Method for leaching germanium from germanium-containing coal ash

Abstract

The invention provides a method for leaching germanium from germanium-containing coal ash, and belongs to the technical field of germanium separation. The method comprises the following steps: (1) mixing germanium-containing coal ash and an alkali solution in a first-stage reaction kettle for stirring reaction to obtain alkaline leaching ore pulp; (2) adding mixed acid into the alkaline leaching ore pulp, stirring, and carrying out mixed acid leaching on the alkaline leaching ore pulp in a secondary reaction kettle to obtain acid leaching ore pulp; and (3) carrying out liquid-solid separation on the acid leaching ore pulp to obtain slag of which the main component is silicon dioxide and leaching liquid rich in germanium. According to the method disclosed by the invention, an alkali fusion process is adjusted to be high-temperature alkali leaching, and then the alkali leaching ore pulp is directly subjected to mixed acid leaching, so that insoluble silicate and silicon dioxide are converted into silicate which is easily dissolved in mixed acid, and the technical problem of efficient leaching of germanium is solved. According to the method, the leaching rate of germanium is high, the technological process is simple, silicon in the leachate can be effectively controlled, and comprehensive recycling of resources is facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of germanium extraction, and particularly to a method for leaching germanium from germanium-containing coal ash. Background Art

[0002] Germanium, as a rare-dispersed metal, is an important strategic metal resource. There are very few germanium deposits that can be independently mined in nature. However, due to its characteristics of being sulfurophilic, ironophilic, and silicophilic, it usually has a relatively high content in sphalerite and lignite. Therefore, at present, the recovery of germanium mainly comes from the extraction of associated germanium in the zinc smelting process and the recovery of germanium in the coal ash from lignite combustion.

[0003] In the hydrometallurgical process of sphalerite, in addition to the process of directly oxygen pressure leaching germanium-containing zinc concentrate and separating and enriching germanium in the solution, there is also a process of obtaining germanium-rich zinc oxide fume by pyro-reduction volatilization of traditional zinc leaching residue, and then separating and enriching germanium from the fume by sulfuric acid leaching.

[0004] The recovery of germanium in germanium-containing lignite mainly focuses on the separation and extraction of germanium in the coal ash from lignite combustion. Compared with the recovery of germanium in germanium-rich zinc oxide fume in the zinc smelting process, the recovery of germanium is more difficult and there are more process methods. Currently, the methods adopted by some enterprises include: pyro-reduction smelting of coal ash to prepare ferro-germanium alloy, secondary reduction volatilization of coal ash to enrich germanium, alkali fusion and water leaching of coal ash, and hydrofluoric acid leaching of coal ash.

[0005] Chinese Patent CN106801151B also discloses a method for enriching germanium by reducing and smelting fly ash, which includes the following steps: (1) mixing fly ash, limestone, and iron ore for batching to obtain a mixed material; (2) granulating the mixed material with water to obtain mixed pellets; (3) conveying pulverized coal and the mixed pellets to a fuming furnace for reduction smelting to obtain germanium-containing flue gas and smelting slag; (4) sequentially subjecting the germanium-containing flue gas to waste heat recovery and cooling and purification treatment to obtain flue gas and germanium-arsenic-containing dust; (5) subjecting the germanium-arsenic-containing dust to oxidative leaching to obtain germanium slag and arsenic-containing leaching solution; (6) evaporating, filtering, and drying the arsenic-containing leaching solution to obtain industrial white arsenic. This method has the advantages of large fly ash treatment capacity, high germanium content in dust, short cycle, and low energy consumption.

[0006] Pyro-reduction smelting to prepare ferro-germanium alloy and secondary reduction volatilization of coal ash to enrich germanium are to secondarily enrich the germanium in coal ash and then leach it, while alkali fusion and water leaching of coal ash and hydrofluoric acid leaching of coal ash are to directly leach the germanium in coal ash to obtain a germanium-containing solution.

[0007] Although the above methods have achieved certain results, there is generally a problem of relatively low germanium recovery rate. The main reasons are the dispersion of germanium and the formation of insoluble germanium-containing silicate during the alkali fusion process, and the direct leaching process is restricted by germanium-containing silicon dioxide in coal ash, resulting in difficulty in leaching germanium. Summary of the Invention

[0008] In view of this, the object of the present invention is to provide a method for leaching germanium from germanium-containing coal ash, aiming at the problems such as low germanium leaching rate existing in the existing germanium recovery processes such as alkaline melting and water leaching of germanium from germanium-containing coal ash and leaching germanium from germanium-containing coal ash with hydrofluoric acid. By adjusting the alkaline melting process to high-temperature alkaline leaching and then directly carrying out mixed acid leaching on the alkaline leaching pulp, the refractory silicate and silicon dioxide are converted into silicate soluble in the mixed acid, so as to achieve efficient leaching of germanium. The process flow of the present invention is simple, the germanium leaching rate is high, and it is beneficial to the comprehensive recovery and utilization of resources.

[0009] In order to achieve the above object, the present application provides a method for leaching germanium from germanium-containing coal ash, comprising the following steps:

[0010] (1) Mix germanium-containing coal ash with an alkaline solution in a first-stage reaction kettle and carry out stirring reaction to obtain alkaline leaching pulp;

[0011] (2) Add mixed acid to the alkaline leaching pulp and stir, and carry out mixed acid leaching on the alkaline leaching pulp in a second-stage reaction kettle to obtain acid leaching pulp;

[0012] (3) Carry out liquid-solid separation on the acid leaching pulp to obtain slag mainly composed of silicon dioxide and leaching solution rich in germanium.

[0013] Preferably, the germanium-containing coal ash contains the following components: the germanium content is 4000-7000 g / t; the silicon content is 18-22 wt%.

[0014] Preferably, the alkaline solution in step (1) is sodium hydroxide solution.

[0015] Preferably, the mass concentration of the alkaline solution in step (1) is 30-40%.

[0016] Preferably, the solid-liquid ratio of the alkaline solution to the germanium-containing coal ash in step (1) is 2-3 g / mL.

[0017] Preferably, the temperature of the mixing reaction in step (1) is 260-280 °C, the reaction time is 60-90 min; the stirring speed is 50-100 r / min.

[0018] Preferably, the mixed acid in step (2) is a mixed solution of sulfuric acid and hydrofluoric acid.

[0019] More preferably, the mass concentration of sulfuric acid in the mixed acid is 180-220 g / L, the mass concentration of hydrofluoric acid is 30-50 g / L; the stirring speed is 50-100 r / min.

[0020] Preferably, the addition amount of the mixed acid in step (2) is added according to the solid-liquid ratio of the mixed acid to the germanium-containing coal ash in step (1) of 2-3 g / mL, and the final pH value of the pulp is 1-2.

[0021] Preferably, the leaching temperature in step (2) is 110-120°C, and the time is 120-150 min.

[0022] The present invention realizes the efficient leaching of germanium in germanium-rich coal ash through a method of continuous cascade leaching and stepwise control. By using high-temperature alkali leaching, silica and refractory silicates in the coal ash are converted into sodium silicate, and refractory germanium minerals are converted into soluble germanium silicate minerals. Then, a mixed acid is used to leach the alkali-leached pulp. Sulfuric acid is used to leach the converted soluble germanium silicate minerals, and hydrofluoric acid is used to enhance the leaching of unconverted silica and refractory silicates to improve the leaching rate of germanium. While leaching germanium, most of the silicates in the system are simultaneously converted into silica by using the change of the pH value at the reaction end point, so that the leached silicon precipitates in the form of silica, realizing the preliminary separation of germanium and silicon, reducing the silicon concentration in the acid leaching solution, and making it conducive to subsequent germanium recovery.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) High leaching rate of germanium. Through high-temperature alkali leaching and directly mixing acid leaching of the alkali-leached pulp in the present invention, refractory silicates and silica are converted into silicates that are soluble in the mixed acid, making germanium easy to leach into the solution. The leaching rate of germanium can be increased to more than 92%, realizing the efficient leaching of germanium.

[0025] (2) Effective control of silicon in the leaching solution. In the processes of alkali fusion water leaching of germanium from germanium-containing coal ash and leaching germanium from germanium-containing coal ash with hydrofluoric acid, a large amount of silicate solution enters the leaching solution while leaching germanium, and the silicon content in the germanium-containing solution is relatively high, making subsequent treatment difficult. However, in the present invention, silicon is precipitated into the slag while leaching germanium, and the silicon content in the germanium-rich leaching solution obtained from the secondary reaction kettle is relatively low, which is easy to recover germanium from the leaching solution subsequently.

[0026] (3) Simple process flow. The present invention adopts a two-stage continuous cascade leaching and stepwise control method, first converting and then leaching. Conversion is carried out in the primary reaction kettle, and leaching is carried out in the secondary reaction kettle. Moreover, the primary leaching pulp does not need liquid-solid separation and flows to the secondary reaction kettle by gravity. Only the primary reaction kettle needs to be heated, and the secondary reaction kettle does not need to be heated. Compared with the process of alkali fusion water leaching of germanium from germanium-containing coal ash, there is no need for pyrometallurgical high-temperature alkali fusion, simplifying the process flow and making the operation simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is the process equipment configuration diagram of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] The present invention provides a method for leaching germanium from germanium-containing coal ash, and the steps are as follows:

[0029] (1) Using germanium-containing coal ash with a germanium content of 4000 - 7000 g / t and a silicon content of 18 - 22 wt% as raw material, mix and stir the germanium-containing coal ash with an alkali solution with a mass concentration of 30 - 40% in a first-stage reaction kettle. Control the solid-liquid ratio of the alkali solution to the germanium-containing coal ash to be 2 - 3 g / mL, control the reaction temperature to be 260 - 280 °C, the reaction time to be 60 - 90 min, and the stirring speed to be 50 - 100 r / min to convert silicon dioxide and insoluble silicates into sodium silicate. The obtained alkali-leached slurry flows by gravity to a second-stage reaction kettle through the pressure difference of the reaction kettle;

[0030] In the above steps, there is no need for liquid-solid separation of the alkali-leached slurry. Utilize the pressure difference system formed by the temperature difference between the two-stage reaction kettles to make the alkali-leached slurry flow by gravity to the acid-leaching reaction kettle;

[0031] (2) Add a mixed acid with a sulfuric acid mass concentration of 180 - 220 g / L and a hydrofluoric acid mass concentration of 30 - 50 g / L to the alkali-leached slurry in the second-stage reaction kettle and stir. Control the solid-liquid ratio of the mixed acid to the germanium-containing coal ash in step (1) to be 2 - 3 g / mL, the temperature to be 110 - 120 °C, the time to be 120 - 150 min, and the stirring speed to be 50 - 100 r / min. In the present invention, control the dosage of the mixed acid to make the pH value of the slurry end point between 1 and 2, and perform mixed acid leaching on the alkali-leached slurry; leach germanium into the solution, synchronously convert most of the silicates into silicon dioxide, precipitate most of the silicon, realize the preliminary separation of germanium and silicon, reduce the silicon concentration in the acid-leached solution, and make it conducive to subsequent germanium recovery

[0032] (3) Perform liquid-solid separation on the acid-leached slurry to obtain a slag mainly composed of silicon dioxide and a leaching solution rich in germanium.

[0033] Figure 1 The process equipment connection diagrams of the first-stage reaction kettle and the second-stage reaction kettle of the present invention are given. In the figure, the first-stage reaction kettle and the second-stage reaction kettle are connected by pipelines. Valves and flow meters are installed on the pipelines, and the height of the second-stage reaction kettle is lower than that of the first-stage reaction kettle. This device is suitable for safe discontinuous operation and continuous operation, especially suitable for continuous operation.

[0034] The first-stage reaction kettle is provided with a pressure regulating port, which is a safety protection device for equipment operation and is used for regulating the pressure in the kettle; both the first-stage and second-stage reaction kettles are equipped with stirring devices for stirring during the reaction process, and cleaning and discharging ports are provided at the bottom for cleaning and emptying the kettle when the equipment is shut down.

[0035] In a specific embodiment of the present invention, germanium-containing coal ash and an alkali solution are added into a first-stage reaction kettle from the mixing feeding port of germanium-containing coal ash and the alkali solution. The pressure regulating port is closed, and the first-stage reaction kettle is heated. The raw materials are stirred and reacted to obtain an alkali-leached pulp. After the reaction is completed, the valve is opened, and the alkali-leached pulp flows by gravity through the flow meter on the pipeline into the second-stage reaction kettle due to the pressure difference between the first-stage reaction kettle and the second-stage reaction kettle; then mixed acid is added into the second-stage reaction kettle through the inlet of the mixed acid pump, and stirring is carried out for acid leaching reaction. After the reaction is completed, the acid-leached pulp is discharged from the discharge port by the pressure inside the kettle.

[0036] The present invention will be further described below in conjunction with embodiments.

[0037] Example 1

[0038] A method for leaching germanium from germanium-containing coal ash is as follows:

[0039] (1) Using germanium-containing coal ash with a germanium content of 6624.61 g / t and a silicon content of 20.76 wt% as raw materials, the germanium-containing coal ash is mixed with a sodium hydroxide solution with a mass concentration of 30% and then added into a first-stage reaction kettle for stirring reaction. The solid-liquid ratio of the sodium hydroxide solution to the germanium-containing coal ash is controlled at 3 g / mL, the reaction temperature is controlled at 280 °C, the stirring speed is 50 r / min, and an alkali-leached pulp is obtained after reacting for 90 min. The alkali-leached pulp flows by gravity into the second-stage reaction kettle through the pressure difference of the reaction kettle.

[0040] (2) A mixed acid solution with a sulfuric acid mass concentration of 220 g / L and a hydrofluoric acid mass concentration of 40 g / L is pumped into the second-stage reaction kettle for stirring reaction. The solid-liquid ratio of the mixed acid to the germanium-containing coal ash is controlled at 2 g / mL, the reaction temperature is controlled at 120 °C, the stirring speed is 100 r / min, and the reaction is carried out for 120 min to directly carry out mixed acid leaching on the alkali-leached pulp; the pH value of the pulp at the end point is 1.06.

[0041] (3) The pulp in the second-stage reaction kettle is subjected to liquid-solid separation to obtain slag mainly composed of silicon dioxide and a leaching solution rich in germanium.

[0042] The germanium leaching rate calculated based on the germanium content in the slag and the germanium content in the coal ash is 94.72%, and the leaching solution contains 0.57 g / L of silicon.

[0043] Example 2

[0044] A method for leaching germanium from germanium-containing coal ash is as follows:

[0045] (1) Using germanium-containing coal ash with a germanium content of 4783.59 g / t and a silicon content of 19.58 wt% as raw material, mix the germanium-containing coal ash with a sodium hydroxide solution of 40% mass concentration and add it to a first-stage reaction kettle for stirring reaction. Control the solid-liquid ratio of the sodium hydroxide solution to the germanium-containing coal ash at 2 g / mL, control the reaction temperature at 260 °C, the stirring speed at 100 r / min, react for 60 min, and let the alkali-leached pulp flow by gravity through the pressure difference of the reaction kettle into the second-stage reaction kettle;

[0046] (2) Pump a mixed acid solution with a sulfuric acid mass concentration of 180 g / L and a hydrofluoric acid mass concentration of 50 g / L into the second-stage reaction kettle for stirring reaction. Control the solid-liquid ratio of the mixed acid to the germanium-containing coal ash at 3 g / mL, control the reaction temperature at 110 °C, the stirring speed at 80 r / min, react for 150 min, and directly carry out mixed acid leaching on the alkali-leached pulp; the pH value at the end of the pulp is 1.97;

[0047] (3) The pulp in the second-stage reaction kettle is subjected to liquid-solid separation to obtain slag mainly composed of silicon dioxide and a leaching solution rich in germanium.

[0048] The germanium leaching rate calculated based on the germanium content in the slag and the germanium content in the coal ash is 92.18%, and the leaching solution contains 1.36 g / L of silicon.

[0049] Example 3

[0050] A method for leaching germanium from germanium-containing coal ash, the steps are as follows:

[0051] (1) Using germanium-containing coal ash with a germanium content of 5972.83 g / t and a silicon content of 21.49 wt% as raw material, mix the germanium-containing coal ash with a sodium hydroxide solution of 35% mass concentration and add it to a first-stage reaction kettle for stirring reaction. Control the solid-liquid ratio of the sodium hydroxide solution to the germanium-containing coal ash at 2.5 g / mL, control the reaction temperature at 270 °C, the stirring speed at 80 r / min, react for 75 min to obtain alkali-leached pulp, and let the alkali-leached pulp flow by gravity through the pressure difference of the reaction kettle into the second-stage reaction kettle;

[0052] (2) Pump a mixed acid solution with a sulfuric acid mass concentration of 200 g / L and a hydrofluoric acid mass concentration of 30 g / L into the second-stage reaction kettle for stirring reaction. Control the solid-liquid ratio of the mixed acid to the germanium-containing coal ash at 2.5 g / mL, control the reaction temperature at 115 °C, the stirring speed at 100 r / min, react for 150 min, and directly carry out mixed acid leaching on the alkali-leached pulp; the pH value at the end of the pulp is 1.53;

[0053] (3) The pulp in the second-stage reaction kettle is subjected to liquid-solid separation to obtain slag mainly composed of silicon dioxide and a leaching solution rich in germanium.

[0054] The germanium leaching rate calculated based on the germanium content in the slag and the germanium content in the coal ash is 93.06%, and the leaching solution contains 0.98 g / L of silicon.

[0055] Comparative Example 1

[0056] A method for leaching germanium from germanium-containing coal ash, the steps are the same as in Example 1, except that in step (1) of Comparative Example 1, the reaction temperature is 120 °C. The calculated germanium leaching rate is 52.13%; the leaching solution contains 0.45 g / L of silicon.

[0057] Comparative Example 2

[0058] A method for leaching germanium from germanium-containing coal ash, the steps are the same as in Example 1, except that in step (1) of Comparative Example 2, the reaction time is 30 min. The calculated germanium leaching rate is 65.12%; the leaching solution contains 0.51 g / L of silicon.

[0059] Comparative Example 3

[0060] A method for leaching germanium from germanium-containing coal ash, the steps are the same as in Example 1, except that in step (2) of Comparative Example 3, the reaction temperature is 150 °C. The calculated germanium leaching rate is 58.67%; the leaching solution contains 0.42 g / L of silicon.

[0061] Comparative Example 4

[0062] A method for leaching germanium from germanium-containing coal ash, the steps are the same as in Example 1, except that in step (2) of Comparative Example 4, the reaction time is 60 min. The calculated germanium leaching rate is 78.39%; the leaching solution contains 1.67 g / L of silicon.

[0063] Comparative Example 5

[0064] A method for leaching germanium from germanium-containing coal ash, the steps are the same as in Example 1, except that Comparative Example 5 does not include step (1). The calculated germanium leaching rate is 45.96%; the leaching solution contains 1.03 g / L of silicon.

[0065] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for leaching germanium from germanium-containing coal ash, characterized in that, It includes the following steps: (1) Mix germanium-containing coal ash with an alkali solution in a first-stage reactor and carry out a stirring reaction to obtain an alkali-leached pulp; (2) Add a mixed acid to the alkali-leached pulp and stir, and carry out mixed acid leaching on the alkali-leached pulp in a second-stage reactor to obtain an acid-leached pulp; (3) Carry out liquid-solid separation on the acid-leached pulp to obtain a slag with the main component of silicon dioxide and a leachate rich in germanium.

2. The method for leaching germanium from germanium-containing coal ash according to claim 1, wherein The germanium-containing coal ash contains the following components: the germanium content is 4000-7000 g / t; the silicon content is 18-22 wt%.

3. The method for leaching germanium from germanium-containing coal ash according to claim 1, wherein The alkali solution in step (1) is a sodium hydroxide solution.

4. The method for leaching germanium from germanium-containing coal ash according to claim 1, wherein The mass concentration of the alkali solution in step (1) is 30-40%.

5. The method for leaching germanium from germanium-containing coal ash according to claim 1, wherein The solid-liquid ratio of the alkali solution to the germanium-containing coal ash in step (1) is 2-3 g / mL.

6. The method for leaching germanium from germanium-containing coal ash according to claim 1, wherein The temperature of the mixing reaction in step (1) is 260-280 °C, and the reaction time is 60-90 min; the rotation speed of the stirring is 50-100 r / min.

7. The method for leaching germanium from germanium-containing coal ash according to claim 1, characterized in that, The mixed acid in step (2) is a mixed solution of sulfuric acid and hydrofluoric acid.

8. The method for leaching germanium from germanium-containing coal ash according to claim 7, characterized in that, The mass concentration of sulfuric acid in the mixed acid is 180-220 g / L, and the mass concentration of hydrofluoric acid is 30-50 g / L.

9. The method for leaching germanium from germanium-containing coal ash according to claim 1, characterized in that, The addition amount of the mixed acid in step (2) is added according to the solid-liquid ratio of the mixed acid to the germanium-containing coal ash in step (1) being 2-3 g / mL, and the end point pH value of the pulp is 1-2.

10. The method for leaching germanium from germanium-containing coal ash according to claim 1, characterized in that, The leaching temperature in step (2) is 110-120 °C, and the time is 120-150 min; the rotation speed of the stirring is 50-100 r / min.

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