There are many kinds of dyes used all over the world. Among them, reactive dyes are being used more and more widely because of their bright colors and complete chromatograms. However, the good hydrophilicity and physical and chemical characteristics of reactive dyes make it one of the dyes that are difficult to remove in printing and dyeing wastewater.
Dyestuffs have very stable characteristics and are difficult to decompose by themselves, so conventional wastewater treatment processes are difficult to work. At present, printing and dyeing wastewater mostly adopts adsorption process, and the commonly used adsorbent is activated carbon. Activated carbon has selectivity to dyes, and is expensive and difficult to regenerate, which limits its application in the adsorption and decolorization of printing and dyeing wastewater. Generally, it is only used in the treatment or advanced treatment of printing and dyeing wastewater with low concentration.
Bentonite has large reserves and is cheap. Montmorillonite, the main component of bentonite ore, has a unique crystal structure, good cation exchange performance and high specific surface area, and is widely used as an adsorbent for wastewater treatment at home and abroad. Bentonite is directly used to treat dye wastewater with almost no treatment effect, so it must be transformed and modified before use.
Since most of the fine particles and colloids in the wastewater are negatively charged, organic bentonite modified with cationic surfactants can be used for the treatment of printing and dyeing wastewater. Surfactants can significantly reduce the surface tension of silicate. The decrease in surface tension leads to an increase in the amount of adsorption, and the increase in interface adsorption increases the charge on the interface, which can adsorb more organic matter.
Modification mechanism of organic bentonite
The organic bentonite prepared by the modification of cationic surfactant, because the quaternary ammonium salt cation enters the interlayer of the bentonite, the interlayer spacing of the organic bentonite is increased to different degrees than the original soil, the organic carbon content increases, and the hydrophobic performance is improved. Therefore, the ability to remove organic matter in water is greatly enhanced.
When the organic bentonite is added to the dye wastewater, the long carbon chain organic cations on the surface of the bentonite will adsorb and bridge the organic dye molecules through hydrogen bonding and van der Waals forces, and make the fine suspension originally dispersed in the dye solution. The liquid and colloidal particles further aggregate to form a large and strong sinking wool-like floc, which then settles down.
The decolorization rate of various modified bentonites for printing and dyeing wastewater is higher than that of original bentonite. However, PDMDAAC-bentonite is prepared by modified bentonite with Poly(Dimethyl diallyl ammonium Chloride) (PDMDAAC), which has better adsorption performance than original bentonite. The decolorization rate of PDMDAAC-bentonite for printing and dyeing wastewater is slightly higher than that of activated carbon, but the treatment time is much shorter than that of activated carbon treatment, indicating that PDMDAAC-bentonite can replace or partially replace activated carbon in the advanced treatment of printing and dyeing wastewater.