Adsorption characteristics of crystal violet on beach sand from aqueous solution

The adsorption of the cationic dye crystal violet on beach sand was studied, employing Freundlich and Langmuir Isotherms. The adsorption isotherm obeys Langmuir equation over a wide range of equilibrium concentration allowing the determination of the monolayer capacities which are considered as measures for the efficiencies of bach sand for the removal of colouring pollutants. It is furthermore evident that the amount of dye removed by the investigated sand is considerably large indication the efficiency of the sand in removing pollutants. The adsorption parameters were determined utilizing various linear regressions of the isotherm. Adsorption process can be enhanced or lowered by varying different parameters like concentration of the adsorbate, the amount of the adsorbent, Ph of the system and the shaking time. The correlation coefficient values indicate that the data fit the Langmuir isotherm better than the Freundlich isotherm, in case of linear and non linear regressions. The results also showed that a rise of temperature can cause transformation of physical adsorption into chemisorption. The value of adsorption enthalpy delta H = 50 kJ mol-1 proves the physical nature of the adsorption by dye on the beach sand surface. This small enthalpy change is insufficient to lead to bond breaking, so the physisorbed molecules of crystal violet retain their identity, although they might be distorted by the presence of the surface within the temperature range 29 to 35 degree centigrade. (author)