Innocent treatment and valuable metal recovery method for arsenic-alkali residues

Abstract

The invention relates to the technical field of comprehensive utilization of non-ferrous metal smelting waste residues, and discloses a harmless treatment and valuable metal recovery method for arsenic-alkali residues, which comprises the following steps: carrying out selective leaching and antimony separation on the arsenic-alkali residues, and precipitating antimony by using solubility product difference to obtain arsenic-containing alkali filtrate; carrying out gradient carbonization crystallization under oxidation-reduction potential clamping on the filtrate, converting sodium carbonate into sodium bicarbonate crystals under the constraint of specific potential by utilizing the salting-out effect of pentavalent arsenic in a saturated sodium bicarbonate solution, separating out the sodium bicarbonate crystals, and filtering and separating to obtain a sodium bicarbonate product and arsenic-rich mother liquor; according to the method, through a coupling mechanism of potential clamping and gradient carbonization crystallization, the solubility difference of arsenic and alkali is constructed, the salting-out effect is utilized, the arsenic-alkali co-dissolution balance is broken on the premise that exogenous foreign ions are not introduced, and the arsenic-rich mother liquor is subjected to terminal mineralization to generate arsenic-containing mineral precipitates. Efficient separation and recovery of antimony and sodium carbonate and deep solidification of arsenic are realized.

Description

Technical Field

[0001] This invention relates to a method for the harmless treatment and valuable metal recovery of arsenic-alkali slag, belonging to the field of comprehensive utilization technology of non-ferrous metal smelting waste residue. Background Technology

[0002] Currently, the removal of arsenic and antimony impurities from crude metals in pyrometallurgical processes for lead and antimony often employs alkali-addition slag-forming technology, generating large amounts of arsenic-containing alkali slag. This waste slag contains high concentrations of soluble arsenates, classifying it as hazardous solid waste, and is rich in sodium carbonate with recycling value and valuable antimony. Existing technologies mainly employ calcification precipitation to remove arsenic or direct crystallization separation based on solubility differences. While calcification precipitation reduces the arsenic content in the solution, it introduces calcium ions that react with carbonate ions to form insoluble calcium carbonate precipitates or convert sodium carbonate into sodium hydroxide, destroying the chemical form of sodium carbonate and hindering the return of raw materials to the smelting system for recycling. This results in a large amount of unusable calcium-arsenic slag, causing secondary pollution and resource waste.

[0003] The limitations of existing technologies in achieving complete harmlessness of arsenic-alkali slag, high-purity recovery of valuable components, and stable production operation and cost control have prompted the industry to continuously seek more optimized all-wet treatment processes. For example, Chinese invention patent CN108441642A discloses a wet resource recovery and harmless treatment process for arsenic-alkali slag from antimony smelting. The process involves eight steps: crushing, dissolution and leaching, antimony removal by oxidation, purification and impurity removal, transformation crystallization, arsenic reduction and precipitation, evaporation crystallization, and secondary slag harmless treatment. The aim is to achieve resource recovery, harmless disposal, and zero discharge of waste residue and wastewater from arsenic-alkali slag. However, the core idea of ​​this scheme is to convert sodium carbonate to sodium bicarbonate through transformation crystallization, utilizing the difference in solubility to achieve initial reaction between alkali and arsenic. The technical approach of separating and enriching arsenic in the first step, followed by reduction and precipitation of arsenic into arsenic sulfide, has the following drawbacks: the purity control of the transformation crystallization process mainly relies on the final pH value. In the complex high-salt system of antimony smelting, it is difficult to sensitively detect the critical point of nucleation of trace impurities in the solution or abrupt changes in rheological properties. It is very easy for impurities to co-precipitate due to over-reaction, causing fluctuations in the purity of sodium bicarbonate products and affecting subsequent reuse. After transformation, the solution needs to be returned to the leaching step to enrich arsenic. Although the arsenic concentration is increased, the solution circulation load is large and the enrichment process lacks targeted control. Once the flue gas contains reducing gases, it is easy for the oxidized pentavalent arsenic to be reduced and reverted at the crystal lattice interface, transforming into trivalent arsenic that can easily enter the crystal lattice. This renders the effect of the front-end oxidation pretreatment ineffective and contaminates the product.

[0004] Therefore, the technical problem to be solved by the present invention is to break the alkali co-solution equilibrium of arsenic without introducing exogenous calcium and magnesium impurities, through precise control of physicochemical conditions, avoid lattice inclusion and interference from reducing atmosphere, and achieve high-purity separation of valuable components and low-cost solidification of arsenic. Summary of the Invention

[0005] To address the problems mentioned in the background art, the technical solution of this invention is as follows: A method for the harmless treatment and valuable metal recovery of arsenic-alkali slag, wherein the method, without introducing exogenous metal impurity ions other than sodium ions, hydrogen ions, carbonate ions and iron ions, establishes a stepwise separation system based on the differences in solubility and crystallization habits of pentavalent arsenic and trivalent arsenic in concentrated carbonate solutions, and the method includes the following steps:

[0006] In the selective leaching and antimony separation step, arsenic-alkali residue is mixed with water and carbon dioxide gas is introduced. The pH value of the leaching system is controlled to be maintained between 9.5 and 10.2. By utilizing the difference in solubility product between antimony oxides or hydroxides and soluble arsenates under this pH window, the antimony component in the residue is converted into precipitate and separated by filtration to obtain antimony concentrate and arsenic-alkali filtrate.

[0007] The gradient carbonization crystallization step under redox potential clamping involves adding an oxidant to the arsenic-containing alkaline filtrate to raise the redox potential of the filtrate to above +300 mV and establish a high-potential dissolution equilibrium. Under the constraint of maintaining the redox potential not lower than +300 mV, the temperature of the filtrate is controlled between 20°C and 35°C, and carbon dioxide gas is introduced until the pH value drops to 8.2 to 8.6, causing sodium carbonate to be converted into sodium bicarbonate crystals and precipitate. The pentavalent arsenic is retained in the liquid phase by utilizing the salting-out effect of saturated sodium bicarbonate solution. The sodium bicarbonate product and arsenic-rich mother liquor are obtained by filtration.

[0008] The final mineralization step of arsenic-rich mother liquor involves adding a mineralizing agent to the arsenic-rich mother liquor and reacting it under acidic conditions to generate arsenic-containing mineral precipitates.

[0009] Preferably, in the gradient carbonization crystallization step under redox potential clamping, the operation of introducing carbon dioxide gas is performed in a pulsed gas thermal coupling cycle mode; the pulsed gas thermal coupling cycle mode includes alternating pressurization nucleation stage and thermal dissolution cleaning stage; in the pressurization nucleation stage, carbon dioxide gas is introduced to induce sodium bicarbonate precipitation; in the thermal dissolution cleaning stage, the introduction of carbon dioxide gas is stopped and the system temperature is raised by 2 degrees Celsius to 4 degrees Celsius and maintained for 5 to 10 minutes, using the temperature difference to drive the preferential dissolution of fine crystal nuclei with high surface energy and crystal defect layers, releasing the arsenic-containing mother liquor encapsulated by the crystals, and entering the pressurization nucleation stage of the next cycle.

[0010] Preferably, in the gradient carbonization crystallization step under redox potential clamping, a gas-phase associated redox buffer mechanism is used to maintain the redox potential. The gas-phase associated redox buffer mechanism includes: premixing carbon dioxide gas and oxygen gas to maintain the oxygen volume fraction in the mixed gas at 3% to 5%; monitoring the redox potential of the system in real time while the mixed gas is introduced for carbonization reaction; when the redox potential is lower than +300 mV, increasing the mixing ratio of oxygen gas or adding oxidant to the system to clamp the redox potential of the system above +300 mV, so as to suppress the reduction and co-crystallization of impurity arsenic at the gas-liquid interface.

[0011] Preferably, in the gradient carbonization crystallization step under redox potential clamping, a conductivity change rate locking mechanism is introduced as the criterion for determining the crystallization endpoint; the conductivity change rate locking mechanism includes: real-time acquisition of conductivity data of the reaction system. And calculate the first and second derivatives of conductivity with respect to time; when the first derivative of conductivity is detected to be negative, and the second derivative satisfies the following abrupt change criterion: ,in, The threshold constant is a preset value used to characterize abrupt changes in the rheological properties of the mother liquor. Once the system reaches the critical point of impurity co-precipitation, the introduction of carbon dioxide gas is immediately stopped and the crystallization reaction is terminated, regardless of whether the pH value of the system has reached the preset endpoint.

[0012] Preferably, in the terminal mineralization step of the arsenic-rich mother liquor, an acidic desorption and self-pressurization coupling mode is adopted; the acidic desorption and self-pressurization coupling mode includes: adding an acidic mineralizing agent to the closed reaction system, using the change in acidity to convert the residual bicarbonate in the arsenic-rich mother liquor into carbon dioxide gas that escapes; collecting the escaped carbon dioxide gas and returning it to the selective leaching and antimony separation step or the gradient carbonization crystallization step under redox potential clamping for recycling; after the carbon dioxide desorption is complete, controlling the temperature and pH of the system in an environment with low carbonate concentration to induce the precipitation of arsenate.

[0013] Preferably, in the selective leaching and antimony separation steps, the aeration rate of carbon dioxide gas is controlled at 0.1 liters per minute per liter of slurry to 0.3 liters per minute per liter of slurry, and the liquid-solid ratio of the stirred leaching is controlled at 3:1 to 5:1.

[0014] Preferably, in the gradient carbonization crystallization step under redox potential clamping, the oxidant is selected from at least one of hydrogen peroxide, ozone or potassium permanganate; before adding the oxidant, the ratio of trivalent arsenic to pentavalent arsenic in the arsenic-containing alkaline filtrate is detected, and the theoretical amount of oxidant to be added is calculated based on the detection results. The actual amount added is 1.1 to 1.3 times the theoretical amount.

[0015] Preferably, the pulsed gas-thermal coupling cycle mode is executed until the pH of the system drops to 8.2 to 8.6; during the pressurized nucleation stage, the carbon dioxide gas injection rate is 0.5 L / min / L solution to 0.8 L / min / L solution; in the next pressurized nucleation stage after the thermal dissolution cleaning stage, the carbon dioxide gas injection rate is reduced to 0.2 L / min / L solution to 0.4 L / min / L solution, inducing sodium bicarbonate to epitaxially grow on the surface of the remaining crystals.

[0016] Preferably, the acidic mineralizing agent is a ferric sulfate solution or an acidic sulfuric acid solution. The acidic desorption and self-pressurization coupling mode specifically includes: controlling the addition rate of the acidic mineralizing agent to gradually reduce the pH value of the system from 8.2 to 4.0 to 5.0 to desorb carbon dioxide; after the pressure inside the reactor no longer rises, the temperature is further increased to 80 degrees Celsius to 90 degrees Celsius and the pH value is adjusted to 1.0 to 2.0 to precipitate arsenic in the form of arsenic trioxide.

[0017] Preferably, after filtration and separation, the sodium bicarbonate product is rinsed with a low-temperature saturated sodium bicarbonate solution. The temperature of the rinsing solution is controlled between 5 and 10 degrees Celsius to remove mother liquor residue from the crystal surface and prevent crystal dissolution and loss.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] 1. In the harmless treatment of arsenic-alkali residue, a gas-heat coupled pulse circulation mechanism is established during the carbonization and crystallization stage. By periodically blocking the continuous crystal growth process and introducing a micro-temperature difference dissolution zone, the surface energy difference of crystals with different particle sizes is utilized to force the preferential dissolution of high surface energy micro-nuclei and growth layers with lattice defects. This allows the arsenic-rich mother liquor, which was physically trapped inside the crystal due to explosive nucleation, to be released back into the liquid phase, blocking the migration path of impurity arsenic into the sodium bicarbonate lattice and inducing the solute to grow epitaxially with low defects on the surface of the remaining dense large crystals. The active introduction of a dissolution-recrystallization cycle eliminates the capture phenomenon of impurities associated with rapid crystallization from the micro-dynamic level, so that the final sodium bicarbonate product can achieve industrial-grade purity without relying on complex recrystallization operations, and the increased crystal particle size is conducive to solid-liquid separation and washing.

[0020] 2. To address the issue of reducing gas interference when directly utilizing smelting flue gas, a gas-phase-accompanied redox potential buffering mechanism is introduced into the crystallization reaction system. By maintaining a specific oxygen partial pressure in the gas source and monitoring and dynamically adjusting the redox potential throughout the reaction, a continuously high-potential chemical barrier is constructed at the gas-liquid-solid three-phase interface. This immediately counteracts the reducing effect caused by the accumulation of sulfur dioxide or carbon monoxide in the flue gas, keeping arsenic in the solution in a pentavalent form that is more mutually exclusive with sodium bicarbonate crystals. This ensures that the process system has high chemical tolerance to low-cost, compositionally fluctuating crude smelting flue gas, avoiding arsenic reversion and product contamination due to local reducing environments, and guaranteeing the stability of the resource utilization process under complex operating conditions.

[0021] 3. By utilizing the abrupt change in the second derivative of conductivity as the basis for determining the crystallization endpoint, it overcomes the lag and blind spots of traditional single-dimensional pH monitoring in complex high-salt systems; by capturing the sign reversal or numerical jump of the rate of change of solution conductivity in real time, it can keenly perceive the microscopic abrupt changes in solution rheological properties and ion mobility caused by microcrystal bursts or impurity supersaturation; based on kinetic trend rather than static numerical control logic, it can accurately cut off the reaction within the latency period of impurity avalanche coprecipitation, ensuring the yield of the main product and avoiding batch-to-batch quality fluctuations due to reaction overshoot. Attached Figure Description

[0022] Figure 1 This is a flow chart of the arsenic-alkali slag resource utilization process of potential clamping and gradient crystallization according to the present invention.

[0023] Figure 2 This is a graph showing the separation characteristics of antimony precipitation rate and arsenic residue rate under different pH windows according to the present invention.

[0024] Figure 3 This is a schematic diagram of the equipment deployment logic and closed-loop control architecture of the process system of the present invention. Detailed Implementation

[0025] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to specific embodiments. It should be noted that, in the absence of conflict, the technical features in the following embodiments can be combined with each other, and the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] This invention provides a method for the harmless treatment and valuable metal recovery of arsenic-alkali slag. In a single flow path, it sequentially achieves selective precipitation of antimony, phase transformation crystallization separation of sodium carbonate to sodium bicarbonate, and final mineralization and solidification of arsenic, forming a closed-loop hydrometallurgical treatment system. During operation, the arsenic-containing alkali slag is mixed with water at a preset liquid-solid ratio to form a slurry. Carbon dioxide gas is introduced as an acidity regulator, and an online pH monitoring feedback loop precisely controls the system's pH, inducing antimony to preferentially precipitate as low-solidity oxides or hydroxides, achieving primary separation of antimony from arsenic and alkali. The filtrate then enters a gradient carbonization crystallization unit, where... The system establishes a strongly oxidizing environment with controlled redox potential (ORP) by introducing a strong oxidant and coordinating with gas phase component regulation. This forces arsenic in the solution to be locked in the pentavalent form. The continuous introduction of carbon dioxide drives the conversion of sodium carbonate to sodium bicarbonate. Through the salting-out effect and solubility difference in the high-concentration sodium salt environment, sodium bicarbonate crystals precipitate out, while arsenate is retained in the mother liquor. Finally, the arsenic-rich mother liquor enters the terminal mineralization unit. Through the coupling mechanism of acidic desorption and self-pressurization, the residual carbon source is recovered and a suitable acidic precipitation environment is created. Calcium-based or iron-based mineralizers are added to directionally convert arsenic into stable arsenic-containing mineral precipitates, completing the closed loop of resource utilization and harmlessness of the entire process.

[0027] To address the metallurgical engineering challenge of the coexistence of antimony and arsenates in arsenic alkali slag leachate, which is difficult to completely separate through simple hydrolysis, this embodiment establishes a selective leaching and antimony separation procedure based on solubility product differences; considering the hydrolysis products of Sb(III) or The leaching tank exhibits significant amphoteric dissolution behavior under strongly alkaline conditions, while its solubility is extremely low in the weakly alkaline range. Even under these conditions, arsenate maintains very high solubility. The system is equipped with a pH-feedback-based gas-liquid linkage control loop. This loop collects real-time pH data from the leaching tank and adjusts the opening of the valve for the flow rate of carbon dioxide-containing gas introduced into the slurry, strictly controlling the pH value of the leaching system within a specific window of 9.5 to 10.2. Under these conditions, the aeration rate is controlled within the range of 0.1 liters per minute per liter of slurry to 0.3 liters per minute per liter of slurry, while stirring during leaching... The liquid-to-solid ratio is maintained at 3:1 to 5:1. By maintaining the above thermodynamic state, the antimony component in the slag is induced to precipitate. After solid-liquid separation, antimony concentrate filter cake and arsenic-containing alkaline filtrate are obtained, thereby achieving efficient recovery and impurity removal of antimony resources at the source. To solve the technical bottleneck of arsenic reversion due to residual reducing components in smelting flue gas during traditional carbonization crystallization, which leads to lattice doping contamination, this embodiment implements a gradient carbonization crystallization process under redox potential clamping in the crystallization section. Based on the solubility of pentavalent arsenic and trivalent arsenic in concentrated carbonate solution and Due to differences in crystallization habits, an oxidant was added to the arsenic-containing alkaline filtrate, raising the redox potential of the filtrate to over +300 mV, establishing a high-potential dissolution equilibrium dominated by pentavalent arsenic. To resist possible reduction reactions at the gas-liquid interface, the system employs a gas-phase accompanying redox buffer mechanism, whereby carbon dioxide-containing gas and oxygen-containing gas are premixed in a static mixer before entering the reactor, maintaining the oxygen volume fraction in the mixed gas at 3% to 5%. During the gas-assisted carbonization process, an online ORP meter monitors the system potential in real time; once detected... If the value falls below the warning line of +300 mV, the control system increases the proportion of oxygen-containing gas or triggers the oxidant dosing pump to replenish the system with oxidant, always keeping the redox potential of the system above +300 mV. Under this potential constraint, the temperature of the filtrate is controlled between 20°C and 35°C, and the mixed gas is continuously introduced until the pH value drops to 8.2 to 8.6, causing sodium carbonate to be converted into sodium bicarbonate crystals and precipitate out. Pentavalent arsenic is excluded from the crystals due to the salting-out effect and remains in the liquid phase, thereby obtaining high-purity sodium bicarbonate product and arsenic-rich mother liquor.

[0028] The implementation of the gas-phase associated redox buffer mechanism achieves control of the redox potential through a closed-loop control model based on the deviation proportional-integral-derivative (PID) algorithm. Real-time clamping, the model is online Real-time potential values ​​acquired by the probe As a feedback signal, to positive millivolts as the target value This enables the system to be highly tolerant of fluctuations in the intake gas composition and to stably lock in the arsenic valence state in the solution. Control parameters ( , and For the initial tuning of ), the Ziegler-Nichols closed-loop tuning method is used to determine the initial value during the initial deployment, by introducing an amplitude of The setpoint step disturbance tuning parameters are adjusted until the system's attenuation ratio under disturbance reaches a certain value. to Within the specified range, the calibrated parameters are stored in the controller memory as a baseline for automated operation. This fine potential control, in conjunction with the pulsed gas thermal coupling cycle mode, forces the preferential dissolution of high surface energy fine crystal nuclei, inducing the solute to grow epitaxially on the remaining crystal surface with low defects. In industrial operation, the arsenic content of sodium bicarbonate products is lower than [a certain value]. This gives the product the value of being returned to the smelting system or sold directly as an industrial-grade commodity.

[0029] To address the micro-kinetic challenges of mother liquor inclusion and fine crystal entrainment during crystallization, leading to substandard product purity, this embodiment further integrates a pulsed gas-thermal coupling circulation mode into the aforementioned gradient carbonization crystallization step. This mode abandons the traditional continuous steady-state gas flow method, instead implementing alternating pressurization nucleation and thermal dissolution cleaning stages through process control. In the pressurization nucleation stage, carbon dioxide-containing gas is introduced at a relatively high rate of 0.5 L / min to 0.8 L / min to rapidly build supersaturation and induce sodium bicarbonate precipitation. The system automatically switches to the thermal dissolution cleaning stage, cutting off the gas supply and using the reactor jacket heating to rapidly raise the system temperature by 2°C to 4°C and maintain it for 5 to 10 minutes. This minute temperature fluctuation utilizes the Kelvin effect, where the solubility of small particles is higher than that of large particles, to drive... The fine crystal nuclei with high surface energy and the growth layer with lattice defects preferentially dissolve, releasing the physically trapped arsenic-containing mother liquor. During the next cycle's pressurized nucleation stage, the aeration rate is reduced from 0.2 L / min / L solution to 0.4 L / min / L solution, inducing epitaxial growth of the solute on the remaining clean crystal surface. This cycle continues until the system pH drops to the endpoint range, achieving in-situ purification and dense crystal growth at the microscopic level. To avoid the lag and control blind spots inherent in traditional pH endpoint determination in complex high-salt systems, which can easily lead to reaction overshoot and impurity co-precipitation, this embodiment introduces a conductivity change rate locking mechanism as the basis for determining the crystallization endpoint. This mechanism utilizes the sensitivity of conductivity to sudden changes in solution ionic strength and rheological properties, and a high-frequency data acquisition system is configured to record the conductivity data of the reaction system in real time. The central processing unit calculates the first and second derivatives of conductivity with respect to time in real time; the system presets a threshold constant to characterize abrupt changes in the rheological properties of the mother liquor. This constant, determined through prior calibration experiments, corresponds to the critical state at which impurity arsenates begin to colloidalize or undergo micronucleus explosions. During operation, when the first derivative of the conductivity is detected to be negative and the second derivative... Less than negative When the system reaches the critical point of impurity co-precipitation, the control system immediately triggers an interlock command to stop the introduction of carbon dioxide gas and terminate the crystallization reaction, regardless of whether the pH value of the system has reached the preset endpoint. This precisely cuts off the path of impurities into the solid phase at the kinetic level, ensuring batch stability of product quality.

[0030] The conductivity change rate locking mechanism in this scheme is based on the threshold constant of abrupt changes in the mother liquor rheological properties. Quantization acquisition, constant The endpoint determination is ensured through an offline calibration process. The calibration process is initiated under the same raw material liquid and process parameters as the production conditions, and conductivity data is collected in real time throughout the process. , synchronize every Liquid phase sampling was performed at 1 minute intervals, and the volume concentration of colloidal particles was determined using a nano-laser particle size analyzer; the rate of increase in colloidal particle volume concentration was observed ( Breakthrough of critical value (preferred) When this occurs, it is marked as the nucleation critical point. ;extract front and back Conductivity data within a minute is used to calculate the second derivative of conductivity using a sliding window algorithm. Record the maximum negative peak value of the second derivative within the time window. Threshold constant Set as to times This value is set before the impurity arsenate reaches a critical state of colloidalization or microcrystal explosion, allowing for a margin of safety for the control system. to A safety cutoff window of minutes is provided to achieve precise kinetic control. Addressing the environmental and cost issues of significant carbonate interference, high reagent consumption, and large slag volume associated with direct mineralization of arsenic-rich mother liquor, this implementation method employs an acidic desorption and self-pressurization coupling mode in the final mineralization step of the arsenic-rich mother liquor. This mode utilizes the acidic environment required for the mineralization reaction as a driving force, pumping the arsenic-rich mother liquor into a closed reactor and adding acidic mineralizing agents, such as ferric sulfate solution or acidic sulfuric acid solution, at a controlled rate. With the addition of the acidic reagent, the pH value of the system gradually decreases from 8.2 to 4.0 to 5.0, reducing the residual arsenic in the mother liquor. During this process, a large amount of bicarbonate ions are rapidly converted into carbon dioxide gas and escape from the liquid phase, resulting in an increase in pressure within the closed system. The high-concentration carbon dioxide gas that escapes is collected and purified, and then returned to the selective leaching step or gradient carbonization crystallization step at the front end for recycling, thus achieving closed-loop recovery of the carbon source. Once the pressure stabilizes, indicating that the carbon dioxide desorption is complete, the system has naturally transformed into an acidic environment with a low carbonate concentration. At this point, the temperature is further increased to 80 to 90 degrees Celsius and the pH value is adjusted to 1.0 to 2.0 to induce arsenic and iron to combine and form a stable arsenic precipitate.

[0031] Example 1: In a technical upgrade project for the resource utilization of arsenic-alkali slag with an annual processing capacity of 5,000 tons, the treated object is long-stored waste slag with arsenic content fluctuating between 15 g / L and 45 g / L, accompanied by high concentrations of low-valence sulfides and organic flotation reagent residues. Simultaneously, the project directly utilizes the purified flue gas emitted from the smelting furnace as a carbonization gas source. The residual sulfur dioxide and carbon monoxide reducing components in this flue gas, during long-term reactions, pose a risk of arsenic reversion and co-precipitation of impurities in the crystallization system. The system initiates selective leaching and antimony separation units, mixing the waste slag with water at a liquid-to-solid ratio of 4:1. An online feedback loop controls the flue gas flow rate and maintains the pH value of the leaching system. The pH is set at 9.8. This weakly alkaline window is used to suppress the co-hydrolysis of arsenate and to preferentially precipitate antimony in the form of oxides. The arsenic-containing alkaline filtrate enters the gradient carbonization crystallization unit under the control of redox potential. In response to the trend that the redox potential (ORP) of the solution drops from the initial +350 mV to +280 mV due to the accumulation of reducing components in the flue gas, the gas-phase associated redox buffer mechanism is triggered. The control system adjusts the gas ratio of the static mixer to increase the oxygen volume fraction in the mixed gas to 4.5%, and forcibly controls the redox potential at the gas-liquid interface above +320 mV, thus building a chemical barrier to counteract the reduction effect of sulfur dioxide and maintain the pentavalent form of arsenic in the solution.

[0032] While maintaining a high-potential environment, the process employs a pulsed gas-thermal coupling circulation mode to interrupt the continuous crystal growth process. In a single cycle, the system is aerated for 12 minutes at a rate of 0.6 liters per minute per liter of solution to induce nucleation. The gas source is then cut off, and the temperature of the reactor is raised by 3 degrees Celsius within 3 minutes using jacket steam and maintained for 8 minutes. The Kelvin effect is used to drive the preferential dissolution of high surface energy microcrystal nuclei and defect layers, releasing the encapsulated arsenic-rich mother liquor. The temperature is then lowered, and aeration is resumed at a low flow rate of 0.3 liters per minute per liter of solution to induce epitaxial growth of the solute on the remaining crystal surface. The second derivative of conductivity lock-in mechanism detects abrupt changes in the rheological properties of the solution and cuts off the reaction. The final sodium bicarbonate product, after low-temperature rinsing, has an arsenic content controlled below 3.5 ppm, an antimony content below 1 ppm, and an average crystal particle size D50 of 185 micrometers.

[0033] Example 2: This example simulates the separation efficiency and engineering stability under complex real industrial conditions. The experimental platform was built on a dual-channel parallel reactor group equipped with a precision process control system, which was set as the control group and the experimental group respectively. The raw material liquid used in the experiment was taken from the actual production filtrate of the arsenic-alkali slag water leaching workshop of a smelter. In order to simulate the interference of real smelting flue gas fluctuations on the process, sulfur dioxide gas with a volume concentration randomly fluctuating between 0.1% and 0.3% and carbon monoxide gas with a volume concentration of 0.05% were artificially introduced at the gas source input end through a dynamic gas proportioner to construct an engineering reality test environment with strong reducing background noise. The sodium carbonate concentration in the raw material filtrate was 138.5 g / L and the total arsenic concentration was 28.4 g / L, of which trivalent arsenic accounted for about 18.5%.

[0034] The control group used a conventional carbonization crystallization process, in which the simulated flue gas containing impurities was directly passed into the filtrate, with the aeration rate controlled at a constant 0.5 L / min / L solution. The reaction temperature was maintained at room temperature, and the reaction endpoint was set when the pH value naturally dropped to 8.4. No artificial intervention in the redox potential or periodic adjustment of the temperature gradient was performed throughout the process. The experimental group strictly followed the combined process based on phase equilibrium control of this invention. In the oxidation-locking stage, based on the detected value of trivalent arsenic in the raw material solution, 1.2 times the theoretical amount of hydrogen peroxide was added to the system. Monitoring with an online redox potentiometer showed that the initial potential (ORP) rapidly increased and stabilized at +380 mV, establishing the pentavalent dominant form of arsenic. The process then entered the gradient carbonization and pulse crystal growth stage. The control system mixed high-purity oxygen into the simulated flue gas. The oxygen partial pressure of the mixed gas was maintained at around 4.5%. During the reaction, despite the presence of reducing disturbances such as sulfur dioxide in the input gas source, the ORP feedback loop successfully clamped the potential of the reaction system above the safe threshold of +320 mV by dynamically adjusting the oxygen injection amount. This effectively shielded the reducing atmosphere from corroding the arsenic valence state. At the same time, a pulsed gas-thermal coupling cycle mode was executed, with the gas flow rate during the pressurization and nucleation period set at 0.7 L / min / L solution for 12 minutes. Then, the hot dissolution and cleaning period began. The gas source was cut off, and the temperature inside the vessel was raised by 3 degrees Celsius within 3 minutes and maintained for 6 minutes using the jacket temperature control system. This unsteady temperature difference was used to drive the dissolution of high surface energy impurity-containing microcrystals. Afterward, the temperature was lowered to restore the vessel and the solution flow rate was reduced to 0.3 L / min / L solution to enter the healing and growth period.

[0035] To determine the crystallization endpoint, the experimental group employed a second derivative locking mechanism for conductivity, with the data acquisition system recording the solution conductivity at a frequency of 1 Hz. Data shows that as the reaction proceeds, the conductivity exhibits a non-linear decreasing trend. When the reaction reaches 210 minutes, although the pH reading still hovers around 8.5, the calculation module captures the second derivative of the conductivity. The amplitude suddenly exceeds the preset threshold. The negative peak, a mathematical feature, characterizes the critical abrupt change in the rheological properties of the mother liquor due to local supersaturation of impurities. Based on this, the system triggers a termination command to cut off any subsequent possible avalanche co-precipitation of impurities. After the reaction, the two groups of products are filtered, washed and dried, and the crystal particle size distribution and chemical composition are tested by laser particle size analyzer and chemical titration, respectively. The comparison of key process data and final product indicators is shown in Table 1.

[0036] Table 1: Data from Process Comparison Tests

[0037]

[0038] Data analysis shows that in the control group, due to the lack of potential protection, the reducing components in the flue gas caused the reaction endpoint ORP value to drop sharply to +145mV, inducing some pentavalent arsenic to be reduced to trivalent arsenic and enter the crystal lattice, resulting in an arsenic content of up to 156.0ppm in the product. Moreover, the uncontrolled explosive nucleation resulted in small crystals (58μm) and severe entrainment. In contrast, although the sodium bicarbonate yield in the experimental group was slightly reduced, sacrificing some supersaturation for purity, the arsenic content in the product was reduced to 2.8ppm, a reduction of more than 98%, the crystal particle size increased to 192μm, and the filter cake moisture content was only 5.5%. This confirms that the redox potential clamping and pulsed gas thermal coupling mechanism have a decisive synergistic effect on blocking arsenic impurity migration and improving crystal growth quality under complex interference conditions, and the conductivity second derivative locking mechanism avoids the quality risk caused by reaction overshoot.

[0039] Example 3: This example combines Figures 1 to 3 This describes a method for the harmless treatment and valuable metal recovery of arsenic-alkali slag, such as... Figure 1 As shown, the process proceeds to the selective leaching and antimony separation steps. In this step, the pH value is maintained between 9.5 and 10.2 by controlling the solubility product difference. After solid-liquid separation, antimony concentrate in the form of oxide or hydroxide precipitates and arsenic-containing alkaline filtrate are obtained. The filtrate enters the gradient carbonization crystallization step under the redox potential clamping. In this step, under the potential regulation of the gas-phase accompanied redox buffer mechanism, oxygen-containing mixed gas and real-time ORP monitoring are used to ensure ORP > 300mV. At the same time, pulsed gas thermal coupling cycle and salting-out effect are combined, and the endpoint is determined according to the second derivative mutation criterion in the conductivity change rate locking mechanism. Thus, high-purity sodium bicarbonate product in crystalline form is precipitated and arsenic-rich mother liquor is filtered and separated. Finally, after adding acidic mineralizing agent, the arsenic-rich mother liquor enters the arsenic-rich mother liquor terminal mineralization step. Through acidic desorption and self-pressurization coupling and arsenic-containing mineral conversion mechanism, harmless solidified arsenic-containing mineral precipitates are generated. The gas generated during the reaction escapes to the carbon dioxide circulation unit and is returned to the front end for recycling as a self-pressurized desorption gas source.

[0040] like Figure 2 As shown, the horizontal axis represents pH value, and the vertical axis represents percentage. The graph contains two curves. The solid curve represents the antimony precipitation rate, showing that as the pH value increases from 9 to 10.4, the antimony precipitation rate exhibits a parabolic shape, first increasing and then decreasing, reaching a peak near pH 9.8. The dashed curve represents the arsenic residue rate, showing that arsenic is mainly retained in the solution phase throughout the entire testing range. The difference in the forms of the two substances within a specific pH range constitutes the thermodynamic basis for selective separation using differences in solubility products. Figure 3 As shown, the system architecture includes three core reaction stations and a through-flowing network. The gas resource circulation loop consists of a leaching reaction station equipped with an online pH probe and a stirring and mixing machine, which executes pH window locking and solubility product difference calculation logic, and issues adjustment commands through aeration rate feedback. The crystallization reaction station is equipped with potential and conductivity sensors and a gas-liquid mixing vessel, and adopts a dual-locking core logic including a potential-clamped PID algorithm and a conductivity mutation judgment model. It uses multi-dimensional feedback control of pulse gas thermal coupling actuators to adjust the gas path ratio and achieve rapid temperature control. The mineralization reaction station is equipped with a pressure-resistant reactor and a recovery booster pump, which executes desorption and solidification deployment logic, and achieves pressure linkage through acid self-pressurization monitoring and gas recovery start / stop. Each station completes the resource closed loop through physical and data links.

[0041] Example 4: This example focuses on key process control parameters involved in the gradient carbonization crystallization step under redox potential clamping, particularly the abrupt change criterion of the second derivative of conductivity. The established procedures and dynamic response logic of the oxidation-reduction potential (ORP) were systematically calibrated and verified to eliminate the parameter black box in process control and ensure the reproducibility of the process under different raw material fluctuations. During the start-up phase of industrial-scale trial operation, a standardized offline calibration procedure was executed to determine the threshold constant characterizing abrupt changes in the rheological properties of the mother liquor. The procedure was carried out in a test vessel of the same specifications as the production line. The raw material liquid maintained the same compositional baseline as in Example 2, i.e., a total arsenic concentration of 28.4 g / L. During the calibration process, the control system continuously collected the conductivity of the reaction system at a frequency of 1 Hz. Simultaneously, offline sampling was performed every 5 minutes. Atomic fluorescence spectrometry was used to rapidly determine the concentration change of colloidal arsenic in the liquid phase, and the evolution curve of arsenic concentration over time was plotted. Data correlation analysis showed that in the later stage of the reaction, when a large amount of sodium bicarbonate precipitated, the number of fine crystal nuclei in the liquid phase increased exponentially, causing nonlinear shifts in the specific surface area and viscosity of the system. When offline detection showed that arsenate in the liquid phase began to undergo a phase transition from the dissolved state to the colloidal phase, and the colloidal rate of arsenic exceeded the inflection point of 0.1%, the second derivative of conductivity was calculated in real time. It exhibits a negative peak characteristic; at the 205th minute of the calibration experiment, the colloidal arsenic concentration surged, and the corresponding second derivative of conductivity dropped sharply from a steady-state value of -0.05 mSiemens per centimeter per square minute to -0.52 mSiemens per centimeter per square minute. Based on this physical correlation, the threshold constant was... The setting is 0.45 millisiemens per centimeter per square minute. This setting can trigger feedback at the early stage of impurity phase change, leaving a safe cutoff window of about 3 to 5 minutes for the system.

[0042] After establishing the endpoint criterion, this embodiment constructs a closed-loop control model based on the deviation proportional-integral-derivative PID algorithm to address the potential disturbances caused by intake air composition fluctuations, targeting the execution logic of the gas-phase associated redox buffer mechanism. This control loop uses the real-time potential value acquired by the online ORP probe as the feedback signal. The target value is set at 320 millivolts. When a sudden increase in sulfur dioxide concentration in flue gas was detected, it caused Value lower than When the dead zone exceeds 5 mV, the controller calculates the required oxygen compensation based on the preset response gain and drives the mass flow controller (MFC) to dynamically adjust the opening of the high-purity oxygen branch. During a continuous 4-hour test, despite artificial high-frequency disturbances to the sulfur dioxide concentration in the inlet flue gas between 0.1% and 0.3%, the closed-loop control logic successfully limited the ORP fluctuation range within the reaction system to a narrow band of +315 mV to +330 mV, effectively preventing arsenic reversion due to excessively low potential and unnecessary oxidant consumption due to excessively high potential. Finally, the calibrated threshold constant is... When the ORP control logic is applied to continuous production, the treated arsenic-rich mother liquor is sampled and analyzed. The results show that the residual sodium bicarbonate supersaturation in the mother liquor is precisely controlled at the edge of the metastable region. This ensures the crystallization yield of the main product and avoids arsenate co-precipitation caused by uncontrolled supersaturation. The sodium bicarbonate crystals produced by this fine control have reduced the arsenic content between crystals to 2.1 ppm without excessive washing. This further verifies the decisive role of the control parameters determined by the quantitative calibration procedure in suppressing impurity migration.

[0043] Example 5: This example details the criterion for abrupt changes in the second derivative of conductivity. This standardized offline calibration procedure aims to eliminate control black boxes caused by raw material fluctuations and ensure that the production line has a consistent process judgment benchmark when processing different batches of arsenic-containing waste residue. Before formal production commences or when the total arsenic concentration in the raw material fluctuates by more than ±10% of the design value, this calibration procedure is executed. A simulated raw material solution of the same concentration as the production line is prepared in a laboratory-scale reactor, and a carbonization reaction is carried out according to the aforementioned process parameters. Conductivity data is continuously collected using an online conductivity meter at a frequency of 1 Hz. Simultaneously, liquid phase samples were extracted every 5 minutes, and the volume concentration of colloidal particles in the liquid phase was measured using a nanolaser particle size analyzer. When an exponential increase in the volume concentration of colloidal particles was detected, and the growth rate exceeded the inflection point of 0.01% per minute, that moment was marked as the nucleation critical point. .

[0044] extract Conductivity data within 10 minutes before and after a given time point were used to calculate the second derivative using a sliding window algorithm. Calculate the maximum negative peak value of the second derivative within this time window. and the threshold constant Set as The selection of this setting value is based on the principle that it can effectively capture the rheological abrupt change signal in the early stage of nucleation, while avoiding misjudgment of random noise caused by early bubble disturbance. Finally, the calibrated value is... The value is input into the central control unit of the production line as the basis for determining the end point of processing for that batch of raw materials.

[0045] Example 6: This example details the PID control parameter tuning procedure for dynamically adjusting the oxygen compensation amount in a gas-phase associated redox buffer mechanism. This tuning procedure is executed when the system is initially deployed or when the raw material characteristics change to determine the proportional gain suitable for the current operating conditions. Integral Time and differential time The system was set to manual control mode, maintaining a constant reaction temperature and carbon dioxide injection rate. A certain amount of interfering sulfur dioxide gas was introduced into the system, and the redox potential was recorded. The step response characteristics of the object are obtained by using the curve of the response over time, and the process gain of the system is calculated based on the response curve. Time constant and pure delay time .

[0046] Calculate the initial values ​​of the PID parameters using the Ziegler-Nichols closed-loop tuning method or the Cohen-Coon open-loop tuning method. Switch to automatic control mode, input the calculated initial PID values, and artificially introduce a step disturbance of 5% of the setpoint. Observe the system's transient response curve. If the overshoot exceeds 10%, appropriately reduce the setpoint. or increase If the response adjustment time is too long, increase it appropriately. or reduce If the system experiences sustained oscillations, the value will be significantly reduced. and increase Repeat the above disturbance and adjustment process until the system's attenuation ratio under a step disturbance reaches the range of 4:1 to 10:1. This is then determined as the final operating parameter. , and The parameters are stored in the controller's non-volatile memory and used as reference parameters for subsequent automated operation.

[0047] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for harmless treatment and valuable metal recovery of arsenic alkali residue, characterized by, The method comprises the following steps: The selective leaching and antimony separation step is to mix the arsenic alkali residue with water and introduce carbon dioxide gas, control the pH value of the leaching system to be maintained at 9.5 to 10.2, use the difference in the solubility product of the oxide or hydroxide of antimony and the soluble arsenate under the pH window to convert the antimony component in the residue into a precipitate to be separated out, and filter to separate antimony concentrate and arsenic-containing alkali filtrate; The gradient carbonation crystallization step under the redox potential clamping is to add an oxidizing agent to the arsenic-containing alkali filtrate, raise the redox potential of the filtrate to above 300 mV and establish a high-potential dissolution equilibrium state; under the constraint condition that the redox potential is not lower than 300 mV, control the temperature of the filtrate to be 20 to 35 DEG C, introduce carbon dioxide gas until the pH value is reduced to 8.2 to 8.6, convert sodium carbonate into sodium bicarbonate crystals to be separated out, use the salting-out effect of pentavalent arsenic in the saturated sodium bicarbonate solution to retain it in the liquid phase, and filter to obtain sodium bicarbonate products and arsenic-rich mother liquor; The terminal mineralization step of the arsenic-rich mother liquor is to add a mineralizing agent to the arsenic-rich mother liquor to generate an arsenic-containing mineral precipitate under acidic conditions.

2. A method for harmless treatment and valuable metal recovery from arsenic alkali residue according to claim 1, characterized in that, In the gradient carbonation crystallization step under the redox potential clamping, the operation of introducing carbon dioxide gas is performed in a pulse gas-heat coupled circulation mode; the pulse gas-heat coupled circulation mode comprises an alternating pressurization nucleation stage and a hot solution cleaning stage; in the pressurization nucleation stage, carbon dioxide gas is introduced to induce sodium bicarbonate to be separated out; in the hot solution cleaning stage, the introduction of carbon dioxide gas is stopped, the temperature of the system is raised by 2 to 4 DEG C and maintained for 5 to 10 minutes, the fine crystal nucleus and the crystal defect layer with high surface energy are preferentially dissolved by using the temperature difference to release the arsenic-containing mother liquor wrapped by the crystal, and enter the pressurization nucleation stage of the next cycle.

3. A method for harmless treatment and valuable metal recovery from arsenic alkali residue according to claim 1, characterized in that, In the gradient carbonation crystallization step under the redox potential clamping, a gas-phase accompanying redox buffer mechanism is adopted to maintain the redox potential; The gas-phase accompanying redox buffer mechanism comprises the following steps: pre-mixing carbon dioxide gas and oxygen-containing gas to maintain the oxygen volume fraction in the mixed gas at 3 to 5 percent; while introducing the mixed gas to perform carbonation reaction, the redox potential of the system is monitored in real time; when the redox potential is lower than 300 mV, the mixing proportion of the oxygen-containing gas is increased or an oxidizing agent is supplemented to the system to clamp the redox potential of the system to be above 300 mV.

4. A method for harmless treatment and valuable metal recovery from arsenic alkali residue according to claim 1, characterized in that, In the gradient carbonation crystallization step under the redox potential clamping, a conductivity change rate locking mechanism is introduced as the basis for judging the crystallization end point; The conductivity change rate locking mechanism comprises: collecting conductivity data of the reaction system in real time , and calculating the first and second order derivatives of the conductivity with respect to time; when the first order derivative of the conductivity is negative and the second order derivative satisfies the following mutation criterion: , wherein, is a preset threshold constant representing the rheological property mutation of the mother liquor; it is determined that the system reaches the impurity coprecipitation critical point, and the carbon dioxide containing gas is immediately stopped from being introduced and the crystallization reaction is terminated, regardless of whether the pH value of the system at this time reaches the preset end point.

5. The method for harmless treatment and valuable metal recovery from arsenic alkali residue according to claim 1, characterized in that, In the terminal mineralization step of the arsenic-rich mother liquor, an acid desorption and self-pressurization coupled mode is adopted; The acid desorption and self-pressurization coupled mode comprises the following steps: adding an acidic mineralizing agent to a closed reaction system, and converting the residual bicarbonate in the arsenic-rich mother liquor into carbon dioxide gas to be released by using the change in acidity. The escaped carbon dioxide gas is collected and recycled to the selective leaching and antimony separation step or the gradient carbonation crystallization step under the redox potential clamping; after the complete desorption of carbon dioxide, the temperature and pH value of the system are controlled in a low carbonate concentration environment to induce the precipitation of arsenate.

6. A method for harmless treatment and valuable metal recovery from arsenic alkali residue according to claim 1, characterized in that, In the selective leaching and antimony separation step, the aeration rate of the carbon dioxide-containing gas is controlled at 0.1 liters per minute per liter of slurry to 0.3 liters per minute per liter of slurry, and the liquid-solid ratio of the agitation leaching is controlled at 3:1 to 5:

1.

7. The method for harmless treatment and valuable metal recovery from arsenic alkali residue according to claim 1, characterized in that, In the gradient carbonation crystallization step under the redox potential clamping, at least one of hydrogen peroxide, ozone or potassium permanganate is selected as the oxidizing agent; before the addition of the oxidizing agent, the ratio of trivalent arsenic to pentavalent arsenic in the arsenic-containing alkaline filtrate is detected, and the theoretical addition amount of the oxidizing agent is calculated according to the detection result, and the actual addition amount is 1.1 times to 1.3 times of the theoretical addition amount.

8. A method for harmless treatment and valuable metal recovery from arsenic alkali residue according to claim 2, characterized in that, The pulse gas-heat coupling cycle mode is executed until the pH value of the system is reduced to 8.2 to 8.6; in the pressurization nucleation stage, the aeration rate of the carbon dioxide-containing gas is 0.5 liters per minute per liter of solution to 0.8 liters per minute per liter of solution; in the next cycle of the pressurization nucleation stage after the heat-solution cleaning stage, the aeration rate of the carbon dioxide-containing gas is reduced to 0.2 liters per minute per liter of solution to 0.4 liters per minute per liter of solution to induce the epitaxial growth of sodium bicarbonate on the surface of the retained crystals.

9. The method for harmless treatment and valuable metal recovery from arsenic alkali residue according to claim 5, characterized in that, The acidic mineralizer is a ferric sulfate solution or an acidic sulfuric acid solution, and the acid desorption and self-pressurization coupling mode specifically includes: controlling the addition rate of the acidic mineralizer to gradually reduce the pH value of the system from 8.2 to 4.0 to 5.0 to desorb carbon dioxide; after the pressure in the kettle no longer rises, the temperature is continued to be raised to 80 degrees Celsius to 90 degrees Celsius and the pH value is adjusted to 1.0 to 2.0 to precipitate arsenic in the form of scorodite.

10. The method for harmless treatment and valuable metal recovery from arsenic alkali residue according to claim 1, characterized in that, After the sodium bicarbonate product is filtered and separated, low-temperature saturated sodium bicarbonate solution is used for leaching, and the temperature of the leaching liquid is controlled at 5 degrees Celsius to 10 degrees Celsius to remove residual mother liquor on the surface of the crystals and prevent the dissolution loss of the crystals.

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