Adsorption of congo red by three Australian kaolins

This study investigated the potential use of kaolin as alternative adsorbents for removal of congo red from wastewater. The effect of adsorbent dosage, dye concentration, pH and temperature were experimentally studied to evaluate the adsorption capacity, kinetics and equilibrium. Experimental results revealed that optimal adsorption took place at acidic pH and high dye concentration. Ceram kaolin had the highest removal efficiency among studied kaolins, followed by K15GR and Q38. The dye uptake process obeyed the pseudo-second order kinetic expression and was best described by the Langmuir isotherm. Intra-particle diffusion studies showed that the adsorption mechanism was not exclusively controlled by the diffusion step and was more likely to be governed by external mass transfer. Thermodynamic studies showed congo red adsorption on all kaolins was exothermic and spontaneous in nature. Recovered Q38 and K15GR kaolin demonstrated an enhanced adsorption capability. The results indicate that these local kaolins could be employed as low-cost alternatives for removal of anionic dyes from industrial wastewater.