Biomass deironing and deliming process based on ultrasonic cavitation and application of biomass deironing and deliming process

Abstract

The invention provides a biomass deironing and deliming process based on ultrasonic cavitation and application of the biomass deironing and deliming process, and belongs to the technical field of electrochemical energy storage material preparation. The method comprises the following steps: dilute acid pretreatment: putting dry biomass into a reaction kettle, and adding dilute acid until the final concentration is 0.5-1.0%; ultrasonic cavitation desorption: applying ultrasonic waves with the frequency of 20-40 kHz and the power density of 0.8-1.5 W / cm, performing micropore aeration at the speed of 0.3-0.7 L / min.L, and monitoring the pH value in real time; and alkaline deep desilicication: when the pH is increased to 4.0-4.5, adding a NaOH solution with the concentration of 0.05-0.2 mol / L, supplementing and applying ultrasonic treatment, carrying out solid-liquid separation on the material, and washing to be neutral. By integrating ultrasonic cavitation, microporous aeration and chemical treatment technologies, the ash content of the biomass raw material can be reduced from 8-11% to 0.5% or below, the iron content can be reduced from 2500 ppm to 60 ppm or below, and the strict purity requirement of the hard carbon negative electrode material of the ion battery is met. The method can be widely applied to biomass energy, electrochemical energy storage materials and environmental protection industries, and has remarkable economic and social benefits.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage material preparation technology, and in particular to a biomass iron removal and deashing process based on ultrasonic cavitation and its application. Background Technology

[0002] Sodium-ion batteries, as an important supplement to lithium-ion batteries, are emerging as a core carrier for large-scale electrochemical energy storage due to their significant advantages, including abundant sodium resources, excellent low-temperature performance, and low cost. Sodium has an abundance of 2.3% in the Earth's crust, far exceeding lithium's 0.002%; even in harsh environments like -20℃, sodium-ion batteries can retain over 85% of their capacity. A 2024 report by the International Energy Agency indicates that the global sodium-ion battery market is projected to exceed $50 billion by 2030, with hard carbon anode materials accounting for over 30% of the total cost. The key raw materials for hard carbon anodes are high-purity phenolic resin and biomass. While phenolic resin has high purity, it is expensive (approximately 40,000 yuan / ton) and relies on petroleum-based raw materials; whereas biomass, such as bagasse, straw, and rice husks, is widely available, with a global annual production exceeding 1 billion tons, and a cost of only about 500 yuan / ton, offering superior cost-effectiveness. Taking sugarcane bagasse as an example, high-performance hard carbon can be produced through carbonization, with a theoretical specific capacity of 300 mAh / g. However, practical applications face severe bottlenecks: the ash content is as high as 8%-11%, of which silicon dioxide accounts for 40%-50%, aluminum oxide for 15%-20%, ferric oxide for 10%-15%, calcium oxide for 5%-10%, and iron content is generally as high as 2000-3000 ppm. Sodium-ion batteries have extremely stringent requirements for the purity of hard carbon anodes; the ash content must be below 0.5%, and the iron content must be controlled below 60 ppm. Otherwise, the battery cycle life will be severely shortened to less than 500 cycles, the efficiency in the first week will plummet to below 70%, and safety hazards such as internal short circuits will be significantly increased.

[0003] Numerous patents have disclosed relevant technologies for biomass ash removal. For example, patent CN 115207320 A discloses a method for preparing lithium / sodium-ion battery anode materials, using a two-step process of acid washing and alkali treatment to deeply remove ash impurities from walnut shells and regulate their microstructure. Patent CN 117735525 A proposes a two-stage carbonization method for biomass hard carbon, combining pretreatment with a mixture of hydrochloric acid and nitric acid with 10-30 minutes of ultrasound. The synergistic effect of the two acids enhances impurity removal, but the nitrate wastewater increases the environmental burden. Patent CN107500263B discloses a process for rice husk-derived hard carbon involving hydrochloric acid impregnation, hydrofluoric acid treatment, and ultrasonic washing. Currently, the industry commonly uses a combined hydrofluoric acid (HF) and high-concentration hydrochloric acid (HCl) process for ash and iron removal, which has significant drawbacks. (1) High toxicity risk: HF LD50 50Even at only 50 mg / kg, it can easily cause skin burns and bone necrosis; operation requires fully enclosed protective gear, and the accident rate is still as high as 0.5%. (2) Equipment corrosion: The corrosion rate of HF on stainless steel reactors exceeds 5 mm / year, requiring the use of polytetrafluoroethylene (PTFE) lining, which causes the equipment cost to surge by 300%; (3) Environmental pressure: The cost of treating fluoride-containing waste liquid is about RMB 800 / ton, and it is easy to cause soil fluoride pollution (exceeding the limit of 10mg / L). (4) Poor economic efficiency: The comprehensive cost reaches RMB 1,500 per ton of biomass, accounting for 15% of the total cost of hard carbon materials, which has become a pain point in the industry.

[0004] Other alternative technologies have not yet overcome bottlenecks. For example, invention patent CN 119637842 A proposes a mild deashing process: biomass is mixed with organophosphonates such as tetrasodium hydroxyethylidene diphosphonate and polyacrylic acid-based deashing agents at a mass ratio of 5:1 to 500:1, allowed to react at 25-120℃, and then washed and dried. This method removes potassium through chelation. + Na + Ca 2+ Mg 2+ Plasma can avoid the damage to the biomass structure caused by strong acids and alkalis, but it cannot remove insoluble inorganic oxides, such as silicon dioxide (SiO2).

[0005] Traditional acid-base methods rely on mechanical stirring and lack auxiliary enhancement methods, resulting in low impurity removal efficiency. The core challenge lies in the fact that inorganic substances such as SiO2 in ash are embedded in the fiber pores as 50–200 nm nanoparticles, making them difficult to remove; iron impurities, in the form of Fe3O4 or Fe2O3, are densely attached to the fiber surface, and strong acids can easily dissolve them and damage the structure. Ultrasonic cavitation technology has the potential for impurity removal due to its ability to generate high temperatures of 5000 K, high pressures of 500 atm, and microjets of 100 m / s. However, existing devices have limitations such as uneven gas-liquid mass transfer, fluctuating cavitation intensity, and insufficient synergy between acid / base and cavitation. Therefore, there is an urgent need to develop a new type of ultrasonic cavitation device that integrates microporous aeration and precise parameter control to achieve safe, efficient, and environmentally friendly iron and ash removal. Summary of the Invention

[0006] In view of this, to address the technical problem of poor iron removal and deashing effects in existing technologies, this invention provides a biomass iron removal and deashing process based on ultrasonic cavitation and its application. By integrating ultrasonic cavitation, microporous aeration, and chemical treatment technologies, the ash content of biomass raw materials can be reduced from 8%–11% to below 0.5%, and the iron content from 2500 ppm to below 60 ppm, meeting the stringent purity requirements of hard carbon anode materials for lithium-ion batteries. This process can be widely applied in biomass energy, electrochemical energy storage materials, and the environmental protection industry, yielding significant economic and social benefits.

[0007] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a biomass iron removal and deashing process based on ultrasonic cavitation, comprising the following steps: Step (1), dilute acid pretreatment: put the dried biomass into the reactor, prepare a suspension, add dilute acid to the final concentration of 0.5-1.0%, and stir evenly; wherein, the dilute acid is one of acetic acid, oxalic acid or hydrochloric acid; Step (2), ultrasonic cavitation desorption: Apply ultrasonic waves with a frequency of 20-40 kHz and a power density of 0.8-1.5 W / cm² to the suspension in step (1), while simultaneously performing microporous aeration at a rate of 0.3-0.7 L / min·L and monitoring the pH in real time. Step (3), alkaline deep desilication: When the pH of the suspension in step (2) rises to 4.0-4.5, add NaOH solution with a concentration of 0.05-0.2mol / L, continue to apply ultrasonic treatment, and after completion, perform solid-liquid separation on the material and wash it until neutral.

[0008] Secondly, the present invention also provides the application of the above-mentioned biomass iron removal and ash removal process based on ultrasonic cavitation in the preparation of hard carbon anode material for sodium-ion batteries, wherein the biomass treated in step (3) is carbonized to obtain hard carbon material with ash content ≤0.5% and iron content ≤60 ppm.

[0009] Compared with the prior art, the present invention has the following beneficial effects: (1) The innovative design of microporous aeration and ultrasound is used to improve the stability of cavitation intensity to >90% by precisely controlling the bubble particle size, thus solving the problem of uneven cavitation in traditional devices.

[0010] (2) This invention proposes a three-stage time-series control of “dilute acid pretreatment → ultrasonic cavitation desorption → alkaline deep desilication”, especially the timing of NaOH addition to avoid silica gelation, thus achieving efficient removal of siliceous ash. The ash content of biomass raw materials is reduced from 8-1% to ≤0.5%, and the iron content is reduced from 2500 ppm to ≤60 ppm.

[0011] (3) Establish a multi-dimensional parameter database covering different biomass characteristics. Through precise control of process parameters, adapt to the differences in characteristics of different biomass raw materials and provide precise guidance for industrialization. Significantly shorten processing time and reduce overall costs to below 500 yuan / ton.

[0012] (4) Environmental breakthrough: Completely abandoning hydrofluoric acid can completely avoid the use of highly toxic chemicals such as hydrofluoric acid, ensuring the safety of operators and environmental friendliness. Biodegradable organic acids are used, and wastewater meets the first-class discharge standard, promoting green manufacturing. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the overall structure of the reaction vessel used in this invention; Figure 2 This is a process flow diagram of the present invention; Figure 3 The parameter optimization curves of this invention are shown below. In this diagram, A is the curve of iron and ash removal rate at different ultrasonic frequencies; B is the iron removal rate curve under dilute acid; C is the silicon removal rate curve under different NaOH concentrations; and D is the curve of bubble particle size, cavitation intensity, and ash removal rate under different aeration rates. In the diagram, 1. Outer shell; 2. PTFE liner; 3. Feed inlet; 4. Exhaust outlet; 5. Drain outlet; 6. Jacket; 7. Jacket inlet; 8. Jacket outlet; 9. Agitator; 10. Motor; 11. Temperature sensor array; 12. Level gauge; 13. Transducer array; 14. Microporous aeration disc; 15. Venturi air inlet pipe; 16. Metering pump; 17. Inlet pipe; 18. pH detector; 19. PLC controller; 20. High-speed camera. Detailed Implementation

[0014] like Figure 2 As shown, this invention provides a biomass iron removal and deashing process based on ultrasonic cavitation, which adopts a three-stage process of "dilute acid pretreatment → ultrasonic cavitation desorption → alkaline deep desilication", with parameters strictly limited within the high-efficiency range.

[0015] The preferred method for this process is as follows: Figure 1 The reaction vessel shown is used for this process. Figure 1 The reactor shown is only a preferred reactor, not a mandatory one. Those skilled in the art can select the appropriate reactor based on actual needs. Figure 1 As shown, the reactor mainly includes an ultrasonic generating system, a reactor system, a microporous aeration system, a chemical reagent addition system, and an intelligent control system. Specifically: The reactor body is composed of the following: Main structure: Vertical cylindrical reactor (outer shell 1 made of 316L stainless steel, PTFE lining 2 as corrosion protection layer), volume 100 L (laboratory grade) or 5 m³ (industrial grade), working pressure 0.1-0.5 MPa, temperature range 5-80℃, with feed inlet 3, exhaust port 4, and drain port 5. The reactor body has an external jacket 6; the temperature control medium enters through the jacket inlet 7 and exits through the jacket outlet 8, controlling the reactor body's operation. Internal design includes: Agitator 9: Anchor-type agitator (driven by motor 10, speed adjustable from 0-200 rpm) to ensure material suspension; Temperature sensor array 11: PT100 platinum resistance thermometer (accuracy ±0.1℃), with several temperature sensors distributed at the bottom, middle, and top of the vessel; Level gauge 12: Ultrasonic type (range 0-100 cm, accuracy ±1 mm). Sampling port: equipped with a rapid cooling valve for process monitoring.

[0016] Ultrasonic generating system Ultrasonic generator: A dual-frequency digital ultrasonic generator is used, with a frequency range of 20-40 kHz continuously adjustable and an accuracy of ±0.1 kHz; power density of 0.5-2.0 W / cm² (based on the volume of the reaction liquid) and an accuracy of ±0.05 W / cm²; and duty cycle adjustable from 10-99%.

[0017] Transducer array 13: Eight titanium alloy transducers (model: T1040) are arranged in a ring on the outer wall of the reactor, with a resonant frequency of 28±2 kHz and an effective radiation area of ​​≥90%; the transducer spacing is 150 mm to ensure the uniformity of the sound field (non-uniformity <15%).

[0018] Acoustic matching layer: A silicone oil coupling layer (2 mm thick) is filled between the transducer and the reactor, with an acoustic impedance matching degree of >95%, reducing energy loss.

[0019] Microporous aeration system Microporous aeration disc 14: Made of 316L stainless steel microporous aeration tube (pore diameter 50-200μm, opening rate 30%), placed at the bottom of the reactor, 50 mm from the bottom of the reactor.

[0020] Gas source: compressed air or nitrogen (purity >99.5%), flow rate 0.1-1.0 L / min·L (based on reaction liquid volume), accuracy ±0.01 L / min.

[0021] Gas-liquid mixer: Venturi tube design, compressed air or nitrogen enters from the Venturi inlet pipe 15, bubble diameter is controlled at 50-300μm, and cavitation nucleus density is improved.

[0022] Chemical reagent addition system Acid storage tank: made of PE material, storing 0.5-1.0% dilute acid (acetic acid, oxalic acid or hydrochloric acid), which is added to the reactor body through metering pump 16 (accuracy ±0.5%) and inlet pipe 17; Alkali storage tank: made of PP material, storing 0.05-0.2 mol / L NaOH solution, with the addition timing triggered by pH detection detector 18 (accuracy ±0.01); Neutralization unit: Ca(OH)2 is automatically added during the post-treatment stage to adjust the pH to 6-7.

[0023] Intelligent control system Core components: PLC controller 19 (model: Siemens S7-1200) + HMI touch screen; Closed-loop control: Real-time monitoring: pH, temperature, sound power, bubble size (analyzed by 20+ images from a high-speed camera); Parameter linkage: Automatic acid replenishment when pH > 3.0, and cooling activation when temperature > 60℃; Safety protection: Automatic frequency reduction when cavitation intensity is abnormal (>2.5 W / cm²).

[0024] This invention provides a biomass iron removal and deashing process based on ultrasonic cavitation, comprising the following steps: Step (1), dilute acid pretreatment: The dried biomass is added to a reactor to prepare a suspension. Dilute acid is added to a final concentration of 0.5-1.0%, and the mixture is stirred until homogeneous. The dilute acid is one of acetic acid, oxalic acid, or hydrochloric acid. The biomass is preferably one of sugarcane bagasse, straw, or rice husk. In step (1), the concentration of the dilute acid is preferably 0.6-0.9%. The treatment temperature is preferably controlled at 30-50℃. The stirring time is preferably 5 minutes.

[0025] Step (2), ultrasonic cavitation desorption: Ultrasonic waves with a frequency of 20-40 kHz and a power density of 0.8-1.5 W / cm² are applied to the suspension from step (1), while microporous aeration is performed at a rate of 0.3-0.7 L / min·L, and pH is monitored in real time. In this step (2), at an ultrasonic frequency of 20-40 kHz, microbubbles (50-300 μm) act as cavitation nuclei, increasing the cavitation intensity by 40-60%. When the frequency is <20 kHz, bubble coalescence reduces efficiency; at 40 kHz, the cavitation bubbles are too small and lack energy. In this step (2), the ultrasonic frequency is preferably 28-32 kHz, and the aeration rate is 0.4-0.6 L / min·L. The bubble size of the microporous aeration is controlled to be 50-300 μm. The ultrasonic cavitation desorption time is 30-60 minutes. The treatment temperature is controlled at 30-50℃.

[0026] Step (3), Alkaline Deep Desilication: When the pH of the suspension from step (2) rises to 4.0-4.5, add a NaOH solution with a concentration of 0.05-0.2 mol / L, and continue to apply ultrasonic treatment. After completion, perform solid-liquid separation on the material and wash until neutral. In this step (3), the concentration of the NaOH solution is preferably 0.08-0.12 mol / L. The frequency of the supplementary ultrasonic treatment is 25-35 kHz. The supplementary ultrasonic treatment lasts for 5-15 minutes. The treatment temperature is controlled at 30-50℃.

[0027] In the process provided by this invention, pretreatment with dilute acid followed by deep alkaline desilication avoids the formation of silica gel (if alkali is added first, SiO2 forms a colloid that blocks the pores). The above process balances the reaction rate and fiber stability at 30-50℃ (cellulose degrades at >60℃).

[0028] The above-mentioned process provided by the present invention is applied to the preparation of hard carbon anode material for sodium-ion batteries. The biomass treated in step (3) is carbonized to obtain hard carbon material with ash content ≤0.5% and iron content ≤60 ppm.

[0029] The process provided by this invention employs a three-stage process of "dilute acid pretreatment → ultrasonic cavitation desorption → alkaline deep desilication". As a preferred embodiment, the total duration is 30-90 minutes, and the process flow can be as follows:

[0030] The technical solution of the present invention will be clearly and thoroughly described below with reference to specific embodiments, as follows: All examples used bagasse as raw material (ash content 10.2±0.5%, iron content 2520±50 ppm), which was crushed to a particle size of 0.8-1.2 mm. Test methods: Ash content: High-temperature calcination method (815℃); Iron content: atomic absorption spectrometry; Cavitation intensity: determined by iodine release method; Hard carbon performance: Assemble half-cells (Na / hard carbon) and test first-cycle efficiency and cycle performance.

[0031] Example 1: Validation of basic process parameters (bagasse, laboratory scale) Device setup: Reactor: 100 L volume, 316L stainless steel + PTFE lining; Ultrasonic system: frequency 28 kHz, power density 1.2 W / cm², duty cycle 80%; Aeration system: microporous aeration tubes (pore size 100μm), airflow rate 0.5 L / min·L; Control system: pH trigger point set to 4.2, temperature upper limit 50℃.

[0032] Operating steps: Step (1): Add 10 kg of sugarcane bagasse to the reactor and add water to make a 15 wt% suspension (liquid-solid ratio 8:1).

[0033] Step (2): Add 0.7% acetic acid (final concentration), stir for 5 min, pH=3.1, temperature 35℃.

[0034] Step (3): Start ultrasound and aeration, and treat for 40 min; during this period, pH rises from 3.1 to 4.2 (monitoring interval 5 min).

[0035] Step (4): When pH=4.2, automatically add 0.10 mol / L NaOH to a final concentration of 0.10 mol / L, and continue sonication for 10 min (frequency 30 kHz).

[0036] Step (5): Stop the reaction, filter, wash three times with deionized water, and dry at 60°C.

[0037] The parameters are recorded in Table 1: Table 1 Parameter Records of the Embodiment

[0038] Results analysis: Ash content: 0.48% (removal rate 95.3%); Iron content: 58 ppm (removal rate 97.7%); Cavitation intensity: 1.35 W / cm² (iodine release 12.8 mg / L); Hard carbon performance: 81.5% efficiency in the first cycle and 91.2% capacity retention after 1000 cycles.

[0039] Conclusion: The basic parameters met the target, acetic acid avoided fiber damage, and precise addition of NaOH improved the desilication efficiency.

[0040] Example 2: Ultrasonic frequency optimization experiment (sugarcane bagasse, parameter comparison) This embodiment investigates the effect of frequency on deashing efficiency, with other parameters fixed: acid is 0.8% hydrochloric acid, aeration is 0.6 L / min·L, and time is 45 min.

[0041] Operating steps: Five parallel experiments were conducted at frequencies of 20, 25, 30, 35, and 40 kHz. Each group was treated with 5 kg of sugarcane bagasse (15 wt% suspension). Record the ash / iron removal rate and energy consumption.

[0042] The parameters and results are shown in Table 2: Table 2 Parameters and Results of Example 2

[0043] Mechanism analysis: The optimal cavitation bubble collapse energy is found at 30 kHz (theoretical calculation: bubble radius R0 = 100 μm, collapse pressure 450 atm). Frequency <25 kHz: Bubble coalescence leads to uneven cavitation intensity and high ash residue; Frequency >35 kHz: Insufficient bubble collapse energy, microjets velocity <80 m / s, and decreased stripping efficiency. Conclusion: 30 kHz is the optimal operating frequency, balancing efficiency and energy consumption.

[0044] Example 3: Effect of Acid Type and Concentration (Sugarcane Bagasse, Verification of Multiple Acid Species) This embodiment tests the effects of three acids at a fixed frequency of 30 kHz, with aeration at 0.5 L / min·L for 40 min.

[0045] Operating steps: Acid types: acetic acid, oxalic acid, hydrochloric acid; Concentration gradient: 0.5%, 0.7%, 1.0%; Each group treated 5 kg of sugarcane bagasse, and recorded the initial / endpoint pH and removal rate.

[0046] The results are shown in Table 3: Table 3 Results data of Example 3

[0047] Fiber damage index: Calculated by the rate of decrease in cellulose degree of polymerization (DP), DP < 500 is considered damage.

[0048] Key findings: Hydrochloric acid is the most efficient (H) + High concentration), but significant fiber damage (DP drops to 420 at 1.0%). The balance between the effects and safety of acetic acid / oxalic acid at a concentration of 0.7% (acetic acid is suitable for high-calcium raw materials, while oxalic acid has a stronger selectivity for iron oxides). Best recommendation: Use 0.7% oxalic acid for sugarcane bagasse (97.5% iron removal rate), and use 0.8% acetic acid for rice husks (to avoid potassium loss).

[0049] Conclusion: The type of acid must be matched with the characteristics of the raw materials. The recommended safe and efficient concentrations are: about 0.7% for organic acids and less than 0.7% for strong acids (such as hydrochloric acid).

[0050] Example 4: Synergistic effect of microporous aeration and cavitation (sugarcane bagasse, gas-liquid mass transfer study) This embodiment verifies the effect of aeration on improving cavitation intensity, with a fixed frequency of 30 kHz and an acid of 0.7% oxalic acid.

[0051] Operating steps: Control group: No aeration; Experimental groups: aeration rates of 0.3, 0.5, and 0.7 L / min·L; The cavitation region was photographed using a high-speed camera (Phantom V2512), and the bubble size distribution was analyzed. Iodine release was measured as an indicator of cavitation intensity.

[0052] The data is summarized in Table 4: Table 4 Summary of data from Example 4

[0053] Mechanism Explanation: Aeration provides cavitation nuclei, increasing the number of bubbles by 3-5 times (nucleus density <10 without aeration). 4 cells / mL, >5×10 at 0.5 L / min·L 4 (pcs / mL) The collapse energy is greatest when the bubble size is 150 μm; aeration >0.7 L / min·L leads to bubble coalescence and disorder in the cavitation region.

[0054] Conclusion: Micropore aeration is the key to improving efficiency, and 0.5 L / min·L is the optimal aeration rate.

[0055] Example 5: Parameter optimization in alkaline desilication stage (sugarcane bagasse, silicon removal project) Sugarcane bagasse contains 45% SiO2. This example focuses on the influence of NaOH concentration and the timing of its addition.

[0056] Operating steps: After completing the acid-ultrasonic phase (pH=4.2), different concentrations of NaOH (0.05, 0.10, 0.15 mol / L) were added. Supplement with ultrasound for 10 minutes (frequency 32 kHz); Silicon content was determined (ICP-OES method).

[0057] The results are shown in Table 5: Table 5 Comparison of Results

[0058] In-depth analysis: Adding NaOH at pH=4.2 prevents the formation of H2SiO3 colloids (SiO2 has low solubility at pH<4 and is prone to gelation at pH>5). The reaction rate is fastest at 0.10 mol / L NaOH (k = 0.15 min). -1 Excessive NaOH causes aluminum impurities to dissolve; Supplementing with ultrasound-enhanced mass transfer increased the diffusion rate of sodium silicate by 3 times. Conclusion: The optimal process parameters are a NaOH concentration of 0.10 mol / L and an addition time at pH 4.0-4.5.

[0059] Example 6: Industrial-scale scale-up verification (5 m³ unit, continuous sugarcane bagasse processing) The feasibility of this embodiment was verified in an industrial field, and the device parameters were scaled up proportionally.

[0060] Device configuration: Reactor: 5 m³ volume, 316L stainless steel, 16 transducers (frequency adjustable from 28-32 kHz); Aeration system: annular microporous tube (pore size 100μm), total airflow 3.0 m³ / h; Control system: DCS system, real-time feedback adjustment.

[0061] Process parameters: Liquid-to-solid ratio: 10:1 (biomass feed 100 kg / h); Acid phase: 0.75% oxalic acid, time 8 min; Cavitation stage: frequency 30 kHz, power density 1.0 W / cm², aeration rate 0.5 L / min·L, time 35 min; Desilication stage: 0.10 mol / L NaOH, time 12 min; Total processing capacity: 1.2 tons / hour.

[0062] The data from 72 hours of continuous operation are shown in Table 6: Table 6 Data from 72 Hours of Continuous Operation

[0063] Economic benefits: With an annual processing capacity of 8,000 tons, the cost savings are: (1,500 - 475) × 8,000 = 8.2 million yuan; Wastewater treatment: pH after neutralization = 6.8, fluoride ions not detected, reuse rate 85%; Hard carbon finished product: Certified by CATL as a supplier, used in the mass production of sodium-ion batteries.

[0064] Conclusion: The industrial-grade application is stable and reliable, with significant economic and environmental advantages.

[0065] Example 7: Adaptability Test of Different Biomass Raw Materials To verify the universality of this invention for straw and rice husks, the parameters were fine-tuned, as shown in Table 7.

[0066] Table 7. Test results for different biomass materials

[0067] Comparative Experiment: A Comprehensive Comparison with the Traditional HF Method Under the same raw material (sugarcane bagasse), the present invention and the traditional HF process are shown in Table 8: Table 8 Comparison of the present invention with the traditional HF method

[0068] Based on the above experimental verification, the present invention has the following significant advantages: Safety: Completely eliminates hydrofluoric acid, using only low-concentration organic / inorganic acids, reducing operational risks by 90% and meeting laboratory safety standards. Efficiency: Ash removal rate ≥95%, reduced from 10% to 0.5%; iron removal rate ≥97.5%, reduced from 2500 ppm to 60 ppm. The processing time is reduced by 50%, from 90 minutes for the traditional HF method to only about 45 minutes for this invention; The stability of cavitation intensity is improved, with fluctuations of <10% in this invention compared to 30% in the traditional HF method.

[0069] Economic benefits: Reagent costs are reduced by 60%, the dilute acid usage of this invention is 0.5 kg / ton, compared to 5 kg / ton in the traditional HF method; wastewater treatment is simplified, with no fluoride ions, and COD after neutralization is <100 mg / L, meeting the first-class standard; the overall cost is approximately 480 yuan / ton, saving 1020 yuan / ton compared to the traditional method.

[0070] Adaptability: Through parameter adjustment, it is suitable for different biomass such as bagasse (high silicon), rice husk (high potassium), and straw (high calcium); the industrial-grade unit (5 m³) has a processing capacity of 1 ton / hour, which meets the annual production demand of 5,000 tons of hard carbon materials.

[0071] Environmental friendliness: Wastewater can be recycled with a recovery rate of >80%; carbon emissions are reduced by 35% and no high-temperature or high-pressure equipment is required.

[0072] Experimental data show that the sugarcane bagasse treated in this invention, when used to prepare hard carbon anodes, achieves a coulombic efficiency of 82% in the first week and a capacity retention rate of >90% after 1000 cycles, fully meeting the requirements of ion batteries.

[0073] In summary, compared with the traditional HF method, the process of the present invention has significant advantages in terms of safety, processing time, cavitation intensity stability, economy, adaptability and environmental protection, while maintaining comparable performance.

[0074] The above are merely preferred embodiments of the present invention; however, the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and its improved concept, should be covered within the scope of protection of the present invention.

Claims

1. A biomass iron removal and deashing process based on ultrasonic cavitation, characterized in that, Includes the following steps: Step (1), dilute acid pretreatment: put the dried biomass into the reactor, prepare a suspension, add dilute acid to the final concentration of 0.5-1.0%, and stir evenly; wherein, the dilute acid is one of acetic acid, oxalic acid or hydrochloric acid; Step (2), ultrasonic cavitation desorption: Apply ultrasonic waves with a frequency of 20-40 kHz and a power density of 0.8-1.5 W / cm² to the suspension in step (1), while simultaneously performing microporous aeration at a rate of 0.3-0.7 L / min·L and monitoring the pH in real time. Step (3), alkaline deep desilication: When the pH of the suspension in step (2) rises to 4.0-4.5, add NaOH solution with a concentration of 0.05-0.2mol / L, continue to apply ultrasonic treatment, and after completion, perform solid-liquid separation on the material and wash it until neutral.

2. The biomass iron removal and deashing process based on ultrasonic cavitation according to claim 1, characterized in that, In step (1), the concentration of dilute acid is 0.6-0.9%.

3. The biomass iron removal and deashing process based on ultrasonic cavitation according to claim 1, characterized in that, In step (2), the ultrasonic frequency is 28-32 kHz and the aeration rate is 0.4-0.6 L / min·L.

4. The biomass iron removal and deashing process based on ultrasonic cavitation according to claim 1, characterized in that, In step (3), the concentration of the NaOH solution is 0.08-0.12 mol / L.

5. The biomass iron removal and deashing process based on ultrasonic cavitation according to claim 1, characterized in that, In step (3), the frequency of the additional ultrasonic treatment is 25-35 kHz.

6. The biomass iron removal and deashing process based on ultrasonic cavitation according to claim 1, characterized in that, In step (2), the bubble size of the microporous aeration is controlled to be 50-300μm.

7. The biomass iron removal and deashing process based on ultrasonic cavitation according to claim 1, characterized in that, In step (1), the stirring time is 5 minutes; In step (2), the ultrasonic cavitation desorption time is 30-60 minutes; In step (3), additional ultrasonic treatment is applied for 5-15 minutes.

8. The biomass iron removal and deashing process based on ultrasonic cavitation according to claim 1, characterized in that, The biomass is one of sugarcane bagasse, straw, or rice husk.

9. A biomass iron removal and deashing process based on ultrasonic cavitation according to any one of claims 1-8, characterized in that, The processing temperature in steps (1)-(3) is controlled at 30-50℃.

10. The application of the biomass iron removal and deashing process based on ultrasonic cavitation according to any one of claims 1-9 in the preparation of hard carbon anode materials for sodium-ion batteries, characterized in that, The biomass treated in step (3) is carbonized to obtain hard carbon material with ash content ≤0.5% and iron content ≤60 ppm.

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