CN115125587B - Device and method for separating tungsten, cobalt and carbon by fused salt electrolysis of hard alloy - Google Patents

Abstract

The present invention relates to a device and method for low-carbon separation of tungsten, cobalt and carbon by electrolysis of cemented carbide molten salt, comprising the following steps: (1) in an inert atmosphere, after the molten salt is completely melted, an anode and a cathode are placed in the molten salt, a power supply is turned on, an electrolysis reaction is carried out, and a precipitate is collected after the electrolysis reaction is completed; the molten salt is a mixture of one or more of calcium salt, strontium salt and aluminum salt in any proportion; the cathode is cemented carbide; (2) the precipitate is washed with water to obtain a gas product and a tungsten-cobalt mixture, and the separation of tungsten, cobalt and carbon in the cemented carbide is completed. In the present invention, cemented carbide is used as a cathode and placed in a molten salt for electrolysis, and the alkali metal precipitated from the cathode reacts with the alloy and carbon to form a tungsten element and a molten salt metal carbide, and the molten salt metal carbide reacts with water to generate gas products such as methane/acetylene and hydroxides. The present invention completes the separation of metal and carbon in the cemented carbide without generating greenhouse gases; the process is short, the efficiency is high, and it is low-carbon and environmentally friendly.

Description

A device and method for separating tungsten, cobalt and carbon by electrolysis of cemented carbide molten salt

Technical Field

The invention relates to the field of waste cemented carbide recovery, and in particular to a device and method for low-carbon separation of tungsten, cobalt and carbon by electrolysis of cemented carbide molten salt.

Background technique

Cemented carbide has attracted much attention for its excellent physical and chemical properties such as high hardness, strength, wear resistance, corrosion resistance, and impact resistance. In recent years, with the continuous development of cemented carbide production technology and the comprehensive expansion of its application fields, China's cemented carbide production has increased year by year. At present, the consumption of cemented carbide has exceeded 50% of tungsten consumption. Therefore, as the amount of scrapped cemented carbide increases year by year, how to achieve efficient resource utilization of scrapped cemented carbide is an important issue that needs to be solved urgently. The tungsten metal content in scrapped cemented carbide is usually as high as 90%, which is significantly higher than the tungsten content in tungsten concentrate (about 65%), and has extremely high recycling and reuse value. In addition, the average content of binder cobalt in scrapped cemented carbide is about 10%. Therefore, the efficient recycling of tungsten and cobalt in scrapped cemented carbide not only has high economic value, but also will greatly alleviate the demand pressure of tungsten and cobalt resources in my country, reduce environmental load, and thus promote the sustainable development of the cemented carbide industry.

At present, dozens of recycling methods for waste cemented carbide and tungsten-based alloys have been reported in the literature, among which the mainstream processes used in industrial production are mechanical crushing, acid leaching, zinc melting, electrochemical method and oxidation method. According to the above methods, the resource utilization technology routes of waste cemented carbide can be summarized into the following two: ① Keep the composition of cemented carbide unchanged and reuse it directly; ② Convert the carbide in the cemented carbide into tungsten oxide first, and then convert it into crude sodium tungstate to produce ammonium paratungstate (APT). Among them, method ① fails to change the grain size of tungsten carbide, which limits the application of recycled tungsten carbide. In method ②, the process of converting tungsten carbide into sodium tungstate involves the oxidation process of carbon, which is bound to cause greenhouse gas emissions.

Summary of the invention

The purpose of the present invention is to overcome the above-mentioned technical deficiencies and provide a device and method for low-carbon separation of tungsten, cobalt and carbon by molten salt electrolysis of cemented carbide, so as to solve the technical problem that greenhouse gases are easily generated when cemented carbide is used to recover metals in the prior art, and at the same time convert carbon into high value-added combustible gas.

In order to achieve the above technical objectives,

In the first aspect, the present invention provides a method for separating tungsten, cobalt and carbon by low-carbon electrolysis of cemented carbide molten salt:

The following steps are involved:

(1) In an inert atmosphere, an anode and a cathode are placed in a molten salt, and after the molten salt is completely melted, a power source is connected to carry out an electrolytic reaction, and after the electrolytic reaction is completed, a precipitate is collected; the molten salt is a mixture of one or more of a calcium salt, a strontium salt and an aluminum salt in any proportion; the cathode is a hard alloy;

(2) Wash the precipitate with water to obtain a gas product and a tungsten-cobalt mixture, thereby completing the separation of tungsten, cobalt and carbon in the cemented carbide.

Furthermore, the temperature of the electrolysis reaction is 850°C to 950°C.

Furthermore, the voltage of the electrolysis reaction is 3-4V.

Furthermore, the electrolysis reaction time is 4 to 8 hours.

Furthermore, during the electrolysis reaction, the upper surfaces of the anode and the cathode are higher than the liquid level of the molten salt or are flush with the liquid level of the molten salt.

Furthermore, the precipitate is first washed with water until no gas product is generated, and then acid washed until the weight of the precipitate remains unchanged, thereby obtaining a pure tungsten-cobalt mixture; the tungsten-cobalt mixture is separated by magnetic separation.

In a second aspect, the present invention provides a device for separating tungsten, cobalt and carbon by electrolyzing low-carbon cemented carbide molten salt:

It comprises a reactor capable of being heated, in which a crucible for filling molten salt is placed, during electrolysis, the molten salt is in a molten state and an anode and a cathode are arranged therein, and the anode and the cathode are connected to an external power supply;

The device is used for low-carbon separation of tungsten, cobalt and carbon by molten salt electrolysis of cemented carbide in the above method.

Furthermore, the crucible comprises a graphite crucible and an alumina crucible which are sleeved from the outside to the inside, and the molten salt is filled in the alumina crucible.

Furthermore, an air inlet and an air outlet are provided on the reactor, and the air inlet and the air outlet are connected with the outside and the inner cavity of the reactor.

Furthermore, the anode is graphite; the anode and the cathode are connected to a power source through nickel current collectors respectively.

Compared with the prior art, the beneficial effects of the present invention include:

1. In the present invention, cemented carbide is used as the cathode and placed in molten salt for electrolysis. The alkali metal precipitated from the cathode reacts with the alloy and carbon to form tungsten and molten salt metal carbides, such as calcium carbide _CaC2 , _SrC2 and/or _Al4C3 . The _tungsten , cobalt without skeleton support and molten salt metal carbides are precipitated at the bottom of the molten salt in the form of cathode mud. After the electrolysis is completed, the cathode mud is washed with water, and calcium carbide, _SrC2 and/or _Al4C3 react with water to generate gas products such as methane/acetylene and _hydroxides . After the hydroxides are completely washed and recovered, the main component of the remaining solid is a mixture of tungsten and cobalt metal elements, completing the separation of metal and carbon in the cemented carbide without generating greenhouse gases. The present invention has a short process, high efficiency, and is low-carbon and environmentally friendly.

2. The present invention has simple steps and strong operability;

3. The present invention provides new ideas and approaches for the green and efficient resource utilization of tungsten-containing waste.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic diagram of molten salt electrolysis in the present invention; wherein 1 is a power supply, 2 is an air inlet, 3 is an air outlet, 4 is a reactor, 5 is a graphite crucible, 6 is an alumina crucible, 7 is a graphite anode, 8 is a cemented carbide cathode, 9 is a nickel current collector, and 10 is a molten calcium salt.

Figure 2 is the XRD diagram of the electrolysis product under the conditions of 800℃-3.5V-8h.

Figure 3 is the XRD diagram of the electrolysis product under the conditions of 900℃-3.5V-8h.

Figure 4 is the XRD diagram of the electrolysis product under the conditions of 900℃-2V-8h.

Figure 5 is the XRD pattern of the electrolysis product under the conditions of 900℃-3V-2h.

FIG6 is an XRD diagram of the electrolysis product under the conditions of 900°C-3V-6h.

Figure 7 is the XRD pattern of the electrolysis product under the conditions of 900℃-3V-8h.

Detailed ways

In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

The present invention directly utilizes the carbon in cemented carbide in the form of non-greenhouse gas by means of molten salt electrolysis and converts it into high value-added C ₂ H ₂ . At the same time, W and Co in cemented carbide are efficiently separated, providing a new idea and approach for the green and efficient resource utilization of tungsten-containing waste, and solving the problem of tungsten-carbon oxidation and greenhouse gas emissions in the common technical route of converting waste cemented carbide into sodium tungstate.

Referring to FIG1 , the device of the present invention comprises a reactor 4, which can be placed in an electric furnace for heating. A heating device is arranged in the electric furnace, such as a heating resistance wire arranged around the inner wall of the electric furnace; an air inlet 2, an air outlet 3 and two through holes are arranged on the reactor 4, a graphite crucible 5 is placed in the inner cavity of the reactor 4, an alumina crucible 6 is placed in the graphite crucible 5, and the alumina crucible 6 is placed in the graphite crucible 5 to prevent the alumina crucible 6 from breaking at high temperature. The alumina crucible 6 is placed in the graphite crucible 5 for protection. The alumina crucible 6 is filled with molten calcium salt 10, a graphite anode 7 and a cemented carbide cathode 8 are arranged in the molten calcium salt 10, the graphite anode 7 and the cemented carbide cathode 8 are respectively connected to a nickel current collector 9, and the nickel current collector 9 passes through the through hole arranged on the reactor 4 to connect to an external power source 1; during electrolysis, the upper surface of the molten calcium salt 10 is flush with the upper surface of the graphite anode 7 and the cemented carbide cathode 8, or the liquid level of the molten calcium salt 10 is lower than the upper surface of the graphite anode 7 and the cemented carbide cathode 8, so as to prevent the current collector from participating in the electrode reaction or being corroded.

As a preferred embodiment, a cathode mud outlet and a control valve may be provided at the bottom of the reactor 4 to form a structure similar to a separatory funnel, which is beneficial for separating the cathode mud after the reaction.

Furthermore, the bottom of the reactor 4 may be configured to be conical, with the cathode mud outlet being located at the bottom of the cone.

Necessary through holes can be opened on the electric furnace to facilitate the installation of components such as ventilation pipes and current collectors.

In the present invention, cemented carbide (tungsten carbide containing cobalt, WC-Co) is used as a cathode and placed in a molten salt for electrolysis. By adjusting the cell pressure, the alkali metal precipitated from the cathode reacts with WC to form W simple substance and molten salt metal carbide, such as calcium carbide _CaC2 , wherein Co will be precipitated at the bottom of the molten salt in the form of cathode mud together with W and _CaC2 as the WC skeleton is destroyed. After the electrolysis is completed, the cathode mud is washed with water, and the calcium carbide reacts with water to generate acetylene gas and calcium hydroxide. After the calcium hydroxide is completely washed and recovered, the main components of the remaining solid are Co and W. Since cobalt has high magnetism, and tungsten is basically non-magnetic, cobalt and tungsten can be separated by magnetic separation.

The electrolysis temperature of the present invention is greater than 800°C; the electrolysis time is greater than 1h; the electrolytic cell voltage is greater than 2.0V;

The preferred electrolysis temperature is 850-950°C; the electrolysis time is 4-8h; the electrolytic cell voltage is 3.0V-4.0V;

More preferably, the electrolysis temperature is 900°C; the electrolysis time is 6h; and the electrolytic cell voltage is 3V.

The present invention is further described in detail below through specific examples.

Example 1

The method for separating tungsten, cobalt and carbon by electrolysis of cemented carbide molten salt comprises the following steps:

(1) Weigh 500 g of anhydrous _CaCl2 and place it in an alumina crucible with an inner diameter of 75 mm and a height of 130 mm. The double-layer crucible is placed in a sealable stainless steel reactor and then placed in an electric furnace. The _CaCl2 salt is dried at 250°C for 48 hours to remove moisture.

(2) The experiment was carried out in an inert atmosphere (Ar or N ₂ ) (with a ventilation flow rate of 0.5 m ³ /h). The mixed salt was heated to 850°C at a rate of 5°C/min, and the temperature was adjusted to the required temperature after the mixed salt was completely melted. In the molten salt electrolysis experiment, a graphite anode was used as the anode and a cemented carbide was used as the cathode. Parallel experiments were carried out under the conditions of temperature above 800°C, electrolytic cell voltage above 2.0V and electrolysis time above 1h. After the electrolysis was completed, the cathode was withdrawn to the top of the molten salt and cooled for 10 minutes under argon protection before being pulled out of the reactor; it was kept at room temperature under an inert atmosphere to avoid subsequent oxidation reactions and experimental interference. The removed samples were first rinsed with deionized water and dried in a vacuum drying oven at 60°C. After the molten salt was cooled, cathode mud precipitates such as CaC ₂ were collected at the bottom of the molten salt, and the solid products obtained were tested after being fully washed with water.

When the cell voltage was kept at 3.5V and the electrolysis time was 8h, the effects of different electrolysis temperatures of 800℃, 850℃, 900℃, 950℃ and 1000℃ on the electrolytic separation of tungsten, cobalt and carbon in cemented carbide were investigated. Combined with the product crystal analysis, as shown in Figure 2, at 800℃, the cathode product was still the WC phase, and the appearance of the alloy did not change significantly, that is, no reaction occurred during the electrolysis at 800℃; after the temperature was raised to 850℃, precipitates were observed at the bottom of the molten salt. After detection, the solid product showed characteristic diffraction peaks of Co and W, and the alloy became finer. When the temperature was raised to 900℃~950℃, as shown in Figure 3, the XRD of the solid product of the cathode showed characteristic diffraction peaks of Co and W, and the precipitates collected at the bottom of the molten salt produced gas during the water washing process, and the washing water was clear lime water. This shows that increasing the temperature is beneficial to promoting the decomposition of cemented carbide, but too high a temperature can easily cause the volatilization of the molten salt. Therefore, the optimal electrolysis temperature is determined to be 900°C.

Example 2

When the electrolysis temperature was maintained at 900°C and the electrolysis time was 8 hours, the effects of different electrolytic cell voltages of 2V, 3V, and 4V on the electrolytic separation of tungsten, cobalt, and carbon from cemented carbide were investigated. The other steps were the same as in Example 1.

Combined with the product crystal form analysis, as shown in Figure 4, when the constant cell pressure is maintained at 2V, the cathode product is still the WC phase, and the appearance of the alloy has no obvious change. After the cell pressure is increased to 3V and 4V, the cathode product shows characteristic diffraction peaks of Co and W, and the alloy becomes finer, and the precipitate is collected at the bottom of the molten salt. The precipitate produces gas during the water washing process, and the washing water is clear lime water. Therefore, it is shown that increasing the cell pressure is beneficial to promote the decomposition of cemented carbide, but too high a cell pressure is likely to increase energy consumption, so the optimal electrolytic cell pressure is determined to be 3V.

Example 3

When the electrolysis temperature was maintained at 900°C and the electrolytic cell voltage was 3V, the influence of different electrolysis times (2h, 4h, 6h, 8h) on the electrolytic separation of tungsten, cobalt and carbon in cemented carbide was investigated. The other steps were the same as in Example 1.

Combined with the product crystal analysis, as shown in Figure 5, after 2 hours of electrolysis, the cathode product is still WC phase, and the alloy coarseness has no obvious change. After the electrolysis time is extended to 4 hours, the cathode product shows characteristic diffraction peaks of WC, Co and W, and the alloy becomes finer, and the precipitate is collected at the bottom of the molten salt. After the electrolysis time is further extended to 6 hours, as shown in Figures 6 and 7, the cathode products are all electrolysis products of Co and W, and _CaC2 is collected at the bottom of the molten salt. Therefore, it is shown that extending the electrolysis time is beneficial to promote the decomposition of cemented carbide, but too long electrolysis time is easy to increase energy consumption, so the optimal electrolysis time is determined to be 6 hours.

In summary, the optimal electrolysis conditions are: electrolysis temperature 900℃, electrolysis time 6h, and electrolytic cell voltage 3V.

Compared with the common process of converting tungsten carbide into sodium tungstate, the method of separating tungsten, cobalt and carbon by electrolysis of cemented carbide molten salt has the following advantages and effects:

(1) The present invention is guided by relevant thermodynamic calculations, uses waste cemented carbide as the cathode, and in molten calcium salt, by regulating the cell pressure, uses the calcium deposited on the cathode surface to reduce WC to generate W and CaC ₂ , and then can separate the two by water washing to obtain high value-added C ₂ H ₂ . In addition, through thermodynamic calculations, it can be known that Sr and Al can also thermally reduce WC to generate corresponding SrC ₂ (hydrolyzed to generate acetylene and strontium hydroxide) and Al ₄ C ₃ (hydrolyzed to generate methane and aluminum hydroxide), and then separate the substances by water washing or water washing plus acid washing, wherein the acid washing uses dilute hydrochloric acid to further generate chlorides such as calcium chloride and other molten salts from hydroxides for recycling and reuse. Therefore, the present invention is also applicable to corresponding molten strontium salts, aluminum salts, or a combination of the above three or mixed molten salts. This method provides a new idea and approach for the green and efficient resource utilization of tungsten-containing waste.

(2) The present invention adopts molten salt electrolysis, which is to reduce pure metal or its alloy product on the working electrode through an electrochemical method in a molten salt electrolyte. The present invention uses graphite as the anode and cemented carbide as the cathode, applies cell pressure in the molten salt, and separates and recovers tungsten, cobalt, and carbon. The present invention can directly utilize the carbon in the cemented carbide in the form of non-greenhouse gas, which can not only further shorten the regeneration process, but also help save energy and reduce emissions, which is in line with the trend of short process, low cost, and environmental friendliness in the development of the metallurgical industry.

The specific implementation of the present invention described above does not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims (8)

1. The method for separating tungsten, cobalt and carbon by molten salt electrolysis of hard alloy is characterized by comprising the following steps of:

(1) Placing an anode and a cathode in molten salt in inert atmosphere, turning on a power supply to perform electrolytic reaction when the molten salt is completely melted, and collecting a precipitate after the electrolytic reaction is finished; the molten salt is calcium salt; the cathode is cobalt-containing tungsten carbide hard alloy;

(2) Washing the precipitate to obtain a gas product and a tungsten-cobalt mixture, and completing the separation of tungsten cobalt and carbon in the cobalt-containing tungsten carbide hard alloy;

the temperature of the electrolytic reaction is 850-950 ℃, and the voltage of the electrolytic reaction is 3-4V.

2. The method for separating tungsten, cobalt and carbon by molten salt electrolysis of cemented carbide according to claim 1, wherein the time of the electrolysis reaction is 4-8 hours.

3. The method for separating tungsten, cobalt and carbon by electrolyzing hard alloy molten salt according to claim 1, wherein the upper surfaces of the anode and the cathode are higher than or flush with the molten salt liquid surface during the electrolysis reaction.

4. The method for separating tungsten, cobalt and carbon by molten salt electrolysis of hard alloy according to claim 1, wherein the precipitate is washed with water until no gas product is produced, and then washed with acid until the weight of the precipitate is unchanged, so as to obtain a pure tungsten-cobalt mixture; the tungsten cobalt mixture is separated by magnetic separation.

5. The device for separating tungsten, cobalt and carbon by using the molten salt of the hard alloy in low carbon electrolysis is characterized by comprising a reactor which can be heated, wherein a crucible for filling the molten salt is arranged in the reactor, and the molten salt is in a molten state and is provided with an anode and a cathode which are externally connected with a power supply during electrolysis;

the device is used for carrying out cemented carbide molten salt electrolysis low-carbon separation of tungsten cobalt and carbon in the method of any one of claims 1-4.

6. The apparatus for separating tungsten, cobalt and carbon by molten salt electrolysis of hard alloy according to claim 5, wherein the crucible comprises a graphite crucible and an alumina crucible which are sleeved from outside to inside, and the alumina crucible is filled with molten salt.

7. The device for separating tungsten, cobalt and carbon by low carbon in molten salt electrolysis of hard alloy according to claim 5, wherein the reactor is provided with an air inlet and an air outlet which are communicated with the outside and the inner cavity of the reactor.

8. The device for separating tungsten, cobalt and carbon by low carbon in molten salt electrolysis of hard alloy according to claim 5, wherein the anode is graphite; the anode and the cathode are respectively connected with a power supply through a nickel current collector.