Study of Adsorption Efficiency to Remove Some of Azo Dyes Using Activated Carbon Derived From Agr-Residues.

Abstract

Many different parts of the world have been facing the problem of dyes contamination of surface and ground water. Dyeing and printing industries are the main source of water pollution, Excessive use of dyes is considered to be the main reason for this contamination. Therefore a simple, practical and economic process to reduce methyl orange dye concentrations in aqueous solutions with high adsorption capacity was the major objective of this research. To achieve this goal, adsorption experiments were conducted using activated carbon as adsorbent. The research method was used to minimize the cost of activated carbon production by preparation of (Modified Seaweed/ Chitosan solution/ Anthracene) composite. Modified Seaweed (MS) as starting material, was homogeneously mixed with Anthracene (An) (solid/solid ratio of 4/1) and then dissolved in Chitosan (Cs) solution, This minute quantity of (An) was selected to achieve the planned goal with minimal costs. The calcinated mixture was gently grounded for further application under the name of MS/Cs/An composite. The physicochemical properties of Modified Seaweed (MS) and (MS/Cs/An) composite were characterized via Fourier transform infrared spectroscopy FT-IR, X-ray diffraction XRD, and thermogravimetric analysis (TGA, DSC), Surface morphology and surface area were also examined using Scanning Electron Microscopy (SEM), and (BET) respectively. The adsorptive properties of MS/Cs/An composite were investigated in terms of adsorbent dose, pH, temperature, contact time, and agitation speed. Experimental tests were conducted in a batch process. The equilibrium adsorption data were interpreted using Langmuir, Freundlich, and Temkin isotherm models. The adsorption was found to follow Langmuir isotherm model. The calculated dimensionless separation factor, RL indicated that the adsorption of methyl orange onto adsorbent was favourable by the composite and the maximum monolayer adsorption capacity (qmax) was (37.04) mg/g. The MO distribution coefficient Kd decreased from 70.7 to 1.3 L g-1 with increasing initial MO concentrations from 20 to 80 mg L-1. In order to investigate the adsorption mechanisms, three simplified kinetic models, i.e., pseudo-first-order, pseudo-second-order and intra-particle diffusion were applied to fit the kinetic data obtained by using experimental data of different initial concentrations. The rate constants for the three models were determined and the correlation coefficients were calculated. The kinetic data supports pseudo-second order model with an R2 of 0.9999. The external (film) diffusion followed by intra-particle diffusion was the major driving process during the early stage of MO sorption. Various Thermodynamic parameters such as standard free energy (∆G0), standard enthalpy (∆H0), and standard entropy change (∆S0) of the adsorption process were calculated, which indicated that the present system was spontaneous, endothermic process in natural, and the adsorption is physicosorption. The electrostatic interaction between the oxygen- and nitrogen-bearing functional groups on the MS/Cs/An surface and MO ions was the key controlling mechanism for the MO sorption process, particularly at pH < pHPZC of the composite. Meanwhile, valuable contributions from Yoshida and dipole–dipole H bonding mechanismscan explain the MO sorption by the addressed composite, especially at pH > pHPZC. Therefore, the developed composite is regarded as a better adsorbent to address industrial wastewater in Libya with low-cost and excellent efficiency.