Equilibrium and thermodynamic studies on the adsorption of the dye tartrazine onto waste "Coconut Husks" carbon and activated carbon

Removal of tartrazine by an agricultural waste, coconut husks (CH), was investigated and compared with activated carbon (AC). The effect of pH, temperature, amount of adsorbent, contact time, initial dye concentration, and particle size on the extent of adsorption by the two adsorbents was investigated. The maximum adsorption capacity was obtained for pH 2.5, adsorbent dose of 3.3 g•L^-1, particle size > 0.15 mm, contact time of 210 min, temperature of 30 °C, and dye concentration of 6•10 ^-5 M for the CH-tartrazine system and pH 2.5, adsorbent dose of 0.3 g•L^-1, particle size > 0.15 mm, contact time of 40 min, temperature of 50 °C, and dye concentration of 6•10^-5 M for the AC-tartrazine system. The negative values of ΔG° indicated that the dye adsorption process is spontaneous in nature. The positive value of ΔH° shows the endothermic nature of the AC-tartrazine system, whereas the negative value of ΔH° indicates the exothermic nature of the CH-tartrazine system. The adsorption was found to undergo pseudo first-order adsorption kinetics. A significant amount of the dye (99 % for AC and 92 % for CH) was recovered by using 1.0 M NaOH as an eluting agent. The results revealed that CH can be used as a economically viable alternative to AC.