Process for purifying low-grade fluorite and co-producing calcium hydroxide product

Abstract

The invention relates to the technical field of fluorite beneficiation, in particular to a process for purifying low-grade fluorite and co-producing a calcium hydroxide product, which aims at solving the problems that calcium carbonate in high-calcium fluorite is similar to the fluorite in surface property and high in separation difficulty, and the calcium carbonate is decomposed into calcium oxide but the fluorite is not decomposed through temperature-controlled calcination; and the fluorite and the calcium hydroxide are efficiently separated and purified through the steps of digestion, screening, flotation and the like. The method specifically comprises the following steps: crushing low-grade high-calcium fluorite raw ore, and calcining at 800-1500 DEG C to decompose calcium carbonate into calcium oxide; adding water into the calcined material for digestion to obtain mixed slurry; screening to obtain oversize rough concentrate mainly containing fluorite, grinding and floating to obtain high-grade fluorite concentrate, and returning flotation tailings to the digestion process; and precipitating, dehydrating and drying the undersize lime slurry to obtain a high-quality calcium hydroxide product. According to the process, a closed-loop process of fluorite purification and calcium hydroxide co-production is realized, and the problems of difficulty in separation of high-calcium fluorite and resource utilization of tailings are solved.

Description

Technical Field

[0001] This invention relates to the field of fluorite beneficiation technology, specifically a process for purifying low-grade fluorite and co-producing calcium hydroxide. Background Technology

[0002] Fluorite, one of China's four major non-metallic strategic minerals, is a core raw material in the fields of metallurgy, semiconductors, fluorochemicals, and special materials. Its efficient utilization is directly related to the safe and sustainable development of multiple strategic industries. With the development of fluorite resources, high-grade fluorite resources are becoming increasingly scarce, while low-grade, high-calcium fluorite resources are abundant. However, because fluorite is closely associated with high-calcium gangue such as calcite, its separation difficulty far exceeds that of ordinary fluorite, making it difficult to utilize effectively. This has become a long-standing bottleneck problem that the industry urgently needs to overcome.

[0003] The main gangue minerals in high-calcium fluorite, calcium carbonate and fluorite, have similar properties, making them difficult to separate using traditional flotation methods. Existing flotation processes consume large amounts of reagents, are costly, and have low separation efficiency. Furthermore, the large amount of tailings generated during the separation of high-calcium fluorite ore cannot be effectively utilized, resulting in land dumping, environmental pollution, and resource waste. Currently, there is no mature process that can efficiently separate fluorite and calcium carbonate while also enabling high-value utilization of the tailings. Therefore, developing a process that can purify fluorite and co-produce high-value-added chemical products has significant technological and market value. Summary of the Invention

[0004] The purpose of this invention is to provide a process for purifying low-grade fluorite and producing calcium hydroxide, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A process for purifying low-grade fluorite and co-producing calcium hydroxide includes the following steps:

[0007] S1. Crush the low-grade, high-calcium fluorite ore to a suitable particle size;

[0008] S2. The crushed ore is calcined under controlled temperature, with the calcination temperature controlled at 800℃-1500℃ and the calcination time at 3 hours, so that the calcium carbonate in the ore decomposes into calcium oxide, while the fluorite does not decompose.

[0009] S3. The calcined material is digested by adding water to convert calcium oxide into calcium hydroxide, resulting in a mixed slurry.

[0010] S4. Screen the digested slurry to obtain the material on the sieve and the lime slurry under the sieve;

[0011] S5. The material over the screen is ground and then enters the flotation process to obtain fluorite concentrate. The flotation tailings are returned to the digestion process in step S3.

[0012] S6. After the lime slurry under sieve is settled, centrifuged to dehydrate, and dried, a high-quality calcium hydroxide product is obtained.

[0013] As a further aspect of the present invention: the calcination temperature in step S2 is 850℃-1000℃.

[0014] As a further aspect of the present invention: the screening in step S4 is a two-stage screening. The first stage screening yields fluorite rough concentrate, and the second stage screening finely screens the lime slurry. The material on the screen is combined with the material on the first stage screen and enters the grinding process.

[0015] As a further aspect of the present invention: in step S3, the digestion temperature is 80°C, the liquid-to-solid ratio is 3:1, and the digestion time is 45 minutes.

[0016] As a further aspect of the present invention: the particle size of the material after grinding in step S5 is less than 100 mesh.

[0017] As a further aspect of the present invention: the fluorite concentrate obtained in step S5 can reach a grade of over 90%.

[0018] As a further aspect of the present invention: the calcination equipment is a rotary kiln, a vertical kiln, or a fluidized bed calciner; the digestion equipment is a trough reactor with stirring; and the flotation equipment is a mechanically stirred flotation machine or a flotation column.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. Efficient separation of fluorite and calcium carbonate: Calcination converts calcium carbonate into easily hydrated calcium oxide, while the physical properties of fluorite remain unchanged, thus solving the separation problem caused by similar surface properties at its root.

[0021] 2. Full utilization of resources: High grade of fluorite concentrate (CaF2≥90%), high purity of calcium hydroxide product (Ca(OH)2≥95%), realizing simultaneous recovery of calcium and fluorine resources;

[0022] 3. Closed-loop environmental protection process: Flotation tailings are returned to the digestion process, there is no solid waste discharge, and wastewater is recycled, which meets the requirements of green mine;

[0023] 4. High adaptability: Suitable for low-grade high-calcium fluorite ores with fluorite content of 15%-30% and calcium carbonate ≥50%;

[0024] 5. Significant economic benefits: Co-producing calcium hydroxide increases overall revenue, reduces fluorite purification costs, and enhances resource competitiveness. Attached Figure Description

[0025] Figure 1 Process diagram for purifying low-grade high-calcium fluorite and producing calcium hydroxide. Detailed Implementation

[0026] The technical solution of this application will be further described in detail below with reference to specific embodiments.

[0027] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0028] Please see Figure 1 In one embodiment of the present invention, a process for purifying low-grade fluorite and co-producing calcium hydroxide includes the following steps:

[0029] S1. Ore crushing: Crush the raw ore to a particle size of ≤10mm to facilitate uniform subsequent calcination reaction.

[0030] S2. Temperature-controlled calcination: The crushed ore is fed into the calcination equipment and calcined at 800℃-1500℃ (preferably 850℃-1000℃) for 2-4 hours. Under these conditions, calcium carbonate decomposes into calcium oxide and carbon dioxide, while fluorite remains structurally stable and does not decompose. At the same time, the ore undergoes dissociation due to thermal stress.

[0031] S3. Digestion reaction: After calcination, the material enters the digestion reactor and water is added at a liquid-solid ratio of (2-5):1. The mixture is stirred and digested at 60℃-90℃ for 30-60 minutes to fully hydrate calcium oxide into calcium hydroxide and form a mixed slurry.

[0032] S4. Multi-stage screening: After digestion, the slurry is first screened (20-50 mesh) to separate the coarse concentrate, which is mainly composed of fluorite; the slurry under screened is then screened (150-300 mesh) to recover the fine fluorite particles and return them for merging, ensuring the fluorite recovery rate.

[0033] S5. Fluorite Flotation: The combined fluorite rough concentrate is ground to ≤100 mesh and then enters the flotation system. Sodium oleate collectors are used for flotation under pH 8-10 conditions to obtain high-grade fluorite concentrate. The flotation tailings are rich in incompletely converted calcium components and are returned to the digestion process for further reaction.

[0034] S6. Preparation of Calcium Hydroxide: The lime slurry passing through the second-stage sieve is precipitated, centrifuged, dehydrated, and dried (100℃-150℃) to obtain high-purity calcium hydroxide powder. Further classification or modification can be performed as needed.

[0035] Example

[0036] A low-grade, high-calcium fluorite ore was taken, with a fluorite content of approximately 20% and a calcium carbonate content greater than 50%. The ore was crushed to -10mm and calcined at 1000℃ for 3 hours to completely decompose the calcium carbonate into calcium oxide. The calcined material was then fed into a digestion reactor, where water was added at a liquid-to-solid ratio of 3:1 and stirred to obtain a mixed slurry.

[0037] The slurry is first screened through a 20-mesh sieve for primary screening, with the oversize material mainly being fluorite rough concentrate. The undersize slurry is then screened through a 200-mesh sieve for secondary screening, with the fine fluorite particles being returned and combined with the rough concentrate. The combined rough concentrate is then ground to -100 mesh in a ball mill, followed by flotation to obtain fluorite concentrate with a grade of ≥90%. The flotation tailings are returned to the digestion process.

[0038] The lime slurry under the second-stage screening is allowed to settle, the supernatant is reused, and the precipitate is centrifuged and dehydrated, then dried at 120℃ to obtain calcium hydroxide powder product with a purity ≥95%.

[0039] This process enables the simultaneous and efficient production of fluorite concentrate and calcium hydroxide products, with a fluorite recovery rate of over 85% and a calcium hydroxide yield of over 90%, significantly improving the overall resource utilization rate.

[0040] This process for purifying low-grade fluorite and producing calcium hydroxide achieves efficient separation of fluorite and calcium carbonate through a combination of calcination-digestion-screening-flotation; it transforms traditional tailings into high-purity calcium hydroxide, realizing closed-loop utilization of resources throughout the entire process; the process is simple, controllable, and environmentally friendly, making it suitable for industrial application; and it provides a feasible technical path for the high-value utilization of low-grade, high-calcium fluorite resources.

[0041] The above are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these should also be considered within the scope of protection of the present invention. These will not affect the effectiveness of the implementation of the present invention or the practicality of the patent.

Claims

1. A process for purifying low-grade fluorite and co-producing calcium hydroxide, characterized in that, Includes the following steps: S1. Crush the low-grade, high-calcium fluorite ore to a suitable particle size; S2. The crushed ore is calcined under controlled temperature, with the calcination temperature controlled at 800℃-1500℃ and the calcination time at 3 hours, so that the calcium carbonate in the ore decomposes into calcium oxide, while the fluorite does not decompose. S3. The calcined material is digested by adding water to convert calcium oxide into calcium hydroxide, resulting in a mixed slurry. S4. Screen the digested slurry to obtain the material on the sieve and the lime slurry under the sieve; S5. The material over the screen is ground and then enters the flotation process to obtain fluorite concentrate. The flotation tailings are returned to the digestion process in step S3. S6. The lime slurry that passes through the sieve is settled, centrifuged to dehydrate, and dried to obtain a high-quality calcium hydroxide product.

2. The process for purifying low-grade fluorite and co-producing calcium hydroxide according to claim 1, characterized in that, The calcination temperature in step S2 is 850℃-1000℃.

3. The process for purifying low-grade fluorite and co-producing calcium hydroxide according to claim 1, characterized in that, The screening in step S4 is a two-stage screening process. The first stage screening yields fluorite rough concentrate, and the second stage screening finely screens the lime slurry. The material on the first stage screening is combined with the material on the first stage screening and enters the grinding process.

4. The process for purifying low-grade fluorite and co-producing calcium hydroxide according to claim 1, characterized in that, In step S3, the digestion temperature is 80℃, the liquid-to-solid ratio is 3:1, and the digestion time is 45 minutes.

5. The process for purifying low-grade fluorite and co-producing calcium hydroxide according to claim 1, characterized in that, In step S5, the particle size of the material after grinding is less than 100 mesh.

6. The process for purifying low-grade fluorite and co-producing calcium hydroxide according to claim 1, characterized in that, The fluorite concentrate obtained in step S5 has a grade of over 90%.

7. The process for purifying low-grade fluorite and co-producing calcium hydroxide according to claim 1, characterized in that, The calcination equipment is a rotary kiln, vertical kiln, or fluidized bed calciner; the digestion equipment is a trough reactor with stirring; and the flotation equipment is a mechanically stirred flotation machine or flotation column.

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