System and method for preparing leather tanning agent by using chromium-containing wastewater

Abstract

The invention discloses a system for preparing a leather tanning agent by using chromium-containing wastewater, the system comprises a drainage pipe and a circulating pipe, the drainage pipe and the circulating pipe are both connected with a tanning drum, a recycling unit is arranged between the drainage pipe and the circulating pipe, and the recycling unit is used for recycling water used by the tanning drum; the invention relates to the technical field of leather tanning agent recycling, in-situ regeneration and closed-loop recycling of chromium-containing wastewater are achieved through an integrated system, the traditional chromium recycling process is shortened, the recycling rate is increased to 95% or above, the physicochemical performance of a regenerated tanning agent completely reaches the standard, the regenerated tanning agent can be directly supplied to a tanning drum, the core problems that a circulation link is too long, and recycling is not thorough are thoroughly solved, and the recovery efficiency is improved. And after being recycled, the chromium is directly used for tanning production by directly reproportioning the chromium, so that the hazardous waste discharge and the production cost are synchronously reduced, and the waste of the chromium material is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of leather tanning agent recovery, in particular to a system and method for preparing leather tanning agent by utilizing chromium-containing wastewater. Background Art

[0002] In the modern leather production process, leather tanning agent is an important auxiliary agent for leather processing. It is an active substance with multiple functional groups. Its molecular structure contains at least two or more functional groups. The tanning agent can form intramolecular bonds with two or more action points in the collagen structure, and at the same time can destroy part of the intramolecular bonds in the collagen and produce more new intermolecular cross-links, thus having a tanning effect.

[0003] During the tanning process of leather, leather tanning agents form new intermolecular bonds in the collagen structure through functional groups, which changes the physical and chemical properties of collagen, increases the strength of collagen fiber bundles, and further increases the shrinkage temperature of the leather, achieving the purpose of water resistance, heat and humidity stability, and non-corruption resistance, thereby increasing the durability and flexibility of the leather.

[0004] Among the commonly used leather tanning agents, chrome tanning is the mainstream technology of modern leather making with basic chromium sulfate as the core tanning agent. The tanning process requires acid pretreatment to adjust the pH value to 2.0-3.0, and commercial chromium powder or self-prepared tanning agents are used to implement staged alkali addition operations. The leather tanned by chrome tanning has the characteristics of high extensibility, softness and fullness, stable resistance to moisture and heat, good water vapor permeability and corrosion resistance, so it is widely used. However, in the application of chrome tanning, the treatment of a large amount of chromium-containing wastewater has always been a major problem.

[0005] The direct discharge of chromium-containing wastewater not only pollutes the environment, but also contains a large amount of recyclable resources. At present, the treatment of chromium-containing wastewater has always been mainly based on recycling. By reversely treating chromium-containing wastewater, the chromium emission can be greatly reduced and the utilization rate of chromium can be improved.

[0006] As described in patent publication number CN102381781 B, the existing leather chrome tanning wastewater recovery process generally adopts wastewater diversion, multiple filtration to remove impurities, and then recovers chrome mud by adding alkali precipitation (assisted by anionic polyacrylamide to accelerate sedimentation). This process can indeed effectively increase the chromium trioxide content in chrome mud (>8wt%), meet the requirements of subsequent deep processing, and make the treated wastewater meet the discharge standards. However, this "chrome mud recovery" model has significant limitations: first, it is highly dependent on additional deep processing systems. The recovered chrome mud requires special deep processing, such as acid dissolution and purification, before it can be converted back into a usable chrome tanning agent, which significantly increases the process complexity and equipment investment costs. Secondly, it cannot be directly reused for tanning. The chrome mud itself is not in a form that can be directly used for tanning and must undergo a conversion step, which cuts off the direct connection between the wastewater and the tanning process. Finally, the circulation chain is lengthy and inefficient. The entire "recovery-deep processing-reuse" process has a long chain and many links, resulting in reduced chromium resource recycling efficiency and increased energy consumption and time. Therefore, a more efficient and economical chromium recovery strategy is urgently needed. In view of this, in-depth research on the above issues has led to the creation of this case. Summary of the Invention

[0007] In view of the deficiencies of the prior art, the present invention provides a system and method for preparing leather tanning agents using chromium-containing wastewater, which solves the problems of the prior art.

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions: a system for preparing leather tanning agents using chromium-containing wastewater, comprising a drainage pipe and a circulation pipe, both of which are connected to a tanning drum, a recycling unit being provided between the drainage pipe and the circulation pipe, and the recycling unit being used to recycle water used in the tanning drum;

[0009] The circulation recovery unit includes a buffer dosing mechanism, which is connected to a drainage pipe and is used to add a treatment agent to the chromium-containing wastewater. The buffer dosing mechanism is connected to a pretreatment mechanism, which is used to pretreat the chromium-containing wastewater. The pretreatment process includes stirring, flocculation and filtration. The pretreatment mechanism is connected to a tanning agent recovery mechanism, which concentrates and separates the pretreated wastewater by membrane concentration. The tanning agent recovery mechanism is connected to a tanning agent ratio adjustment mechanism, which performs pH calibration and re-proportioning on the concentrated and separated chromium-containing water. The tanning agent ratio adjustment mechanism is connected to the circulation pipe through a buffer storage device.

[0010] The buffer dosing mechanism, pretreatment mechanism, tanning agent recovery mechanism and tanning agent ratio adjustment mechanism are all integrated on the skid-mounted frame;

[0011] The pretreatment mechanism includes a crushing structure, which is connected to the buffer dosing mechanism. The crushing structure is connected to a rotary separator. The crushing structure crushes the hair and flocculants in the chromium-containing wastewater, and the rotary separator separates the flocculants and hair.

[0012] The tanning agent recovery mechanism includes a tanning agent recovery rack, which is installed on a skid-mounted rack. A membrane separation box is provided on the tanning agent recovery rack, which is connected to a rotary separator. A membrane separation structure is provided on the membrane separation box, and a control component is connected to one side of the membrane separation structure. The control component is used to control the control pressure of the membrane separation structure.

[0013] The skid-mounted frame is a rectangular frame. A support frame welded from I-beams is provided at the bottom of the skid-mounted frame. A controller is provided on one side of the skid-mounted frame.

[0014] The buffer dosing mechanism includes a buffer tank, which is installed on a tanning agent recovery rack. A drainage pump is connected to one side of the buffer tank, and the drainage pump is connected to a drainage pipe. A drain pipe is provided on the top of the buffer tank. An automatic dosing device is provided on the buffer tank, and the automatic dosing device is a piston dosing device controlled by an electric push rod.

[0015] The crushing structure includes a crushing box, which is connected to a drain pipe. A rotating shaft is installed on the crushing box. Crushing blades are arranged on the rotating shaft. The crushing blades are installed on the rotating shaft in a multi-stage series manner.

[0016] The rotary separator includes a rotary membrane separation box, which is installed on one side of the crushing tank. A separation drum is provided in the rotary separation box, and the separation drum is connected to the rotating shaft. The rotary separation box is connected to the crushing box through several water supply pipes. Filter holes are evenly distributed on the separation drum, and a separation component is provided on the outside of the separation drum.

[0017] The separation assembly includes a separation spiral plate, which is arranged outside the separation drum and contacts the inner wall of the rotary separation box. A discharge port is provided on one side of the rotary separation box, and a telescopic discharger controlled by a cylinder is provided on the discharge port.

[0018] The membrane separation structure includes a membrane separation box, which is installed on one side of the rotating separation box. The membrane separation box is communicated with the rotating separation box, and the membrane separation box is connected to a guide frame. A pair of guide blocks are provided on the guide frame, and a separation membrane group is assembled on the guide frame. A control component is installed on the membrane separation box, and the control component is used to control the guide frame to expand and contract in the membrane separation box to adjust the osmotic pressure of the separation membrane group.

[0019] The membrane separation box is a hollow shell with a rectangular structure. The membrane separation box is connected to the rotary separation box through a connecting pipe. The guide frame is a frame with a rectangular structure. The separation membrane group includes a membrane frame with a rectangular structure. Several separation cylinders are arranged in a matrix on the membrane frame. The separation cylinders are double-layer membrane cylinders, namely nanofiltration membrane and reverse osmosis membrane.

[0020] The control component includes an adjusting motor, which is installed on the membrane separation box. The driving end of the adjusting motor is connected to a gear set, the gear set is connected to a control sleeve, the control sleeve is threaded with a telescopic rod, and the telescopic rod is connected to the guide frame.

[0021] The tanning agent ratio adjustment mechanism includes a mixing cylinder, which is connected to the membrane separation box. A power component is provided on one side of the mixing cylinder. A mixing shaft is installed in the mixing cylinder and is connected to the power component. A mixer is provided on the mixing shaft. The mixing shaft and the rotating shaft are linked to the separation drum. A pH detector is provided on the mixing cylinder, and a mixing doser is provided on the mixing cylinder.

[0022] The buffer storage includes a buffer box, the buffer box is communicated with the mixing cylinder, the mixing cylinder is connected to a circulation pipe, and a reflux control valve is provided on the circulation pipe.

[0023] A method for preparing a leather tanning agent using chromium-containing wastewater comprises the following steps:

[0024] Step 1: Reduction treatment of chromium-containing wastewater: The wastewater discharged from the tanning drum is pumped into the buffer tank through the drainage pipe, and a quantitative reducing agent NaHSO3 solution is injected through the electric push rod piston dosing device. The stirrer is started and mixed for 15-20 minutes to reduce the highly toxic Cr 6+ Reduction to Cr 3+ , and simultaneously adjust the pH to 3.0-4.0 to complete the toxicity transformation and reaction environment preparation;

[0025] Step 2: Solid-phase impurity crushing and separation: After the wastewater enters the pulverizing box, multi-stage series pulverizing blades rotate at a high speed of 1200 rpm to shred hair and flocculants. The shredded mixture enters the rotary separation box through the water supply pipe. The separation drum rotates synchronously to generate centrifugal force, allowing the filtrate to penetrate the 0.5mm filter pores. The external separation spiral plate rotates closely against the box wall with a gap of ≤1mm, pushing the residue axially to the discharge port. The cylinder drives the telescopic discharger to extend 100mm according to the set cycle, opening the slag discharge channel to discharge solid slag with a moisture content of less than 30%;

[0026] Step 3: Dynamic switching of membrane separation mode: The filtrate flows into the membrane separation box through the membrane separation box, and the regulating motor drives the control sleeve to rotate through the reduction gear set, driving the ball screw type telescopic rod to push the guide frame to move: the telescopic rod extends to make the membrane group close to the box wall, and the nanofiltration membrane retains organic matter with a molecular weight cutoff of 200Da; when the conductivity of the concentrate is greater than 80mS / cm, the telescopic rod retracts 150mm, leaving the membrane group suspended in the air, and switches to reverse osmosis mode;

[0027] Step 4: High-pressure enrichment of chromium ions: In reverse osmosis mode, the control system dynamically increases the membrane pressure to 3.0 MPa, and the reverse osmosis membrane selectively intercepts Cr. 3+ Ions are continuously concentrated to a concentration of ≥80g / L, and the liquid inlet valve is automatically closed at the end of concentration;

[0028] Step 5: Dynamic adjustment of the proportion online: After the concentrate enters the mixing cylinder, the pH detector monitors the pH in real time. When the pH is less than 2.5, the metering pump is triggered to inject 10% sodium carbonate solution. 3+ The concentration sensor is linked to add 5% sodium formate masking agent;

[0029] The mixing shaft is linked to the crushing shaft at a speed ratio of 1:2 through a chain drive, driving the blades to form a three-dimensional mixing flow field, and stirring at a constant speed of 60 rpm for 20 minutes;

[0030] Step 6 Standardized quality control of regenerated tanning agent: Continue stirring until the solution reaches Cr2O3 content ≥ 26% and alkalinity 40% ± 2% detected by hydrometer, and the solution is blue-green and transparent. After meeting the standards, it is injected into the buffer tank through the delivery pump;

[0031] Step 7: Temporary buffer storage: The liquid level sensor in the buffer tank controls the storage in the range of 70%-90%, and the constant temperature system maintains 25±2℃ to prevent chromium ion oxidation;

[0032] Step 8: Closed-loop precise recycling control: When the tanning drum sends a rehydration signal, the pneumatic butterfly valve opens to the set opening within 1 second; the flow meter accurately delivers the regenerated tanning agent at 5%-10% of the drum volume; the tensile strength of the leather after recycling is monitored online to be ≥18MPa and the chromium content, and the data is fed back to the PLC to optimize subsequent ratio parameters.

[0033] Beneficial effects

[0034] The present invention provides a system and method for preparing leather tanning agents using chromium-containing wastewater. This system achieves the following beneficial effects: Through an integrated system, in-situ regeneration and closed-loop reuse of chromium-containing wastewater are achieved, shortening the traditional chromium recovery process and increasing the recovery rate to over 95%. The regenerated tanning agent fully meets the physical and chemical performance standards and can be directly supplied to the tanning drum, thoroughly resolving the core issues of excessively long recycling links and incomplete recovery. After recovery, the chromium is directly re-proportioned and used directly in tanning production, simultaneously reducing hazardous waste emissions and production costs, and avoiding waste of chromium materials. The system also has the following advantages:

[0035] 1. Dynamic membrane separation technology achieves efficient enrichment of chromium ions (concentration ≥ 80g / L) through mechanical pressure regulation (0.5→3.0MPa gradient switching) combined with nanofiltration-reverse osmosis dual membrane synergy, and the recovery rate jumps from 65% of the traditional process to 95%. The crushing-separation linkage mechanism synchronizes crushing and centrifugal filtration, greatly improving the efficiency of solid residue treatment. The moisture content of the residue is less than 30% and can be directly incinerated to avoid secondary pollution.

[0036] 2. The online proportioning system is linked to the metering pump through the pH detector to accurately inject the masking agent and alkalinity regulator to ensure that the Cr2O3 content of the regenerated tanning agent is ≥26% and the alkalinity is 40%±2%. The tensile strength and tear strength of leather tanned with the regenerated tanning agent are improved to meet the high-end leather mechanical standards.

[0037] 3. The closed-loop system eliminates the need for chrome sludge transportation and reprocessing, effectively reducing energy consumption and significantly reducing emissions of chrome-containing sludge. The cyanide-free and palladium-free formula + inert gas protection buffer reduces wastewater treatment costs and heavy metal emissions, complying with the RoHS directive.

[0038] 4. The PLC system monitors membrane pressure, pH and slag discharge cycle in real time, and abnormal data triggers audible and visual alarms; the pneumatic butterfly valve responds to the drum refill demand within 1 second, and the flow meter accurately controls the reuse amount to achieve zero-interruption production. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a first stereoscopic structural schematic diagram of a system and method for preparing leather tanning agents using chromium-containing wastewater according to the present invention.

[0040] Figure 2 This is a second stereoscopic structural schematic diagram of a system and method for preparing leather tanning agents using chromium-containing wastewater according to the present invention.

[0041] Figure 3 This is a third stereoscopic structural schematic diagram of a system and method for preparing leather tanning agents using chromium-containing wastewater as described in the present invention.

[0042] Figure 4 This is a fourth stereoscopic structural schematic diagram of a system and method for preparing leather tanning agents using chromium-containing wastewater as described in the present invention.

[0043] Figure 5 This is a fifth stereoscopic structural schematic diagram of a system and method for preparing leather tanning agents using chromium-containing wastewater as described in the present invention.

[0044] Figure 6 This is the sixth stereoscopic structural schematic diagram of the system and method for preparing leather tanning agent using chromium-containing wastewater according to the present invention.

[0045] Figure 7This is the seventh stereoscopic structural schematic diagram of a system and method for preparing leather tanning agents using chromium-containing wastewater as described in the present invention.

[0046] Figure 8 This is the eighth stereoscopic structural schematic diagram of the system and method for preparing leather tanning agent using chromium-containing wastewater as described in the present invention.

[0047] Figure 9 This is the ninth stereoscopic structural schematic diagram of the system and method for preparing leather tanning agent using chromium-containing wastewater as described in the present invention.

[0048] In the figure: 1. Drainage pipe; 2. Circulation pipe; 3. Buffer dosing mechanism; 4. Pretreatment mechanism; 5. Tanning agent recovery mechanism; 6. Tanning agent ratio adjustment mechanism; 7. Buffer storage; 8. Skid-mounted rack; 9. Controller; 31. Buffer tank; 32. Drainage pump; 33. Drain pipe; 34. Automatic dosing device; 41. Crushing structure; 42. Rotary separator; 51. Tanning agent recovery rack; 52. Membrane separation box; 53. Membrane separation structure; 54. Control component; 61. Mixing cylinder; 62. Power component; 63. Mixing Dispenser; 64, pH detector; 65, mixing and adding device; 71, buffer box; 411, crushing box; 412, rotating shaft; 413, crushing blade; 421, rotating separation tank; 422, separation drum; 423, water supply pipe; 424, separation spiral plate; 425, discharge port; 426, telescopic discharger; 531, guide block; 532, separation membrane group; 533, membrane frame; 534, separation cylinder; 541, regulating motor; 542, gear set; 543, control shaft sleeve; 544, telescopic rod. DETAILED DESCRIPTION

[0049] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0050] See also Figure 1-9 The present invention provides an implementation scheme: In modern leather manufacturing processes, leather tanning primarily utilizes leather tanning agents to alter the physical properties of leather, improving its flexibility, durability, breathability, and corrosion resistance. Chrome tanning is widely used due to its high tanning efficiency and excellent tanning results. However, this method produces a large amount of chromium-containing wastewater. Currently, the recovery of chromium-containing wastewater primarily focuses on separating chromium mud and then reproducing chromium powder from the mud. This results in an excessively long recycling process during the application process, resulting in incomplete chromium recovery and the inability of the separated chromium to directly contribute to the tanning process.

[0051] According to the instruction manual Figure 1-9 It can be seen that in order to solve the above problems, the present application discloses a system for preparing leather tanning agent using chromium-containing wastewater, comprising a drainage pipe 1 and a circulation pipe 2, both of which are connected to a tanning drum, and a recycling unit is provided between the drainage pipe 1 and the circulation pipe 2, which is used to recycle and recycle the water used in the tanning drum;

[0052] The unit is highly integrated through a skid-mounted frame 8, which is a rectangular structural frame. The I-beam support frame at the bottom carries the equipment operating load, and the side controller 9 centrally monitors the operating status.

[0053] According to the instruction manual Figure 1-9 It can be seen that the above-mentioned recycling unit includes a buffer dosing mechanism 3, which is connected to the drainage pipe 1. The automatic dosing device 34 on the top of the buffer tank 31 adopts an electric push rod piston type to accurately inject the reducing agent. The drainage pump 32 synchronously transports the chromium-containing wastewater to complete the hexavalent chromium reduction reaction in the tank; the buffer dosing mechanism 3 is connected to the pretreatment mechanism 4, which is used to pretreat the chromium-containing wastewater. The pretreatment process includes stirring, flocculation and filtration. Specifically, the multi-stage series crushing blades 413 of the crushing structure 41 rotate at high speed to chop solid impurities, and the separation drum 422 of the rotary separator 42 rotates synchronously to implement solid-liquid separation - the separation spiral plate 424 rotates close to the box wall, and pushes the residue after extrusion and dehydration to the cylinder-controlled telescopic discharger 426 for regular discharge;

[0054] According to the instruction manual Figure 1-9 It can be seen that the tanning agent recovery mechanism 5 is connected to the back of the pretreatment mechanism 4. The tanning agent recovery mechanism 5 concentrates and separates the pretreated wastewater through membrane concentration. The guide frame in the membrane separation box 52 moves in a controlled manner: the regulating motor 541 drives the control sleeve 543 to rotate through the gear set 542, driving the threaded telescopic rod 544 to push the frame to move, dynamically adjusting the working pressure of the separation membrane group 532, and removing organic matter through low-pressure nanofiltration → concentrating chromium ions through high-pressure reverse osmosis;

[0055] The tanning agent recovery mechanism 5 is connected to a tanning agent ratio adjustment mechanism 6, which calibrates the pH of the concentrated and separated chromium-containing water and re-proportions it. The pH detector 64 of the mixing cylinder 61 monitors the pH of the solution in real time, and the mixing and dosing device 65 is linked to inject chemical agents.

[0056] The mixing shaft rotates synchronously with the rotating shaft 412 through a linkage mechanism, driving the mixer 63 to evenly mix the ingredients and output a qualified regenerated tanning agent. The tanning agent ratio adjustment mechanism 6 is connected to the circulation pipe 2 through the buffer storage 7. The buffer tank 71 temporarily stores the regenerated tanning agent. The reflux control valve is intelligently opened and closed according to the demand of the drum, realizing a closed-loop reuse of chromium resources.

[0057] The buffer dosing mechanism 3, the pretreatment mechanism 4, the tanning agent recovery mechanism 5 and the tanning agent ratio adjustment mechanism 6 are all integrated on the skid-mounted frame 8, which facilitates the overall deployment of the equipment;

[0058] According to the instruction manual Figure 1-9 As can be seen, the above-mentioned pretreatment mechanism 4 includes a crushing structure 41, which is sealedly connected to the buffer dosing mechanism 3 through a drain pipe 33. When the wastewater enters the crushing box 411, it is chopped into impurities by the high-speed rotating crushing blades 413. The crushing structure 41 is connected to a rotary separator 42. The crushing structure 41 crushes the hair and flocculants in the chromium-containing wastewater. The chopped mixture enters the rotary separation box through the water supply pipe 423. The rotary separator 42 separates the flocculants and hair. The separation drum 422 rotates synchronously with the crushing shaft. The surface filter holes separate the filtrate. The external separation spiral plate 424 pushes the residue to the telescopic discharger 426.

[0059] According to the instruction manual Figure 1-9 It can be seen that the above-mentioned tanning agent recovery mechanism 5 includes a tanning agent recovery frame 51, which is installed on the skid-mounted frame 8. A membrane separation box 52 is provided on the tanning agent recovery frame 51, and the membrane separation box 52 is connected to the rotary separator 42. The membrane separation box 52 receives the filtrate of the rotary separator 42 and transmits it to the membrane separation box 52. A membrane separation structure 53 is provided on the membrane separation box 52, and a control component 54 is connected to one side of the membrane separation structure 53. The control component 54 is used to control the control pressure of the membrane separation structure 53; the telescopic rod 544 accurately adjusts the position of the guide frame according to the system instructions, changes the gap between the membrane group and the box body to control the osmotic pressure.

[0060] The skid-mounted frame 8 is a rectangular frame. A support frame made of I-beams is provided at the bottom of the skid-mounted frame 8. A controller 9 is provided on one side of the skid-mounted frame 8. The panel displays the membrane pressure status, dosage and slag discharge cycle in real time.

[0061] According to the instruction manual Figure 1-9 It can be seen that the above-mentioned buffer dosing mechanism 3 includes a buffer tank 31, which is installed on the tanning agent recovery frame 51. A drainage pump 32 is connected to one side of the buffer tank 31, and the drainage pump 32 is connected to the drainage pipe 1. A drain pipe 33 is provided on the top of the buffer tank 31, and an automatic dosing device 34 is provided on the buffer tank 31. The automatic dosing device 34 is a piston dosing device controlled by an electric push rod; the electric push rod pushes the piston according to the PLC instruction to realize the quantitative and accurate dosing of the reducing agent.

[0062] According to the instruction manual Figure 1-9It can be seen that the above-mentioned crushing structure 41 includes a crushing box 411, which is connected to the drain pipe 33. After the wastewater enters, it is cut by the multi-stage crushing blades 413. A rotating shaft 412 is installed on the crushing box 411, and crushing blades 413 are arranged on the outer cover of the rotating shaft 412. The crushing blades 413 are installed on the rotating shaft 412 in a multi-stage series manner. The multi-stage blades form a stepped crushing chamber to ensure that the impurities are fully crushed.

[0063] According to the instruction manual Figure 1-9 It can be seen that the above-mentioned rotary separator 42 includes a rotary membrane separation box 52, which is installed on one side of the crushing tank. The two boxes are sealed and connected by a flange. A separation drum 422 is provided in the rotary separation box. The separation drum 422 is rigidly connected to the rotating shaft 412 through a coupling to achieve synchronous rotation with the crushing blade 413. The rotary separation box is connected to the crushing box 411 through a number of water supply pipes 423. Filter holes are evenly distributed on the separation drum 422. When rotating at high speed, centrifugal force is generated to accelerate the penetration of the filtrate. A separation component is provided on the outside of the separation drum 422.

[0064] According to the instruction manual Figure 1-9 It can be seen that the above-mentioned separation component includes a separation spiral plate 424, and a separation spiral plate 424 is arranged outside the separation drum 422. The separation spiral plate 424 rotates with a gap of ≤1mm with the inner wall of the rotating separation box, continuously pushing the residue to move axially, and a discharge port 425 is provided on one side of the rotating separation box. A cylinder-controlled telescopic discharger 426 is provided on the discharge port 425; the cylinder pushes the discharger out according to the set cycle to open the slag discharge channel.

[0065] The membrane separation structure 53 includes a membrane separation box 52, which is installed on one side of the rotating separation box. The two boxes are connected by a corrosion-resistant connecting pipe. The membrane separation box 52 is connected to the guide frame. A pair of guide blocks 531 are provided on the guide frame, which slide precisely along the guide rails in the box. The guide frame is equipped with a separation membrane group 532. A control component 54 is installed on the membrane separation box 52. The control component 54 controls the guide frame to extend and retract in the membrane separation box 52 to adjust the osmotic pressure of the separation membrane group 532; when the telescopic rod 544 is displaced, the distance between the membrane group and the box wall is changed to realize the mode switching between low-pressure nanofiltration and high-pressure reverse osmosis.

[0066] The membrane separation box 52 is a hollow shell with a rectangular structure. The membrane separation box 52 is connected to the rotary separation box through a connecting pipe. The guide frame is a rectangular frame. The separation membrane group 532 includes a rectangular membrane frame 533. A plurality of separation cylinders 534 are arranged in a matrix on the membrane frame 533. The separation cylinders 534 are double-layer membrane cylinders, namely nanofiltration membrane and reverse osmosis membrane; the nanofiltration membrane layer first intercepts organic matter, and the reverse osmosis membrane layer deeply concentrates chromium ions.

[0067] The control component 54 includes an adjusting motor 541, which is installed on the membrane separation box 52. The driving end of the adjusting motor 541 is connected to a gear set 542 to achieve torque amplification and speed control. The gear set 542 is connected to a control sleeve 543, and the control sleeve 543 is threadedly connected to a telescopic rod 544, which is connected to the guide frame; the threaded transmission converts rotational motion into linear displacement to accurately control the position of the membrane group.

[0068] The tanning agent recovery mechanism 5 is connected to a tanning agent ratio adjustment mechanism 6, which includes a mixing cylinder 61. The mixing cylinder 61 is connected to the membrane separation box 52 to receive the concentrated chromium liquid. A power component 62 is provided on one side of the mixing cylinder 61. A mixing shaft is assembled in the mixing cylinder 61 and is connected to the power component 62. A speed ratio linkage is formed with the rotating shaft 412 through a chain drive. A mixer 63 is provided on the mixing shaft. The blades of the mixer 63 generate radial and axial mixed flow fields. The mixing shaft, the rotating shaft 412 and the separation drum 422 are linked. A pH detector 64 is provided on the mixing cylinder 61 to provide real-time feedback on the pH value of the solution. A mixing doser 65 is provided on the mixing cylinder 61; the masking agent and alkalinity regulator are automatically injected according to the pH and concentration data.

[0069] The buffer storage 7 includes a buffer box 71, which is connected to the mixing cylinder 61 and stores qualified regenerated tanning agent. The mixing cylinder 61 is connected to the circulation pipe 2, and a reflux control valve is provided on the circulation pipe 2; the pneumatic butterfly valve responds to the drum demand signal to accurately control the reflux amount of tanning agent.

[0070] In order to match the above-mentioned equipment, the present application also discloses a method for preparing a leather tanning agent using chromium-containing wastewater, comprising the following steps:

[0071] Step 1: Reduction treatment of chromium-containing wastewater: The wastewater discharged from the tanning drum is pumped into the buffer tank through the drainage pipe, and a quantitative reducing agent NaHSO3 solution is injected through the electric push rod piston dosing device. The stirrer is started and mixed for 15-20 minutes to reduce the highly toxic Cr 6+ Reduction to Cr 3+ , and simultaneously adjust the pH to 3.0-4.0 to complete the toxicity transformation and reaction environment preparation;

[0072] Step 2: Solid-phase impurity crushing and separation: After the wastewater enters the pulverizing box, multi-stage series pulverizing blades rotate at a high speed of 1200 rpm to shred hair and flocculants. The shredded mixture enters the rotary separation box through the water supply pipe. The separation drum rotates synchronously to generate centrifugal force, allowing the filtrate to penetrate the 0.5mm filter pores. The external separation spiral plate rotates closely against the box wall with a gap of ≤1mm, pushing the residue axially to the discharge port. The cylinder drives the telescopic discharger to extend 100mm according to the set cycle, opening the slag discharge channel to discharge solid slag with a moisture content of less than 30%;

[0073] Step 3: Dynamic switching of membrane separation mode: The filtrate flows into the membrane separation box through the membrane separation box, and the regulating motor drives the control sleeve to rotate through the reduction gear set, driving the ball screw type telescopic rod to push the guide frame to move: the telescopic rod extends to make the membrane group close to the box wall, and the nanofiltration membrane retains organic matter with a molecular weight cutoff of 200Da; when the conductivity of the concentrate is greater than 80mS / cm, the telescopic rod retracts 150mm, leaving the membrane group suspended in the air, and switches to reverse osmosis mode;

[0074] Step 4: High-pressure enrichment of chromium ions: In reverse osmosis mode, the control system dynamically increases the membrane pressure to 3.0 MPa, and the reverse osmosis membrane selectively intercepts Cr. 3+ Ions are continuously concentrated to a concentration of ≥80g / L, and the liquid inlet valve is automatically closed at the end of concentration;

[0075] Step 5: Dynamic adjustment of the proportion online: After the concentrate enters the mixing cylinder, the pH detector monitors the pH in real time. When the pH is less than 2.5, the metering pump is triggered to inject 10% sodium carbonate solution. 3+ The concentration sensor is linked to add 5% sodium formate masking agent;

[0076] The mixing shaft is linked to the crushing shaft at a speed ratio of 1:2 through a chain drive, driving the blades to form a three-dimensional mixing flow field, and stirring at a constant speed of 60 rpm for 20 minutes;

[0077] Step 6 Standardized quality control of regenerated tanning agent: Continue stirring until the solution reaches Cr2O3 content ≥ 26% and alkalinity 40% ± 2% detected by hydrometer, and the solution is blue-green and transparent. After meeting the standards, it is injected into the buffer tank through the delivery pump;

[0078] Step 7: Temporary buffer storage: The liquid level sensor in the buffer tank controls the storage in the range of 70%-90%, and the constant temperature system maintains 25±2℃ to prevent chromium ion oxidation;

[0079] Step 8: Closed-loop precise recycling control: When the tanning drum sends a rehydration signal, the pneumatic butterfly valve opens to the set opening within 1 second; the flow meter accurately delivers the regenerated tanning agent at 5%-10% of the drum volume; the tensile strength of the leather after recycling is monitored online to be ≥18MPa and the chromium content, and the data is fed back to the PLC to optimize subsequent ratio parameters.

[0080] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A system for preparing leather tanning agent using chromium-containing wastewater, comprising a drainage pipe (1) and a circulation pipe (2), wherein the drainage pipe (1) and the circulation pipe (2) are both connected to a tanning drum, characterized in that: A recycling unit is provided between the drainage pipe (1) and the circulation pipe (2), and the recycling unit is used to carry out recycling treatment on the water used in the tanning drum; The recycling unit comprises a buffer dosing mechanism (3), the buffer dosing mechanism (3) is connected to the drainage pipe (1), the buffer dosing mechanism (3) is used to add a treatment agent to the chromium-containing wastewater, the buffer dosing mechanism (3) is connected to a pretreatment mechanism (4), the pretreatment mechanism (4) is used to pretreat the chromium-containing wastewater, and the pretreatment process includes stirring, flocculation and filtration, the pretreatment mechanism (4) is connected to a tanning agent recovery mechanism (5), the tanning agent recovery mechanism (5) concentrates and separates the pretreated wastewater by membrane concentration, the tanning agent recovery mechanism (5) is connected to a tanning agent ratio adjustment mechanism (6), the tanning agent ratio adjustment mechanism (6) performs pH calibration and re-proportioning on the concentrated and separated chromium-containing water, and the tanning agent ratio adjustment mechanism (6) is connected to the circulation pipe (2) via a buffer storage (7); The buffer dosing mechanism (3), pretreatment mechanism (4), tanning agent recovery mechanism (5) and tanning agent ratio adjustment mechanism (6) are all integrated on a skid-mounted frame (8); The pretreatment mechanism (4) includes a crushing structure (41), the crushing structure (41) is connected to the buffer dosing mechanism (3), the crushing structure (41) is connected to a rotary separator (42), the crushing structure (41) crushes the hair and flocculants in the chromium-containing wastewater, and the rotary separator (42) separates the flocculants and hair; The tanning agent recovery mechanism (5) comprises a tanning agent recovery frame (51), the tanning agent recovery frame (51) is mounted on a skid-mounted frame (8), a membrane separation box (52) is provided on the tanning agent recovery frame (51), the membrane separation box (52) is connected to a rotary separator (42), a membrane separation structure (53) is provided on the membrane separation box (52), one side of the membrane separation structure (53) is connected to a control component (54), and the control component (54) is used to control the control pressure of the membrane separation structure (53).

2. A system for preparing leather tanning agents using chromium-containing wastewater according to claim 1, characterized in that: The skid-mounted frame (8) is a rectangular frame. A support frame welded from I-beams is provided at the bottom of the skid-mounted frame (8). A controller (9) is provided on one side of the skid-mounted frame (8).

3. A system for preparing leather tanning agents using chromium-containing wastewater according to claim 2, characterized in that: The buffer dosing mechanism (3) comprises a buffer tank (31), the buffer tank (31) is mounted on a tanning agent recovery frame (51), a drainage pump (32) is connected to one side of the buffer tank (31), the drainage pump (32) is connected to a drainage pipe (1), a drain pipe (33) is provided on the top of the buffer tank (31), and an automatic dosing device (34) is provided on the buffer tank (31), and the automatic dosing device (34) is a piston dosing device controlled by an electric push rod.

4. A system for preparing leather tanning agents using chromium-containing wastewater according to claim 3, characterized in that: The crushing structure (41) comprises a crushing box (411), the crushing box (411) is connected to the drain pipe (33), a rotating shaft (412) is mounted on the crushing box (411), a crushing blade (413) is provided on the outer cover of the rotating shaft (412), and the crushing blade (413) is mounted on the rotating shaft (412) in a multi-stage series manner.

5. The system for preparing leather tanning agents using chromium-containing wastewater according to claim 4, characterized in that: The rotary separator (42) includes a rotary membrane separation box (52), which is installed on one side of the crushing tank. A separation drum (422) is provided in the rotary separation box, and the separation drum (422) is connected to the rotating shaft (412). The rotary separation box is connected to the crushing box (411) through a plurality of water supply pipes (423). Filter holes are evenly distributed on the separation drum (422), and a separation component is provided on the outside of the separation drum (422).

6. The system for preparing leather tanning agents using chromium-containing wastewater according to claim 5, characterized in that: The membrane separation structure (53) includes a membrane separation box (52), the membrane separation box (52) is installed on one side of the rotary separation box, the membrane separation box (52) is connected to the rotary separation box, the membrane separation box (52) is connected to a guide frame, a pair of guide blocks (531) are provided on the guide frame, a separation membrane group (532) is assembled on the guide frame, and a control component (54) is installed on the membrane separation box (52). The control component (54) controls the guide frame to expand and contract in the membrane separation box (52) to adjust the osmotic pressure of the separation membrane group (532).

7. A system for preparing leather tanning agents using chromium-containing wastewater according to claim 6, characterized in that: The control assembly (54) includes an adjusting motor (541), which is installed on the membrane separation box (52). The driving end of the adjusting motor (541) is connected to a gear set (542), the gear set (542) is connected to a control sleeve (543), the control sleeve (543) is threadedly connected to a telescopic rod (544), and the telescopic rod (544) is connected to a guide frame.

8. The system for preparing leather tanning agents using chromium-containing wastewater according to claim 7, characterized in that: The tanning agent ratio adjustment mechanism (6) includes a mixing cylinder (61), the mixing cylinder (61) is connected to the membrane separation box (52), a power assembly (62) is provided on one side of the mixing cylinder (61), a mixing shaft is assembled in the mixing cylinder (61) and is connected to the power assembly (62), a mixer (63) is provided on the mixing shaft, the mixing shaft, the rotating shaft (412) and the separation drum (422) are linked, a pH detector (64) is provided on the mixing cylinder (61), and a mixing doser (65) is provided on the mixing cylinder (61).

9. The system for preparing leather tanning agents using chromium-containing wastewater according to claim 8, characterized in that: The buffer storage (7) comprises a buffer box (71), the buffer box (71) is communicated with a mixing cylinder (61), the mixing cylinder (61) is connected to a circulation pipe (2), and a reflux control valve is provided on the circulation pipe (2).

10. A method for preparing leather tanning agents using chromium-containing wastewater, applied to a system for preparing leather tanning agents using chromium-containing wastewater as claimed in any one of claims 1 to 9, characterized in that: The steps include: Step 1: Reduction treatment of chromium-containing wastewater: The wastewater discharged from the tanning drum is pumped into the buffer tank through the drainage pipe, and a quantitative reducing agent NaHSO3 solution is injected through the electric push rod piston dosing device. The stirrer is started and mixed for 15-20 minutes to reduce the highly toxic Cr 6+ Reduction to Cr 3+ , and simultaneously adjust the pH to 3.0-4.0 to complete the toxicity transformation and reaction environment preparation; Step 2: Solid-phase impurity crushing and separation: After the wastewater enters the pulverizing box, multi-stage series pulverizing blades rotate at a high speed of 1200 rpm to shred hair and flocculants. The shredded mixture enters the rotary separation box through the water supply pipe. The separation drum rotates synchronously to generate centrifugal force, allowing the filtrate to penetrate the 0.5mm filter pores. The external separation spiral plate rotates closely against the box wall with a gap of ≤1mm, pushing the residue axially to the discharge port. The cylinder drives the telescopic discharger to extend 100mm according to the set cycle, opening the slag discharge channel to discharge solid slag with a moisture content of less than 30%; Step 3: Dynamic switching of membrane separation mode: The filtrate flows into the membrane separation box through the membrane separation box, and the regulating motor drives the control sleeve to rotate through the reduction gear set, driving the ball screw type telescopic rod to push the guide frame to move: the telescopic rod extends to make the membrane group close to the box wall, and the nanofiltration membrane retains organic matter with a molecular weight cutoff of 200Da; when the conductivity of the concentrate is greater than 80mS / cm, the telescopic rod retracts 150mm, leaving the membrane group suspended in the air, and switches to reverse osmosis mode; Step 4: High-pressure enrichment of chromium ions: In reverse osmosis mode, the control system dynamically increases the membrane pressure to 3.0 MPa, and the reverse osmosis membrane selectively intercepts Cr. 3+ Ions are continuously concentrated to a concentration of ≥80g / L, and the liquid inlet valve is automatically closed at the end of concentration; Step 5: Dynamic adjustment of the proportion online: After the concentrate enters the mixing cylinder, the pH detector monitors the pH in real time. When the pH is less than 2.5, the metering pump is triggered to inject 10% sodium carbonate solution. 3+ The concentration sensor is linked to add 5% sodium formate masking agent; The mixing shaft is linked to the crushing shaft at a speed ratio of 1:2 through a chain drive, driving the blades to form a three-dimensional mixing flow field, and stirring at a constant speed of 60 rpm for 20 minutes; Step 6 Standardized quality control of regenerated tanning agent: Continue stirring until the solution reaches Cr2O3 content ≥ 26% and alkalinity 40% ± 2% detected by hydrometer, and the solution is blue-green and transparent. After meeting the standards, it is injected into the buffer tank through the delivery pump; Step 7: Temporary buffer storage: The liquid level sensor in the buffer tank controls the storage in the range of 70%-90%, and the constant temperature system maintains 25±2℃ to prevent chromium ion oxidation; Step 8: Closed-loop precise recycling control: When the tanning drum sends a rehydration signal, the pneumatic butterfly valve opens to the set opening within 1 second; the flow meter accurately delivers the regenerated tanning agent at 5%-10% of the drum volume; the tensile strength of the leather after recycling is monitored online to be ≥18MPa and the chromium content, and the data is fed back to the PLC to optimize subsequent ratio parameters.

Images