Method for comprehensive utilization of chromium-containing leather solid waste

Abstract

The present application relates to a kind of comprehensive utilization method of chromium-containing leather solid waste.First, water, glue extraction agent and chromium-containing leather solid waste are mixed to carry out glue extraction, and collagen product and chromium-containing filter residue are obtained;Then, chromium-containing filter residue is placed in anaerobic environment and pyrolysis carbonization is carried out at high temperature, and chromium-collagen anaerobic carbonized material is obtained;Finally, a series of treatments such as acid leaching, filtration, alkali precipitation and regeneration are carried out on chromium-collagen anaerobic carbonized material, and finally chromium-free anaerobic carbonized material and regenerated chrome tanning agent are obtained.The present application overcomes the problems of chromium-containing leather solid waste treatment difficulty, high treatment cost and other problems, completely solves the industry bottleneck problem of chromium-containing leather scrap and trimming edge material after extracting collagen, not only greatly reduces the treatment cost of chromium-containing leather solid waste, but also avoids environmental pollution caused by chromium-containing solid waste, and has good economic and social benefits.

Description

Technical Field

[0001] This invention relates to the field of leather technology, and more specifically to a method for the comprehensive utilization of chromium-containing leather solid waste. Background Technology

[0002] For a long time, chrome tanning has been the most important and widely used tanning method in leather manufacturing. It endows leather with excellent thermal stability, a comfortable feel, and superior leather-making properties. Currently, chrome tanning still holds an absolute dominant position in the leather industry. Statistics show that approximately 400,000 tons of chromium-containing leather scraps are produced worldwide annually. This heavy metal chromium pollution makes it difficult for the leather industry to break free from its traditional high-consumption, high-pollution production methods. Chromium-containing leather waste scraps are classified as hazardous waste, resulting in a lack of appropriate treatment methods for the leveling shavings, edge trimming solid waste, and chromium-containing sludge generated by leather tanneries. Currently, there are very few qualified companies to handle these hazardous wastes, leading to a continuous increase in treatment costs and adding significant storage, transportation, and disposal costs for leather tanneries.

[0003] The treatment and disposal of chromium-containing leather solid waste has always been a bottleneck restricting the development of leather tanning enterprises. Studies have shown that the main components of chromium-containing leather solid waste are collagen and chromium salts, but most of the trivalent chromium has coordinated with the carboxyl groups on the leather collagen fibers. Current research focuses on extracting collagen from chromium-containing leather scraps, but the remaining chromium-containing filter residue has drawbacks or problems such as low shrinkage temperature and dull appearance when directly or indirectly preparing chromium tanning agents for reuse, due to its complex composition, the difficulty in removing complexes formed by chromium and organic carboxylic acids, and the lack of relevant engineering application technologies for the utilization of chromium-containing waste residue. Under these circumstances, most leather tanning enterprises can only entrust qualified companies to handle the waste, and have to pay high treatment costs.

[0004] Anaerobic carbonization technology involves loading solid waste into a carbonization device and, under anaerobic conditions, using external heating, pyrolyzing the organic matter in the solid waste into non-toxic, harmless, and combustible gases, which are then directly reintroduced into the furnace as fuel. The final solid residue in the furnace consists of easily recyclable carbonides and inorganic substances. The fully sealed anaerobic carbonization technology effectively solves the problem of large amounts of hexavalent chromium produced during direct incineration of chromium-containing solid waste. After anaerobic carbonization, organic matter in the solid residue is effectively removed, and trivalent chromium is more easily recycled. Therefore, the implementation of this technology can effectively solve the environmental pollution problem of chromium-containing leather waste in the leather industry. It can also be used in conjunction with existing integrated equipment for the resource utilization of chromium-containing leather scraps, which is crucial for the green development of the leather industry. Furthermore, porous carbon materials prepared through anaerobic carbonization show great promise in water treatment, agricultural fertilizers, and catalysis due to their environmental friendliness, easily controllable pore structure, rich surface chemical functional groups, and significant adsorption and catalytic efficiency. Summary of the Invention

[0005] This invention primarily addresses the long-standing problems in the leather industry, such as the difficulty, high cost, and poor overall efficiency of treating chromium-containing leather solid waste. It provides a novel method for the comprehensive utilization of chromium-containing leather solid waste. This method creatively introduces an anaerobic carbonization process, which can sequentially separate and extract high-value collagen, anaerobic carbonization materials, and recycled chromium tanning agents from chromium-containing leather solid waste. This not only significantly reduces the treatment cost of chromium-containing leather solid waste but also avoids the environmental pollution caused by chromium-containing solid waste, resulting in significant economic and social benefits.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A comprehensive utilization method for chromium-containing leather solid waste mainly includes the following steps: First, the chromium-containing leather solid waste is subjected to pyrolysis and carbonization treatment under anaerobic conditions to obtain chromium-collagen anaerobic carbonization material; the chromium-collagen anaerobic carbonization material is further subjected to regeneration treatment to finally obtain regenerated chromium tanning agent and dechromium-removing anaerobic carbonization material.

[0008] Furthermore, the chromium-containing leather solid waste specifically includes chromium-containing shavings or wet blue leather trimming scraps from cowhide, sheepskin, and pigskin, with a chromium content (calculated as chromium trioxide) of 3.5%-5%.

[0009] Furthermore, the chromium-containing leather waste underwent a collagen extraction process before pyrolysis and carbonization. The specific process is as follows: the chromium-containing leather waste was washed several times, then mixed with an extractant and heated and stirred to extract the collagen. Finally, solid-liquid separation was performed to obtain a collagen solution and chromium-containing filter residue. The main component of chromium-containing leather scraps or offcuts is collagen, which can be used in industrial applications. Therefore, if carbonization is performed directly, the peptides in the collagen are destroyed, resulting in resource waste. The purpose of this invention in extracting collagen is to maximize the resource utilization of chromium-containing leather waste, and the chromium content in the obtained collagen can be controlled below 50 ppm.

[0010] Furthermore, the extractant comprises an alkali and an enzyme, wherein the alkali is selected from at least one of sodium carbonate, magnesium oxide, sodium hydroxide, potassium hydroxide, calcium oxide, calcium hydroxide, and ammonia water, and the enzyme is selected from at least one of 1398 enzyme, 2709 enzyme, trypsin, papain, and Bacillus subtilis neutral protease. Using an alkali method or an alkali-enzyme combination method, the hydrolyzed chromium can be precipitated, and after filtration, it can be easily separated from the collagen.

[0011] Furthermore, an appropriate amount of water was added during the extraction process, and the extraction temperature was 35-100℃. Water, as a dispersion medium, can maximize the dissolution and extraction of collagen. The chromium-containing slag is separated from the water phase after pressure filtration.

[0012] Furthermore, the specific process of the pyrolysis carbonization treatment is as follows: the chromium-containing leather solid waste or chromium-containing filter residue is thoroughly dried, then placed in a sealed container and heated and kept warm in an oxygen-free environment, and finally naturally cooled to room temperature to obtain chromium-collagen oxygen-free carbonized material.

[0013] Furthermore, the oxygen-free environment is achieved by filling the container with a protective atmosphere, which is selected from at least one of nitrogen, argon, and helium. The pyrolysis carbonization process of this invention has strict requirements on oxygen content; therefore, a method of replacing oxygen with a protective gas is chosen to ensure a consistently oxygen-free pyrolysis environment. Vacuuming, on the other hand, cannot completely eliminate the presence of oxygen.

[0014] Furthermore, the heating and holding processes during pyrolysis carbonization are divided into at least two stages, as follows: First, the temperature is increased from room temperature to 150-250℃ at a rate of 5-10℃ / min, and held at this temperature for 0.5-1.0h. The main purpose of this operation is to volatilize residual moisture and small molecule organic matter. Then, the temperature is increased to 400-900℃ at a rate of 5-10℃ / min, and held at this temperature for 3-48h. The main purpose of this operation is to ensure that the chromium-rubber raw materials are fully and thoroughly carbonized.

[0015] Furthermore, the specific process of the regeneration treatment is as follows: First, the chromium-collagen oxygen-free carbonized material is subjected to acid extraction to fully dissolve the chromium trioxide and completely enter the extraction solution, thereby obtaining the dechromated oxygen-free carbonized material and the chromium-rich extraction solution respectively; then, the pH of the chromium-rich extraction solution is adjusted to alkaline to generate chromium hydroxide precipitate, and after pressure filtration, a chromium cake is obtained; finally, the chromium cake is mixed with an acid reagent, and a masking agent is added to adjust the alkalinity of the mixture to improve the alkali resistance of the chromium tanning agent, and aged for more than 48 hours to obtain the regenerated chromium tanning agent.

[0016] Furthermore, the acidic medium used for acid extraction is selected from at least one of hydrochloric acid, sulfuric acid, and nitric acid, and the mass fraction of the acidic medium is 20%-98%.

[0017] Furthermore, the acid leaching temperature is 25-80℃, and the acid leaching time is 12-96h; after acid leaching, the filter is filtered to obtain filter residue and filtrate. The filter residue is repeatedly washed with water to obtain dechromium-free oxygen-free carbonized material. The washing liquid and filtrate are combined to obtain chromium-rich leaching solution.

[0018] Furthermore, the pH of the chromium-rich extract is adjusted to 8-10 using an alkali to induce precipitation. The alkali is selected from at least one of sodium carbonate, magnesium oxide, sodium hydroxide, and calcium oxide.

[0019] Furthermore, after the chromium cake and acid reagent are mixed evenly, the mixture is stirred at 35-95℃ for 40-60 minutes to completely dissolve the chromium cake. Then, an occlusive agent equivalent to 2%-6% of the weight of the chromium cake is added and stirred at 50-70℃ for 1-3 hours to improve the alkali resistance of the complex and make the tanned leather soft, full, and with a fine grain. After the mixture cools to room temperature, an alkaline reagent is added while stirring to adjust its alkalinity to 30%-38%. This operation is to control the chromium tanning agent to maintain an appropriate molecular size for better penetration.

[0020] Furthermore, the acid reagent is specifically sulfuric acid, the masking agent is selected from small molecule organic acid masking agents such as sodium formate, sodium acetate, and glycolic acid, or large molecule masking agents such as sodium phthalate, sodium lactate, and sodium citrate, and the alkaline reagent is specifically an aqueous solution of sodium bicarbonate, sodium carbonate, or ammonium bicarbonate.

[0021] The second objective of this invention is to provide a chromium-collagen oxygen-free carbonized material, which can be further applied to adsorbent materials, elastomer reinforcement materials, and catalyst-supported materials.

[0022] The third objective of this invention is to provide a dechromated oxygen-free carbonization material and to use it in biochar-based compound fertilizers, adsorbent materials, elastomer reinforcing materials, and catalyst-supported materials.

[0023] The fourth objective of this invention is to provide a recycled chrome tanning agent and to use it in leather tanning.

[0024] The method of this invention has the advantages of simple process and low cost. It can be used for the treatment and disposal of various types of chromium-containing leather solid waste and realize full recycling. The intermediate product chromium-collagen anaerobic carbonization material obtained during the process can be used to prepare adsorbent materials, elastomer reinforcement materials, and catalyst adsorbent materials. The dechromium-free anaerobic carbonization material obtained can also be used for biochar-based compound fertilizer materials and other applications. Comparative experimental results show that the tanning performance of the extracted regenerated chromium tanning agent is comparable to that of commercially available new chromium tanning agent, especially the shrinkage temperature index of the tanned blue wet leather is basically similar.

[0025] Compared with existing similar technologies, the advantages of this invention are mainly reflected in the following aspects:

[0026] (1) This invention extracts collagen from chromium-containing leather scraps and further utilizes the chromium-containing filter residue obtained by filtration through anaerobic carbonization technology to obtain a series of products with different uses and economic value, such as chromium-collagen anaerobic carbonization material, dechromiumized anaerobic carbonization material, and regenerated chromium tanning agent. It not only has a high resource utilization rate but also completely solves the problem of disposal of chromium-containing leather solid waste.

[0027] (2) The present invention carbonizes chromium-containing filter residue under anaerobic conditions to ensure that trivalent chromium ions are always stable. In contrast, trivalent chromium ions are easily oxidized into highly toxic hexavalent chromium during conventional incineration. Therefore, the method of the present invention is more conducive to the comprehensive development and utilization of trivalent chromium.

[0028] (3) In this invention, after the chromium-containing filter residue is pyrolyzed at high temperature and oxygen-free, the organic matter therein is fully carbonized. The remaining chromium trioxide can be obtained as a regenerated chromium tanning agent after acidification, alkali precipitation and regeneration. Compared with other existing chromium tanning agent regeneration methods, the method of this invention completely eliminates the small molecule organic matter that is bound to chromium, restores the tanning properties of the chromium tanning agent to the greatest extent, and makes its tanning performance comparable to that of new chromium tanning agents. It not only effectively recovers chromium for resource utilization, but also solves the problem of chromium salt emission pollution generated by the leather industry, and reduces the production, processing and environmental protection costs of the leather industry.

[0029] (4) By adjusting the parameters of the anaerobic carbonization process, this invention not only obtains regenerated chromium tanning agent, but also prepares a batch of porous biocarbon materials, which provides more possibilities for further processing and production of adsorbent materials, agricultural compound fertilizers and high-performance shoe elastomer composite materials, and the comprehensive benefits are particularly significant.

[0030] (5) The oxygen-free carbonization material and its dechromium removal treatment method provided by the present invention have good operability, are easy to promote and apply on a large scale, and have good market competitiveness. Detailed Implementation

[0031] To enable those skilled in the art to fully understand the technical solution and beneficial effects of the present invention, the following detailed description is provided in conjunction with specific embodiments.

[0032] The specific process of the comprehensive utilization method for chromium-containing leather solid waste provided by this invention is as follows:

[0033] (1) Wash the chromium-containing leather solid waste several times with water, squeeze out the water and add it to the reactor. Then add an appropriate amount of water and a gum extractant (alkali or alkali-enzyme). Heat the resulting mixture to 35-100℃ and stir for a period of time to obtain a mixture containing collagen and chromium-containing organic matter. Filter the extracted mixture to obtain collagen liquid and chromium-containing filter residue formed by the above-mentioned chromium-containing organic matter.

[0034] (2) After drying the chromium-containing filter residue, it is added to an anaerobic carbonization device. N2 is introduced into the anaerobic carbonization device to replace the air. Under anaerobic conditions, the temperature is raised to 150-250℃ at a heating rate of 5-10℃ / min and held at this temperature for 0.5-1.0h. Then, the temperature is further raised to 400-900℃ at a heating rate of 5-10℃ / min and held at this temperature for 3-48h. This completes the anaerobic pyrolysis carbonization of the chromium-containing filter residue, ultimately yielding a chromium-collagen anaerobic carbonized material. This material can be used as an adsorbent, an elastomer reinforcement material, a catalyst adsorbent, or can be further processed.

[0035] (3) Trivalent chromium is extracted by acid extraction and precipitated to prepare chromium tanning agent. (a) Acid extraction: The chromium-collagen oxygen-free carbonized material is soaked in an acidic medium (hydrochloric acid, sulfuric acid or nitric acid) with a mass fraction of 20%-98%, and the resulting mixture is extracted at 25℃-80℃ for 12-96h; (b) Filtration: After extraction, the material is filtered using a filtration device, and the chromium-rich extract is collected; (c) Water washing: The filter residue is washed with water 2-3 times, and the washing liquid is collected. The water-washed filter residue obtained here (i.e., dechromated oxygen-free carbonized material) can be used to prepare biochar-based compound fertilizer materials, as well as adsorbent materials, elastomer reinforcing materials, or catalyst loading materials; (d) Alkali precipitation of leachate: The collected chromium-rich leachate and water-washed liquid are mixed, and the pH of the mixture is adjusted to 8-10 using alkali (sodium carbonate, magnesium oxide, calcium oxide, or sodium hydroxide) to ensure that chromium is fully and completely precipitated. After filtration, chromium cake is obtained; (e) Preparation of regenerated chromium tanning agent: The chromium cake is mixed with sulfuric acid, and the resulting mixture is stirred and reacted at 35-95℃ for 40-60 min. Then, sodium formate and other masking agents equivalent to 2%-6% of the weight of the chromium cake are added, and the mixture is heated to 50-70℃ and stirred and reacted for 1-3 h. After the mixture cools to room temperature, a sodium bicarbonate solution with a mass concentration of about 5% is added under stirring to adjust its alkalinity to 30%-38%. The mixture is stirred for about 30 min, and the resulting mixture is aged overnight to obtain the regenerated chromium tanning agent.

[0036] Example 1

[0037] In this embodiment, the chromium-containing leather solid waste is derived from chromium-containing sheepskin shavings, which have a moisture content of about 50% and a chromium content of 3.8%.

[0038] Take 1000g of chromium-containing sheepskin shavings and wash them three times with room temperature water for 20 minutes each time, squeezing them dry after each wash. Add the washed chromium-containing sheepskin shavings to a 5L reactor, along with 2500g of water and 40g of magnesium oxide. Place the reactor in a water bath and heat to 95℃ with stirring for 3 hours to hydrolyze. Cool to 50℃ and add 3.0g of 2709 enzyme, continuing stirring and hydrolysis for another hour. After hydrolysis, heat again to 90℃ and maintain for 30 minutes to obtain a mixture of chromium-containing collagen solution and chromium-containing organic matter. Filter the mixture after collagen extraction to obtain collagen solution and chromium-containing filter residue, respectively.

[0039] 1000g of chromium-containing filter residue was dried to constant weight and placed in a box-type atmosphere furnace, where N2 was introduced to remove oxygen. Under anaerobic conditions, the temperature was increased from room temperature to 200℃ at a rate of 5℃ / min and held for 1 hour. Then, the temperature was increased to 800℃ at a rate of 10℃ / min and held for 3 hours. Finally, the temperature was allowed to cool naturally to room temperature to obtain chromium-collagen oxygen-free carbonized material.

[0040] 200g of chromium-collagen oxygen-free carbonized material was placed in a 1000mL Erlenmeyer flask, and 500mL of 50% sulfuric acid was added. The resulting mixture was heated to 40℃ and shaken for 72 hours to complete the acid extraction. The mixture was filtered, and the filter residue was washed repeatedly with water. The filtrate, washing liquid, and filter residue were collected separately. The filtrate and washing liquid were combined, and the filter residue was dried and weighed for later use. The pH of the filtrate was adjusted to 8.0 using sodium hydroxide aqueous solution to fully precipitate the chromium. After filtration, a chromium cake was obtained.

[0041] 10g of chromium cake was mixed with 100mL of 50% sulfuric acid. The mixture was heated to 35℃ and stirred for 1 hour. Then, sodium citrate, equivalent to 2% of the weight of the chromium cake, was added, and the mixture was heated to 70℃ and stirred for another 2 hours. After the solution cooled naturally to room temperature, a 5% sodium bicarbonate solution was added while stirring to adjust the pH of the mixture to 3.0. The mixture was stirred for another 30 minutes and then aged for at least 48 hours to obtain the regenerated chromium tanning liquor. Test results showed that the regenerated chromium tanning liquor contained 2.86% chromium trioxide and had an alkalinity of 33%.

[0042] Example 2

[0043] In this embodiment, the chromium-containing leather solid waste comes from the trimming scraps of wet blue pigskin leather (after crushing and pretreatment), which has a moisture content of about 40% and a chromium content of 4.2%.

[0044] Take 1000g of crushed pigskin blue wet leather trimming scraps, wash them three times with room temperature water for 20 minutes each time, and squeeze dry after washing. Add the washed pigskin blue wet leather trimming scraps to a 5L reactor, then add 2000g of water and 40g of sodium hydroxide. Place the reactor in a water bath and heat to 90℃, stirring and hydrolyzing for 1.5 hours to obtain a mixture of chromium-containing collagen solution and chromium-containing organic matter. Filter the mixture after collagen extraction to obtain collagen solution and chromium-containing filter residue, respectively.

[0045] 1000g of chromium-containing filter residue was dried to constant weight and placed in a box-type atmosphere furnace, where N2 was introduced to remove oxygen. Under anaerobic conditions, the temperature was increased from room temperature to 200℃ at a rate of 10℃ / min and held for 0.5h. Then, the temperature was increased to 400℃ at a rate of 10℃ / min and held for 10h. Finally, the material was allowed to cool naturally to room temperature to obtain chromium-collagen oxygen-free carbonized material.

[0046] 200g of chromium-collagen oxygen-free carbonized material was placed in a 1000mL Erlenmeyer flask, and 300mL of 98% sulfuric acid was added. The resulting mixture was heated to 60℃ and shaken for 12 hours to complete the acid extraction. The mixture was filtered, and the filter residue was washed repeatedly with water. The filtrate, washing liquid, and filter residue were collected separately. The filtrate and washing liquid were combined, and the filter residue was dried and weighed for later use. The pH of the filtrate was adjusted to 8.5 using magnesium oxide to fully precipitate the chromium. After filtration, a chromium cake was obtained.

[0047] 10g of chromium cake was mixed with 80mL of 30% sulfuric acid. The mixture was heated to 50℃ and stirred for 50min. Then, sodium formate (equivalent to 5% of the weight of the chromium cake) was added, and the mixture was heated to 50℃ and stirred for 2h. After the solution cooled naturally to room temperature, a 5% sodium bicarbonate solution was added while stirring to adjust the pH of the mixture to 2.8. The mixture was stirred for another 30min and then aged for at least 48h to obtain the regenerated chromium tanning liquor. Test results showed that the regenerated chromium tanning liquor contained 2.89% chromium trioxide and had an alkalinity of 32%.

[0048] Example 3

[0049] In this embodiment, the chromium-containing leather solid waste is derived from chromium-containing cowhide shavings, which have a moisture content of about 40% and a chromium content of 4.7%.

[0050] Take 1000g of chromium-containing cowhide shavings and wash them twice with room temperature water for 20 minutes each time, squeezing them dry after washing. Add the washed chromium-containing cowhide shavings to a 5L reactor, then add 2200g of water and 8g of calcium hydroxide. Place the reactor in a water bath and heat to 95℃, stirring and hydrolyzing for 30 minutes. Then cool to 35℃ and add 20g of a complex composed of 1398 enzyme, papain, and Bacillus subtilis neutral protease (weight ratio 1:1:1). Stir and hydrolyze the resulting mixture for 1.5 hours, then heat to 90℃ again and maintain for 30 minutes to obtain a chromium-containing collagen solution and a mixture of chromium-containing organic matter. Filter the mixture after collagen extraction to obtain collagen solution and chromium-containing filter residue, respectively.

[0051] 1000g of chromium-containing filter residue was dried to constant weight and placed in a box-type atmosphere furnace, where N2 was introduced to remove oxygen. Under anaerobic conditions, the temperature was increased from room temperature to 200℃ at a rate of 10℃ / min and held for 0.5h. Then, the temperature was increased to 800℃ at a rate of 10℃ / min and held for 20h. Finally, the material was naturally cooled to room temperature to obtain chromium-collagen oxygen-free carbonized material.

[0052] 200g of chromium-collagen oxygen-free carbonized material was placed in a 1000mL Erlenmeyer flask, and 600mL of 60% nitric acid was added. The resulting mixture was heated to 40℃ and shaken for 48 hours to complete the acid extraction. The mixture was filtered, and the filter residue was washed repeatedly with water. The filtrate, washing liquid, and filter residue were collected separately. The filtrate and washing liquid were combined, and the filter residue was dried and weighed for later use. The pH of the filtrate was adjusted to 8.5 using sodium carbonate aqueous solution to ensure complete precipitation of chromium. After filtration, a chromium cake was obtained.

[0053] 10g of chromium cake was mixed with 100mL of 50% sulfuric acid. The mixture was heated to 80℃ and stirred for 40min. Then, sodium acetate (equivalent to 6% of the chromium cake's weight) was added, and the mixture was heated to 70℃ and stirred for 2h. After the solution cooled naturally to room temperature, a 5% sodium carbonate solution was added while stirring to adjust the pH to 3.2. The mixture was stirred for another 30min and then aged for 48h to obtain the regenerated chromium tanning liquor. Test results showed that the regenerated chromium tanning liquor contained 2.92% chromium trioxide and had an alkalinity of 35%.

[0054] Example 4

[0055] In this embodiment, the chromium-containing leather solid waste is derived from chromium-containing pigskin shavings, which have a moisture content of about 40% and a chromium content of 3.9%.

[0056] Take 1000g of chromium-containing pigskin shavings and wash them three times with room temperature water for 20 minutes each time, squeezing them dry after each wash. Add the washed chromium-containing pigskin shavings to a 5L reactor, then add 1500g of water and 40g of sodium hydroxide. Place the reactor in a water bath and heat to 90℃, stirring and hydrolyzing for 1.5 hours to obtain a mixture of chromium-containing collagen solution and chromium-containing organic matter. Filter the mixture after collagen extraction to obtain collagen solution and chromium-containing filter residue, respectively.

[0057] 1000g of chromium-containing filter residue was dried to constant weight and placed in a box-type atmosphere furnace, where N2 was introduced to remove oxygen. Under anaerobic conditions, the temperature was increased from room temperature to 200℃ at a rate of 10℃ / min and held for 0.5h. Then, the temperature was increased to 900℃ at a rate of 10℃ / min and held for 6h. Finally, the material was allowed to cool naturally to room temperature to obtain chromium-collagen oxygen-free carbonized material.

[0058] 200g of chromium-collagen oxygen-free carbonized material was placed in a 1000mL Erlenmeyer flask, and 600mL of 40% sulfuric acid was added. The resulting mixture was heated to 50℃ and shaken for 36 hours to complete the acid extraction. The mixture was filtered, and the filter residue was washed repeatedly with water. The filtrate, washing liquid, and filter residue were collected separately. The filtrate and washing liquid were combined, and the filter residue was dried and weighed for later use. The pH of the filtrate was adjusted to 9.0 using sodium hydroxide aqueous solution to ensure complete precipitation of chromium. After filtration, a chromium cake was obtained.

[0059] 10g of chromium cake was mixed with 50mL of 40% sulfuric acid. The mixture was heated to 95℃ and stirred for 40min. Then, sodium lactate (equivalent to 3% of the chromium cake's weight) was added, and the mixture was heated to 60℃ and stirred for 2h. After the solution cooled naturally to room temperature, a 5% sodium bicarbonate solution was added while stirring to adjust the pH to 2.5. The mixture was stirred for another 30min and then aged for 48h to obtain the regenerated chromium tanning liquor. Test results showed that the chromium trioxide content in the regenerated chromium tanning liquor was 3.01%, and the alkalinity was 30%.

[0060] Example 5

[0061] In this embodiment, the chromium-containing leather solid waste is derived from chromium-containing sheepskin shavings, which have a moisture content of about 40% and a chromium content of 4.6%.

[0062] Take 1000g of chromium-containing sheepskin shavings and wash them three times with 400g of room temperature water for 20 minutes each time, squeezing out the excess water after each wash. Add 100g of the washed chromium-containing sheepskin shavings to a 500mL reactor, then add 400g of water and 80g of calcium oxide. Place the reactor in a water bath and heat to 95℃ with stirring for 3 hours to hydrolyze. Then, cool to 50℃ and add 2g of 2709 enzyme, continuing to stir and hydrolyze for 1 hour. Reheat to 90℃ and maintain for 30 minutes to obtain a mixture of chromium-containing collagen solution and chromium-containing organic matter. Filter the mixture after collagen extraction to obtain collagen solution and chromium-containing filter residue, respectively.

[0063] 1000g of chromium-containing filter residue was dried to constant weight and placed in a box-type atmosphere furnace, where argon gas was introduced to remove oxygen. Under anaerobic conditions, the residue was heated from room temperature to 200℃ at a heating rate of 10℃ / min and held for 0.5h. Then, it was heated to 600℃ at a heating rate of 10℃ / min and held for 6h. Finally, it was naturally cooled to room temperature to obtain chromium-collagen oxygen-free carbonized material.

[0064] 200g of chromium-collagen oxygen-free carbonized material was placed in a 1000mL Erlenmeyer flask, and 400mL of 40% nitric acid was added. The resulting mixture was heated to 25℃ and shaken for 48 hours to complete the acid extraction. The mixture was filtered, and the residue was washed repeatedly with water. The filtrate, washing liquid, and residue were collected separately. The filtrate and washing liquid were combined, and the residue was dried and weighed for later use. The pH of the filtrate was adjusted to 8.0 using sodium hydroxide aqueous solution to ensure complete precipitation of chromium. After filtration, a chromium cake was obtained.

[0065] 10g of chromium cake was mixed with 50mL of 20% sulfuric acid. The resulting mixture was heated to 95℃ and stirred for 1 hour. Then, sodium citrate, equivalent to 3% of the weight of the chromium cake, was added, and the mixture was heated to 50℃ and stirred for another 2 hours. After the solution cooled naturally to room temperature, a 5% ammonium bicarbonate solution was added while stirring to adjust the pH of the mixture to 3.5. After stirring for another 30 minutes, the mixture was aged for 48 hours to obtain the regenerated chromium tanning agent. Test results showed that the regenerated chromium tanning agent contained 2.98% chromium trioxide and had an alkalinity of 38%.

[0066] Example 6

[0067] In this embodiment, the chromium-containing leather solid waste is derived from chromium-containing pigskin shavings, which have a moisture content of about 50% and a chromium content of 5%.

[0068] Take 1000g of chromium-containing pigskin shavings and wash them three times with room temperature water for 20 minutes each time, squeezing them dry after each wash. Add the washed chromium-containing pigskin shavings to a 5L reactor, then add 1500g of water and 80g of calcium oxide. Place the reactor in a water bath and heat to 90℃, stirring and hydrolyzing for 1.5 hours to obtain a mixture of chromium-containing collagen solution and chromium-containing organic matter. Filter the mixture after collagen extraction to obtain collagen solution and chromium-containing filter residue, respectively.

[0069] 1000g of chromium-containing filter residue was dried to constant weight and placed in a box-type atmosphere furnace, through which helium was introduced to remove oxygen. Under anaerobic conditions, the temperature was increased from room temperature to 200℃ at a heating rate of 5℃ / min and held for 1 hour. Then, the temperature was increased to 800℃ at a heating rate of 5℃ / min and held for 3 hours. Finally, the material was naturally cooled to room temperature to obtain chromium-collagen anaerobic carbonized material.

[0070] 200g of chromium-collagen oxygen-free carbonized material was placed in a 1000mL Erlenmeyer flask, and 300mL of 50% sulfuric acid was added. The resulting mixture was heated to 40℃ and shaken for 24 hours to complete the acid extraction. The mixture was filtered, and the filter residue was washed repeatedly with water. The filtrate, washing liquid, and filter residue were collected separately. The filtrate and washing liquid were combined, and the filter residue was dried and weighed for later use. The pH of the filtrate was adjusted to 8.5 using magnesium oxide to fully precipitate the chromium. After filtration, a chromium cake was obtained.

[0071] 10g of chromium cake was mixed with 100mL of 30% sulfuric acid. The mixture was heated to 80℃ and stirred for 40min. Then, sodium acetate (equivalent to 4% of the chromium cake's weight) was added, and the mixture was heated to 70℃ and stirred for 2h. After the solution cooled naturally to room temperature, a 5% sodium bicarbonate solution was added while stirring to adjust the pH to 2.6. The mixture was stirred for another 30min and then aged for 48h to obtain the regenerated chromium tanning liquor. Test results showed that the regenerated chromium tanning liquor contained 2.88% chromium trioxide and had an alkalinity of 32%.

[0072] Example 7

[0073] In this embodiment, the chromium-containing leather solid waste comes from the trimming scraps of wet cowhide blue leather (after crushing and pretreatment), with a moisture content of about 40% and a chromium content of 4.5%.

[0074] Take 1000g of trimmed scraps from wet bovine blue leather. Wash it three times with room temperature water for 20 minutes each time, and squeeze dry after each wash. Add the washed trimmed scraps from wet bovine blue leather to a 5L reactor, add 2000g of water, and adjust the pH of the mixture in the reactor to 9.5 with calcium oxide to achieve the suitable pH for the enzyme. Then add 8g of a complex composed of Bacillus subtilis neutral protease and papain (weight ratio 1:2) to the mixture. Place the reactor in a water bath and heat to 50℃, stirring and hydrolyzing for 4 hours to obtain a chromium-containing collagen solution and a mixture of chromium-containing organic matter. Filter the mixture after collagen extraction to obtain collagen solution and chromium-containing filter residue, respectively.

[0075] 1000g of chromium-containing filter residue was dried to constant weight and placed in a box-type atmosphere furnace, where N2 was introduced to remove oxygen. Under anaerobic conditions, the temperature was increased from room temperature to 200℃ at a rate of 5℃ / min and held for 1 hour. Then, the temperature was increased to 800℃ at a rate of 10℃ / min and held for 24 hours. Finally, the material was naturally cooled to room temperature to obtain chromium-collagen oxygen-free carbonized material.

[0076] 200g of chromium-collagen oxygen-free carbonized material was placed in a 1000mL Erlenmeyer flask, and 400mL of 36% hydrochloric acid was added. The resulting mixture was heated to 60℃ and shaken for 72 hours to complete the acid extraction. The mixture was filtered, and the filter residue was washed repeatedly with water. The filtrate, washing liquid, and filter residue were collected separately. The filtrate and washing liquid were combined, and the filter residue was dried and weighed for later use. The pH of the filtrate was adjusted to 9 using sodium hydroxide aqueous solution to ensure complete precipitation of chromium. After filtration, a chromium cake was obtained.

[0077] 10g of chromium cake was mixed with 100mL of 40% sulfuric acid. The mixture was heated to 50℃ and stirred for 50min. Then, glycolic acid, equivalent to 4% of the weight of the chromium cake, was added, and the mixture was heated to 60℃ and stirred for 2h. After the solution cooled naturally to room temperature, a 5% sodium bicarbonate solution was added while stirring to adjust the pH of the mixture to 3.0. After stirring for another 30min, the mixture was aged for at least 48h to obtain the regenerated chromium tanning agent. Test results showed that the regenerated chromium tanning agent contained 2.98% chromium trioxide and had an alkalinity of 32%.

[0078] Application Example 1

[0079] The regenerated chromium tanning agent obtained in Example 1 was used for cowhide tanning: 300g of split top-grain cowhide (grey hide) was delimed and softened using conventional processes, and then pickled according to the following steps:

[0080] Acid soaking: 300g of water was injected into the drum at 25℃. First, 24g of sodium chloride was added and the mixture was rotated for 5 minutes. Then, 2.7g of formic acid (mass fraction 85%, diluted with 5 times the amount of water) was added and the mixture was rotated for 10 minutes. Finally, 2.1g of sulfuric acid (mass fraction 98%, diluted with 10 times the amount of water) was added and the mixture was rotated for 1 hour. The pH of the bath solution was measured to be 2.5.

[0081] Tanning: Add 190g of the regenerated chromium tanning liquor prepared in Example 1 to the drum and rotate for 60 minutes. Then add 3g of sodium formate (diluted with 10 times the amount of water) and 8g of sodium bicarbonate (diluted with 10 times the amount of water) in 6 portions, 30 minutes apart, until the final pH is 3.8. Heat water to raise the internal temperature to 40°C and continue rotating for 3 hours. Stop the drum and let it sit overnight. The next day, rotate for 30 minutes and remove the leather from the drum to obtain wet blue leather.

[0082] The shrinkage temperature of wet blue leather was tested according to QB / T 2713-2005. The results showed that the shrinkage temperature of the finished leather made using this recycled chrome tanning liquor was greater than 100℃.

[0083] Comparative Example 1

[0084] Following the process of Application Example 1, 24g of Chromosal B chromium tanning agent (Brother Technology, 26% chromium trioxide content) was added to replace the recycled chromium tanning agent for pickling, resulting in blue wet leather with a shrinkage temperature greater than 100°C, similar to the results of Application Example 1.

[0085] Application Example 2

[0086] The regenerated chromium tanning agent obtained in Example 6 was applied to the tanning of cowhide: 300g of top-grain cowhide (grey hide) after splitting was delimed and softened using conventional processes, and then pickled according to the following steps:

[0087] Acid soaking: 300g of water was injected into the drum at 25℃. First, 24g of sodium chloride was added and the mixture was rotated for 5 minutes. Then, 2.7g of formic acid (mass fraction 85%, diluted with 5 times the amount of water) was added and the mixture was rotated for 10 minutes. Finally, 2.1g of sulfuric acid (mass fraction 98%, diluted with 10 times the amount of water) was added and the mixture was rotated for 1 hour. The pH of the bath solution was measured to be 2.5.

[0088] Tanning: Add 195g of the regenerated chromium tanning liquor prepared in Example 6 to the drum and rotate for 60 minutes. Then add 3g of sodium formate (diluted with 10 times the amount of water) and 8g of sodium bicarbonate (diluted with 10 times the amount of water) in 6 portions, 30 minutes apart, until the final pH is 3.8. Heat water is added to raise the temperature of the bath to 40°C, and the drum is rotated for another 3 hours. The drum is then stopped and left overnight. The next day, the drum is rotated for 30 minutes before being removed and the leather is mounted to obtain wet blue leather.

[0089] The shrinkage temperature of wet blue leather was tested, and the results showed that the shrinkage temperature of the finished leather made using this recycled chrome tanning agent was greater than 100℃.

[0090] Comparative Example 2

[0091] Following the process of Application Example 2, 24g of Chromosal B chromium tanning agent (Brother Technology, 26% chromium trioxide content) was added to replace the recycled chromium tanning agent, resulting in a shrinkage temperature of blue wet leather greater than 100°C, which is similar to the result of Application Example 2.

Claims

1. A method for the comprehensive utilization of chromium-containing leather solid waste, characterized in that, The method includes the following steps: Chromium-containing leather solid waste is mixed with a gum-extracting agent and water for gum extraction to obtain collagen liquid and chromium-containing filter residue. The chromium-containing filter residue was thoroughly dried, then placed in a sealed container and heated and kept warm in an oxygen-free environment for pyrolysis and carbonization treatment. After natural cooling to room temperature, chromium-collagen oxygen-free carbonized material was obtained. The chromium-collagen oxygen-free carbonized material is regenerated to obtain regenerated chromium tanning agent and dechromium-free oxygen-free carbonized material. The regeneration process includes: acid extraction of the chromium-collagen oxygen-free carbonized material to obtain dechromium-free oxygen-free carbonized material and chromium-rich extract; then adjusting the pH of the chromium-rich extract to alkaline for precipitation, and filtering to obtain chromium cake; finally, mixing the chromium cake with an acid reagent, adding a saturating agent to adjust the alkalinity of the mixture, and aging it thoroughly to obtain the regenerated chromium tanning agent. The chromium-containing leather solid waste includes chromium-containing shavings or wet blue leather trimming scraps from cowhide, sheepskin, and pigskin. The guar gum extractant includes an alkali and an enzyme, wherein the alkali is selected from at least one of sodium carbonate, magnesium oxide, sodium hydroxide, potassium hydroxide, calcium oxide, calcium hydroxide, and ammonia water, and the enzyme is selected from at least one of 1398 enzyme, 2709 enzyme, trypsin, and papain.

2. The method as described in claim 1, characterized in that: The chromium content of the chromium-containing leather waste is 3.5%-5% (calculated as chromium trioxide).

3. The method as described in claim 1, characterized in that... The specific process of the colloid extraction process is as follows: the solid waste containing chromium leather is washed several times, then mixed with colloid extractant and water and heated to 35-100℃ for colloid extraction. Finally, the solid and liquid are separated to obtain collagen liquid and chromium-containing filter residue.

4. The method as described in claim 1, characterized in that: An oxygen-free environment is achieved by filling the container with a protective atmosphere, which is selected from at least one of nitrogen, argon, and helium.

5. The method as described in claim 4, characterized in that... The heating and holding process during pyrolysis carbonization is divided into at least two stages, as follows: First, the temperature is increased from room temperature to 150-250℃ at a heating rate of 5-10℃ / min, and held at this temperature for 0.5-1.0h; then, the temperature is increased to 400-900℃ at a heating rate of 5-10℃ / min, and held at this temperature for 3-48h.

6. The method as described in claim 1, characterized in that: The acidic medium used for acid extraction is selected from at least one of hydrochloric acid, sulfuric acid, and nitric acid, with a mass fraction of 20%-98%. The acid extraction temperature is 25-80℃, and the acid extraction time is 12-96h. After acid extraction, the filter is filtered to obtain filter residue and filtrate. The filter residue is repeatedly washed with water to obtain dechromiumized oxygen-free carbonized material. The washing liquid and filtrate are combined to obtain chromium-rich extract.

7. The method as described in claim 1, characterized in that: Precipitation is achieved by adjusting the pH of the chromium-rich extract to 8-10 using an alkali selected from at least one of sodium carbonate, magnesium oxide, sodium hydroxide, and calcium oxide.

8. The method as described in claim 1, characterized in that: After the chromium cake and acid reagent are mixed evenly, they are stirred thoroughly at 35-95℃ to completely dissolve the chromium cake; then, a masking agent equivalent to 2%-6% of the weight of the chromium cake is added and stirred thoroughly at 50-70℃; after the mixture cools to room temperature, an alkaline reagent is added while stirring to adjust its alkalinity to 30%-38%; the acid reagent is specifically sulfuric acid, the masking agent is selected from sodium formate, sodium acetate, glycolic acid small molecule organic acid masking agent or sodium phthalate, sodium lactate, sodium citrate macromolecule masking agent, and the alkaline reagent is specifically an aqueous solution of sodium bicarbonate, sodium carbonate or ammonium bicarbonate.