Method for selectively chlorinating and separating calcium and magnesium from calcium-magnesium containing minerals

Abstract

This invention discloses a method for selectively separating calcium and magnesium from calcium-magnesium minerals by chlorination, belonging to the field of hydrometallurgical technology. The method includes the following steps: S1, pretreating the calcium-magnesium minerals to obtain calcium-magnesium mineral powder; S2, passing the calcium-magnesium mineral powder through chlorine gas and carrying out a selective chlorination reaction in a non-reducing environment at a temperature not lower than 550°C to obtain a chlorinated product; S3, subjecting the chlorinated product to water leaching, followed by solid-liquid separation to obtain an aqueous solution rich in calcium chloride and a magnesium-rich solid. This method, without any reducing agent, utilizes the differential reaction characteristics of chlorine gas on calcium and magnesium oxides at a specific temperature to achieve selective calcium conversion with extremely low magnesium loss. It has advantages such as short process, low energy consumption, no carbon dioxide emissions, good selectivity, and high product purity.

Description

Technical Field

[0001] This invention belongs to the field of hydrometallurgical technology, and specifically relates to a method for selectively chlorinating calcium and magnesium-containing minerals to separate calcium and magnesium. Background Technology

[0002] Dolomite (CaMg(CO3)2) is a naturally abundant calcium-magnesium complex carbonate mineral, widely used in the production of basic industrial raw materials such as metallic magnesium, magnesium oxide, and calcium chloride. Currently, the mainstream industrial methods for achieving efficient separation of calcium and magnesium from dolomite are mainly divided into wet acid leaching and thermal reduction processes.

[0003] The wet acidolysis process typically uses hydrochloric acid or sulfuric acid to directly decompose dolomite, allowing calcium and magnesium to simultaneously enter the solution, followed by complex carbonization, precipitation, and crystallization steps for separation. This process suffers from problems such as a lengthy process, high acid and alkali consumption, and difficult wastewater treatment. The thermal reduction method, represented by the Pidgeon process, uses ferrosilicon to reduce calcined dolomite under high temperature and high vacuum conditions to produce metallic magnesium. This process is extremely energy-intensive and generates large amounts of waste residue and greenhouse gas emissions, contradicting the current trend of green and low-carbon development.

[0004] In recent years, the "ammonia leaching method" has also been explored, which uses ammonium chloride solution to leach calcined dolomite in steps. However, this type of method usually requires high-temperature calcination of the dolomite beforehand, and still requires complex chemical separation steps afterward, failing to fundamentally solve the problems of long process and high energy consumption.

[0005] Therefore, there is an urgent need to develop a new method that has a short process flow, low energy consumption, no carbon emissions, and can efficiently and selectively separate calcium and magnesium from dolomite. Summary of the Invention

[0006] To address the aforementioned problems, the main objective of this invention is to provide a method for selectively chlorinating and separating calcium and magnesium from calcium- and magnesium-containing minerals. This method achieves selective conversion of calcium by utilizing the differential reaction characteristics of chlorine gas with calcium and magnesium oxides at specific temperatures without any reducing agent. The magnesium loss rate is extremely low, and the method has advantages such as short process, low energy consumption, no carbon dioxide emissions, good selectivity, and high product purity.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for selectively separating calcium and magnesium from calcium-containing minerals by chlorination, comprising the following steps: S1, Pre-treat the calcium-magnesium minerals to obtain calcium-magnesium mineral powder; S2, the calcium-magnesium mineral powder is passed through chlorine gas and selectively chlorinated in a non-reducing environment at a temperature of not less than 550°C to obtain the chlorinated product; S3, the chlorinated product is subjected to water leaching treatment, and then solid-liquid separation is performed to obtain an aqueous solution rich in calcium chloride and a magnesium-rich solid.

[0008] Furthermore, after step S1 and before step S2, a pre-calcination step is also included: calcining the calcium-magnesium mineral powder in air or an inert atmosphere at 800-1000°C for 0.5-3 hours.

[0009] Furthermore, following step S3, the following steps are also included: The calcium chloride product is obtained by evaporating, concentrating, and crystallizing an aqueous solution rich in calcium chloride. Magnesium-rich solids are washed and dried to obtain magnesium oxide products.

[0010] Furthermore, in step S2, the amount of chlorine gas introduced is 1.0-3.0 times the amount of chlorine gas required for the theoretical reaction.

[0011] Furthermore, in step S2, the selective chlorination reaction takes 20-300 minutes.

[0012] Furthermore, in step S2, the temperature of the selective chlorination reaction is 550-1000℃.

[0013] Furthermore, in step S3, the liquid-to-solid mass ratio of the water immersion treatment is 3:1-8:1.

[0014] Furthermore, the water immersion treatment time is 0.5-2 hours.

[0015] Furthermore, the particle size of the calcium-magnesium mineral powder is 100-500 mesh.

[0016] Furthermore, the calcium- and magnesium-containing minerals include one or more of dolomite and asbestos tailings.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) The selective chlorination method for separating calcium and magnesium from calcium-magnesium minerals provided by this invention is carried out without any reducing agent to ensure that magnesium is not chlorinated. Based on the thermodynamic difference in the reaction of chlorine with CaO and MgO at a temperature not lower than 550°C, selective chlorination of calcium is achieved, so that the calcium component in the calcium-magnesium minerals is converted into soluble calcium chloride, while the magnesium component remains as insoluble magnesium oxide. The entire chlorination process does not require any carbonaceous reducing agent, thus eliminating the generation of greenhouse gases and toxic gases such as CO2 and CO from the reaction principle, making it green and environmentally friendly.

[0018] (2) Based on the core steps of “selective chlorination-water leaching”, this invention greatly simplifies the complex solution treatment steps in traditional wet processes and the high-energy-consuming reduction steps in thermal processes, shortens the process, and reduces energy consumption and operating costs.

[0019] (3) The method provided by the present invention has high selectivity for calcium and magnesium separation. When the high selective chlorination conversion of calcium is achieved, the magnesium loss rate is extremely low. The calcium component separated from the calcium-magnesium minerals is used to produce calcium chloride product. No calcium component is detected in the separated magnesium-rich solid. After drying, magnesium oxide product is obtained.

[0020] Other features and effects of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 The X-ray diffraction (XRD) analysis results of the reaction products of Example 1 of the present invention are shown. Figure 2 The X-ray diffraction (XRD) analysis results of the reaction products of Comparative Example 1 according to the present invention are shown. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] To achieve the above objectives, embodiments of the present invention provide a method for selective chlorination separation of calcium and magnesium from calcium- and magnesium-containing minerals, comprising the following steps: S1, Pre-treat the calcium-magnesium minerals to obtain calcium-magnesium mineral powder; S2, the calcium-magnesium mineral powder is passed through chlorine gas and selectively chlorinated in a non-reducing environment (i.e. without a reducing agent) at a temperature not lower than 550°C to obtain the chlorinated product; S3, the chlorinated product is subjected to water leaching treatment, and then solid-liquid separation is performed to obtain an aqueous solution rich in calcium chloride and a magnesium-rich solid.

[0025] The method for selectively separating calcium and magnesium from calcium-magnesium minerals provided by this invention involves a chlorination reaction process carried out without any carbonaceous reducing agent to ensure that magnesium is not chlorinated. Based on the thermodynamic difference in the reaction of chlorine with CaO and MgO at a temperature not lower than 550°C, selective chlorination of calcium is achieved, converting the calcium component in the calcium-magnesium minerals into soluble calcium chloride, while the magnesium component remains as insoluble magnesium oxide. Specifically, the reaction principle is as follows: Within a temperature range not lower than 550℃, the Gibbs free energy change (ΔG) for the reaction CaO + Cl2 → CaCl2 + 0.5O2 is negative, indicating that the reaction can proceed spontaneously. However, the ΔG for the reaction MgO + Cl2 → MgCl2 + 0.5O2 is positive, and it cannot proceed spontaneously under standard conditions. Therefore, by precisely controlling the reaction temperature and maintaining a carbon-free atmosphere, chlorine gas can selectively react with the calcium component in calcium- and magnesium-containing minerals to generate soluble calcium chloride (CaCl2), while the magnesium component remains in the solid phase as insoluble magnesium oxide (MgO), thus achieving in-situ selective conversion of calcium and magnesium. Finally, through water leaching and solid-liquid separation, the soluble calcium chloride dissolves in the aqueous solution, while the magnesium component remains in the solid product, achieving highly selective separation of calcium and magnesium.

[0026] The separation method provided by this invention greatly simplifies the complex solution treatment steps in traditional wet processes and the energy-intensive reduction steps in thermal processes, shortening the process and reducing energy consumption and operating costs. Furthermore, the entire chlorination process requires no carbonaceous reducing agents (including but not limited to coke, coal, and CO), thus eliminating the generation of greenhouse gases and toxic gases such as CO2 and CO from the reaction principle, making it green and environmentally friendly.

[0027] In some preferred embodiments of the present invention, a pre-calcination step is included after step S1 and before step S2: the calcium-magnesium mineral powder is calcined in air or an inert atmosphere at 800-1000°C for 0.5-3 hours. This pre-calcination step pre-decomposes the calcium-magnesium mineral into a mixture of calcium oxide (CaO) and magnesium oxide (MgO), facilitating efficient and selective separation in the subsequent selective chlorination reaction. More preferably, the pre-calcination temperature is 850-950°C, and the time is 1-2 hours.

[0028] In some preferred embodiments of the present invention, after step S3, the following steps are further included: The calcium chloride-rich aqueous solution is evaporated and concentrated at 75-90℃, and then cooled and crystallized at a controlled temperature of 25-30℃ to obtain the calcium chloride product. Magnesium-rich solids are washed and dried to obtain magnesium oxide products.

[0029] In some preferred embodiments of the present invention, the selective chlorination reaction is carried out at a temperature of 550-1000°C, for example, selected from 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, and 1000°C. More preferably, the selective chlorination reaction is carried out at a temperature of 600-850°C. The duration of the selective chlorination reaction is 20-300 minutes, for example, selected from 20 minutes, 40 minutes, 60 minutes, 80 minutes, 90 minutes, 100 minutes, 120 minutes, 150 minutes, 180 minutes, 200 minutes, 220 minutes, 240 minutes, 250 minutes, 260 minutes, 280 minutes, and 300 minutes. More preferably, it is 90-120 minutes. The selective chlorination reaction can be carried out, for example, in a tubular furnace, a vertical chlorination furnace, or a rotary kiln.

[0030] In order to further improve the utilization rate of chlorine while ensuring sufficient chlorine supply, in some preferred embodiments of the present invention, the amount of chlorine introduced in step S2 is 1.0-3.0 times the amount of chlorine required for the theoretical reaction.

[0031] To further improve the separation effect of calcium and magnesium from the chloride products, in some preferred embodiments of the present invention, the liquid-to-solid mass ratio of the water immersion treatment is 3:1-8:1, for example, selected from 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, and more preferably 4:1-6:1. The water immersion treatment time is 0.5-2 hours, for example, selected from 0.5 hours, 0.6 hours, 0.8 hours, 1.0 hours, 1.2 hours, 1.5 hours, 1.8 hours, and 2.0 hours. The solid-liquid separation method is, for example, filtration, sedimentation, or centrifugation.

[0032] In some preferred embodiments of the present invention, the calcium-magnesium minerals are pretreated by crushing, grinding, etc., to form calcium-magnesium mineral powder with a particle size of 100-500 mesh. This particle size is more conducive to increasing the reaction contact area and improving the reaction rate and conversion rate.

[0033] In some preferred embodiments of the present invention, the calcium-magnesium minerals include, but are not limited to, one or more of dolomite and asbestos tailings.

[0034] The present invention will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed by the present invention.

[0035] Example 1 A method for selectively separating calcium and magnesium from calcium- and magnesium-containing minerals by chlorination includes the following steps: (1) Take 100g of natural dolomite ore, crush and grind it to a particle size of 200 mesh. Place the powder in a muffle furnace and pre-calcine it in air at 900℃ for 2 hours to obtain calcined white (CaO•MgO mixture).

[0036] (2) Place the calcined white material from step 1 in a tubular atmosphere furnace and heat it to 850°C under nitrogen protection. After the temperature stabilizes, switch to chlorine gas and introduce it at a flow rate of 1 L / min. Maintain the reaction at this temperature for 120 min. The amount of chlorine gas is 1.5 times the theoretical amount. After the reaction is complete, allow it to cool naturally to room temperature under a nitrogen atmosphere to obtain the chlorinated product.

[0037] (3) The chlorination product was added to deionized water at a liquid-to-solid mass ratio of 5:1 and stirred at room temperature for 1 hour. Then, vacuum filtration was performed to obtain a clear filtrate and a filter cake. The filter cake was washed three times with deionized water and then dried at 120°C for 4 hours to obtain a magnesium-rich solid product.

[0038] (4) Analysis and detection: The filtrate obtained in step (3) was analyzed for chemical element content, and the result showed that the calcium chlorination extraction rate was 93.1%. The magnesium-rich solid was analyzed by XRD, and the results are as follows: Figure 1 Its main crystalline phase is MgO, and no obvious CaO or CaCO3 diffraction peaks were detected.

[0039] Example 2 A method for selectively separating calcium and magnesium from calcium- and magnesium-containing minerals by chlorination is basically the same as that in Example 1, except that the pre-calcination treatment in Example 1 is not performed and the temperature and time of the selective chlorination reaction are adjusted. Specifically, the method includes the following steps: (1) Take 100g of natural dolomite ore, crush and grind it to a particle size of 200 mesh to obtain dolomite raw ore powder.

[0040] (2) Place the raw dolomite powder in a tubular atmosphere furnace and heat it to 950℃ under nitrogen protection. After the temperature stabilizes, switch to chlorine gas and introduce it at a flow rate of 1L / min. Maintain the reaction at this temperature for 210min. The amount of chlorine gas is 1.5 times the theoretical amount. After the reaction is completed, allow it to cool naturally to room temperature under a nitrogen atmosphere to obtain the chlorinated product.

[0041] (3) The chlorination product was added to deionized water at a liquid-to-solid mass ratio of 5:1 and stirred at room temperature for 1 hour. Then, vacuum filtration was performed to obtain a clear filtrate and a filter cake. The filter cake was washed three times with deionized water and then dried at 120°C for 4 hours to obtain a magnesium-rich solid product.

[0042] (4) Analysis and detection: The filtrate obtained in this embodiment was analyzed by chemical element content analysis. The calcium chlorination extraction rate was 91.5%. The magnesium-rich solid was analyzed by XRD. The main crystalline phase was MgO, and no obvious CaO or CaCO3 diffraction peaks were detected. This indicates that even without pre-calcination, good calcium and magnesium separation can be obtained by appropriately increasing the temperature and extending the reaction time, but the efficiency is slightly lower than that of the pre-calcination scheme.

[0043] Comparative Example 1 A method for selectively separating calcium and magnesium from calcium- and magnesium-containing minerals by chlorination is provided. The steps are basically the same as in Example 1, except that the chlorination reaction is carried out in a reducing atmosphere. Specifically, in step (2), anthracite (a carbonaceous reducing agent) at a mass ratio of 10% of the natural dolomite ore is introduced into the tubular atmosphere furnace to simulate a carbon-containing atmosphere. The final solid product is analyzed by XRD, and the results are as follows: Figure 2 The results showed that, at the same temperature and time, not only was calcium completely chlorinated, but magnesium was also almost completely chlorinated, and MgO was almost undetectable in the solid product.

[0044] Comparative Example 2 A method for selectively separating calcium and magnesium from calcium-containing minerals by chlorination is provided. The steps are basically the same as in Example 1, except that the chlorination reaction temperature in step (2) is adjusted to 450°C and the reaction time is adjusted to 120 min. At this chlorination reaction temperature, the calcium and magnesium components are basically not chlorinated, and the phases of the solid product show almost no calcium chloride or magnesium chloride components.

[0045] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for selectively chlorinating calcium and magnesium-containing minerals to separate calcium and magnesium, characterized in that, Includes the following steps: S1, Pre-treat the calcium-magnesium minerals to obtain calcium-magnesium mineral powder; S2, the calcium-magnesium mineral powder is passed through chlorine gas and selectively chlorinated in a non-reducing environment at a temperature of not less than 550°C to obtain the chlorinated product; S3, the chlorinated product is subjected to water leaching treatment, and then solid-liquid separation is performed to obtain an aqueous solution rich in calcium chloride and a magnesium-rich solid.

2. The method for selective chlorination separation of calcium and magnesium from calcium- and magnesium-containing minerals according to claim 1, characterized in that, After step S1 and before step S2, a pre-calcination step is also included: the calcium-magnesium mineral powder is calcined in air or an inert atmosphere at 800-1000℃ for 0.5-3 hours.

3. The method for selective chlorination separation of calcium and magnesium from calcium- and magnesium-containing minerals according to claim 1 or 2, characterized in that, Following step S3, the following steps are also included: The calcium chloride product is obtained by evaporating, concentrating, and crystallizing an aqueous solution rich in calcium chloride. Magnesium-rich solids are washed and dried to obtain magnesium oxide products.

4. The method for selective chlorination separation of calcium and magnesium from calcium- and magnesium-containing minerals according to claim 1 or 2, characterized in that, In step S2, the amount of chlorine gas introduced is 1.0-3.0 times the amount of chlorine gas required for the theoretical reaction.

5. The method for selective chlorination separation of calcium and magnesium from calcium- and magnesium-containing minerals according to claim 1 or 2, characterized in that, In step S2, the selective chlorination reaction takes 20-300 minutes.

6. The method for selective chlorination separation of calcium and magnesium from calcium- and magnesium-containing minerals according to claim 1 or 2, characterized in that, In step S2, the temperature of the selective chlorination reaction is 550-1000℃.

7. The method for selective chlorination separation of calcium and magnesium from calcium- and magnesium-containing minerals according to claim 1 or 2, characterized in that, In step S3, the liquid-to-solid mass ratio of the water immersion treatment is 3:1-8:

1.

8. The method for selective chlorination separation of calcium and magnesium from calcium- and magnesium-containing minerals according to claim 1 or 2, characterized in that, The water immersion treatment time is 0.5-2 hours.

9. The method for selective chlorination separation of calcium and magnesium from calcium- and magnesium-containing minerals according to claim 1 or 2, characterized in that, The particle size of the calcium-magnesium mineral powder is 100-500 mesh.

10. The method for selective chlorination separation of calcium and magnesium from calcium- and magnesium-containing minerals according to claim 1, characterized in that, The calcium- and magnesium-containing minerals include one or more of dolomite and asbestos tailings.

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