The removal of reactive azo dyes by natural and modified zeolites

Abstract

The adsorption mechanism of three reactive dyes by zeolite has been examined with the aim of identifying the ability of zeolite to remove textile dyes from aqueous solutions. Towards this aim, a series of batch adsorption experiments was carried out, along with determination of the electrokinetic properties of both natural and modified zeolites. The adsorbent in this study is a clinoptilolite from the Gördes region of Turkey. The reactive dyes CI Reactive Black 5, Red 239 and Yellow 176 are typical azo dyes extensively used in textile dyeing. Adsorption tests were carried out as a function of mixing time, solids concentration, dye concentration and pH. The adsorption results indicate that the natural zeolite has a limited adsorption capacity for reactive dyes but is substantially improved upon modifying its surfaces with quaternary amines. An electrostatic adsorption mechanism involving the formation of a bilayer of amine molecules on the clinoptilolite surface onto which anionic dye molecules adsorb, depending on their polarities, is proposed. The results are also supported by electrokinetic measurements. The adsorption data were fitted to the Langmuir isotherm and it was found that the modified sepiolite yields adsorption capacities (q e ) of 111, 89 and 61 mg g −1 for Red, Yellow and Black, respectively. These results are comparable to a popular adsorbent, activated carbon.

Adsorption of methylene blue and orange II onto unmodified and surfactant-modified zeolite

“…The results suggest that the adsorption of MB onto the unmodified and SDBS-and SDS-modified zeolites increased gradually over the first 30 min and then remained unchanged with further increasing equilibrium time. However, the adsorption of OII onto unmodified zeolite was almost instantaneous and an apparent equilibrium was reached within the first 10 min, which is faster than with other studies [17,20,21]. It should be pointed out that apparent equilibrium was reached after 60 min for CPB-and HDTMA-modified zeolites (Fig.…”

Organic xenobiotics removal in constructed wetlands, with emphasis on the importance of the support matrix

“…The high ion exchange capacity of zeolites, their extensive porosities and specific surface areas, as well as their relatively cheap prices, make natural zeolites attractive adsorbents [208][209][210][211][212][213][214][215][216][217][218][219][220][221][222]. However, synthetic zeolites are also widely tested, especially because through synthesis a useful control can be obtained over the Si/Al ratio in the zeolite composition.…”

“…However, surface modification can change the surface functionality by adding cationic surfactants or other hydrophobic groups thus making them applicable for adsorption of various anions and organics. The most common surface modifiers are salts of a variety of quaternary amines such as hexadecyltrimethylammonium (HDTMA, the most popular surfactant) [210][211][212][213][214]224,226,[234][235][236], octadecyldimethylbenzylammonium (ODMBA) [216][217][218], stearyldimethylbenzylammonium (SDBA) [219,224] or benzyltetradecyl ammonium (BDTDA) [212]. Other posibilities are cetylpyridinium salts [211,220], cyclodextrins [208] and chlorosilanes [209].…”

“…Among some of the organic compounds that have been observed to be successfully removed by zeolites are phenolic compounds [208,[210][211][212]223,225,228,232,238], PAHs [209,231], BTEX [209][210][211]236], other aromatics such as nitrobenzene, bisphenol A, aniline and aniline derivatives [208,210,226,232,235], dyes [146,[213][214][215]230,233], pesticides [219,227] and pharmaceuticals [220][221][222]229].…”

Removal of bacteria by clinoptilolite rich mineral and its surfactant modified forms

“…The values of surface coverage were found from the ratio of the cross sectional area of surfactant molecule and packing areas for the surfactant on clinoptilolite rich mineral [55,56]. These values gave the idea about the surfactant configuration on the clinoptilolite rich mineral surface.…”