A method for recycling and utilizing a major repair slag resource

Abstract

The application discloses a method for recycling and utilizing a major repair slag, which comprises the following steps: reacting the major repair slag with a certain amount of calcium chloride and a small amount of hydrogen peroxide under a pressurized condition, so that lithium elements in the major repair slag enter into a solution, and soluble fluorine ions combine with calcium ions to generate calcium fluoride products; then, a leaching residue is separated by step-by-step flotation to sequentially obtain carbon concentrate, calcium fluoride and cryolite products, and a water solution is recycled to a flotation process; and the leaching solution is prepared into a high-value lithium carbonate product by impurity removal, concentration and hydrothermal treatment. The method can recover various valuable substances in the major repair slag with low energy consumption and high value, and realizes the recycling and utilization of the major repair slag.

Description

Technical Field

[0001] This invention belongs to the field of hazardous waste resource recycling and reuse, and mainly relates to a method for the resource recycling and reuse of overhaul slag. Background Technology

[0002] With the development of a resource-saving and environmentally friendly society, people have increasingly higher requirements for environmental protection. Overhaul slag, as one of the hazardous solid wastes generated during the electrolytic aluminum production process, will cause serious pollution if indiscriminately stockpiled or landfilled. Currently, the disposal of overhaul slag can only involve its harmless treatment or its processing into low-value products, failing to truly extract the high-value elements contained within it. In particular, there is currently no method to recover the high lithium content in overhaul slag.

[0003] Application No. 202110723747.X discloses a method for recovering fluoride salts from aluminum electrolysis overhaul slag under pressure alkaline leaching. This method first uses a sodium hydroxide solution for wet grinding to prevent the volatilization of harmful cyanides. Then, the slurry is leached under pressure using sodium hydroxide and hydrogen peroxide agents. The gas is prepared as ammonium sulfate, and the leachate is precipitated to obtain aluminum fluoride and sodium sulfate, respectively. The precipitate is used as an additive in steel smelting, cement production, and refractory material preparation. While this method effectively renders the overhaul slag harmless, it fails to recover the carbon elements it contains, and the resulting product is of low value, failing to truly recover the high-value elements contained in the overhaul slag. Application No. 202210821960.9 discloses a method for the resource recovery of aluminum electrolysis overhaul slag. This method involves crushing the overhaul slag, adding a defluorinating agent, and then grinding it to obtain a mixture. A cyanide removal agent and acid are then added, and leaching is performed under heating conditions. After filtration and cooling, sodium fluorosilicate is obtained. The leaching is then carried out in a circulating aqueous solution, and the final products are carbonaceous material and sodium fluorosilicate, with no pollutants discharged. This invention effectively recovers the carbonaceous material, fluorides, and destroys harmful cyanides contained in the overhaul slag. However, this method only considers the recovery of substances with higher content in the overhaul slag and fails to recover and utilize the high-value lithium element, resulting in significant economic losses.

[0004] Therefore, how to recover high-value elements such as Li, Al, and F from overhaul slag is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] In view of the above-mentioned technical problems in the existing methods for treating overhaul slag, the present invention provides a method for the resource recycling of overhaul slag that can recover high-value elements such as Li, Al, and F.

[0006] This invention discloses a method for the resource recovery and utilization of overhaul slag, comprising the following steps:

[0007] 1) The overhaul residue is pretreated by crushing, ball milling and screening to obtain pretreated overhaul residue with a suitable leaching particle size;

[0008] 2) The pretreated overhaul residue obtained in step 1) is mixed with predetermined amounts of calcium chloride, hydrogen peroxide, and water, and then subjected to a leaching reaction in a high-pressure reactor to obtain the reacted material.

[0009] 3) Filter the reacted material obtained in step 2), then remove impurities from the water leaching solution to obtain a purified solution, and then perform flotation on the water leaching residue;

[0010] 4) The purified solution obtained in step 3) is evaporated and concentrated to obtain a high-concentration lithium-containing solution;

[0011] 5) Filter the solution after flotation in step 3) to obtain cryolite product, which can be recycled back into the electrolytic aluminum process. The aqueous solution is recycled back to the flotation process in step 4).

[0012] Preferably, the overhaul slag is crushed to less than 1mm, and the oversize material obtained from screening is recycled back to the crushing process for further crushing.

[0013] Preferably, step 2) involves mixing the overhaul residue, calcium chloride, and water in a mass ratio of 1:0.3-0.6:6-12, with hydrogen peroxide accounting for 3‰-6‰ of the overhaul residue, and adding it to a high-pressure reactor for leaching reaction.

[0014] Preferably, the heating rate of the autoclave is controlled at 5-10℃ / min, the reaction temperature is 150-300℃, the pressure is 2-3.5MPa, the reaction time is 1-3h, and the stirring rate is 300-600rpm.

[0015] Preferably, the impurity removal agent used in step 3) includes one or a mixture of several of the following: oxalic acid, potassium hydroxide, sodium hydroxide, sodium benzoate, and sodium carbonate.

[0016] Preferably, the flotation reagents used in step 3) include one or a mixture of two or more of the following: kerosene, xanthate, citric acid, sodium oleate, and water glass.

[0017] Preferably, the flotation in step 3) is a two-stage flotation, where the primary flotation concentrate is high-grade carbon powder and the secondary flotation concentrate is calcium fluoride.

[0018] Preferably, the impurity remover is composed of 1-3 mol / L oxalic acid, 2-3 mol / L sodium benzoate, or a mixture of 1-2 mol / L oxalic acid and sodium benzoate.

[0019] Preferably, the flotation reagent is a mixture of 10-15 mg / L kerosene, 5-10 mg / L xanthate, 5-10 mg / L citric acid, 3-6 mg / L water glass, and 20-30 mg / L sodium oleate.

[0020] Preferably, the high-concentration lithium-containing solution obtained in step 4) is added to a sodium carbonate solution of 100-200 g / L at a temperature of 80℃-90℃ at a rate of 1-2 L / min, and the stirring speed is controlled at 300-500 rpm. The lithium carbonate product is obtained by filtration.

[0021] The principle of this invention: This invention uses overhaul slag from an electrolytic aluminum plant as raw material. Under high-pressure leaching with calcium chloride and hydrogen peroxide, lithium is effectively leached into the solution, fluorides are converted into stable substances, and harmful cyanides are oxidized and decomposed. The filter residue can be processed stepwise to obtain carbon concentrate, calcium fluoride, and cryolite products under the action of flotation reagents. The water leaching solution, after impurity removal, concentration, and carbonization processes, yields high-purity lithium carbonate. The filtrate is returned to the leaching process via a recycling process. The substances obtained by this invention are all high-value products, resulting in high economic benefits.

[0022] The beneficial effects of this invention are as follows: This invention effectively oxidizes and decomposes cyanide through pressure leaching of overhaul slag; simultaneously, it separates or reprocesses valuable substances contained in the slag into high-value products (carbon concentrate, calcium fluoride, cryolite, lithium carbonate), and the aqueous solution is recycled, resulting in no pollutant discharge. This invention transforms hazardous waste overhaul slag into various high-value substances after treatment, providing raw materials and generating high-value revenue for the aluminum plant's continued operation. Attached Figure Description

[0023] Figure 1 This is a process flow diagram for the resource recycling and utilization of overhaul slag. Detailed Implementation

[0024] The following examples are intended to further illustrate the present invention, but not to limit the scope of protection of the claims. Unless otherwise specified, the relevant percentages refer to mass percentages.

[0025] Table 1. Main elemental composition and content of overhaul slag

[0026]

[0027] The method of this invention can separate or reprocess high-value elements into high-value products, such as carbon concentrate, calcium fluoride, cryolite, and lithium carbonate, and the aqueous solution can be recycled without pollutant discharge. See details for the specific process. Figure 1 .

[0028] from Figure 1 The detailed process flow of the overhaul slag resource recycling method of the present invention can be seen. Based on this process flow, the inventors conducted the following experiments:

[0029] Implementation Case 1

[0030] Using overhaul slag from an electrolytic aluminum plant in Hunan as raw material, the following steps were followed:

[0031] Preparation of the mixture: First, crush the overhaul slag and sieve it with a 1mm sieve. After pre-treatment by sieving, the pre-treated overhaul slag raw material is obtained. Take 50g of the overhaul slag raw material, 15g of calcium chloride, 300g of water and 0.15g of hydrogen peroxide and mix them evenly to obtain the mixture.

[0032] Pressure leaching process: The above mixture is placed in a high-pressure reactor, the temperature is raised to 300℃ at a heating rate of 10℃ / min, the pressure is controlled at 3.5Mpa, the reaction time is controlled at 1h, and the stirring rate is controlled at 300rpm.

[0033] Flotation process: After pressure leaching, the filtered water leaching residue is first floated in 10 mg / L kerosene, 10 mg / L xanthate and 5 mg / L citric acid to obtain carbon concentrate with a grade of 97% and a recovery rate of 98%. Then, 20 mg / L sodium oleate and 3 mg / L water glass are added to the solution to obtain calcium fluoride with a grade of 72% after drying. The remaining solution is filtered to obtain cryolite product.

[0034] Lithium removal and precipitation process: After pressure leaching, the leachate obtained by filtration is treated with 3 mol / L oxalic acid to remove excess calcium impurities. After filtration, the pH of the leachate is adjusted to 12 with sodium hydroxide solution. Then, the solution is concentrated to a lithium concentration of 20 g / L by heating and evaporation. The solution is then added to a 100 g / L sodium carbonate solution at 80°C at a rate of 1 L / min, with the stirring speed controlled at 300 rpm. After filtration, a lithium carbonate product with a purity of 99.8% can be obtained.

[0035] Implementation Case 2

[0036] Using overhaul slag from an electrolytic aluminum plant in Hunan as raw material, the following steps were followed:

[0037] Preparation of the mixture: The overhaul slag is pretreated by crushing and sieving. Take 50g of the pretreated overhaul slag raw material, 20g of calcium chloride, 400g of water and 0.25g of hydrogen peroxide and mix them evenly to obtain the mixture.

[0038] Pressure leaching process: The mixture is placed in a high-pressure reactor, the temperature is raised to 200℃ at a heating rate of 8℃ / min, the pressure is controlled at 2.5Mpa, the reaction time is controlled at 1.5h, and the stirring rate is controlled at 400rpm.

[0039] Flotation process: After pressure leaching, the filtered water leaching residue is first floated in 15 mg / L kerosene, 5 mg / L xanthate and 8 mg / L citric acid to obtain carbon concentrate with a grade of 98.5% and a recovery rate of 97.3%. Then, 25 mg / L sodium oleate and 5 mg / L water glass are added to the solution to obtain calcium fluoride with a grade of 70% after drying. The remaining solution is filtered to obtain cryolite product.

[0040] Lithium removal and precipitation process: After pressure leaching, the leachate obtained by filtration is treated with 3 mol / L sodium benzoate to remove excess calcium impurities. After filtration, the pH of the leachate is adjusted to 13 with potassium hydroxide solution. Then, the solution is concentrated to a lithium concentration of 25 g / L by heating and evaporation. The solution is then added to a 150 g / L sodium carbonate solution at 85°C at a rate of 2 L / min, with the stirring speed controlled at 400 rpm. After filtration, a lithium carbonate product with a purity of 99.9% can be obtained.

[0041] Implementation Case 3

[0042] Preparation of the mixture: The overhaul slag produced by an electrolytic aluminum plant in Hunan Province was used as raw material for pretreatment. 50g of the pretreated overhaul slag raw material, 30g of calcium chloride, 600g of water and 0.30g of hydrogen peroxide were mixed evenly and added to the high pressure vessel.

[0043] Pressure leaching process: The mixture is placed in a high-pressure reactor, the temperature is raised to 150℃ at a heating rate of 5℃ / min, the pressure is controlled at 2.0 MPa, the reaction time is controlled at 3h, and the stirring rate is controlled at 600 rpm.

[0044] Flotation process: After pressure leaching, the filtered water leaching residue is first floated in 15 mg / L kerosene, 10 mg / L xanthate and 10 mg / L citric acid to obtain carbon concentrate with a grade of 98.0% and a recovery rate of 99.2%. Then, 30 mg / L sodium oleate and 10 mg / L water glass are added to the solution to obtain calcium fluoride with a grade of 76% after drying. The remaining solution is filtered to obtain cryolite product.

[0045] Lithium removal and precipitation process: After pressure leaching, the leachate obtained by filtration is treated by adding a 2 mol / L mixed solution of oxalic acid and sodium benzoate to remove excess calcium impurities. After filtration, the pH of the leachate is adjusted to 13 with potassium hydroxide solution. Then, the solution is concentrated to a lithium concentration of 30 g / L by heating and evaporation. The solution is then added to a 200 g / L sodium carbonate solution at 90°C at a rate of 2 L / min, with the stirring speed controlled at 500 rpm. After filtration, a lithium carbonate product with a purity of 99.9% can be obtained.

[0046] The above experiments show that it can effectively oxidize and decompose cyanide, while separating or reprocessing valuable substances contained in the overhaul slag into high-value products, recycling the aqueous solution, and discharging no pollutants.

Claims

1. A method for recycling and utilizing a large overhaul slag resource, comprising the following steps: 1) crushing, ball milling and screening the large overhaul slag for pretreatment to obtain a pretreated large overhaul slag with a suitable leaching particle size; 2) mixing the pretreated large overhaul slag obtained in step 1) with a predetermined amount of calcium chloride, hydrogen peroxide and water, and carrying out a leaching reaction in a high-pressure reactor to obtain a reacted material; 3) filtering the reacted material obtained in step 2), then removing impurities from the water leaching solution to obtain a purified solution, and carrying out flotation on the water leaching residue; 4) evaporating and concentrating the purified solution obtained in step 3) to obtain a high-concentration lithium-containing solution; 5) filtering the solution after flotation in step 3) to obtain a cryolite product, which is recycled into an electrolytic aluminum process, and the aqueous solution is recycled to the flotation process in step 3); In step 2), the large overhaul slag, calcium chloride and water are mixed in a mass ratio of 1:0.3-0.6:6-12, the hydrogen peroxide accounts for 3‰-6‰ of the large overhaul slag, and the mixture is added to a high-pressure reactor for leaching reaction; the heating rate of the high-pressure reactor is controlled at 5-10 ℃ / min, the reaction temperature is 150-300 ℃, the pressure is 2-3.5 MPa, the reaction time is 1-3 h, and the stirring rate is 300-600 rpm; In step 3), the impurity removal agent includes oxalic acid, sodium benzoate or a mixture of oxalic acid and sodium benzoate; the impurity removal agent is 1-3 mol / L of oxalic acid or 2-3 mol / L of sodium benzoate or a mixture of 1-2 mol / L of oxalic acid and sodium benzoate; In step 3), the flotation reagent is a mixture of 10-15 mg / L of kerosene, 5-10 mg / L of xanthate, 5-10 mg / L of citric acid, 3-6 mg / L of water glass and 20-30 mg / L of sodium oleate.

2. The method for resource recycling of overhauled slag according to claim 1, characterized in that: The large overhaul slag is crushed to less than 1 mm, and the oversize material obtained by screening is recycled back to the crushing process for further crushing.

3. The method of reclaiming and recycling the spent grinding charge material according to claim 1, characterized in that In step 3), the flotation adopts secondary flotation, the primary flotation concentrate is high-grade carbon powder, and the secondary flotation concentrate is calcium fluoride product.

4. The method of reclaiming and recycling the spent grinding charge material of claim 1, wherein The high-concentration lithium-containing solution obtained in step 4) is added to a 100-200 g / L sodium carbonate solution at a rate of 1-2 L / min and a temperature of 80-90 ℃, the stirring speed is controlled at 300-500 rpm, and the lithium carbonate product is obtained by filtration.

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