Process method for multi-stage oxidation recovery of iodine from various iodine-rich evaporation mother liquor and other iodine-rich waste liquor

Abstract

The invention discloses a process method for multi-stage oxidation recovery of iodine from various iodine-rich evaporation mother liquor and other iodine-rich waste liquid, and relates to the technical field of industrial waste liquid resource utilization, the method comprises the steps of raw material pretreatment, gradient cooling crystallization, solid-liquid separation, first-stage oxidation precipitation, second-stage oxidation precipitation and iodine product treatment, through gradient cooling crystallization, the mother liquor is cooled to 20 DEG C through a precooler and a cooler, and potassium chloride and sodium chloride are separated out for desalination; adjusting the pH value of the desalted clear liquid to 2.0, carrying out two-stage oxidation precipitation by adopting hydrogen peroxide, recovering main iodine in the first stage, and strengthening residual iodine recovery in the second stage; according to the present invention, the problems of low recovery efficiency and insufficient purity of the low concentration iodine in the high salt environment are solved, the efficient resource utilization is achieved, the reuse water utilization rate is more than or equal to 85%, and the method is suitable for the resource recovery of the iodine in the industrial waste liquid.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of industrial waste liquid resource utilization, in particular to a process method for multi-stage oxidation recovery of iodine from various iodine-rich evaporation mother liquor and other iodine-rich waste liquid. BACKGROUND

[0002] Iodine is an important chemical raw material, widely used in medical, agricultural, industrial and human and animal nutrition products, etc. For example, it plays a key role in the production of X-ray contrast agents, bactericides, preservatives, pharmaceutical intermediates, LCD and LED screen polarizing films, etc. According to statistics, the global demand for iodine in 2023 was about 38.6 million tons, of which the demand from X-ray contrast agents, pharmaceutical manufacturing, liquid crystal panel manufacturing and other fields accounted for 57%. However, China's iodine production has been at a low level for a long time, with annual production of less than 1,000 tons, while the domestic demand for iodine is very large, with an import volume of about 7,381 tons in 2023, and a high degree of dependence on imports, which has seriously restricted the sustainable and stable development of China's iodine industry. In the industrial production process, after high-zinc materials are washed with water and evaporated to extract potassium chloride and sodium chloride, a certain amount of iodine (usually about 2 g / L) will be enriched in the evaporation mother liquor. Such mother liquor contains high concentrations of sodium chloride (187 g / L) and potassium chloride (145 g / L). If the low-concentration iodine in it can be efficiently recovered, not only the resource utilization rate can be improved, but also the problem of domestic iodine resource shortage can be alleviated.

[0003] In the prior art, the methods for recovering iodine from solution mainly include oxidation precipitation method, adsorption method, ion exchange method, etc. Among them, the oxidation precipitation method is widely used because of its simple operation and low cost. For example, Chinese invention patent CN104961100B discloses a method for recovering iodine from iodine-containing wastewater. The method adjusts the pH of the wastewater and then adds an oxidizing agent for oxidation precipitation to directly recover elemental iodine. However, this method does not consider the influence of high-salt environment on the precipitation efficiency. In the presence of high-concentration sodium salt and potassium salt, the precipitation of iodine is not complete, and the recovery rate is low.

[0004] In the iodine recovery process of high-zinc material evaporation mother liquor, the core technical problem is how to realize the efficient recovery of low-concentration iodine under high-salt interference. Specifically, the concentration of sodium chloride in the mother liquor is as high as 187 g / L, and the concentration of potassium chloride is as high as 145 g / L. High-concentration salt ions not only inhibit the oxidation reaction kinetics of iodine ions, leading to incomplete oxidation, but also precipitate with elemental iodine during the precipitation process, resulting in excessive salt impurities in the product. At the same time, the iodine concentration in the mother liquor is only 2 g / L, which belongs to low-concentration iodine resources. The recovery rate of conventional oxidation precipitation method is low under this condition, which is difficult to meet the needs of industrial production. The existing technology lacks targeted desalination pretreatment and intensified oxidation separation means, which cannot effectively solve the problem of high-salt interference, resulting in low iodine recovery efficiency and insufficient product purity (difficult to reach more than 85%), and cannot realize the resource utilization of idle iodine resources.

[0005] Therefore, in view of the characteristics of high-zinc material evaporation mother liquor, it is urgent to develop a process method integrating desalination pretreatment and intensified oxidation precipitation, which can effectively remove high-salt impurities to reduce their interference with the oxidation reaction, and improve the recovery efficiency of low-concentration iodine by optimizing the oxidation precipitation process, so as to realize the directional and efficient extraction of low-concentration iodine in high-salt mother liquor, and obtain crude iodine products with iodine content > 85%, to fill the gap in this field of the existing technology. SUMMARY

[0006] The purpose of the present application is to overcome the shortcomings of the prior art, and provide a multi-stage oxidation recovery process for iodine from various iodine-rich evaporation mother liquor and other iodine-rich waste liquid. The method integrates gradient cooling crystallization desalination and two-stage oxidation precipitation to extract iodine. The evaporation mother liquor is initially cooled by a pre-cooler, then cooled to 20℃ by a cooler to realize the crystallization and separation of potassium chloride and sodium chloride, effectively removing high-salt impurities. The pH of the desalted clear liquid is adjusted to 2.0, and sodium chlorate or hydrogen peroxide is used for two-stage oxidation precipitation. The first-stage oxidation ensures the precipitation of main iodine, and the second-stage oxidation enhances the recovery of low-concentration residual iodine. Finally, the dehydrated product is obtained, which has an iodine content of > 85%. The process solves the problems of low recovery efficiency and insufficient purity of low-concentration iodine under high-salt interference, and realizes the efficient resource utilization of idle iodine resources.

[0007] To solve the above technical problems, the present application provides the following technical solutions: on the one hand, a multi-stage oxidation recovery process for iodine from various iodine-rich evaporation mother liquor and other iodine-rich waste liquid, comprising the following steps: S100, raw material pretreatment: the potassium chloride centrifugal mother liquor of the evaporation system is input into the mother liquor tank, and the mother liquor contains 187 g / L of sodium chloride, 145 g / L of potassium chloride, and 2 g / L of iodine; S200, gradient cooling crystallization: the mother liquor is lifted by a pump and sequentially passes through a pre-cooler and a cooler, wherein the pre-cooler is preliminarily cooled by a circulating cooling water system, and the cooler is cooled to 20℃ by forced circulation of ethylene glycol refrigerant; after cooling, the mother liquor enters a cooling crystallizer to precipitate potassium chloride and sodium chloride crystals; S300, solid-liquid separation: the solid-containing mother liquor at the bottom of the cooling crystallizer is separated by a centrifugal machine, the separated solid is returned to the evaporation system, and the separated liquid is combined with the clear liquid at the upper part of the cooling crystallizer and then enters a primary clear liquid tank; S400, primary oxidation and precipitation: hydrochloric acid is added to the primary clear liquid tank to adjust the pH to 2.0, and then an oxidizing agent is added to perform an iodine ion oxidation reaction; after the reaction is completed, solid-liquid separation is performed to obtain primary iodine mud and primary supernatant; S500, secondary oxidation and precipitation: the primary supernatant is input into a secondary oxidation tank, and an oxidizing agent is added again to perform a secondary oxidation reaction; after the reaction is completed, solid-liquid separation is performed to obtain secondary iodine mud and secondary supernatant, and the secondary supernatant is returned to the evaporation system; S600, iodine product treatment: the primary iodine mud and the secondary iodine mud are combined and dehydrated to obtain a crude iodine product with an iodine content of >85%, the pre-cooler and the cooler in the step S200 are connected in series, a stirring device is arranged in the cooling crystallizer, the oxidizing agent in the steps S400 and S500 is hydrogen peroxide, and the oxidation reaction time is controlled to be 30-60 minutes, and the dehydration in the step S600 is performed by using a plate-and-frame filter press.

[0008] Further, in the gradient cooling crystallization process, the pre-cooler is supplied with water by a circulating cooling water system, the inlet water temperature is ≤32℃, and the outlet temperature is controlled to be 30-35℃; the cooler is connected with a double-stage compression refrigerator set to provide -5℃ ethylene glycol refrigerant, and the pipe material is TA2 titanium alloy.

[0009] Further, the cooling crystallizer is a stirred tank with a jacket, the tank volume is 15m³, the material is 2205 duplex stainless steel, -3~0℃ ethylene glycol refrigerant is introduced into the jacket, a double-layer inclined-blade paddle is used as the stirrer, the paddle diameter to tank diameter ratio is 0.4-0.5, the rotating speed is 20-40rpm, the crystallization residence time is 2-4 hours, and the crystal particle size is controlled to be 0.2-0.5mm.

[0010] Further, the oxidizing agent is a sodium chlorate solution with a mass concentration of 10% or 30% hydrogen peroxide; the oxidizing agent addition amount in the primary oxidation stage is 1.05 times the molar amount of iodine, and the addition amount in the secondary oxidation stage is 0.25 times; the oxidation reaction is performed under the control of a DCS system, the ORP value is set to +450mV~+550mV, and the reaction time is 30-60 minutes.

[0011] Further, the primary oxidation precipitation is carried out in a settling tank, the surface load is ≤0.8 m³ / (m²·h), the gravity settling time is ≥1 hour, and the secondary oxidation precipitation is carried out in a precipitator, the hydraulic retention time is ≥1.5 hours.

[0012] Further, the dewatering treatment adopts a clear flow type plate and frame filter press, the filter cloth is 750D polypropylene reinforced type, the operating pressure is 0.6-0.8 MPa, the pressing time is 30 minutes, the filter cake thickness is 25 mm, and the moisture content is ≤35%.

[0013] Further, the filtrate recycling system comprises: The filtrate pipeline of the plate and frame filter press is connected with a pH adjusting tank; The washing water of the centrifugal machine is collected into a recycling water tank; The recycling water tank is connected with an oxidant preparation tank through a metering pump, the recycling water utilization rate is ≥85%, and the wastewater discharge amount is ≤0.5 m³ / h.

[0014] On the other hand, a system for multi-stage oxidation recovery of iodine from various iodine-rich evaporation mother liquor and other iodine-rich waste liquid, comprising: A material treatment unit: the mother liquor tank has a volume of 10 m³ and is provided with a 45° folding paddle agitator, the pre-cooler is a tube-shell heat exchanger with a shell material of 316L, and the cooler is a forced circulation heat exchanger with a circulation amount ≥100 m³ / h; An energy unit: an ethylene glycol refrigeration unit is provided with a double-screw compressor, a refrigerant R134a, and a circulating water system with a water supply pressure of 0.3 MPa; An oxidation control unit: the hydrochloric acid storage tank has a volume of 30 m³ and is made of PE, the oxidant storage tank has a volume of 30 m³ and is provided with a liquid level interlock, and a diaphragm metering pump is used for oxidant addition with an accuracy of ±1%; A DCS system: containing a PH / ORP online monitor, a temperature sensor, and communicating with a control room through a ModbusTCP protocol.

[0015] Compared with the prior art, the process method for multi-stage oxidation recovery of iodine from various iodine-rich evaporation mother liquor and other iodine-rich waste liquid has the following beneficial effects: The present application realizes directional and efficient extraction of low-concentration iodine under high-salt interference through gradient cooling crystallization pretreatment, salt crystals are precipitated by cooling to 20℃ through a pre-cooler and a cooler, the salt concentration is significantly reduced, two-stage oxidation precipitation is carried out, primary oxidation ensures the precipitation of main iodine, secondary oxidation strengthens the recovery of residual iodine, and finally, a crude iodine product with an iodine content of >85% is obtained, the resource utilization rate is improved, and the problems of low recovery efficiency and insufficient product purity of low-concentration iodine in high-salt mother liquor are effectively solved.

[0016] The application optimizes equipment parameters, adopts 2205 duplex stainless steel material and specific stirring parameters for cooling crystallizer, ensures stable salt crystal precipitation, adopts DCS system to control ORP value and precise oxidant dosage in the oxidation process, ensures sufficient oxidation reaction, constructs filtrate recycling system, recycling water utilization rate is greater than or equal to 85%, waste water discharge is less than or equal to 0.5m³ / h, reduces water resource consumption and environmental protection pressure.

[0017] Other advantages, objects, and features of the application will be set forth in part in the following specification taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art from a consideration of the following specification and drawings, or can be learned from the practice of the application. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0019] Figure 1 It is an operation flow chart of a process method for multi-stage oxidation recovery of iodine from various iodine-rich evaporation mother liquor and other iodine-rich waste liquid; Figure 2 It is a process method step chart for multi-stage oxidation recovery of iodine from various iodine-rich evaporation mother liquor and other iodine-rich waste liquid; Figure 3 It is a system composition chart of a process method for multi-stage oxidation recovery of iodine from various iodine-rich evaporation mother liquor and other iodine-rich waste liquid. DETAILED DESCRIPTION

[0020] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined application purpose, the following will combine the drawings and the preferred embodiments to specifically describe the specific embodiments, structures, features and effects of the present application.

[0021] Example 1

[0022] As Figure 2 and Figure 3As shown, the embodiment discloses a process method for recovering iodine from various iodine-rich evaporation mother liquor and other iodine-rich waste liquid, aiming at the potassium chloride centrifugal mother liquor of the evaporation system containing sodium chloride 187g / L, potassium chloride 145g / L and iodine 2g / L, and adopting the integrated process of "gradient cooling crystallization desalination + two-stage oxidation precipitation iodine extraction". The salt crystallization separation is realized by the cascade cooling of the pre-cooler and the cooler to 20°C, the clear liquid after desalination is adjusted to pH 2.0 by hydrochloric acid, and the first-stage and second-stage oxidation precipitation are sequentially carried out by using sodium chlorate solution, the two-stage iodine mud is combined and dehydrated by the plate and frame filter press, and finally the crude iodine product with iodine content >85% is obtained, the second-stage supernatant and the separated salt are returned to the evaporation system, and the filtrate is recycled by the recycling system.

[0023] The implementation process of the raw material pretreatment unit operation is as follows: The raw material used in the embodiment is the potassium chloride centrifugal mother liquor of the evaporation system, which comes from the 15m³ / h evaporation crystallization system matched by Tangshan Zinc Technology Co., Ltd., and its composition is as follows: sodium chloride 187g / L, potassium chloride 145g / L and iodine 2g / L. The treatment capacity is 2m³ / h, and the 24-hour continuous operation system is adopted, and the annual working time is 330 days.

[0024] The core equipment of the raw material pretreatment unit is the mother liquor tank, which has a volume of 10m³. A 45° folding paddle agitator is arranged in the tank body, the power of the agitator is 1.5kw, and the material is 2205 duplex stainless steel. When operating, the potassium chloride centrifugal mother liquor discharged from the evaporation system flows into the mother liquor tank through the pipeline, the agitator is started to stir at a speed of 20-40rpm, so as to ensure the uniformity of the mother liquor composition and avoid local concentration difference. A liquid level meter is arranged at the top of the mother liquor tank, with a measuring range of 0-6m, which can monitor the liquid level in real time. When the liquid level reaches 80%, the closing signal of the feeding valve is triggered to stop the liquid feeding. When the liquid level drops to 20%, the opening signal of the feeding valve is triggered to restore the liquid feeding, so as to maintain the stability of the liquid level in the mother liquor tank. At the same time, a blowdown port is arranged at the bottom of the mother liquor tank, and the blowdown valve is opened regularly every week to remove a small amount of impurities that may deposit at the bottom of the tank, so as to ensure the purity of the mother liquor entering the subsequent process.

[0025] The implementation process of the gradient cooling crystallization unit operation is as follows: The gradient cooling crystallization unit is composed of a pre-cooler, a cooler, a cooling crystallizer and a supporting circulating water system and a two-stage compression chiller set, and each equipment is connected in series.

[0026] The pre-cooler is a tubular heat exchanger, the shell side material is 316L stainless steel, and the tube side material is TA2 titanium alloy. The circulating water system supplies water at a pressure of 0.3MPa, and the inlet water temperature is controlled at ≤32°C. The circulating cooling water is introduced into the pre-cooler shell side through the pipeline, and the mother liquor is pumped into the pre-cooler tube side by the mother liquor pump (model: wear-resistant and corrosion-resistant pump, parameters Q = 12 m³ / h, H = 30 m, N = 3 kw)The mother liquor is lifted to the pre-cooler tube, and the indirect heat exchange is carried out between the tube and the shell circulating cooling water. The pre-cooler outlet mother liquor temperature is controlled at 30-35°C by adjusting the circulating water flow, and the heat-exchanged circulating cooling water is returned to the cooling tower for cooling and then recycled.

[0027] The cooler is a forced circulation heat exchanger, and the circulation amount is set to 100 m³ / h. The tube material is TA2 titanium alloy, and the coolant is-5°C ethylene glycol refrigerant provided by a two-stage compression refrigeration unit. The pre-cooled mother liquor enters the tube of the cooler, and the heat exchange is carried out with the ethylene glycol refrigerant in the shell. The refrigerant flow is controlled by the DCS system, so that the mother liquor is cooled to 20°C by the cooler and then discharged.

[0028] The cooled mother liquor enters the cooling crystallizer, which is a jacketed stirred tank with a volume of 15 m³ and a material of 2205 duplex stainless steel. The jacket is supplied with-3~0°C ethylene glycol refrigerant to maintain a low temperature environment in the tank. The agitator in the tank uses a double-layer inclined blade paddle with a paddle diameter to tank diameter ratio of 0.4-0.5 and a rotational speed set to 20-40 rpm. The stirring makes the temperature of the mother liquor uniform and promotes the growth of crystals. The residence time of the mother liquor in the cooling crystallizer is controlled to be 2-4 hours. During this process, potassium chloride and sodium chloride gradually precipitate crystals due to the decrease in solubility. The crystal size is controlled to be 0.2-0.5 mm by adjusting the stirring speed and residence time. The crystallizer is provided with an overflow port at the top, and the supernatant is discharged through the overflow port. The bottom is provided with a solid-containing mother liquor outlet, and the mother liquor containing crystals is discharged periodically.

[0029] The implementation process of the solid-liquid separation unit is as follows: The main equipment of the solid-liquid separation unit is a centrifuge and a primary clear liquid tank. The solid-containing mother liquor at the bottom of the cooling crystallizer is transported to the centrifuge through a pipeline. The centrifuge operates at a rotational speed of 1500 rpm to separate the solid-containing mother liquor. The separated solid is a mixture of potassium chloride and sodium chloride crystals, which is transported back to the evaporation system by a screw conveyor (transport capacity ≤40 m³ / h, N=15 kw, material carbon steel lined with plastic) to participate in the evaporation crystallization process again.

[0030] The liquid after centrifugal separation and the clear liquid overflowing from the upper part of the cooling crystallizer are combined and enter the primary clear liquid tank together. The primary clear liquid tank has a volume of 10 m³ and is made of 316L stainless steel. A liquid level sensor is installed in the tank to monitor the liquid level in real time. When the liquid level reaches the set high level, the clear liquid pump is started to transport the clear liquid to the next process. When the liquid level is lower than the set low level, the clear liquid pump is stopped to ensure that there is enough clear liquid in the primary clear liquid tank for subsequent processing. At the same time, a breather valve is provided at the top of the primary clear liquid tank to balance the pressure in the tank and avoid affecting the clear liquid transportation due to pressure fluctuations.

[0031] The implementation process of the primary oxidation precipitation unit is as follows: The primary oxidation and precipitation unit comprises a primary clear liquid tank, a hydrochloric acid adding system, an oxidant adding system and a sedimentation tank.

[0032] The clear liquid in the primary clear liquid tank is delivered to the sedimentation tank (diameter 3.5 m, effective water depth 4 m) by a clear liquid pump, and the pH value is first adjusted by starting the hydrochloric acid adding system. The hydrochloric acid storage tank has a volume of 30 m³ and is made of PE, and a diaphragm metering pump (accuracy ±1%) is used to add hydrochloric acid with a mass concentration of 30% to the inlet pipeline of the sedimentation tank according to the calculated amount, and the clear liquid is fully mixed with the hydrochloric acid before entering the sedimentation tank. The DCS system monitors the pH value of the liquid in the sedimentation tank in real time through an online pH monitor (measurement range 0-14, output 4-20 mA signal), and automatically adjusts the amount of hydrochloric acid added according to the monitoring results, so that the pH value of the liquid in the tank is stably controlled at 2.0.

[0033] After the pH value is adjusted, the oxidant adding system is started. In this embodiment, a sodium chlorate solution with a mass concentration of 10% is selected as the oxidant, and the oxidant storage tank has a volume of 30 m³ and is equipped with a liquid level interlocking device. A diaphragm metering pump is used to add the sodium chlorate solution to the sedimentation tank. The amount of oxidant added in the primary oxidation stage is 1.05 times the molar amount of iodine in the mother liquor, and the DCS system automatically calculates the amount of oxidant to be added according to the flow rate of the mother liquor and the iodine concentration, and monitors the ORP value of the reaction system through an ORP online monitor (measurement range -1000~+1000 mV, output 4-20 mA signal), and stably controls the ORP value at +450 mV~+550 mV. The oxidation reaction time is set to 30-60 minutes, during which the iodine ions are oxidized to elemental iodine and form a precipitate.

[0034] The surface load of the sedimentation tank is controlled to be ≤0.8 m³ / (m²・h), and the gravity settling time is ≥1 hour. The elemental iodine precipitate gradually settles to the bottom of the tank under the action of gravity to form primary iodine mud, and the supernatant is discharged from the overflow port at the top of the sedimentation tank to enter the secondary oxidation unit. A mud discharge valve is provided at the bottom of the sedimentation tank, and when the iodine mud at the bottom reaches a certain thickness, the mud discharge valve is opened to discharge the primary iodine mud to an iodine mud storage tank.

[0035] The implementation process of the secondary oxidation and precipitation unit is as follows: The secondary oxidation and precipitation unit comprises a secondary oxidation tank, a precipitator and a matching oxidant adding system. The supernatant after the primary oxidation and precipitation is delivered to the secondary oxidation tank through a pipeline, and the secondary oxidation tank has a volume of 5 m³ and is equipped with a stirring device with a rotating speed of 20 rpm to ensure uniform mixing of the liquid.

[0036] The sodium chlorate solution with a mass concentration of 10% was also used as the oxidant, and the oxidant was added in the second oxidation stage at a dosage of 0.25 times the molar amount of iodine in the mother liquor. The oxidant was precisely added into the second oxidation tank through a diaphragm metering pump according to the dosage calculated by the DCS system. The oxidation reaction was carried out under the control of the DCS system, and the ORP value was maintained at +450 mV to +550 mV. The reaction time was 30-60 minutes, and the residual iodine ions in the supernatant were further oxidized.

[0037] After the reaction was completed, the mixed solution entered an oxidation precipitator, and the hydraulic retention time was ≥1.5 h. The residual elemental iodine was precipitated in the precipitator to form secondary iodine mud, and a mud discharge port was arranged at the bottom of the precipitator. The secondary iodine mud was periodically discharged to the iodine mud storage tank and combined with the primary iodine mud. The supernatant after the secondary oxidation and precipitation was returned to the evaporation system through a pipeline to participate in the evaporation crystallization process again, realizing resource recycling.

[0038] The implementation process of the iodine product treatment and filtrate recycling unit is as follows. The core equipment of the iodine product treatment unit is a clear flow type plate and frame filter press, and the filter cloth is selected to be 750D polypropylene reinforced. After the primary iodine mud and the secondary iodine mud in the iodine mud storage tank are mixed, they are transported to the plate and frame filter press through a filter press feed pump. The operating pressure is set to be 0.6-0.8 MPa, and the pressing time is 30 minutes. During the filter pressing process, the filtrate seeps out through the filter cloth, and the filter cake is gradually formed in the filter chamber. The thickness is controlled to be 25 mm, and the moisture content of the dewatered filter cake is ≤35%, that is, the iodine content of the filter cake is >85%. The filter cake is taken out from the filter press by manual or mechanical means and is packaged and stored.

[0039] The filtrate recycling system includes a pH adjusting tank, a recycling water tank, and a metering pump. The filtrate of the plate and frame filter press is transported to the pH adjusting tank through a pipeline, and the pH is adjusted to neutral before entering the recycling water tank. The washing water collected from the centrifuge is also transported to the recycling water tank. The volume of the recycling water tank is 5 m³, and the recycling water is transported to the oxidant preparation tank through a metering pump (accuracy ±1%) to be used for preparing the oxidant solution. The utilization rate of the recycling water is ≥85%, the wastewater discharge amount is controlled to be ≤0.5 m³ / h, and the waste of water resources and environmental pollution are reduced.

[0040] In summary, the process of efficiently recovering iodine from the evaporation mother liquor is realized through the collaborative operation of the seven units of raw material pretreatment, gradient cooling crystallization, solid-liquid separation, primary oxidation and precipitation, secondary oxidation and precipitation, iodine product treatment, and filtrate recycling. The parameters of the equipment in each unit are reasonably set, and the operation process is stable and controllable. The online monitoring and automatic adjustment of the key parameters such as pH, ORP, and temperature are realized through the DCS system, which ensures the salt crystallization and separation effect and the iodine ion oxidation and precipitation efficiency. The iodine content of the final crude iodine product is >85%. The secondary supernatant and the separated salts are returned to the evaporation system, and the filtrate is recycled through the recycling system. The entire process meets the technical requirements of industrial waste liquid resource utilization.

[0041] Example 2

[0042] As shown in Figure 2 and Figure 3 The present embodiment discloses a process for multi-stage oxidation recovery of iodine from various iodine-rich evaporation mother liquor and other iodine-rich waste liquid. For the evaporation system potassium chloride centrifugal mother liquor containing 187 g / L of sodium chloride, 145 g / L of potassium chloride, and 2 g / L of iodine, an integrated process of "gradient cooling crystallization desalination + two-stage oxidation precipitation iodine extraction" is adopted. The salt crystallization separation is achieved by cooling to 20°C through the series connection of a pre-cooler and a cooler. The desalination clear liquid is adjusted to pH 2.0 by hydrochloric acid, and then subjected to one-stage and two-stage oxidation precipitation by 30% hydrogen peroxide in sequence. The two-stage iodine mud is combined and subjected to dewatering treatment by a plate and frame filter press, and finally the crude iodine product with iodine content > 85% is obtained. The two-stage supernatant and separated salts are returned to the evaporation system, and the filtrate is recycled by a recycling system.

[0043] The implementation process of the raw material pretreatment unit operation is as follows: The raw material used in the present embodiment is the potassium chloride centrifugal mother liquor from the evaporation system, which is the centrifugal mother liquor produced by the 15 m³ / h evaporation crystallization system of Tangshan Zinc Technology Co., Ltd. The composition of the centrifugal mother liquor is stable, i.e., 187 g / L of sodium chloride, 145 g / L of potassium chloride, and 2 g / L of iodine. The treatment capacity is 2 m³ / h, and the continuous 24-hour operation mode is adopted, with an annual cumulative working time of 330 days.

[0044] The core equipment of the raw material pretreatment unit is the mother liquor tank, which has a design volume of 10 m³. The tank body is made of 2205 duplex stainless steel, and is internally configured with a 45° folding paddle stirrer with a stirring power of 1.5 kw. During operation, the potassium chloride centrifugal mother liquor discharged from the evaporation system flows into the mother liquor tank through a DN100 pipeline, and the stirrer is started to continuously stir at a speed of 25 rpm, so as to ensure that the components in the mother liquor are uniformly mixed and the local concentration of iodine ions or salts is avoided. An online liquid level meter (measurement range 0-6 m, output 4-20 mA signal) is installed at the top of the mother liquor tank, and forms interlocking control with the pneumatic valve on the feed pipeline: when the liquid level rises to 8 m³ (80% of the volume), the liquid level meter sends a signal to the DCS system, and the feed valve is closed; when the liquid level drops to 2 m³ (20% of the volume), the DCS system instructs the feed valve to open, so as to maintain the stability of the liquid level in the mother liquor tank. A DN50 blowdown valve is provided at the bottom of the mother liquor tank, which is regularly opened for 10 minutes every Monday morning to remove a small amount of mechanical impurities deposited at the bottom of the tank, and the blowdown liquid is collected in a waste liquid temporary storage tank for unified treatment.

[0045] The implementation process of the gradient cooling crystallization unit operation is as follows: The gradient cooling crystallization unit is composed of a pre-cooler, a cooler, a cooling crystallizer, and a supporting circulating water system and a two-stage compression chiller set. The devices are connected in series through pipelines to form a continuous cooling process.

[0046] The pre-cooler uses a tube-shell heat exchanger, the shell material is 316L stainless steel, the tube material is TA2 titanium alloy, and the heat exchange area is 35 m². The circulating water system provides water at a stable pressure of 0.3 MPa, and the inlet water temperature is controlled at 28-32°C. The circulating cooling water flows through the shell, and the mother liquor is lifted to the tube by a mother liquor pump (fluoroplastic centrifugal pump, parameters Q=15 m³ / h, H=32 m, N=4 kw) to realize preliminary cooling through indirect heat exchange between the tube and shell. The DCS system controls the outlet mother liquor temperature of the pre-cooler at 32°C±1°C by adjusting the circulating water inlet valve opening, and the heat exchanged circulating water returns to the cooling tower (treatment capacity 400 m³ / h, N=15 kw) for cooling and recycling.

[0047] The cooler is a forced circulation heat exchanger, the circulation capacity is set to 110 m³ / h, the tube material is TA2 titanium alloy, the heat exchange area is 45 m², and the coolant is -5°C ethylene glycol refrigerant provided by a two-stage compression refrigeration unit. The pre-cooled mother liquor enters the tube of the cooler and exchanges heat with the forced circulation ethylene glycol refrigerant in the shell. The refrigeration capacity of the refrigeration unit is 300 kW, and the refrigerant flow (50-80 m³ / h) is adjusted by the DCS system to ensure that the temperature of the mother liquor after passing through the cooler is accurately reduced to 20°C±0.5°C. A temperature sensor (measurement range 0-50°C, accuracy ±0.1°C) is installed on the outlet pipeline of the cooler to monitor the temperature of the mother liquor in real time, and automatically adjust the refrigerant valve opening when the temperature deviates from the set value.

[0048] The cooled mother liquor enters the cooling crystallizer, which is a vertical agitated tank with a jacket. The tank volume is 15 m³, the material is 2205 duplex stainless steel, and -2°C ethylene glycol refrigerant (flow rate 60 m³ / h) is circulated in the jacket to maintain a low temperature environment. The agitator in the tank is a double-layer inclined blade paddle with a paddle diameter of 1.2 m (tank diameter of 2.5 m, paddle diameter to tank diameter ratio of 0.48), and the rotation speed is set to 30 rpm. The temperature field of the mother liquor is uniform through stirring, promoting the orderly growth of salt crystals. The residence time of the mother liquor in the crystallizer is controlled to be 3 hours by adjusting the feed flow rate. During this process, potassium chloride and sodium chloride precipitate due to the decrease in solubility with temperature, forming crystal particles. The crystal particle size is monitored by an online particle size analyzer to ensure that it is controlled within the range of 0.3-0.4 mm. If the particle size is too small, the stirring speed is appropriately reduced to 25 rpm; if the particle size is too large, the stirring speed is increased to 35 rpm. An overflow port (height 1.8 m) is provided at the top of the crystallizer, and the supernatant enters the buffer tank through the overflow pipe; a DN150 discharge port is provided at the bottom, and the solid-containing mother liquor (solid content about 15%) is discharged to the solid-liquid separation unit at regular intervals.

[0049] The operation process of the solid-liquid separation unit is as follows: The solid-liquid separation unit is composed of a centrifuge and a primary clear liquid tank, which is responsible for separating the salt crystals after crystallization and the desalted clear liquid.

[0050] The solid-containing mother liquor discharged from the bottom of the cooling crystallizer is transported to a centrifuge (model HR-400N, power 18.5kw, screen mesh material 2205 duplex stainless steel) through a DN150 pipeline. The centrifuge is set to operate at a speed of 1600rpm to centrifugally separate the solid-containing mother liquor. During the separation process, the crystals are intercepted inside the screen mesh under the action of centrifugal force to form a filter cake, which is scraped off by a scraper to a screw conveyor (conveying capacity 30m³ / h, N=11kw, material carbon steel lined with plastic) and then transported to a salt recovery bin and finally returned to the evaporation system to participate in crystallization again; the centrifugal mother liquor is discharged through the centrifuge filtrate port and combined with the supernatant overflowing from the top of the cooling crystallizer to enter a primary supernatant tank.

[0051] The primary supernatant tank has a volume of 12m³ and is made of 316L stainless steel. An agitator (speed 15rpm, N=2.2kw) is installed in the tank to prevent trace crystals in the supernatant from settling. A liquid level sensor is installed on the top of the tank and connected to a bottom supernatant pump (Q=10m³ / h, H=25m, N=3kw) to form an interlock: when the liquid level is ≥8m³, the supernatant pump is automatically started; when the liquid level is ≤3m³, the supernatant pump is stopped. An online densimeter (measurement range 1.1-1.3g / cm³) is installed on the outlet pipeline of the tank to monitor the density of the supernatant in real time, so as to ensure that the concentration of sodium chloride in the desalted supernatant is ≤50g / L and the concentration of potassium chloride is ≤40g / L. If the density exceeds the standard, the flow of the refrigerant in the cooling crystallizer is increased to strengthen the crystallization of salts.

[0052] The implementation process of the operation of the primary oxidation precipitation unit is as follows: The primary oxidation precipitation unit includes a settling tank, a hydrochloric acid dosing system and a hydrogen peroxide dosing system. The preliminary oxidation precipitation of iodine ions is achieved by adjusting the pH and adding oxidants.

[0053] The desalted supernatant in the primary supernatant tank is transported to the settling tank (diameter 3.5m, effective water depth 4m, material 316L stainless steel) by a supernatant pump. First, the hydrochloric acid dosing system is started to adjust the pH value. The hydrochloric acid storage tank has a volume of 30m³ and is made of PE. It stores industrial hydrochloric acid with a mass concentration of 31%. A diaphragm metering pump (flow range 0-50L / h, accuracy ±1%) is used to add hydrochloric acid to the static mixer of the inlet pipeline of the settling tank. After being fully mixed with the supernatant, the mixture enters the settling tank. The DCS system automatically adjusts the frequency of the metering pump according to the real-time data of the online pH monitor (measurement range 0-14, accuracy ±0.01pH) to stably control the pH of the liquid in the settling tank at 2.0±0.05.

[0054] After the pH adjustment is completed, the oxidant dosing system is started. In this embodiment, 30% hydrogen peroxide is selected as the oxidant, the hydrogen peroxide storage tank has a volume of 30 m³ and is made of PE, a breather valve and a liquid level interlocking device (low liquid level alarm value 5 m³) are installed on the top of the tank. The dosage of hydrogen peroxide in the first oxidation stage is calculated as 1.05 times the molar amount of iodine: according to the mother liquor treatment capacity of 2 m³ / h and the iodine content of 2 g / L, the iodine mass per hour is 4000 g (molar amount 31.75 mol), and the theoretical dosage of hydrogen peroxide is 31.75 x 1.05 x 34 / 0.3 = 39.2 L / h (30% hydrogen peroxide density 1.11 g / cm³, molecular weight 34). The hydrogen peroxide is dosed into the stirring zone in the settling tank through a diaphragm metering pump (flow range 0-100 L / h, accuracy ±1%), and the agitator (speed 10 rpm, paddle diameter 1.5 m) in the tank ensures uniform mixing of the oxidant and the supernatant. The DCS system controls the ORP value of the reaction system to be stable at +500 mV ± 20 mV through an ORP online monitor (measurement range -500~+800 mV, accuracy ±5 mV), and the reaction time is set to 45 minutes.

[0055] The surface load of the settling tank is controlled at 0.6 m³ / (m²·h), the gravity settling time is 1.5 hours, and the elemental iodine precipitate gradually settles to the bottom of the tank under gravity to form the first iodine mud. A conical hopper (cone angle 60°) is provided at the bottom of the settling tank, and when the thickness of the iodine mud reaches 0.5 m (monitored by an ultrasonic level meter), the bottom mud discharge valve (DN100) is opened to discharge the first iodine mud into the iodine mud temporary storage tank (volume 5 m³ with stirring). The supernatant is discharged from the top overflow weir of the settling tank and enters the secondary oxidation and precipitation unit.

[0056] The implementation process of the secondary oxidation and precipitation unit is as follows: The secondary oxidation and precipitation unit is composed of a secondary oxidation tank and a precipitator, and is used for deep recovery of residual iodine ions after the first oxidation.

[0057] The supernatant after the first oxidation and precipitation is transported to the secondary oxidation tank through a DN100 pipeline, and the agitator (speed 15 rpm, paddle diameter 1.2 m) in the tank continuously stirs to ensure uniform mixing of the liquid. 30% hydrogen peroxide is still used as the oxidant in the secondary oxidation stage, and the dosage is 0.25 times the initial molar amount of iodine, i.e. 31.75 x 0.25 x 34 / 0.3 = 9.3 L / h per hour, which is accurately dosed into the oxidation tank through a diaphragm metering pump (parameters same as the first stage). The DCS system controls the ORP value of the reaction system to be maintained at +520 mV ± 20 mV, and the reaction time is 40 minutes, to ensure that the residual iodine ions are fully oxidized to elemental iodine.

[0058] The mixed solution after the reaction is fed into a precipitator, the upward flow rate is controlled at 0.8 mm / s, and the hydraulic retention time is 90 minutes. The residual elemental iodine particles are gathered into larger flocs in the inclined pipe, slide down the inclined pipe to the bottom hopper to form secondary iodine mud. The bottom hopper of the precipitator is provided with a pneumatic sludge discharge valve, which is opened twice a day (9 am and 5 pm) for 10 minutes each time to discharge the secondary iodine mud into the iodine mud temporary storage tank to be combined with the primary iodine mud. The supernatant after secondary precipitation is collected through an overflow tank and returned to the feed tank of the evaporation system through a pipeline to participate in the salt evaporation crystallization process again.

[0059] The implementation process of the iodine product treatment and filtrate recycling unit is as follows: The core equipment of the iodine product treatment unit is a clear-flow type plate-and-frame filter press, which is used for dewatering treatment of the combined iodine mud to obtain a crude iodine product.

[0060] The mixed solution of the primary and secondary iodine mud (solid content of about 20%) in the iodine mud temporary storage tank is delivered to the plate-and-frame filter press (filter cloth is 750D polypropylene reinforced) through a filter pressing feed pump. The filter pressing process is divided into three steps: first step, low-pressure feeding, operating pressure is 0.3 MPa, lasting for 10 minutes, so that the iodine mud is uniformly distributed in the filter chamber; second step, pressure squeezing, pressure is raised to 0.7 MPa, lasting for 30 minutes, to deeply remove water; third step, pressure holding and unloading, the pressure is maintained at 0.7 MPa for 5 minutes and then slowly unloaded. The thickness of the dewatered filter cake is controlled at 35 mm ± 2 mm, which is detected by an online water content detector to ensure that the water content is ≤35%. After the filter pressing is completed, the filter cake (i.e. the crude iodine product) is manually unloaded to a tray through the opening of the plate-and-frame, and after the iodine content is detected to be >85%, it is packed into a ton bag for storage and sale.

[0061] The filtrate recycling system is composed of a pH adjusting tank, a recycled water tank and a metering pump. The filtrate (COD ≤500 mg / L) of the plate-and-frame filter press is fed into the pH adjusting tank (volume 5 m³, with stirring) through a pipeline, sodium hydroxide solution with a mass concentration of 10% is added to adjust the pH to 6-7, and then pumped into the recycled water tank (volume 10 m³). The washing water (daily consumption about 5 m³) of the centrifuge is also delivered to the recycled water tank, and the recycled water is delivered to the oxidizing agent preparation tank through the metering pump (Q=8 m³ / h, H=30 m, N=2.2 kw) for diluting 30% hydrogen peroxide to the required concentration. The utilization rate of the recycled water is stably controlled at 88%, the wastewater discharge amount is controlled at 0.4 m³ / h, and after reaching the standard, it is discharged into the plant area wastewater treatment station.

[0062] In summary, the embodiment realizes efficient recovery of low-concentration iodine in evaporation mother liquor through continuous operation of seven units of raw material pretreatment, gradient cooling crystallization, solid-liquid separation, primary oxidation precipitation, secondary oxidation precipitation, iodine product treatment, and filtrate recycling. The parameters of each unit device are reasonably matched, and the online monitoring and automatic control of key parameters such as pH, ORP, temperature, and liquid level are realized through the DCS system, ensuring sufficient salt crystallization separation and complete oxidation of iodine ions. The 30% hydrogen peroxide is used as the oxidizing agent, and the two-stage oxidation precipitation is completed under the conditions of pH = 2.0 and ORP + 450 mV ~ + 550 mV. The iodine content of the obtained crude iodine product is > 85%, the secondary supernatant and salt crystals are returned to the evaporation system to realize resource recycling, the filtrate recycling rate is more than 85%, the entire process is continuous and stable, and meets the requirements of industrial production.

[0063] Example 3

[0064] As Figure 1 shown, the embodiment provides a process method for multi-stage oxidation recovery of iodine from various iodine-rich evaporation mother liquor and other iodine-rich waste liquid. The specific steps of the working process during operation are as follows: 1. Raw material pretreatment The potassium chloride centrifugal mother liquor (containing NaCl 187 g / L, KCl 145 g / L, and I⁻ 2 g / L) discharged from the evaporation system is self-flowed into the mother liquor tank and is homogenized by the stirrer (20-40 rpm). The liquid level is interlocked controlled by the DCS system (high position stops feeding, low position starts feeding).

[0065] 2. Gradient cooling crystallization The mother liquor is lifted by the pump and sequentially passes through: Pre-cooler: The circulating cooling water (≤ 32℃) is preliminarily cooled to 30-35℃. Cooler: The ethylene glycol freezing liquid (-5℃) is forced to circulate to be cooled to 20℃. After cooling, the mother liquor enters the cooling crystallizer (-3~0℃ jacket cooling) and stays for 2-4 hours to precipitate NaCl / KCl crystals (particle size 0.2-0.5 mm).

[0066] 3. Solid-liquid separation The solid-containing mother liquor at the bottom of the crystallizer is separated by the centrifugal machine, and the solid (salt crystal) is returned to the evaporation system. The centrifugal liquid is combined with the supernatant at the top of the crystallizer and enters the primary supernatant tank.

[0067] 4. Primary oxidation precipitation The supernatant is pumped into the settling tank and is adjusted to pH = 2.0 by adding hydrochloric acid. The oxidizing agent (sodium chlorate or hydrogen peroxide, 1.05 times of iodine molar amount) is added, the ORP control is +450~550 mV, and the reaction is performed for 30-60 min. Gravitational sedimentation ≥ 1 hour, the first grade iodine mud and supernatant were separated.

[0068] 5. Secondary oxidation precipitation The first grade supernatant was pumped into the secondary oxidation tank, and the oxidant was added again (0.25 times of iodine molar amount), and the ORP control was +450~550mV. The reaction liquid entered the precipitator (upflow velocity ≤2.0mm / s), and the hydraulic retention was ≤45min. The secondary iodine mud was separated, and the secondary supernatant was returned to the evaporation system.

[0069] 6. Iodine product processing The first grade and secondary iodine muds were combined and sent to the plate and frame filter press: The operating pressure was 0.6-0.8MPa, and the squeezing time was 30min. The filter cake (water content ≤35%, iodine content >85%) was output as a crude iodine product.

[0070] 7. Filtrate recycling The filter press filtrate and centrifugal rinse water were collected into the recycling water tank. The recycling water was transported to the oxidant preparation tank after pH adjustment, and the utilization rate was ≥85%. The wastewater discharge amount was ≤0.5m³ / h.

[0071] The above is only a preferred embodiment of the present application, and does not limit the present application in any form. Although the present application has been disclosed as above, it is not intended to limit the present application. Any person skilled in the art can make some changes or modifications to the above disclosed technical content without departing from the scope of the technical solution of the present application, and any brief introduction, modification, equivalent change and modification of the above embodiments according to the technical essence of the present application are still within the scope of the technical solution of the present application.

Claims

1. A process for the multistage oxidative recovery of iodine from various iodine-rich evaporation mother liquors and other iodine-rich waste streams, characterized in that, The method comprises the following steps: S100, raw material pretreatment: the potassium chloride centrifugal mother liquor of the evaporation system is input into a mother liquor tank, the mother liquor containing 187 g / L of sodium chloride, 145 g / L of potassium chloride and 2 g / L of iodine; S200, gradient cooling crystallization: the mother liquor is lifted by a pump and sequentially passes through a pre-cooler and a cooler, the pre-cooler is preliminarily cooled by circulating cooling water, the cooler is forcedly cooled to 20 DEG C by glycol refrigerant, and after cooling, the mother liquor enters a cooling crystallizer to precipitate potassium chloride and sodium chloride crystals; S300, solid-liquid separation: the solid-containing mother liquor at the bottom of the cooling crystallizer is separated by a centrifugal machine, the separated solid is returned to the evaporation system, and the separated liquid is combined with the clear liquid at the upper part of the cooling crystallizer and then enters a primary clear liquid tank; S400, primary oxidation precipitation: hydrochloric acid is added into the primary clear liquid tank to adjust the pH value to 2.0, then an oxidizing agent is added to perform an iodine ion oxidation reaction, and after the reaction is completed, solid-liquid separation is performed to obtain primary iodine mud and primary supernatant; S500, secondary oxidation precipitation: the primary supernatant is input into a secondary oxidation tank, an oxidizing agent is added again to perform a secondary oxidation reaction, and after the reaction is completed, solid-liquid separation is performed to obtain secondary iodine mud and secondary supernatant, and the secondary supernatant is returned to the evaporation system; S600, iodine product treatment: the primary iodine mud and the secondary iodine mud are combined and dehydrated to obtain a crude iodine product with an iodine content of > 85%, the pre-cooler and the cooler in the step S200 are connected in series, a stirring device is arranged in the cooling crystallizer, the oxidizing agent in the steps S400 and S500 is hydrogen peroxide, the oxidation reaction time is controlled to be 30-60 minutes, and the dehydration in the step S600 is performed by using a plate-frame filter press.

2. A process for the multistage oxidative recovery of iodine from various iodine-rich evaporation mother liquors and other iodine-rich waste streams according to claim 1, characterized in that, In the gradient cooling crystallization process, the pre-cooler is supplied with water by a circulating cooling water system, the inlet water temperature is ≤ 32 DEG C, and the outlet temperature is controlled to be 30-35 DEG C, the cooler is connected with a double-stage compression refrigerator set to provide -5 DEG C glycol refrigerant, and the pipe material is TA2 titanium alloy.

3. A process for the multistage oxidative recovery of iodine from various iodine-rich evaporation mother liquors and other iodine-rich waste streams according to claim 1, characterized in that, The cooling crystallizer is a stirred tank with a jacket, the tank volume is 15 m³, the material is 2205 duplex stainless steel, -3 DEG C to 0 DEG C glycol refrigerant is introduced into the jacket, the stirrer is a double-layer inclined-blade paddle, the paddle diameter to tank diameter ratio is 0.4-0.5, the rotating speed is 20-40 rpm, the crystallization residence time is 2-4 hours, and the crystal size is controlled to be 0.2-0.5 mm.

4. A process for the multistage oxidative recovery of iodine from various iodine-rich evaporation mother liquors and other iodine-rich waste streams according to claim 1, characterized in that, The oxidizing agent is a sodium chlorate solution with a mass concentration of 10% or 30% hydrogen peroxide, the oxidizing agent addition amount in the primary oxidation stage is 1.05 times the molar amount of iodine, the addition amount in the secondary oxidation stage is 0.25 times, the oxidation reaction is performed under the control of a DCS system, the ORP value is set to be +450 mV to +550 mV, and the reaction time is 30-60 minutes.

5. A process for the multistage oxidative recovery of iodine from various iodine-rich evaporation mother liquors and other iodine-rich waste streams according to claim 1, characterized in that, The primary oxidation precipitation is performed in a settling tank, the surface load is ≤ 0.8 m³ / (m²·h), and the gravity settling time is ≥ 1 hour, and the secondary oxidation precipitation is performed in a precipitator, the hydraulic residence time is ≥ 1.5 hours.

6. A process for the multistage oxidative recovery of iodine from various iodine-rich evaporation mother liquors and other iodine-rich waste streams according to claim 1, characterized in that, The dehydration treatment adopts a clear-flow plate-frame filter press, the filter cloth is 750D polypropylene reinforced type, the operating pressure is 0.6-0.8 MPa, the pressing time is 30 minutes, the filter cake thickness is 25 mm, and the moisture content is ≤ 35%.

7. A process for the multistage oxidative recovery of iodine from various iodine-rich evaporation mother liquors and other iodine-rich waste streams according to claim 1, characterized in that, The filtrate recycling system comprises: The filtrate pipeline of the plate-and-frame filter is connected with a pH adjusting tank. The flushing water of the centrifuge is collected into a reuse water tank. The reuse water utilization rate of the reuse water tank connected with the oxidant preparation tank through a metering pump is ≥85%, and the wastewater discharge is ≤0.5 m³ / h.

8. A system for the multistage oxidative recovery of iodine from various iodine-rich evaporation mother liquors and other iodine-rich waste streams, suitable for use in a process according to any one of claims 1 to 7, characterized in that It comprises: The material processing unit: the mother liquor tank has a volume of 10 m³ and is provided with a 45° folding paddle agitator, the pre-cooler is a tube-shell heat exchanger with a shell material of 316L, and the cooler is a forced circulation heat exchanger with a circulation amount ≥100 m³ / h; The energy unit: an ethylene glycol refrigeration unit is provided with a double-screw compressor, the refrigerant is R134a, and the circulating water system supplies water at a pressure of 0.3 MPa; The oxidation control unit: the hydrochloric acid storage tank has a volume of 30 m³ and is made of PE, the oxidant storage tank has a volume of 30 m³ and is provided with a liquid level interlock, the oxidant is added by using a diaphragm metering pump with an accuracy of ±1%, and The DCS system: contains a PH / ORP online monitor, a temperature sensor, and communicates with the central control room through a ModbusTCP protocol.

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