A method for recovering iodine and boric acid from iodine-containing waste liquid

Abstract

The present invention provides a method for recovering iodine and boric acid from iodine-containing waste liquid. The method includes: subjecting the iodine-containing waste liquid to primary acidification after pretreatment, followed by solid-liquid separation to obtain boric acid and iodine-containing solution; sequentially performing secondary acidification and oxidation on the iodine-containing solution to obtain a solid-liquid mixture containing iodine and boric acid; adjusting the pH value of the solid-liquid mixture with alkali and then performing solid-liquid separation to obtain iodine and a salt-containing solution; subjecting the iodine vapor generated during the reaction to condensation and spray absorption in sequence, and returning the condensed iodine for co-recovery. The method of the present invention first precipitates boric acid through acidification treatment according to the composition of the iodine-containing waste liquid, recovers the boric acid product, and then obtains a high-purity iodine product through further acidification and oxidation reactions; the present invention condenses and spray-absorbs the iodine vapor to avoid iodine loss and possible environmental pollution, and ensures the iodine recovery rate; the method is simple to operate, has mild conditions, low cost, and realizes the resource utilization of the waste liquid.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste liquid recovery and treatment, and relates to a method for recovering iodine and boric acid from iodine-containing waste liquid. Background Art

[0002] With the continuous development of the electronics industry, the use of liquid crystal screens has become increasingly common. As a core component of liquid crystal panels, polarizers are divided into three categories according to different materials: metal polarizers, iodine-based polarizers, and dye polarizers. Among them, iodine-based polarizers, which are combined by iodine molecules and polyvinyl alcohol, have the highest market share. During the preparation of iodine-based polarizers, the polyvinyl alcohol film needs to be dyed in an iodine-containing solution. The main components of such iodine-containing solutions include iodine and potassium iodide, and boric acid is usually added to improve the hardness of the polyvinyl alcohol film. As the iodine-containing solution is consumed during the dyeing process, the iodine-containing waste liquid obtained after it can no longer be used needs to be treated.

[0003] The common treatment method for iodine-containing waste liquid is through pretreatment, distillation, and separation. By utilizing the difference in solubility, iodine-containing crude boric acid solids are obtained. However, the purity of the iodine-containing crude boric acid at this time is relatively low, and generally has no economic value for utilization. Therefore, it is necessary to purify and recover the products as much as possible when treating iodine-containing waste liquid. The acidification method is the most common method for boric acid purification at present. Since boric acid is a weak acid, strong acids can be used to convert borates into boric acid. Although the operation is simple, the resulting salt-containing filtrate has a large output and high treatment difficulty. The salt-containing filtrate is mainly composed of boric acid and inorganic salts, and is an acidic waste liquid with a high salt content. Generally, it is distilled to obtain a mixed solid, which is directly landfilled, or undergoes extraction and separation, and the latter process requirements are relatively strict. At present, the treatment of iodine-containing waste liquid mainly focuses on the recovery of boric acid, but there is no clear method for how to recover iodine.

[0004] CN 109970073A discloses a method for recovering boric acid and potassium chloride from polarizer waste liquid. The method includes: pulping, the polarizer waste liquid is distilled and concentrated to obtain iodine-containing crude boric acid, which is washed by pulping with potassium sulfite solution, and solid-liquid separation is carried out to obtain boric acid after pulping; primary acidification, adjusting the pH value of the boric acid after pulping to 3, cooling and crystallizing to obtain finished boric acid and salt-containing boric acid solution; calcification, heating the salt-containing boric acid solution and adding calcium hydroxide for reaction to obtain calcium mud and salt-containing filtrate; secondary acidification, adding hydrochloric acid to the calcium mud for acidification until the pH value is 3 to obtain finished boric acid and calcium chloride solution; concentration, distilling the salt-containing filtrate to obtain crude potassium chloride, redissolving and removing impurities and then distilling to obtain high-purity potassium chloride products. This method uses the method of generating calcium borate by calcium hydroxide and boron to treat the salt-containing boric acid solution after extracting boric acid, but this method requires heating, and the consumption of calcium hydroxide is large, and at the same time, there is no clear treatment for iodine recovery.

[0005] CN 109553116A discloses a method for purifying boric acid-containing potassium iodide waste liquid, which comprises: removing impurities in the boric acid-containing potassium iodide waste liquid with activated carbon, concentrating the solution after impurities removal to a potassium iodide concentration of 25-35wt%, adding calcium hydroxide to react with boric acid in the concentrated solution to generate calcium borate, and using a chelating ion exchange resin to remove calcium ions in the remaining solution after solid-liquid separation. The method still focuses on the treatment of boric acid in the waste liquid and converting it into calcium borate, but does not effectively recover the boric acid product, and finally obtains a potassium iodide solution, and does not recover the iodine product, especially the iodine element.

[0006] CN 111498861A discloses a method for treating polarizing plate waste liquid, which comprises: pre-treating and acidifying the polarizing plate waste liquid to obtain boric acid and a saline boric acid solution; and acidifying the saline boric acid solution with a hydrofluoric acid solution to prepare potassium fluoroborate. The method focuses on the recovery of the boron element and obtains a potassium fluoroborate product by using hydrofluoric acid, but does not specify how to recover iodine in the iodine-containing filtrate obtained therein, and the waste liquid treatment is insufficient, and the enrichment of iodine is likely to cause subsequent pollution problems.

[0007] In summary, for the recovery and treatment of iodine-containing waste liquid generated in the preparation process of polarizing plates, it is necessary to adopt corresponding processes to separate and recover iodine and boric acid in the waste liquid according to the composition of the waste liquid, so as to obtain high-purity recycled products with a high recovery rate, thereby realizing the resource utilization of the waste liquid. Summary of the invention

[0008] In view of the problems existing in the prior art, the object of the present invention is to provide a method for recovering elemental iodine and boric acid from iodine-containing waste liquid. The method firstly carries out an acidification treatment to precipitate boric acid according to the composition of the iodine-containing waste liquid, then carries out an oxidation treatment to obtain elemental iodine, and then separates to obtain a high-purity iodine product, and at the same time absorbs the iodine vapor generated in the reaction process to ensure the recovery rate of iodine and avoid environmental pollution.

[0009] To achieve this object, the present invention adopts the following technical solutions:

[0010] In one aspect, the present invention provides a method for recovering iodine and boric acid from iodine-containing waste liquid, characterized in that the method comprises the following steps:

[0011] (1) acidifying the iodine-containing waste liquid after pretreatment, and separating the solid and liquid to obtain boric acid and iodine-containing solution;

[0012] (2) subjecting the iodine-containing solution obtained in step (1) to secondary acidification and oxidation in sequence to obtain a solid-liquid mixture containing elemental iodine and boric acid;

[0013] (3) Adjust the pH value of the solid-liquid mixture obtained in step (2) and then perform solid-liquid separation to obtain iodine and a salt-containing solution;

[0014] (4) Condense and spray-absorb the iodine vapor generated during the reaction in step (2) in sequence. The condensed iodine is returned to step (3) for co-recovery.

[0015] In the present invention, according to the source of the iodine-containing waste liquid, in addition to iodides, it also contains borates. First, the iodine-containing waste liquid is concentrated and then acidified to convert the borates into boric acid for precipitation, and the boric acid product is recovered. Then, through further acidification to meet the conditions of the oxidation reaction, an oxidant is used to oxidize iodide ions into iodine. After adjusting the pH with alkali, the simultaneously generated boric acid is dissolved again, thereby obtaining an iodine product. The salt-containing solution is recycled for treatment to improve the recovery rate of boric acid. According to the characteristics of iodine, the iodine vapor generated during the reaction is condensed and spray-absorbed to avoid iodine loss, ensure the iodine recovery rate, and also avoid potential environmental pollution caused by iodine vapor. The method has simple operation, mild conditions, and low required cost, and helps to realize the resource utilization of waste liquid.

[0016] The following are the preferred technical solutions of the present invention, but do not limit the technical solutions provided by the present invention. Through the following technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved.

[0017] As a preferred technical solution of the present invention, the source of the iodine-containing waste liquid in step (1) includes the polarizer preparation process.

[0018] Preferably, the composition of the iodine-containing waste liquid in step (1) includes iodides of alkali metals and borates of alkali metals.

[0019] Preferably, the alkali metal includes sodium or potassium.

[0020] Preferably, the concentration of iodides in the iodine-containing waste liquid in step (1) is 0.1 - 3 wt%, such as 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt% or 3 wt%, etc., but not limited to the listed values. Other unlisted values within this numerical range are equally applicable; the concentration of borates is 0.5 - 4 wt%, such as 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt% or 4 wt%, etc., but not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0021] In the present invention, in the iodine-containing waste liquid, in addition to the composition of iodides and borates, it also contains a small amount of mechanical impurities.

[0022] As a preferred technical solution of the present invention, the pretreatment in step (1) includes concentration treatment.

[0023] Preferably, the way of the concentration treatment includes evaporation.

[0024] Preferably, the end point of the concentration treatment is to concentrate to a concentration of iodide of 40 wt% or more, such as 40 wt%, 42 wt%, 45 wt%, 48 wt% or 50 wt% etc., but not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0025] In the present invention, the concentration treatment is carried out in a concentration device, and then enters a reaction kettle for acidification and oxidation reactions.

[0026] As a preferred technical solution of the present invention, the primary acidification in step (1) is: adding an acid solution to the pretreated iodine-containing waste liquid.

[0027] Preferably, the acid solution includes any one or a combination of at least two of hydrochloric acid, nitric acid or sulfuric acid. Typical but non-limiting examples of the combination are: a combination of hydrochloric acid and nitric acid, a combination of nitric acid and sulfuric acid, a combination of hydrochloric acid, nitric acid and sulfuric acid, etc.

[0028] Preferably, during the addition of the acid solution, stirring reaction is carried out, and borate is converted into boric acid and precipitated.

[0029] Preferably, the end point of the primary acidification in step (1) is to adjust the pH value of the solution to 3 - 5, such as 3, 3.5, 4, 4.5 or 5 etc., but not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0030] In the present invention, the pH value adjusted by the primary acidification is controlled according to the characteristics of boric acid. At this time, the proportion of the precipitated boric acid in the total borate is 85 - 90%, and the remaining boric acid is still dissolved in the solution. If the pH value is adjusted too low, a large amount of iodine vapor will be generated when filtering boric acid; if the pH value is too high, the borate cannot be fully converted into boric acid, or even if boric acid is generated, it cannot be precipitated.

[0031] As a preferred technical solution of the present invention, the solid-liquid separation in step (1) includes filtration.

[0032] Preferably, the boric acid obtained by filtration is dried to obtain a boric acid product, and the obtained filtrate is continuously added with an acid solution for reaction.

[0033] Preferably, the acid solution added in the secondary acidification in step (2) is the same as that in the primary acidification.

[0034] Preferably, the pH value is adjusted to less than 2 in the secondary acidification in step (2), such as 2, 1.8, 1.5, 1.2, 1 or 0.5, etc., but not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0035] Preferably, an oxidant is added after the secondary acidification in step (2) for an oxidation reaction.

[0036] Preferably, the oxidant includes sodium perborate or hydrogen peroxide, and preferably sodium perborate.

[0037] Preferably, the addition amount of the oxidant is 1 to 1.3 times the theoretical addition amount, such as 1 time, 1.05 times, 1.1 times, 1.15 times, 1.2 times, 1.25 times or 1.3 times, etc., but not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0038] In the present invention, the addition of the oxidant needs to satisfy the oxidation of iodide ions without introducing new impurity ions. When sodium perborate is selected, the reaction is relatively mild, and the generated boric acid can be dissolved or precipitated by adjusting the pH value; while when hydrogen peroxide is selected, the generated products are water and oxygen, and the oxygen can be discharged in time, and violent reactions can be avoided by controlling the temperature; among them, the theoretical addition amount is the amount of the oxidant required for complete oxidation of iodide ions in the iodine-containing waste liquid.

[0039] As a preferred technical solution of the present invention, the temperature of the oxidation in step (2) is controlled below 25 °C, such as 25 °C, 24 °C, 22 °C, 20 °C, 18 °C or 15 °C, etc., but not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0040] Preferably, the oxidation in step (2) is carried out under stirring conditions.

[0041] Preferably, the oxidation time in step (2) is 0.5 to 2 h, such as 0.5 h, 0.75 h, 1 h, 1.25 h, 1.5 h, 1.75 h or 2 h, etc., but not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0042] As a preferred technical solution of the present invention, the base in step (3) is added in the form of an alkali solution.

[0043] Preferably, the alkali solution includes sodium hydroxide solution or potassium hydroxide solution.

[0044] Preferably, the pH value is adjusted to 5.5 to 8.5 by adding the base in step (3), and boric acid is converted into borate and dissolved, such as 5.5, 6, 6.5, 7, 7.5, 8 or 8.5, etc., but not limited to the listed values, and other unlisted values within this value range are equally applicable.

[0045] Preferably, after adjusting the pH value in step (3), the solid-liquid mixture is discharged and then filtered.

[0046] In the present invention, the solid-liquid mixture is discharged into a suction filtration tank, and the solution phase is separated to obtain an industrial-grade crude iodine product.

[0047] Preferably, the solid obtained after the suction filtration includes a crude iodine product, and the obtained filtrate is returned to step (1) for cyclic treatment.

[0048] Preferably, the purity of the crude iodine product is above 90wt%, for example 90wt%, 91wt%, 92wt%, 93wt%, 94wt%, 95wt% or 96wt%, etc., but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0049] As a preferred technical solution of the present invention, the condensation in step (4) is carried out in a condenser, and a spray component is provided in the condenser.

[0050] Preferably, in step (4), the iodine vapor is condensed to form iodine element which is adsorbed in the condenser, and the iodine element is washed off with water and returned to the reaction solution.

[0051] In the present invention, the medium used for condensation in the condenser can be water, the temperature of which is controlled below 20° C. and is cooled by a refrigerator or a cooling fan to maintain the temperature of the condensing medium.

[0052] As a preferred technical solution of the present invention, the spray absorption in step (4) uses an absorption liquid to absorb the uncondensed iodine vapor.

[0053] In the present invention, the spray absorption is carried out using a spray tower. In order to ensure that the iodine vapor is fully absorbed, a multi-stage spray tower can be set.

[0054] Preferably, the absorption liquid is a mixed solution of ethanol and potassium iodide solution.

[0055] Preferably, the volume ratio of the ethanol and potassium iodide solution is (0.5-2):1, for example 0.5:1, 0.75:1, 1:1, 1.25:1, 1.5:1, 1.75:1 or 2:1, etc., but is not limited to the listed values. Other unlisted values within the numerical range are also applicable, preferably 1:1.

[0056] In the present invention, the potassium iodide in the absorption liquid may be a solution with a concentration of 15 to 25 wt%, such as 15 wt%, 16 wt%, 18 wt%, 20 wt%, 22 wt% or 25 wt%, etc.; the selection of the absorption liquid composition is mainly based on having a good absorption and fixation effect on the generated iodine vapor. The use of ethanol can enhance the absorption effect of the solution on iodine vapor and combine with the absorbed iodine to form a substance that is not easily sublimated.

[0057] As a preferred technical solution of the present invention, the method includes the following steps:

[0058] (1) Pretreat the iodine-containing waste liquid and then perform primary acidification. The composition of the iodine-containing waste liquid includes iodides of alkali metals and borates of alkali metals. Among them, the concentration of iodides is 0.1 to 3 wt%, and the concentration of borates is 0.5 to 4 wt%. The pretreatment includes concentration treatment, and the concentration treatment method includes evaporation. The end point is to concentrate to a concentration of iodides above 40 wt%. The primary acidification is as follows: Add an acid solution to the pretreated iodine-containing waste liquid. The acid solution includes any one or a combination of at least two of hydrochloric acid, nitric acid or sulfuric acid. Stir and react during the addition of the acid solution. The end point of the primary acidification is to adjust the pH value of the solution to 3 to 5, and the borate is converted into boric acid and precipitated. After solid-liquid separation, boric acid and an iodine-containing solution are obtained;

[0059] (2) Continue to add an acid solution to the iodine-containing solution obtained in step (1) for secondary acidification. The acid solution added in the secondary acidification is the same as that in the primary acidification. Adjust the pH to below 2, and then add an oxidant for oxidation. The oxidant includes sodium perborate or hydrogen peroxide. The addition amount of the oxidant is 1 to 1.3 times the theoretical addition amount. The temperature of the oxidation is controlled below 25 °C and carried out under stirring conditions. The oxidation time is 0.5 to 2 h to obtain a solid-liquid mixture containing iodine and boric acid;

[0060] (3) Adjust the pH value of the solid-liquid mixture obtained in step (2) to 5.5 to 8.5 with an alkali solution. The alkali solution includes sodium hydroxide solution or potassium hydroxide solution. The boric acid is converted into borate and dissolved. Then, the solid-liquid mixture is discharged and filtered to obtain iodine and a salt-containing solution. The salt-containing solution is returned to step (1) for cyclic treatment;

[0061] (4) The iodine vapor generated during the reaction in step (2) is successively condensed and spray-absorbed. The condensation is carried out in a condenser. A spray component is provided in the condenser. After the iodine vapor sublimates, iodine is adsorbed in the condenser. The iodine is washed down with water and returned to step (3) for joint recovery. The spray absorption uses an absorption liquid to absorb the uncondensed iodine vapor. The absorption liquid is a mixed solution of ethanol and potassium iodide solution with a volume ratio of (0.5 to 2):1.

[0062] Compared with the prior art, the present invention has the following beneficial effects:

[0063] (1) The method of the present invention comprises the following steps: firstly subjecting the iodine-containing waste liquid to an acidification treatment to precipitate boric acid, recovering the boric acid product, and then subjecting the waste liquid to further acidification and oxidation to obtain elemental iodine, and then adjusting the pH to dissolve the boric acid generated simultaneously, thereby obtaining an elemental iodine product, the purity of which can reach more than 90 wt %;

[0064] (2) The present invention condenses and sprays the iodine vapor generated during the reaction to avoid iodine loss and environmental pollution caused by iodine vapor, ensuring that the recovery rate of iodine in the waste liquid reaches more than 98%;

[0065] (3) The method of the present invention is simple to operate, has mild conditions, requires low costs, and realizes resource utilization of waste liquid. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 The present invention is a schematic diagram of a process flow of a method for recovering elemental iodine and boric acid from iodine-containing waste liquid provided in a specific embodiment 1 of the present invention. DETAILED DESCRIPTION

[0067] In order to better illustrate the present invention and facilitate understanding of the technical solution of the present invention, the present invention is further described in detail below. However, the following embodiments are only simple examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0068] The specific embodiment of the present invention provides a method for recovering iodine and boric acid from iodine-containing waste water. The process flow diagram of the method is as follows: Figure 1 As shown, the following steps are included:

[0069] (1) acidifying the iodine-containing waste liquid after pretreatment, and separating the solid and liquid to obtain boric acid and iodine-containing solution;

[0070] (2) subjecting the iodine-containing solution obtained in step (1) to secondary acidification and oxidation in sequence to obtain a solid-liquid mixture containing elemental iodine and boric acid;

[0071] (3) adding alkali to the solid-liquid mixture obtained in step (2) to adjust the pH value and then separate the solid and liquid to obtain elemental iodine and a salt solution;

[0072] (4) The iodine vapor generated during the reaction of step (2) is sequentially condensed and sprayed for absorption, and the condensed iodine is returned to step (3) for recovery.

[0073] The following are typical but non-limiting embodiments of the present invention:

[0074] Embodiment 1:

[0075] This embodiment provides a method for recovering iodine and boric acid from iodine-containing waste liquid. The method includes the following steps:

[0076] (1) The iodine-containing waste liquid is pretreated and then subjected to primary acidification. The iodine-containing waste liquid is the waste liquid generated in the polarizer preparation process, and its composition includes potassium iodide and potassium borate. Among them, the concentration of potassium iodide is 1.5 wt%, and the concentration of potassium borate is 2 wt%. The pretreatment includes concentration treatment, and the concentration treatment method is MVR evaporation. The end point is to concentrate to a potassium iodide concentration of 45 wt%. The primary acidification is as follows: hydrochloric acid solution is added to the pretreated iodine-containing waste liquid, and stirring reaction is carried out during the addition of the hydrochloric acid solution. The end point of the primary acidification is to adjust the pH value of the solution to 4, and potassium borate is converted into boric acid and precipitated. After filtration and separation, boric acid and iodine-containing solution are obtained;

[0077] (2) The iodine-containing solution obtained in step (1) is continuously added with hydrochloric acid solution for secondary acidification, and the pH is adjusted to 1.5. Then an oxidant is added for oxidation. The oxidant is sodium perborate, and the addition amount of the oxidant is 1.2 times the theoretical addition amount. The oxidation temperature is controlled below 25 °C and carried out under stirring conditions. The oxidation time is 1 h to obtain a solid-liquid mixture containing iodine and boric acid;

[0078] (3) The solid-liquid mixture obtained in step (2) is adjusted to pH 7 with an alkali solution. The alkali solution is potassium hydroxide solution, and boric acid is converted into potassium borate and dissolved. Then the solid-liquid mixture is discharged and suction-filtered to obtain iodine and a salt-containing solution. The salt-containing solution is returned to step (1) for cyclic treatment;

[0079] (4) The iodine vapor generated during the reaction in step (2) is successively subjected to condensation and spray absorption. The condensation is carried out in a condenser, and a spray component is provided in the condenser. After the iodine vapor sublimates, iodine is adsorbed in the condenser. Water is used to wash the iodine and return it to step (3) for co-recovery. The spray absorption uses an absorption liquid to absorb the uncondensed iodine vapor. The absorption liquid is a mixed solution of ethanol and 20 wt% potassium iodide solution with a volume ratio of 1:1.

[0080] In this embodiment, when the above method is used to treat the iodine-containing waste liquid, the purity of the obtained iodine product is 92 wt%, the recovery rate of iodine is 98.8%, and the total recovery rate of boric acid is 95%.

[0081] Example 2:

[0082] This embodiment provides a method for recovering iodine and boric acid from iodine-containing waste liquid. The method includes the following steps:

[0083] (1) The iodine-containing waste liquid is pretreated and then acidified once. The iodine-containing waste liquid is the waste liquid generated in the polarizer preparation process, and its composition includes potassium iodide and potassium borate. Among them, the concentration of potassium iodide is 3 wt%, and the concentration of potassium borate is 4 wt%. The pretreatment includes concentration treatment, and the concentration treatment method is single-effect evaporation. The end point is to concentrate until the concentration of potassium iodide is 40 wt%. The first acidification is as follows: add nitric acid solution to the pretreated iodine-containing waste liquid, and stir and react during the addition of the nitric acid solution. The end point of the first acidification is to adjust the pH value of the solution to 5, and potassium borate is converted into boric acid and precipitated. After filtration and separation, boric acid and iodine-containing solution are obtained;

[0084] (2) Continue to add nitric acid solution to the iodine-containing solution obtained in step (1) for secondary acidification, adjust the pH to 2, and then add an oxidant for oxidation. The oxidant is sodium perborate, and the addition amount of the oxidant is 1.05 times the theoretical addition amount. The temperature of the oxidation is controlled below 25 °C and carried out under stirring conditions. The oxidation time is 2 h to obtain a solid-liquid mixture containing iodine and boric acid;

[0085] (3) Add alkali solution to the solid-liquid mixture obtained in step (2) to adjust the pH value to 8.5. The alkali solution is potassium hydroxide solution, and boric acid is converted into potassium borate and dissolved. Then, the solid-liquid mixture is discharged and filtered to obtain iodine and a salt-containing solution. The salt-containing solution is returned to step (1) for cyclic treatment;

[0086] (4) The iodine vapor generated during the reaction in step (2) is sequentially condensed and spray-absorbed. The condensation is carried out in a condenser, and a spray component is provided in the condenser. After the iodine vapor sublimates, iodine is adsorbed in the condenser. Water is used to wash the iodine and return it to step (3) for joint recovery. The spray absorption uses an absorption liquid to absorb the uncondensed iodine vapor. The absorption liquid is a mixed solution of ethanol and 25 wt% potassium iodide solution with a volume ratio of 2:1.

[0087] In this example, the iodine-containing waste liquid is treated by the above method. The purity of the obtained iodine product is 91 wt%, the recovery rate of iodine is 98.5%, and the total recovery rate of boric acid is 93%.

[0088] Example 3:

[0089] This example provides a method for recovering iodine and boric acid from iodine-containing waste liquid. The method includes the following steps:

[0090] (1) The iodine-containing waste liquid is acidified once after pretreatment. The source of the iodine-containing waste liquid is the waste liquid generated in the polarizer preparation process, and its composition includes potassium iodide and potassium borate. Among them, the concentration of potassium iodide is 0.3 wt%, and the concentration of potassium borate is 0.5 wt%. The pretreatment includes concentration treatment, and the concentration method is multi-effect evaporation. The end point is to concentrate to a potassium iodide concentration of 42 wt%. The first acidification is as follows: Add a nitric acid solution to the pretreated iodine-containing waste liquid, and stir and react during the addition of the nitric acid solution. The end point of the first acidification is to adjust the pH value of the solution to 3, and potassium borate is converted into boric acid and precipitated. After filtration and separation, boric acid and an iodine-containing solution are obtained;

[0091] (2) The iodine-containing solution obtained in step (1) is continuously added with a nitric acid solution for secondary acidification, and the pH is adjusted to 1. Then, an oxidant is added for oxidation. The oxidant is hydrogen peroxide, and the addition amount of the oxidant is 1.3 times the theoretical addition amount. The temperature of the oxidation is controlled below 25 °C, and it is carried out under stirring conditions. The oxidation time is 0.5 h to obtain a solid-liquid mixture containing iodine and boric acid;

[0092] (3) The solid-liquid mixture obtained in step (2) is adjusted to a pH value of 5.5 with an alkali solution. The alkali solution is a potassium hydroxide solution, and boric acid is converted into potassium borate and dissolved. Then, the solid-liquid mixture is discharged and filtered to obtain iodine and a salt-containing solution. The salt-containing solution is returned to step (1) for cyclic treatment;

[0093] (4) The iodine vapor generated during the reaction in step (2) is successively condensed and spray-absorbed. The condensation is carried out in a condenser, and a spray assembly is provided in the condenser. After the iodine vapor sublimes, iodine is adsorbed in the condenser. The iodine is washed down with water and returned to step (3) for joint recovery. The spray absorption uses an absorption liquid to absorb the uncondensed iodine vapor. The absorption liquid is a mixed solution of ethanol and a 15 wt% potassium iodide solution with a volume ratio of 0.5:1.

[0094] In this example, by using the above method to treat the iodine-containing waste liquid, the purity of the obtained iodine product is 91.5 wt%, the recovery rate of iodine is 98.4%, and the total recovery rate of boric acid is 94%.

[0095] Example 4:

[0096] This example provides a method for recovering iodine and boric acid from an iodine-containing waste liquid. The method includes the following steps:

[0097] (1) The iodine-containing waste liquid is pretreated and then acidified once. The iodine-containing waste liquid is the waste liquid generated in the polarizer preparation process, and its composition includes sodium iodide and sodium borate. Among them, the concentration of sodium iodide is 1 wt%, and the concentration of sodium borate is 3 wt%. The pretreatment includes concentration treatment, and the concentration treatment method is MVR evaporation. The end point is to concentrate to a sodium iodide concentration of 44 wt%. The first acidification is as follows: hydrochloric acid solution is added to the pretreated iodine-containing waste liquid, and stirring reaction is carried out during the addition of the hydrochloric acid solution. The end point of the first acidification is to adjust the pH value of the solution to 3.5, and sodium borate is converted into boric acid and precipitated. After filtration and separation, boric acid and iodine-containing solution are obtained;

[0098] (2) The iodine-containing solution obtained in step (1) is continuously added with hydrochloric acid solution for secondary acidification, and the pH is adjusted to 0.5. Then an oxidant is added for oxidation. The oxidant is sodium perborate, and the addition amount of the oxidant is 1.1 times the theoretical addition amount. The oxidation temperature is controlled below 25 °C and carried out under stirring conditions. The oxidation time is 1.5 h, and a solid-liquid mixture containing iodine and boric acid is obtained;

[0099] (3) The solid-liquid mixture obtained in step (2) is adjusted to pH 6 with an alkali solution. The alkali solution is sodium hydroxide solution, and boric acid is converted into sodium borate and dissolved. Then the solid-liquid mixture is discharged and suction-filtered to obtain iodine and a salt-containing solution. The salt-containing solution is returned to step (1) for cyclic treatment;

[0100] (4) The iodine vapor generated during the reaction in step (2) is successively condensed and spray-absorbed. The condensation is carried out in a condenser, and a spray component is provided in the condenser. After the iodine vapor sublimes, iodine is adsorbed in the condenser. Water is used to wash the iodine and return it to step (3) for joint recovery. The spray absorption uses an absorption liquid to absorb the uncondensed iodine vapor. The absorption liquid is a mixed solution of ethanol and 20 wt% potassium iodide solution with a volume ratio of 1:1.

[0101] In this example, the iodine-containing waste liquid is treated by the above method. The purity of the obtained iodine product is 90.8 wt%, the recovery rate of iodine is 98.6%, and the total recovery rate of boric acid is 94.5%.

[0102] Example 5:

[0103] (1) The iodine-containing waste liquid is pretreated and then acidified once. The iodine-containing waste liquid is the waste liquid generated in the polarizer preparation process, and its composition includes sodium iodide and sodium borate. Among them, the concentration of sodium iodide is 2.4 wt%, and the concentration of sodium borate is 1.5 wt%. The pretreatment includes concentration treatment, and the concentration treatment method is multi-effect evaporation. The end point is to concentrate to a sodium iodide concentration of 40 wt%. The first acidification is as follows: Sulfuric acid solution is added to the pretreated iodine-containing waste liquid, and stirring reaction is carried out during the addition of the sulfuric acid solution. The end point of the first acidification is to adjust the pH value of the solution to 4.5, and sodium borate is converted into boric acid and precipitated. After filtration and separation, boric acid and iodine-containing solution are obtained;

[0104] (2) The iodine-containing solution obtained in step (1) is continuously added with sulfuric acid solution for secondary acidification, and the pH is adjusted to 1. Then an oxidant is added for oxidation. The oxidant is sodium perborate, and the addition amount of the oxidant is 1.15 times the theoretical addition amount. The oxidation temperature is controlled below 25 °C and carried out under stirring conditions. The oxidation time is 1.2 h, and a solid-liquid mixture containing iodine and boric acid is obtained;

[0105] (3) The solid-liquid mixture obtained in step (2) is adjusted to a pH value of 8 with an alkali solution. The alkali solution is sodium hydroxide solution, and boric acid is converted into sodium borate and dissolved. Then the solid-liquid mixture is discharged and filtered by suction to obtain iodine and a salt-containing solution, and the salt-containing solution is returned to step (1) for recycling treatment;

[0106] (4) The iodine vapor generated during the reaction in step (2) is successively condensed and spray-absorbed. The condensation is carried out in a condenser, and a spray component is provided in the condenser. After the iodine vapor sublimes, iodine is adsorbed in the condenser. Water is used to wash the iodine and return it to step (3) for joint recovery. The spray absorption uses an absorption liquid to absorb the uncondensed iodine vapor. The absorption liquid is a mixed solution of ethanol and 18 wt% potassium iodide solution with a volume ratio of 1.2:1.

[0107] In this example, by using the above method to treat the iodine-containing waste liquid, the purity of the obtained iodine product is 91.2 wt%, the iodine recovery rate is 98.2%, and the total recovery rate of boric acid is 93.5%.

[0108] Comparative Example 1:

[0109] This comparative example provides a method for recovering iodine and boric acid from iodine-containing waste liquid. The method refers to the method in Example 1, and the difference is only that the first acidification and the second acidification are combined, and the pH is directly adjusted to 1.5.

[0110] In this comparative example, when boric acid is precipitated by acidifying the iodine-containing waste liquid, the pH is directly adjusted to below 2. At this time, boric acid can still be precipitated from the boric acid solution, but a large amount of iodine vapor will be generated and dissipated during filtration, resulting in a decrease in the iodine recovery rate and environmental pollution.

[0111] Comparative Example 2:

[0112] This comparative example provides a method for recovering iodine and boric acid from iodine-containing waste liquid. The method refers to the method in Example 1, with the only difference being that it does not include the operation of adjusting the pH value in step (3).

[0113] In this comparative example, since the solid generated after the oxidation reaction includes iodine and boric acid, and it is directly separated without pH adjustment, the purity of iodine in the obtained product is relatively low and cannot be directly used, and further separation and purification are required.

[0114] Comparative Example 3:

[0115] This comparative example provides a method for recovering iodine and boric acid from iodine-containing waste liquid. The method refers to the method in Example 1, with the only difference being that it does not include the operation in step (4).

[0116] In this comparative example, due to the characteristics of iodine, iodine vapor will be generated during the reaction process. If it is not recovered, it is easy to cause the dissipation of iodine vapor, affecting the iodine recovery rate. At this time, the iodine recovery rate is about 85%, and it will also cause environmental pollution.

[0117] From the above examples and comparative examples, it can be seen that the method of the present invention first undergoes acidification treatment to precipitate boric acid according to the composition of the iodine-containing waste liquid, and the boric acid product is recovered. Then, through further acidification and oxidation reactions, iodine is obtained. The pH is adjusted to dissolve the simultaneously generated boric acid, thereby obtaining an iodine product with a purity of over 90 wt%. The iodine vapor generated during the reaction process in the present invention is condensed and spray-absorbed to avoid iodine loss and environmental pollution that may be caused by iodine vapor, ensuring that the iodine recovery rate in the waste liquid reaches over 98%. The method is simple to operate, has mild conditions, requires low costs, and realizes the resource utilization of the waste liquid.

[0118] The applicant declares that the present invention uses the above examples to illustrate the detailed method of the present invention, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvement to the present invention, equivalent replacement of the method of the present invention, addition of auxiliary steps, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for recovering iodine and boric acid from iodine-containing waste liquid, characterized in that, The method comprises the following steps: (1) Pretreat the iodine-containing waste liquid, perform primary acidification, and carry out solid-liquid separation to obtain boric acid and an iodine-containing solution; the end point of the primary acidification is to adjust the pH value of the solution to 3-5; (2) Sequentially perform secondary acidification and oxidation on the iodine-containing solution obtained in step (1) to obtain a solid-liquid mixture containing iodine and boric acid; the secondary acidification adjusts the pH to below 2; (3) Add alkali to adjust the pH value of the solid-liquid mixture obtained in step (2), and then carry out solid-liquid separation to obtain iodine and a salt-containing solution; (4) Condense and spray-absorb the iodine vapor generated during the reaction in step (2) in sequence, and the condensed iodine is returned to step (3) for co-recovery.

2. The method according to claim 1, wherein The source of the iodine-containing waste liquid in step (1) includes the polarizer preparation process.

3. The method according to claim 1, wherein The composition of the iodine-containing waste liquid in step (1) includes iodides of alkali metals and borates of alkali metals.

4. The method according to claim 3, wherein The alkali metal includes sodium or potassium.

5. The method according to claim 3, characterized in that, In the iodine-containing waste liquid in step (1), the concentration of iodide is 0.1-3 wt%, and the concentration of borate is 0.5-4 wt%.

6. The method according to claim 1, wherein The pretreatment in step (1) includes concentration treatment.

7. The method according to claim 6, wherein The concentration treatment method includes evaporation.

8. The method according to claim 6, wherein The end point of the concentration treatment is to concentrate to a concentration of iodide above 40 wt%.

9. The method according to claim 1, wherein The primary acidification in step (1) is as follows: add an acid solution to the pretreated iodine-containing waste liquid.

10. The method according to claim 9, characterized in that, The acid solution includes any one or a combination of at least two of hydrochloric acid, nitric acid, or sulfuric acid.

11. The method according to claim 9, wherein During the addition of the acid solution, stir and react, and the borate is converted into boric acid and precipitates.

12. The method according to claim 1, characterized in that The solid-liquid separation in step (1) includes filtration.

13. The method according to claim 12, wherein The boric acid obtained by filtration is dried to obtain a boric acid product, and the obtained filtrate is continuously added with an acid solution for reaction.

14. The method according to claim 1, characterized in that, The acid solution added in the secondary acidification in step (2) is the same as that in the primary acidification.

15. The method according to claim 1, characterized in that, After the secondary acidification in step (2), add an oxidant for oxidation reaction.

16. The method according to claim 15, wherein The oxidant includes sodium perborate or hydrogen peroxide.

17. The method according to claim 16, wherein The oxidant is sodium perborate.

18. The method according to claim 15, wherein The addition amount of the oxidant is 1-1.3 times the theoretical addition amount.

19. The method according to claim 1, characterized in that, The temperature of the oxidation in step (2) is controlled below 25 °C.

20. The method according to claim 1, characterized in that, The oxidation in step (2) is carried out under stirring conditions.

21. The method according to claim 1, wherein, The oxidation time in step (2) is 0.5-2 h.

22. The method according to claim 1, wherein The alkali in step (3) is added in the form of an alkali solution.

23. The method according to claim 22, characterized in that, The alkali solution includes sodium hydroxide solution or potassium hydroxide solution.

24. The method according to claim 1, wherein In step (3), add alkali to adjust the pH value to 5.5-8.5, and the boric acid is converted into borate and dissolved.

25. The method according to claim 1, characterized in that, After adjusting the pH value in step (3), discharge the solid-liquid mixture, and then carry out suction filtration.

26. The method according to claim 25, wherein The solid obtained after the suction filtration includes a crude iodine product, and the obtained filtrate is returned to step (1) for cyclic treatment.

27. The method according to claim 26, wherein The purity of the crude iodine product is above 90 wt%.

28. The method according to claim 1, characterized in that, The condensation in step (4) is carried out in a condenser, and a spraying component is provided in the condenser.

29. The method according to claim 1, characterized in that, After the iodine vapor sublimates in step (4) to form iodine adsorbed in the condenser, use water to wash the iodine down and return it to the reaction solution.

30. The method according to claim 1, characterized in that, The spray absorption in step (4) uses an absorption liquid to absorb the uncondensed iodine vapor.

31. The method according to claim 30, characterized in that, The absorption liquid is a mixed solution of ethanol and potassium iodide solution.

32. The method according to claim 31, wherein The volume ratio of ethanol to potassium iodide solution is (0.5-2):

1.

33. The method according to claim 32, wherein The volume ratio of ethanol to potassium iodide solution is 1:

1.

34. The method according to any one of claims 1-33, characterized in that, The method comprises the following steps: (1) Subject the iodine-containing waste liquid to primary acidification after pretreatment. The composition of the iodine-containing waste liquid includes iodides of alkali metals and borates of alkali metals. Among them, the concentration of iodide is 0.1-3 wt%, and the concentration of borate is 0.5-4 wt%. The pretreatment includes concentration treatment, and the concentration treatment method includes evaporation. The end point is to concentrate to a concentration of iodide above 40 wt%. The primary acidification is as follows: Add an acid solution to the pretreated iodine-containing waste liquid. The acid solution includes any one or a combination of at least two of hydrochloric acid, nitric acid or sulfuric acid. Stir and react during the addition of the acid solution. The end point of the primary acidification is to adjust the pH value of the solution to 3-5. The borate is converted into boric acid and precipitated. After solid-liquid separation, boric acid and an iodine-containing solution are obtained; (2) Continue to add an acid solution to the iodine-containing solution obtained in step (1) for secondary acidification. The acid solution added in the secondary acidification is the same as that in the primary acidification. Adjust the pH to below 2, and then add an oxidant for oxidation. The oxidant includes sodium perborate or hydrogen peroxide. The addition amount of the oxidant is 1-1.3 times the theoretical addition amount. The oxidation temperature is controlled below 25°C and carried out under stirring conditions. The oxidation time is 0.5-2 h to obtain a solid-liquid mixture containing iodine and boric acid; (3) Adjust the pH value of the solid-liquid mixture obtained in step (2) to 5.5-8.5 with an alkali solution. The alkali solution includes sodium hydroxide solution or potassium hydroxide solution. The boric acid is converted into borate and dissolved. Then, discharge the solid-liquid mixture and filter it by suction to obtain iodine and a salt-containing solution. The salt-containing solution is returned to step (1) for cyclic treatment; (4) The iodine vapor generated during the reaction in step (2) is sequentially subjected to condensation and spray absorption. The condensation is carried out in a condenser. A spray assembly is provided in the condenser. After the iodine vapor sublimates, iodine is adsorbed in the condenser. Wash the iodine with water and return it to step (3) for co-recovery. The spray absorption uses an absorption liquid to absorb the uncondensed iodine vapor. The absorption liquid is a mixed solution of ethanol and potassium iodide solution with a volume ratio of (0.5-2):1.

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