Method for recovering elemental iodine

Abstract

The invention discloses a method for recovering elemental iodine, which comprises the following steps of: performing adsorption-elution treatment on waste gas or waste oil generated in the preparation process of anhydrous lithium iodide, and recovering the elemental iodine from eluent. According to the method, the iodine simple substance escaped by evaporation in the preparation process of lithium iodide trihydrate and the iodine simple substance dissolved in the vacuum pump oil after the lithium iodide trihydrate is subjected to gradient vacuum drying can be efficiently recovered, so that the defects of serious volatilization loss, serious pollution and high occupational risk of the iodine simple substance in the existing preparation process of anhydrous lithium iodide are overcome; the efficient recovery of iodine resources is realized, the production cost is reduced, and meanwhile, the pollution to the environment and the harm to people are reduced.

Description

Technical Field

[0001] This invention relates to the field of iodine recovery technology, and more specifically, to a method for recovering iodine. Background Technology

[0002] Anhydrous lithium iodide (LiI) is a white crystalline powder with typical characteristics of alkali metal iodides. It is readily soluble in water and also soluble in polar organic solvents such as ethanol, methanol, and acetone. It has high hygroscopicity and good solubility.

[0003] Anhydrous lithium iodide is not only a key raw material for the preparation of other iodides, but also serves as a synthetic intermediate in the pharmaceutical field for drugs treating thyroid diseases. In organic synthesis reactions, it acts as a catalyst or reagent, driving specific chemical reactions; it is also frequently used in spectroscopic analysis. In particular, it has important applications in batteries. For example, the lithium-iodine battery, invented and used since 1972, had a real impact on implantable pacemakers, lasting approximately 10 years and still being the power source for many pacemaker manufacturers today. In battery liquid electrolytes, the importance of anhydrous lithium iodide lies in its ability to increase battery energy density, reduce self-discharge rate, and extend battery life. For instance, lithium iron phosphate battery electrolytes typically use a mixture of anhydrous lithium iodide, lithium perchlorate, lithium trifluoromethanesulfonate, and other electrolytes with organic solvents; anhydrous lithium iodide exhibits higher conductivity at the same molar concentration. Adding anhydrous lithium iodide to solid-state electrolytes in batteries can stabilize the lithium / electrolyte interface, prevent side reactions, suppress lithium dendrites, and improve safety; reduce interface impedance, improve rate performance and cycle life; and broaden the application window of solid-state electrolytes, enabling high-performance electrolytes such as sulfides to be paired with lithium metal anodes.

[0004] Anhydrous lithium iodide is typically prepared by dehydrating or directly from the precursor lithium iodide trihydrate. Currently, the main methods for preparing anhydrous lithium iodide include: ① Neutralization method: Hydroiodic acid reacts with lithium carbonate or lithium hydroxide in a neutralization reaction. After heating and concentration, followed by cooling and crystallization, lithium iodide trihydrate is obtained. Dehydrating the lithium iodide trihydrate yields anhydrous lithium iodide. ② Hydrazine method: A diluted hydrazine hydrate solution is added to a reaction apparatus containing lithium hydroxide and elemental iodine. After heating and concentration, followed by cooling and crystallization, lithium iodide trihydrate crystals are obtained. Drying then yields anhydrous lithium iodide. ③ Solid-phase method: Molten lithium metal reacts with elemental iodine at high temperatures in a synthetic reaction. High-purity anhydrous lithium iodide can be prepared through purification. Of the three methods mentioned above, the solid-phase method can directly prepare anhydrous lithium iodide, but the reaction is incomplete, the product purity is low, and it requires purification by organic solvents. Furthermore, it involves high-temperature and high-pressure containers, posing a risk of explosion. Therefore, further drying and dehydration using the neutralization and hydrazine methods to prepare anhydrous lithium iodide has become a reliable method for producing large quantities of anhydrous lithium iodide. Currently, methods for preparing anhydrous lithium iodide from trihydrate lithium iodide include vacuum drying, spray drying, and inert gas-protected heating dehydration, etc. The mainstream method used in both industry and laboratories is vacuum heating dehydration, which lowers the boiling point of water through a vacuum environment to achieve low-temperature dehydration. However, the waste gas generated during the dehydration process contains a large amount of elemental iodine, which is emitted into the atmosphere, polluting the environment and wasting resources. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned shortcomings of the prior art and provide a method for recovering elemental iodine during the preparation of anhydrous lithium iodide.

[0006] The technical problem solved by this invention is achieved by the following technical solution.

[0007] The present invention provides a method for recovering elemental iodine, which includes: recovering elemental iodine from the eluent after adsorption-elution treatment of waste gas or waste oil generated during the preparation of anhydrous lithium iodide.

[0008] The present invention has the following beneficial effects: This invention provides a method for recovering elemental iodine, comprising: treating the waste gas or waste oil generated during the preparation of anhydrous lithium iodide by adsorption-elution to obtain an eluent, and then recovering elemental iodine from the eluent. The above method can achieve efficient recovery of elemental iodine evaporated during the preparation of lithium trihydrate and elemental iodine dissolved in the vacuum pump oil after gradient vacuum drying of lithium trihydrate, reducing the environmental pollution caused by waste gas or waste oil during the preparation of anhydrous lithium iodide, and the recovered elemental iodine can be reused, thereby improving resource utilization. Detailed Implementation

[0009] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0010] The following is a detailed description of a method for recovering elemental iodine provided by an embodiment of the present invention.

[0011] This invention provides a method for recovering elemental iodine, comprising: treating the waste gas or waste oil generated during the preparation of anhydrous lithium iodide with adsorption-elution, and then recovering elemental iodine from the eluent.

[0012] Anhydrous lithium iodide is typically produced by gradually dehydrating the precursor lithium iodide trihydrate during heating. The dehydration process is as follows: above 70.5℃: water of crystallization begins to dissolve; 75-80℃: all water of crystallization is lost, transforming into a dihydrate; 80℃-120℃: further water loss forms a monohydrate; above 300℃: complete dehydration produces anhydrous lithium iodide (under vacuum conditions, the vacuum drying temperature will be lower, but it is usually above 200℃). The above process for preparing anhydrous lithium iodide from lithium iodide trihydrate, including heating concentration and vacuum drying, is carried out at relatively high temperatures. Under the combined action of high temperature and air, iodide ions (I₂O₃) are produced. - The iodine vapor will be rapidly oxidized into elemental iodine and released as vapor (the volatilization temperature of elemental iodine is 45℃-77℃). The released iodine vapor will not only cause strong irritation and damage to the respiratory tract of operators, posing a significant occupational hazard; but also, as the dehydration temperature increases, the volatilization of elemental iodine will be severe, and elemental iodine is expensive, resulting in a large amount of material waste.

[0013] To overcome the shortcomings of existing methods for preparing anhydrous lithium iodide, such as severe iodine volatilization loss, high pollution, and high occupational risks, this invention provides a method for recovering elemental iodine during the preparation of anhydrous lithium iodide. The method includes: treating the waste gas or waste oil generated during the preparation of anhydrous lithium iodide with adsorption-elution, and then recovering elemental iodine from the eluent. This method achieves efficient recovery of iodine resources, reduces production costs, and minimizes environmental pollution and harm to humans.

[0014] In some optional embodiments, the waste gas and waste oil are respectively the tail gas and waste vacuum pump oil generated during the heating, concentration and subsequent vacuum drying of lithium trihydrate to prepare anhydrous lithium iodide. Preferably, the lithium trihydrate is prepared by neutralization or hydrazine method.

[0015] In some optional embodiments, the adsorption material used for adsorption is an activated carbon adsorption column, which is obtained by packing activated carbon particles into a quartz tube, wherein the particle size of the activated carbon particles is 0.5-1.0 mm. Activated carbon particles have a high adsorption capacity and can quickly and effectively adsorb elemental iodine contained in waste gas or waste oil, reducing the pollution of waste gas and waste oil to the environment. Preferably, the particle size of the activated carbon particles packed in the activated carbon adsorption column is 0.5-1.0 mm. Since the smaller the particle size of activated carbon, the larger the specific surface area and the better the adsorption effect, activated carbon with an excessively large particle size is not selected. At the same time, if the particle size of activated carbon particles is too small, the loss will be large and more dust will be generated.

[0016] In some optional embodiments, when treating waste gas, a condenser sleeve is provided on the outside of the activated carbon adsorption column. Water is introduced into the condenser sleeve as the condensing medium. Preferably, the condensation temperature for adsorption treatment is 25°C. The saturated activated carbon particles are then removed for elution. Since the waste gas is generated during the heating and concentration of lithium iodide trihydrate, the gas temperature is relatively high. Providing a condenser sleeve on the outside of the activated carbon adsorption column can rapidly reduce the waste gas temperature. Gas liquefaction not only improves adsorption efficiency but also reduces energy consumption. Adsorption treatment is performed at room temperature, which reduces energy consumption and treatment costs.

[0017] In some optional embodiments, when treating waste oil, the waste oil is passed through an activated carbon adsorption column at a flow rate of 1.5-2.0 mL / min. Activated clay is added to the waste oil exiting the adsorption column for adsorption and decolorization. The mixture is stirred at 60-80°C for 1-2 hours, and then the clay is removed by centrifugation to obtain clear and transparent regenerated oil. The saturated activated carbon particles are then removed and eluted. Adsorption and decolorization treatment of the waste oil exiting the activated carbon adsorption column yields regenerated oil, which can be reused, improving the utilization rate of vacuum pump oil.

[0018] To better treat waste oil, four aspects can be controlled: flow rate, adsorption phenomenon, temperature, and time. For example, ① controlling the waste oil flow rate to 1.5-2.0 mL / min can balance adsorption efficiency and treatment efficiency, ensuring the waste oil maintains a reasonable residence time within the adsorption column. This allows sufficient time for the activated carbon pores to capture impurities in the oil (such as pigments and small organic molecules). When the flow rate is below 1.5 mL / min, the amount of waste oil treated per unit time is small, the treatment time is prolonged, and equipment operating costs, energy consumption, and labor costs increase; when the flow rate exceeds 2.0 mL / min... ① **Adsorption rate:** Waste oil passes rapidly through the adsorption column at a flow rate of mL / min. Impurities are not fully adsorbed before flowing out with the waste oil, resulting in a significant decrease in adsorption efficiency and low recovery efficiency. ② **Adsorption phenomenon:** When the oil sample exiting the adsorption column changes color from brownish-red to yellow or light yellow, and the activated carbon at the rear end of the adsorption column maintains its original color for a long time, it indicates effective adsorption and that the activated carbon adsorption has not reached saturation. In practice, adsorption can be repeated based on the adsorption column phenomenon and the color of the oil. ③ **Temperature:** The adsorption of impurities in oil by activated clay is a form of "physical adsorption." Within the range of 60-80℃, increased temperature will not damage its pore structure; on the contrary, it can break the binding force between some impurities and oil, making it easier for the clay to capture impurities and increasing the adsorption capacity per unit mass of clay. If the temperature exceeds 80℃, it may cause the light components in the waste oil to volatilize or cause some oil oxidation and decomposition, thus reducing the quality of the recycled oil. If the temperature is below 60℃, molecular movement slows down, and the adsorption efficiency will decrease significantly. ④ **Time:** 1-2 hours is sufficient to ensure complete adsorption reaction. Extending the time further will increase energy consumption but will not significantly improve the decolorization and purification effect.

[0019] In some optional embodiments, the elution solvent is a low-carbon alcohol, preferably ethanol, and elution is carried out at 40-60°C for 1-3 hours. After elution, the eluent is filtered to obtain a dark brown eluent. Iodine is soluble in organic solvents such as ethanol, benzene, diethyl ether, chloroform, glycerol, potassium iodide solution, methanol, carbon disulfide, and carbon tetrachloride. For considerations of solubility, environmental protection, and cost, ethanol is preferred as the elution solvent in this invention. Controlling the elution temperature at 40-60°C accelerates the thermal motion of iodine and its desorption from the surface of activated carbon particles; simultaneously, the elution temperature should be kept below the boiling point of ethanol (78°C) to prevent volatilization, reduce solvent loss, and maintain the stability of the elution system. Controlling the time at 1-3 hours balances time cost while ensuring complete desorption.

[0020] In some alternative embodiments, recovering elemental iodine from the eluent includes: removing the solvent by vacuum distillation of the eluent, and sublimating the remaining concentrate to obtain elemental iodine. After adsorbing elemental iodine from waste gas or waste oil, the saturated activated carbon particles are eluted to remove most of the solvent from the dark brown eluent obtained from the elution, followed by sublimation to volatilize the elemental iodine and obtain pure elemental iodine.

[0021] In some alternative embodiments, the apparatus used for vacuum distillation is a rotary evaporator, preferably operated at a temperature of 60-80°C and a pressure of 1.3-2.0 kPa. Vacuum distillation, conducted at a low pressure of 1.3-2.0 kPa, lowers the boiling point of ethanol. Maintaining a temperature of 60-80°C not only achieves the vaporization of iodine but also prevents its sublimation, thus enabling the recovery of iodine.

[0022] In some alternative embodiments, the apparatus used for the sublimation treatment is a sublimation apparatus, and the sublimation treatment is preferably carried out at a temperature of 100-130°C and a pressure of 0.1-0.3 kPa.

[0023] The sublimation process is carried out at a temperature of 100-130℃ and a pressure of 0.1-0.3kPa, achieving efficient sublimation of elemental iodine at relatively low temperature and pressure.

[0024] In some alternative embodiments, the method further includes: using the recovered iodine with a purity of 99.80% as a raw material, and preparing high-purity anhydrous lithium iodide by neutralization or hydrazine method.

[0025] As can be seen from the above, this invention provides a method for recovering elemental iodine during the preparation of anhydrous lithium iodide. Through a two-step recovery process, firstly, adsorption-elution treatment is performed, and then elemental iodine is recovered from the resulting eluent. This method can efficiently recover elemental iodine evaporated during the preparation of trihydrate lithium iodide and elemental iodine dissolved in the vacuum pump oil after gradient vacuum drying of trihydrate lithium iodide. It can also recycle most of the waste generated during the preparation of anhydrous lithium iodide. Furthermore, the recovered elemental iodine can be used as a raw material to prepare high-purity anhydrous lithium iodide using neutralization or hydrazine methods. This invention achieves the recycling of elemental iodine, reduces occupational hazards and preparation costs in the production process of anhydrous lithium iodide, reduces resource waste and environmental pollution, and the purity of the prepared anhydrous lithium iodide can reach over 99.9%, meeting the high-end application needs in the electronics, energy, and other fields.

[0026] The following detailed description, in conjunction with embodiments, illustrates a method for recovering elemental iodine during the preparation of anhydrous lithium iodide provided by the present invention. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0027] Example 1 A method for recovering evaporated iodine during the preparation of lithium iodide trihydrate includes the following steps: (1) An activated carbon adsorption column is connected to the outlet of (100g) lithium iodide trihydrate prepared by the neutralization method. The activated carbon adsorption column is assembled from activated carbon particles (15g, diameter = 0.5mm) and a quartz tube. There is also a condensation layer on the outer layer of the adsorption column. The medium of the condensation layer is water and the condensation temperature is 25℃.

[0028] (2) Remove the adsorption-saturated activated carbon obtained in step (1) from the column and elute it with 60 mL of ethanol solution (AR, 95%) at 50 °C for 2 h. Filter to obtain a dark brown eluent.

[0029] (3) The eluent obtained in step (2) is subjected to vacuum distillation to remove ethanol. The vacuum distillation device is a rotary evaporator (70℃, 2.0kPa). Finally, 40mL of ethanol is recovered.

[0030] (4) The remaining concentrate obtained in step (3) was transferred to a sublimation apparatus (0.3 kPa, 110 °C) to obtain 13.1 g of high-purity iodine, which was tested and found to be 99.80% pure.

[0031] Example 2 A method for recovering evaporated iodine during the preparation of lithium iodide trihydrate includes the following steps: (1) An activated carbon adsorption column is connected to the outlet of the hydrazine process for preparing lithium iodide trihydrate. The activated carbon adsorption column is assembled from activated carbon particles (10g, diameter = 0.5-1.0mm) and a quartz tube. There is also a condensation layer on the outer layer of the adsorption column. The medium of the condensation layer is water, and the condensation temperature is 25℃.

[0032] (2) Remove the adsorption-saturated activated carbon obtained in step (1) from the column and elute it with 50 mL of ethanol solution (AR, 95%) at 50 °C for 2 h. Filter to obtain a dark brown eluent.

[0033] (3) The eluent obtained in step (2) was subjected to vacuum distillation to remove ethanol. The vacuum distillation device was a rotary evaporator (70℃, 2.0kPa). Finally, 42mL of ethanol was recovered.

[0034] (4) The remaining concentrate obtained in step (3) was transferred to a sublimation apparatus (0.3 kPa, 110 °C) to obtain 3.1 g of high-purity iodine, which was tested and found to be 99.78% pure.

[0035] Example 3 A method for recovering evaporated iodine during the vacuum drying process in the preparation of anhydrous lithium iodide includes the following steps: (1) Under the condition of keeping warm at 40℃, 100g of waste oil is passed through the activated carbon adsorption column at a flow rate of 1.5 mL / min. The waste oil is the waste vacuum pump oil in the process of multiple vacuum drying of lithium trihydrate lithium iodide and anhydrous lithium iodide. The activated carbon adsorption column is assembled from activated carbon particles (15g, diameter = 0.5mm) and quartz tube.

[0036] (2) Remove the adsorption-saturated activated carbon obtained in step (1) from the column and elute it with 50 mL of ethanol solution (AR, 95%) at 50 °C for 2 h. Filter to obtain a dark brown eluent.

[0037] (3) The eluent obtained in step (2) was subjected to vacuum distillation to remove ethanol. The vacuum distillation device was a rotary evaporator (70℃, 2.0kPa). Finally, 42mL of ethanol was recovered.

[0038] (4) The remaining concentrate obtained in step (3) was transferred to a sublimation apparatus (0.3 kPa, 110 °C) to obtain 9.5 g of high-purity iodine, which was tested and found to be 99.72%.

[0039] (5) Purify the waste oil flowing out of the adsorption column in step (1). Add 0.49g of activated clay to the waste oil (about 98g) for adsorption and decolorization, and stir at 60℃ for 1 hour. Remove the activated clay by centrifugation to obtain clear and transparent regenerated oil. Its kinematic viscosity (40℃) is 18.2 mm² / s and its acid value is 0.04 mgKOH / g, which meets the new oil standard and can be reused.

[0040] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for recovering elemental iodine, characterized in that, It includes: The waste gas or waste oil generated during the preparation of anhydrous lithium iodide is treated by adsorption-elution to recover elemental iodine from the eluent.

2. The method according to claim 1, characterized in that, The waste gas and waste oil are tail gas and waste vacuum pump oil generated during the heating, concentration and subsequent vacuum drying of lithium trihydrate to prepare anhydrous lithium iodide, respectively. Preferably, the lithium trihydrate is prepared by neutralization or hydrazine method.

3. The method according to claim 1, characterized in that, The adsorption material used for adsorption is an activated carbon adsorption column, which is obtained by filling activated carbon particles into a quartz tube, wherein the particle size of the activated carbon particles is 0.5-1.0 mm.

4. The method according to claim 3, characterized in that, When treating the waste gas, a condensing sleeve is provided on the outside of the activated carbon adsorption column. The condensing medium introduced into the condensing sleeve is water. The preferred condensing temperature for adsorption treatment is 25°C. Then, the saturated activated carbon particles are taken out for elution treatment.

5. The method according to claim 3, characterized in that, When treating the waste oil, the waste oil is passed through the activated carbon adsorption column at a flow rate of 1.5-2.0 mL / min. Activated clay is added to the waste oil flowing out of the activated carbon adsorption column for adsorption and decolorization. The mixture is stirred at 60-80℃ for 1-2 hours. Then, the clay is removed by centrifugation to obtain clear and transparent regenerated oil. The saturated activated carbon particles are then removed for elution treatment.

6. The method according to claim 1, characterized in that, The solvent used for elution is a low-carbon alcohol, preferably ethanol, and elution is carried out at 40-60℃ for 1-3 hours. After elution, the eluent is filtered to obtain a dark brown eluent.

7. The method according to claim 1, characterized in that, The recovery of elemental iodine from the eluent includes: removing the solvent by vacuum distillation of the eluent, and sublimating the remaining concentrate to obtain elemental iodine.

8. The method according to claim 7, characterized in that, The apparatus used for vacuum distillation is a rotary evaporator, preferably carried out at a temperature of 60-80℃ and a pressure of 1.3-2.0 kPa.

9. The method according to claim 7, characterized in that, The apparatus used for sublimation treatment is a sublimation apparatus, and sublimation treatment is preferably carried out at a temperature of 100-130℃ and a pressure of 0.1-0.3kPa.

10. The method according to any one of claims 1-9, characterized in that, Also includes: Using recycled iodine with a purity of 99.80% as raw material, high-purity anhydrous lithium iodide is prepared by neutralization or hydrazine method.