CN105347635B - One kind extracts chromium and resource utilization method from leather industry chromium-bearing sludge - Google Patents

Abstract

The invention discloses a method for extracting chromium from chromium-containing sludge in the leather industry and utilizing it as a resource. In the leather industry, chrome tanning is one of the important tanning methods. Due to the large amount of chrome tanning agent used in the chrome tanning process of bare hides and furs, and the low absorption rate of chrome tanning agents by leather, a large amount of chrome-containing sludge is generated. . In the present invention, the content of the main components in the chromium-containing sludge is first measured, the chromium is extracted by acid hydrolysis with sulfuric acid solution, then filtered and the filtrate is adjusted to alkaline with sodium hydroxide solution, and then flocculated with anionic polyacrylamide, followed by pressure filtration and dehydration. Acidification, followed by digestion with a compound oxidant consisting of ammonium persulfate and potassium dichromate, and finally reduction with glucose to obtain chrome tanning agent. The quality and performance of the wet blue leather tanned by the chrome tanning agent are comparable to those of the commercial chrome tanning agent. The invention can extract more than 90% of the chromium in the chrome sludge, and make it into a chrome tanning agent, turn waste into wealth, reduce environmental pollution from chromium-containing sludge and save chromium resources.

Description

A method for extracting chromium from leather industry chromium-containing sludge and resource utilization

technical field

The invention relates to the field of leather tanning agents, in particular to a method for extracting chromium from chromium-containing sludge in the leather industry and utilizing it as a resource.

Background technique

Tanning is an important process in the leather industry. It is a key process from leather to leather. The tanning method and degree of tanning directly affect the quality of finished leather. Among various tanning methods, the chrome tanning method has been occupying a leading position in the leather industry since its invention in the middle of the nineteenth century due to its advantages such as easy operation, excellent tanning properties, and excellent comprehensive performance of the finished leather. The widest range of tanning techniques. However, during the chrome tanning process, the absorption rate of chrome to bare hide is 60-70%, and the remaining 30%-40% of chromium is left in the chrome tanning wastewater (Huo Xiaoping, Liu Cunhai. A review of the current situation of chrome tanning wastewater treatment[J] . Western Leather, 2009, 31(23):37-42.). If it is directly discharged into the environment, chromium will accumulate in plants, sludge and water organisms, and has certain ecotoxicity (Ma Hongrui, Huang Ningxuan, Zhang Jingfei, etc. The adsorption of chromium in the solution by peat and its role in the treatment of tannery wastewater Application [J]. Environmental Chemistry, 2003, 22 (6): 596-600.); At the same time, chromium is a non-renewable resource, and my country's chromium ore resources are particularly scarce. Therefore, the recovery and effective utilization of chromium in chrome tanning wastewater has significant practical significance for the sustainable and healthy development of my country's leather industry.

For many years, researchers at home and abroad have conducted continuous research on the recycling technology of chromium in chrome tanning wastewater. These technologies can be mainly divided into three methods: alkali precipitation recovery, incineration oxidation and direct recycling. Simple, low cost, good effect and widely used. The principle of this method is based on adjusting the pH of the chrome tanning waste liquid to 8-9, the trivalent chromium in the solution is converted into chromium hydroxide and precipitated, and then the precipitate is made into chromium-containing sludge (chromium-containing filter cake) by pressure filtration , to achieve the separation of chromium and water. The recovery rate of chromium in this process is above 99%, and the chromium content in the treated aqueous solution can easily meet the discharge standard requirements, but the effective utilization of chromium-containing sludge has become a practical problem faced by tanning enterprises (Dong Guiping, Lan Yunjun, Bao Lihong . The road to green leather technology - recycling of chrome tanning waste [J]. West Leather, 2006,28(4):12-17.).

Chromium-containing sludge can be reprocessed into chrome tanning agent, which can be used in the leather production process to realize the recycling of chromium. This is also the best way to utilize chromium-containing sludge (Geng Shisuo, Yuan Sibing. Chromium recovery in leather industry and waste water reuse[J].Environmental Science and Technology,1994,67(4):8-10.Wang Junyao,Su Haijia,Tan Tianwei.Recovery and treatment of chromium in tannery chrome tanning wastewater[J].Environmental Engineering Journal, 2007, 1(1):23-26.). However, chromium-containing sludge is different from the high-purity red alum (dichromate) used in the production process of conventional chrome tanning agents, because the composition of chromium-containing sludge is complex and changeable due to different precipitation techniques. For example, the alkali used for precipitation can be Ca(OH) ₂ , NaOH or MgO, and in order to improve the precipitation effect, it is necessary to add iron salt, aluminum salt or organic polymer flocculant at the same time (Liu Cunhai. Application in chrome tanning wastewater [J]. China Leather, 2003, 32(5): 28-30. Cheng Baozhen, Zou Danhui. Treatment and resource utilization of chrome tanning wastewater [J]. Journal of Tianjin University of Science and Technology, 2011, 26( 3):36-38.); In addition, chrome-rich mud also contains organic substances such as oil, leather fiber and protein (Boast DA. Large scale chrome recovery from chrome wash liquors[J].Journal of the American Leather Chemists Association ,1988,83(1):17-24.MaiaRA.Clean technologies-targets already achieved and trends for the comingyears[J].Journal of the Society of Leather Technologists and Chemists,1998,82(3):111-113. Kanagaraj J, Chandra Babu NK, Mandal AB. Recovery and reuse of chromium from chrome tanning waste water aiming towards zero discharge of pollution [J]. Journal of Cleaner Production, 2008,16(16):1807-1813.). Therefore, the content of inorganic and organic components in chromium-containing sludge produced by different alkali precipitation technologies is quite different, which will affect the effect of its resource utilization.

At home and abroad, there is little research on the treatment of chromium-containing sludge. In foreign countries, after enzymatic hydrolysis of collagen in chromium-containing sludge, the remaining chromium is used for the production of pigments. Domestic researchers have also carried out some research and exploration on the preparation of chrome tanning agents by using chrome mud, and have adopted different methods to obtain regenerated chrome tanning agents (Wang Kunyu, Pan Zhijuan, Zhou Wanjian. The preparation of chromium-containing main tanning agents and their application properties by chrome mud Exploration [J]. China Leather, 2002,31(19):13-15. Liu Na, Ding Zhiwen, Liu Cheng, etc. Research on the preparation of chrome tanning agent from H ₂ O ₂ chromium oxide mud [J]. China Leather, 2012,41(1):16-20. Cheng Zhengping, Ding Zhiwen, Liu Na, etc. Preparation of chrome tanning agent from chrome sludge[J].Leather and Chemical Industry, 2012,29(1):11-14 .). Due to immature technology and other reasons, it has not been applied industrially.

Therefore, in view of the current specific situation of chromium-containing sludge, it is necessary to systematically analyze the main component content (total chromium, total ash) of chromium-containing sludge, establish a unified component content index, and lay a technical foundation for its resource utilization. At the same time, study the feasible and recycling method to extract the chromium in the chromium-containing sludge and utilize it as a resource. In addition, it can also standardize and unify the current alkali precipitation recovery technology in enterprises to better promote the sustainable and healthy development of the regional leather industry.

Contents of the invention

In view of the above problems, the present invention provides a method for extracting chromium from chromium-containing sludge in the leather industry and its resource utilization method, which realizes the extraction of chromium by measuring the relevant indicators in the chromium-containing sludge and analyzing the components of the chromium-containing sludge And resource utilization, turning waste into treasure, reducing the pollution of chromium to the environment.

For this reason, the present invention adopts the following technical scheme: a method for extracting chromium from chromium-containing sludge in the leather industry and its resource utilization method, which is characterized in that, firstly, the content of main components in the chromium-containing sludge is measured, and 29-31wt% of Chromium is extracted by acidolysis with sulfuric acid solution, then filtered and the filtrate made alkaline with sodium hydroxide solution, flocculated with anionic polyacrylamide (PAM), followed by press filtration and acidified, followed by ammonium persulfate and potassium dichromate The composite oxidant is digested, and finally the chrome tanning agent is obtained by glucose reduction.

The above method includes the following specific steps:

1) Testing of related indicators of chromium-containing sludge

The relevant indicators of chromium-containing sludge are moisture content, Cr ₂ O ₃ content and ash content, which are tested by oven method (national standard method), sodium peroxide oxidation and spectrophotometry and muffle furnace burning method;

2) Acid hydrolysis

Put 390-530 parts by weight of chromium-containing sludge into the reaction kettle, the moisture content of the chromium-containing sludge is _48-62 %, the _Cr2O3 content is 18-26%, and the ash content is 40-50%. While stirring, add 460-490 parts by weight of 29-31wt% sulfuric acid solution twice, stir at 35-45°C for 70-80min, cool to room temperature, and filter;

3) Flocculation

Put 500 parts by weight of the filtrate obtained in step 2) into the reactor, add 200 to 240 parts by weight of 29-31 wt% sodium hydroxide solution, stir at room temperature for 70 to 80 minutes, and let stand overnight to stabilize the pH value at 8 ~10; then add 140~150 parts by weight of 0.04-0.06wt% anionic polyacrylamide, stir to make it evenly mixed, and let stand for 55~65min;

4) Press filtration and acidification

Filter the flocs obtained in step 3) into chromium cakes on a filter press, and control the moisture content of the chromium cakes at 20-30%; take 500 parts by weight of the chromium cakes and put them into a reaction kettle, and add 100-120 parts by weight of sulfuric acid solution, the volume ratio of sulfuric acid to water in the sulfuric acid solution is 1:1, stir to dissolve the chromium cake, and make the pH 2-4;

5) Digestion and reduction

Add 80 to 120 parts by weight of ammonium persulfate and 8 to 10 parts by weight of potassium dichromate in a reactor containing 500 parts of acidified chromium solution, and digest it for 40 to 60 minutes at a temperature of 95 to 105° C.; then cool down to 90-95°C, add 20-30 parts by weight of glucose during the stirring process, react for 25-35 minutes, and cool down; then adjust the alkalinity with 8-10 parts by weight of soda ash to obtain a pH of 2-4 and a Cr ₂ O ₃ of 8- 12% chrome tanning liquor with an alkalinity of 33-35%.

The present invention extracts the chrome tanning liquor with a pH of 2-4, a _{Cr2O3 of} 12%, and an alkalinity of 33-35%. After tanning, the shrinkage temperature of the wet blue leather can reach above 100°C, and the appearance is light gray It is blue with clear and natural grain pattern, which can be compared with commercial chrome tanning agent tanning effect. The tensile strength, tear strength, elongation at break, and softness of the resulting leather all meet the corresponding ministerial standards for chrome tanned leather, and are suitable for tanning and retanning of various light leathers tanned from pig, cow, and sheepskin .

Further, described ammonium persulfate, potassium dichromate, glucose and soda ash are all industrial products.

Furthermore, the molecular weight of anionic polyacrylamide is preferably 18 million.

Further, the reactor is equipped with an anchor type or a frame type stirring blade, and the stirring speed is controlled at 60-80 rpm.

Compared with the prior art, the present invention has the following beneficial effects:

1. It is suitable for all light leather chrome tanning and chrome retanning requirements in the current market. The shrinkage temperature and physical and mechanical indicators of the finished leather meet the chrome tanned leather standards issued by the Ministry of Light Industry in 2005.

2. With this extraction method, the extraction rate of chromium can reach 85-95%.

3. The chromium solution is effectively concentrated by using anionic polyacrylamide (PAM) flocculant.

4. Ammonium persulfate and potassium dichromate composite oxidant are used to digest the organic matter in the chromium solution, which also has the effect of supplementing chromium.

5. The shrinkage temperature of the wet blue leather tanned by the present invention is above 100° C., it is light gray blue and has a flat and fine grain surface, and its state and leather-forming performance can be compared with the tanning effect of commercial chrome tanning agents.

Detailed ways

The present invention is specifically described below by way of examples. It is necessary to point out that the following examples are only used to further illustrate the present invention, and cannot be interpreted as limiting the protection scope of the present invention. Those skilled in the art can make some non-essential improvements and improvements to the present invention according to the content of the above-mentioned invention. Adjustment.

Example 1

1) Testing of related indicators of chromium-containing sludge

The relevant indicators of chromium-containing sludge are moisture content, Cr ₂ O ₃ content, ash content, etc., which are tested by oven method (national standard method), sodium peroxide oxidation and spectrophotometry, and muffle furnace burning method.

2) Acid hydrolysis

Put 390 parts of chromium-containing sludge (moisture content is 48%, _Cr2O3 content is ₁₈ %, ash content is 40%) into the reaction kettle, slowly add 460 parts of 30wt% sulfuric acid solution twice while stirring , stirred at 40°C for 60 min, cooled to room temperature, and filtered.

3) Flocculation

Put 500 parts of the filtrate into the reactor, slowly add 200 parts of 30wt% sodium hydroxide solution, stir at room temperature for 60 min, and let stand overnight to stabilize the pH value at 8. Then add 140 parts of 0.05 wt% anionic polyacrylamide, stir to make it evenly mixed, and let stand for 60 minutes.

4) Press filtration and acidification

The flocs are press-filtered on a filter press to form a chromium cake (the moisture content of the chromium cake is 65%). Get 500 parts of chrome cake and insert in the reactor, add 100 parts and be the sulfuric acid solution of 1:1 (V _{H SO} : V _water ), stir and make it dissolve, make its pH 2;

5) Digestion and reduction

Add 80 parts of ammonium persulfate and 8 parts of potassium dichromate to the reaction kettle containing 500 parts of acidified chromium solution, digest at 100°C for 40 minutes; then cool down to 90°C, and add 20 parts of Glucose was reacted for 30 minutes and cooled; then 8 parts of soda ash was used to adjust the alkalinity to obtain a chrome tanning solution with a pH of ₂ , a _Cr2O3 of 8%, and an alkalinity of 33%.

Example 2

1) Testing of related indicators of chromium-containing sludge

The relevant indicators of chromium-containing sludge are moisture content, Cr ₂ O ₃ content, ash content, etc., which are tested by oven method (national standard method), sodium peroxide oxidation and spectrophotometry, and muffle furnace burning method.

2) Acid hydrolysis

Put 530 parts of chromium-containing sludge (moisture content is 62%, _Cr2O3 content is ₂₆ %, ash content is 50%) into the reaction kettle, slowly add 490 parts of 30wt% sulfuric acid solution twice while stirring , stirred at a temperature of 40°C for 60min, cooled to room temperature, and filtered;

3) Flocculation

Put 500 parts of the filtrate into the reactor, slowly add 240 parts of 30wt% sodium hydroxide solution, stir at room temperature for 60 min, and let stand overnight to stabilize the pH value at 10. Then add 150 parts of 0.05 wt% anionic polyacrylamide, stir to make it evenly mixed, and let stand for 60 minutes.

4) Press filtration and acidification

The flocs were press-filtered on a filter press to form a chromium cake (the moisture content of the chromium cake was 72.5%). Get 500 parts of chromium cakes and insert in the reactor, add 120 parts of sulfuric acid solution that is 1:1 (V _{H SO} : V _water ), stir to make it dissolve, make its pH 4.

5) Digestion and reduction

Add 120 parts of ammonium persulfate and 10 parts of potassium dichromate to the reaction kettle containing 500 parts of acidified chromium solution, and digest at 100°C for 60 minutes; then cool down to 95°C, and add 30 parts of Glucose was reacted for 30 minutes and cooled; then 10 parts of soda ash was used to adjust the alkalinity to obtain a chrome tanning solution with a pH of ₄ , a _Cr2O3 of 12%, and an alkalinity of 35%.

Example 3

1) Testing of related indicators of chromium-containing sludge

The relevant indicators of chromium-containing sludge are moisture content, Cr ₂ O ₃ content, ash content, etc., which are tested by oven method (national standard method), sodium peroxide oxidation and spectrophotometry, and muffle furnace burning method.

2) Acid hydrolysis

Put 460 parts of chromium-containing sludge (moisture content is ₅₅ %, _Cr2O3 content is 22%, ash content is 45%) into the reaction kettle, and slowly add 475 parts of 30wt% sulfuric acid solution twice while stirring , stirred at 40°C for 60 min, cooled to room temperature, and filtered.

3) Flocculation

Put 500 parts of the filtrate into the reactor, slowly add 220 parts of 30wt% sodium hydroxide solution, stir at room temperature for 60 min, and let stand overnight to stabilize the pH value at 9. Then add 145 parts of 0.05 wt% anionic polyacrylamide, stir to make it evenly mixed, and let it stand for 60 minutes.

4) Press filtration and acidification

The flocs are press-filtered on a filter press to form a chromium cake (the moisture content of the chromium cake is 80%). Get 500 parts of chromium cakes and insert in the reactor, add 110 parts of sulfuric acid solution that is 1:1 (V _{H SO} : V _water ), stir to make it dissolve, make its pH 3.

5) Digestion and reduction

Add 100 parts of ammonium persulfate and 9 parts of potassium dichromate into the reaction kettle containing 500 parts of acidified chromium solution, and digest at 100°C for 50 minutes; then cool down to 92.5°C, and add 25 parts of Glucose was reacted for 30 minutes and cooled; then 9 parts of soda ash was used to adjust the alkalinity to obtain a chrome tanning solution with a pH of ₃ , a _Cr2O3 of 12%, and an alkalinity of 34%.

Claims (4)

1. A method for extracting chromium and resource utilization from leather industry chromium-containing sludge, characterized in that, at first measure the main component content in the chromium-containing sludge, and extract chromium with 29～31wt% sulfuric acid solution acidolysis, and then Filtrate and adjust the filtrate to alkaline with sodium hydroxide solution, then flocculate with anionic polyacrylamide, then press filter and acidify, then digest with a composite oxidant composed of ammonium persulfate and potassium dichromate, and finally use glucose to reduce to obtain chromium Tanning agent; Described method comprises the following specific steps: 1) Testing of related indicators of chromium-containing sludge The relevant indicators of chromium-containing sludge are moisture content, Cr ₂ O ₃ content and ash content, which are tested by oven method, sodium peroxide oxidation and spectrophotometry method and muffle furnace burning method respectively; 2) Acid hydrolysis Put 390-530 parts by weight of chromium-containing sludge into the reaction kettle, the moisture content of the chromium-containing sludge is _48-62 %, the _Cr2O3 content is 18-26%, and the ash content is 40-50%. While stirring, add 460-490 parts by weight of 29-31wt% sulfuric acid solution twice, stir at 35-45°C for 70-80min, cool to room temperature, and filter; 3) Flocculation Put 500 parts by weight of the filtrate obtained in step 2) into the reactor, add 200 to 240 parts by weight of 29 to 31 wt% sodium hydroxide solution, stir at room temperature for 70 to 80 minutes, and let stand overnight to stabilize the pH value at 8 ~10; then add 140~150 parts by weight of 0.04~0.06wt% anionic polyacrylamide, stir to make it evenly mixed, and let stand for 55~65min; 4) Press filtration and acidification Filter the flocs obtained in step 3) into chromium cakes on a filter press, the moisture content of the chromium cakes is controlled at 65-80%; take 500 parts by weight of the chromium cakes and put them into the reactor, add 100-120 parts by weight of sulfuric acid solution, the volume ratio of sulfuric acid to water in the sulfuric acid solution is 1:1, stir to dissolve the chromium cake, and make the pH 2-4; 5) Digestion and reduction Add 80 to 120 parts by weight of ammonium persulfate and 8 to 10 parts by weight of potassium dichromate in a reactor containing 500 parts of acidified chromium solution, and digest it for 40 to 60 minutes at a temperature of 95 to 105° C.; then cool down to 90-95°C, add 20-30 parts by weight of glucose during the stirring process, react for 25-35 minutes, and cool down; then adjust the alkalinity with 8-10 parts by weight of soda ash to obtain a pH of 2-4 and a Cr ₂ O ₃ of 8- 12% chrome tanning liquor with an alkalinity of 33-35%. 2. the method for extracting chromium and resource utilization from leather industry chromium-containing sludge as claimed in claim 1, is characterized in that, described ammonium persulfate, potassium dichromate, glucose and soda ash are all industrial products. 3. The method for extracting chromium and resource utilization from leather industry chromium-containing sludge as claimed in claim 1, wherein the molecular weight of the anionic polyacrylamide is 18 million. 4. The method for extracting chromium and resource utilization from chromium-containing sludge in the leather industry as claimed in claim 1, wherein the reactor is equipped with an anchor type or frame type stirring paddle, and the stirring speed is controlled at 60 ~ 80rpm.