Adsorption/desorption behavior of cationic dyes on Moroccan clay: Equilibrium and mechanism

Moroccan clay were prepared and tested as adsorbent for removal of three basic dyes: basic red 46 (br46),methylene blue (bm) and green malachite (gm) from aqueous solution. the adsorption kinetic was studied,the experimental data isotherms were analysed using the langmuir,freundlich and redlich peterson models. thermodynamical parameters (δh°,δs°,δg°,and ea were also calculated for the dyes adsorption onto clay,it revealed that the adsorption process is exothermic in nature for the br46 dye. nevertheless,it is endothermic for bm and gm. the ea values for br46,bm and gm are observed to be 40,64 and 76 kj/ mole,respectively. these results indicates that the adsorption has a low potential barrier for br46 dye and assigned to a physisorption. whereas,the chemical adsorption mechanism is occurred for the bm and the gm dye. the desorption of the basic dyes using nacl and cacl2 at different salt dyes ratio onto raw clay samples were studied using a batch adsorption. results showed that the presence of other ions (na+ and ca2+) reduces the dyes uptake onto clay and promote significatively the dyes desorption when the salt dye ratio is less than 1,whereas,the desorption effect is limited when this ratio is more than 1. the adsorption mechanism has been confirmed by ir spectra decomposition. © 2017,university of mohammed premier oujda morocco.