product.

2. The production method for enriching phosphate rock and preparing calcium nitrate and magnesium carbonate by a two-step ammonium method according to claim 1, wherein In step S5, the density of the supernatant of the concentrated slurry is 1.1 - 1.5 g / cm 3 .

3. The production method for enriching phosphate rock and preparing calcium nitrate and magnesium carbonate by a two-step ammonium method according to claim 1, characterized in that, In step S8, the temperature of the ammonium decomposition reaction is 40 - 50 °C.

4. A production method for enriching phosphate rock and preparing calcium nitrate and magnesium carbonate by a two-step ammonium method according to claim 1, characterized in that, In step S10, the temperature of the reaction during primary decalcification is 30 - 40 °C.

5. The production method for enriching phosphate rock and preparing calcium nitrate and magnesium carbonate by a two-step ammonium method according to claim 1, characterized in that, In step S12, the carbonization reaction temperature is 30 - 40 °C.

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