A method for leaching germanium from germanium-containing coal ash

Abstract

The present invention provides a method for leaching germanium from germanium-containing coal ash, belonging to the technical field of germanium precipitation. The method of the present invention comprises the following steps: (1) mixing the germanium-containing coal ash with an alkaline solution in a primary reactor for stirring and reacting to obtain an alkaline leached pulp; (2) adding mixed acid to the alkaline leached pulp for stirring, and subjecting the alkaline leached pulp to mixed acid leaching in a secondary reactor to obtain an acid leached pulp; (3) subjecting the acid leached pulp to liquid-solid separation to obtain a slag whose main component is silicon dioxide and a leachate rich in germanium. The method of the present invention adjusts the alkaline fusion process to high-temperature alkaline leaching, and then directly subjects the alkaline leached pulp to mixed acid leaching, thereby converting insoluble silicates and silicon dioxide into silicates that are easily soluble in mixed acid, thereby solving the technical problem of efficient germanium leaching. The method of the present invention has a high germanium leaching rate, a simple process flow, and can effectively control the silicon in the leachate, which is conducive to the comprehensive recycling and utilization of resources.

Description

Technical Field

[0001] The invention relates to the technical field of germanium precipitation, in particular to a method for leaching germanium from germanium-containing coal ash. Background Art

[0002] Germanium, as a rare metal, is an important strategic metal resource. There are very few independently minable germanium deposits in nature. However, due to its affinity for sulfur, iron, and silicon, its content is usually high in sphalerite and lignite. Therefore, the current recovery of germanium mainly comes from the extraction of associated germanium in the zinc smelting process and the recovery of germanium from the coal ash of lignite combustion.

[0003] In the wet smelting process of sphalerite, in addition to the process of direct oxygen pressure leaching and solution separation and enrichment of germanium from germanium-containing zinc concentrate, there is also a process of obtaining germanium-rich zinc oxide smoke through the traditional pyroreduction volatilization method of zinc leaching slag, and then separating and enriching germanium from the smoke through sulfuric acid leaching.

[0004] The recovery of germanium from germanium-containing lignite primarily involves separating and extracting germanium from the coal ash from lignite combustion. Compared to the recovery of germanium from germanium-containing zinc oxide dust from the zinc smelting process, the recovery of germanium from this dust is more challenging and involves a variety of process methods. Currently, some companies utilize methods such as pyrometallurgical reduction smelting of coal ash to produce iron-germanium alloys, secondary reduction and volatilization of coal ash to enrich germanium, alkaline 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 reduction smelting of fly ash, comprising the following steps: (1) mixing fly ash, limestone, and iron ore to obtain a mixture; (2) adding water to the mixture to form pellets to obtain mixed pellets; (3) conveying fly ash and the mixed pellets to a fuming furnace for reduction smelting to obtain germanium-containing flue gas and smelting slag; (4) subjecting the germanium-containing flue gas to waste heat recovery and cooling and purification treatment in sequence to obtain flue gas and germanium- and arsenic-containing flue dust; (5) subjecting the germanium- and arsenic-containing flue dust to oxidation leaching to obtain germanium slag and arsenic-containing leachate; and (6) evaporating, filtering, and drying the arsenic-containing leachate to obtain industrial white arsenic. This method has the advantages of large fly ash processing capacity, high germanium content in the flue dust, short cycle time, and low energy consumption.

[0006] The preparation of iron-germanium alloy by pyrometallurgical reduction smelting and the secondary reduction volatilization enrichment of germanium by coal ash are to enrich the germanium in the coal ash for the second time and then leach it out, while the coal ash alkali melting water leaching and coal ash hydrofluoric acid leaching are to directly leach the germanium in the coal ash to obtain a germanium-containing solution.

[0007] Although the above methods have achieved certain results, there is a general problem of low germanium recovery rate. The main reason is that the dispersion and alkali fusion process of germanium generates insoluble germanium-containing silicates, and the direct leaching process is limited by the germanium-containing silica in the coal ash, making it difficult to leach germanium. Summary of the Invention

[0008] In view of this, the present invention aims to address the low germanium leaching rates associated with existing germanium recovery processes, such as alkali fusion water leaching of germanium from germanium-containing coal ash and hydrofluoric acid leaching of germanium from germanium-containing coal ash. By adjusting the alkali fusion process to high-temperature alkali leaching, and then directly subjecting the alkali-leached slurry to mixed acid leaching, the present invention converts insoluble silicates and silicon dioxide into silicates that are readily soluble in mixed acid, achieving efficient germanium leaching. The present invention has a simple process flow, high germanium leaching rates, and is beneficial for comprehensive resource recovery and utilization.

[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) mixing germanium-containing coal ash and alkaline solution in a primary reactor and stirring the mixture to obtain an alkaline leached slurry;

[0011] (2) adding mixed acid to the alkali leached pulp and stirring, and leaching the alkali leached pulp with mixed acid in a secondary reactor to obtain an acid leached pulp;

[0012] (3) The acid leaching slurry is subjected to liquid-solid separation to obtain slag whose main component is silicon dioxide and a leachate rich in germanium.

[0013] Preferably, the germanium-containing coal ash comprises the following components: a germanium content of 4000 to 7000 g / t; and a silicon content of 18 to 22 wt%.

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

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

[0016] Preferably, the solid-to-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, and 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, and the mass concentration of hydrofluoric acid is 30-50 g / L; and the stirring speed is 50-100 r / min.

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

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

[0022] The present invention achieves efficient leaching of germanium from germanium-rich coal ash through a continuous step-by-step leaching and step-by-step control method. High-temperature alkaline leaching is used to convert silica and insoluble silicates in the coal ash into sodium silicate, converting insoluble germanium minerals into silicate minerals that are easily soluble in germanium. Alkaline leaching pulp is leached using mixed acid, with converted silicate minerals that are easily soluble in germanium leached using sulfuric acid, and unconverted silica and insoluble silicates are leached using hydrofluoric acid to enhance the leaching rate of germanium. While leaching germanium, the pH value of the system changes at the end of the reaction to simultaneously convert most of the silicates in the system into silicon dioxide, causing the leached silicon to precipitate as silicon dioxide, achieving preliminary separation of germanium from silicon, and reducing the silicon concentration in the acid leaching solution, which is beneficial for subsequent germanium recovery.

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

[0024] (1) High germanium leaching rate. The present invention uses high-temperature alkaline leaching and alkaline leached slurry to directly perform mixed acid leaching, converting insoluble silicates and silicon dioxide into silicates that are easily soluble in mixed acid, making it easy for germanium to leach into the solution. The germanium leaching rate can be increased to over 92%, achieving efficient germanium leaching.

[0025] (2) Effective control of silicon in the leachate. In the processes of leaching germanium from germanium-containing coal ash using alkali molten water or adding hydrofluoric acid to germanium-containing coal ash, a large amount of silicate solution enters the leachate during the leaching of germanium. This results in a high silicon content in the germanium-containing solution, making subsequent processing difficult. However, the present invention precipitates silicon into the slag while leaching germanium. The silicon content in the germanium-rich leachate obtained in the secondary reactor is low, making it easier to recover germanium from the leachate.

[0026] (3) The process is simple. The present invention adopts a two-stage continuous cascade leaching and step-by-step control method, first converting and then leaching. The conversion is carried out in the first reactor and the leaching is carried out in the second reactor. The first-stage leaching slurry does not require liquid-solid separation and flows to the second reactor by gravity. Only the first reactor needs to be heated, and the second reactor does not need to be heated. Compared with the germanium-containing coal ash alkali fusion water leaching process, the present invention does not require high-temperature alkali fusion by pyrolysis, which simplifies the process and is simple to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a configuration diagram of the process equipment of the present invention. DETAILED DESCRIPTION

[0028] The present invention provides a method for leaching germanium from germanium-containing coal ash, comprising the following steps:

[0029] (1) Using germanium-containing coal ash having a germanium content of 4000-7000 g / t and a silicon content of 18-22 wt% as raw material, the germanium-containing coal ash is mixed with an alkaline solution having a mass concentration of 30-40% and stirred in a primary reactor for reaction, the solid-liquid ratio of the alkaline solution to the germanium-containing coal ash is controlled to be 2-3 g / mL, the reaction temperature is controlled to be 260-280° C., the reaction time is controlled to be 60-90 min, and the stirring speed is controlled to be 50-100 r / min to convert silicon dioxide and insoluble silicate into sodium silicate, and the obtained alkaline leached slurry is self-flowed to a secondary reactor through the pressure difference of the reactor;

[0030] In the above steps, the alkali leaching slurry does not need liquid-solid separation, and the pressure difference system formed by the temperature difference between the two-stage reactors is used to make the alkali leaching slurry flow to the acid leaching reactor by gravity;

[0031] (2) adding a mixed acid having a sulfuric acid mass concentration of 180-220 g / L and a hydrofluoric acid mass concentration of 30-50 g / L to the alkaline leaching pulp in the secondary reactor and stirring the mixture, controlling 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. The present invention controls the amount of the mixed acid so that the end pH value of the pulp is between 1 and 2, and performs mixed acid leaching on the alkaline leaching pulp; leaching the germanium into the solution, simultaneously realizing the conversion of most silicates into silicon dioxide, precipitating most silicon, realizing the preliminary separation of germanium and silicon, reducing the silicon concentration in the acid leaching solution, and making it conducive to the subsequent recovery of germanium

[0032] (3) The acid leaching slurry is subjected to liquid-solid separation to obtain slag whose main component is silicon dioxide and a leachate rich in germanium.

[0033] Figure 1 A process equipment connection diagram for the present invention's primary and secondary reactors is provided. The diagram shows the primary and secondary reactors connected by a pipeline equipped with a valve and flowmeter. The secondary reactor is lower than the primary reactor. This device is suitable for both safe intermittent and continuous operation, particularly continuous operation.

[0034] The first-stage reactor is provided with a pressure regulating port, which is a safety protection device for equipment operation and is used for regulating the pressure inside the reactor; both the first-stage and second-stage reactors contain stirring devices for stirring the reaction process, and are provided with a cleaning discharge port at the bottom for cleaning and emptying the reactor when the equipment is shut down.

[0035] In a specific embodiment of the present invention, germanium-containing coal ash and alkaline solution are added to the primary reactor from the germanium coal ash and alkaline solution mixing feed port, the pressure regulating port is closed, the primary reactor is heated, and the raw materials are stirred to react to obtain alkaline leached slurry. After the reaction is completed, the valve is opened, and the alkaline leached slurry flows into the secondary reactor through the flow meter on the pipeline using the pressure difference between the primary reactor and the secondary reactor; then, mixed acid is added to the secondary reactor through the inlet of the mixed acid pump, and stirred to perform acid leaching reaction. After the reaction is completed, the acid leached slurry is discharged from the discharge port using the pressure in the reactor.

[0036] The present invention will be further described below with reference to the embodiments.

[0037] Example 1

[0038] A method for leaching germanium from germanium-containing coal ash, comprising the following steps:

[0039] (1) Using germanium-containing coal ash having a germanium content of 6624.61 g / t and a silicon content of 20.76 wt % as a raw material, the germanium-containing coal ash was mixed with a sodium hydroxide solution having a mass concentration of 30%, and then added to a primary reactor for stirring reaction, the solid-liquid ratio of the sodium hydroxide solution to the germanium-containing coal ash was controlled to be 3 g / mL, the reaction temperature was controlled to be 280° C., the stirring speed was controlled to be 50 r / min, and the reaction was carried out for 90 min to obtain an alkaline leached slurry, and the alkaline leached slurry was self-flowed to a secondary reactor through the pressure difference in the reactor;

[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 was pumped into a secondary reactor for stirring reaction, and the solid-liquid ratio of the mixed acid to the germanium-containing fly ash was controlled to be 2 g / mL, the reaction temperature was controlled to be 120°C, the stirring speed was controlled to be 100 r / min, the reaction was carried out for 120 min, and the alkaline leached pulp was directly subjected to mixed acid leaching; the endpoint pH value of the pulp was 1.06;

[0041] (3) The slurry in the secondary reactor is separated into liquid and solid to obtain slag whose main component is silicon dioxide and leachate 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 silicon content of the leaching solution is 0.57 g / L.

[0043] Example 2

[0044] A method for leaching germanium from germanium-containing coal ash, comprising the following steps:

[0045] (1) Using germanium-containing coal ash having a germanium content of 4783.59 g / t and a silicon content of 19.58 wt% as raw material, the germanium-containing coal ash was mixed with a sodium hydroxide solution having a mass concentration of 40%, and then added to a primary reactor for stirring reaction. The solid-liquid ratio of the sodium hydroxide solution to the germanium-containing coal ash was controlled to be 2 g / mL, the reaction temperature was controlled to be 260° C., the stirring speed was controlled to be 100 r / min, the reaction was carried out for 60 min, and the alkaline leached slurry was allowed to flow by gravity to a secondary reactor due to the pressure difference in the reactor;

[0046] (2) A mixed acid solution with a sulfuric acid mass concentration of 180 g / L and a hydrofluoric acid mass concentration of 50 g / L was pumped into a secondary reactor for stirring reaction, and the solid-liquid ratio of the mixed acid to the germanium-containing fly ash was controlled to be 3 g / mL, the reaction temperature was controlled to be 110°C, the stirring speed was controlled to be 80 r / min, the reaction was carried out for 150 min, and the alkaline leached pulp was directly subjected to mixed acid leaching; the endpoint pH value of the pulp was 1.97;

[0047] (3) The slurry in the secondary reactor is separated into liquid and solid to obtain slag whose main component is silicon dioxide and leachate 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 silicon content of the leaching solution is 1.36 g / L.

[0049] Example 3

[0050] A method for leaching germanium from germanium-containing coal ash, comprising the following steps:

[0051] (1) Using germanium-containing coal ash having a germanium content of 5972.83 g / t and a silicon content of 21.49 wt % as a raw material, the germanium-containing coal ash was mixed with a sodium hydroxide solution having a mass concentration of 35%, and then added to a primary reactor for stirring reaction, the solid-liquid ratio of the sodium hydroxide solution to the germanium-containing coal ash was controlled to be 2.5 g / mL, the reaction temperature was controlled to be 270° C., the stirring speed was controlled to be 80 r / min, and the reaction was carried out for 75 min to obtain an alkali leached slurry, and the alkali leached slurry was self-flowed to a secondary reactor through the pressure difference in the reactor;

[0052] (2) A mixed acid solution with a sulfuric acid mass concentration of 200 g / L and a hydrofluoric acid mass concentration of 30 g / L was pumped into a secondary reactor for stirring reaction, and the solid-liquid ratio of the mixed acid to the germanium-containing fly ash was controlled to be 2.5 g / mL, the reaction temperature was controlled to be 115°C, the stirring speed was controlled to be 100 r / min, the reaction was carried out for 150 min, and the alkaline leached pulp was directly subjected to mixed acid leaching; the endpoint pH value of the pulp was 1.53;

[0053] (3) The slurry in the secondary reactor is separated into liquid and solid to obtain slag whose main component is silicon dioxide and leachate 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 silicon content of the leaching solution is 0.98 g / L.

[0055] Comparative Example 1

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

[0057] Comparative Example 2

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

[0059] Comparative Example 3

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

[0061] Comparative Example 4

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

[0063] Comparative Example 5

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

[0065] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for leaching germanium from germanium-containing coal ash, characterized in that: The following steps are involved: (1) Mixing germanium-containing coal ash and alkaline solution in a primary reactor and stirring to react to obtain alkaline leaching slurry; (2) adding mixed acid to the alkali leached pulp and stirring it, and leaching the alkali leached pulp with mixed acid in a secondary reactor to obtain an acid leached pulp; (3) performing liquid-solid separation on the acid leaching slurry to obtain slag mainly composed of silicon dioxide and a leachate rich in germanium; The alkaline solution in step (1) is a sodium hydroxide solution; The reaction temperature in step (1) is 260-280°C, and the reaction time is 60-90 minutes; The mixed acid in step (2) is a mixed solution of sulfuric acid and hydrofluoric acid, wherein 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; The leaching temperature in step (2) is 110-120° C. and the leaching time is 120-150 min; The endpoint pH value of the slurry is 1-2.

2. The method for leaching germanium from germanium-containing coal ash according to claim 1, characterized in that: The germanium-containing coal ash comprises the following components: a germanium content of 4000-7000 g / t; and a silicon content of 18-22 wt%.

3. The method for leaching germanium from germanium-containing coal ash according to claim 1, characterized in that: The mass concentration of the alkaline solution in step (1) is 30-40%.

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

5. The method for leaching germanium from germanium-containing coal ash according to claim 1, characterized in that: The stirring speed in step (1) is 50-100 r / min.

6. The method for leaching germanium from germanium-containing coal ash according to claim 1, characterized in that: The amount of the mixed acid added in step (2) is such that the solid-liquid ratio of the mixed acid to the germanium-containing coal ash in step (1) is 2-3 g / mL.

7. The method for leaching germanium from germanium-containing coal ash according to claim 1, characterized in that: The stirring speed in step (2) is 50-100 r / min.

Images