Surface and groundwaters become contaminated with dyes due to discharge into the environment, which increases the risk of a number of human diseases. Many methods of dye removal from discharge waters at the source have been developed, but few are effective and the most effective method (activated carbon) is very expensive. The purpose of the present study was to test a natural zeolite (clinoptilolite type) as a potentially effective and inexpensive method to remediate dye discharge into the environment. In the removal experiments, malachite green (MG) and rhodamine B (RB) cationic dyes were used. The effects of various experimental conditions such as initial dye concentration, pH, and temperature on dye removal were investigated in a single-dye system. The degree of removal of MG and RB increased with increasing initial concentration and temperature of the dye in a single-dye system. An increase in pH decreased RB removal, but increased MG removal. In a two-dye system, MG and RB adsorption decreased by ~41.74 and 21.51%, respectively, due to competitive adsorption of the two dyes. Adsorption reflected a pseudo-second order kinetics model with high correlation coefficients (r2 = 0.996–1.000) in single-dye and two-dye systems. Adsorption was most consistent with the Langmuir-1 and the Redlich-Peterson isotherm models with high correlation coefficients (r2 = 0.987–0.999) in both systems. The Langmuir-1 adsorption capacities were determined as 43.86 and 44.25 mg/g for the removal of MG and RB in single-dye systems, respectively. In a two-dye system, the Langmuir-1 capacities were 20.62 and 31.54 mg/g for the removal of MG and RB, respectively.

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