A method for increasing the whiteness of low-whiteness talc by low-temperature calcination

Abstract

The present invention discloses a method for increasing the whiteness of talc by low-temperature calcination. Low-whiteness talc with a particle size of ≤2 mm is mixed with a calcination additive and pulverized to a particle size of ≤0.045 mm to obtain a mixed ore sample. The mixed ore sample is subjected to calcination treatment in a weakly reducing atmosphere, with a calcination temperature of 500-600 °C and a time of 10-60 min. After cooling to room temperature, acid leaching, multi-stage magnetic separation, filtration, and drying are carried out to obtain the finished talc powder. The method of the present invention overcomes the drawbacks such as high calcination temperature and long calcination time in the process of increasing the whiteness of low-whiteness and low-grade talc, and has the advantages of low energy consumption, environmental friendliness, simple operation, and low cost. It can significantly improve the whiteness of talc powder on the premise of maximizing the preservation of the talc phase, and has good economic and social benefits.

Description

Technical Field

[0001] The present invention belongs to the field of mineral processing, and relates to a method for increasing the whiteness of talc by low-temperature calcination, specifically, a method for preparing high-whiteness and high-purity talc from medium-low grade and low-whiteness talc minerals by removing organic carbonaceous matter and iron impurities. Technical Background

[0002] As an important non-metallic mineral resource, talc occupies a special position in modern industrial and economic development. Due to its excellent physical and chemical properties such as lubrication, anti-adhesion, flow aid, insulation, fire resistance and acid resistance, talc is widely used in industries such as papermaking, ceramics, plastics, coatings and medicine. Although the total reserves of talc resources in China are relatively rich, the reserves of high-whiteness high-quality talc are lower than the world average level. In recent years, with the wide application of engineering plastics in fields such as automobiles, electronics, electrical and aerospace in China, the high-quality talc resources with high whiteness and purity are gradually exhausted, and the domestic demand for high-grade talc is increasing, and the high-end talc market seriously relies on imports. In addition, 70% of the current talc resources in China are medium-low grade talc, and their whiteness often cannot meet the use requirements and cannot be effectively utilized, while the whiteness of talc is an important index determining its industrial application value. Therefore, efficiently improving the whiteness of medium-low grade talc and increasing the development and utilization of medium-low grade talc are of great significance for alleviating the supply-demand contradiction in the current high-grade talc resource market and meeting China's future strategic and development needs.

[0003] Organic carbonaceous matter and trace iron elements in medium- and low-grade talc are the main factors causing the current blackening of talc. Magnetic separation and acid washing can reduce the content of some magnetic iron and soluble iron in talc. For the removal of organic carbonaceous matter in talc, calcination is the main technical means for whitening current black talc. For example, patents such as "Process for Making High-White and Superfine Talc Powder from Black Talc" (Application No. 200610101218.1) and "Preparation Method of Low-Cost High-Whiteness Calcined Talc" (Application No. PCT / CN2018 / 120234) both use calcination to improve the whiteness of talc. However, the calcination temperature of the current talc whitening process is mostly higher than the phase transition temperature of talc (850 °C). Therefore, the talc products after calcination treatment are extremely easy to transform into enstatite, losing the original smoothness of talc minerals. Their products can only be used in low-value-added industries such as ceramics and coatings, seriously wasting the layered silicate crystal structure and physical and chemical properties of talc. In addition, the too-long calcination treatment time greatly increases the production cost and also severely restricts the efficient development and utilization of medium- and low-grade talc resources. The patent "Low-Temperature Calcination Whitening Process for a Talc Mine, Its Products and Applications" (Application No. 202010066331.0) realizes the low-temperature (500 - 800 °C) calcination whitening of talc by adding chemical agents to make pulp. Although this method reduces the calcination temperature, the too-long calcination time inevitably increases the production cost, and the removal effect on insoluble iron or refractory iron in iron-containing talc is not good. Therefore, overcoming the deficiencies of the existing technology and developing a process for removing organic matter and iron impurities in talc at low temperature to improve the whiteness of talc ore will greatly broaden the application prospects of medium- and low-grade talc resources. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the disadvantages such as high calcination temperature, easy phase transition and long calcination time during the whitening process of low-whiteness and low-grade talc, and to propose a low-temperature, high-efficiency and simple-operation talc whitening method. Using inexpensive and easily available medium- and low-grade talc as raw materials, high-quality talc products are prepared by combining and implementing means such as grinding, calcination, acid leaching and magnetic separation.

[0005] A low-temperature calcination whitening method for low-whiteness talc includes the following process steps:

[0006] Mix low-whiteness talc with a particle size of ≤2 mm and a calcination additive evenly and crush them to obtain a mixed ore sample; after calcining the mixed ore sample in a weakly reducing atmosphere and cooling it to room temperature, then carry out acid leaching, multi-stage magnetic separation, filtration and drying to obtain the finished talc powder.

[0007] The above-mentioned processed talc ore is taken from Baishan City, Jilin Province and belongs to carbonate-type talc. The main mineral component is talc, accompanied by a certain amount of carbonate minerals such as magnesite and dolomite, as well as a certain amount of pyrite. In addition, very fine organic carbonaceous matter is dispersed in the talc, without a definite form, not having reflected light, and is dispersed in the talc sample in small dots, locally concentrated in spots and laminar patterns. The whiteness of the low-whiteness talc is 60% - 80%, SiO2 ≥ 57%, Fe2O3 ≥ 1%, and the organic carbonaceous matter content is 1% - 3%.

[0008] Further, the calcination additive is a mixture of sodium thiosulfate and sodium chloride. Among them, the addition amount of sodium thiosulfate is 0.5% - 3.0% of the mass of the low-whiteness talc, and the addition amount of sodium chloride is 0.5% - 5.0% of the mass of the low-whiteness talc.

[0009] Further, the pulverization is to grind the mixed ore sample to a particle size ≤ 0.045 mm using a dry pulverization device.

[0010] Preferably, the dry pulverization device is one of a vibration mill, a stirring mill, and a Raymond mill.

[0011] Further, the calcination treatment is to put the mixed ore sample into a covered ceramic crucible for calcination, maintaining a weak reduction atmosphere during the calcination process. The calcination temperature is 500 - 600 °C, and the calcination time is 10 - 60 min. For the specific manufacturing method of the weak reduction atmosphere, a mixed gas of CO and CO2 or a mixed gas of H2 and CO2 can be introduced into the furnace, or the "sealed carbon method" can be used to put carbon substances in the calcination container. The 1% - 3% organic carbonaceous matter contained in the low-whiteness talc processed by the present invention can be used as a carbon source to generate CO reduction gas during the calcination process, creating a weak reduction calcination atmosphere in the covered crucible.

[0012] Further, the acid leaching uses a mixed acid, and the mixed acid is a mixture of one of hydrochloric acid or sulfuric acid and hydrofluoric acid. The molar ratio of hydrochloric acid or sulfuric acid to hydrofluoric acid is 1:1 - 3, and the liquid-solid ratio of the mixed acid to the mixed ore sample is 2 - 4:1.

[0013] Preferably, the acid leaching time is 30 - 60 min, and a water bath heating at 50 - 80 °C is used.

[0014] Further, the magnetic separation method is wet magnetic separation, the magnetic field intensity ≥ 20000 Oe, and during the magnetic separation process, washing water is required to wash the magnetic separation products.

[0015] Finally, the whiteness of the talc product obtained by implementing the low-temperature calcination and whitening method of talc proposed by the present invention reaches 88% - 93%.

[0016] A preferred technical solution of the low-whiteness talc low-temperature calcination whitening method of the present invention includes the following technological steps:

[0017] (1) Crush the low-whiteness talc to a particle size of -2 mm, add a calcination additive and mix well, and further crush it to a particle size of -0.045 mm using a dry powder grinding device to obtain a mixed ore sample;

[0018] (2) Place the mixed ore sample in a covered crucible for calcination treatment, maintain a weak reducing atmosphere during the calcination process, the calcination temperature is 500-600 °C, the time is 10-60 min, and then naturally cool to room temperature;

[0019] (3) Acid-leach the calcined product with a mixed acid, the acid-leaching time is 30-60 min, and use a water bath at 50-80 °C for heating. After leaching, filter to obtain the leached residue material;

[0020] (4) Perform multi-stage wet magnetic separation on the leached residue material, the magnetic field strength ≥ 20000 Oe, and during the magnetic separation process, it is necessary to use flushing water to wash the magnetic separation products, and then obtain the finished talc powder after filtration and drying.

[0021] Compared with the existing talc whitening process, the advantages of the talc low-temperature calcination whitening process proposed by the present invention are that the calcination temperature ≤ 600 °C, the calcination time is short, the operation is simple, and it is easy to carry out continuous production operations. More importantly, the present invention can significantly improve the whiteness of talc on the premise of maximizing the maintenance of the talc phase, and there is basically no chemical reagent residue in the calcined and whitened products, and it has a wide range of application routes. Description of the Drawings

[0022] Figure 1 It is the process flow diagram of the talc low-temperature calcination whitening process described in the embodiment of the present invention. Detailed Embodiments

[0023] The following non-limiting embodiments can enable those of ordinary skill in the art to more comprehensively understand the present invention, but do not limit the present invention in any way. Non-essential improvements and adjustments made by those skilled in the art based on the above-mentioned invention content still fall within the protection scope of the present invention.

[0024] The test methods described in the following embodiments are all conventional methods unless otherwise specified; the reagents and materials are all commercially available unless otherwise specified.

[0025] Example 1

[0026] (1) Crush the talc lumpy ore with an initial whiteness of 71.5% to a particle size of -2 mm, weigh 0.5% of sodium thiosulfate and 0.5% of sodium chloride based on the mass of the ore, and mix the calcination additive with the sieved talc ore sample to be processed;

[0027] (2) Use a vibration mill to perform dry grinding on the above talc ore sample and calcination additive. While fully mixing the ore sample and the calcination additive, crush the talc ore sample to a particle size of -0.045 mm;

[0028] (3) Take the above qualified particle size sample and place it in a covered ceramic crucible. Maintain a weak reducing atmosphere during calcination, set the calcination temperature to 560 °C, and the calcination time to 60 min. After natural cooling to room temperature, take out the sample;

[0029] (4) Prepare a mixed solution of hydrochloric acid and hydrofluoric acid with a molar concentration of 1 mol / L each, and perform acid leaching on the calcined talc sample. Fix the liquid-solid ratio of the mixed acid solution to the talc ore sample at 4:1, use a water bath at 60 °C for heating, set the leaching time to 60 min. After leaching, filter to obtain the leached residue material, and the leaching solution is reserved for recycling;

[0030] (5) Take the leached residue material for multi-stage wet magnetic separation treatment, set the magnetic field intensity to 20000 Oe. After magnetic separation, filter and dry to obtain qualified talc powder, and the measured whiteness of the talc powder is 88.6%.

[0031] Example 2

[0032] (1) Crush the talc lumpy ore with an initial whiteness of 71.5% to a particle size of -2 mm. Weigh 0.5% of sodium thiosulfate and 3.0% of sodium chloride based on the ore mass, and mix the calcination additive with the screened talc ore sample to be treated;

[0033] (2) Use a vibration mill to perform dry grinding on the above talc ore sample and calcination additive. While fully mixing the ore sample and the calcination additive, crush the talc ore sample to a particle size of -0.045 mm;

[0034] (3) Take the above qualified particle size sample and place it in a covered ceramic crucible. Maintain a weak reducing atmosphere during calcination, set the calcination temperature to 560 °C, and the calcination time to 60 min. After natural cooling to room temperature, take out the sample;

[0035] (4) Prepare a mixed solution of hydrochloric acid and hydrofluoric acid with a molar concentration of 1 mol / L each, and perform acid leaching on the calcined talc sample. Fix the liquid-solid ratio of the mixed acid solution to the talc ore sample at 4:1, use a water bath at 60 °C for heating, set the leaching time to 60 min. After leaching, filter to obtain the leached residue material, and the leaching solution is reserved for recycling;

[0036] (5) Take the leached residue material for multi-stage wet magnetic separation treatment, set the magnetic field intensity to 20000 Oe. After magnetic separation, filter and dry to obtain qualified talc powder, and the measured whiteness of the talc powder is 89.3%.

[0037] Example 3

[0038] (1) Crush the talc ore block with an initial whiteness of 71.5% to a particle size of -2 mm. Weigh 0.5% of sodium thiosulfate and 3.0% of sodium chloride based on the mass of the ore, and mix the calcination additive with the talc ore sample to be processed under the sieve.

[0039] (2) Use a vibratory mill to conduct dry grinding treatment on the above talc ore sample and the calcination additive. While fully mixing the ore sample and the calcination additive, crush the talc ore sample to a particle size of -0.045 mm.

[0040] (3) Take the above qualified particle size sample and place it in a covered ceramic crucible. Maintain a weak reducing atmosphere during the calcination process, set the calcination temperature to 580 °C, and the calcination time to 60 min. After natural cooling to room temperature, take out the sample.

[0041] (4) Prepare a mixed solution of hydrochloric acid and hydrofluoric acid with a molar concentration of 1 mol / L each, and conduct acid leaching treatment on the calcined talc sample. Fix the liquid-solid ratio of the mixed acid solution to the talc ore sample at 4:1, heat it in a 60 °C water bath, set the leaching time to 60 min. After leaching, filter to obtain the leached residue material, and the leaching solution is reserved for recycling.

[0042] (5) Take the leached residue material for multi-stage wet magnetic separation treatment, set the magnetic field intensity to 20000 Oe. After magnetic separation, filter and dry to obtain qualified talc powder, and the measured whiteness of the talc powder is 90.5%.

[0043] Example 4

[0044] (1) Crush the talc ore block with an initial whiteness of 75.1% to a particle size of -2 mm. Weigh 0.5% of sodium thiosulfate and 3.0% of sodium chloride based on the mass of the ore, and mix the calcination additive with the talc ore sample to be processed under the sieve.

[0045] (2) Use a vibratory mill to conduct dry grinding treatment on the above talc ore sample and the calcination additive. While fully mixing the ore sample and the calcination additive, crush the talc ore sample to a particle size of -0.045 mm.

[0046] (3) Take the above qualified particle size sample and place it in a covered ceramic crucible. Maintain a weak reducing atmosphere during the calcination process, set the calcination temperature to 580 °C, and the calcination time to 15 min. After natural cooling to room temperature, take out the sample.

[0047] (4) Prepare a mixed solution of hydrochloric acid and hydrofluoric acid with a molar concentration of 1 mol / L each, and conduct acid leaching treatment on the calcined talc sample. Fix the liquid-solid ratio of the mixed acid solution to the talc ore sample at 3:1, heat it in a 60 °C water bath, set the leaching time to 60 min. After leaching, filter to obtain the leached residue material, and the leaching solution is reserved for recycling.

[0048] (5) Take the leached residue material for multi-stage wet magnetic separation treatment, set the magnetic field intensity to 20000 Oe, filter and dry after magnetic separation to obtain qualified talc powder, and the measured whiteness of the talc powder is 91.3%.

[0049] Example 5

[0050] (1) Crush the talc block ore with an initial whiteness of 75.1% to a particle size of -2 mm, weigh 0.5% of sodium thiosulfate and 3.0% of sodium chloride based on the ore mass, and mix the calcination additive with the screened talc ore sample to be treated.

[0051] (2) Use a vibration mill to perform dry grinding treatment on the above talc ore sample and the calcination additive. While fully mixing the ore sample and the calcination additive, crush the talc ore sample to a particle size of -0.045 mm.

[0052] (3) Take the above qualified particle size sample and place it in a covered ceramic crucible. Maintain a weak reducing atmosphere during calcination, set the calcination temperature to 580 °C, and the calcination time to 15 min. After natural cooling to room temperature, take out the sample.

[0053] (4) Prepare a mixed solution of sulfuric acid and hydrofluoric acid with a molar concentration of 1 mol / L each, and perform acid leaching treatment on the calcined talc sample. Fix the liquid-solid ratio of the mixed acid solution to the talc ore sample at 3:1, use a 60 °C water bath for heating, set the leaching time to 60 min, and filter after leaching to obtain the leached residue material. The leaching solution is reserved for recycling.

[0054] (5) Take the leached residue material for multi-stage wet magnetic separation treatment, set the magnetic field intensity to 20000 Oe, filter and dry after magnetic separation to obtain qualified talc powder, and the measured whiteness of the talc powder is 91.5%.

[0055] Example 6

[0056] (1) Crush the talc block ore with an initial whiteness of 75.1% to a particle size of -2 mm, weigh 0.5% of sodium thiosulfate and 3.0% of sodium chloride based on the ore mass, and mix the calcination additive with the screened talc ore sample to be treated.

[0057] (2) Use a vibration mill to perform dry grinding treatment on the above talc ore sample and the calcination additive. While fully mixing the ore sample and the calcination additive, crush the talc ore sample to a particle size of -0.045 mm.

[0058] (3) Take the above qualified particle size sample and place it in a covered ceramic crucible. Maintain a weak reducing atmosphere during calcination, set the calcination temperature to 580 °C, and the calcination time to 15 min. After natural cooling to room temperature, take out the sample.

[0059] (4) Prepare a mixed solution of sulfuric acid and hydrofluoric acid with molar concentrations of 1 mol / L and 2 mol / L respectively, and perform acid leaching treatment on the calcined talc sample. Fix the liquid-solid ratio of the mixed acid solution to the talc ore sample at 3:1, heat it in a 60 °C water bath, set the leaching time to 60 min. After leaching, filter to obtain the leached residue material, and the leachate is reserved for recycling;

[0060] (5) Take the leached residue material for multi-stage wet magnetic separation treatment, set the magnetic field intensity to 20000 Oe. After magnetic separation, filter and dry to obtain qualified talc powder, and the measured whiteness of the talc powder is 91.8%.

[0061] Example 7

[0062] (1) Crush the talc lumps with an initial whiteness of 71.5% to a particle size of -2 mm, weigh 2.5% of sodium thiosulfate and 4.0% of sodium chloride based on the mass of the ore, and mix the calcination additive with the screened talc ore sample to be processed;

[0063] (2) Use a vibration mill to perform dry grinding treatment on the above talc ore sample and the calcination additive. While fully mixing the ore sample and the calcination additive, crush the talc ore sample to a particle size of -0.045 mm;

[0064] (3) Take the above qualified particle size sample and place it in a covered ceramic crucible, maintain a weak reducing atmosphere during calcination, set the calcination temperature to 500 °C, and the calcination time to 60 min. After natural cooling to room temperature, take out the sample;

[0065] (4) Prepare a mixed solution of hydrochloric acid with a molar concentration of 1 mol / L and hydrofluoric acid with a molar concentration of 3 mol / L, and perform acid leaching treatment on the calcined talc sample. Fix the liquid-solid ratio of the mixed acid solution to the talc ore sample at 4:1, heat it in a 60 °C water bath, set the leaching time to 60 min. After leaching, filter to obtain the leached residue material, and the leachate is reserved for recycling;

[0066] (5) Take the leached residue material for multi-stage wet magnetic separation treatment, set the magnetic field intensity to 20000 Oe. After magnetic separation, filter and dry to obtain qualified talc powder, and the measured whiteness of the talc powder is 88.2%.

[0067] Comparative Example 1

[0068] Replace the covered ceramic crucible in step (3) of Example 1 with an uncovered ceramic crucible, that is, the air in the container can freely circulate during calcination. The other steps are the same as those in Example 1. It is found that the color of the final talc product is significantly red, which cannot meet the whiteness requirements of high-grade talc products, and the measured whiteness of the final talc powder is 81.7%.

[0069] Comparative Example 2

[0070] Step (4) in Example 4 is deleted, that is, the calcined talc ore sample is not subjected to acid leaching treatment, and the remaining steps are the same as those in Example 4. It is found that the whiteness of the finally obtained talc powder is 85.3%.

[0071] From the test results of the above examples and comparative examples, it can be seen that the method proposed by the present invention can not only achieve the whitening of talc by calcination at a temperature lower than the phase transition temperature of talc and maintain the talc phase unchanged to the greatest extent, but also greatly shorten the calcination time. The operation process is simple and convenient for continuous production operations. Therefore, the method for low-temperature calcination and whitening of talc proposed by the present invention is of great significance for broadening the utilization ways of medium and low-grade talc resources.

Claims

1. A method for increasing the whiteness of low-whiteness talc by low-temperature calcination, characterized in that: The method includes the following technological steps: Mix low whiteness talc with a particle size ≤ 2 mm and a calcination additive, and then crush them to obtain a mixed ore sample; after calcining the mixed ore sample in a weakly reducing atmosphere and cooling it to room temperature, perform acid leaching, multi-stage magnetic separation, filtration, and drying to obtain the finished talcum powder. The calcination treatment is to calcine the mixed ore sample in a weakly reducing atmosphere, the calcination temperature is 500 - 600 °C, and the calcination time is 10 - 60 min. The specific method for creating the weakly reducing atmosphere is to introduce a mixed gas of CO and CO2 or a mixed gas of H2 and CO2. The acid leaching uses a mixed acid, which is a mixture of one of hydrochloric acid or sulfuric acid and hydrofluoric acid. The molar ratio of hydrochloric acid or sulfuric acid to hydrofluoric acid is 1:1 - 3, and the liquid-solid ratio of the mixed acid to the mixed ore sample is 2 - 4:

1. The time for acid leaching is 30 - 60 min, and a water bath at 50 - 80 °C is used for heating. The calcination additive is a mixture of sodium thiosulfate and sodium chloride. Among them, the addition amount of sodium thiosulfate is 0.5% - 3.0% of the mass of the low whiteness talc to be treated, and the addition amount of sodium chloride is 0.5% - 5.0% of the mass of the low whiteness talc to be treated. The crushing is to grind the mixed ore sample to a particle size ≤ 0.045 mm using a dry grinding device. The magnetic separation method is wet magnetic separation, the magnetic field strength ≥ 20000 Oe, and during the magnetic separation process, washing water is required to wash the magnetic separation products.

2. The method according to claim 1, wherein: The whiteness of the low whiteness talc is 60% - 80%, and the organic carbon content is 1% - 3%.

3. The method according to claim 2, characterized in that: The dry grinding device is one of a vibration mill, a stirring mill, and a Raymond mill.

4. The method according to claim 1, wherein: The whiteness of the finished talcum powder obtained by using the method is 88% - 93%.

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