Chemical purification method of kaolin

Abstract

The invention relates to the technical field of kaolin purification, in particular to a chemical purification method of kaolin. The method comprises the following steps: S1, adding water into dried kaolin to prepare ore pulp A, adding a dispersing agent into the ore pulp A, adjusting the pH value to 8-9, performing stirring operation at the same time, and performing centrifugal classification and drying treatment on the stirred slurry; s2, grinding and uniformly mixing the kaolin dried in the step S1 with potassium formate, adding deionized water while grinding, sufficiently and uniformly mixing, and roasting; and S3, stirring the roasted product in the step S2 with an acid solution at a low speed at a certain temperature, reacting for a certain time, then centrifugally dewatering, pickling, washing with water, and drying to obtain the purified kaolin. According to the method, the kaolin is subjected to specific pretreatment before acid leaching, and the occurrence state or reaction activity of iron-containing minerals is changed, so that the acid consumption of subsequent acid leaching is remarkably reduced, the reaction time is shortened, and the damage to the kaolin structure is reduced while the iron removal efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of kaolin purification technology, and more particularly to a chemical purification method for kaolin. Background Technology

[0002] Kaolin, as an important non-metallic mineral material, has wide applications in ceramics, papermaking, rubber, coatings, and other fields. Natural kaolin often contains colored impurities such as iron and titanium. In particular, the presence of iron significantly reduces the whiteness and performance of kaolin. Therefore, iron removal from kaolin is a key step in its deep processing.

[0003] Currently, chemical purification of kaolin mainly involves adding reagents or calcination to induce chemical reactions in impurities, thereby selectively removing them. These methods include acid leaching, oxidation, reduction, redox reactions, and chlorination roasting. Among these, acid leaching is widely used due to its relatively simple operation and significant iron removal effect. Traditional acid leaching typically uses strong acids such as hydrochloric acid and sulfuric acid to directly treat kaolin. Through the chemical reaction between the acid and iron-containing minerals, insoluble iron compounds are converted into soluble iron ions, which are then removed through washing and separation.

[0004] However, the traditional acid leaching method has the following technical drawbacks: 1. Environmental and safety issues: The large-scale use of strong acids will generate acidic wastewater and waste gas. Improper handling will cause serious environmental pollution. In addition, there are safety hazards in the storage, use and waste liquid treatment of strong acids.

[0005] 2. Structural damage problem: While dissolving iron impurities, strong acid will also erode the aluminum-oxygen octahedral layer in the layered structure of kaolinite, leading to the destruction of the kaolinite crystal structure and weakening of interlayer bonding, thereby reducing its physical and chemical properties and application value.

[0006] 3. High economic cost: To achieve the ideal iron removal effect, high concentration of acid, long reaction time or high reaction temperature are often required, resulting in high consumption of reagents and energy, and a large amount of neutralization treatment is required afterward, which increases the overall cost.

[0007] 4. Limited efficiency: For iron impurities in the form of hematite, pyrite, etc., especially iron ore phases that are wrapped inside kaolinite particles or tightly bound to aluminum, the direct acid leaching reaction kinetics are slow and the iron removal efficiency is low, making it difficult to meet the production requirements of high-quality kaolin.

[0008] Therefore, there is an urgent need for an improved method for iron removal and purification of kaolin, which can effectively improve iron removal efficiency while reducing the amount of strong acid used, and at the same time preserve the integrity of the crystal structure of kaolin to the maximum extent, so as to achieve economical, environmentally friendly and efficient deep processing of kaolin. Summary of the Invention

[0009] The purpose of this invention is to address the aforementioned shortcomings of the prior art by proposing a chemical purification method for kaolin.

[0010] The present invention provides a method for chemical purification of kaolin, comprising the following steps: S1. Add water to the dried kaolin to prepare slurry A. Add dispersant to slurry A and adjust the pH to 8-9. Stir at the same time. Centrifuge, classify and dry the slurry after stirring. S2. Take the dried kaolin from S1 and grind it with potassium formate until it is well mixed. While grinding, add deionized water and calcine after mixing thoroughly. S3. Take the calcined product from S2 and stir it with acid solution at a certain temperature and speed. After reacting for a certain time, centrifuge to dehydrate, acid wash and water wash, and dry to obtain purified kaolin.

[0011] Further, in step S1, 0.5% by mass of dispersant is added to slurry A.

[0012] Further, in step S1, the solid-liquid ratio of the kaolin to water is (50~200) g: 400 mL, the stirring speed is 1000 rpm, and the stirring time is 240~300 min.

[0013] Furthermore, in step S1, the centrifuge is used for grading. The first centrifugation speed is 4000~5000 rpm and the centrifugation time is 4~6 min. After the remaining slurry is removed, a second centrifugation is performed. The second centrifugation speed is 9000~10000 rpm and the centrifugation time is 4~6 min.

[0014] Further, in step S1, the precipitate after the second centrifugation is dried for 300-600 min at a temperature of 90-100℃.

[0015] Further, in step S2, the kaolin and potassium formate are in a mass ratio of 1:0.005~0.1.

[0016] Furthermore, in step S2, the calcination temperature is 150~400℃, the heating rate is 10~30℃ / min, and the temperature is held for 3~5 hours.

[0017] Further, in step S3, the solid-liquid ratio of the product to the acid solution is (10~30) g: 200 mL, the concentration of the acid solution is 0.5~4 mol / L, the reaction temperature is 30~80℃, the stirring speed is 800-1000 rpm, and the stirring time is 90~150 min.

[0018] Furthermore, in step S3, a centrifuge is used for dehydration treatment, with a centrifugation speed of 5000~7000 rpm and a centrifugation time of 4~6 min.

[0019] Further, in step S3, the acid used for pickling is hydrochloric acid with a concentration of 0.5~1mol / L, the solid-liquid ratio of the product to the acid is (10~30)g:200mL, and the number of pickling cycles is 1~2. In step S3, the water used for washing is deionized water, the solid-liquid ratio of the product to water is (10~20) g: 200 mL, and the number of times the water is washed is 2~3 times.

[0020] This invention significantly reduces acid consumption and shortens reaction time by subjecting kaolin to specific pretreatment before acid leaching, thereby altering the occurrence state or reactivity of iron-containing minerals. This improves iron removal efficiency while minimizing damage to the kaolin structure, achieving a balance between technical and economic efficiency and environmental friendliness, and providing a new approach for the high-value utilization of kaolin. Attached Figure Description

[0021] Figure 1 The X-ray diffraction pattern of raw kaolin ore; Figures 2a-2d X-ray diffraction patterns of purified kaolin under different potassium formate dosages, hydrochloric acid concentrations, calcination temperatures, and reaction temperatures. Detailed Implementation

[0022] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0023] Example 1: In this embodiment, kaolin was purified by treating it with different amounts of potassium formate (0.5~10%). The iron content of the kaolin was 1.45%, and the natural whiteness was 54.08.

[0024] Add 4L of deionized water to 1kg of dried kaolin to prepare slurry A. Add 5g of sodium hexametaphosphate to slurry A, and add diluted sulfuric acid or sodium hydroxide to adjust the pH range to 8-9. Maintain a stirring speed of 1000rpm and adjust the pH every half hour during stirring. After stirring for 300min, pour the slurry into a 250mL centrifuge bottle and centrifuge at 5000rpm for 5min. Pour the unprecipitated slurry into another centrifuge bottle and centrifuge at 9000rpm for 5min. Take the precipitate and dry it for later use.

[0025] Take 10g of dried sample, add 0.05g, 0.07g, 0.1g, 0.3g, 0.5g and 1g of potassium formate and grind and mix well. Add deionized water during grinding until fully mixed. Transfer to a crucible and place in a muffle furnace for calcination. The heating rate is 10℃ / min. Keep at 400℃ for 4h. After cooling to room temperature, grind for later use.

[0026] The ground sample was added to 200 mL of 4 mol / L sulfuric acid solution and stirred at 800 rpm for 2 h at a reaction temperature of 80℃. The solution was then transferred to a centrifuge bottle and centrifuged at 5000 rpm for 5 min. After centrifugation, the solid precipitate was retained, and 200 mL of 0.5 mol / L hydrochloric acid solution was added. After stirring and mixing, the precipitate was dehydrated at 5000 rpm for 5 min. The same procedure was repeated twice, adding 200 mL of deionized water. The precipitate was then dried, ground, and stored for later use. The final iron content of the kaolin was 0.96%, 0.96%, 0.94%, 0.91%, 0.89%, and 0.83%, with iron reduction rates of 33.79%, 33.79%, 35.17%, 37.24%, 38.62%, and 42.76%, respectively. The natural whiteness values ​​were 61.22, 63.24, 63.28, 63.62, 63.28, and 68.77, with whiteness improvement rates of 13.20%, 16.94%, 17.01%, 17.64%, 17.01%, and 27.16%, respectively. This indicates that potassium formate plays an important role in the chemical purification of kaolin, and the optimal dosage of potassium formate is 10%.

[0027] Example 2: In this embodiment, kaolin was chemically purified using different concentrations of hydrochloric acid (0.5~4 mol / L).

[0028] Add 4L of deionized water to 1kg of dried kaolin to prepare slurry A. Add 5g of sodium hexametaphosphate to slurry A, and add diluted sulfuric acid or sodium hydroxide to adjust the pH range to 8-9. Maintain a stirring speed of 1000rpm and adjust the pH every half hour during stirring. After stirring for 300min, pour the slurry into a 250mL centrifuge bottle and centrifuge at 5000rpm for 5min. Pour the unprecipitated slurry into another centrifuge bottle and centrifuge at 9000rpm for 5min. Take the precipitate and dry it for later use.

[0029] Take 10g of dried sample, add 1g of potassium formate and grind until well mixed. Add deionized water during grinding until fully mixed. Transfer to a crucible and place in a muffle furnace for calcination. Heat at 10℃ / min for 4 hours at 400℃. After cooling to room temperature, grind for later use.

[0030] The ground samples were added to 200 mL of sulfuric acid solutions with concentrations of 0.5 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 3.5 mol / L, and 4 mol / L. The mixture was stirred at 800 rpm for 2 hours at 80℃. The solutions were then transferred to centrifuge bottles and centrifuged at 5000 rpm for 5 minutes. After centrifugation, the solid precipitate was retained. 200 mL of 0.5 mol / L hydrochloric acid solution was added, and the mixture was stirred and dehydrated at 5000 rpm for 5 minutes. This process was repeated twice, with the addition of 200 mL of deionized water. The precipitate was then dried, ground, and stored for later use. The final iron content of the kaolin was 1.35%, 0.94%, 0.92%, 0.89%, 0.89%, and 0.92%, with iron reduction rates of 6.90%, 35.17%, 36.55%, 38.62%, 38.62%, and 36.55%, respectively. The natural whiteness values ​​were 58.50, 67.92, 69.10, 67.88, 69.96, and 66.96, with natural whiteness improvement rates of 8.17%, 25.59%, 27.77%, 25.52%, 29.36%, and 23.82%, respectively. This indicates that the hydrochloric acid concentration affects the iron removal rate, with the optimal condition being 3.5 mol / L.

[0031] Example 3: In this embodiment, kaolin was chemically purified after being treated at different calcination temperatures.

[0032] Add 4L of deionized water to 1kg of dried kaolin to prepare slurry A. Add 5g of sodium hexametaphosphate to slurry A, and add diluted sulfuric acid or sodium hydroxide to adjust the pH range to 8-9. Maintain a stirring speed of 1000rpm and adjust the pH every half hour during stirring. After stirring for 300min, pour the slurry into a 250mL centrifuge bottle and centrifuge at 5000rpm for 5min. Pour the unprecipitated slurry into another centrifuge bottle and centrifuge at 9000rpm for 5min. Take the precipitate and dry it for later use.

[0033] Take 10g of dried sample, add 0.5g of potassium formate and grind until well mixed. Add deionized water during grinding until fully mixed. Transfer to a crucible and place in a muffle furnace for calcination. The heating rate is 10℃ / min. Keep at 150℃, 200℃, 250℃, 300℃, 350℃ and 400℃ for 4 hours. After cooling to room temperature, grind for later use.

[0034] The ground sample was added to 200 mL of 3 mol / L sulfuric acid solution and stirred at 800 rpm for 2 h at a reaction temperature of 80℃. The solution was then transferred to a centrifuge bottle and centrifuged at 5000 rpm for 5 min. After centrifugation, the solid precipitate was retained, and 200 mL of 0.5 mol / L hydrochloric acid solution was added. After stirring and mixing, the precipitate was dehydrated at 5000 rpm for 5 min. The same procedure was repeated twice, adding 200 mL of deionized water. The precipitate was then dried, ground, and stored for later use. The final iron content of the kaolin was 0.97%, 0.99%, 0.96%, 0.96%, 0.93%, and 0.88%, with iron reduction rates of 33.10%, 31.72%, 33.79%, 33.79%, 35.86%, and 39.31%, respectively. The natural whiteness was 64.07, 66.93, 67.38, 67.75, 66.93, and 66.77, with natural whiteness improvement rates of 18.47%, 23.76%, 24.59%, 25.28%, 23.76%, and 23.47%, respectively. This indicates that different roasting temperatures lead to differences in subsequent purification effects, with the optimal condition being 400℃.

[0035] Example 4: In this embodiment, kaolin was purified by different acid leaching temperatures after roasting.

[0036] Add 4L of deionized water to 1kg of dried kaolin to prepare slurry A. Add 5g of sodium hexametaphosphate to slurry A, and add diluted sulfuric acid or sodium hydroxide to adjust the pH range to 8-9. Maintain a stirring speed of 1000rpm and adjust the pH every half hour during stirring. After stirring for 300min, pour the slurry into a 250mL centrifuge bottle and centrifuge at 5000rpm for 5min. Pour the unprecipitated slurry into another centrifuge bottle and centrifuge at 9000rpm for 5min. Take the precipitate and dry it for later use.

[0037] Take 10g of dried sample, add 0.5g of potassium formate and grind until well mixed. Add deionized water during grinding until fully mixed. Transfer to a crucible and place in a muffle furnace for calcination. The heating rate is 10℃ / min. Keep at 300℃ for 4 hours. After cooling to room temperature, grind for later use.

[0038] The ground sample was added to 200 mL of 3 mol / L sulfuric acid solution and stirred at 800 rpm for 2 h at reaction temperatures of 30℃, 40℃, 50℃, 60℃, 70℃, and 80℃. The solution was transferred to a centrifuge bottle and centrifuged at 5000 rpm for 5 min. After centrifugation, the solid precipitate was retained, and 200 mL of 0.5 mol / L hydrochloric acid solution was added. After stirring and mixing, the precipitate was dehydrated at 5000 rpm for 5 min. The same operation was repeated twice, adding 200 mL of deionized water. The precipitate was then dried, ground, and stored for later use. The final iron content of the kaolin was 1.23%, 1.18%, 1.16%, 1.10%, 1.05%, and 0.94%, with iron reduction rates of 15.17%, 18.62%, 20.00%, 24.14%, 27.59%, and 35.17%, respectively. The natural whiteness values ​​were 60.26, 62.57, 64.74, 64.16, 66.63, and 68.09, with natural whiteness improvement rates of 11.43%, 15.70%, 19.71%, 18.64%, 23.21%, and 25.91%, respectively. This indicates that the acid leaching temperature also affects iron removal, with the optimal condition being 80℃.

[0039] Reference Appendix Figure 1 Kaolinite ore has a large number of peaks with high intensity and is relatively abundant. Quartz has a strong peak intensity and is the main gangue mineral. Vermiculite only has one peak at a low angle and is less abundant. Garnet and other gangue minerals with low content are also present.

[0040] Reference Appendix Figure 2a , 2b Adjusting the amount of potassium formate, the concentration of hydrochloric acid, the calcination temperature, and the reaction temperature in steps 2c and 2d all showed that the main crystalline phase remained stable without the formation of a new phase. When the variables were controlled within a suitable range, the characteristic diffraction peaks of kaolin changed from broadening and blurring to sharp and regular, and the interference of impurity peaks gradually weakened. The intensity of characteristic peaks increased with the adjustment of suitable variables, while the intensity of impurity peaks decreased synchronously, and this corresponded positively to the performance changes of reduced iron content and increased whiteness of purified kaolin.

[0041] For any points not covered above, existing technologies shall apply.

[0042] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for chemical purification of kaolin, characterized in that, Includes the following steps: S1. Add water to the dried kaolin to prepare slurry A. Add dispersant to slurry A and adjust the pH to 8-9. Stir at the same time. Centrifuge, classify and dry the slurry after stirring. S2. Take the dried kaolin from S1 and grind it with potassium formate until it is well mixed. While grinding, add deionized water and calcine after mixing thoroughly. S3. Take the calcined product from S2 and stir it with acid solution at a certain temperature and speed. After reacting for a certain time, centrifuge to dehydrate, acid wash and water wash, and dry to obtain purified kaolin.

2. The chemical purification method for kaolin as described in claim 1, characterized in that, In step S1, 0.5% of the mass of slurry A dispersant is added to slurry A.

3. The chemical purification method for kaolin as described in claim 1, characterized in that, In step S1, the solid-liquid ratio of kaolin to water is (50~200) g: 400 mL, the stirring speed is 1000 rpm, and the stirring time is 240~300 min.

4. The chemical purification method for kaolin as described in claim 1, characterized in that, In step S1, a centrifuge is used for grading. The first centrifugation speed is 4000~5000 rpm and the centrifugation time is 4~6 min. After the remaining slurry is removed, a second centrifugation is performed. The second centrifugation speed is 9000~10000 rpm and the centrifugation time is 4~6 min.

5. The chemical purification method for kaolin as described in claim 4, characterized in that, In step S1, the precipitate after the second centrifugation is dried for 300-600 min at a temperature of 90-100℃.

6. The chemical purification method for kaolin as described in claim 1, characterized in that, In step S2, the kaolin and potassium formate are in a mass ratio of 1:0.005~0.

1.

7. The chemical purification method for kaolin as described in claim 1, characterized in that, In step S2, the calcination temperature is 150~400℃, the heating rate is 10~30℃ / min, and the temperature is held for 3~5 hours.

8. The chemical purification method for kaolin as described in claim 1, characterized in that, In step S3, the solid-liquid ratio of the product to the acid solution is (10~30) g: 200 mL, the concentration of the acid solution is 0.5~4 mol / L, the reaction temperature is 30~80℃, the stirring speed is 800-1000 rpm, and the stirring time is 90~150 min.

9. The chemical purification method for kaolin as described in claim 1, characterized in that, In step S3, a centrifuge is used for dehydration, with a centrifugation speed of 5000~7000 rpm and a centrifugation time of 4~6 min.

10. The chemical purification method for kaolin as described in claim 1, characterized in that, In step S3, the acid used for pickling is hydrochloric acid with a concentration of 0.5~1mol / L. The solid-liquid ratio of the product to the acid is (10~30)g:200mL, and the pickling is performed 1~2 times. In step S3, the water used for washing is deionized water, the solid-liquid ratio of the product to water is (10~20) g: 200 mL, and the number of times the water is washed is 2~3 times.

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