A method and system for recycling a cobalt oxide waste liquid mother liquor

Abstract

This invention relates to the field of industrial wastewater treatment technology, and particularly to a method and system for the resource-based treatment of cobalt tetroxide waste mother liquor. The method includes: sequentially subjecting the mother liquor to advanced oxidation, carbonate removal, coagulation sedimentation, ceramic membrane filtration, nanofiltration for salt separation, concentration and volume reduction, and evaporation crystallization; sequentially subjecting the wash water to ceramic membrane filtration and reverse osmosis concentration; incorporating the reverse osmosis concentrate into the mother liquor nanofiltration for salt separation; simultaneously collecting multidimensional data from the nanofiltration membrane module to construct an impurity accumulation index, a salt purity index, and a membrane fouling index; determining the real-time operating status of the nanofiltration and evaporation systems; predicting the remaining healthy operating time and impurity removal time of the nanofiltration membrane; and implementing a graded control strategy and dynamically adjusting the impurity removal threshold. This invention achieves synergistic treatment and intelligent closed-loop control of waste liquid and wash water, maximizing water resource and ammonium salt recovery rates while ensuring the purity of ammonium chloride products.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, and in particular to a method for the resource-based treatment of cobalt tetroxide waste mother liquor. Background Technology

[0002] In existing technologies, the treatment of mother liquor and wash water from cobalt tetroxide waste liquid is typically operated as two independent process lines. The mother liquor line uses a combination of advanced oxidation, coagulation sedimentation, membrane separation, and evaporation crystallization to recover ammonium chloride, while the wash water line partially reuses the waste water after simple filtration and reverse osmosis desalination. However, the two lines exhibit significant mutual interference in actual operation.

[0003] Because the reverse osmosis concentrate used for washing water contains residual ammonium salts and trace amounts of heavy metals, when it is directly returned to the nanofiltration unit of the mother liquor line, fluctuations in its water quality can alter the composition of the nanofiltration feed water, leading to decreased salt purity and accelerated membrane fouling. Current technologies do not provide for water quality prediction or adaptive control of this backflow. On the other hand, when the concentrated permeate from the mother liquor line's evaporation and crystallization is replenished to the washing water line, if impurities accumulate in the mother liquor evaporation system or there are operational fluctuations, trace impurities carried in the replenished permeate will accumulate on the surface of the reverse osmosis membrane in the washing water, causing fouling of the washing water membrane system and deterioration of the product water quality. However, current technologies lack real-time monitoring and coordinated intervention methods for the interaction between the two lines. Furthermore, the two lines each use offline detection methods with fixed thresholds, failing to perceive the differentiation trend of the nanofiltration membrane's separation behavior along the process and the dynamic accumulation process of impurities in the evaporation mother liquor. This results in poor salt separation stability, membrane cleaning cycles relying on experience, and a disconnect between impurity removal strategies and product purity, ultimately limiting the overall resource recovery rate and system operational reliability. Summary of the Invention

[0004] Therefore, the present invention provides a resource-based treatment method for cobalt tetroxide waste liquid mother liquor, which overcomes the problems in the prior art where the purity of nanofiltration desalination along the process and the accumulation trend of evaporation impurities are not synergistically quantified, resulting in fluctuations in desalination quality, sluggish membrane fouling response, and the inability to dynamically match the impurity discharge decision with fluctuations in incoming water quality.

[0005] To achieve the above objectives, on the one hand, the present invention provides a resource-based treatment method for cobalt tetroxide waste mother liquor, the method comprising: sequentially subjecting the mother liquor to advanced oxidation, decarbonate removal, coagulation sedimentation, ceramic membrane filtration, nanofiltration desalination, concentration and volume reduction and evaporation crystallization treatment, and sequentially subjecting the wash water to ceramic membrane filtration and reverse osmosis concentration treatment, and incorporating the reverse osmosis concentrate of the wash water into the mother liquor nanofiltration desalination process;

[0006] The method also includes the coordinated monitoring and control of the nanofiltration salt separation process and the evaporation crystallization process, including:

[0007] Acquire pressure gradient distribution data and conductivity gradient distribution data along the water flow direction of the nanofiltration membrane module, and collect acoustic characteristic data of the membrane surface particles;

[0008] Real-time acquisition of physical information of the mother liquor from evaporation is used to determine the concentration of ammonium chloride.

[0009] The impurity accumulation index is determined based on the concentration of each impurity ion and the concentration of ammonium chloride; the salt purity index is determined based on the pressure gradient distribution data and the conductivity gradient distribution data; and the membrane fouling index is determined based on the acoustic characteristic data.

[0010] The operating status of the nanofiltration system is determined based on the salt purity index and membrane fouling index, and the operating status of the evaporation system is determined based on the impurity accumulation index of the mother liquor.

[0011] Based on the changing trends of the salt purity index, membrane fouling index, and evaporation mother liquor impurity accumulation index, the remaining healthy operating time of the nanofiltration membrane and the remaining impurity removal time of the evaporation system are predicted respectively.

[0012] The corresponding collaborative processing strategy is executed according to the operating status of the evaporation system and the nanofiltration system, and the impurity removal threshold is dynamically adjusted according to the adjusted ammonium chloride product purity data.

[0013] As a preferred technical solution for the resource-based treatment of cobalt tetroxide waste mother liquor, the collection of the pressure differential gradient distribution data and conductivity gradient distribution data includes:

[0014] Select the inlet section, middle section, and outlet section of the nanofiltration membrane module;

[0015] Obtain the product water side pressure and concentrate side pressure at each cross section, calculate the transmembrane pressure difference value at the corresponding cross section, and form pressure difference gradient distribution data along the water flow direction;

[0016] Obtain the concentrate-side conductivity and product-side conductivity of each cross section, and form conductivity gradient distribution data along the water flow direction.

[0017] A preferred technical solution for the resource-based treatment of cobalt tetroxide waste mother liquor includes the following process for determining the ammonium chloride concentration:

[0018] The concentration of ammonium chloride in the evaporating mother liquor was calculated using the ion charge balance method based on the concentrations of chloride ions, sodium ions, and sulfate ions.

[0019] Alternatively, the concentration of ammonium chloride in the mother liquor can be calculated using multiple parameters, based on the density, conductivity, and temperature of the mother liquor.

[0020] The physical information of the mother liquor includes density, conductivity, temperature, and concentration data of various impurity ions, including sulfate ions, sodium ions, and chloride ions.

[0021] A preferred technical solution for the resource-based treatment of cobalt tetroxide waste mother liquor includes the following process for determining the impurity accumulation index, salt purity index, and membrane fouling index:

[0022] The relative concentration of each impurity ion is obtained by calculating the ratio of the concentration of each impurity ion to the concentration of ammonium chloride. The weighted sum of the relative concentrations of each impurity ion is then used to obtain the initial impurity accumulation index.

[0023] The initial impurity accumulation index within a preset time window is discretized using the sliding window standard deviation discretization method to obtain the impurity accumulation index.

[0024] The relative pressure difference of the corresponding section is obtained by calculating the ratio of the transmembrane pressure difference of each section to the transmembrane pressure difference of the inlet section. The relative retention rate of the corresponding section is obtained by calculating the ratio of the conductivity retention rate of each section to the average conductivity retention rate of the section.

[0025] The spatial variation coefficient of the product of the relative pressure difference and the relative retention rate at each cross section is denoted as the salt purity index.

[0026] Determine the rate of change of each acoustic emission energy value along the water flow direction and take the maximum rate of change as the initial membrane fouling index;

[0027] The linear regression slope of the continuous membrane fouling index within a preset time window is calculated using the trend slope discretization method, and the membrane fouling index is determined based on the sign and absolute value of the slope.

[0028] A preferred technical solution for the resource-based treatment of cobalt tetroxide waste mother liquor includes determining the operating status of the nanofiltration system based on the salt purity index and the membrane fouling index, comprising:

[0029] In response to the membrane fouling index being within the membrane fouling reference range and the salt purity index exceeding the salt purity reference range, the nanofiltration system is determined to be in a salt separation deviation state.

[0030] In response to the membrane fouling index exceeding the membrane fouling benchmark range, the nanofiltration system is determined to be in a membrane fouling development state.

[0031] The nanofiltration system's operating status includes a normal state and an abnormal state, and the abnormal state includes salt separation deviation and membrane fouling development.

[0032] A preferred technical solution for the resource-based treatment of cobalt tetroxide waste mother liquor includes determining the operating status of the evaporation system based on the impurity accumulation index of the evaporation mother liquor, including:

[0033] When the impurity accumulation index exceeds the preset impurity accumulation benchmark range, the evaporation system is determined to be in an impurity over-limit state.

[0034] The operating status of the evaporation system includes normal status and impurity exceeding the limit status.

[0035] A preferred technical solution for the resource-based treatment of cobalt tetroxide waste mother liquor includes a process for predicting the remaining healthy operating time of the nanofiltration membrane and the remaining time of impurity removal from the evaporation system based on the changing trends of the salt purity index, membrane fouling index, and evaporation mother liquor impurity accumulation index.

[0036] Linear fitting was performed on the salt purity index sequence and membrane fouling index sequence within the preset historical time window to obtain the slope of salt purity change and the slope of membrane fouling change.

[0037] Determine the ratio of the slope of change in salt purity to the upper limit of the salt purity reference range and the ratio of the slope of change in membrane fouling to the upper limit of the membrane fouling reference range. The relatively larger value between the purity slope ratio and the fouling slope ratio is determined as the remaining healthy operating time of the nanofiltration membrane.

[0038] Linear fitting is performed on the impurity accumulation index sequence within a preset historical time window to obtain the impurity accumulation change slope. The remaining time for impurity removal from the evaporation system is determined based on the ratio of the impurity accumulation change slope to the upper limit of the preset impurity accumulation benchmark range.

[0039] The length of the preset historical time window is determined by the product of the hydraulic residence time of the nanofiltration system and the sampling period.

[0040] A preferred technical solution for the resource-based treatment of cobalt tetroxide waste mother liquor includes the following step: Executing a corresponding synergistic treatment strategy based on the operating status of the evaporation system and the nanofiltration system.

[0041] In response to the nanofiltration system operating in a normal state, a collaborative treatment strategy is formulated based on the evaporation system operating state, including:

[0042] Based on the determination that the evaporation system is in normal operating condition, the current operating parameters of the nanofiltration salt separation step and the evaporation crystallization step are maintained, and all the mother liquor is returned to the concentration and reduction step for recycling.

[0043] Based on the determination that the evaporation system is in a state of excessive impurities, part of the evaporated mother liquor will be discharged and recycled back to the nanofiltration desalination step for reprocessing, while keeping the operating parameters of the nanofiltration desalination step unchanged.

[0044] In response to an abnormal operating state of the nanofiltration system, a collaborative treatment strategy is formulated based on the operating state of the evaporation system, including:

[0045] Based on the determination that the evaporation system is in normal operating condition, the collaborative treatment strategy is to perform graded control operations on the nanofiltration desalination step. The graded control operations include adjusting the nanofiltration influent flow rate distribution or reducing the nanofiltration recovery rate.

[0046] Based on the determination that the evaporation system is in a state of excessive impurities, the graded control operation of the nanofiltration salt separation step and the operation of discharging and refluxing part of the mother liquor are performed simultaneously.

[0047] A preferred technical solution for the resource-based treatment of cobalt tetroxide waste mother liquor includes dynamically adjusting the impurity removal threshold based on the adjusted ammonium chloride product purity data, including:

[0048] Obtain the purity test value of the ammonium chloride product obtained from the evaporation and crystallization step;

[0049] The purity test value is compared with the product purity target value;

[0050] When the purity test values ​​of several consecutive batches are all lower than the target value of product purity, the upper limit of the benchmark range of impurity accumulation index is reduced.

[0051] When the purity test values ​​of several consecutive batches are all higher than the sum of the product purity target value and the preset purity margin, the upper limit of the benchmark range of the impurity accumulation index is increased.

[0052] The impurity removal threshold is the upper limit of the benchmark range of the impurity accumulation index, and its adjustment step size is determined according to the deviation direction between the purity detection value and the product purity target value.

[0053] On the other hand, the present invention also provides a processing system, comprising: an advanced oxidation reactor, a carbon removal reaction tank, a coagulation sedimentation tank, a first ceramic membrane filtration device, a nanofiltration device, an electrodialysis device or a high-pressure reverse osmosis device, and an evaporation crystallizer connected in sequence; and a second ceramic membrane filtration device, a first-stage reverse osmosis device, and a second-stage reverse osmosis device connected in sequence.

[0054] The freshwater outlet of the electrodialysis device or high-pressure reverse osmosis device is connected to the inlet of the first-stage reverse osmosis device; the concentrated water outlet of the first-stage reverse osmosis device is connected to the pipeline between the product water outlet of the first ceramic membrane filtration device and the inlet of the nanofiltration device.

[0055] The processing system also includes:

[0056] The data acquisition unit is used to collect differential pressure data, conductivity data, density data, temperature data, impurity ion concentration data, and acoustic emission energy values.

[0057] The processor is used to calculate the impurity accumulation index, salt purity index, and membrane fouling index; determine the operating status of the nanofiltration system and the evaporation system; predict the remaining healthy operating time of the nanofiltration membrane and the remaining time for impurity removal from the evaporation system; and generate corresponding collaborative processing instructions.

[0058] Impurity removal threshold controller, which is used to adjust the upper limit of the impurity accumulation index reference range based on the comparison result between the purity detection value and the product purity target value;

[0059] An actuator, electrically connected to the processor, includes a flow regulating valve located at the inlet of the nanofiltration unit and a reflux valve located on the circulating mother liquor pipeline of the evaporator crystallizer. The actuator operates in response to control commands generated by the processor.

[0060] Compared with existing technologies, the advantages of this invention lie in its ability to simultaneously collect pressure gradient and conductivity gradient distribution data at multiple points along the axial direction of the nanofiltration membrane module. Combined with multi-dimensional parameters such as the density, conductivity, temperature, and impurity ion concentration of the evaporation mother liquor, an impurity accumulation index, a salt purity index, and a membrane fouling index are constructed. This enables real-time quantitative characterization and discretization trend determination of nanofiltration membrane separation behavior, membrane surface fouling trends, and the degree of impurity enrichment in the evaporation mother liquor. Based on this, the system can automatically determine the operating status of the nanofiltration and evaporation systems, predict the remaining healthy operating time of the nanofiltration membrane, and the remaining time for impurity removal in the evaporation system. According to the state combination, a graded control strategy is implemented. While ensuring the stable and compliant purity of the ammonium chloride product, the impurity removal threshold is dynamically adjusted through product purity feedback, improving the recovery rate of water and ammonium salt resources, significantly reducing the risk of membrane system fouling and evaporation crystallization energy consumption, and achieving efficient recovery of valuable resources. Attached Figure Description

[0061] Figure 1 This is a flowchart of a method for resource recovery treatment of cobalt tetroxide waste mother liquor according to an embodiment of the present invention;

[0062] Figure 2 This is a logic diagram of how the impurity removal threshold is dynamically adjusted based on the adjusted ammonium chloride product purity data in an embodiment of the present invention.

[0063] Figure 3 This is a schematic diagram of the processing system according to an embodiment of the present invention. Detailed Implementation

[0064] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely for explaining the present invention and are not intended to limit the present invention.

[0065] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0066] It should be noted that in the description of this invention, the terms "upper", "lower", "left", "right", "inner", "outer", etc., which indicate directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description and is not intended to indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0067] Furthermore, it should be noted that, in the description of this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0068] To better understand this invention, the device described below is explained:

[0069] The cobalt tetroxide waste liquid mother liquor resource utilization system described in this embodiment adopts a structure of two independently operating but deeply coupled process lines for mother liquor treatment and wash water treatment. The mother liquor treatment line consists of an advanced oxidation reactor, a carbon removal reaction tank, a coagulation sedimentation tank, a first ceramic membrane filter, a nanofiltration unit, an electrodialysis unit or a high-pressure reverse osmosis unit, and an evaporator crystallizer connected in series, used to purify the mother liquor and recover high-purity ammonium chloride products. The wash water treatment line consists of a second ceramic membrane filter, a first-stage reverse osmosis unit, and a second-stage reverse osmosis unit connected in series, used to purify the wash water and produce recycled production water. The two process lines operate through precise material flow coupling: the freshwater outlet of the electrodialysis unit or high-pressure reverse osmosis unit is connected to the inlet of the first-stage reverse osmosis unit, and the concentrate outlet of the first-stage reverse osmosis unit is connected to the pipeline between the permeate outlet of the first ceramic membrane filter and the inlet of the nanofiltration unit.

[0070] Existing systems with this coupling structure generally suffer from insufficient monitoring. They fail to coordinate and quantify the purity of nanofiltration desalination along the process and the accumulation trend of evaporation impurities. They can only collect the total influent and effluent parameters of the nanofiltration membrane module, and cannot detect local changes on the membrane surface. Furthermore, the use of a fixed threshold for impurity removal can easily lead to fluctuations in desalination quality, delayed membrane fouling response, and mismatch in impurity removal decisions.

[0071] To address the aforementioned issues, this system incorporates a multi-dimensional online monitoring system: pressure and conductivity sensors are installed on the concentrate and product water sides of the nanofiltration membrane module's inlet, middle, and outlet sections, respectively; acoustic emission sensors are installed on the corresponding outer walls of the membrane housing; and an online particle counter is installed at the concentrate outlet. A density meter, conductivity electrode, temperature sensor, and ion-selective electrode are installed in the circulating mother liquor pipeline of the evaporator crystallizer, and a purity monitoring device is installed at the product outlet.

[0072] It is understandable that the concentration and reduction steps only achieve high concentration of the solution without changing the relative ratio of ammonium chloride to impurity ions. The quality of the influent is entirely determined by the nanofiltration desalination effect. The high-impurity mother liquor generated by evaporation and crystallization is returned to the nanofiltration desalination step before the concentration and reduction steps through the impurity discharge pipeline, thus forming a direct material closed loop between nanofiltration desalination and evaporation and crystallization.

[0073] Fluctuations in nanofiltration desalination efficiency directly impact the evaporation and crystallization process, causing changes in the accumulation rate of impurities in the evaporation mother liquor. Furthermore, the amount of impurities discharged on the evaporation side directly affects the influent load and impurity composition of the nanofiltration unit, thus influencing the desalination efficiency. The concentration and reduction stage lacks independent operational status determination and control requirements; its operating parameters are entirely determined by the nanofiltration permeate flow rate and concentration. Adjusting only the evaporation side impurity discharge rate or nanofiltration side operating parameters would lead to overall system imbalance, failing to maximize resource recovery while ensuring the purity of the ammonium chloride product. Therefore, it is essential to coordinate and monitor the nanofiltration desalination and evaporation / crystallization processes, implementing corresponding treatment strategies based on the combined operating states of both.

[0074] Based on the aforementioned sensor data, an impurity accumulation index, a salt purity index, and a membrane fouling index were constructed. The impurity accumulation index was obtained by weighted summation of the ratios of each impurity ion concentration to the ammonium chloride concentration, followed by discretization using a sliding window standard deviation. The salt purity index was obtained by the spatial variation coefficient of the product of the relative pressure difference and the relative rejection rate at each cross-section. The membrane fouling index was obtained by the maximum rate of change of acoustic emission energy along the path at each cross-section, followed by discretization using the trend slope. The operating status of the nanofiltration and evaporation systems was then determined based on these indices, predicting the remaining healthy operating time of the nanofiltration membrane and the remaining time for impurity removal from the evaporation system. A graded control strategy and dynamic adjustment of the impurity removal threshold were then implemented based on the state combination, ultimately achieving intelligent collaborative treatment and resource reuse of waste liquid, mother liquor, and wash water. The collaborative monitoring and control process of the method is described in detail below.

[0075] Furthermore, after the wash water is treated by the second ceramic membrane filtration unit and the first-stage reverse osmosis unit, its concentrate is incorporated into the pipeline between the product water outlet of the first ceramic membrane filtration unit and the inlet of the nanofiltration unit. Therefore, the wash water treatment only directly affects the nanofiltration desalination process, slightly increasing the influent flow rate and treatment load of the nanofiltration unit. However, the wash water itself has a low contaminant concentration and has already undergone two stages of pretreatment. The impurity content carried by its concentrate is far lower than that of the mother liquor itself, and it will not significantly change the impurity composition of the nanofiltration influent or the difficulty of desalination. Moreover, the wash water treatment process has no direct effect on the evaporation and crystallization process. Its operational fluctuations can only be indirectly transmitted through the nanofiltration desalination stage. That is, changes in the reverse osmosis concentrate flow rate of the wash water will change the total amount and concentration of the nanofiltration product water, thereby affecting the treatment load of subsequent concentration and reduction, and ultimately indirectly affecting the evaporation rate of evaporation and crystallization. It will not directly change the relative ratio of ammonium chloride and impurity ions in the evaporation mother liquor. Compared to the direct material closed-loop interaction between nanofiltration desalination and evaporation crystallization, the impact of wash water treatment on both is relatively low. Therefore, the core collaborative monitoring and control logic of this invention revolves only around the nanofiltration desalination process and the evaporation crystallization process.

[0076] Please see Figures 1-3 As shown, the present invention provides a resource-based treatment method for cobalt tetroxide waste mother liquor. The method includes: sequentially subjecting the mother liquor to advanced oxidation, carbonate removal, coagulation sedimentation, ceramic membrane filtration, nanofiltration desalination, concentration and volume reduction and evaporation crystallization treatment, and sequentially subjecting the wash water to ceramic membrane filtration and reverse osmosis concentration treatment, and incorporating the reverse osmosis concentrate of the wash water into the mother liquor nanofiltration desalination process.

[0077] The method also includes synergistic monitoring and control of the nanofiltration salt separation process and the evaporation crystallization process, including:

[0078] Step S1: Determine the pressure gradient distribution data and conductivity gradient distribution data along the water flow direction on the concentrate side and product water side of the nanofiltration membrane module at the inlet, middle section and outlet.

[0079] Step S2: Real-time data collection of the density, conductivity, temperature, and impurity ion concentration of the mother liquor, and determination of the ammonium chloride concentration;

[0080] Step S3: Collect acoustic wave characteristic data of the membrane particles respectively;

[0081] Step S4: Determine the impurity accumulation index based on the concentration of each impurity ion and the concentration of ammonium chloride; determine the salt purity index based on the pressure gradient distribution data and the conductivity gradient distribution data; and determine the membrane fouling index based on the acoustic characteristic data.

[0082] Step S5: Determine the operating status of the nanofiltration system based on the salt purity index and membrane fouling index, and determine the operating status of the evaporation system based on the impurity accumulation index of the evaporation mother liquor;

[0083] Step S6: Based on the changing trends of the salt purity index, membrane fouling index, and evaporation mother liquor impurity accumulation index, predict the remaining healthy operating time of the nanofiltration membrane and the remaining time of impurity removal from the evaporation system, respectively.

[0084] Step S7: Execute the corresponding processing strategy according to the operating status of the evaporation system and the nanofiltration system, and dynamically adjust the impurity removal threshold according to the adjusted ammonium chloride product purity data.

[0085] In implementation, the advanced oxidation reaction adopts one or a combination of Fenton process, ozone oxidation process or electrochemical oxidation process; the acid added in the carbonate removal treatment is hydrochloric acid; the coagulant in the coagulation and sedimentation step is polyaluminum chloride or aluminum sulfate, and the flocculant is polyacrylamide; the concentration and reduction device preferably adopts an electrodialysis device, which has higher concentration efficiency for high salinity wastewater, relatively lower energy consumption, and can significantly reduce the amount of water treated by subsequent evaporation and crystallization, thereby reducing the overall operating cost of the system.

[0086] The mother liquor treatment process includes the following steps:

[0087] Advanced oxidation: The mother liquor is subjected to advanced oxidation treatment to degrade the organic pollutants it contains;

[0088] Carbonate removal: Acid is added to the mother liquor after advanced oxidation treatment, and the reaction removes carbonate ions;

[0089] Coagulation and sedimentation: Coagulants and flocculants are added to cause the residual suspended solids, colloids and some heavy metal ions in the water to form flocs and precipitate and separate.

[0090] Ceramic membrane filtration: The supernatant after coagulation and sedimentation is filtered through a ceramic membrane to remove fine particulate matter;

[0091] Nanofiltration desalination: The water produced by ceramic membrane filtration is subjected to nanofiltration desalination to separate monovalent salts from polyvalent salts;

[0092] Concentration and reduction: Nanofiltration desalination permeate is concentrated and reduced through high-pressure reverse osmosis or electrodialysis;

[0093] Evaporation crystallization: The concentrated solution is evaporated and crystallized to obtain ammonium chloride product.

[0094] The washing water treatment process includes the following steps:

[0095] Ceramic membrane filtration: Wash water is filtered through a ceramic membrane to remove suspended solids and colloids;

[0096] First-stage reverse osmosis concentration: The permeate from ceramic membrane filtration and the fresh water produced in the concentration and reduction step are combined and then concentrated by first-stage reverse osmosis. The concentrated water from first-stage reverse osmosis is then incorporated into the permeate from ceramic membrane filtration so that they can be jointly introduced into the nanofiltration desalination step.

[0097] Secondary reverse osmosis deep treatment: The primary reverse osmosis permeate is treated by secondary reverse osmosis, and the secondary reverse osmosis permeate is reused in the production system.

[0098] In implementation, the nanofiltration membrane module is a spiral wound membrane element, installed within a pressure-bearing membrane housing. Three detection ports are located along the axial direction of the housing, corresponding to the inlet, middle, and outlet positions of the membrane element. At each detection port, an insertion-type pressure sensor is installed at the location on the membrane housing corresponding to the concentrate side flow channel of the membrane element, serving as the concentrate-side pressure sensor. Another pressure sensor is installed at the outlet position of the central pipe on the permeate side of the corresponding section, also serving as the permeate-side pressure sensor. The signal lines of the two pressure sensors are connected to the input and output terminals of the same differential pressure transmitter, which constitutes the differential pressure acquisition device group for that section, enabling real-time measurement of the transmembrane pressure difference between the concentrate and permeate sides at that section. After synchronous acquisition of the output signals from the differential pressure transmitters at the three sections, they are arranged in spatial order from the inlet to the outlet, forming differential pressure gradient distribution data reflecting the change in membrane surface resistance along the water flow direction.

[0099] Meanwhile, insertion-type conductivity electrodes are installed on the concentrate side and product water side of each detection interface. The concentrate side conductivity electrode is used to measure the real-time conductivity of the concentrate at that cross section, and the product water side conductivity electrode is used to measure the real-time conductivity of the product water at that cross section. Arranged in spatial position, they form a flow distribution sequence of concentrate side conductivity and flow distribution sequence of product water conductivity, which together constitute conductivity gradient distribution data.

[0100] In this invention, the acquisition of pressure gradient distribution data and conductivity gradient distribution data enables independent and synchronous observation of the membrane separation state at different axial positions inside the nanofiltration membrane module. This overcomes the limitation that relying solely on the total influent and effluent parameters of the membrane module is insufficient to determine local changes in membrane behavior, and provides original data support for the subsequent spatial resolution calculation of salt purity index and membrane fouling index.

[0101] The evaporator crystallizer is equipped with a circulating pump and a circulating mother liquor pipeline, which continuously circulates the mother liquor discharged from the bottom of the crystallizer back to the evaporation chamber. An online monitoring flow cell is installed on the circulating mother liquor pipeline, connected in series with the main pipeline or a bypass branch. The mother liquor flows continuously through the flow cell. An online density meter probe, an online conductivity electrode, and a temperature sensor probe are sequentially installed along the liquid flow direction within the flow cell, simultaneously outputting the real-time density, conductivity, and temperature values ​​of the mother liquor.

[0102] At the pipeline branch interface downstream of the flow cell, sulfate ion selective electrode, sodium ion selective electrode and chloride ion selective electrode are installed respectively. The sensitive membrane surface of each electrode is in full contact with the flowing mother liquor. The electrode signal is converted into the real-time concentration value of the corresponding ion by its respective ion concentration transmitter.

[0103] Ammonium chloride concentration is determined through two methods: First, based on real-time measurements of chloride, sodium, and sulfate ion concentrations, the concentration is calculated using the principle of solution charge balance. The calculation considers the valence state of each ion and incorporates the mother liquor conductivity value for correction, eliminating interference from unmonitored ions. Second, based on density, conductivity, and temperature, a pre-established correlation database or fitting function, calibrated through limited batch evaporation experiments, is used to directly output the ammonium chloride concentration. This calibration process involves chemical analysis of mother liquor samples taken at different concentration stages under laboratory conditions. The obtained ammonium chloride concentration is then correlated with synchronously recorded density, conductivity, and temperature data through regression analysis. Either method can be used or used for mutual verification. This online detection device allows for continuous, real-time quantification of the mother liquor impurity enrichment trend and ammonium chloride concentration during evaporation and crystallization, providing a continuous data basis for determining the evaporation system's operating status and dynamically adjusting the impurity removal threshold.

[0104] It is understandable that during the operation of a nanofiltration membrane module, suspended particles, colloids, and precipitated microcrystals in the feed solution will generate acoustic emission signals of specific frequencies upon deposition or collision on the membrane surface. The strength and frequency distribution of these signals are closely related to the behavior of the particles on the membrane surface. Therefore, acoustic emission sensors are installed on the outer wall of the membrane housing at the inlet, middle, and outlet sections of the nanofiltration membrane module, respectively. The sensors are tightly attached to the membrane housing surface through a coupling agent to receive the acoustic wave signals transmitted from inside the membrane to the housing wall.

[0105] During the acquisition process, the waveform signals output by each acoustic emission sensor are subjected to Fourier transform to obtain a spectrum composed of frequency components and their corresponding amplitudes. The acoustic spectrum is the sum of the squares of the amplitudes of all frequency components. The centroid of the acoustic emission frequency is the center frequency value obtained by weighting all frequency components with the squares of their amplitudes as weights. The acoustic emission energy value reflects the intensity of the interaction between particles and the membrane surface, while the centroid of the frequency indicates the type of the main sound source. High-frequency components mostly correspond to particle impacts, while low-frequency components mostly correspond to deposition layer friction or peeling.

[0106] In this invention, the variation trend of acoustic emission energy along the axial direction of the membrane module reflects the spatial development of membrane fouling, particle concentration helps determine the evolution of the overall retention efficiency of the membrane system, and particle size distribution distinguishes between fouling dominated by fine colloids and fouling dominated by large particle accumulation. Through multi-dimensional sensing arrangements, the membrane fouling process is expanded from simple transmembrane pressure differential monitoring to a synergistic characterization of acoustic and particle features, providing a comprehensive data foundation for the accurate calculation of the membrane fouling index and the differentiation of fouling types.

[0107] To determine the impurity accumulation index, after obtaining the real-time concentrations of sulfate ions, sodium ions, chloride ions, and ammonium chloride, the ratio of each impurity ion concentration to the ammonium chloride concentration is calculated as the relative concentration. Since different impurity ions have varying degrees of influence on the purity of the ammonium chloride crystallized product, the weighting coefficients of each ion are calibrated experimentally. The calibration method is as follows: Simulated mother liquors with different impurity ratios are prepared under laboratory conditions for evaporation and crystallization experiments. The purity of the resulting ammonium chloride product is measured. A correlation model between the relative concentrations of each impurity and the product purity is established through multiple linear regression analysis. The regression coefficients of each variable in the model are normalized and used as the weighting coefficients of the corresponding impurity ions. Generally, the weighting coefficients are 0.5 for sulfate ions, 0.3 for sodium ions, and 0.2 for chloride ions. The initial impurity accumulation index is obtained by multiplying each relative concentration by its corresponding weighting coefficient and then summing the results.

[0108] Understandably, relativistic calculations can eliminate the interference of fluctuating influent conditions, statistical methods can extract the essential characteristics of the data, and discretization transforms continuously changing values ​​into state indicators that are easy for the system to execute. The sliding window standard deviation discretization method is employed, taking several consecutive sampling periods prior to the current moment as a preset time window of one hour. The mean and standard deviation of the initial impurity accumulation index within this window are calculated. The final impurity accumulation index is obtained by dividing the deviation of the current initial impurity accumulation index from the mean by the standard deviation. This multiple reflects the degree of deviation of the current impurity accumulation level from the recent steady state.

[0109] For example, the initial impurity accumulation index was continuously collected for ten sampling periods within a preset time window. The calculated mean within this window was 1.2, and the standard deviation was 0.3. If the initial impurity accumulation index at the current moment is 1.3, then the deviation is 0.1, and the ratio of the deviation to the standard deviation is 0.33. Therefore, the final impurity accumulation index is determined to be 0.33. This value is relatively small, indicating that the current impurity accumulation level is close to the recent historical average and is within the normal fluctuation range, meaning the evaporation system can maintain normal circulation.

[0110] If the initial impurity accumulation index rises to 2.1 at the current moment, while the mean within the same window remains at 1.2 and the standard deviation is 0.3, then the deviation is 0.9, and the ratio of the deviation to the standard deviation is 3.0. At this point, the final impurity accumulation index is determined to be 3.0. This value is significantly larger than the daily fluctuation range, indicating that the impurity accumulation level has significantly deviated from the steady state.

[0111] If the initial impurity accumulation index suddenly rises to 3.6 at the current moment, with a mean of 1.2 and a standard deviation of 0.3 within the same window, the deviation is 2.4, and the ratio of the deviation to the standard deviation is 8.0. At this point, the final impurity accumulation index is determined to be 8.0, indicating that impurities are accumulating at a rate far exceeding the normal rate.

[0112] If, after the impurity removal operation, the initial impurity accumulation index drops to 0.8, the window mean is 1.2, and the standard deviation is 0.3, then the deviation is -0.4, and the ratio of the deviation to the standard deviation is -1.33. Therefore, the final impurity accumulation index is determined to be -1.33.

[0113] Understandably, the significance of using a ratio rather than absolute concentration in the impurity accumulation index is to eliminate the effect of a simultaneous increase in overall concentration caused by water evaporation during the evaporation and crystallization process. This ensures that the index only reflects the enrichment degree of impurities relative to the target product, ammonium chloride, avoiding interference from changes in the concentration factor on the judgment results. The relative concentrations are multiplied by their corresponding weighting coefficients and then summed. These weighting coefficients, obtained through experimental calibration, reflect the varying degrees of influence of different impurity ions on the purity of the ammonium chloride crystallized product. Sulfate ions readily form complex salt co-precipitates with ammonium ions, sodium ions affect crystal particle size distribution, and while chloride ions are the main component, their excess can also affect the crystallization yield. Therefore, it is necessary to differentiate the weights to accurately characterize the overall impurity accumulation level. Finally, the sliding window standard deviation discretization method was adopted to discretize the initial impurity accumulation index. The principle is as follows: the initial impurity accumulation index is a continuously changing value. When used directly for state determination, it is easy to make misjudgments due to instantaneous disturbances or measurement noise. By calculating the standard deviation multiple of the current value relative to the mean within the preset time window, the continuous value can be transformed into a discretized multiple that reflects statistical significance. This multiple is essentially a standardized score in statistics, which can distinguish between normal fluctuations and deviations from the true trend, and provide a quantitative basis with statistical confidence for the state determination of the evaporation system.

[0114] To determine the salt separation purity index, the relative pressure difference of each cross-section is obtained by dividing the transmembrane pressure difference at each cross-section by the transmembrane pressure difference at the inlet cross-section. The relative retention rate of each cross-section is obtained by dividing the conductivity retention rate of each cross-section by the average conductivity retention rate of the three cross-sections. The conductivity retention rate is the percentage of the difference between the concentrate-side conductivity and the product-side conductivity of that cross-section relative to the concentrate-side conductivity. The product of the relative pressure difference and the relative retention rate at each cross-section is calculated; this product comprehensively reflects the actual separation effect under a unit driving pressure difference. The ratio of the standard deviation to the average value of this product for the three cross-sections is calculated to obtain the spatial variation coefficient, which is directly used as the salt separation purity index.

[0115] Understandably, the significance of normalization lies in eliminating the influence of differences in absolute pressure difference and absolute rejection rate values ​​under different operating conditions, making data from different times and under different influent conditions comparable. Relative pressure difference reflects the degree of change in hydraulic resistance at that cross-section relative to the influent end, while relative rejection rate reflects the degree of deviation of separation selectivity at that cross-section from the average level of the entire membrane. The product of these two factors comprehensively characterizes the distribution of actual separation efficiency along the membrane under a unit driving pressure difference. The spatial variation coefficient of this product is taken as the salt separation purity index. Its significance lies in the fact that the spatial variation coefficient itself is a dimensionless discrete index, directly reflecting the consistency of separation behavior at each cross-section of the nanofiltration membrane. A larger value indicates more uneven separation behavior along the membrane surface and poorer salt separation purity. This index does not require further discretization processing because its calculation process has already completed spatial discrete sampling and normalization, and the values ​​under different operating conditions are directly comparable.

[0116] For the membrane fouling index, the rate of change of each acoustic emission energy value along the water flow direction is calculated, i.e., the ratio of the energy difference between adjacent sections to the distance between sections. The maximum rate of change among the three sections is taken as the initial membrane fouling index. A trend slope discretization method is used to perform a univariate linear regression on the initial membrane fouling index sequence within a preset time window to obtain the slope of the regression line. The final membrane fouling index is determined based on the sign and absolute value of the slope: a positive slope indicates a positive membrane fouling index, signifying that fouling is in the development stage, with a larger absolute value indicating faster development; a negative slope indicates a negative membrane fouling index, signifying that fouling is in the mitigation stage; and a slope close to zero indicates a zero membrane fouling index, signifying a stable fouling state. The length of the preset time window is determined experimentally based on the product of the hydraulic residence time of the nanofiltration system and the sampling period, ideally covering a complete hydraulic renewal cycle.

[0117] Understandably, acoustic emission energy reflects the intensity of particle collisions or deposition on the membrane surface, while the rate of change along the flow path reflects the spatial gradient of fouling development along the water flow direction. The maximum rate of change is taken as the initial membrane fouling index because membrane fouling typically forms and expands first in localized locations, and the maximum rate of change corresponds to the most active area of ​​fouling development. The state of this area best characterizes the real-time development trend of membrane fouling. A trend slope discretization method is used to discretize the initial membrane fouling index. This method considers that the initial membrane fouling index at a single moment cannot distinguish whether fouling is in the development or mitigation stage, nor can it quantify the development rate. By performing linear regression on the initial membrane fouling index sequence within a preset time window, the slope is obtained. The sign of the slope directly indicates the direction of fouling development, and the absolute value of the slope directly reflects the rate of development or mitigation. This transforms the continuously changing degree of fouling into a discretized state indicator with trend-discriminating significance, providing a clear basis for deciding the timing of membrane cleaning.

[0118] During implementation, in the initial stage of system commissioning or after thorough cleaning and restoration to baseline conditions, the salt purity index and membrane fouling index are continuously collected for several cycles. The mean and standard deviation of each index are calculated, and the mean plus or minus twice the standard deviation is used as the corresponding baseline range. For example, the baseline range for the salt purity index can be set to 0.8 to 1.2 times the historical mean, the baseline range for the membrane fouling index can be set to -0.5 to 0.5, and the baseline range for the impurity accumulation index can be set to 0 to 70% of the historical maximum value.

[0119] In actual operation, when the salt purity index exceeds the upper limit of the benchmark range while the membrane fouling index remains within the benchmark range, it indicates a decrease in membrane separation selectivity but no significant fouling has yet occurred, and is thus classified as a salt separation deviation state. When the membrane fouling index exceeds the upper limit of the benchmark range, regardless of the salt purity index, it indicates that perceptible fouling accumulation has occurred on the membrane surface, and is thus classified as a membrane fouling development state. When the impurity accumulation index exceeds the upper limit of the benchmark range, it indicates that the enrichment of impurities in the evaporation mother liquor has affected the crystallization environment, and is thus classified as an impurity exceedance state. Each benchmark range can be periodically updated based on recent historical data as the system operates, to adapt to the natural decline in membrane performance and seasonal fluctuations in influent water quality.

[0120] Understandably, the salt separation purity index reflects the consistency of separation behavior across different sections of the nanofiltration membrane along the water flow direction. When concentration polarization or localized salt leakage occurs on the membrane surface, the difference in retention rates across different sections increases, and the salt separation purity index rises accordingly. The membrane fouling index reflects the development trend of membrane fouling. When particulate matter deposits on the membrane surface or forms a filter cake layer, the transmembrane pressure differential distribution changes along the membrane, the acoustic emission signal strengthens, and the membrane fouling index changes accordingly. Both describe the working state of the nanofiltration membrane from the dimensions of separation selectivity and hydraulic resistance, respectively, but their evolution timelines are not synchronized. The decrease in salt separation purity may precede or lag the increase in the membrane fouling index, therefore, they need to be monitored and judged independently. Regarding the evaporation system, the impurity accumulation index reflects the enrichment degree of impurity ions in the mother liquor relative to ammonium chloride. When this index continues to rise, it indicates that the impurity concentration in the crystallization environment has affected the nucleation and growth process of ammonium chloride crystals, requiring timely intervention.

[0121] Understandably, the changing trends of the salt purity index and membrane fouling index reflect the rate of performance degradation of the nanofiltration membrane. Without external intervention, this degradation rate is continuous in the short term. Therefore, the remaining time for performance to meet standards at the current rate can be obtained by linearly extrapolating the current trend to the upper limit of the baseline range. Since either the salt purity index or the membrane fouling index reaching a threshold indicates that the nanofiltration system has entered an unhealthy state, the shorter of the two remaining times is taken as the remaining healthy operating time of the nanofiltration membrane for timely warning. The prediction of the remaining time for impurity removal in the evaporation system is similar. The rate of increase of the impurity accumulation index reflects the enrichment rate of impurities in the mother liquor; linear extrapolation to the upper limit of the baseline range yields the remaining time required for impurity removal.

[0122] The preset historical time window length is the product of the hydraulic residence time and the sampling period of the nanofiltration system. For example, if the hydraulic residence time is 30 minutes and the sampling period is 2 minutes, the window length is set to 15 sampling points to ensure that the data within the window covers a complete hydraulic update cycle and eliminates the interference of short-term disturbances on trend judgment. Within the window, least squares linear fitting is performed on the salt purity index sequence and the membrane fouling index sequence, respectively. The resulting slopes represent the rate of deterioration of salt purity and the rate of development of membrane fouling, respectively.

[0123] Understandably, when the nanofiltration system is in normal condition and the evaporation system is in normal circulation, it indicates that the entire system is operating smoothly and no intervention is required. The current operating parameters of the nanofiltration salt separation and evaporation crystallization steps remain unchanged, and all the mother liquor from the evaporation is returned to the concentration and reduction step to continue the cycle, so as to maximize the recovery of water resources and salt.

[0124] When the nanofiltration system is normal but the evaporation system enters a state of excessive impurities, it indicates that the problem only occurs in the accumulation of impurities on the evaporation side. At this time, only the evaporation side is intervened. Part of the evaporated mother liquor is discharged through the impurity discharge pipeline and returned to the ceramic membrane filter product water pipeline before the nanofiltration desalination step to participate in the desalination treatment again. The operating parameters on the nanofiltration side remain unchanged. The risk of impurity enrichment is eliminated by single-sided control. The impurity discharge ratio can be set to 5% to 15% of the circulating mother liquor flow rate. This ratio is determined by experimental calibration of product purity and recovery rate under different impurity discharge rates.

[0125] When a nanofiltration system enters a state of desalination deviation or membrane fouling development, it indicates a decline in separation performance or membrane fouling on the nanofiltration side. In this case, a graded control operation is performed on the nanofiltration desalination step: If it is only a state of desalination deviation, the opening of the flow distribution valve at the inlet of the nanofiltration membrane module is adjusted first to improve the uniformity of water flow distribution on the membrane surface. The adjustment range is gradually adjusted from ±10% to ±20% of the current opening. After each adjustment, a stable observation period of one sampling cycle is maintained until the desalination purity index returns to the reference range. If the desalination purity index does not return to the reference range within the preset adjustment period after adjustment, or if it is directly in a state of membrane fouling development, the operating recovery rate of the nanofiltration system is reduced to reduce the membrane load. The reduction range is gradually reduced from 5% to 10% of the current recovery rate. After each reduction, a stable observation period of 30 to 60 minutes is maintained until the membrane fouling index falls back to the reference range.

[0126] When the nanofiltration system is in an abnormal state and the evaporation system is simultaneously experiencing excessive impurities, intervention is required at both ends. In this case, simultaneous staged control operations on the nanofiltration side and mother liquor discharge and reflux operations on the evaporation side are performed to quickly restore the system's health in a coordinated manner. The specific values ​​of the aforementioned control parameters can be obtained through a limited number of tests during the initial stage of system commissioning and adjusted and optimized based on the actual response during operation.

[0127] A purity testing device is installed at the product outlet of the evaporator crystallizer to test the purity of each batch of ammonium chloride produced. The obtained purity value is compared with a preset product purity target value, which is set according to the downstream application's requirements for ammonium chloride quality. For example, if the purity requirement for industrial-grade ammonium chloride is not less than 99.0%, then this value can be set to 99.0%. The preset purity margin is determined based on the process control precision and the detection error range, and is generally set to 0.2%.

[0128] The adjustment rules for the impurity removal threshold are as follows: When the purity test values ​​of three consecutive batches are all lower than the product purity target value, it indicates that the current impurity removal conditions are too lenient and the accumulation of impurities has affected the product quality. The upper limit of the impurity accumulation index benchmark range needs to be lowered by one adjustment step, for example, the step is set to 5% of the current benchmark range upper limit value, so as to make the impurity removal trigger more sensitive. When the purity test values ​​of three consecutive batches are all higher than the sum of the product purity target value and the purity margin, it indicates that the current impurity removal conditions are too strict and the system still has impurity tolerance space. The upper limit of the impurity accumulation index benchmark range can be increased by one adjustment step to relax the impurity removal trigger conditions and reduce the discharge of mother liquor.

[0129] The initial value of the upper limit of the benchmark range was obtained through a limited batch evaporation test. Specifically, under normal operating conditions, the change in the impurity accumulation index was continuously monitored, and the impurity accumulation index corresponding to the first instance of product purity failing to meet the standard was taken as the initial upper limit value. This feedback adjustment mechanism allows the impurity removal threshold to dynamically self-tune based on actual product quality, achieving an adaptive balance between ensuring quality and improving recovery rate.

[0130] On the other hand, this embodiment also provides a processing system, including: an advanced oxidation reactor, a carbon removal reaction tank, a coagulation sedimentation tank, a first ceramic membrane filtration device, a nanofiltration device, an electrodialysis device or a high-pressure reverse osmosis device, and an evaporation crystallizer connected in sequence; and a second ceramic membrane filtration device, a first-stage reverse osmosis device, and a second-stage reverse osmosis device connected in sequence.

[0131] The freshwater outlet of the electrodialysis device or high-pressure reverse osmosis device is connected to the inlet of the first-stage reverse osmosis device; the concentrated water outlet of the first-stage reverse osmosis device is connected to the pipeline between the product water outlet of the first ceramic membrane filtration device and the inlet of the nanofiltration device.

[0132] Also includes:

[0133] The data acquisition unit is used to collect differential pressure data, conductivity data, density data, temperature data, impurity ion concentration data, and acoustic emission energy values.

[0134] The processor is used to calculate the impurity accumulation index, salt purity index, and membrane fouling index; determine the operating status of the nanofiltration system and the evaporation system; predict the remaining healthy operating time of the nanofiltration membrane and the remaining time for impurity removal from the evaporation system; and generate corresponding control commands.

[0135] Impurity removal threshold controller, which is used to adjust the upper limit of the impurity accumulation index benchmark range based on the comparison result between the purity detection value and the product purity target value;

[0136] An actuator, electrically connected to the processor, includes a flow regulating valve located at the inlet of the nanofiltration unit and a reflux valve located on the circulating mother liquor pipeline of the evaporator crystallizer. The actuator operates in response to control commands generated by the processor.

[0137] In practice, the pore size range of the first and second ceramic membrane filtration devices is 50-200 nm; the nanofiltration device uses nanofiltration membranes with a molecular weight cutoff range of 100-300 Da.

[0138] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

[0139] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for resourceful treatment of a cobaltic oxide waste solution mother liquor, comprising: The method involves pretreatment, filtration, nanofiltration desalination, concentration, and evaporation crystallization of waste liquid mother liquor, as well as sequential filtration and concentration of wash water. The characteristic feature is that the waste liquid mother liquor treatment process further includes coordinated monitoring and control of the nanofiltration desalination and evaporation crystallization processes, including: Acquire pressure gradient distribution data and conductivity gradient distribution data along the water flow direction of the nanofiltration membrane module, and collect acoustic characteristic data of the membrane surface particles; The physical information of the mother liquor is collected in real time to determine the concentration of ammonium chloride. The physical information of the mother liquor includes density, conductivity, temperature and concentration data of various impurity ions, including sulfate ions, sodium ions and chloride ions. The impurity accumulation index is determined based on the concentration of each impurity ion and the concentration of ammonium chloride; the salt purity index is determined based on the pressure gradient distribution data and the conductivity gradient distribution data; and the membrane fouling index is determined based on the acoustic characteristic data. The operating status of the nanofiltration system is determined based on the salt purity index and membrane fouling index, and the operating status of the evaporation system is determined based on the impurity accumulation index of the evaporation mother liquor. Based on the changing trends of the salt purity index, membrane fouling index, and evaporation mother liquor impurity accumulation index, the remaining healthy operating time of the nanofiltration membrane and the remaining impurity removal time of the evaporation system are predicted respectively. The corresponding collaborative processing strategy is executed according to the operating status of the evaporation system and the nanofiltration system, and the impurity removal threshold is dynamically adjusted according to the adjusted ammonium chloride product purity data.

2. The method for resourceful treatment of the cobaltic oxide waste solution mother liquor according to claim 1, characterized in that, The acquisition of the pressure gradient distribution data and conductivity gradient distribution data includes: Select the inlet section, middle section, and outlet section of the nanofiltration membrane module; Obtain the product water side pressure and concentrate side pressure at each cross section, calculate the transmembrane pressure difference value at the corresponding cross section, and form pressure difference gradient distribution data along the water flow direction; Obtain the concentrate-side conductivity and product water-side conductivity of each cross section, and form conductivity gradient distribution data along the water flow direction.

3. The method for resourceful treatment of the trivalent cobalt waste liquid mother liquor according to claim 2, characterized in that, The process of determining the concentration of ammonium chloride includes: The concentration of ammonium chloride in the evaporating mother liquor was calculated using the ion charge balance method based on the concentrations of chloride ions, sodium ions, and sulfate ions. Alternatively, the concentration of ammonium chloride in the mother liquor can be calculated using multiple parameters, based on the density, conductivity, and temperature of the mother liquor.

4. The method for resource-based treatment of cobalt tetroxide waste mother liquor according to claim 3, characterized in that, The process of determining the impurity accumulation index, the salt purity index, and the membrane fouling index includes: The relative concentration of each impurity ion is obtained by calculating the ratio of the concentration of each impurity ion to the concentration of ammonium chloride. The weighted sum of the relative concentrations of each impurity ion is then used to obtain the initial impurity accumulation index. The initial impurity accumulation index within a preset time window is discretized using the sliding window standard deviation discretization method to obtain the impurity accumulation index. The relative pressure difference of the corresponding section is obtained by calculating the ratio of the transmembrane pressure difference of each section to the transmembrane pressure difference of the inlet section. The relative retention rate of the corresponding section is obtained by calculating the ratio of the conductivity retention rate of each section to the average conductivity retention rate of the section. The spatial variation coefficient of the product of the relative pressure difference and the relative retention rate at each cross section is denoted as the salt purity index. Determine the rate of change of each acoustic emission energy value along the water flow direction and take the maximum rate of change as the initial membrane fouling index; The linear regression slope of the continuous membrane fouling index within a preset time window is calculated using the trend slope discretization method, and the membrane fouling index is determined based on the sign and absolute value of the slope.

5. The method for resourceful treatment of the trivalent cobalt waste solution mother liquor according to claim 4, characterized in that, Determining the operating status of the nanofiltration system based on the salt purity index and the membrane fouling index includes: In response to the membrane fouling index being within the membrane fouling reference range and the salt purity index exceeding the salt purity reference range, the nanofiltration system is determined to be in a salt separation deviation state. In response to the membrane fouling index exceeding the membrane fouling benchmark range, the nanofiltration system is determined to be in a membrane fouling development state. The nanofiltration system's operating status includes a normal state and an abnormal state, and the abnormal state includes salt separation deviation and membrane fouling development.

6. The method for resourceful treatment of spent solution mother liquor of tricobalt tetroxide according to claim 4, characterized in that, The operating status of the evaporation system is determined based on the impurity accumulation index of the mother liquor, including: When the impurity accumulation index exceeds the preset impurity accumulation benchmark range, the evaporation system is determined to be in an impurity over-limit state. The operating status of the evaporation system includes normal status and impurity exceeding the limit status.

7. The method according to claim 6, characterized in that, The process of predicting the remaining healthy operating time of the nanofiltration membrane and the remaining time of impurity removal from the evaporation system based on the changing trends of the salt purity index, membrane fouling index, and evaporation mother liquor impurity accumulation index includes: Linear fitting was performed on the salt purity index sequence and membrane fouling index sequence within the preset historical time window to obtain the slope of salt purity change and the slope of membrane fouling change. Determine the ratio of the slope of change in salt purity to the upper limit of the salt purity reference range and the ratio of the slope of change in membrane fouling to the upper limit of the membrane fouling reference range. The relatively larger value between the purity slope ratio and the fouling slope ratio is determined as the remaining healthy operating time of the nanofiltration membrane. Linear fitting is performed on the impurity accumulation index sequence within a preset historical time window to obtain the impurity accumulation change slope. The remaining time for impurity removal from the evaporation system is determined based on the ratio of the impurity accumulation change slope to the upper limit of the preset impurity accumulation benchmark range. The length of the preset historical time window is determined by the product of the hydraulic residence time of the nanofiltration system and the sampling period.

8. The method for resourceful treatment of spent solution mother liquor of cobaltic oxide according to claim 6, characterized in that, The step of executing corresponding collaborative processing strategies based on the operating status of the evaporation system and the nanofiltration system includes: In response to the nanofiltration system operating in a normal state, a collaborative treatment strategy is formulated based on the evaporation system operating state, including: Based on the determination that the evaporation system is in normal operating condition, the current operating parameters of the nanofiltration salt separation step and the evaporation crystallization step are maintained, and all the mother liquor is returned to the concentration and reduction step for recycling. Based on the determination that the evaporation system is in a state of excessive impurities, part of the evaporated mother liquor will be discharged and recycled back to the nanofiltration desalination step for reprocessing, while keeping the operating parameters of the nanofiltration desalination step unchanged. In response to an abnormal operating state of the nanofiltration system, a collaborative treatment strategy is formulated based on the operating state of the evaporation system, including: Based on the determination that the evaporation system is in normal operating condition, the collaborative treatment strategy is to perform graded control operations on the nanofiltration desalination step. The graded control operations include adjusting the nanofiltration influent flow rate distribution or reducing the nanofiltration recovery rate. Based on the determination that the evaporation system is in a state of excessive impurities, the graded control operation of the nanofiltration salt separation step and the operation of discharging and refluxing part of the mother liquor are performed simultaneously.

9. The method according to claim 6, characterized in that, The impurity removal threshold is dynamically adjusted based on the adjusted ammonium chloride product purity data, including: Obtain the purity test value of the ammonium chloride product obtained from the evaporation and crystallization step; The purity test value is compared with the product purity target value; When the purity test values ​​of several consecutive batches are all lower than the target value of product purity, the upper limit of the benchmark range of impurity accumulation index is reduced. When the purity test values ​​of several consecutive batches are all higher than the sum of the product purity target value and the preset purity margin, the upper limit of the benchmark range of the impurity accumulation index is increased. The impurity removal threshold is the upper limit of the benchmark range of the impurity accumulation index, and its adjustment step size is determined according to the deviation direction between the purity detection value and the product purity target value.

10. A treatment system for the resource recovery treatment of cobalt tetroxide waste mother liquor according to any one of claims 1-9, comprising: The advanced oxidation reactor, carbon removal reaction tank, coagulation sedimentation tank, first ceramic membrane filtration device, nanofiltration device, electrodialysis device or high-pressure reverse osmosis device, and evaporator crystallizer are connected in sequence. And a second ceramic membrane filtration device, a first-stage reverse osmosis device, and a second-stage reverse osmosis device connected in sequence; The freshwater outlet of the electrodialysis device or high-pressure reverse osmosis device is connected to the inlet of the first-stage reverse osmosis device; the concentrated water outlet of the first-stage reverse osmosis device is connected to the pipeline between the product water outlet of the first ceramic membrane filtration device and the inlet of the nanofiltration device. Its characteristic is that it further includes: The data acquisition unit is used to collect differential pressure data, conductivity data, density data, temperature data, impurity ion concentration data, and acoustic emission energy values. The processor is used to calculate the impurity accumulation index, salt purity index, and membrane fouling index; determine the operating status of the nanofiltration system and the evaporation system; predict the remaining healthy operating time of the nanofiltration membrane and the remaining time for impurity removal from the evaporation system; and generate corresponding collaborative processing instructions. Impurity removal threshold controller, which is used to adjust the upper limit of the impurity accumulation index benchmark range based on the comparison result between the purity detection value and the product purity target value; An actuator, electrically connected to the processor, includes a flow regulating valve located at the inlet of the nanofiltration unit and a reflux valve located on the circulating mother liquor pipeline of the evaporator crystallizer. The actuator operates in response to control commands generated by the processor.

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