Study of chemical absorption of chromium by rice stem using physico-chemical adsorption isotherm model

One of the main objectives of the adsorption isotherm models is to determine the maximum capacity of the adsorbent. The main purpose of this study is to investigate the chemical absorption rate of chromium from aqueous solution by rice stem, using physico-chemical adsorption isotherm model of Shamohammadi and to compare adsorption isotherm models for determining the maximum capacity of the adsorbent.
The rice stem with particle sizes of 75, 300, 850 and 1200 micron, and the chromium solution with concentrations of 15 to 40 (mg/L) were used in this study.
Findings: The maximum adsorption efficiency of 96.30 % was obtained in in pH=2 using 10 (g/l) of rice stem with particle size of 75 micron. The maximum adsorption capacities of chromium by Langmuir model and Shamohammadi model for the rice stem were obtained as 2.918 and 4.926 (mg/g) in particle size of 75 microns, 2.206 and 3.310 (mg/g) in particle size of 300 microns, 1.838 and 2.617 (mg/g) in particle size of 850 microns and 1.037 and 1.322 (mg/g) in particle size of 1200 microns respectively.
Isotherm absorption studies showed that, based on Shamohammadi model, averagely 20.5% of adsorption occurs as initial adsorption. Moreover, by considering equilibrium adsorption (qe) as a function of initial concentration (C0), not only the precision of the model will be enhanced (according to evaluation criteria), but also the equilibrium capacity of adsorption increases to an average of 26.5% compared to the Langmuir model. Thus, application of the Shamohammadi model increases the capacity of chromium absorption by rice stem by an average of 47% compared to the Langmuir model.