Adsorption of Reactive Red 158 Dye by Chemically Treated Cocos nucifera L. Shell Powder

Abstract

The effective removal of dyes from aqueous wastes is an important issue for many industrialised countries. The traditional treatment methods used to remove dyes from wastewaters have certain disadvantages such as incomplete dye removal, high reagent and energy requirements, generation of toxic sludge or other waste products that require further disposal. The search for alternative and innovate treatment techniques has focused attention on the use of biological materials for dye removal and recovery technologies. In this respect, adsorption has gained an important credibility during recent years because of its good performance and low cost performance as a pollutant removal technology. In this research study, chemically conditioned Cocos nucifera L. shell powder was used as low-cost, readily available and renewable adsorbent for the removal of reactive textile Red-158 dye from aqueous solutions. Batch experiments were carried out for the adsorption kinetics and isotherms with pre-treated C. nucifera L. Operating variables studied were pH, initial dye concentration and dosage of adsorbent. Results indicated that the adsorption capacity had been enhanced with increasing dosage of the biosorbent and the maximum colour removal was 57.18% at a pH of 2.00 ± 0.01 with an adsorbent dosage of 20 g/L and dye concentration of 20 mg/L. Equilibrium adsorption data were very well represented by the Langmuir, Freundlich, Dubinin–Radushkevich and Temkin isotherm models with all having correlation coefficients higher than 0.85 for all tested adsorption systems. R _L values obtained for the Langmuir model were greater than 1 and the n values of Freundlich being in the range of 2–10 collectively indicated that the biosorption process with C. nucifera L. was feasible. Equilibrium kinetic data followed the second-order equation and intra diffusion model very well, supported by the high correlations coefficients of the respective linearised models. Batch column experiments were also carried out with operating variables such as bed height, initial dye concentration and input volume of dye solution. The dye uptake was higher with increasing bed heights such that dye removal uptake was 73.60% at a bed height of 6 cm and 92.49% at bed height of 10 cm. At constant bed heights and with constant dye concentrations, the dye removal efficiency decreased as input volume of dye solution to the column rises and so dye uptake in first 120 min was 92.63% for an input of 100 mL dye solution and 60% with higher input volume of 250 mL while an increase in initial dye concentration leads to a decrease in the uptake of reactive red 158 dye. Experimental data exhibited a characteristic “S” shape and could be fitted effectively to the Thomas model which had high correlation coefficients (above 0.85).