Ahmad Talaat, M. Abdelkreem, Eman Ashour, Asma Abdelsattar
The aim of this work is to study the removal of Congo red (CR) dye from wastewater using raw rice straw (RRS) and different modifications of it, namely (acid treated rice straw (ATRS), base treated rice straw (BTRS), modified rice straw (MRS) and magnetite loaded rice straw (MLRS)). The effect of contact time, pH, adsorbent dose, mixing rate, particle size and solution temperature on the adsorbed amount of the dye were investigated. The adsorbents were characterized using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM). The applicability of Langmuir, Freundlich, Temkin and D-R adsorption isotherm equations for the present system was tested. The experimental data fitted well to Langmuir model for RRS and MLRS and to Freundlich model for other modifications. Kinetic data was analyzed using the pseudo-first-order, pseudo-second-order, Elovich, intra particle diffusion, and film diffusion (Boyd) models and were found to closely follow the pseudo-second-order model. Thermodynamic equations were applied and the results showed that the adsorption was nonspontaneous and exothermic for MRS and spontaneous and endothermic for MLRS.