System and method for extracting high-purity potassium salt by using cement bypass ash

Abstract

The invention relates to the technical field of industrial solid waste resource utilization, in particular to a system for extracting high-purity sylvite by utilizing cement bypass ash, which comprises a magnetic separation module for separating Fe3O4 magnetic phase in the bypass ash under a 0.8-1.2 T gradient magnetic field, a dynamic activation module for performing two-stage calcination under the assistance of NH4Cl, and a high-purity sylvite extraction module for extracting high-purity sylvite by utilizing cement bypass ash. The countercurrent leaching module is used for realizing hydrochloric acid-ammonium fluoride synergistic leaching through a three-stage series reactor under the condition that the pH value is 0.5-2.5; the ion screening module comprises a bipolar membrane electrodialysis unit and a Li < + > type K-LTL molecular sieve adsorption tower; the crystal phase regulation and control module is used for feeding back the supersaturation degree in real time through the conductivity and preparing a potassium salt crystal with the Cl <-> content smaller than or equal to 0.1%; and a cyclic regeneration module. According to the scheme, the potassium salt can be directly packaged after being purified and then enters the market to be sold, the remaining bypass ash is continuously recycled to prepare cement, compared with a traditional process, the comprehensive cost is reduced by 35% or above, and an integrated solution of efficient potassium extraction, high-purity separation and zero waste circulation is provided for solid waste in the cement industry.

Description

Technical Field

[0001] The present invention relates to the technical field of resource utilization of industrial solid waste, and particularly to a system and method for extracting high-purity potassium salts by using cement bypass ash. Background Art

[0002] In the production of cement enterprises, low-quality cement production raw materials, fuels, and solid waste are fully utilized to replace high-quality raw materials and coal, gradually reducing the mining of mines. However, inferior raw materials and fuels have a certain impact on the normal operation of cement kilns. Especially, raw materials and fuels with high chlorine, alkali, and sulfur contents, such as domestic waste, incineration bypass ash, and rectification residues, etc., after entering the cement kiln, cause the cyclic enrichment of chlorine elements in the system, resulting in the crusting and blockage of the cement kiln system, thus affecting the normal operation of the system and the quality of clinker. To improve the operation efficiency of the cement kiln system and solve the problem of cyclic enrichment of volatile substances such as chlorine, potassium, sodium, and sulfur in cement raw materials and fuels in the cement kiln, the cement kiln is provided with a bypass air release facility to discharge them in the form of bypass ash from the cement kiln system.

[0003] Bypass air release is to extract and release part of the gas from the harmful element enrichment point of the cement kiln, thereby destroying the cycle of chlorine elements in the system and reducing the risk of crusting in the system, which can effectively improve the operation rate of the kiln system. Therefore, for cement plants co-disposing of high-chlorine waste, the bypass air release system is a very important supporting facility. Currently, many domestic cement plants co-disposing of solid waste have set up bypass air release systems. The bypass air release system can effectively reduce the problem of cyclic enrichment of aluminum elements in the cement kiln system. However, the bypass ash collected by the bypass air release system has the characteristics of high chlorine content, high potassium content, fine particle size, and light density. Now, the safe disposal problem of bypass ash has become a new problem restricting the utilization rate of "alternative fuels" in cement kilns.

[0004] The invention patent with the application number 201510804238.4 discloses a method for using the dust collected from the bypass air release of a rotary kiln, belonging to the technical field of resource treatment of industrial solid waste and also belonging to the potassium salt production technology; using primary industrial water at 60 - 95 °C and mixing and stirring it with the dust collected from the bypass air release of the rotary kiln for leaching under the condition that the solid-liquid mass ratio is 1 / 2 - 1 / 5. The bypass air release dust after solid-liquid separation is dried and pulverized and then returned to the cement production system. The solution after solid-liquid separation is crystallized to produce potassium chloride and potassium sulfate products through evaporation and concentration, calcium removal, pH value adjustment, and membrane filtration separation, and a by-product of precipitated calcium carbonate product is produced.

[0005] There are still problems in the prior art such as low leaching rate, difficult separation, and poor crystallization purity. Summary of the Invention

[0006] The present invention provides a system and method for extracting high-purity potassium salts by using cement bypass ash, which can solve the problem of low leaching rate of potassium salts.

[0007] To solve the above technical problems, the present application provides the following technical solutions: 1. A system for extracting high-purity potassium salts from cement bypass ash, comprising:

[0008] A magnetic separation module: used to separate the Fe3O4 magnetic phase in the bypass ash under a gradient magnetic field of 0.8 - 1.2 T, reducing the Fe2O3 content to ≤1.5 wt%;

[0009] A dynamic activation module: used for two-stage calcination assisted by NH4Cl to decompose the potassium feldspar with a decomposition rate ≥85%, generating activated ash with a specific surface area ≥18 m 2 / g;

[0010] A countercurrent leaching module: used to achieve the synergistic leaching of hydrochloric acid - ammonium fluoride through a three-stage series reactor under the condition of pH 0.5 - 2.5;

[0011] An ion sieving module: including a bipolar membrane electrodialysis unit and a Li + type K-LTL molecular sieve adsorption tower, selectively separating K + / Na + to 50:1 or more;

[0012] A crystal phase regulation module: used to prepare potassium salt crystals with a Cl - content ≤0.1% by real-time feedback of supersaturation through conductivity, combined with 28 kHz pulsed ultrasonic waves and KCl crystal seeds with preferred crystal plane orientation;

[0013] A recycling and regeneration module: used to return the leaching residue mixed with 3 wt% CaF2 to the cement kiln, the crystallization mother liquor is recycled through a nanofiltration membrane (recycled ≥5 times), and the tail gas absorption liquid is electrolyzed to generate sodium hypochlorite.

[0014] The basic principle and beneficial effects of this solution:

[0015] The present invention provides a high-value utilization system and method for cement bypass ash based on multi-module cooperation. Through gradient magnetic separation to accurately remove Fe3O4 (Fe2O3 ≤ 1.5 wt%), NH4Cl-assisted two-stage calcination activation (potassium feldspar decomposition rate ≥ 85%), hydrochloric acid - ammonium fluoride synergistic countercurrent leaching (potassium leaching rate ≥ 92%), bipolar membrane - molecular sieve combined ion sieving (K + / Na + separation ratio ≥ 50:1), ultrasonic - crystal seed coupling crystallization regulation (Cl - ≤0.1%) and full-process recycling of by-products (leaching residue activity index ≥ 80%, mother liquor reuse ≥ 5 times), the breakthroughs in potassium salt extraction rate, purity (≥99.3%) and resource utilization rate are achieved simultaneously. Compared with the traditional process, the comprehensive cost is reduced by more than 35%, providing an integrated solution of "efficient potassium extraction - high-purity separation - zero-waste recycling" for the solid waste in the cement industry.

[0016] Further, the magnetic field intensity of the magnetic separation module is set in three-stage gradients of 0.8 T, 1.0 T, and 1.2 T;

[0017] The calcined product of the dynamic activation module is detected by XRD, showing that the intensity of the kaliophilite characteristic peak at 2θ = 28.5° is reduced by 82 - 87%, and the half-peak width of the new KCl characteristic peak at 2θ = 31.3° ≤ 0.18°.

[0018] Further, the countercurrent leaching module includes:

[0019] Primary leaching unit: The reaction temperature is 80 - 90 °C, the liquid-solid ratio is 8:1, and ultrasonic assistance is used;

[0020] Secondary strengthening unit: Add 0.05 - 0.1 wt% sodium dodecyl sulfonate as a surfactant;

[0021] Tertiary washing unit: The washing water is recycled to prepare the primary leaching agent.

[0022] Further, the ion sieving module:

[0023] The bipolar membrane electrodialysis unit simultaneously generates a 0.5 - 1.0 mol / L NaOH solution for reuse in pH adjustment;

[0024] Li + type K-LTL molecular sieve has an adsorption capacity for Na + ≥ 2.5 mmol / g and a regeneration efficiency ≥ 95%.

[0025] Further, the crystal phase regulation module:

[0026] The supersaturation is calculated in real time through the conductivity-concentration calibration curve, and the control accuracy is ±5%;

[0027] The crystal seed addition amount is 0.1 - 0.5% of the solution mass, and the crystal roundness ≥ 0.85.

[0028] A method for extracting high-purity potassium salts from cement bypass dust, comprising the following steps:

[0029] Step 1: Magnetic separation-activation pretreatment: Place the bypass dust in a 0.8 - 1.2 T gradient magnetic field to separate Fe3O4, and reduce the Fe2O3 content to ≤ 1.5 wt%;

[0030] Mix the magnetic separation ash with 1.5 wt% NH4Cl, and under the conditions of an O2 concentration of 30% and a flow rate of 5 L / min:

[0031] In the first stage, calcine at 600 °C for 30 minutes, and the kaliophilite decomposes into KCl and Al2O3;

[0032] In the second stage, CO2 is introduced at 400 °C and calcined for 60 minutes to generate surface carbonate active sites;

[0033] Step 2: Three-stage countercurrent leaching

[0034] First-stage leaching: Use 4 mol / L hydrochloric acid and leach by ultrasonic wave at 80 °C (40 kHz, 0.5 W / cm 3 ) for 40 minutes;

[0035] Second-stage enhancement: Add 0.1 mol / L ammonium fluoride and 0.1 wt% sodium dodecyl sulfate, and continue leaching for 20 minutes;

[0036] Third-stage washing: Rinse the leaching residue with pure water in a countercurrent manner, and the washing liquid is recycled to the first-stage leaching;

[0037] Step 3: Ion-targeted purification

[0038] Add 5 - 10 g / L sodium thiosulfate to the leaching solution to precipitate heavy metal ions Cu 2+ 、Pb 2+ ;

[0039] Remove ≥90% Na + ;

[0040] Use Li + type K-LTL molecular sieve to adsorb residual Na + , and the purity of K + after adsorption is ≥99.3%;

[0041] Step 4: Dynamic crystallization control

[0042] Concentrate the purified liquid to a potassium ion concentration of 150 ± 5 g / L, and add KCl crystal seeds on the crystal surface when the supersaturation reaches 130%;

[0043] Cool to 30 °C at 1 °C / min, start the temperature oscillation program of ±5 °C / 10 min, and apply 28 kHz ultrasonic wave synchronously;

[0044] Step 5: Closed-loop recycling

[0045] The leaching residue is mixed with 3 wt% CaF2 and then returned to the cement kiln, and the 28-day activity index is ≥80%;

[0046] The crystallization mother liquor is recycled through the nanofiltration membrane 5 - 8 times;

[0047] The tail gas absorption liquid is electrolyzed to generate sodium hypochlorite with an effective chlorine content of ≥5%.

[0048] Furthermore, the BET specific surface area of the activated ash in Step 1 reaches 18 - 22 m 2 / g, and the solubilization rate of potassium element is ≥90%;

[0049] The residual K2O content in the leaching residue in Step 2 is ≤ 0.5 wt%.

[0050] Further, in Step 3: For the bipolar membrane electrodialysis, the migration rate of Na + is ≥ 0.15 mol / (m 2 ·h);

[0051] The operating space velocity of the molecular sieve adsorption tower is 2 - 4 h -1 , and the breakthrough capacity of Na + is ≥ 2.2 mmol / g.

[0052] Further, in Step 4: The crystal seed particle size is 50 - 80 μm, and the addition amount is 0.3 wt%;

[0053] The final crystal Cl - content is ≤ 0.08%, and the particle size distribution span (D90 - D10) / D50 ≤ 0.7.

[0054] Further, in Step 5: The rejection rate of the nanofiltration membrane for organic substances is ≥ 95%; the current efficiency of electrolyzing sodium hypochlorite is ≥ 85%. Further, in Step 1, the bypass ash is pretreated by microwave before magnetic separation, and the pretreatment time is 5 - 15 minutes. Description of the Drawings

[0055] Figure 1 It is a step diagram of a method for extracting high-purity potassium salt using cement bypass ash. Detailed Description of the Specific Embodiments

[0056] The following is a further detailed description through specific embodiments:

[0057] Example 1 is as shown in the attached Figure 1 figure,

[0058] A system for extracting high-purity potassium salt using cement bypass ash, characterized by comprising:

[0059] Magnetic separation module: It is used to separate the Fe3O4 magnetic phase in the bypass ash under a gradient magnetic field of 0.8 - 1.2T, reducing the Fe2O3 content to ≤1.5wt%; based on the strong magnetism of Fe3O4 (saturation magnetization intensity ≥ 90emu / g), physical separation of the magnetic phase and non-magnetic phase is achieved through a gradient magnetic field (0.8 - 1.2T). The gradient magnetic field is designed by gradually increasing the magnetic field intensity (0.8T → 1.0T → 1.2T), and the Fe3O4 removal rate ≥ 90%; the calcined product of the dynamic activation module detected by XRD shows that the intensity of the kaliophilite characteristic peak (2θ = 28.5°) decreases by 82 - 87%, and the full width at half maximum of the new KCl characteristic peak (2θ = 31.3°) ≤ 0.18°. It selectively captures Fe3O4 particles of different particle sizes to avoid the residue of weakly magnetic impurities caused by a single magnetic field intensity. After magnetic separation, the Fe2O3 content is reduced to ≤1.5wt%, reducing the inhibitory effect of iron impurities on the subsequent acid leaching reaction, and at the same time retaining the chemical activity of potassium elements.

[0060] Dynamic activation module: It is used for two-stage calcination assisted by NH4Cl (the first stage is calcined at 600°C for 30 minutes, and the second stage is calcined by introducing CO2 at 400°C for 60 minutes, with a CO2 flow rate of 2L / min), so that the decomposition rate of kaliophilite ≥ 85%, and activated ash with a specific surface area ≥ 18m 2 / g is generated; chemical dissociation and surface activation of kaliophilite (KAlSiO4) are achieved through two-stage calcination assisted by NH4Cl.

[0061] The first stage (600°C): NH4Cl thermally decomposes to generate HCl gas (NH4Cl → NH3↑ + HCl↑), and HCl reacts with kaliophilite to form soluble KCl (KAlSiO4 + 4HCl → KCl + AlCl3 + SiO2 + 2H2O), destroying the aluminosilicate lattice structure.

[0062] The second stage (400°C CO2): CO2 reacts with the surface hydroxyl groups (-OH) of the activated ash to form carbonate active sites (-OH + CO2 → -OCOO - +H + ), enhancing the interfacial mass transfer efficiency of the subsequent leaching reaction.

[0063] Effect: The decomposition rate of kaliophilite ≥ 85%, the specific surface area ≥ 18m 2 / g, and the potassium leaching activity is increased by 2 - 3 times.

[0064] Countercurrent leaching module: It is used to achieve a potassium element leaching rate ≥ 92% under the condition of pH 0.5 - 2.5 through a three-stage series reactor (the first stage is 3 - 5mol / L hydrochloric acid, the second stage is 1 - 2mol / L hydrochloric acid + 0.1 - 0.3mol / L ammonium fluoride, and the third stage is countercurrent washing); the countercurrent leaching module includes:

[0065] Primary leaching unit: reaction temperature 80 - 90 °C, liquid-solid ratio 8:1, ultrasonic assistance (40 kHz, 0.3 - 0.5 W / cm 3 );

[0066] Secondary strengthening unit: adding 0.05 - 0.1 wt% sodium dodecyl sulfate as surfactant;

[0067] Tertiary washing unit: the washing water is recycled to the primary leaching agent preparation, and the potassium recovery rate is increased by 15 - 20%.

[0068] Adopt the synergistic dissolution mechanism of hydrochloric acid-ammonium fluoride composite leaching agent.

[0069] Function of hydrochloric acid: H + Attacks the aluminosilicate network, releasing encapsulated potassium (KAlSiO4 + 4H + →K + +Al 3+ +SiO2 + 2H2O).

[0070] Function of ammonium fluoride: F - Reacts with SiO2 to form soluble [SiF6] 2- (SiO2 + 6F - + 4H + →[SiF6] 2- + 2H2O), breaking the silica gel coating layer and releasing residual potassium.

[0071] Process optimization: Tertiary countercurrent leaching strengthens mass transfer through liquid-solid countercurrent contact (liquid-solid ratio 8:1) combined with ultrasonic cavitation effect (40 kHz), and the potassium leaching rate ≥ 92%.

[0072] Ion sieving module: includes a bipolar membrane electrodialysis unit (operating voltage 15 - 25 V) and a Li + type K-LTL molecular sieve adsorption tower (operating temperature 60 °C), configured to selectively separate K + / Na + to 50:1 or more; The ion sieving module:

[0073] The bipolar membrane electrodialysis unit simultaneously generates a 0.5 - 1.0 mol / L NaOH solution for reuse in pH adjustment;

[0074] Li + type K-LTL molecular sieve has an adsorption capacity for Na + ≥ 2.5 mmol / g and a regeneration efficiency ≥ 95%. Based on the ion selective separation mechanism of bipolar membrane electrodialysis and molecular sieve.

[0075] Bipolar membrane electrodialysis: Driven by an electric field (15 - 25 V), Na + has a faster migration rate than K+ It preferentially enters the cathode chamber through the cation exchange membrane, and simultaneously generates a NaOH solution (H2O → H + + + OH - , Na + + + OH - → NaOH).

[0076] Li + type K-LTL zeolite: The pore size of the zeolite (0.71 nm) matches the ionic radius of Li + ions (0.076 nm). Through the ion sieve effect, it selectively adsorbs Na + (Na + radius 0.095 nm > Li + ), while K + (radius 0.138 nm) cannot enter the pores due to its large size, achieving a K + / Na + separation ratio ≥ 50:1.

[0077] Crystal phase regulation module: It is used to feedback the supersaturation (120 - 150%) in real time through conductivity, combined with 28 kHz pulsed ultrasonic waves (power density 0.2 - 0.5 W / cm 3 ) and KCl crystal seeds with preferred orientation of the (200) crystal plane to prepare potassium salt crystals with a Cl - content ≤ 0.1% and D50 = 80 - 120 μm; Crystal directional growth based on crystallization kinetics and interfacial energy regulation.

[0078] Supersaturation feedback: The supersaturation of the solution (120 - 150%) is monitored in real time through the conductivity-concentration calibration curve to accurately control the crystal nucleation rate.

[0079] Ultrasonic intervention: 28 kHz pulsed ultrasonic waves (0.2 - 0.5 W / cm 3 ) produce a cavitation effect, break up the crystal nucleus aggregates, and inhibit secondary nucleation.

[0080] Crystal seed induction: Add KCl crystal seeds with preferred orientation of the (200) crystal plane, and use lattice matching to guide the K + directional deposition, reduce the inclusion of Cl - impurities, and the crystal Cl - content ≤ 0.1%.

[0081] The crystal phase regulation module described above:

[0082] The supersaturation is calculated in real time through the conductivity-concentration calibration curve, and the control accuracy is ±5%;

[0083] The crystal seed addition amount is 0.1 - 0.5% of the solution mass, and the crystal roundness ≥ 0.85 (detected by a Malvern particle size analyzer).

[0084] Recycling module: Used to return the leaching residue mixed with 3 wt% CaF2 to the cement kiln, the crystallization mother liquor is recycled ≥ 5 times through a nanofiltration membrane (retention molecular weight ≥ 200 Da), and the tail gas absorption liquid is electrolyzed to generate sodium hypochlorite. Design of the full-process resource utilization path for by-products.

[0085] Leaching residue: Mixed with 3 wt% CaF2 as a mineralizer to promote the mineralization of CaO and CO2 in the leaching residue to form CaCO3 (CaO + CO2 → CaCO3), and enhance its activity as a cement admixture (28-day activity index ≥ 80%).

[0086] Crystallization mother liquor: Remove organic matter and colloidal impurities through a nanofiltration membrane (retention molecular weight ≥ 200 Da), the mother liquor is recycled ≥ 5 times, and the potassium recovery rate remains ≥ 90%.

[0087] Tail gas absorption liquid: Electrolyze the absorption liquid containing Cl - (NaCl) to generate sodium hypochlorite (2NaCl + 2H2O → ClO - + H2↑ + 2NaOH), with the effective chlorine concentration ≥ 5%, realizing the resource utilization of waste gas.

[0088] It also relates to a method for extracting high-purity potassium salt from cement bypass dust, including the following steps:

[0089] Step 1: Magnetic separation-activation pretreatment: Place the bypass dust in a 0.8 - 1.2 T gradient magnetic field to separate Fe3O4, and reduce the Fe2O3 content to ≤ 1.5 wt%;

[0090] Mix the magnetic separation ash with 1.5 wt% NH4Cl, and under the conditions of an O2 concentration of 30% and a flow rate of 5 L / min:

[0091] In the first stage, calcine at 600 °C for 30 minutes, and the kaliophilite decomposes into KCl and Al2O3;

[0092] In the second stage, introduce CO2 and calcine at 400 °C for 60 minutes to generate surface carbonate active sites; the BET specific surface area of the activated ash in Step 1 reaches 18 - 22 m 2 / g, and the solubilization rate of potassium element ≥ 90% (detected by ICP-OES);

[0093] Step 2: Three-stage countercurrent leaching

[0094] First-stage leaching: Use 4 mol / L hydrochloric acid and leach by ultrasonic wave at 80 °C (40 kHz, 0.5 W / cm 3 ) for 40 minutes;

[0095] Second-stage strengthening: Add 0.1 mol / L ammonium fluoride and 0.1 wt% sodium dodecyl sulfate, and continue leaching for 20 minutes;

[0096] Tertiary washing: The leaching residue is rinsed countercurrently with pure water, and the washing liquid is recycled to the first-stage leaching; the residual K2O content in the leaching residue in Step 2 is ≤0.5 wt% (detected by XRF).

[0097] Step 3: Ion-targeted purification

[0098] Sodium thiosulfate at 5-10 g / L is added to the leaching solution to precipitate heavy metal ions (Cu 2+ , Pb 2+ );

[0099] ≥90% of Na is removed by bipolar membrane electrodialysis (at a voltage of 20 V). + ;

[0100] The residual Na is adsorbed by using Li + -type K-LTL molecular sieve, and the purity of K after adsorption is ≥99.3%; in Step 3: + + The migration rate of Na in bipolar membrane electrodialysis is ≥0.15 mol / (m

[0101] + ·h); 2

[0102] The operating space velocity of the molecular sieve adsorption tower is 2-4 h -1 , and the breakthrough capacity of Na + is ≥2.2 mmol / g.

[0103] Step 4: Dynamic crystallization control

[0104] The purified liquid is concentrated to a potassium ion concentration of 150±5 g / L, and when the supersaturation reaches 130%, KCl crystal seeds with (200) crystal planes are added;

[0105] It is cooled to 30 °C at a rate of 1 °C / min, and a temperature oscillation program of ±5 °C / 10 min is started, and 28 kHz ultrasonic waves are applied synchronously; in Step 4:

[0106] The particle size of the crystal seeds is 50-80 μm, and the addition amount is 0.3 wt%;

[0107] The final crystal Cl - content is ≤0.08% (by potentiometric titration), and the particle size distribution span (D90-D10) / D50 ≤0.7.

[0108] Step 5: Closed-loop recycling

[0109] The leaching residue is mixed with 3 wt% CaF2 and then returned to the cement kiln, and the 28-day activity index is ≥80%;

[0110] The crystallization mother liquor is recycled 5-8 times through a nanofiltration membrane (operating pressure 2.0 MPa); ​​​

[0111] The electrolysis of the tail gas absorption liquid (current density 25 mA / cm 2 ) generates sodium hypochlorite with an available chlorine content of ≥ 5%.

[0112] In step 5:

[0113] The rejection rate of the nanofiltration membrane for organic matter is ≥ 95% (detected by UV-Vis);

[0114] The current efficiency of the electrolysis of sodium hypochlorite is ≥ 85% (calibrated by the iodometric method). Specific implementation method:

[0116] Magnetic separation module: Feed the bypass ash into a gradient magnetic field (0.8 T → 1.0 T → 1.2 T), the removal rate of Fe3O4 is 91.5%, and the Fe2O3 content decreases from 4.2 wt% to 1.3 wt%;

[0117] Dynamic activation module: Mix the magnetic separation ash with 1.5 wt% NH4Cl, calcine at 600 °C for 30 min, then pass in CO2 (2 L / min) and calcine at 400 °C for 60 min. The specific surface area of the activated ash is 21.5 m 2 / g, and the decomposition rate of kaliophilite is 87.3%;

[0118] Countercurrent leaching module:

[0119] Primary leaching: 4 mol / L hydrochloric acid, ultrasonic treatment at 80 °C (40 kHz, 0.5 W / cm 3 ) for 40 min;

[0120] Secondary strengthening: Leach with 0.1 mol / L ammonium fluoride + 0.1 wt% sodium dodecyl sulfonate for 20 min;

[0121] Tertiary washing: After countercurrent rinsing, the total potassium recovery rate is 96.2%;

[0122] Ion sieving module: Bipolar membrane electrodialysis (20 V) removes 92.5% of Na + , and the purity of K + after molecular sieve adsorption is 99.5%;

[0123] Crystal phase regulation module: Concentrate to a potassium concentration of 152 g / L, add KCl crystal seeds with a (200) crystal plane of 50 μm, and assist crystallization with 28 kHz ultrasonic waves. The Cl - content of the crystal is 0.07%, and D50 = 105 μm;

[0124] Circulation and regeneration module: After adding 3 wt% CaF2 to the leaching residue, the cement activity index is 82%, and the leaching rate remains 90% after the mother liquor is recycled 7 times.

[0125] Index Traditional acid leaching method The present invention Potassium leaching rate 78％ 94％ <![CDATA[K + / Na + Separation ratio]]> 18:1 58:1 <![CDATA[Crystal Cl - content]]> 0.25％ 0.07％ Number of times of mother liquor reuse Non-reusable 7 times

[0126] This solution significantly improves the leaching rate of potassium compared with the traditional acid leaching method, while reducing the Cl - content and increasing the reuse times of the mother liquor.

[0127] The main functions of the bypass ash elution and washing liquid purification module are to dissolve soluble salts in the bypass ash and separate solid from liquid. During the separation process, through the mutual cooperation of various reactors, the soluble chlorine content in the bypass ash is removed for subsequent resource treatment and utilization. A large amount of suspended solids and calcium and magnesium ions in the bypass ash washing liquid are reduced, and its turbidity is also reduced, so that the water quality hardness index of the treated bypass ash washing liquid is controlled below 200 mg / L and the turbidity index is controlled below 5 NTU, providing an effective guarantee for the subsequent evaporation and salt separation module.

[0128] After purification, the potassium salt in this solution can be directly packaged and sold in the market, while the remaining bypass ash is reused to make cement. Compared with the traditional process, the comprehensive cost is reduced by more than 35%, providing an integrated solution of "efficient potassium extraction - high-purity separation - zero-waste cycle" for the solid waste in the cement industry.

[0129] The bypass ash and process water are respectively metered and then enter the pre-stirring system for stirring and mixing. After pre-stirring, when the original ash and water are fully contacted and mixed evenly, they enter the first-stage washing system. The ash and slag separated by solid-liquid separation after passing through the first-stage washing system successively enter the second-stage washing system and the third-stage washing system. The ash and slag meeting the chlorine content requirements enter the raw material mill or clinker, and the washing liquid separated by solid-liquid separation at the first stage enters the washing liquid purification unit for treatment.

[0130] The washing liquid is transported to the softening unit by a water pump. The calcium and magnesium ion remover preparation and dosing system is used to add calcium and magnesium ion remover to the softening reactor. The decalcified washing liquid successively passes through the water treatment plate and frame and neutralization treatment and then enters the evaporation water supply system.

[0131] The MVR evaporation method can be considered. The principle of a mechanical vapor recompression (MVR) evaporator is to use a high-energy steam compressor to compress the secondary steam generated by evaporation, convert electrical energy into heat energy, increase the enthalpy of the secondary steam, and inject the secondary steam with increased heat energy into the evaporation chamber for heating, so as to recycle the existing heat energy of the secondary steam, so that only a very small amount of external fresh steam needs to be supplemented to ensure the heat energy balance of the system, and the purpose of evaporation and concentration is achieved through the self-circulation of the evaporator.

[0132] The forced circulation evaporation crystallization system can greatly reduce the risk of pipe blockage and scaling due to precipitation crystallization caused by possible chemical reactions. After evaporation in the forced circulation evaporator, the material reaches a supersaturated state, and at this time, crystallization begins to precipitate continuously. In order to ensure the salt output effect and achieve wastewater crystallization, a thermal crystallization process is adopted to cause a large amount of crystallization of the material in the separator. Subsequently, the crystalline salt is discharged from the bottom of the crystallization separator to the thickener. After further increasing the solid content of the solution, it is discharged into a centrifugal device for centrifugation. The centrifuged crystalline salt is discharged from the system, and the mother liquor continues to flow back for evaporation, with only a small amount of mother liquor discharged.

[0133] The MVR system compresses the secondary steam through a compressor, increases the pressure and saturation temperature, and then sends it into the evaporator as a heat source to replace the fresh steam for recycling. At the same time, the secondary steam cooling system is also omitted, and the operating cost is relatively low.

[0134] In the process of removing the Fe3O4 magnetic phase by using a gradient magnetic field, the decrease in the Fe2O3 content is due to the following reasons: Physical adsorption and entrainment: Fe3O4 has magnetism, and during the process of being adsorbed and removed by the magnetic field, it may entrain some Fe2O3 particles that are tightly combined with it or physically adsorbed on its surface. When Fe3O4 is accurately removed in three sections by the gradient magnetic field, these entrained Fe2O3 will also be removed accordingly, resulting in a decrease in the overall Fe2O3 content. Crystal structure and transformation: There is a certain correlation between the crystal structures of Fe3O4 and Fe2O3. Under the action of the gradient magnetic field, the magnetic behavior of Fe3O4 may affect the electronic structure on its surface or inside, and then promote the oxidation reaction of some Fe3O4 to transform into Fe2O3. The newly formed Fe2O3 may be more easily removed by the separation process under the magnetic field due to its particle characteristics or interaction with other substances, ultimately reducing the Fe2O3 content in the system. Although the main purpose of the process is to remove the Fe3O4 magnetic phase, the above mechanisms also reduce the Fe2O3 content, achieving a better impurity removal effect and reducing the inhibitory effect of iron impurities on subsequent reactions.

[0135] Example 2

[0136] The difference between this example and Example 1 is that in step 1, the bypass ash is pretreated with microwaves (300 - 500 MHz) before magnetic separation, and the pretreatment time is 5 - 15 minutes.

[0137] The effects after microwave pretreatment include:

[0138] 1. Improved magnetic separation efficiency

[0139] Microwaves selectively heat Fe3O4, break the agglomerated structure, and improve the dispersion degree. The recovery rate of Fe3O4 is increased from 78% to 94%, and the residual amount of Fe2O3 is reduced from 4.2 wt% to 1.1 wt%.

[0140] 2. Mineral Activation and Decomposition

[0141] Mechanism: Microwave penetrative heating promotes the lattice vibration of aluminosilicates (such as leucite), reducing the decomposition temperature. The decomposition rate of leucite increases from 85% to 92%, and the calcination temperature decreases from 600 °C to 550 °C.

[0142] 3. Heavy Metal Solidification

[0143] Microwave induces the formation of a stable silicate glass phase from PbO and SiO2. The Pb concentration in the leachate 2+ decreases from 120 ppm to 15 ppm.

[0144] 4. Energy Consumption and Process Optimization

[0145] Microwave "volume heating" shortens the calcination time and reduces the heat gradient loss. The calcination time is shortened from 90 minutes to 60 minutes, and the energy consumption is reduced by 25%.

[0146] 5. Resource Utilization of By-products

[0147] Microwave generates a porous Fe3O4 magnetic adsorbent. The adsorption capacity of Fe3O4 for Cr 6+ reaches 120 mg / g.

[0148] The specific data are as follows:

[0149]

[0150]

[0151] Microwave pretreatment realizes a comprehensive improvement in magnetic separation efficiency, resource recovery rate, and environmental protection performance through selective heating, structural reconstruction, and promotion of chemical reactions, while reducing energy consumption and reagent consumption.

[0152] The above are only embodiments of the present invention. The invention is not limited to the fields involved in this embodiment. Common general knowledge such as the specific structures and characteristics known in the art is not described in detail herein. Those of ordinary skill in the art know all the common general knowledge in the technical field to which the invention belongs before the filing date or the priority date, are able to know all the prior art in this field, and have the ability to apply the conventional experimental means before this date. Those of ordinary skill in the art can, under the inspiration given in this application, combine their own abilities to improve and implement this solution. Some typical well-known structures or well-known methods should not become an obstacle for those of ordinary skill in the art to implement this application. It should be noted that for those skilled in the art, without departing from the structure of the present invention, several deformations and improvements can also be made, which should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicality of the patent. The protection scope required by this application should be based on the content of its claims, and the specific implementation manners and the like recorded in the specification can be used to interpret the content of the claims.

Claims

1. A system for extracting high-purity potassium salts from cement bypass dust, characterized in that, Including: Magnetic separation module: used to separate the Fe3O4 magnetic phase in the bypass ash under a gradient magnetic field of 0.8 - 1.2T, reducing the Fe2O3 content to ≤1.5wt%; Dynamic activation module: Used for two-stage calcination assisted by NH4Cl to decompose nepheline with a decomposition rate of ≥85%, and generate activated ash with a specific surface area of ≥18 m 2 / g; Countercurrent leaching module: used to achieve the synergistic leaching of hydrochloric acid - ammonium fluoride through a three - stage series reactor under the condition of pH 0.5 - 2.5; Ion sieving module: including a bipolar membrane electrodialysis unit and a Li + type K-LTL molecular sieve adsorption tower for selectively separating K + / Na + to above 50:1; Crystal phase regulation module: used to prepare potassium salt crystals with a Cl content ≤ 0.1% by real-time feedback of supersaturation through conductivity, combined with 28 kHz pulsed ultrasonic waves and KCl seeds with preferred crystal plane orientation - content; Circulation and regeneration module: used to return the leaching residue to the cement kiln after adding 3wt% CaF2, and the crystallization mother liquor is electrolyzed through a nanofiltration membrane and tail gas absorption liquid to generate sodium hypochlorite.

2. A high - purity potassium salt extraction system using cement bypass ash according to claim 1, characterized in that: The magnetic field intensity of the magnetic separation module is set in three - stage gradients of 0.8T, 1.0T, and 1.2T; The calcined product of the dynamic activation module is detected by XRD, and the intensity of the kaliophilite characteristic peak at 2θ = 28.5° is reduced by 82 - 87%, and the half - peak width of the new KCl characteristic peak at 2θ = 31.3° is ≤0.18°.

3. A high - purity potassium salt extraction system using cement bypass ash according to claim 1, characterized in that: The countercurrent leaching module includes: First - stage leaching unit: reaction temperature 80 - 90°C, liquid - to - solid ratio 8:1, ultrasonic assistance; Second - stage strengthening unit: adding 0.05 - 0.1wt% sodium dodecyl sulfonate as a surfactant; Third - stage washing unit: the washing water is recycled to the first - stage leaching agent preparation.

4. A high - purity potassium salt extraction system using cement bypass ash according to claim 1, characterized in that: The ion sieving module: The bipolar membrane electrodialysis unit simultaneously generates a 0.5 - 1.0mol / L NaOH solution for reuse in pH adjustment; Li + The adsorption capacity of Type K-LTL molecular sieve for Na + is ≥ 2.5 mmol / g, and the regeneration efficiency is ≥ 95%.

5. A high - purity potassium salt extraction system using cement bypass ash according to claim 1, characterized in that: The crystal phase regulation module: The supersaturation is calculated in real - time through the conductivity - concentration calibration curve, and the control accuracy is ±5%; The amount of crystal seeds added is 0.1 - 0.5% of the solution mass, and the crystal roundness ≥0.

85.

6. A method for extracting high-purity potassium salts from cement bypass dust, characterized in that, Including the following steps: Step 1: Magnetic separation - activation pretreatment: Place the bypass ash in a gradient magnetic field of 0.8 - 1.2T to separate Fe3O4, reducing the Fe2O3 content to ≤1.5wt%; Mix the magnetic - separated ash with 1.5wt% NH4Cl, under the conditions of O2 concentration of 30% and flow rate of 5L / min: In the first stage, calcine at 600°C for 30 minutes, and the kaliophilite decomposes into KCl and Al2O3; In the second stage, introduce CO2 and calcine at 400°C for 60 minutes to generate surface carbonate active sites; Step 2: Three - stage countercurrent leaching First - stage leaching: Use 4mol / L hydrochloric acid to leach for 40 minutes in an ultrasonic environment at 80°C; Second - stage strengthening: Add 0.1mol / L ammonium fluoride and 0.1wt% sodium dodecyl sulfonate, and continue to leach for 20 minutes; Third - stage washing: Rinse the leaching residue with pure water in a countercurrent manner, and the washing liquid is recycled to the first - stage leaching; Step 3: Ion - targeted purification Add 5 - 10 g / L of sodium thiosulfate to the leaching solution to precipitate heavy metal ions Cu 2+ , Pb 2+ ; Removing ≥90% Na through bipolar membrane electrodialysis + ; Using Li + type K-LTL molecular sieve to adsorb residual Na + , after adsorption, the purity of K + ≥99.3%; Step 4: Dynamic crystallization control Concentrate the purified liquid to a potassium ion concentration of 150 ± 5g / L, and add KCl crystal seeds on the crystal surface when the supersaturation reaches 130%; Cool down to 30 °C at a rate of 1 °C / min, start the temperature oscillation program of ±5 °C / 10 min, and apply 28 kHz ultrasonic waves synchronously. Step 5: Closed-loop recycling The leaching residue is returned to the cement kiln after adding 3 wt% CaF2, and the 28-day activity index is ≥80%. The crystallization mother liquor is recycled through the nanofiltration membrane 5 - 8 times. The tail gas absorption liquid is electrolyzed to generate sodium hypochlorite with an effective chlorine content of ≥5%.

7. A method for extracting high-purity potassium salts using cement bypass ash according to claim 6, characterized in that: The BET specific surface area of the activated ash in Step 1 reaches 18 - 22 m 2 / g, and the solubilization rate of potassium element is ≥90%; The residual K2O content in the leaching residue in step 2 is ≤0.5 wt%.

8. A method for extracting high-purity potassium salts using cement bypass ash according to claim 6, characterized in that, In step 3: Na in bipolar membrane electrodialysis + Migration rate ≥ 0.15 mol / (m 2 ·h); The operating space velocity of the molecular sieve adsorption tower is 2 - 4 h -1 , Na + The breakthrough capacity is ≥ 2.2 mmol / g.

9. A method for extracting high-purity potassium salts using cement bypass ash according to claim 6, characterized in that, In step 4: The crystal seed particle size is 50 - 80 μm, and the addition amount is 0.3 wt%. Final crystal Cl - Content ≤ 0.08%, particle size distribution span (D90 - D10) / D50 ≤ 0.

7.

10. A method for extracting high-purity potassium salt using cement bypass ash according to claim 6, characterized in that, In step 1, the bypass ash is pretreated by microwave before magnetic separation, and the pretreatment time is 5 - 15 minutes.

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