A method for separating calcium and magnesium from magnesium oxide

Abstract

The application provides a method for separating calcium and magnesium from magnesium oxide, and relates to the technical field of calcium-magnesium separation in oxide. The method comprises the following steps: adding calcium-containing magnesium oxide into a magnesium nitrate solution to perform a dissolution filtration reaction to obtain filtrate 1 and magnesium hydroxide precipitate 1; recycling the filtrate 1 into the previous dissolution filtration reaction to obtain filtrate 2 and magnesium hydroxide precipitate 2; calcining the magnesium hydroxide precipitate 1 and the magnesium hydroxide precipitate 2 to obtain high-purity magnesium oxide; introducing carbon dioxide into the filtrate 2, adding magnesium oxide to adjust the pH value, and performing a carbonization reaction to obtain calcium carbonate precipitate and recycled magnesium nitrate solution. The method ingeniously recycles the magnesium hydroxide, magnesium oxide and magnesium nitrate obtained in the preparation process of calcium-containing magnesium oxide, reduces the production cost, and cooperatively improves the utilization rate of magnesium and calcium in the calcium-containing magnesium oxide, so that the process flow is simple and the method is beneficial to large-scale industrial production and popularization and use.

Description

Technical Field

[0001] This invention relates to the technical field of calcium and magnesium separation from oxides, and more particularly to a method for separating calcium and magnesium from magnesium oxides. Background Technology

[0002] Calcium and magnesium share a similarity principle, and they generally coexist in nature. Common methods for separating calcium and magnesium from oxides include the hydrochloric acid-lime method.

[0003] The hydrochloric acid-lime method involves first dissolving calcium and magnesium oxides into brine, then adding lime to adjust the pH, resulting in magnesium precipitate and calcium solution, which are then separated. Most of the magnesium hydroxide products have a calcium oxide content of ≥0.1%, but the products have a high chloride ion content, causing significant pollution, high cost, and high equipment requirements, thus limiting their use in downstream industries.

[0004] For example, Chinese patent CN107032384A discloses a method for separating and recovering calcium and magnesium from calcium and magnesium minerals. The method involves first stirring the calcium and magnesium minerals into a hydrochloric acid solution to dissolve them, then filtering to obtain brine containing CaCl2 and MgCl2. Next, Ca(OH)2 is stirred into the brine, and the pH of the solution is adjusted to precipitate magnesium. This is then filtered to obtain a Mg(OH)2 filter cake and a post-precipitation liquid. The Mg(OH)2 filter cake is purified with MgCl2 solution and dried to obtain magnesium hydroxide. The post-precipitation liquid is acidified by adding concentrated hydrochloric acid or passing HCl gas to force magnesium chloride to crystallize. The crystallized product (CaCl2·6H2O) and its crystallization mother liquor are obtained by filtration. The resulting crystallization mother liquor is returned to the brine preparation process for continued use.

[0005] Obviously, the method used in the above patent is the commonly used hydrochloric acid-lime method. However, the chloride ion content is very high. In particular, the chloride ion content in the product is increased by dissolving in hydrochloric acid and acidifying with concentrated hydrochloric acid or by passing in HCl gas. Although the CaO content in the Mg(OH)2 product can be ≤0.05%, the chloride ion content has not been effectively reduced.

[0006] Chinese patent CN102417982A discloses a method for removing calcium and magnesium using an extraction method. It employs di(2-ethylhexyl)phosphoric acid for pre-extraction and main extraction to remove calcium ions, and 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester for main extraction to remove magnesium ions. This method of separating calcium and magnesium requires the participation of a large amount of organic solvents, resulting in high costs and the inability to obtain commercially viable magnesium oxide and calcium carbonate products. Therefore, it is not suitable for industrial production and promotion.

[0007] Chinese patent CN111215430A discloses a method for separating calcium and magnesium from alkaline residue using a phase transfer method. The method uses alkaline residue as raw material, removes soluble salts by washing with water, and then converts the carbonate and hydroxide phases into oxide phases through heat treatment. Then, the calcium and magnesium are separated by a phase transfer method, in which calcium ions enter the liquid phase and magnesium elements enter the solid phase. Finally, calcium carbonate products are prepared from the calcium-containing solution after phase transfer, while the magnesium elements in the solid phase are enriched and can be used to produce magnesium products.

[0008] Obviously, the calcium carbonate and magnesium products prepared by the methods in the above patents contain complex metal ions from the alkali residue, resulting in low product purity. Furthermore, the cost of water washing is high, the heat treatment consumes a lot of heat energy, and the citric acid used for phase transfer is not suitable for industrial production. Summary of the Invention

[0009] The technical problem to be solved by the present invention is that the calcium carbonate and magnesium oxide products prepared by the current methods of separating calcium and magnesium from magnesium oxides have low purity, high cost, and are not suitable for industrial production and promotion; in particular, the products prepared by the hydrochloric acid-lime method have high chloride ion content, serious pollution, and high material requirements for the preparation equipment, while the method of separating calcium and magnesium by extracting with organic solvents has both high pollution and consumption.

[0010] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0011] A method for separating calcium and magnesium from magnesium oxides, wherein the specific steps of the method are as follows:

[0012] S1. Add calcium-containing magnesium oxide to magnesium nitrate solution for dissolution and filtration to obtain filtrate 1 and magnesium hydroxide precipitate 1;

[0013] S2. Filter 1 from S1 is recycled for the previous dissolution and filtration reaction to obtain filtrate 2 and magnesium hydroxide precipitate 2.

[0014] S3. Calcine the magnesium hydroxide precipitate 1 from S1 and the magnesium hydroxide precipitate 2 from S2 to obtain high-purity magnesium oxide.

[0015] S4. Carbon dioxide is introduced into the filtrate 2 of S2, and magnesium oxide is added to adjust the pH and carry out a carbonation reaction to obtain calcium carbonate precipitate and magnesium nitrate solution for recycling.

[0016] Preferably, the main chemical components of calcium-containing magnesium oxide in S1 include: Ca 2.5-6 wt.%, Mg 52-59 wt.%.

[0017] Preferably, the concentration of magnesium nitrate solution in S1 is 50-300 g / L.

[0018] Preferably, calcium-containing magnesium oxide in S1 is added to magnesium nitrate solution for dissolution and filtration reaction, and mixed at a liquid-solid mass ratio of 2-6:1. The temperature of the dissolution and filtration reaction is 25-90℃, and the time is 1-5h.

[0019] Preferably, the calcium content of filtrate 1 in S1 is 2-30 g / L and the magnesium content is 5-50 g / L.

[0020] Preferably, the dissolution and filtration reaction in S2 requires the addition of a solution containing calcium-containing magnesium oxide and 50-300 g / L magnesium nitrate.

[0021] Preferably, in step S2, the dissolution temperature is 25-90℃ and the time is 1-5 hours. This step dissolves the calcium in calcium-containing magnesium oxide, yielding filtrate 2 and magnesium hydroxide precipitate, achieving the first separation of calcium and magnesium using the common ion effect.

[0022] Preferably, the calcium content of filtrate 2 in S2 is 30-50 g / L, and the magnesium content is 5-50 g / L.

[0023] Preferably, the magnesium hydroxide in S3 is calcined at 400-700℃, the calcium content of the high-purity magnesium oxide is 0.07-0.9%, the magnesium content is 58.8-59.9%, and the magnesium recovery rate is 95-98%.

[0024] Preferably, the carbon dioxide flow rate in step S4 is 0.01-0.1 L / min, and the flow time is 1-4 h; magnesium oxide is added to adjust the pH to 7-10, the molar ratio of magnesium oxide to calcium is 1:1-3, and the carbonation reaction temperature is 40-90℃. This step carbonizes the calcium nitrate solution, yielding a magnesium nitrate solution and calcium carbonate precipitate. The secondary separation of calcium and magnesium is achieved using the principles of metathesis reaction and solubility, and the magnesium nitrate solution is recycled.

[0025] Preferably, the calcium content of the calcium carbonate precipitate in S4 is 39-39.6%, the magnesium content is 0.28-0.71%, and the calcium recovery rate is 98-99.5%.

[0026] The above technical solution has at least the following advantages compared with the existing technology:

[0027] The present invention proposes a method for separating calcium and magnesium from magnesium oxides, which can solve the problems of low purity, high cost, and unsuitability for industrial production and promotion of calcium carbonate and magnesium oxide products prepared in the prior art, so that the prepared calcium and magnesium products can be used as raw materials for commercial and industrial production.

[0028] The method of the present invention uses calcium-containing magnesium oxide as raw material, and uses the common ion effect to achieve the first separation of calcium and magnesium to obtain filtrate 2 and magnesium hydroxide; and uses the double decomposition reaction and solubility principle to achieve the second separation of calcium and magnesium to obtain calcium carbonate and magnesium nitrate solution.

[0029] The materials used in this invention are all common industrial products that are easy to purchase and inexpensive; the entire process is simple and easy to operate, low in cost, with a wide range of raw material sources, easy to scale up, and easy to industrialize.

[0030] The high-purity magnesium oxide prepared by this invention has a calcium content of 0.07-0.9%, a magnesium content of 58.8-59.9%, and a magnesium recovery rate of 95-98%; the calcium carbonate precipitate has a calcium content of 39-39.6%, a magnesium content of 0.28-0.71%, and a calcium recovery rate of 98-99.5%.

[0031] In summary, compared with other traditional methods, the method of the present invention ingeniously recycles the magnesium hydroxide, magnesium oxide and magnesium nitrate obtained in the preparation of calcium-containing magnesium oxide, reduces production costs, and synergistically improves the utilization rate of magnesium and calcium in calcium-containing magnesium oxide. The process is simple and conducive to large-scale industrial production and widespread use. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a process flow diagram of a method for separating calcium and magnesium from magnesium oxide according to the present invention. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0035] Example 1

[0036] A method for separating calcium magnesium from magnesium oxide, wherein the main chemical composition of calcium-containing magnesium oxide includes: Ca 4.11 wt.%, Mg 56.45 wt.%; such as Figure 1As shown, the specific steps of the method for separating calcium and magnesium from magnesium oxides are as follows:

[0037] S1. Add calcium-containing magnesium oxide to a 100 g / L magnesium nitrate solution at a liquid-to-solid mass ratio of 4:1 and stir to dissolve. Perform a dissolution and filtration reaction at 50°C for 1 hour to obtain filtrate 1 and magnesium hydroxide precipitate 1. The calcium content of filtrate 1 is 6.5 g / L and the magnesium content is 9.6 g / L.

[0038] S2. Filter 1 from S1 is recycled for the dissolution and filtration reaction of S1. A solution containing calcium magnesium oxide and 100 g / L magnesium nitrate needs to be added. The dissolution temperature is 50℃ and the time is 1 h. This cycle is repeated to obtain filtrate 2 and magnesium hydroxide precipitate 2. The calcium content of filtrate 2 is 35.4 g / L and the magnesium content is 5.2 g / L.

[0039] S3. Magnesium hydroxide precipitate 1 from S1 and magnesium hydroxide precipitate 2 from S2 are calcined at 550℃ to obtain high-purity magnesium oxide; wherein: the calcium content of high-purity magnesium oxide is 0.57%, the magnesium content is 59.51%, and the magnesium recovery rate is 96%.

[0040] S4. Carbon dioxide is introduced into filtrate 2 of S2 at a flow rate of 0.03 L / min for 1 h. Magnesium oxide is added to adjust the pH to 8 and to carry out a carbonation reaction. The molar ratio of magnesium oxide to calcium is 1:1, and the carbonation reaction temperature is 50 °C. Calcium carbonate precipitate and recycled magnesium nitrate solution are obtained. The calcium content of the calcium carbonate precipitate is 39.5%, the magnesium content is 0.36%, and the calcium recovery rate is 99%.

[0041] Example 2

[0042] A method for separating calcium magnesium from magnesium oxide, wherein the main chemical composition of calcium-containing magnesium oxide includes: Ca 4.11 wt.%, Mg 56.45 wt.%; such as Figure 1 As shown, the specific steps of the method for separating calcium and magnesium from magnesium oxides are as follows:

[0043] S1. Add calcium-containing magnesium oxide to a 150 g / L magnesium nitrate solution at a liquid-to-solid mass ratio of 5:1 and stir to dissolve. Then carry out the dissolution and filtration reaction at 50℃ for 2 hours to obtain filtrate 1 and magnesium hydroxide precipitate 1. The calcium content of filtrate 1 is 7.8 g / L and the magnesium content is 16.5 g / L.

[0044] S2. Filter 1 from S1 is recycled for the dissolution and filtration reaction of S1. A solution containing calcium magnesium oxide and 150 g / L magnesium nitrate needs to be added. The dissolution temperature is 50℃ and the time is 2 h. This cycle is repeated to obtain filtrate 2 and magnesium hydroxide precipitate 2. The calcium content of filtrate 2 is 40 g / L and the magnesium content is 8.5 g / L.

[0045] S3. Magnesium hydroxide precipitate 1 from S1 and magnesium hydroxide precipitate 2 from S2 are calcined at 550℃ to obtain high-purity magnesium oxide; wherein: the calcium content of the high-purity magnesium oxide is 0.22%, the magnesium content is 59.8%, and the magnesium recovery rate is 96.5%.

[0046] S4. Carbon dioxide is introduced into filtrate 2 from S2 at a flow rate of 0.02 L / min for 1 hour. Magnesium oxide is added to adjust the pH to 8 and to initiate a carbonation reaction. The molar ratio of magnesium oxide to calcium is 1:1, and the carbonation reaction temperature is 50℃. Calcium carbonate precipitate and recycled magnesium nitrate solution are obtained. The calcium content of the calcium carbonate precipitate is 39.54%, the magnesium content is 0.32%, and the calcium recovery rate is 98.5%.

[0047] Example 3

[0048] A method for separating calcium magnesium from magnesium oxide, wherein the main chemical composition of calcium-containing magnesium oxide includes: Ca 4.11 wt.%, Mg 56.45 wt.%; such as Figure 1 As shown, the specific steps of the method for separating calcium and magnesium from magnesium oxides are as follows:

[0049] S1. Add calcium-containing magnesium oxide to a 100 g / L magnesium nitrate solution at a liquid-to-solid mass ratio of 4:1 and stir to dissolve. Perform a dissolution and filtration reaction at 60℃ for 1 hour to obtain filtrate 1 and magnesium hydroxide precipitate 1. The calcium content of filtrate 1 is 8.9 g / L and the magnesium content is 7.2 g / L.

[0050] S2. Filter 1 from S1 is recycled for the dissolution and filtration reaction of S1. A solution containing calcium magnesium oxide and 100 g / L magnesium nitrate needs to be added. The dissolution temperature is 60℃ and the time is 1 h. This cycle is repeated to obtain filtrate 2 and magnesium hydroxide precipitate 2. Among them, the calcium content of filtrate 2 is 38.6 g / L and the magnesium content is 5.1 g / L.

[0051] S3. Magnesium hydroxide precipitate 1 from S1 and magnesium hydroxide precipitate 2 from S2 are calcined at a high temperature of 550℃ to obtain high-purity magnesium oxide; wherein: the calcium content of high-purity magnesium oxide is 0.32%, the magnesium content is 59.72%, and the magnesium recovery rate is 97%.

[0052] S4. Carbon dioxide is introduced into filtrate 2 from S2 at a flow rate of 0.02 L / min for 1 hour. Magnesium oxide is added to adjust the pH to 8 and to initiate a carbonation reaction. The molar ratio of magnesium oxide to calcium is 1:1, and the carbonation reaction temperature is 50℃. Calcium carbonate precipitate and recycled magnesium nitrate solution are obtained. The calcium content of the calcium carbonate precipitate is 39.53%, the magnesium content is 0.33%, and the calcium recovery rate is 98.4%.

[0053] Example 4

[0054] A method for separating calcium magnesium from magnesium oxide, wherein the main chemical composition of calcium-containing magnesium oxide includes: Ca 4.11 wt.%, Mg 56.45 wt.%; such as Figure 1 As shown, the specific steps of the method for separating calcium and magnesium from magnesium oxides are as follows:

[0055] S1. Add calcium-containing magnesium oxide to a 100 g / L magnesium nitrate solution at a liquid-to-solid mass ratio of 4:1 and stir to dissolve. Then carry out the dissolution and filtration reaction at a temperature of 70℃ for 1 hour to obtain filtrate 1 and magnesium hydroxide precipitate 1. The calcium content of filtrate 1 is 9.2 g / L and the magnesium content is 6.9 g / L.

[0056] S2. Filter 1 from S1 is recycled for the dissolution and filtration reaction of S1. A solution containing calcium magnesium oxide and 100 g / L magnesium nitrate needs to be added. The dissolution temperature is 70℃ and the time is 1 h. This cycle is repeated to obtain filtrate 2 and magnesium hydroxide precipitate 2. The calcium content of filtrate 2 is 39.8 g / L and the magnesium content is 5.2 g / L.

[0057] S3. Magnesium hydroxide precipitate 1 from S1 and magnesium hydroxide precipitate 2 from S2 are calcined at 550℃ to obtain high-purity magnesium oxide; wherein: the calcium content of high-purity magnesium oxide is 0.23%, the magnesium content is 59.8%, and the magnesium recovery rate is 97.5%.

[0058] S4. Carbon dioxide is introduced into filtrate 2 of S2 at a flow rate of 0.02 L / min for 1 h. Magnesium oxide is added to adjust the pH to 9 and to carry out a carbonation reaction. The molar ratio of magnesium oxide to calcium is 1:1, and the carbonation reaction temperature is 50℃. Calcium carbonate precipitate and recycled magnesium nitrate solution are obtained. The calcium content of the calcium carbonate precipitate is 39.3%, the magnesium content is 0.49%, and the calcium recovery rate is 99.2%.

[0059] Example 5

[0060] A method for separating calcium magnesium from magnesium oxide, wherein the main chemical composition of calcium-containing magnesium oxide includes: Ca 4.11 wt.%, Mg 56.45 wt.%; such as Figure 1As shown, the specific steps of the method for separating calcium and magnesium from magnesium oxides are as follows:

[0061] S1. Add calcium-containing magnesium oxide to a 100 g / L magnesium nitrate solution at a liquid-to-solid mass ratio of 4:1 and stir to dissolve. Perform a dissolution and filtration reaction at 70°C for 2 hours to obtain filtrate 1 and magnesium hydroxide precipitate 1. The calcium content of filtrate 1 is 9.5 g / L and the magnesium content is 6.7 g / L.

[0062] S2. Filter 1 from S1 is recycled for the dissolution and filtration reaction of S1. A solution containing calcium magnesium oxide and 100 g / L magnesium nitrate needs to be added. The dissolution temperature is 70℃ and the time is 2 h. This cycle is repeated to obtain filtrate 2 and magnesium hydroxide precipitate 2. The calcium content of filtrate 2 is 41.2 g / L and the magnesium content is 5.1 g / L.

[0063] S3. Magnesium hydroxide precipitate 1 from S1 and magnesium hydroxide precipitate 2 from S2 are calcined at 550℃ to obtain high-purity magnesium oxide; wherein: the calcium content of high-purity magnesium oxide is 0.17%, the magnesium content is 59.85%, and the magnesium recovery rate is 97.6%.

[0064] S4. Carbon dioxide is introduced into filtrate 2 of S2 at a flow rate of 0.02 L / min for 2 hours. Magnesium oxide is added to adjust the pH to 8 and to carry out a carbonation reaction. The molar ratio of magnesium oxide to calcium is 1:1, and the carbonation reaction temperature is 50℃. Calcium carbonate precipitate and recycled magnesium nitrate solution are obtained. The calcium content of the calcium carbonate precipitate is 39.55%, the magnesium content is 0.32%, and the calcium recovery rate is 99%.

[0065] Example 6

[0066] A method for separating calcium magnesium from magnesium oxide, wherein the main chemical composition of calcium-containing magnesium oxide includes: Ca 4.11 wt.%, Mg 56.45 wt.%; such as Figure 1 As shown, the specific steps of the method for separating calcium and magnesium from magnesium oxides are as follows:

[0067] S1. Add calcium-containing magnesium oxide to a 150 g / L magnesium nitrate solution at a liquid-to-solid mass ratio of 5:1 and stir to dissolve. Perform a dissolution and filtration reaction at 70°C for 2 hours to obtain filtrate 1 and magnesium hydroxide precipitate 1. The calcium content of filtrate 1 is 8.1 g / L and the magnesium content is 16.2 g / L.

[0068] S2. Filter 1 from S1 is recycled for the dissolution and filtration reaction of S1. A solution containing calcium magnesium oxide and 150 g / L magnesium nitrate needs to be added. The dissolution temperature is 70℃ and the time is 2 h. This cycle is repeated to obtain filtrate 2 and magnesium hydroxide precipitate 2. The calcium content of filtrate 2 is 47.5 g / L and the magnesium content is 5.1 g / L.

[0069] S3. Magnesium hydroxide precipitate 1 from S1 and magnesium hydroxide precipitate 2 from S2 are calcined at 550℃ to obtain high-purity magnesium oxide; wherein: the calcium content of high-purity magnesium oxide is 0.12%, the magnesium content is 59.89%, and the magnesium recovery rate is 97.8%.

[0070] S4. Carbon dioxide is introduced into filtrate 2 from S2 at a flow rate of 0.02 L / min for 3 hours. Magnesium oxide is added to adjust the pH to 8 and to initiate a carbonation reaction. The molar ratio of magnesium oxide to calcium is 1:1, and the carbonation reaction temperature is 50℃. Calcium carbonate precipitate and recycled magnesium nitrate solution are obtained. The calcium content of the calcium carbonate precipitate is 39.58%, the magnesium content is 0.3%, and the calcium recovery rate is 99.3%.

[0071] Comparative Example 1

[0072] A method for separating calcium magnesium from magnesium oxide, wherein the main chemical composition of calcium-containing magnesium oxide includes: Ca 4.11 wt.%, Mg 56.45 wt.%; such as Figure 1 As shown, the specific steps of the method for separating calcium and magnesium from magnesium oxides are as follows:

[0073] S1. Add calcium-containing magnesium oxide to a 100 g / L magnesium nitrate solution at a liquid-to-solid mass ratio of 1:1 and stir to dissolve. Perform a dissolution and filtration reaction at 50°C for 1 hour to obtain filtrate 1 and magnesium hydroxide precipitate 1. The calcium content of filtrate 1 is 3.6 g / L and the magnesium content is 12.6 g / L.

[0074] S2. Filter 1 from S1 is recycled for the dissolution and filtration reaction of S1. A solution containing calcium magnesium oxide and 100 g / L magnesium nitrate needs to be added. The dissolution temperature is 50℃ and the time is 1 hour. This cycle is repeated to obtain filtrate 2 and magnesium hydroxide precipitate 2. The calcium content of filtrate 2 is 29.5 g / L and the magnesium content is 6.8 g / L.

[0075] S3. Magnesium hydroxide precipitate 1 from S1 and magnesium hydroxide precipitate 2 from S2 are calcined at a high temperature of 550℃ to obtain high-purity magnesium oxide; wherein: the calcium content of high-purity magnesium oxide is 2.6%, the magnesium content is 57.81%, and the magnesium recovery rate is 93%.

[0076] S4. Carbon dioxide is introduced into filtrate 2 of S2 at a flow rate of 0.03 L / min for 1 h. Magnesium oxide is added to adjust the pH to 8 and to carry out a carbonation reaction. The molar ratio of magnesium oxide to calcium is 1:1, and the carbonation reaction temperature is 50 °C. Calcium carbonate precipitate and recycled magnesium nitrate solution are obtained. The calcium content of the calcium carbonate precipitate is 39.2%, the magnesium content is 0.57%, and the calcium recovery rate is 94%.

[0077] Comparative Example 2

[0078] A method for separating calcium magnesium from magnesium oxide, wherein the main chemical composition of calcium-containing magnesium oxide includes: Ca 4.11 wt.%, Mg 56.45 wt.%; such as Figure 1 As shown, the specific steps of the method for separating calcium and magnesium from magnesium oxides are as follows:

[0079] S1. Add calcium-containing magnesium oxide to a 100 g / L magnesium nitrate solution at a liquid-to-solid mass ratio of 7:1 and stir to dissolve. Perform a dissolution and filtration reaction at 50°C for 1 hour to obtain filtrate 1 and magnesium hydroxide precipitate 1. The calcium content of filtrate 1 is 3.2 g / L and the magnesium content is 12.9 g / L.

[0080] S2. Filter 1 from S1 is recycled for the dissolution and filtration reaction of S1. Calcium-containing magnesium oxide and 100 g / L magnesium nitrate solution need to be added. The dissolution temperature is 50℃ and the time is 1 hour. This cycle is repeated to obtain filtrate 2 and magnesium hydroxide precipitate 2. The calcium content of filtrate 2 is 30 g / L, and the magnesium content is 14.2 g / L.

[0081] S3. Magnesium hydroxide precipitate 1 from S1 and magnesium hydroxide precipitate 2 from S2 are calcined at a high temperature of 550℃ to obtain high-purity magnesium oxide; wherein: the calcium content of high-purity magnesium oxide is 0.47%, the magnesium content is 59.6%, and the magnesium recovery rate is 90%.

[0082] S4. Carbon dioxide is introduced into filtrate 2 of S2 at a flow rate of 0.03 L / min for 1 h. Magnesium oxide is added to adjust the pH to 8 and to carry out a carbonation reaction. The molar ratio of magnesium oxide to calcium is 1:1, and the carbonation reaction temperature is 50℃. Calcium carbonate precipitate and recycled magnesium nitrate solution are obtained. The calcium content of the calcium carbonate precipitate is 38.18%, the magnesium content is 1.3%, and the calcium recovery rate is 90%.

[0083] The present invention proposes a method for separating calcium and magnesium from magnesium oxides, which can solve the problems of low purity, high cost, and unsuitability for industrial production and promotion of calcium carbonate and magnesium oxide products prepared in the prior art, so that the prepared calcium and magnesium products can be used as raw materials for commercial and industrial production.

[0084] The method of the present invention uses calcium-containing magnesium oxide as raw material, and uses the common ion effect to achieve the first separation of calcium and magnesium to obtain filtrate 2 and magnesium hydroxide; and uses the double decomposition reaction and solubility principle to achieve the second separation of calcium and magnesium to obtain calcium carbonate and magnesium nitrate solution.

[0085] The materials used in this invention are all common industrial products that are easy to purchase and inexpensive; the entire process is simple and easy to operate, low in cost, with a wide range of raw material sources, easy to scale up, and easy to industrialize.

[0086] The high-purity magnesium oxide prepared by this invention has a calcium content of 0.07-0.9%, a magnesium content of 58.8-59.9%, and a magnesium recovery rate of 95-98%; the calcium carbonate precipitate has a calcium content of 39-39.6%, a magnesium content of 0.28-0.71%, and a calcium recovery rate of 98-99.5%.

[0087] In summary, compared with other traditional methods, the method of the present invention ingeniously recycles the magnesium hydroxide, magnesium oxide and magnesium nitrate obtained in the preparation of calcium-containing magnesium oxide, reduces production costs, and synergistically improves the utilization rate of magnesium and calcium in calcium-containing magnesium oxide. The process is simple and conducive to large-scale industrial production and widespread use.

[0088] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for separating calcium and magnesium from magnesium oxides, characterized in that, The specific steps of the method for separating calcium and magnesium from magnesium oxides are as follows: S1. Calcium-containing magnesium oxide is dissolved and filtered in magnesium nitrate solution to obtain filtrate 1 and magnesium hydroxide precipitate 1. The main chemical components of the calcium-containing magnesium oxide include: Ca 2.5-6 wt.%, Mg 52-59 wt.%; the concentration of magnesium nitrate solution is 50-300 g / L; the calcium content of filtrate 1 is 2-30 g / L, and the magnesium content is 5-50 g / L. In S1, the calcium-containing magnesium oxide is dissolved and filtered in magnesium nitrate solution at a liquid-to-solid mass ratio of 2-6:

1. The temperature of the dissolution and filtration reaction is 25-90℃, and the time is 1-5 h. S2. Filtrate 1 from S1 is recycled for the dissolution and filtration reaction in S1 to obtain filtrate 2 and magnesium hydroxide precipitate 2. The calcium content of filtrate 2 is 30-50 g / L, and the magnesium content is 5-50 g / L. The dissolution and filtration reaction in S2 requires the addition of the calcium-containing magnesium oxide and magnesium nitrate solution. S3. Calcine the magnesium hydroxide precipitate 1 from S1 and the magnesium hydroxide precipitate 2 from S2 to obtain high-purity magnesium oxide; the calcination temperature of the magnesium hydroxide precipitate is 400-700℃, the calcium content of the high-purity magnesium oxide is 0.07-0.9%, and the magnesium content is 58.8-59.9%; the magnesium recovery rate is 95-98%. S4. Carbon dioxide is introduced into the filtrate 2 of S2, and magnesium oxide is added to adjust the pH to 8-9 and carry out a carbonation reaction to obtain calcium carbonate precipitate and recycled magnesium nitrate solution. The calcium content of the calcium carbonate precipitate is 39-39.6%, the magnesium content is 0.28-0.71%, and the calcium recovery rate is 98-99.5%. The flow rate of carbon dioxide in S4 is 0.01-0.1 L / min, and the introduction time is 1-4 h. The molar ratio of magnesium oxide to calcium is 1:1-3, and the temperature of the carbonation reaction is 40-90℃.

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