Method for preparing ultrapure coal by chemical method and recovering waste liquid

Abstract

The invention provides a method for preparing ultra-pure coal by using a chemical method and recovering waste liquid, which comprises the following steps: mixing coal with an alkaline solution, carrying out alkali dissolution treatment, and carrying out solid-liquid separation to obtain alkali dissolution filter residues; mixing the alkali-soluble filter residues with water, carrying out dealkalization treatment, and carrying out solid-liquid separation to obtain dealkalized filter residues; mixing the dealkalized filter residues with an acid solution, carrying out acid dissolution treatment, and carrying out solid-liquid separation to obtain acid-dissolved filter residues; and drying the acid-soluble filter residues to obtain the ultra-pure coal. Wherein the alkaline solution comprises sodium ions, calcium ions and hydroxyl ions, the molar ratio of the sodium ions to the aluminum element in the coal is (18-30): 1, the molar ratio of the calcium ions to the silicon element in the coal is (1.0-1.1): 1, and the concentration of the hydroxyl ions is 15-18 mol / L. According to the method provided by the invention, not only is the ultra-pure coal with relatively low ash content prepared, but also the removal rate of aluminum in the coal is increased, and aluminum recovery is realized; the consumption of the alkaline solution is reduced, and the cost is reduced.

Description

Technical Field

[0001] The present invention relates to the field of coal deashing, and in particular to a method for preparing ultra-pure coal and recovering waste liquid by chemical method. Background Art

[0002] China has large coal reserves and complex types of coal. At this stage, the way coal is used has changed from direct fuel use to the use of both chemical raw materials and fuel. The ash content in coal has, to a certain extent, restricted the depth of clean transformation and utilization of coal and the breadth of its application.

[0003] Ultra-pure coal refers to ultra-low ash coal with an ash content of <1% after deep deashing by physical or chemical methods. Ultra-pure coal has the characteristics of high calorific value, low pollution and low ash residue. The combustible slurry made from ultra-pure coal pulverization can replace heavy oil for power generation or transportation industries. Ultra-pure coal can be used to prepare carbon-based materials, such as porous carbon materials, anode materials for aluminum smelting, electrodes, graphene, etc., and has broad application prospects.

[0004] The existing coal deashing methods are mainly physical and chemical methods. Physical methods include jigging, flotation, gravity separation, OTP method and oil agglomeration-flotation method. Physical methods are generally only suitable for preliminary deashing of raw coal, and it is difficult to meet the requirements for the preparation of ultra-pure coal (ash content <1-3%). Chemical methods achieve deashing through the reaction of chemical agents with mineral components in coal, such as hydrofluoric acid method, conventional acid-base method and molten alkali leaching method. Among them, the conventional acid-base method is the most widely used method. Its basic principle is: alkaline solution reacts with inorganic minerals under certain conditions, and then acid is used to leach to form inorganic compounds, and the coal and organic matter are separated by filtration and washing. Patent CN107892971A discloses a process for preparing ultra-pure coal using a physical-chemical method for anthracite. The method uses a conventional acid-base method to purify anthracite with a high coalification degree. The ash content of the ultra-pure coal obtained by this method is still relatively high (1.85wt%), and it cannot be used for purifying coal with a low coalification degree (bituminous coal, lignite). When this method is used to deash bituminous coal and lignite with a low coalification degree, the consumption of alkali and acid is large, and the aluminum in the inorganic components of the coal cannot be recovered, resulting in high process costs.

[0005] Therefore, there is an urgent need to develop a method that can purify high-ash coal to prepare ultra-pure coal and recover aluminum. Summary of the invention

[0006] The main purpose of the present invention is to provide a method for preparing ultra-pure coal and recycling waste liquid by chemical method, so as to solve the problems of difficult recovery of aluminum in coal, large consumption of alkaline solution and acid solution and high process cost in the prior art when preparing ultra-pure coal.

[0007] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, a method for preparing ultra-pure coal and recovering waste liquid by chemical method is provided, comprising the following steps: step S1, mixing coal with an alkaline solution, and sequentially performing alkaline dissolution treatment and solid-liquid separation to obtain an alkaline soluble filtrate and an alkaline soluble filter residue; wherein the alkaline solution comprises sodium ions, calcium ions and hydroxide ions, the molar ratio of sodium ions to aluminum elements in coal is 18 to 30:1, the molar ratio of calcium ions to silicon elements in coal is 1.0 to 1.1:1, and the concentration of hydroxide ions is 15 to 18 mol / L; step S2, mixing the alkaline soluble filter residue with water, sequentially performing dealkalization treatment and solid-liquid separation to obtain a dealkalized filtrate and a dealkalized filter residue; step S3, mixing the dealkalized filter residue with an acidic solution, sequentially performing acid dissolution treatment and solid-liquid separation to obtain an acid soluble filtrate and an acid soluble filter residue; step S4, drying the acid soluble filter residue to obtain ultra-pure coal.

[0008] Furthermore, in step S1, the sodium ions are derived from a sodium-containing compound, and the sodium-containing compound is selected from sodium hydroxide.

[0009] Furthermore, in step S1, the calcium ions are derived from a calcium-containing compound, and the calcium-containing compound is selected from at least one of calcium oxide and calcium hydroxide, and is further calcium hydroxide.

[0010] Furthermore, in step S1, the temperature of the alkali dissolution treatment is 240-280° C., and the time of the alkali dissolution treatment is 1-3 hours.

[0011] Furthermore, in step S2, the temperature of the dealkalization treatment is 60-100° C., and the time of the dealkalization treatment is 1-3 hours.

[0012] Furthermore, in step S3, the concentration of the acidic solution is 0.5 to 2.5 mol / L.

[0013] Further, in step S3, the acidic solution includes at least one of a hydrochloric acid solution and a nitric acid solution, and further is a hydrochloric acid solution.

[0014] Furthermore, in step S3, the mass ratio of the dealkalization residue to the acidic solution is 1:4-8.

[0015] Furthermore, in step S3, the temperature of the acid dissolution treatment is 50 to 90° C., and the time of the acid dissolution treatment is 1.5 to 4.0 hours.

[0016] Furthermore, step S2 includes step S21 and step S22: step S21, mixing the alkali-soluble filter residue with water, and sequentially performing washing treatment and solid-liquid separation to obtain a washing filtrate and a washing filter residue; step S22, mixing the washing filter residue with water, and sequentially performing dealkalization treatment and solid-liquid separation to obtain a dealkalization filtrate and a dealkalization filter residue.

[0017] Furthermore, the method also includes waste liquid recovery, which includes: mixing the alkaline filtrate, the washing filtrate and the dealkalization filtrate, and concentrating the filtrate to obtain a concentrated solution. If the aluminum ion concentration in the concentrated solution is ≥60 g / L, the concentrated solution is used to prepare alumina through the Bayer process; if the aluminum ion concentration in the concentrated solution is <60 g / L, returning to step (1) to mix with the alkaline solution for alkaline dissolution treatment.

[0018] The technical solution of the present invention is applied to mix coal with an alkaline solution containing calcium ions, sodium ions and hydroxide ions for alkaline dissolution treatment, so that the aluminum in the coal reacts with the sodium ions and hydroxide ions in the alkaline solution to generate soluble sodium tetrahydroxyaluminate (NaAl(OH) 4 ), the silicon in the coal reacts with the calcium ions, sodium ions and hydroxide ions in the alkaline solution to form insoluble calcium sodium hydrogen silicate (CaNaHSiO 4 ), solid-liquid separation, to obtain an alkali-soluble filtrate containing sodium tetrahydroxyaluminate and an alkali-soluble filter residue containing sodium calcium hydrogen silicate. The alkali-soluble filter residue is mixed with water for dealkalization treatment to decompose the sodium calcium hydrogen silicate into calcium silicate and sodium hydroxide. After solid-liquid separation, the sodium hydroxide is dissolved in the dealkalization filtrate, and the calcium silicate is attached to the dealkalization filter residue. The dealkalization filter residue is then mixed with an acidic solution for acid dissolution treatment, so that the calcium silicate in the dealkalization filter residue reacts with the acidic solution to generate silicic acid and soluble calcium salts. The silicon and calcium impurities in the dealkalization filter residue are removed by solid-liquid separation to obtain an acid-soluble filter residue. The acid-soluble filter residue is dried to obtain ultra-pure coal with a low ash content.

[0019] In addition, the present application recovers the alkali-soluble filtrate and the dealkalization filtrate from the waste liquid, thereby realizing the recovery of aluminum and sodium. The alkali-soluble filtrate and the dealkalization filtrate are collected, mixed and concentrated, and when the aluminum ion concentration in the concentrated solution is ≥60g / L, alumina is prepared by the Bayer process; when the aluminum ion concentration in the concentrated solution is <60g / L, the process returns to step (1) for alkali dissolution treatment. The method provided by the present application can also save the consumption of alkali solution, acid solution and water, and reduce process costs. DETAILED DESCRIPTION

[0020] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail with reference to the embodiments below.

[0021] As analyzed in the background technology of this application, in the prior art, when preparing ultra-pure coal, there are problems such as difficulty in recovering aluminum in coal, large consumption of alkaline solution and acid solution, and high process cost. In order to solve this problem, this application provides a method for preparing ultra-pure coal and recovering waste liquid by chemical method.

[0022] In a typical embodiment of the present application, a method for preparing ultra-pure coal and recovering waste liquid by chemical method is provided, comprising the following steps: step S1, mixing coal with an alkaline solution, and sequentially performing alkaline dissolution treatment and solid-liquid separation to obtain an alkaline soluble filtrate and an alkaline soluble filter residue; wherein the alkaline solution comprises sodium ions, calcium ions and hydroxide ions, the molar ratio of sodium ions to aluminum elements in coal is 18 to 30:1, the molar ratio of calcium ions to silicon elements in coal is 1.0 to 1.1:1, and the concentration of hydroxide ions is 15 to 18 mol / L; step S2, mixing the alkaline soluble filter residue with water, sequentially performing dealkalization treatment and solid-liquid separation to obtain a dealkalized filtrate and a dealkalized filter residue; step S3, mixing the dealkalized filter residue with an acidic solution, sequentially performing acid dissolution treatment and solid-liquid separation to obtain an acid soluble filtrate and an acid soluble filter residue; step S4, drying the acid soluble filter residue to obtain ultra-pure coal.

[0023] In the present application, calcium ions include calcium components of all calcium-containing compounds in the alkaline solution, and hydroxide includes hydroxides of all hydroxide-containing compounds in the alkaline solution.

[0024] The present invention mixes coal with an alkaline solution containing calcium ions, sodium ions and hydroxide ions for alkaline dissolution treatment, so that the aluminum in the coal reacts with the sodium ions and hydroxide ions in the alkaline solution to generate soluble sodium tetrahydroxyaluminate (NaAl(OH) 4 ), the silicon in the coal reacts with the calcium ions, sodium ions and hydroxide ions in the alkaline solution to form insoluble calcium sodium hydrogen silicate (CaNaHSiO 4 ), solid-liquid separation, to obtain an alkali-soluble filtrate containing sodium tetrahydroxyaluminate and an alkali-soluble filter residue containing sodium calcium hydrogen silicate. The alkali-soluble filter residue is mixed with water for dealkalization treatment to decompose the sodium calcium hydrogen silicate into calcium silicate and sodium hydroxide. After solid-liquid separation, the sodium hydroxide is dissolved in the dealkalization filtrate, and the calcium silicate is attached to the dealkalization filter residue. The dealkalization filter residue is then mixed with an acidic solution for acid dissolution treatment, so that the calcium silicate in the dealkalization filter residue reacts with the acidic solution to generate silicic acid and soluble calcium salts. The silicon and calcium impurities in the dealkalization filter residue are removed by solid-liquid separation to obtain an acid-soluble filter residue. The acid-soluble filter residue is dried to obtain ultra-pure coal with a low ash content.

[0025] In addition, the present application realizes the recovery of aluminum and sodium by recycling the alkali-soluble filtrate and the dealkalization filtrate through waste liquid. The alkali-soluble filtrate and the dealkalization filtrate are collected, mixed and concentrated, and when the aluminum ion concentration in the concentrated solution is ≥60g / L, alumina is prepared by the Bayer process; when the aluminum ion concentration in the concentrated solution is <60g / L, the process returns to step (1) for alkali dissolution treatment. The method provided by the present application can also save the consumption of alkali solution, acid solution and water, and reduce process costs.

[0026] Typically but not limitatively, in the method for preparing ultra-pure coal and recovering waste liquid by chemical method provided in the present application, the molar ratio of sodium ions to aluminum elements in coal is 18:1, 20:1, 22:1, 24:1, 26:1, 28:1, 30:1 or a range consisting of any two values; the molar ratio of calcium ions to silicon elements in coal is 1.0:1, 1.02:1, 1.04:1, 1.05:1, 1.06:1, 1.08:1, 1.1:1 or a range consisting of any two values; the concentration of hydroxide ions is 15 mol / L, 15.5 mol / L, 16 mol / L, 16.5 mol / L, 17 mol / L, 17.5 mol / L, 18 mol / L or a range consisting of any two values.

[0027] In step S1, the coal is mixed with an alkaline solution for alkaline dissolution treatment. During this process, the coal and the alkaline solution undergo a first chemical reaction to leach out the silicon and aluminum components in the coal, reduce the coal ash content, and create favorable conditions for the recovery of aluminum in the subsequent process. The inorganic component aluminum in the coal reacts chemically with the sodium ions and hydroxide ions in the alkaline solution to generate soluble sodium tetrahydroxyaluminate (NaAl(OH) 4 ), the inorganic component silicon in coal reacts chemically with sodium ions, calcium ions, and hydroxide ions in alkaline solution to form insoluble calcium sodium hydrogen silicate (CaNaHSiO 4 ), solid-liquid separation, so that most of the aluminum is removed from the coal and dissolved in the alkaline filtrate, and silicon is attached to the alkaline filtrate residue in the form of sodium calcium hydrogen silicate.

[0028] The chemical reaction equation in step S1 is as follows:

[0029] 2SiO 2 ·Al 2 O 3 +4NaOH+2Ca(OH) 2 +H 2 O=2NaCaHSiO 4 +2NaAl(OH) 4 Al 2 O 3 +4NaOH+H 2 O=2NaAl(OH) 4

[0030] In some embodiments, the molar ratio of alkali metal elements to aluminum elements in coal, the molar ratio of alkaline earth metal elements to silicon elements in coal, and the concentration of hydroxide can be calculated according to the above chemical reaction equation, and the amount of alkaline solution can be adaptively adjusted to more efficiently achieve the conversion of aluminum components into sodium tetrahydroxyaluminate and the conversion of silicon components into sodium calcium hydrogen silicate.

[0031] In some embodiments, the calcium ions in the alkaline solution are derived from calcium-containing compounds. In order to more efficiently leach the silicon and aluminum components in the coal and recover the aluminum and sodium in the filtrate, the calcium-containing compound is selected from any one or more of calcium oxide and calcium hydroxide, preferably calcium hydroxide.

[0032] In some embodiments, the sodium ions in the alkaline solution are derived from sodium-containing compounds. In order to more efficiently leach silicon and aluminum components from the coal and recover aluminum and sodium in the filtrate, the sodium-containing compound is selected from sodium hydroxide.

[0033] In the present application, the source of the hydroxide ions in the alkaline solution is not specifically limited, and it only needs to provide an alkaline environment for the reaction in step S1, including but not limited to a hydroxide-containing base.

[0034] In some embodiments, the alkali metal element further includes potassium, and preferably the potassium element comes from a potassium-containing compound, and the potassium-containing compound is selected from potassium hydroxide.

[0035] In some embodiments, the temperature of the alkali dissolution treatment is 240-280°C, and the time of the alkali dissolution treatment is 1-3 hours, so as to further improve the leaching of silicon and aluminum components. If the temperature of the alkali dissolution treatment in step S1 is too low, the aluminum and silicon components in the coal will not react fully with the alkaline solution, and it will be difficult to convert the aluminum component into sodium tetrahydroxyaluminate (NaAl(OH) 4 ), the silicon component is converted into calcium sodium hydrogen silicate (CaNaHSiO 4 ); If the temperature of the alkaline dissolution treatment is too high, it will place stringent requirements on the reaction equipment.

[0036] Typically but not limiting, the temperature of the alkali dissolution treatment is 240°C, 250°C, 260°C, 270°C, 280°C or a range consisting of any two values; the time of the alkali dissolution treatment is 1h, 1.5h, 2h, 2.5h, 3h or a range consisting of any two values.

[0037] In step S2, the alkali-soluble filter residue is mixed with water for dealkalization treatment. The alkali-soluble filter residue undergoes a second chemical reaction in a dilute alkaline aqueous solution environment to decompose the sodium calcium hydrogen silicate in the alkali-soluble filter residue to generate calcium silicate precipitate and sodium hydroxide. The reaction equation is as follows: NaCaHSiO 4 =NaOH+CaSiO 3 After solid-liquid separation, the decomposed sodium hydroxide is dissolved in the dealkalization filtrate, while the calcium silicate is attached to the dealkalization residue.

[0038] In some embodiments, the temperature of the dealkalization treatment is 60 to 100° C., and the time of the dealkalization treatment is 1 to 3 hours, so as to efficiently decompose sodium calcium hydrogen silicate to generate sodium hydroxide and reduce energy consumption. The decomposition reaction of sodium calcium hydrogen silicate occurs in a dilute alkaline aqueous solution. If the temperature of the dealkalization treatment is too low, the decomposition reaction rate will be low and the decomposition of sodium calcium hydrogen silicate will not be sufficient; if the temperature of the dealkalization treatment is too high, the energy consumption will increase, and the reaction rate will not increase significantly.

[0039] Typically but not limiting, the temperature of the dealkalization treatment is 60°C, 70°C, 80°C, 90°C, 100°C or a range consisting of any two values; the time of the dealkalization treatment is 1h, 1.5h, 2h, 2.5h, 3h or a range consisting of any two values.

[0040] In some embodiments, step S2 includes step S21 and step S22. In step S21, the alkali-soluble filter residue is mixed with water and subjected to washing treatment and solid-liquid separation in sequence to obtain washing filtrate and washing filter residue. The washing treatment further reduces the impurities on the surface of the alkali-soluble filter residue, thereby increasing the decomposition rate of sodium calcium hydrogen silicate in the filter residue; in step S22, the washing filter residue is mixed with water and subjected to dealkalization treatment and solid-liquid separation in sequence to obtain dealkalization filtrate and dealkalization filter residue. In order to be more conducive to dealkalization treatment, dealkalization treatment is carried out after washing treatment, which can further reduce energy consumption and promote the decomposition of sodium calcium hydrogen silicate.

[0041] In step S3, the de-alkali residue is mixed with an acid solution for acid dissolution treatment, and the de-alkali residue and the acid solution undergo a third chemical reaction, so that the calcium silicate in the de-alkali residue reacts with the acid solution to generate silicic acid and soluble calcium salts, and then the silicic acid and soluble calcium salts in the de-alkali residue are removed by solid-liquid separation to obtain an acid-soluble residue. The reaction equation is:

[0042]

[0043] In some embodiments, in step S3, the acidic solution includes any one or more of a hydrochloric acid solution and a nitric acid solution, and is more preferably a hydrochloric acid solution. The acidic solution can convert the silicon and calcium components in the dealkalization residue into silicic acid and soluble calcium salts, which are then removed by solid-liquid separation, thereby further reducing the ash content in the coal.

[0044] In some embodiments, the concentration of the acidic solution is 0.5-2.5 mol / L, so as to further increase the reaction rate between the calcium silicate in the dealkalized filter residue and the acidic solution, thereby further reducing the ash content in the coal.

[0045] Typically but not limiting, the concentration of the acidic solution is 0.5 mol / L, 1.0 mol / L, 1.5 mol / L, 2.0 mol / L, 2.5 mol / L or a range consisting of any two values.

[0046] The mass ratio of the dealkalized filter residue to the acid solution in the acid dissolution treatment can be obtained according to the stoichiometry of the reaction equation, and the amount of the acid solution can be adaptively adjusted to fully convert the silicon and calcium components in the dealkalized filter residue into silicic acid and soluble calcium salts. In the present application, the mass ratio of the dealkalized filter residue to the acid solution is preferably 1:4-8.

[0047] Typically but not limiting, the mass ratio of dealkalization residue to acidic solution is 1:4, 1:5, 1:6, 1:7, 1:8 or a range consisting of any two values.

[0048] In some embodiments, the temperature of the acid dissolution treatment is 50-90°C, and the time of the acid dissolution treatment is 1.5-4.0 hours, so as to further improve the removal rate of silicon and calcium components in the dealkalization filter residue and reduce the ash content in the coal. The time of the acid dissolution treatment has an impact on the ash content in the coal. When the acid dissolution treatment time is too short or the temperature is too low, the calcium silicate in the dealkalization filter residue will not react fully with the acidic solution, which will lead to low removal rates of silicon and calcium components and increased ash in the coal; when the acid dissolution treatment time is too long or the temperature is too high, the filtration efficiency of silicate will be low, and the ash content in the coal will also increase.

[0049] Typically but not limiting, the temperature of the acid dissolution treatment is 50°C, 60°C, 70°C, 80°C, 90°C or a range consisting of any two values; the time of the acid dissolution treatment is 1.5h, 2.0h, 2.5h, 3.0h, 4.0h or a range consisting of any two values.

[0050] In step S4, the acid-soluble filter residue is dried to obtain ultra-pure coal. The drying method is not limited in the present application, and any drying method commonly used in the art that can remove moisture from the acid-soluble filter residue can be used.

[0051] In some embodiments, the method provided in the present application also includes waste liquid recovery, and the waste liquid recovery includes: mixing the above-mentioned alkaline filtrate, washing filtrate and dealkalization filtrate, and concentrating them to obtain a concentrated solution. If the aluminum ion concentration in the concentrated solution is ≥60g / L, the concentrated solution is prepared by the Bayer process to obtain alumina; if the aluminum ion concentration in the concentrated solution is <60g / L, returning to step (1) and mixing with the alkaline solution to perform the alkaline dissolution treatment.

[0052] The alkali-soluble filtrate, the washing filtrate, and the dealkalization filtrate contain a large amount of sodium, aluminum, and hydroxide. The waste filtrate is recovered and concentrated to make the sodium and hydroxide in the concentrated solution reach the required concentration in step (1). The concentrated solution is then returned to step (1) and mixed with the alkaline solution for alkali dissolution treatment, thereby realizing the recovery and recycling of sodium, saving costs, and reducing environmental pollution. In addition, the concentrated solution can be used to prepare aluminum oxide by the Bayer process. In order to improve the production efficiency of aluminum oxide prepared by the Bayer process, the concentrated solution is circulated multiple times to increase the concentration of aluminum ions in the solution. When the concentration of aluminum ions in the concentrated solution is ≥60 g / L, aluminum oxide is prepared by the Bayer process, thereby realizing aluminum recovery.

[0053] Sodium in alkaline solution can be converted into sodium tetrahydroxyaluminate (NaAl(OH) 4 ) is recovered in the form of an alkaline filtrate, or in the form of sodium calcium hydrogen silicate, which is recovered by washing and dealkalization to form NaOH dissolved in the washing filtrate and dealkalization filtrate. However, since the dealkalization filter residue is mixed with the acidic solution, the sodium is dissolved in the acid filtrate in the form of sodium salt, and this part of the sodium cannot be recycled and is the lost sodium.

[0054] The beneficial effects of the present application will be further illustrated below in combination with embodiments and comparative examples.

[0055] Example 1

[0056] (1) Calcium hydroxide and sodium hydroxide are dissolved in water to obtain an alkaline solution, and then coal is added and stirred to make the molar ratio of sodium ions in the alkaline solution to aluminum elements in the coal be 26:1, the molar ratio of calcium ions in the alkaline solution to silicon elements in the coal be 1.05:1, and the concentration of hydroxide in the alkaline solution be 17 mol / L. Then, alkaline solution is treated for 3 hours at a temperature of 270° C., and an alkaline filtrate and an alkaline filtrate residue are obtained after filtration and separation;

[0057] (2) mixing the alkali-soluble filter residue and water in a mass ratio of 1:3, stirring evenly, filtering and separating, and obtaining a washing filtrate and a washing filter residue;

[0058] (3) mixing the washed filter residue with water in a mass ratio of 1:3, and then subjecting the mixture to dealkalization treatment at a temperature of 100° C. for 3 h, and filtering and separating to obtain a dealkalization filtrate and a dealkalization filter residue;

[0059] (4) The dealkalized filter residue is mixed with a hydrochloric acid solution having a concentration of 2 mol / L and stirred, and then acid-dissolved for 2.5 h at a temperature of 60° C., filtered and separated to obtain an acid-dissolved filtrate and an acid-dissolved filter residue, wherein the mass ratio of the dealkalized filter residue to the hydrochloric acid solution is 1:6.

[0060] (5) Dry the acid-soluble filter residue at 60°C for 4 hours to obtain ultra-pure coal.

[0061] (6) collecting the alkaline filtrate, washing filtrate and dealkalization filtrate, mixing them and concentrating the mass concentration of sodium hydroxide to 45 wt % by evaporation; returning the concentrated solution to step (1) and mixing it with the alkaline solution to carry out alkaline dissolution treatment; the cycle is repeated 5 times until the aluminum concentration in the concentrated solution increases to 60 g / L, and alumina is prepared by the Bayer process.

[0062] The coal comes from the Jungar mining area in Ordos, Inner Mongolia. Its components and component contents are shown in Table 1:

[0063] Table 1

[0064]

[0065] Example 2

[0066] The difference from Example 1 is that Example 2 adjusts the dosage of calcium hydroxide, sodium hydroxide and coal, so that the molar ratio of sodium ions in the alkaline solution to the aluminum element in the coal is 30:1, the molar ratio of calcium ions in the alkaline solution to the silicon element in the coal is 1.10:1, and the concentration of hydroxide in the alkaline solution is 18 mol / L.

[0067] Example 3

[0068] The difference from Example 1 is that Example 3 adjusts the dosage of calcium hydroxide, sodium hydroxide and coal, so that the molar ratio of sodium ions in the alkaline solution to the aluminum element in the coal is 18:1, the molar ratio of calcium ions in the alkaline solution to the silicon element in the coal is 1.00:1, and the concentration of hydroxide in the alkaline solution is 15 mol / L.

[0069] Example 4

[0070] The difference from Example 1 is that Example 4 adjusts the conditions of the alkali dissolution treatment in step (1) so that the temperature of the alkali dissolution treatment is 240° C. and the time of the alkali dissolution treatment is 3 hours.

[0071] Example 5

[0072] The difference from Example 1 is that Example 5 adjusts the conditions of the alkali dissolution treatment in step (1) so that the temperature of the alkali dissolution treatment is 280° C. and the time of the alkali dissolution treatment is 1 hour.

[0073] Example 6

[0074] The difference from Example 1 is that Example 6 adjusts the temperature of the alkali dissolution treatment in step (1) so that the temperature of the alkali dissolution treatment is 180°C.

[0075] Example 7

[0076] The difference from Example 1 is that Example 7 adjusts the temperature of the alkali dissolution treatment in step (1) so that the temperature of the alkali dissolution treatment is 350°C.

[0077] Example 8

[0078] The difference from Example 1 is that Example 8 adjusts the conditions of the dealkalization treatment in step (3) so that the temperature of the dealkalization treatment is 60° C. and the time of the dealkalization treatment is 3 hours.

[0079] Example 9

[0080] The difference from Example 1 is that Example 9 adjusts the conditions of the dealkalization treatment in step (3) so that the temperature of the dealkalization treatment is 100° C. and the time of the dealkalization treatment is 1 hour.

[0081] Example 10

[0082] The difference from Example 1 is that Example 10 adjusts the temperature of the dealkalization treatment in step (3) so that the temperature of the dealkalization treatment is 30°C.

[0083] Embodiment 11

[0084] The difference from Example 1 is that Example 11 adjusts the temperature of the dealkalization treatment in step (3) so that the temperature of the dealkalization treatment is 150°C.

[0085] Example 12

[0086] The difference from Example 1 is that Example 12 adjusts the conditions of the acid dissolution treatment in step (4) so ​​that the temperature of the acid dissolution treatment is 50° C. and the time of the acid dissolution treatment is 4 hours.

[0087] Embodiment 13

[0088] The difference from Example 1 is that Example 13 adjusts the conditions of the acid dissolution treatment in step (4) so ​​that the temperature of the acid dissolution treatment is 90° C. and the time of the acid dissolution treatment is 1.5 h.

[0089] Embodiment 14

[0090] The difference from Example 1 is that Example 14 adjusts the temperature of the acid dissolution treatment in step (4) so ​​that the temperature of the acid dissolution treatment is 25°C.

[0091] Embodiment 15

[0092] The difference from Example 1 is that Example 15 adjusts the temperature of the acid dissolution treatment in step (4) so ​​that the temperature of the acid dissolution treatment is 140°C.

[0093] Comparative Example 1

[0094] The difference from Example 1 is that in Comparative Example 1, the amounts of calcium hydroxide, sodium hydroxide and coal are adjusted so that the molar ratio of sodium ions in the alkaline solution to the aluminum element in the coal is 20:1, the molar ratio of calcium ions in the alkaline solution to the silicon element in the coal is 0.50:1, and the concentration of hydroxide in the alkaline solution is 10 mol / L.

[0095] Comparative Example 2

[0096] The difference from Example 1 is that in Comparative Example 2, the amounts of calcium hydroxide, sodium hydroxide and coal are adjusted so that the molar ratio of sodium ions in the alkaline solution to the aluminum element in the coal is 40:1, the molar ratio of calcium ions in the alkaline solution to the silicon element in the coal is 3.00:1, and the concentration of hydroxide in the alkaline solution is 19 mol / L.

[0097] Comparative Example 3

[0098] The difference from Example 1 is that in Comparative Example 3, only sodium hydroxide is added, so that the molar ratio of sodium ions in the alkaline solution to aluminum elements in the coal is 26:1, and the concentration of hydroxide in the alkaline solution is 17 mol / L.

[0099] Comparative Example 4

[0100] The difference from Example 1 is that in Comparative Example 4, only calcium hydroxide is added, so that the molar ratio of calcium ions in the alkaline solution to silicon elements in the coal is 1.05:1, and the concentration of hydroxide in the alkaline solution is 4 mol / L.

[0101] Test example

[0102] The ash content in the ultrapure coal provided in the test examples and comparative examples was tested, and the aluminum leaching rate in the coal and the amount of NaOH loss per kilogram of coal were tested and calculated. The results are shown in Table 2.

[0103] 1. Test the ash content in ultra-pure coal according to GB / T 30732-2014 "Industrial Analysis Methods for Coal - Instrumental Methods".

[0104] 2. Aluminum leaching rate in coal = (aluminum content in alkaline filtrate / aluminum content in coal) × 100%, where the aluminum content in the alkaline filtrate is measured according to GB / T 6730.63-2024 "Determination of aluminum, calcium, magnesium, manganese, phosphorus, silicon and titanium contents in iron ore - Inductively coupled plasma optical emission spectrometry".

[0105] 3. The amount of NaOH loss per kg of coal = (Na in acid filtrate + mass of Na / relative atomic mass of Na)×relative molecular mass of NaOH.

[0106] Table 2

[0107]

[0108]

[0109] It can be seen from the experimental data of Examples 1-3 and Comparative Examples 1-4 that when the alkaline solution includes sodium ions, calcium ions and hydroxide ions, and the molar ratio of sodium ions to aluminum in coal is 18 to 30:1, the molar ratio of calcium ions to silicon in coal is 1.0 to 1.1:1, and the concentration of hydroxide ions is 15 to 18 mol / L, the ash content in coal is reduced by the method of the present application, and ultra-pure coal with a low ash content is obtained, and Al in coal carbon can have a higher leaching rate, and aluminum recovery is achieved. The NaOH loss per kilogram of coal carbon is also low, so that sodium also achieves a high recovery rate. When the components in the alkaline solution are changed or the component content is changed, the ash content in the coal is higher, the leaching rate of Al in the coal carbon is significantly reduced, and aluminum is difficult to recover; the NaOH loss per kilogram of coal carbon increases, and the recovery rate of sodium is also reduced.

[0110] It can be seen from the experimental data of Examples 4-7 that when the temperature of the alkali dissolution treatment is 240-280°C and the time of the alkali dissolution treatment is 1-3 hours, ultra-pure coal with a low ash content can be obtained, and the leaching rate of Al in the coal is high, and aluminum recovery is achieved. When the temperature of the alkali dissolution treatment is low, the leaching rate of Al in the coal is significantly reduced, and the ash content increases. When the temperature of the alkali dissolution treatment is high, although the ultra-pure coal obtained has a low ash content, the equipment requirements are high at the same time, which increases the operating cost.

[0111] It can be seen from the experimental data of Examples 8-11 that when the dealkalization treatment temperature is 60-100°C and the dealkalization treatment time is 1-3 hours, ultra-pure coal with a low ash content can be obtained. When the dealkalization treatment temperature is too high or too low, the ash content in the coal increases.

[0112] It can be seen from the experimental data of Examples 12-15 that when the acid dissolution treatment temperature is 50-90°C and the acid dissolution treatment time is 1.5-4.0 hours, ultra-pure coal with a low ash content can be obtained. When the acid dissolution treatment temperature is too high or too low, the ash content in the coal increases.

[0113] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0114] The present invention mixes coal with an alkaline solution containing calcium ions, sodium ions and hydroxide ions for alkaline dissolution treatment, so that the aluminum in the coal reacts with the sodium ions and hydroxide ions in the alkaline solution to generate soluble sodium tetrahydroxyaluminate (NaAl(OH) 4), the silicon in the coal reacts with the calcium ions, sodium ions and hydroxide ions in the alkaline solution to form insoluble calcium sodium hydrogen silicate (CaNaHSiO 4 ), solid-liquid separation, to obtain an alkali-soluble filtrate containing sodium tetrahydroxyaluminate and an alkali-soluble filter residue containing sodium calcium hydrogen silicate. The alkali-soluble filter residue is mixed with water for dealkalization treatment to decompose the sodium calcium hydrogen silicate into calcium silicate and sodium hydroxide. After solid-liquid separation, the sodium hydroxide is dissolved in the dealkalization filtrate, and the calcium silicate is attached to the dealkalization filter residue. The dealkalization filter residue is then mixed with an acidic solution for acid dissolution treatment, so that the calcium silicate in the dealkalization filter residue reacts with the acidic solution to generate silicic acid and soluble calcium salts. The silicon and calcium impurities in the dealkalization filter residue are removed by solid-liquid separation to obtain an acid-soluble filter residue. The acid-soluble filter residue is dried to obtain ultra-pure coal with a low ash content.

[0115] At the same time, the present application recovers the alkali-soluble filtrate and the dealkalization filtrate through waste liquid, thereby realizing the recovery of aluminum and sodium. The alkali-soluble filtrate and the dealkalization filtrate are collected, mixed and concentrated, and when the aluminum ion concentration in the concentrated solution is ≥60g / L, alumina is prepared by the Bayer process; when the aluminum ion concentration in the concentrated solution is <60g / L, the process returns to step (1) for alkali dissolution treatment. The method provided by the present application can also save the consumption of alkali solution, acid solution and water, and reduce process costs.

[0116] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing ultra-pure coal and recovering waste liquid by chemical method, characterized in that: The following steps are involved: Step S1, mixing coal with an alkaline solution, and sequentially performing alkaline dissolution treatment and solid-liquid separation to obtain an alkaline soluble filtrate and an alkaline soluble filter residue; wherein the alkaline solution comprises sodium ions, calcium ions and hydroxide ions, the molar ratio of the sodium ions to the aluminum element in the coal is 18 to 30:1, the molar ratio of the calcium ions to the silicon element in the coal is 1.0 to 1.1:1, and the concentration of the hydroxide ions is 15 to 18 mol / L; Step S2, mixing the alkali-soluble filter residue with water, and sequentially performing dealkalization treatment and solid-liquid separation to obtain a dealkalized filtrate and a dealkalized filter residue; Step S3, mixing the dealkalized filter residue with an acidic solution, and sequentially performing acid dissolution treatment and solid-liquid separation to obtain an acid-soluble filtrate and an acid-soluble filter residue; Step S4, drying the acid-soluble filter residue to obtain ultra-pure coal.

2. The method for preparing ultrapure coal and recovering waste liquid by chemical method according to claim 1, characterized in that: In step S1, the sodium ions are derived from a sodium-containing compound, and the sodium-containing compound is selected from sodium hydroxide.

3. The method for preparing ultrapure coal and recovering waste liquid by chemical method according to claim 1, characterized in that: In step S1, the calcium ions are derived from a calcium-containing compound, and the calcium-containing compound is selected from at least one of calcium oxide and calcium hydroxide, preferably calcium hydroxide.

4. The method for preparing ultrapure coal and recovering waste liquid by chemical method according to claim 1, characterized in that: In step S1, the temperature of the alkali dissolution treatment is 240-280° C., and the time of the alkali dissolution treatment is 1-3 hours.

5. The method for preparing ultrapure coal and recovering waste liquid by chemical method according to claim 1, characterized in that: In step S2, the temperature of the dealkalization treatment is 60-100° C., and the time of the dealkalization treatment is 1-3 hours.

6. The method for preparing ultrapure coal and recovering waste liquid by chemical method according to claim 1, characterized in that: In step S3, the concentration of the acidic solution is 0.5 to 2.5 mol / L; And / or, the acidic solution includes at least one of a hydrochloric acid solution and a nitric acid solution, preferably a hydrochloric acid solution.

7. The method for preparing ultrapure coal and recovering waste liquid by chemical method according to claim 1, characterized in that: In the step S3, the mass ratio of the dealkalization residue to the acidic solution is 1:4-8.

8. The method for preparing ultrapure coal and recovering waste liquid by chemical method according to claim 1, characterized in that: In step S3, the temperature of the acid dissolution treatment is 50-90° C., and the time of the acid dissolution treatment is 1.5-4.0 hours.

9. The method for preparing ultrapure coal and recovering waste liquid by chemical method according to any one of claims 1 to 8, characterized in that: Step S2 includes step S21 and step S22: Step S21, mixing the alkali-soluble filter residue with water, and sequentially performing washing treatment and solid-liquid separation to obtain a washing filtrate and a washing filter residue; Step S22, mixing the washed filter residue with water to sequentially perform dealkalization treatment and solid-liquid separation to obtain the dealkalization filtrate and the dealkalization filter residue.

10. The method for preparing ultrapure coal and recovering waste liquid by chemical method according to any one of claims 1 to 8, characterized in that: The method further comprises waste liquid recovery, wherein the waste liquid recovery comprises: The alkaline filtrate, the washing filtrate and the dealkalization filtrate are mixed and concentrated to obtain a concentrated solution. If the aluminum ion concentration in the concentrated solution is ≥60 g / L, the concentrated solution is used to prepare alumina through the Bayer process. If the aluminum ion concentration in the concentrated solution is <60 g / L, the concentrated solution is returned to step (1) and mixed with the alkaline solution to perform the alkaline dissolution treatment.

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