A comprehensive treatment device and method for electrolytic aluminum overhaul slag

Abstract

The present invention discloses a comprehensive treatment device and treatment method for electrolytic aluminum overhaul slag. The device is a diaphragm electrolysis device, comprising a plurality of unit cells, wherein the unit cells are separated by an anode and a cathode. In the unit cells, an anion membrane is arranged near the anode, and a cation membrane is arranged near the cathode. A partition with a chamber is arranged between the anode, the anion membrane, the cation membrane, and the cathode, respectively, to separate the unit cells from the anode to the cathode into an anode chamber, a solution chamber, and a cathode chamber; multiple groups of unit cells are connected in series, and the cells are connected in parallel, or multiple groups of unit cells are connected in parallel and the cells are connected in series. The method comprises the steps of sorting and crushing, wet grinding and immersion, filtering, and diaphragm electrolysis. This scheme can effectively classify and treat the overhaul slag and dispose of it harmlessly. The diaphragm electrolysis method is adopted to enrich sodium fluoride while electrochemically breaking cyanide, so as to realize the recycling of aluminum slag, carbon blocks, refractory materials, and sodium fluoride.

Description

Technical Field

[0001] The present invention belongs to the technical field of harmless disposal of hazardous wastes, and specifically relates to a comprehensive treatment device and method for electrolytic aluminum overhaul slag, which is used for harmlessly disposing of electrolytic aluminum overhaul slag and comprehensively recycling and utilizing the resources therein. Background Art

[0002] my country is a major producer of primary aluminum. During the production of electrolytic aluminum, the electrolytic cell must be regularly inspected and repaired, and the inner lining of the electrolytic cell must be replaced every 5 to 6 years. Overhaul slag is a general term for the waste cell lining removed during the overhaul of the electrolytic cell, which contains carbonaceous materials, refractory insulation materials and fluorides, each accounting for about 30% of its total weight, and about 0.2% of cyanide salts. In 2018 alone, the new overhaul slag generated by my country's electrolytic aluminum enterprises exceeded 1 million tons, and the amount is even larger when the overhaul slag is piled in the open air or landfilled in fixed slag yards. The "National List of Hazardous Wastes" revised on March 30, 2016 clearly defines the waste slag (i.e. overhaul slag) generated by the maintenance and disposal of electrolytic cells during the production of electrolytic aluminum as hazardous waste, with waste category: HW48, waste code: 321-023-48, and hazardous characteristics T (toxicity). Therefore, overhaul slag urgently needs to be harmlessly disposed and comprehensively utilized.

[0003] Patent CN109332352 A discloses a method for solidifying soluble fluorine in electrolytic aluminum overhaul slag, which uses calcium hydroxide, calcium oxide, carbide slag, and desulfurization slag to solidify soluble fluorine in the slag, thereby treating waste with waste, but does not solve the cyanide pollution problem.

[0004] Patent CN 111517349 A discloses a method for recovering aluminum fluoride from aluminum electrolytic cell overhaul slag, wherein the overhaul slag is acid leached to obtain a soluble fluoride solution, which is converted into crude aluminum fluoride by aluminum hydroxide precipitation, thereby recovering fluorine in the overhaul slag. The problem of cyanide pollution is not mentioned.

[0005] Patent CN111495923 A discloses a method for treating waste slag from overhaul of electrolytic aluminum, which uses calcium hypochlorite to break cyanide and calcium chloride to fix fluorine for harmless treatment before landfill. Fluorine resources and carbon electrode materials are not effectively utilized, and the introduction of chloride ions during harmless disposal will produce a large amount of waste salt. The solid waste after treatment cannot be reused due to its high chlorine content.

[0006] Patent CN107313075 A discloses a heap leaching method for waste refractory materials used in aluminum electrolysis cells, in which the crushed refractory materials are heap leached with sodium hydroxide solution, cyanide is broken with hydrogen peroxide, and then neutralized with carbon dioxide to produce a mixture of sodium bicarbonate, sodium carbonate and sodium fluoride, thereby rendering the waste refractory materials harmless. The product cannot be used directly, and hydrogen peroxide is a hazardous chemical. The transportation of hydrogen peroxide liquid may pose certain safety risks.

[0007] In summary, the current treatment of electrolytic aluminum overhaul slag in China generally adopts harmless disposal, and the comprehensive utilization level is low, resulting in waste of resources. Especially at present, governments at all levels attach importance to the construction of waste-free cities and waste removal action plans. How to effectively achieve the harmlessness of electrolytic aluminum overhaul slag and how to make high value-added resource utilization have become hot spots and difficulties in the research of the scientific and industrial circles. Summary of the invention

[0008] The purpose of the present invention is to provide a comprehensive treatment device and method for electrolytic aluminum overhaul slag, which can achieve the maximum comprehensive utilization of resources while solving the harmless disposal of overhaul slag without introducing new impurities, and can obtain carbon block materials, sodium fluoride and harmless residues, which belongs to a green process.

[0009] The present invention is realized by the following technical scheme: a comprehensive treatment device for electrolytic aluminum overhaul slag, characterized in that: the device is a diaphragm electrolysis device, comprising a plurality of unit cells, the unit cells are separated by an anode and a cathode, an anion membrane is arranged near the anode in the unit cells, a cation membrane is arranged near the cathode, and a partition with a chamber is arranged between the anode, the anion membrane, the cation membrane and the cathode, respectively, to separate the unit cells from the anode to the cathode into an anode chamber, a solution chamber and a cathode chamber;

[0010] Multiple groups of unit slots are connected in series and the slots are connected in parallel, or multiple groups of unit slots are connected in parallel and the slots are connected in series.

[0011] Furthermore: the anode is an electrode that is inert to the anolyte; the separator is made of an insulating material and serves as a framework to isolate the electrode and the ion membrane.

[0012] A comprehensive treatment method for electrolytic aluminum overhaul slag, using the above-mentioned device, is characterized in that: the method includes: sorting and crushing, wet grinding and immersion, filtering, and diaphragm electrolysis steps:

[0013] The sorting and crushing step is to manually sort the overhaul slag into aluminum slag, carbon blocks, and refractory materials, and then crush them;

[0014] In the wet grinding and water soaking step, the crushed overhaul slag is ground into 80-200 meshes with water to form a slurry with a solid-liquid ratio of 1:2-10, and the solid-liquid contact time is extended to 10-60 minutes by water soaking;

[0015] In the diaphragm electrolysis step, the ore pulp is filtered and then injected into the solution chamber. The cathode chamber and the anode chamber are both sodium hydroxide solutions. After the electrodes are energized, F in the filtrate - , CN - In the anode chamber, cyanide is enriched and broken, producing sodium fluoride, Na + Sodium hydroxide is produced in the cathode chamber.

[0016] Furthermore, in the wet grinding and water soaking step, the crushed overhaul slag is ground into 150-200 meshes with water to form a slurry with a solid-liquid ratio of 1:3-5, and the solid-liquid contact time is extended to 20-40 minutes by water soaking.

[0017] The advantages of the present invention are: the method of the present invention can effectively classify and harmlessly dispose of overhaul slag. The diaphragm electrolysis method is adopted to enrich sodium fluoride while electrochemically destroying cyanide, so as to realize the recycling of aluminum slag, carbon block, refractory material and sodium fluoride respectively. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the parallel structure in the diaphragm electrolyzer of the present invention;

[0019] Figure 2 It is a schematic diagram of the series structure in the diaphragm electrolyzer of the present invention;

[0020] Figure 3 This is a schematic diagram of the structure of a unit cell in a diaphragm electrolyzer of the present invention;

[0021] Description of the serial numbers in the figure:

[0022] 1 is an electrode, 2 is an anion membrane, 3 is a cation membrane, 4 is an anode chamber, 5 is a cathode chamber, 6 is a solution chamber, 7 is an anode, 8 is a cathode, and 9 is a separator. DETAILED DESCRIPTION

[0023] like Figure 1-3 The structure of the present invention is a comprehensive treatment device for overhaul slag of electrolytic aluminum. The device is a diaphragm electrolysis device, including multiple groups of unit cells, multiple groups in each unit cell are connected in series and in parallel between cells, or multiple groups in the unit cell are connected in parallel and in series between cells. The unit cell is separated by an anode 7 and a cathode 8. In the unit cell, an anion membrane 2 is arranged near the anode, and a cation membrane 3 is arranged near the cathode. A partition 9 is arranged between the anode, anion membrane, cation membrane, and cathode, respectively. A chamber is formed between the partition and the adjacent two parts of the structure. Each polar plate, ion membrane, and partition divide the unit cell from the anode to the cathode into an anode chamber 4, a solution chamber 6, and a cathode chamber 5. A liquid inlet and a liquid outlet are arranged on the partition. The anode chamber 4, the solution chamber 6, and the cathode chamber 5 are all in the partition 9 cavity. Under the action of direct current, anions in the solution in the solution chamber 6 pass through the anion membrane 2 into the anode chamber 4, accumulate in the anode liquid, and the easily oxidizable ions will be oxidized; cations in the solution in the solution chamber 6 pass through the cation membrane 3 into the cathode chamber 5, accumulate in the cathode liquid, and the easily reducible ions will be reduced.

[0024] Preferably, the anode is an electrode inert to the anolyte, and when the electrolytic unit cells are connected in series, the middle electrode is shared by the unit cells on both sides, one side is the cathode, and the other side is the anode.

[0025] Preferably, the separator is made of insulating material and serves as a skeleton (or frame) to separate the electrodes and the ion membrane. The conductive liquid is introduced into the separator to form the anode chamber, the solution chamber and the cathode chamber together with the electrodes and the ion membrane.

[0026] Preferably, the anode liquid, solution and cathode liquid in the anode chamber, solution chamber and cathode chamber are circulated separately.

[0027] The present invention also discloses a comprehensive treatment method for electrolytic aluminum overhaul slag, which is carried out by using the above-mentioned device. The method comprises the steps of sorting and crushing, wet grinding and water immersion, filtering, and diaphragm electrolysis:

[0028] The sorting and crushing step is to manually sort the overhaul slag into aluminum slag, carbon blocks, and refractory materials, and then crush them;

[0029] In the wet grinding and water soaking step, the crushed overhaul slag is ground into 80-200 meshes with water to form a slurry with a solid-liquid ratio of 1:2-10, and the solid-liquid contact time is extended to 10-60 minutes by water soaking;

[0030] In the diaphragm electrolysis step, the slurry is filtered and then injected into the solution chamber. The cathode chamber and the anode chamber are both sodium hydroxide solutions. After the electrodes are energized, F in the filtrate - , CN - In the anode chamber, cyanide is enriched and broken to produce sodium fluoride, Na + Sodium hydroxide is produced in the cathode chamber.

[0031] Preferably, in the wet grinding and water soaking step, the crushed overhaul slag is ground into 150-200 meshes with water to form a slurry with a solid-liquid ratio of 1:3-5, and the solid-liquid contact time is prolonged to 20-40 minutes by water soaking.

[0032] The present invention will be further described below by means of specific examples.

[0033] Example 1: Take 100g of -120 mesh waste refractory (aluminum electrolytic overhaul slag), add 500ml of water, stir mechanically at room temperature for 30 minutes, filter the water extract and extract fluoride (in F - 2674mg / l, cyanide (in CN - The electrolytic cell is divided into 6 zones with a spacing of 1 cm in the order of graphite plate, anion membrane, cation membrane, and graphite plate. The volume of each zone is about 120 ml. Three graphite electrodes are connected in series. The voltage is 8.5 V. The anolyte is 10% NaOH and the cathode is 2% NaOH. The anolyte, cathode, and water immersion liquid are not circulated. After 1 hour of electrolysis, the anolyte F - 2632mg / l, CN - <1mg / l, water extract F - 35mg / l, CN -<1mg / l, so the F in the water extract - Most of it is transferred to the anolyte and enriched, CN - Transferred to the anolyte for oxidative decomposition.

[0034] Example 2: After sorting, the carbon blocks were crushed and passed through a 120-mesh sieve. 100 g of the material was taken, 450 ml of water was added, and mechanical stirring was performed at room temperature for 40 minutes. After filtering, the fluoride (in F) in the water extract was - 3249mg / l, cyanide (in CN - The anolyte F was 16.2 mg / l, and the water solution was electrolyzed at constant pressure by diaphragm electrolysis. The electrolysis conditions were the same as those in Example 1. After 1 hour of electrolysis, the anolyte F - 3186mg / l, CN - <1mg / l, water extract F - 58mg / l, CN - <1mg / l, so the F in the water extract - Most of it is transferred to the anolyte and enriched, CN - Transferred to the anolyte for oxidative decomposition.

[0035] Example 3: Take 100g of -120 mesh waste refractory material each time, add 500ml of recycled water after diaphragm electrolysis, stir mechanically at room temperature for 30 minutes, filter the water leaching liquid through diaphragm electrolysis (electrolysis conditions are the same as in Example 1), return to water leaching for recycling, only replace the water leaching liquid during diaphragm electrolysis, and use the anolyte and cathode liquid continuously. After 4 cycles, the anolyte F - 10.23g / l, CN - <1mg / l, water extract F - 84mg / l, CN - <1mg / l, while cyanide is broken in the anode chamber, F in the anode liquid - The result is enrichment, which greatly reduces the energy consumption during NaF concentration and crystallization.

Claims

1. A comprehensive treatment device for electrolytic aluminum overhaul slag, characterized by: The device is a diaphragm electrolysis device, comprising a plurality of unit cells, wherein the unit cells are separated by an anode and a cathode, wherein an anion membrane is arranged near the anode, and a cation membrane is arranged near the cathode, and a partition with a chamber is arranged between the anode, the anion membrane, the cation membrane, and the cathode, respectively, to separate the unit cells into an anode chamber, a solution chamber, and a cathode chamber from the anode to the cathode; Multiple groups of unit slots are connected in series and the slots are connected in parallel, or multiple groups of unit slots are connected in parallel and the slots are connected in series.

2. The device according to claim 1, characterized in that: The anode is an electrode inert to the anolyte; the separator is made of insulating material and serves as a framework for isolating the electrode and the ion membrane.

3. A comprehensive treatment method for electrolytic aluminum overhaul slag, using the device as claimed in claim 1 or 2, characterized in that: The method comprises the steps of sorting and crushing, wet grinding and water soaking, filtering, and diaphragm electrolysis: The sorting and crushing step is to manually sort the overhaul slag into aluminum slag, carbon blocks, and refractory materials, and then crush them; In the wet grinding and water soaking step, the crushed overhaul slag is ground into 80-200 meshes with water to form a slurry with a solid-liquid ratio of 1:2-10, and the solid-liquid contact time is extended to 10-60 minutes by water soaking; In the diaphragm electrolysis step, the ore pulp is filtered and then injected into the solution chamber. The cathode chamber and the anode chamber are both sodium hydroxide solutions. After the electrodes are energized, F in the filtrate - , CN - In the anode chamber, cyanide is enriched and broken, producing sodium fluoride, Na + Sodium hydroxide is produced in the cathode chamber.

4. The method according to claim 3, characterized in that: In the wet grinding and water soaking step, the crushed overhaul slag is ground into 150-200 meshes with water to form a slurry with a solid-liquid ratio of 1:3-5, and the solid-liquid contact time is prolonged to 20-40 minutes by water soaking.

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