Cryolite and preparation method thereof

Abstract

The invention belongs to the technical field of material preparation, and particularly relates to cryolite and a preparation method thereof. The preparation method comprises the following steps: (1) mixing an electrolyte and alkali to obtain an alkali leaching solution; mixing carbon powder with acid to obtain an acid leaching solution; (2) adding the acid leaching solution into the alkaline leaching solution, and reacting to obtain cryolite; wherein in the step (1), the electrolyte contains sodium fluoride and aluminum oxide; in the step (2), the rate of adding the acid leaching solution into the alkaline leaching solution is 1.2 ml / min to 6 ml / min. The preparation method is easy and convenient to operate, wastewater treatment is achieved through acid-base neutralization, in addition, the sedimentation rate (yield) of cryolite in the preparation method can reach 95.6%, and meanwhile the purity can reach 97%.

Description

Technical Field

[0001] The invention belongs to the technical field of material preparation, and in particular relates to cryolite and a preparation method thereof. Background Art

[0002] The chemical formula of cryolite is NaAlF 6 (3NaF·AlF 3 ), chemical name is sodium aluminum fluoride or sodium hexafluoroaluminate, melting point is about 1000℃, density is 3.0g / cm 3 , easy to absorb water and moisture, is a colorless monoclinic crystal structure. Cryolite is now mainly used in the electrolytic aluminum industry, and can also be used in wear-resistant fillers, metal flux, glass sunscreen and enamel opal. It is a relatively important industrial raw material.

[0003] At present, the method of preparing cryolite from discarded cathode carbon blocks from discarded aluminum electrolysis is gradually becoming a more popular method for preparing cryolite because it is environmentally friendly and can be recycled. The preparation of cryolite from discarded cathode carbon blocks from discarded aluminum electrolysis mainly includes: roasting method, flotation method and alkali leaching-carbonization method. These methods have their own advantages and disadvantages. The roasting method requires high-temperature sintering, which is costly and produces tail gas; the flotation method cannot completely separate the carbon powder from other valuable elements, which not only affects the purity of the carbon powder, but also causes waste of valuable elements; the alkali leaching-carbonization method is relatively cumbersome and requires strict control of the precipitation pH and the carbon dioxide introduction rate. The parameter requirements are very strict and it is easy to produce dawsonite (NaAl(OH) 2 CO 3 ) By-product impurities. If the carbon powder is subsequently subjected to acid leaching treatment, the acid leaching wastewater cannot be effectively treated.

[0004] Therefore, it is necessary to develop a method for preparing cryolite with mild preparation conditions (no high temperature required) and simple preparation method. Summary of the invention

[0005] The present invention develops a method for preparing cryolite. After mixing electrolyte raw materials and alkali, acid leaching solution is mixed with alkali leaching solution at a certain addition rate to react to prepare cryolite. The preparation method is simple and the reaction conditions are mild.

[0006] In order to achieve the above object, the present invention can adopt the following technical solutions:

[0007] On one hand, the present invention provides a method for preparing cryolite, comprising: (1) mixing an electrolyte with an alkali to obtain an alkali leaching solution; mixing carbon powder with an acid to obtain an acid leaching solution; (2) adding the acid leaching solution into the alkali leaching solution for reaction to obtain cryolite; wherein, in step (1), the electrolyte comprises sodium fluoride and aluminum oxide; and in step (2), the rate at which the acid leaching solution is added to the alkali leaching solution is 1.2 ml / min-6 ml / min.

[0008] Preferably, the preparation method satisfies one or more combinations of the following conditions: (a) the acid leaching solution is added after the temperature of the alkaline leaching solution is adjusted to 20°C-100°C; (b) the electrolyte is obtained by separating waste cathode carbon blocks from electrolytic aluminum; (c) after the reaction in step (2) is completed, the pH value is adjusted to 6-12; (d) in step (2), the reaction time is 20min-360min.

[0009] Preferably, in the above-mentioned preparation method, the method of separating the electrolyte from the waste cathode carbon blocks of electrolytic aluminum comprises: crushing the waste cathode carbon blocks of electrolytic aluminum, slurrying, flotation, and separating to obtain the electrolyte.

[0010] Preferably, in the above preparation method, the method for separating the electrolyte from the waste cathode carbon block of electrolytic aluminum satisfies one or more combinations of the following conditions: (a) the particle size D90 after crushing is 50μm-95μm; (b) in the powder after crushing, the mass proportion of 200 mesh particles is 65%-90%; (c) the concentration of the slurry after slurry adjustment is 15%-30%; (d) flotation is carried out using a flotation machine, the speed of the flotation machine is 1600r / min-2200r / min, and the inflation volume is 0.1m 2 / h-0.3m 2 / h, the scraper speed is 15r / min-30r / min; (e) flotation agent is added during flotation.

[0011] Preferably, in the above preparation method, the rate of adding the acid leaching solution into the alkaline leaching solution is 2 ml / min-5.2 ml / min.

[0012] Preferably, the preparation method satisfies one or more combinations of the following conditions: (a) the temperature for mixing the electrolyte and the alkali is 70°C-100°C; (b) the time for mixing the electrolyte and the alkali is 30 min-180 min; (c) the solid-liquid ratio in the alkali leaching solution is 1:8-1:18; (d) the alkali is selected from sodium hydroxide and / or potassium hydroxide; (e) the temperature for mixing the carbon powder and the acid is 70°C-100°C; (f) the time for mixing the carbon powder and the acid is 30 min-180 min; (g) the solid-liquid ratio in the acid leaching solution is 1:4-1:12; (h) the acid is selected from hydrochloric acid and / or hydrofluoric acid.

[0013] Another aspect of the present invention provides cryolite, which is prepared by the preparation method described in the present invention.

[0014] The beneficial effects of the present invention include at least: the preparation method provided by the present invention has mild conditions, is easy to operate, and realizes wastewater treatment by acid-base neutralization. In addition, the sedimentation rate (yield) of cryolite in the preparation method can reach 95.6%, and the purity can reach 97%. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is the XRD pattern of cryolite prepared in Example 5. DETAILED DESCRIPTION

[0016] The examples are provided to better illustrate the present invention, but the present invention is not limited to the examples. Therefore, those skilled in the art may make non-essential improvements and adjustments to the implementation scheme according to the above invention content, which still fall within the protection scope of the present invention.

[0017] The terms used herein are only used to describe specific embodiments and are not intended to limit the present disclosure. Unless the context has a significantly different meaning, expressions in the singular include expressions in the plural. As used herein, it should be understood that terms such as "include", "have", "include" are intended to indicate the presence of features, numbers, operations, materials, or combinations. The terms of the present invention are disclosed in the specification, and are not intended to exclude the possibility that one or more other features, numbers, operations, materials, or combinations thereof may exist or may be added. As used herein, " / " may be interpreted as "and" or "or", depending on the circumstances.

[0018] An embodiment of the present invention provides a method for preparing cryolite, comprising: (1) mixing an electrolyte with an alkali to obtain an alkali leaching solution; mixing carbon powder with an acid to obtain an acid leaching solution; (2) adding the acid leaching solution into the alkali leaching solution for reaction to obtain cryolite; wherein, in step (1), the electrolyte comprises sodium fluoride and aluminum oxide; and in step (2), the rate at which the acid leaching solution is added to the alkali leaching solution is 1.2 ml / min-6 ml / min.

[0019] Specifically, in the present invention, by controlling the rate at which the acid leaching solution is added to the alkaline leaching solution, the sedimentation rate (yield) and purity of cryolite can be comprehensively controlled. Too fast a dripping rate will cause the local pH of the solution to be too low, forming Al 2 (OH) 2.76 F 3.24 ·H 2O impurities, reducing the purity of the product and the F ion sedimentation rate; too fast a drop rate will lead to too high a precipitation nucleation rate, a large number of crystals will not have time to grow and exist in the form of fine particles, and the fine crystals are more easily dissolved under stirring, reducing the sedimentation rate of F ions; when the rate is 1.2ml / min-6ml / min, such as 2ml / min, 2.5ml / min, 3ml / min, 3.5ml / min, 4ml / min, 4.5ml / min or 5ml / min, the prepared cryolite has both a high sedimentation rate and purity; the sedimentation rate can reach 95.6%, and the purity can reach 97%. In addition, when the electrolyte is mixed with the alkali to obtain the alkaline leaching solution, when insoluble matter appears, the alkaline leaching solution is obtained by filtering or the like. In addition, the above-mentioned electrolyte also contains substances such as cryolite (in a relatively small amount).

[0020] In some specific examples, the above preparation method satisfies one or more combinations of the following conditions:

[0021] (a1) After the alkaline leaching solution is adjusted to a temperature of 20°C-100°C, the acid leaching solution is added; after the alkaline leaching solution is adjusted to a temperature of 20°C-100°C, the acid leaching solution is added; and the alkaline leaching solution is adjusted to a temperature of 20°C-100°C; Specifically, the temperature of the alkaline leaching solution also has an effect on the preparation of cryolite. As the temperature increases, the reaction rate accelerates. However, when the temperature increases by ≥90°C, the solubility of cryolite increases, resulting in a decrease in the sedimentation rate of F ions. Too high a temperature will lead to poor crystallinity of cryolite, and there will be by-product Al 2 (OH) 2.76 F 3.24 ·H 2 O impurities are generated, reducing the purity; in addition, when the temperature is lower than 20°C, the reaction temperature is low, the cryolite sedimentation rate is low, and when the temperature is higher than 100°C, the sedimentation rate does not change much from 100°C, so 20°C-100°C is selected in the present invention, such as 30°C, 40°C, 50°C, 60°C, 70°C, 80°C or 90°C;

[0022] (b1) The electrolyte is obtained by separating waste cathode carbon blocks from aluminum electrolysis; specifically, the electrolyte containing sodium fluoride and aluminum oxide in the present invention is any electrolyte that meets this condition and is known in the art; the electrolyte separated from waste cathode carbon blocks from aluminum electrolysis can be preferred in the present invention, so that the purpose of resource treatment of aluminum electrolysis waste can be achieved, and the pollution of fluorine-containing and cyanide-containing waste to the surrounding environment, soil and groundwater can be greatly reduced; in addition, the preparation method of the present invention also effectively recovers cryolite and carbon from waste cathode carbon blocks, wherein the cryolite separated and purified has a high purity and can be returned to the aluminum electrolysis industry for continued use, thereby reducing the consumption of strategic resource fluorite;

[0023] (c1) After the reaction in step (2) is completed, the pH value is adjusted to 6-12, such as 7, 8, 9, 10 or 11; specifically, pH < 6 will allow aluminum and fluorine to Combine in the same form to form Al 2 (OH) 2.76 F 3.24 ·H 2 O impurities, so the pH value needs to be controlled; when the pH>6 begins to rise, aluminum and fluorine gradually turn into The combination in the form of etc. is easier to react to form cryolite; cryolite is soluble in alkaline solution. When the pH is greater than 12, the reaction gradually increases, causing the cryolite to begin to react with the alkali and dissolve; so the pH value selected in the present invention is 6-12; preferably 9, the sedimentation rate of cryolite prepared under this pH condition is higher than that of other pH values, and the purity is also higher than that of other pH values.

[0024] (d1) In step (2), the reaction time is 20 min-360 min; specifically, in step (2), the reaction time refers to the reaction time after the addition of the alkaline leaching solution is completed, and the reaction time can be 20 min-360 min, such as 50 min, 80 min, 100 min, 150 min, 200 min, 250 min or 300 min; in addition, extending the time will cause the sedimentation of the F ions to first increase and then decrease. If the time is too long, a small amount of precipitate will redissolve, resulting in an increase in the F ion concentration in the solution, which will correspondingly reduce the sedimentation rate of the F ions.

[0025] It should be noted that the preparation method of the present invention can satisfy one of the conditions (a1) to (d1), preferably satisfy two or more conditions at the same time, more preferably satisfy all the conditions at the same time, and even more preferably satisfy the preferred conditions of all the conditions at the same time.

[0026] In some specific examples, in the above-mentioned preparation method, the method of separating the electrolyte from the waste cathode carbon blocks of electrolytic aluminum includes: crushing the waste cathode carbon blocks of electrolytic aluminum, slurrying, flotation, and separating to obtain the electrolyte.

[0027] Specifically, the pulverization, slurry preparation, flotation, and separation in the above preparation method are all well-known operations in the art and have no special meaning. For example, pulverization is performed by using a pulverizer; slurry preparation is performed by adding water for stirring and grinding, etc.

[0028] In some specific examples, in the above preparation method, the method of obtaining the electrolyte by separating the waste cathode carbon blocks of electrolytic aluminum satisfies one or more combinations of the following conditions:

[0029] (a2) The particle size after crushing is D90 of 50 μm-95 μm; specifically, crushing the waste cathode carbon block of electrolytic aluminum can increase the contact area of ​​the reaction and increase the reaction rate. If the crushing particle size is too small, it is easy to cause raw material loss, and if the particle size is too large, it is not conducive to the reaction. Therefore, 50 μm-95 μm is selected in the present invention, such as 60 μm, 70 μm, 80 μm or 90 μm;

[0030] (b2) In the crushed powder, the mass proportion of 200 mesh particles is 65%-90%, such as 70%, 75%, 80% or 85%; specifically, the purpose of 200 mesh particles accounting for 65%-90% is to dissociate the monomers between the electrolyte and the carbon powder; in addition, 200 mesh particles accounting for 65%-90% is a better flotation particle size; if the particle size is too coarse, the dissociation degree between the electrolyte and the carbon powder is insufficient, resulting in poor selectivity; if the particle size is too fine, the mineral muddling phenomenon is serious, and the electrolyte and the carbon powder cannot be effectively separated;

[0031] (c2) The concentration of the slurry after slurry adjustment is 15%-30%, such as 20%, 23% or 27%, etc.; specifically, the slurry concentration in the present invention refers to the mass ratio of the mineral and water, that is, the mass ratio of the crushed powder to water is 15%-30%; in addition, the slurry concentration will affect the recovery rate and purity of the mineral. The lower the slurry concentration, the higher the purity of the product and the lower the recovery rate; the higher the slurry concentration, the lower the purity of the product and the higher the recovery rate.

[0032] (d2) Flotation: A flotation machine is used for flotation. The speed of the flotation machine is 1600r / min-2200r / min and the air volume is 0.1m 2 / h-0.3m 2 / h, scraper speed is 15r / min-30r / min;

[0033] (e2) Flotation agents are added during flotation, and the flotation agents include collectors, frothers, inhibitors and pH adjusters. Specifically, during flotation, pH adjuster, inhibitor, collector and frother can be added in sequence for flotation; wherein, the collector includes kerosene and / or diesel, and the amount of collector added is 320g / t-640g / t; the frother can be pine oil, and the amount of addition is 40g / t-80g / t; the inhibitor can be sodium silicate and / or sodium dodecylbenzene sulfonate, and the amount of addition can be 500g / t-1000g / t; in addition, the "g / t" unit in the amount of addition refers to the mass ratio of the collector, frother, inhibitor or pH adjuster to the solid in the slurry, for example, the amount of collector added is 320g / t-640g / t, which means that if the slurry contains 1t of solid, then 320g-640g of collector is added; in addition, the pH adjuster includes sodium hydroxide and / or potassium hydroxide, and the amount is determined according to the pH of the slurry, and the pH of the slurry is adjusted to 8-10; specifically, the pH of the ore pulp is in an alkaline environment, OH - Adsorption on the surface of mineral particles increases the zeta potential on the surface of mineral particles, enhances the dispersion between mineral particles, and reduces the agglomeration between carbon particles and electrolyte particles; therefore, in the present invention, the main effect of pH adjustment on flotation lies in the hydrophobicity of mineral particles, which is more conducive to the flotation separation of carbon and electrolyte.

[0034] It should be noted that the preparation method of the present invention can satisfy one of the conditions (a2) to (e2), preferably satisfy two or more conditions at the same time, more preferably satisfy all the conditions at the same time, and even more preferably satisfy the preferred conditions of all the conditions at the same time.

[0035] It should also be noted that the preparation method of the present invention can satisfy one of the conditions (a1) to (d1) and (a2) to (e2), preferably satisfy two or more conditions at the same time, more preferably satisfy all the conditions at the same time, and even more preferably, satisfy the preferred conditions of all the conditions at the same time.

[0036] In some specific examples, in the above preparation method, the rate of adding the acid leaching solution into the alkaline leaching solution is 2 ml / min-5.2 ml / min.

[0037] Specifically, as mentioned above, by controlling the rate at which the acid extract is added to the alkaline extract, the sedimentation rate (yield) and purity of cryolite can be comprehensively controlled. The rate in the present invention can preferably be 2 ml / min-5.2 ml / min, such as 2.8 ml / min, 3.2 ml / min, 3.8 ml / min, 4.6 ml / min, 4.9 ml / min, 5.1 ml / min, etc.; more preferably 3.6 ml / min, at this rate, the sedimentation rate and purity of cryolite are better than other rates.

[0038] In some specific examples, the above preparation method satisfies one or more combinations of the following conditions:

[0039] (a3) The temperature at which the electrolyte and the alkali are mixed is 70°C to 100°C; for example, 80°C, 90°C or 95°C;

[0040] (b3) the time for mixing the electrolyte and the base is 30 min to 180 min; for example, 50 min, 70 min, 100 min, 120 min, 150 min or 170 min;

[0041] (c3) In the alkaline leaching solution, the solid-liquid ratio is 1:8-1:18; for example, 1:10, 1:13, 1:15 or 1:17; specifically, the solid-liquid ratio in the present invention is the mass ratio of the electrolyte to the volume ratio of the alkaline solution; the concentration of the alkaline solution can be 3 mol / L-5 mol / L;

[0042] (d3) the base is selected from sodium hydroxide and / or potassium hydroxide; specifically, the base in the present invention is a base known in the art, such as sodium hydroxide and / or potassium hydroxide; it should be understood that in the specific preparation process, the base can be added with water medium to prepare an alkaline solution, which is more conducive to the reaction;

[0043] (e3) The temperature at which the carbon powder and the acid are mixed is 70°C to 100°C; for example, 80°C, 90°C or 95°C;

[0044] (f3) the mixing time of the carbon powder and the acid is 30 min to 180 min; for example, 50 min, 70 min, 100 min, 120 min, 150 min or 170 min;

[0045] (g3) In the acid leaching solution, the solid-liquid ratio is 1:4-1:12; for example, 1:7, 1:9 or 1:11;

[0046] (h3) The acid is selected from hydrochloric acid and / or hydrofluoric acid; specifically, the base in the present invention is an acid known in the art, such as hydrochloric acid and / or hydrofluoric acid; it should be understood that in the specific preparation process, the acid can be added with an aqueous medium to prepare an acid solution of a certain concentration according to the specific circumstances.

[0047] It should be noted that the preparation method of the present invention may satisfy one of the conditions (a3) ​​to (h3), preferably satisfy two or more conditions at the same time, and more preferably satisfy all the conditions at the same time.

[0048] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with specific examples, but the content of the present invention is not limited to the following examples.

[0049] In the following embodiments, the sedimentation rate of cryolite is calculated according to the following steps: the fluoride ions in the solution are detected and analyzed by a fluoride ion electrode to obtain the fluoride ion concentration C1 of the solution V1 before the reaction and the fluoride ion concentration C2 of the solution V2 after the reaction; the F content in the cryolite sample is detected by X-ray fluorescence spectroscopy (XRF) to obtain the mass G3; wherein, the sedimentation rate = (V1*C1-V2*C2) / G3*100%.

[0050] In the following examples, the purity of cryolite is calculated and fitted by X-ray diffraction analysis (XRD) and standard card PDF#70-1606 (PDF#70-1606 is derived from the International Centre for Diffraction Data (ICDD), which is the only ISO-certified crystallographic database in the world; the PDF database has a wide coverage, high accuracy, strong compatibility, and powerful functions, covering more than 30 fields. It is an indispensable database for scientific research and industrial production such as materials science, physics, chemistry, geology, pharmacology, biology, inspection and quarantine, and forensic identification).

[0051] Example 1

[0052] (1) Using a crusher to crush the waste cathode carbon blocks to a D90 of 50 μm-95 μm;

[0053] (2) Weigh 300 g of the waste cathode carbon powder obtained in step (1), add 850 ml of water to stir and slurry, place it in a 1 L single tank flotation machine, add flotation agent (add sodium hydroxide (pH adjuster) to adjust the pH to 9, then add 800 g / t of sodium silicate (inhibitor), then add 500 g / t of kerosene (collector), and finally add 50 g / t of pine oil (foaming agent)) and aerate flotation (the flotation machine speed is 2200 r / min, the inflation volume is 0.3 m 2 / h, the scraper speed is 30r / min), and the carbon powder and electrolyte are separated;

[0054] (3) Weighing 18 g of the electrolyte obtained in step (3) and 72 ml of sodium hydroxide solution (concentration of 5 mol / L), placing them together in a three-diameter flask for alkali leaching (alkali leaching temperature of 80° C., alkali washing time of 100 min), and filtering to obtain an alkali leaching filtrate; weighing 18 g of carbon powder and 72 ml of a hydrochloric acid-hydrofluoric acid mixed solution (hydrochloric acid of 10% concentration hydrochloric acid, hydrofluoric acid of 10% concentration hydrofluoric acid), placing them together in a three-diameter flask for acid leaching (acid leaching temperature of 80° C., acid washing time of 100 min), and obtaining an acid leaching waste liquid;

[0055] (4) Take 72 ml of the alkaline leaching solution obtained in step (3) and heat it to 100° C. Then, drip the acid leaching waste liquid obtained in step (3) into the heated alkaline leaching filtrate at a rate of 3.6 ml / min. After the dripping is completed, react for 120 minutes, adjust the pH to 9, and cryolite can be obtained.

[0056] The calculated sedimentation rate and purity of cryolite are 84.8% and 91% respectively.

[0057] Example 2

[0058] The difference between Example 2 and Example 1 is that step (4) is different; step (4) in Example 2 is: heating the alkaline leaching solution obtained in step (3) to 40°C, dripping the acid leaching waste liquid obtained in step (3) into the heated alkaline leaching filtrate at a rate of 3.6 ml / min, and after the dripping is completed, reacting for 60 minutes, adjusting the pH to 8; the other steps are the same as in Example 1, and cryolite can be obtained.

[0059] The calculated sedimentation rate and purity of cryolite are 80.5% and 78% respectively.

[0060] Example 3

[0061] The difference between Example 2 and Example 1 is that step (4) is different; step (4) in Example 3 is: heating the alkaline leaching solution obtained in step (3) to 70°C, dripping the acid leaching waste liquid obtained in step (3) into the heated alkaline leaching filtrate at a rate of 2.0 ml / min, and after the dripping is completed, reacting for 240 minutes, adjusting the pH to 10; the other steps are the same as in Example 1, and cryolite can be obtained.

[0062] The calculated sedimentation rate and purity of cryolite are 81.4% and 77% respectively.

[0063] Example 4

[0064] The difference between Example 4 and Example 1 is that step (4) is different; step (4) in Example 4 is: heating the alkaline leaching solution obtained in step (3) to 100°C, dripping the acid leaching waste liquid obtained in step (3) into the heated alkaline leaching filtrate at a rate of 5.2 ml / min, and after the dripping is completed, reacting for 60 minutes, adjusting the pH to 8; the other steps are the same as in Example 1, and cryolite can be obtained.

[0065] The calculated sedimentation rate and purity of cryolite are 83.2% and 80% respectively.

[0066] Example 5

[0067] The difference between Example 5 and Example 1 is that step (4) is different; step (4) in Example 5 is: heating the alkaline leaching solution obtained in step (3) to 70°C, dripping the acid leaching waste liquid obtained in step (3) into the heated alkaline leaching filtrate at a rate of 3.6 ml / min, and after the dripping is completed, reacting for 120 minutes, adjusting the pH to 9; the other steps are the same as in Example 1, and cryolite can be obtained.

[0068] The calculated sedimentation rate and purity of cryolite are 95.6% and 97% respectively.

[0069] In addition, the prepared cryolite was subjected to XRD test and compared with the cryolite standard card PDF#70-1606. The results are as follows: Figure 1 As shown, the standard card is the standard diffraction peak data of the substance. By comparing the diffraction peaks of the two, we can see the crystallinity and purity of the prepared cryolite (that is, whether there are impurity peaks, which means that the standard card has no peaks). If the peaks basically match, it means that the purity of the cryolite is relatively high, and the specific purity value of the product can be obtained by calculation.

[0070] Example 6

[0071] The difference between Example 6 and Example 1 is that step (4) is different; step (4) in Example 6 is: heating the alkaline leaching solution obtained in step (3) to 70°C, dripping the acid leaching waste liquid obtained in step (3) into the heated alkaline leaching filtrate at a rate of 5.2 ml / min, and after the dripping is completed, reacting for 180 minutes, adjusting the pH to 9; the other steps are the same as in Example 1, and cryolite can be obtained.

[0072] The calculated sedimentation rate and purity of cryolite are 89.7% and 81% respectively.

[0073] Example 7

[0074] The difference between Example 7 and Example 1 is that step (4) is different; step (4) in Example 7 is: heating the alkaline leaching solution obtained in step (3) to 40°C, dripping the acid leaching waste liquid obtained in step (3) into the heated alkaline leaching filtrate at a rate of 2.0 ml / min, and after the addition is completed, reacting for 120 minutes, adjusting the pH to 10; the other steps are the same as in Example 1, and cryolite can be obtained.

[0075] The calculated sedimentation rate and purity of cryolite are 69.3% and 74% respectively.

[0076] Example 8

[0077] The difference between Example 8 and Example 1 is that step (4) is different; step (4) in Example 8 is: heating the alkaline leaching solution obtained in step (3) to 70°C, dripping the acid leaching waste liquid obtained in step (3) into the heated alkaline leaching filtrate at a rate of 3.6 ml / min, and after the dripping is completed, reacting for 180 minutes, adjusting the pH to 9; the other steps are the same as in Example 1, and cryolite can be obtained.

[0078] The calculated sedimentation rate and purity of cryolite are 94.2% and 94% respectively.

[0079] Example 9

[0080] The difference between Example 9 and Example 5 is that step (4) is different; step (4) of Example 9 is: heating the alkaline leaching solution obtained in step (3) to 70°C, dripping the acid leaching waste liquid obtained in step (3) into the heated alkaline leaching filtrate at a rate of 1.2 ml / min, and after the dripping is completed, reacting for 120 minutes, adjusting the pH to 9; the other steps are the same as in Example 5, and cryolite can be obtained.

[0081] The calculated sedimentation rate and purity of cryolite are 95.3% and 97% respectively.

[0082] Example 10

[0083] The difference between Example 9 and Example 5 is that step (4) is different; step (4) of Example 9 is: heating the alkaline leaching solution obtained in step (3) to 70°C, dripping the acid leaching waste liquid obtained in step (3) into the heated alkaline leaching filtrate at a rate of 6 ml / min, and after the dripping is completed, reacting for 120 minutes, adjusting the pH to 9; the other steps are the same as in Example 5, and cryolite can be obtained.

[0084] The calculated sedimentation rate and purity of cryolite are 91.3% and 85% respectively.

[0085] Comparative Example 1

[0086] The difference between Comparative Example 1 and Example 5 is that step (4) is different; step (4) of Comparative Example 1 is: heating the alkaline leaching solution obtained in step (3) to 70°C, dripping the acid leaching waste liquid obtained in step (3) into the heated alkaline leaching filtrate at a rate of 0.8 ml / min, and after the addition is completed, reacting for 120 minutes, adjusting the pH to 9; the other steps are the same as in Example 5, and cryolite can be obtained.

[0087] The calculated sedimentation rate and purity of cryolite are 94.1% and 95% respectively.

[0088] Comparative Example 2

[0089] The difference between Comparative Example 2 and Example 5 is that step (4) is different; step (4) of Comparative Example 2 is: heating the alkaline leaching solution obtained in step (3) to 70°C, dripping the acid leaching waste liquid obtained in step (3) into the heated alkaline leaching filtrate at a rate of 6.5 ml / min, and after the addition is completed, reacting for 120 minutes, adjusting the pH to 9; the other steps are the same as in Example 5, and cryolite can be obtained.

[0090] The calculated sedimentation rate and purity of cryolite are 90.7% and 84% respectively.

[0091] Comparative Example 3

[0092] The difference between Comparative Example 3 and Example 5 is that step (4) is different; step (4) of Comparative Example 3 is: heating the alkaline leaching solution obtained in step (3) to 70°C, dripping the acid leaching waste liquid obtained in step (3) into the heated alkaline leaching filtrate at a rate of 3.6 ml / min, and after the addition is completed, reacting for 120 minutes, adjusting the pH to 5; the other steps are the same as in Example 5, and cryolite can be obtained.

[0093] The calculated sedimentation rate and purity of cryolite are 52.9% and 63% respectively.

[0094] Comparative Example 4

[0095] The difference between Comparative Example 4 and Example 5 is that step (4) is different; step (4) of Comparative Example 4 is: heating the alkaline leaching solution obtained in step (3) to 70°C, dripping the acid leaching waste liquid obtained in step (3) into the heated alkaline leaching filtrate at a rate of 3.6 ml / min, and after the addition is completed, reacting for 120 minutes, adjusting the pH to 13; the other steps are the same as in Example 5, and cryolite can be obtained.

[0096] The sedimentation rate and purity of cryolite were calculated to be 23.6% and 61% respectively.

[0097] The parameters of step (4) of Examples 1 to 10 and Comparative Examples 1 to 4 and the sedimentation rate and purity data of the prepared cryolite are tabulated in Table 1 below.

[0098] Table 1 Preparation of cryolite in Examples and Comparative Examples

[0099]

[0100]

[0101] From Table 1 above, we can know that:

[0102] By comparing Example 1 and Example 5, it can be seen that when the addition rate of the acid leaching solution is 3.6 ml / min, the pH of the alkaline leaching solution is 9, and the reaction time is the same as 120 min, different reaction temperatures have an effect. When the temperature is 70°C, the sedimentation rate and purity of the prepared cryolite are both higher than 100°C;

[0103] Comparative Examples 5 and 8 show that when the rate of addition of the acid leaching solution is 3.6 ml / min, the pH of the alkaline leaching solution is 9, and the reaction temperature is the same as 70°C, different reaction times have an effect. When the reaction time is extended from 120 min to 180 min, the sedimentation rate decreases slightly and the purity also decreases, indicating that the extension of the reaction time has a certain effect on the sedimentation rate and purity of the prepared ice crystals.

[0104] Comparative Example 5 and Comparative Example 1 show that the addition rate of the acid leaching solution in Comparative Example 1 is reduced from 3.6 ml / min in Example 5 to 0.8 ml / min, and other conditions are the same as in Example 5, and the sedimentation rate and purity of the prepared cryolite are significantly reduced;

[0105] Comparative Examples 5 and 2 show that the addition rate of the acid leaching solution in Comparative Example 1 is increased from 3.6 ml / min in Example 5 to 6.5 ml / min, and other conditions are the same as those in Example 5. The sedimentation rate of the prepared cryolite is significantly increased, but the purity is significantly decreased;

[0106] Comparative Examples 5 and 3 show that the pH of the alkaline leaching solution in Comparative Example 1 is reduced from 9 in Example 5 to 5, and the other conditions are the same as those in Example 5, and the sedimentation rate and purity of the prepared cryolite are greatly reduced;

[0107] From Comparative Examples 5 and 4, it can be seen that the pH of the alkaline leaching solution in Comparative Example 1 is increased from 9 in Example 5 to 13, and other conditions are the same as those in Example 5. The sedimentation rate and purity of the prepared cryolite are greatly reduced.

[0108] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be covered by the scope of the claims of the present invention.

Claims

1. A method for preparing cryolite, characterized in that: include: (1) mixing an electrolyte and an alkali to obtain an alkali leaching solution; mixing carbon powder and an acid to obtain an acid leaching solution; (2) adding the acid leaching solution into the alkaline leaching solution to react and obtain cryolite; Wherein, in step (1), the electrolyte comprises sodium fluoride and aluminum oxide; In step (2), the rate at which the acid leaching solution is added to the alkaline leaching solution is 1.2 ml / min-6 ml / min.

2. The preparation method according to claim 1, characterized in that: The preparation method meets one or more combinations of the following conditions: (a) After the alkaline leaching solution is adjusted in temperature, the acid leaching solution is added, and the temperature of the alkaline leaching solution is adjusted to 20°C-100°C; (b) The electrolyte is obtained by separating the waste cathode carbon blocks from electrolytic aluminum; (c) after the reaction in step (2) is completed, adjusting the pH value to 6-12; (d) In step (2), the reaction time is 20 min to 360 min.

3. The preparation method according to claim 2, characterized in that: The method for separating the electrolyte from the waste cathode carbon blocks of electrolytic aluminum comprises: crushing the waste cathode carbon blocks of electrolytic aluminum, slurry mixing, flotation, and separation to obtain the electrolyte.

4. The preparation method according to claim 3, characterized in that: The method for obtaining electrolyte by separating waste cathode carbon blocks from electrolytic aluminum meets one or more combinations of the following conditions: (a) The particle size after crushing is D90 of 50 μm-95 μm; (b) After crushing, the mass proportion of 200-mesh particles is 65%-90%; (c) the concentration of the slurry after slurry adjustment is 15%-30%; (d) Flotation: A flotation machine is used for flotation. The speed of the flotation machine is 1600r / min-2200r / min and the air volume is 0.1m 2 / h-0.3m 2 / h, scraper speed is 15r / min-30r / min; (e) Add flotation agent during flotation.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The rate of adding the acid leaching solution into the alkaline leaching solution is 2ml / min-5.2ml / min.

6. The preparation method according to any one of claims 1 to 4, characterized in that: The preparation method meets one or more combinations of the following conditions: (a) The temperature at which the electrolyte and the alkali are mixed is 70°C to 100°C; (b) the time for mixing the electrolyte and the alkali is 30 min to 180 min; (c) In the alkaline leaching solution, the solid-liquid ratio is 1:8-1:18; (d) the base is selected from sodium hydroxide and / or potassium hydroxide; (e) the temperature at which the carbon powder and the acid are mixed is 70°C to 100°C; (f) the mixing time of the carbon powder and the acid is 30 min to 180 min; (g) In the acid leaching solution, the solid-liquid ratio is 1:4-1:12; (h) The acid is selected from hydrochloric acid and / or hydrofluoric acid.

7. The preparation method according to claim 6, characterized in that: The rate of adding the acid leaching solution into the alkaline leaching solution is 2ml / min-5.2ml / min.

8. Cryolite, characterized in that The compound is prepared by the preparation method according to any one of claims 1 to 7.

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