Treatment of printing and dyeing wastewater application of Bentonite

Printing and dyeing wastewater is one of the main harmful and difficult to treat industrial wastewater in China. The main pollutants are dyes, size, additives, fiber impurities, oil agents, acid and alkali, inorganic salts, etc. It is characterized by large amount of waste water, complex water quality, high concentration of organic matter, difficult biodegradation, deep color, rapid and irregular water quality change, among which dye pollution is the most serious. Even if the concentration of the remaining dye components is very low, it will also cause the reduction of water transmittance, leading to the destruction of the ecological environment. Therefore, how to decolorize printing and dyeing waste is an important problem.

At present, the treatment of printing and dyeing wastewater in China is mainly biochemical method, some of which are also supplemented by chemical method, but there are many disadvantages, such as large investment, high operation cost, poor treatment effect, difficulty in removing chromaticity and so on. On this basis, physical and chemical treatment methods are often used to remove certain COD and chroma through adsorption, coagulation and chemical oxidation. Among them, the adsorption and decolorization technology relies on the adsorption of adsorbents to remove dye molecules. Adsorbents include renewable adsorbents such as activated carbon, ion-exchange fiber and non renewable adsorbents such as various natural minerals (bentonite, diatomite), industrial wastes (coal slag, fly ash) and natural wastes (charcoal, sawdust), etc. Bentonite is a kind of clay with montmorillonite as its main component. Montmorillonite is a 2:1 type layered aluminosilicate with exchangeable calcium, magnesium and sodium plasma between layers. There are often negative and positive charges on the surface of bentonite particles, and the negative charges include constant negative charges and pH controlled negative charges. These properties determine that bentonite has good adsorption, ion exchange and other properties. In dyeing waste Water treatment has been widely used. In this paper, the application of bentonite in the treatment of printing and dyeing wastewater is reviewed and discussed.

2. Application of bentonite in the treatment of printing and dyeing wastewater

2.1 direct treatment of printing and dyeing wastewater with natural bentonite

Hang Hu et al. [1] studied the adsorption characteristics of natural bentonite to cationic, disperse, reductive, neutral, reactive and direct organic dyes. The influence of pH value of solution on the adsorption of bentonite can be divided into two categories: one is disperse dye and reducing dye, which are low in water solubility, mainly dispersed in water as fine particles, easy to adsorb on the soil particles and settle, and the decolorization rate is relatively high and has little relationship with pH value; the other is water-soluble and contains amine dyes in molecules, such as direct bright red and active red, whose decolorization rate increases with the decrease of pH value 。

Zhao Dongyuan et al. [2] treated the printing and dyeing wastewater with the natural montmorillonite mainly composed of Liaoning Fushun bentonite. The effects of pH value, catalyst, amount of montmorillonite, reaction temperature, reaction time and other factors were investigated, and the best process conditions were explored. The results showed that montmorillonite had better treatment ability for the printing and dyeing wastewater containing acid cation dyes The decolorization rate is over 90% and the COD removal rate is 96.9%. Montmorillonite is used to treat printing and dyeing wastewater through adsorption mechanism, which has the characteristics of simple operation, moderate cycle, easy regeneration and less investment.

2.2 dyeing wastewater treatment after Bentonite Modification

Because the unmodified bentonite has poor effect on the removal of organics and decolorization in wastewater, the bentonite used in wastewater treatment generally needs to be modified to increase its specific surface area and improve the adsorption capacity. At present, there are three methods to modify bentonite: roasting, acid leaching and salt leaching. These three methods can change the surface structure of bentonite and improve its adsorption capacity [3,4].

2.2.1 roasting method

Liu De mercury [5] mixed high-quality coal powder and bentonite at a ratio of 3%, calcined at 550 ℃ for 2 hours, and then treated the printing and dyeing wastewater. The results showed that the modified bentonite mixed with coal powder calcined at high temperature had stronger adsorption capacity than the modified bentonite calcined directly. After water treatment, only a short time of static can realize liquid-solid separation, and it can be repeatedly used after high temperature activation. Therefore, the high temperature calcination of bentonite and coal powder is a low-cost modification method.

Wang Lianjun et al. [6] discussed the structure and modification mechanism of bentonite through the determination of specific surface, scanning electron microscope and X-ray energy spectrum elements. The results show that the high-temperature roasting method has a good effect on the activation of bentonite, which has a good removal capacity for COD and chroma of dyeing wastewater. When 0.11% modified bentonite is added, the removal rate of COD can reach 74%, and the decolorization rate can reach more than 95%. It provides a valuable reference for the surface modification of natural bentonite and its application in the treatment of dyeing wastewater.

2.2.2 acid leaching

The main component of bentonite is montmorillonite. Its crystal is composed of alumina octahedron and silica tetrahedron. It has the properties of ion exchange and adsorption. After its acid activation, it has a larger specific surface and pore diameter, which can achieve a better effect on the treatment of printing and dyeing wastewater [7].

The optimal range of pH value is 5.5 ~ 8.0. When the dosage is 200mg / L, the decolorization rate can reach more than 90%, and the effect is good.

Xia Xinkui et al. [9] activated the calcium bentonite acid, and then decolorized the printing and dyeing wastewater. When the pH value was 7.0 ~ 8.0 and the adding amount was 30g / L, when the stirring time was 35min at room temperature, the one-time COD removal rate was 76% and the chroma removal rate was 87%. If the two-layer filter column was used for filtration, the chroma removal rate was over 93%, the COD removal rate was 78%, and the treated printing and dyeing wastewater was up to To the national emission requirements.

Zhou Shan [10] adjusted the pH value of 200ml acid blue printing and dyeing wastewater with 10000 times of chroma, 0.2480 of absorbance A and 6 of pH value, added 30g of 20% hydrochloric acid treated bentonite, stirred it slowly for 10min, stood it for 20min, took the filtrate to measure chroma, the chroma of filtrate decreased from 10000 times to 400 times, and the chroma removal rate was as high as 96%. If added with 600mg / L FeCl3 flocculant, After the flocculant precipitated, the chroma was further reduced to 20 times, which could meet the chroma requirements of the national secondary discharge standard for industrial wastewater (GB8978-88).

2.2.3 salt leaching

Qiu Zunan et al. [11] modified bentonite with metal ions (aluminum salt magnesium salt) and carried out adsorption and decolorization of reactive brilliant red dye in water. It was found that the modified bentonite also had certain photochemical catalytic degradation effect.

Calcium bentonite was activated by acid, heat, TiCl4, hydroxy aluminum and AlCl3. It was found that the decolorization rate of basic purple dye solution by using TiCl4 and AlCl3 activated bentonite was above 89% and 98% respectively, which was significantly higher than that of original bentonite. Through X-ray analysis, it was found that: the activated bentonite of TiCl4 and AlCl3 had larger layer spacing, while And the adsorption performance is improved obviously. When the modified bentonite adsorbs the alkaline violet solution, it mainly through cation exchange and co precipitation between dye molecules and bentonite particles [12].

2.2.4 other modification methods

Shao Ying et al. [13] studied the modification of bentonite and its decolorization treatment in disperse red solution, adopted a new inorganic organic modification method to modify the bentonite in Lin'an, Zhejiang Province, effectively introduced the double long-chain cationic surfactant into the bentonite layer, thus improving the lipophilicity of the organic bentonite and the adsorption capacity of organic pollutants in the wastewater. After the modification, the bentonite was modified When the bentonite is treated with disperse scarlet, the equilibrium speed is fast, the adsorption performance is good, and the decolorization rate is up to 90%. Jijingping [14] studied the modification of bentonite and the treatment of dye wastewater. The experiments of acid scarlet BS, reactive brilliant red ke-3b and acid black 10B show that the bentonite modified by poly iron has a stable removal effect on all kinds of dye wastewater. The author thinks that the transformation and modification of bentonite make the bentonite form a layered association structure from single crystals in water, thus forming a space for adsorption and accommodation of organic macromolecules between association particles, increasing the crystal surface spacing and the specific surface area of bentonite. The bentonite saturated by adsorption can be used for industrial brick burning, which makes the organic matter burn and decompose, and reduces the secondary pollution. The results of jijingping [10] show that when the dosage of bentonite adsorbent modified by sodium and hydroxy iron is 5-6G / L, the COD removal rate of acid scarlet is 45%, the COD removal rate of active brilliant red is 71%, and the COD removal rate of acid black is 60%. The organobentonites were prepared by the reaction of cetylpyridinium chloride (CPC) or cetyltrimethylamine bromide (CTMAB) with bentonites, filtration, drying at 80-90 ℃, activation at 105 ℃, and grinding and sieving at 100 mesh. The modified bentonites were used to treat wastewater containing aniline dyes with good effect.

2.3 treatment of printing and dyeing wastewater with modified bentonite coagulant

Zhang Jianying [17] discussed the modified bentonite coagulant SCPB (modified bentonite coagulant SCPB is 80 mesh solid particles modified by bentonite added with SCMC and PAC). The main components are bentonite, PAC and SCMC) for the treatment of printing and dyeing wastewater. The results show that SCPB can not only make COD removal rate over 60%, turbidity removal rate over 70% and decolorization rate over 60% in a short time, but also has a wide range of pH application. Feng xionghan et al. [18] studied the performance of organic bentonite coagulant in the treatment of cationic dye wastewater, and investigated the influence of pH value, reaction temperature, reaction time, bentonite dosage, additives, inorganic salts and other factors. The composite modified bentonite with acid and organic ammonium salt was used to treat the wastewater containing 100mg / L cationic dye. When 400mg / L composite modified bentonite was used, the average decolorization rate was over 99%, the COD removal rate was over 92%, and the saturated adsorption capacity was significantly better than that of the original bentonite.

2.4 treatment of printing and dyeing wastewater with bentonite and other processes

Zhou Shan et al. [19] studied the treatment of printing and dyeing wastewater by bentonite flocculation internal electrolysis. The results show that after bentonite and flocculation, the removal rate of chroma is 99.5%, and after internal electrolysis, the removal rate of COD is 98.2%, which meets the first level discharge standard of national printing and dyeing wastewater (GB4287-92).

Hang Hu et al. [20] compared the decolorization effect of bentonite adsorption flocculation method with that of pure flocculation method. The decolorization rate of the former is 40% ~ 200% higher than that of the latter, and the decolorization rate of dyeing wastewater mainly composed of cationic dyes can reach 94% ~ 100% by using 0.01% bentonite and 0.005% polyaluminium chloride.

Xiao Zijing and Ye Ling [21] mixed bentonite Na Mont with AlCl3 crosslinker, starch s, PVA, Azodicarbonamide azo and other materials or compounds, mixed them with water, extruded and dried them in the oven. Then, the bentonite based porous clay material was prepared by burning for 4 hours at 600 ℃ in an electric furnace, and then burning for 1 hour at 800 ℃. It can be used to adsorb direct red and cationic red X-GRL which are the most difficult to be treated in red dye wastewater. The results show that the porous material has a good decolorization effect on printing and dyeing wastewater, and can overcome the shortcomings of secondary pollution caused by the increase of sludge.

3 outlook

Bentonite has a wide range of sources, low cost and good adsorption performance. It has the advantages of small investment and simple method, especially suitable for the treatment of small and medium-sized printing and dyeing wastewater. However, at present, the treatment of printing and dyeing wastewater with bentonite is still in the laboratory research stage, and there are few reports on its application in industrial production. Therefore, in order to further expand the application in the treatment of bentonite printing and dyeing wastewater, it is necessary to strengthen the research of Bentonite Modification Methods and adsorption saturated bentonite treatment technology in the future research.

In addition, because the water quality of printing and dyeing wastewater is very complex, single adsorption decolorization technology is often difficult to achieve the desired results. Especially for the complex wastewater of various types of dyes and other organic matters, it is necessary to develop and study the composite adsorbent and integrated decolorization process with a wide range of application.