NL2026854B1 - Method for preparing mercury removal catalyst from cathode scrap material and use of catalyst for mercury removal - Google Patents

Abstract

The disclosure provides a method for preparing a mercury (Hg) removal catalyst from a cathode scrap material, including the following steps: step (1): dealuminating a cathode scrap material to obtain a dealuminated cathode material; step (2): heat treating the dealuminated cathode material obtained in step (1) in the presence of an inert gas to obtain a metal oxide/carbon composite catalyst; step (3): grinding the metal oxide/carbon composite catalyst obtained in step (2), heating and activating in a reducing gas, and cooling to obtain a mercury removal catalyst. The disclosure also provides use of the above mercury removal catalyst. The disclosure uses a scrap ternary cathode material as a raw material to prepare a mercury removal catalyst, which turns a scrap material into a useful material, achieving resource recycling. Moreover, the disclosure has a low cost of raw material for preparing the mercury removal catalyst and a high economic value. The catalyst of the disclosure is highly efficient in Hg removal with a catalytic oxidation efficiency reaching more than 90%, which can significantly improve economic benefits.

Description

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METHOD FOR PREPARING MERCURY REMOVAL CATALYST FROM CATHODE SCRAP MATERIAL AND USE OF CATALYST FOR MERCURY REMOVAL

TECHNICAL FIELD The disclosure belongs to the technical field of catalysts, and particularly relates to a method for preparing a mercury removal catalyst and use of the mercury removal catalyst.

BACKGROUND In traditional industrial production processes such as coal burning, smelting, and cement producing, mercury (Hg) in coal and minerals volatilize into flue gas at high temperature, forming an Hg-containing flue gas. China is a major producer of electricity, metals and cement, producing a large amount of atmospheric Hg emissions. In order to reduce harmful effects of Hg on environment and humans, it is essential to reduce atmospheric Hg emissions in China. The Hg in the flue gas is mainly present in three forms: oxidized Hg (Hg®"), particulate Hg (Hef) and elemental mercury (Hg). A vast majority of Hg?" and Hg? can be removed during washing and dust removal of flue gas respectively. Compared with Hg** and He, He" can hardly be removed by existing flue gas treatment equipment due to its low solubility and high chemical stability. Therefore, it is necessary to adopt special technology to achieve efficient removal of Hg". Hg’ removal technology nowadays mainly includes two strategies, adsorption and catalytic oxidation. Adsorption technology mainly makes use of affinity of Hg" to activated carbon, halogen, sulfide and other substances to finally convert Hg” into Hg®. Although the adsorption technology can capture Hg’. the Hg-containing particulate formed after the capture still has a risk of secondary pollution of Hg, and there is a relatively high cost in operation. Catalytic oxidation technology oxidizes Hg” to Hg** through catalysis with a low cost in operation and a high oxidation efficiency, thus, it has become an effective way to reduce Hg" emissions. At present, catalysts for Hg” mainly include copper oxides, precious metals, rare earth metal oxides and the like. A relatively high cost in material production thereof limits their use in a wide variety of applications. Therefore, it is necessary to develop a composite metal catalyst that is cost effective and efficient.

SUMMARY To overcome the existing shortcomings and deficiencies, the disclosure aims to provide a method for preparing a mercury removal catalyst from a cathode scrap material and use of the

2. mercury removal catalyst.

The catalyst prepared from a cathode scrap material is cost effective and efficient, and achieves recycling of resources.

In order to solve the above technical problem, a technical solution proposed by the disclosure is: A method for preparing a mercury removal catalyst from a cathode scrap material includes the following steps: step (1): dealuminating a cathode scrap material to obtain a dealuminated cathode material; step (2): heat treating the dealuminated cathode material obtained in step (1) in the presence of an inert gas (for example, nitrogen or argon with a high purity) to obtain a metal oxide/carbon composite catalyst; step (3): grinding the metal oxide/carbon composite catalyst obtained in step (2), heating and activating in a reducing gas, and cooling to obtain a mercury removal catalyst.

In the disclosure, metal oxides in power battery are adhered to an aluminum foil by a binder to form a cathode material.

Therefore, during recycling of scrap power battery, part of the aluminum foil is inevitably present in an obtained scrap cathode material.

If aluminum is not removed, the aluminum foil will reduce an activity of catalyst in a subsequent catalyst preparation process.

For example. the aluminum foil will react with the metal oxides during roasting in an inert atmosphere to form a composite with a low activity.

Therefore, dealumination is required.

Moreover, the cathode scrap material contains a certain amount of lithium, which mainly exists in forms of lithium cobaltate, lithium cobalt manganate and the like.

In the above method for preparing a mercury removal catalyst, the inert gas is preferably a flowing inert gas at a flow rate of 0.5-1.2 L/min.

In the above method for preparing a mercury removal catalyst, the heat treating is preferably carried out at 600-800°C for 30-90 min with a heating rate of 2-6°C/min.

The above heat treating parameters can ensure that organic matters in the cathode scrap material are all volatilized or carbonized.

The heat treating temperature, heating rate and holding time can ensure efficient carbonization of organic matters (for example, binders) and facilitate formation of a porous composite catalyst.

In the above method for preparing a mercury removal catalyst, the reducing gas is preferably a mixed gas of hvdrogen and nitrogen with the hydrogen taking up a volume of 2-5%, or a mixed gas of carbon monoxide and nitrogen with the carbon monoxide taking up a volume of 4-10%. The reducing gas should not be used in an excessively high amount.

Its application amount is related to activation time and temperature with a main purpose of preventing excessive reduction and formation of a large amount of elemental metals.

In the above method for preparing a mercury removal catalyst, the heating and activating is preferably carried out at an activation temperature of 400-600°C for an activation time period ie of 5-15 min. The heating and activating in a reducing gas is carried out to reduce stable oxides such as LiCoO: on a surface to form active sites of electron pairs such as Co’"/Co** and Mn**/Mn** to promote the catalytic oxidation of Hg. Too high a heating temperature and too long an activation time period will lead to excessive reduction which reduces the activity of the catalyst. Too low a heating temperature and too short an activation time period will lead to insufficient reduction and fewer catalytic active sites on the surface, which is not advantageous for catalysis of Hg.

In the above method of preparing a mercury removal catalyst, the dealuminating is preferably implemented by adding the cathode scrap material to an alkaline solution at pH 10-12 in a solid-to-liquid ratio (mass ratio) of 1:( 3-7) and stirring for dissolution.

In the above method for preparing a mercury removal catalyst, the stirring for dissolution is preferably carried out at 400-800 r/min and 40-60°C for 0.5-1.5 h.

In the above method for preparing a mercury removal catalyst, the cathode scrap material is preferably a nickel-cobalt-manganese ternary cathode material.

Asa general technical concept, the disclosure also provides use of the mercury removal catalyst prepared by the above methods in catalytic oxidation of elemental Hg in an Hg- containing flue gas at 100-250°C. The mercury removal catalyst in the disclosure is particularly suitable for treatment of Hg-containing flue gases in industries such as coal burning, non-ferrous metals, and cement. Moreover, studies show that, the specific catalyst in the disclosure appropriately functions at 100-250°C with a high efficiency of catalytic oxidation.

The disclosure directly utilizes a cathode scrap material to prepare a mercury removal catalyst. The cathode scrap material contains carbonaceous substances such as binders and conductive agents and cobalt/manganese/nickel oxides. After heat treatment in an inert gas, the carbonaceous substances such as binders and conductive agents in the cathode scrap material form a porous carbon material skeleton, which provides a carrier for active metal oxides in the cathode material, forming a composite material of carbon with the metal oxides. Moreover, after the heat treatment, the cathode material forms some holes, which increases a specific surface area of the material, thereby improving catalytic performance. Stable high-valence cobalt/manganese/nickel oxides in the cathode material undergo controllable reduction and form heterojunction active sites with a high activity, such as C0.03/CoO and MnQ,/Mn;04 heterojunctions. The heterojunctions formed on the surface of the catalyst containing electron pairs such as highly active Co**/Co?* can achieve efficient catalytic oxidation of elemental Hg in a flue gas.

The cathode scrap material contains a certain amount of lithium, which mainly exists in forms of lithium cobaltate, lithium cobalt manganate and the like.

-4- Compared with the prior art, advantages of the disclosure are as follows: I. The disclosure uses a scrap ternary cathode material as a raw material to prepare a mercury removal catalyst, which turns a scrap material into a useful material, achieving resource recycling. Moreover, the disclosure has a low cost of raw material for preparing the mercury removal catalyst and a high economic value.

2. The catalyst of the disclosure is prepared by a simple and environmentally friendly process which meets industrial production requirements.

3. The catalyst of the disclosure is highly efficient in Hg removal with a catalytic oxidation efficiency reaching more than 90%, which can significantly improve economic benefits.

4. An adsorbent of the disclosure can be widely used in Hg removal of various industrial flue gases, and directly applied to existing flue gas treatment equipment without changing existing treatment processes.

DETAILED DESCRIPTION In order to facilitate the understanding of the disclosure, the disclosure will be described more fully and in detail below with reference to preferred examples, but the protection scope of the disclosure is not limited to the following specific examples.

Unless otherwise defined, all technical terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific examples, and are not intended to limit the protection scope of the disclosure.

Unless otherwise specified, various raw materials, reagents, instruments, equipment, and the like used in the disclosure are commercially available or can be prepared by existing methods. Example 1: This example provided a method for preparing a mercury removal catalyst from a cathode scrap material which was a nickel-cobalt-manganese ternary cathode material with a molar ratio of the three of 1:1:1, including the following steps: Step (1): 100 mL of NaOH solution at pH 11 was prepared, added with 30 g of scrap cathode material and stirred at 500 r/min. Reaction was carried out at 30°C for lh. After the reaction, a slurry was filtered, washed and dried at 60°C for more than 10 h to obtain a dealuminated cathode material.

Step (2): The dealuminated cathode material was placed in a tube furnace. N; with a high purity was introduced as a protective gas at a flow rate of 1 L/min. Heating was carried out at a heating rate of 5°C/min to obtain different temperatures (see Table 1 below for specific temperatures). The temperatures were held for 30 min to obtain different metal oxide/carbon composite catalysts.

-5- Step (3): The metal oxide/carbon composite catalysts prepared above were ground and placed in an atmosphere furnace. A reducing gas, 5%H>+95%N: (in volume), was introduced and heated to 500°C for activation. The activation was carried out for 10 min. After reaction, introduction of the reducing gas was stopped. A temperature was naturally cooled to room temperature to obtain the catalysts for Hg removal of this example. The prepared catalysts for Hg removal were placed in a fixed bed for evaluation of catalysis. Specifically, 50 mg of mercury removal catalyst was fixed on the fixed bed, a reaction was carried out at 150°C with a gas flow rate of 1 L/min, and a flue gas included 10 ppm HCI + 5% 0; + 180 pg/m* He’. Final efficiencies of catalytic oxidation of Hg” were shown in Table 1.

Table 1: Effect of different heating temperatures on oxidation efficiency of Hg’ Core [a It can be seen from Table 1 that, roasting at a high temperature in an inert atmosphere can significantly increase the oxidation efficiency of Hg". When the heating temperature was within the range of 600-800°C, the efficiency of catalytic oxidation of Hg" was above 90%.

The above control group was treated at room temperature, and the rest steps were the same as those in other groups.

Example 2: This example provided a method for preparing a mercury removal catalyst from a cathode scrap material which was a nickel-cobalt-manganese ternary cathode material with a molar ratio of the three of 1:1: 1, including the following steps: Step (1): 100 mL of NaOH solution at pH 11 was prepared, added with 30 g of scrap cathode material and stirred at 500 r/min. Reaction was carried out at 50°C for 1h. After the reaction, a slurry was filtered, washed and dried at 60°C for more than 10 h to obtain a dealuminated cathode material.

Step (2): The obtained dealuminated cathode material was placed in a tube furnace. N; with a high purity was introduced as a protective gas at a flow rate of 1 L/min. Heating was carried out at a heating rate of 5°C/min to obtain a temperature of 700 °C. The temperatures were held for 30 min to obtain metal oxide/carbon composite catalysts.

Step (3): The metal oxide/carbon composite catalysts prepared above were ground and placed in an atmosphere furnace. A reducing gas, 5%9H;+95%4N: (in volume), was introduced and

-6- heated to different activation temperatures. Activation was carried out for different time periods (see Table 2 below). After reaction, introduction of the reducing gas was stopped. A temperature was naturally cooled to room temperature to obtain the catalysts for Hg removal of this example.

The prepared catalysts for Hg removal were placed in a fixed bed for evaluation of catalysis. Specifically, 50 mg of mercury removal catalyst was fixed on the fixed bed, a reaction was carried out at 150°C with a gas flow rate of 1 L/min, and a flue gas included 10 ppm HCI + 5% 0+ 180 ug/m’ He’. Final efficiencies of catalytic oxidation of He? were shown in Table 2. Table 2: Effect of different roasting temperatures and temperature holding time in activation on efficiency of catalytic oxidation of Hg" Sample Activation Temperature holding Efficiency of catalytic we

62.8 group we wr It can be seen from Table 2 that. reduction activation can significantly improve the Hg removal efficiency of the catalyst. The efficiency of catalytic oxidation of Hg" at an activation temperature of 400-600°C was relatively high. The temperature holding time being too short or too long was not advantageous in forming active oxygen vacancies on the catalyst surface, leading to a decrease of the oxidation efficiency of Hg".

Example 3: This example provided a method for preparing a mercury removal catalyst from a cathode scrap material which was a nickel-cobalt-manganese ternary cathode material with a molar ratio of the three of 1:1: 1, including the following steps: Step (1): 100 mL of NaOH solution at pH 11 was prepared, added with 30 g of scrap cathode material and stirred at 500 r/min. Reaction was carried out at 50°C for 1h. After the reaction, a slurry was filtered. washed and dried at 60°C for more than 10 h to obtain a dealuminated cathode material.

Step (2): The obtained dealuminated cathode material was placed in a tube furnace. N; with a high purity was introduced as a protective gas at a flow rate of 1 L/min. Heating was carried

-7- out at a heating rate of 5°C/min to obtain a temperature of 700 °C. The temperatures were held for 30 min to obtain metal oxide/carbon composite catalysts. Step (3): The metal oxide/carbon composite catalysts prepared above were ground and placed in an atmosphere furnace. A reducing gas, 5%H>+95%N; (in volume), was introduced and heated to 500°C for activation. The activation was carried out for 10 min. After reaction, introduction of the reducing gas was stopped. A temperature was naturally cooled to room temperature to obtain the catalysts for Hg removal of this example. The prepared catalysts for Hg removal were placed in a fixed bed for evaluation of catalysis. Specifically, 50 mg of mercury removal catalyst was fixed on the fixed bed, a gas flow rate was 1 L/min, and a flue gas included 180 pg/m* Hg". Temperature for catalytic reaction and concentrations of HCI and O; in the flue gas were changed to determine appropriate conditions for application of the catalysts. Final efficiencies of catalytic oxidation of Hg" were shown in Table 3. Table 3: Effect of different catalvtic reaction temperatures and flue gas compositions on oxidation efficiency of Hg" Sample Catalysis Efficiency of oxidation HCI (ppm) O: (v%) Ee i, ee

B EN A ww fe It can be seen from Table 3 that, the optimal temperature for the catalyst was 100-250°C. Both HCI and O: can improve Hg" oxidation by the catalysts. The efficiency of He’ oxidation can still reach 80% in the absence of HCI, indicating that the catalysts can enable oxidation of Hg without chlorine.

Example 4: This example provided a method for preparing a mercury removal catalyst from a scrap lithium cobaltate cathode material, including the folowing steps:

-8- Step (1): 100 mL of NaOH solution at pH 11 was prepared, added with 30 g of scrap lithium cobaltate cathode material and stirred at 500 r/min. Reaction was carried out at 50°C for 1h. After the reaction, a slurry was filtered, washed and dried at 60°C for more than 10 h to obtain a dealuminated lithium cobaltate cathode material.

Step (2): The obtained dealuminated lithium cobaltate was placed in a tube furnace. N: with a high purity was introduced as a protective gas at a flow rate of 1 L/min. Heating was carried out at a heating rate of 5°C/min to obtain a temperature of 700 °C. The temperatures were held for 30 min to obtain a metal oxide/carbon composite catalyst.

Step (3): The metal oxide/carbon composite catalyst prepared above was ground and placed in an atmosphere furnace. A reducing gas, 5%H:+95%N: (in volume), was introduced and heated to 500°C for activation. The activation was carried out for 10 min. After reaction, introduction of the reducing gas was stopped. A temperature was naturally cooled to room temperature to obtain the mercury removal catalyst of this example. The prepared mercury removal catalyst was placed in a fixed bed for evaluation of catalysis. Specifically. 50 mg of mercury removal catalyst was fixed on the fixed bed, a reaction was carried out at 150°C with a gas flow rate of 1 L/min, and a flue gas included 10 ppm HCI + 5% 0: + 180 ug/m’ Hg". A final efficiency of catalvtic oxidation of Hg” by the lithium cobaltate catalyst was 83.4%.

Claims (9)

Claims L Process for preparing a catalyst to remove mercury from a cathode scrap material, the method comprising the steps of: step (1): dealuminating a cathode scrap material to obtain a dealuminated cathode scrap material; step (2) heat treating the dealuminated cathode material obtained in step (1) in the presence of an inert gas to obtain a metal oxide/carbon composite catalyst; step (3) grinding the metal oxide/carbon composite catalyst obtained in step (2), heating and activating in a reducing gas, and cooling to obtain a catalyst for removing mercury. The process for preparing a catalyst for removing mercury according to claim 1, wherein the inert gas is a flowing inert gas having a flow rate of 0.5 - 1.2 L/min. The method for preparing a catalyst for removing mercury according to claim 1, wherein the heat treatment is carried out at 600-800°C for 30-90 min at a heating rate of 2-6°C/min. The process for preparing a catalyst for removing mercury according to claim 1, wherein the reducing gas is a mixed gas of hydrogen and nitrogen wherein the hydrogen occupies a volume of 2 - 5%, or a mixed gas of carbon monoxide and nitrogen wherein the carbon monoxide occupies a volume of 4 — 10%. The process for preparing a catalyst for removing mercury according to claim 1, wherein the heating and activation is carried out at an activation temperature of 400-600°C for an activation time period of 5-15 min. 6. Method of preparing a catalyst to remove mercury -10- according to any one of claims 1 to 5, wherein the dealumination is implemented by adding the cathode scrap material to an alkaline solution of pH 10-12 in a solid to liquid ratio of 1:(3 - 7) and the stirring for solution. A process for preparing a catalyst for removing mercury according to claim 6, wherein the stirring for dissolution is carried out at 400-800 r/min and 40-60°C for 0.5-1.5 hours. A process for preparing a mercury removal catalyst according to any one of claims 1 to 5, wherein the cathode scrap material is a nickel-cobalt-manganese ternary cathode material. Use of the mercury removal catalyst according to any one of claims 1 to 8 in catalytic oxidation of elemental mercury in a flue gas containing mercury at 100 to 250°C.