Equilibrium, Thermodynamic and Mechanism Studies of Malachite Green Adsorption on Used Black Tea Leaves from Acidic Solution

Abstract

Abstract. This study reports the equilibrium adsorption mechanism and thermodynamics for the removal of Malachite Green (MG) from acidic solution using Used Black Tea Leaves (UBTL) as a low cost adsorbent. The effect of initial dye concentration, processing temperature and the presence of electrolytes on the adsorption from acidic solutions were investigated in batch process. Adsorption process was attained to the equilibrium at about 24 hours. Adsorption isotherms of MG on UBTL for different temperatures were constructed at pH 2.0 and the equilibrium adsorption data were analyzed using different model equations such as Langmuir, Freundlich, Temkin, DubininRadushkevich (D-R), Harkin-Jura, Halsey, Elovich-Larionov and Flory-Huggens isotherms. The experimental results were reasonably correlated by Langmuir, Flory-Huggins and D-R models than other isotherm models. The maximum adsorption capacity (q m ), intensity of adsorption (b) and separation factor (R b ) were calculated from Langmuir plot and activation energy of adsorption (E ad ) was determined from D-R isotherm. At pH 2.0, the equilibrium adsorption capacity of UBTL to MG is 110 mg•g -1 at 30°C, which was increased with increasing temperature suggested endothermic nature of adsorption. Thermodynamics parameters: ΔG ads , ΔH ads and ΔS ads were calculated from Langmuir constant (b). The positive values of enthalpy and free energy, and negative value of entropy suggested that the adsorption is less spontaneous and surface migration or fragmentation of MG molecules on UBTL surface might be occur. Again, the low value of activation energy of adsorption (E ad = 0.3 kJ•mol -1 <8 kJ•mol -1 ) suggested that the adsorption is controlled by physical in nature. A possible mechanism involvement of protonation is proposed from the effect of electrolytes during the adsorption of MG on UBTL at pH 2.0.

Correlation of Activated Carbonized Avocado Pear Seeds (Persea Americana) and Activated Carbonized Orange Peels (Citrus Sinensis) Adsorptive Potency in Eliminating Cd2+ Ions in contaminated water

“…Isotherm model of Dubinin-Radushkevich is unfounded on ideal assumptions for instance, steric encumbrance nonexistence in the middle of adsorbed and entering particles, equal efficacy of the adsorption locations and surface uniformity on microscopic level as in Langmuir isotherm (Sarı and Tuzen, 2009;Amin et al, 2015;Moftakhar et al, 2016). The Dubinin-Radushkevich equation (equation 5) has been broadly applied to expound energetic heterogeneousness of solid at low level coverage as onetracklayer zones in micropores (Hossain et al, 2016;Inyinbor et al, 2016). Dubinin-Radushkevich isotherm is regularly applied to illustrate solo solute systems adsorption isotherms (Essomba et al, 2014).…”

Low-cost Adsorbents Derived from Agricultural By-products/Wastes for Enhancing Contaminant Uptakes from Wastewater: A Review

“…A kinetic evaluation on the adsorptive removal of malachite green (MG) was carried out by Abul Hossain and Hossain (2014) [113] to evaluate the adsorptive removal of (MG) by used black tea leaves (UBTL) as a low-cost adsorbent in a batch mode system. Their results showed good adsorption capacity of UBTL to MG at 227.3 mg /g at pH 6.0 and 30ºC.…”

Comparative Adsorption of Methylene Blue on Different Low Cost Adsorbents by Continuous Column Process

“…As a result, a large amount of bi-product as well as used black tea leaves is produced in tea industry. Like as bagasse, cellulose and lignin are the main compositions of used black tea leaves [14,[25][26][27][28][29][30][31][32][33][34][35][36][37][38] which might be effective for adsorption of methylene blue.…”