Mathematical modeling and stimulation of thermodynamic parameters for the removal for Cr6+ from wastewater using chitosan cross-linked glutaraldehyde adsorbent

Abstract

The presence of heavy metals such as chromium within water sources are considered as one of the most vital problem to the environment. Accumulating of chromium within the human body, can cause various diseases and disorders. Chitosan cross-linked glutaraldehyde adsorbent (formed from the acetyl group of chitin from alkaline solution) is widely a well-known adsorbent fore chromium metal removal present in solution. In the current study, mathematical modelling and the stimulation of thermodynamic parameters were done on crab chitosan cross-linked glutaraldehyde adsorbent for chromium (VI), Cr6+ removal. This was obtained through the prepared dichromate wastewater solution of 0.81 mg/L of Cr6+ per litre of distilled water. Adsorption experiments were also conducted in a bath system and the effect of stirring speed, chitosan cross-linked glutarladehyde dosages, contact time and temperature on the adsorption of Cr6+ were in investigated. The effectiveness of the cross-linked adsorbent at an optimum dosage (0.16 mg/L) for Cr6+) removal, from wastewater solution which was 82.3% of the initial concentration (0.81 mg/L) was found to be 0.8 g at 30 °C. The time required for the latter adsorption process to attain equilibrium was 80 min. For the thermodynamic study of the process of adsorption, properties such as Gibbs free energy (ΔGads), entropy (ΔSads) and enthalpy (ΔHads) values in the temperature ranges from 25 to 65 °C were also calculated in order to characterize the process. The free sorption energy was −47.56 kJ/mol which suggests the process was physical. The enthalpy of adsorption was −18.09 kJ/mol and the Gibbs free energies were all negative, thus the process was spontaneous and exothermic. The observed results in the current study indicated strange behavior that could not be depicted using the classical decay mathematical model. We concluded that only fractional differential operators with different kernels including the exponential decay, the power law and the generalized Mittag-Leffler function could be used to depict such observations.