Method for efficient detoxification and reduction safe treatment of fused salt chlorination slag

Abstract

The invention discloses an efficient detoxification reduction safe treatment method for fused salt chlorination slag, which comprises the following steps: (1) after the fused salt chlorination slag is discharged from a furnace, adding a detoxification agent, uniformly mixing in a reaction tank, carrying out mineral phase conversion at a preset temperature, and after the reaction is finished, cooling a product to room temperature to obtain phase conversion slag; (2) crushing the phase conversion slag, and carrying out water leaching; (3) after leaching, carrying out solid-liquid separation to obtain a sodium chloride leaching solution and leaching residues, and after evaporating and crystallizing the sodium chloride leaching solution, circularly feeding the sodium chloride leaching solution into a molten salt chlorination furnace or applying the sodium chloride leaching solution to chlor-alkali industrial brine; and the leached residues can be directly stacked in a residue field, or valuable metal recovery is carried out. According to the method, the main component sodium chloride in the fused salt chlorination slag is recovered in a mode of combining pyrometallurgy and hydrometallurgy. After treatment in a phase inversion-water leaching mode, the amount of residues is reduced by 70% or above, the properties of the residues are stable, the leaching toxicity is obviously reduced, and the residues can be directly stacked in a residue field or valuable metal elements can be extracted. The technological process is simple, energy consumption is low, cyclic utilization of sodium chloride in the fused salt chlorination slag can be achieved, and the problem that a large amount of fused salt chlorination slag is piled up and pollutes the environment is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of safe disposal of solid waste, and specifically relates to a method for safely treating molten salt chloride slag with high efficiency, detoxification and reduction. The method recovers sodium chloride from the molten salt chloride slag discharged during the process of preparing TiCl4 by the molten salt chlorination method, and achieves high efficiency, detoxification and reduction of the molten salt chloride slag. Background Art

[0002] Titanium and its alloys are of strategic importance to the development of high technology. The volume of titanium used and the level of development of the titanium industry are key indicators of a country's overall strength. Titanium boasts the highest specific strength among metals, excellent corrosion resistance, good heat resistance, and low damping resistance, earning it the nickname "space metal." The widespread use of titanium and the increased application of advanced titanium materials are key measures to advance aerospace technology. With the rapid development of global aerospace, demand for high-end titanium materials is expected to grow rapidly.

[0003] TiCl4 is an important intermediate raw material for the preparation of titanium sponge and titanium metal, and its purity has a significant impact on the performance of titanium products. Currently, there are two methods for preparing TiCl4: the molten salt chlorination method and the boiling chlorination method. The boiling chlorination method has the advantages of high chlorination efficiency and large output, and is widely used in Western countries. However, this method has strict requirements on the quality of the furnace charge, requiring the use of high-quality titanium-rich materials with CaO+MgO less than 1.5%, and the raw materials must meet the appropriate particle size range. The molten salt chlorination method, on the other hand, has less stringent requirements on the chemical composition of the furnace charge and can process titanium-containing raw materials with high calcium and magnesium contents. The TiCl4 intermediate product obtained by the molten salt chlorination method is of higher purity and better quality than the boiling chlorination method.

[0004] my country's titanium resources are high in calcium and magnesium impurities, making the molten salt chlorination method more suitable for producing TiCl4. However, due to the deterioration of the molten salt properties and the increase in chlorination temperature during the production process, the molten salt chlorination method requires the continuous discharge of waste salt and the replenishment of new salt to maintain the stability of the molten salt chlorination system. According to statistics, domestic molten salt chlorination furnaces currently discharge 300-400 kg of molten salt chlorination slag for every ton of TiCl4 produced, a significant amount of emissions. Furthermore, frequent salt discharge also results in the loss of titanium and carbon, leading to a decrease in titanium resource utilization.

[0005] The soluble components in molten salt chloride slag are greater than 70%, and the content of heavy metal elements (chromium, arsenic, lead, etc.) therein is far higher than the national emission standards. It is a hazardous waste that is difficult to treat and recycle. At present, the methods for treating molten salt chloride slag at home and abroad are mainly alkali neutralization method and direct water dissolution method. The molten salt chloride slag is mixed and stirred with lime milk to solidify the heavy metals and metal chloride salts therein. The residue after alkali neutralization is directly piled up in the slag yard. This method leads to a significant increase in the residue stockpile and occupies land. The direct water dissolution method directly dissolves the discharged molten salt chloride slag in water, and the leached slag is harmlessly piled up in the slag yard. A precipitant is added to the leachate to remove the impurity ions therein step by step to obtain a higher purity sodium chloride solution. After evaporation and crystallization, it is returned to the molten salt chlorination furnace for recycling. However, the composition of molten salt chloride slag is complex, the types of impurities are many, the step-by-step impurity removal process is long, and the economic benefits are low. In addition, the heavy metal elements in the leaching process all enter the leachate, and the problem of secondary solid waste treatment and disposal formed in the impurity removal process remains unsolved. It can be seen that the current alkali neutralization method and direct water dissolution method have not fundamentally solved the problem of harmless and reduced treatment and disposal of molten salt chlorination slag. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for efficiently detoxifying and reducing the amount of molten salt chloride slag with low treatment cost and good economic benefits, so as to solve the problems of "salination of molten salt chloride slag and contamination of groundwater" and the like, and at the same time realize the recycling and utilization of sodium chloride in the molten salt chloride slag.

[0007] In order to achieve the above object, the present invention provides a method for efficiently detoxifying, reducing and safely treating molten salt chloride slag, comprising the following steps:

[0008] (1) After the molten salt chloride slag is discharged from the furnace, a detoxifying agent is added, the mixture is mixed in a reaction tank, and the mineral phase is transformed at a preset temperature. After the reaction is completed, the product is cooled to room temperature to obtain a phase transformation slag;

[0009] (2) crushing the phase transformation slag obtained in step (1) and leaching it with water;

[0010] (3) After leaching, the solid and liquid are separated to obtain sodium chloride leachate and leach residue. The sodium chloride leachate is evaporated and crystallized and then circulated into the molten salt chlorination furnace or used in chlor-alkali industrial brine; the leach residue can be directly piled in the slag yard or be used for valuable metal recovery.

[0011] In a preferred embodiment, in step (1), the detoxifying agent is one or more of carbonates, bicarbonates, and silicates, including but not limited to sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, sodium silicate, and potassium silicate.

[0012] In a more preferred embodiment, the molar amount of the detoxifying agent is 0 to 2 times the total molar amount of calcium chloride, magnesium chloride, manganese chloride, ferric chloride, etc. in the molten salt chloride slag, and more preferably 0.8 to 1.2 times.

[0013] In a preferred embodiment, in step (1), the temperature for the mineral phase conversion is 500-700°C, the reaction time is 1-3 hours, and the reaction is cooled to room temperature after completion. During the mineral phase conversion process, under the action of the detoxifying agent, chloride salts such as CaCl2, MgCl2, MnCl2, FeCl3, and ScCl3 undergo mineral phase conversion to form insoluble metal carbonates or metal oxides, while NaCl remains in the form of a chloride salt.

[0014] In a more preferred embodiment, the reaction temperature is 700° C. and the holding time is 3 h.

[0015] In a preferred embodiment, in step (2), the solidified phase transformation slag is crushed to less than 1 mm to ensure that the sodium chloride and the metal carbonates and metal oxides in the solidified slag are fully dissociated, which is conducive to the subsequent water leaching process in which the sodium chloride is fully dissolved into the leachate and the carbonates and metal oxides or metal silicates enter the leached slag.

[0016] In a preferred embodiment, in step (2), the amount of water used in the water leaching process should be 1 to 1.3 times the saturated solubility of sodium chloride in the solidified slag. The amount of water used in the leaching process should be minimized to reduce the energy consumption of subsequent evaporation crystallization or sodium chloride concentration, preferably 1.1 times.

[0017] In a preferred embodiment, in step (2), the equipment used for crushing the solidified residue is a jaw crusher, a ball mill, or a vibration mill.

[0018] In a preferred embodiment, in step (3), the solid-liquid separation method is one of pressure filtration, vacuum filtration or centrifugal filtration.

[0019] In a preferred embodiment, in step (3), after the sodium chloride leachate is continuously circulated and washed with water, its sodium chloride concentration and impurity ion content meet the requirements of primary brine, and the sodium chloride crystals obtained by direct evaporation and crystallization are returned to the molten salt chlorination furnace for recycling; or directly incorporated into the brine for secondary refining to prepare water for chlor-alkali industry.

[0020] In a preferred embodiment, in step (3), after the phase conversion-water leaching treatment, the leached residue is reduced by more than 70%, and its properties are stable, and the leaching toxicity is significantly reduced, and it can be directly piled in a slag yard or recovered for valuable metals.

[0021] In a preferred embodiment, in step (3), the main components of the leached residue are metal carbonates and metal oxides or metal silicates, which are stable in nature and meet the national standards for leaching toxicity. The residue can be directly deposited in a slag field or valuable metal elements can be extracted therefrom.

[0022] Compared with the prior art, the advantages and effects of the present invention are:

[0023] The process proposed by the invention is simple, has low energy consumption, can realize the recycling of sodium chloride in molten salt chloride slag, and solves the problems of large stockpiles of molten salt chloride slag discharged during the production of TiCl4 by the molten salt chlorination method, difficulty in disposal, and environmental pollution.

[0024] The present invention adopts a combination of pyrometallurgy and hydrometallurgy. After treatment by phase conversion-water leaching, the residue is reduced by more than 70%, and the residue properties are stable. The leaching toxicity of the phase conversion residue is significantly reduced. The slag can be directly piled up in a slag field or valuable metal elements can be extracted, thereby achieving harmlessness and reduction of molten salt chloride slag. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0026] The present invention is further described below with reference to specific embodiments:

[0027] Example 1

[0028] The detoxifying agent sodium carbonate is added to the discharged molten salt chloride slag (NaCl 46.24wt%, CaCl2 12.63wt%, MgCl2 19.71wt%, MnCl2 11.32wt%, FeCl3 7.66wt%, Sc 220ppm, Nb 300ppm). The additive dosage is controlled to be 1.2 times the total molar amount of calcium chloride, magnesium chloride, manganese chloride, and ferric chloride in the molten salt chloride slag. The reaction temperature is maintained at 500°C for 2 hours, and then gradually cooled to room temperature after completion. The solidified slag is crushed and leached in water, with the NaCl content in the leachate reaching 99.65%. After evaporation and crystallization, the leached slag is returned to the molten salt chlorination furnace for recycling. Compared to the discharged molten salt chloride slag, the residual leached slag has a mass reduction of 74%. According to the leaching toxicity test method HJT300-2007, the leaching toxicity of molten salt chloride slag and leaching slag and the fourth-level groundwater heavy metal content standard (GB / T 14848-2017) are compared as shown in Table 1. The leaching amount of heavy metal elements in the leaching slag is significantly reduced.

[0029] Table 1 Leaching toxicity test results of molten salt chloride slag and leaching slag (mg / L)

[0030]

[0031] Example 2

[0032] The detoxifying agent sodium carbonate is added to the discharged molten salt chloride slag (NaCl 46.24wt%, CaCl2 12.63wt%, MgCl2 19.71wt%, MnCl2 11.32wt%, FeCl3 7.66wt%, Sc 220ppm, Nb 300ppm). The additive dosage is controlled to be 1.1 times the total molar amount of calcium chloride, magnesium chloride, manganese chloride, and ferric chloride in the molten salt chloride slag. The reaction temperature is maintained at 700°C for 3 hours, and then gradually cooled to room temperature after completion. The solidified residue is crushed and leached in water, with the NaCl content reaching 99.96%. The saturated sodium chloride solution is used in the chlor-alkali industry or, after evaporation and crystallization, is returned to the molten salt chlorination furnace for recycling. The remaining leached residue has a mass reduction of 80% compared to the discharged molten salt chloride slag. Table 2 shows a comparison of the leaching toxicity of molten salt chloride slag and leaching slag according to the leaching toxicity test method HJT300-2007, as well as the Level 4 groundwater heavy metal content standard (GB / T 14848-2017). The leaching amount of heavy metal elements from the leaching slag is significantly lower. Furthermore, the higher the reaction temperature, the lower the amount of heavy metal elements leached, indicating that the phase conversion method is more effective in solidifying heavy metal elements.

[0033] Table 2 Leaching toxicity test results of molten salt chloride slag and leaching slag (mg / L)

[0034]

[0035] Example 3

[0036] The detoxifying agent sodium carbonate is added to the discharged molten salt chloride slag (NaCl 46.24wt%, CaCl2 12.63wt%, MgCl2 19.71wt%, MnCl2 11.32wt%, FeCl3 7.66wt%, Sc 220ppm, Nb 300ppm). The additive dosage is controlled to be 0.8 times the total molar amount of calcium chloride, magnesium chloride, manganese chloride, and ferric chloride in the molten salt chloride slag. The reaction temperature is maintained at 600°C for 3 hours, and then gradually cooled to room temperature after completion. The solidified residue is crushed and leached in water, with the NaCl content in the leachate reaching 93.34%. The saturated sodium chloride solution is then evaporated and crystallized, then recycled back to the molten salt chlorination furnace. The remaining leached residue has a 68% reduction in mass compared to the discharged molten salt chloride slag. Table 3 shows a comparison of the leaching toxicity of molten salt chloride slag and leaching slag according to the leaching toxicity test method HJT300-2007 and the fourth-level groundwater heavy metal content standard (GB / T 14848-2017). The leaching amount of heavy metal elements in the leaching slag is significantly reduced. However, when the additive dosage is reduced, the solidification effect of the heavy metal elements is relatively poor.

[0037] Table 3 Leaching toxicity test results of molten salt chloride slag and leaching slag (mg / L)

[0038]

[0039] Example 4

[0040] The detoxifying agent potassium carbonate is added to the discharged molten salt chloride slag (NaCl 46.24wt%, CaCl2 12.63wt%, MgCl2 19.71wt%, MnCl2 11.32wt%, FeCl3 7.66wt%, Sc 220ppm, Nb 300ppm). The additive dosage is controlled to be 1.2 times the total molar amount of calcium chloride, magnesium chloride, manganese chloride, and ferric chloride in the molten salt chloride slag. The reaction temperature is maintained at 700°C for 3 hours, and then gradually cooled to room temperature after completion. The solidified residue is crushed and leached in water, with the NaCl + KCl content in the leachate reaching 99.89%. The saturated sodium chloride and potassium chloride solutions can be used in the chlor-alkali industry or recycled back into the molten salt chlorination furnace after evaporation and crystallization. The remaining leached residue is 80% less in mass than the discharged molten salt chloride slag. According to the leaching toxicity test method HJT300-2007, the leaching toxicity of molten salt chloride slag and leaching slag and the fourth-level groundwater heavy metal content standard (GB / T14848-2017) are compared as shown in Table 4. The leaching amount of heavy metal elements in the leaching slag is significantly reduced, and the solidification effect of heavy metals by sodium carbonate and potassium carbonate is similar.

[0041] Table 4 Leaching toxicity test results of molten salt chloride slag and leaching slag (mg / L)

[0042]

[0043] Example 5

[0044] The detoxifying agent sodium bicarbonate is added to the discharged molten salt chloride slag (NaCl 46.24wt%, CaCl2 12.63wt%, MgCl2 19.71wt%, MnCl2 11.32wt%, FeCl3 7.66wt%, Sc 220ppm, Nb 300ppm). The additive dosage is controlled to be 1.2 times the total molar amount of calcium chloride, magnesium chloride, manganese chloride, and ferric chloride in the molten salt chloride slag. The reaction temperature is maintained at 700°C for 3 hours, and then gradually cooled to room temperature after completion. The solidified residue is crushed and leached in water, with the NaCl content in the leachate reaching 99.99%. The saturated sodium chloride solution is used in the chlor-alkali industry or, after evaporation and crystallization, is returned to the molten salt chlorination furnace for recycling. Compared to the discharged molten salt chloride slag, the remaining leached residue has a mass reduction of 79%. According to the leaching toxicity test method HJT300-2007, the leaching toxicity of molten salt chloride slag and leaching slag and the fourth-level groundwater heavy metal content standard (GB / T14848-2017) are compared as shown in Table 5. The leaching amount of heavy metal elements in the leaching slag is significantly reduced.

[0045] Table 5 Leaching toxicity test results of molten salt chloride slag and leaching slag (mg / L)

[0046]

[0047] Comparative Example 1

[0048] The molten salt chloride slag (NaCl 46.24wt%, CaCl2 12.63wt%, MgCl2 19.71wt%, MnCl2 11.32wt%, FeCl3 7.66wt%, Sc 220ppm, Nb 300ppm) was calcined under an inert atmosphere at 700°C for 3 hours. After the reaction, the slag was cooled to room temperature under an inert atmosphere. The residue was crushed and leached with water. All metal chlorides (NaCl, CaCl2, MgCl2, MnCl2, FeCl3) and heavy metal chlorides in the calcined slag were dissolved into the solution. As shown in Table 6, the leaching solution had a similar toxicity to the molten salt chloride slag and did not achieve the detoxification effect of the molten salt chloride slag.

[0049] Table 6 Heavy metal element test results of molten salt chloride slag and leachate (mg / L)

[0050]

[0051] Comparative Example 2

[0052] The molten salt chloride slag (NaCl 46.24wt%, CaCl2 12.63wt%, MgCl2 19.71wt%, MnCl2 11.32wt%, FeCl3 7.66wt%, Sc 220ppm, Nb 300ppm) was added with the detoxifying agent sodium carbonate. The amount of the additive was controlled to be 1.1 times the total molar amount of calcium chloride, magnesium chloride, manganese chloride, and ferric chloride in the molten salt chloride slag. The reaction temperature was 300°C, the heat was maintained for 3 hours, and the reaction was gradually cooled to room temperature after completion. As shown in Table 7, after the solidified residue was crushed and leached with water, the impurity content of Ca, Mg, Mn, Fe, and heavy metal elements in the leachate was high, and the NaCl content was low, making it difficult to meet the needs of returning to the molten salt chlorination furnace and the chlor-alkali industry. Due to the low reaction temperature, the detoxifying agent is difficult to play the role of solidifying impurity elements and heavy metal elements.

[0053] Table 7 Heavy metal element test results of molten salt chloride slag and leachate (mg / L)

[0054]

[0055] The above is only a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited to the above embodiment. For those skilled in the art, improvements and modifications obtained without departing from the technical concept of the present invention should also be considered as the scope of protection of the present invention.

Claims

1. A method for efficiently detoxifying, reducing and safely treating molten salt chloride slag, characterized in that: The following steps are involved: (1) After the molten salt chloride slag is discharged from the furnace, a detoxifying agent is added, the mixture is mixed in a reaction tank, and the mineral phase is transformed at a preset temperature. After the reaction is completed, the product is cooled to room temperature to obtain a phase transformation slag; (2) crushing the phase transformation slag obtained in step (1) and leaching it with water; (3) After leaching, the solid and liquid are separated to obtain sodium chloride leachate and leach residue. The sodium chloride leachate is evaporated and crystallized and then circulated into the molten salt chlorination furnace or used in chlor-alkali industrial brine; the leach residue can be directly piled in the slag yard or used for valuable metal recovery.

2. The method for efficiently detoxifying, reducing and safely treating molten salt chloride slag according to claim 1, characterized in that: In step (1), the detoxification agent is one or more of carbonates, bicarbonates, and silicates, including but not limited to sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, sodium silicate, and potassium silicate.

3. The method for efficiently detoxifying, reducing and safely treating molten salt chloride slag according to claim 2, characterized in that: The molar amount of the detoxifying agent is 0 to 2 times the total molar amount of calcium chloride, magnesium chloride, manganese chloride and ferric chloride in the molten salt chloride slag, and more preferably 0.8 to 1.2 times.

4. The method for efficiently detoxifying, reducing and safely treating molten salt chloride slag according to claim 1, characterized in that: In step (1), the temperature for mineral phase conversion is 500-700° C., the reaction time is 1-3 hours, and the reaction is cooled to room temperature after completion of the reaction.

5. The method for efficiently detoxifying, reducing and safely treating molten salt chloride slag according to claim 4, characterized in that: The reaction temperature is 700°C and the holding time is 3h.

6. The method for efficiently detoxifying, reducing and safely treating molten salt chloride slag according to claim 1, characterized in that: In step (2), the solidified phase transformation slag is crushed to less than 1 mm.

7. The method for efficiently detoxifying, reducing and safely treating molten salt chloride slag according to claim 1, characterized in that: In step (2), the amount of water used in the water leaching process should be 1 to 1.3 times the saturated solubility of sodium chloride in the solidified slag.

8. The method for efficiently detoxifying, reducing and safely treating molten salt chloride slag according to claim 1, characterized in that: In step (2), the equipment used for crushing the solidified residue is one of a jaw crusher, a ball mill, and a vibration mill.

9. The method for efficiently detoxifying, reducing and safely treating molten salt chloride slag according to claim 1, characterized in that: In step (3), the solid-liquid separation method is one of pressure filtration, vacuum filtration or centrifugal filtration.

10. The method for efficiently detoxifying, reducing and safely treating molten salt chloride slag according to claim 1, characterized in that: In step (3), the leached slag is reduced by more than 70% and can be directly piled up in a slag yard or used for valuable metal recovery.

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