The Langmuir isotherm suggests monolayer adsorption

The Langmuir isotherm suggests monolayer adsorption on a homogeneous surface with a finite number of adsorption sites and without any interaction between the adsorbed molecules (Acharya et al., 2009a, 2009b). The Langmuir equation relates solid phase adsorbate concentration (qe), the uptake, to the equilibrium liquid concentration (Ce) as follows:where KL and b are the Langmuir constants, representing the maximum adsorption capacity for the solid phase loading and the Aminoallyl-dCTP - Cy3 constant related to the heat of adsorption, respectively. It can be seen from Fig. 5 that the isotherm data fits the Langmuir equation well (R2 = 0.999). The outcome values of parameters k, n, KL, b, R2 for all the experiments with pH of solution equal to 2 for maximum removal of chromium (VI) are presented in Table 1. Langmuir equation can also be used to calculate a dimensionless equilibrium parameter, RL also known as the separation factor and can be expressed as:where, C0 is the initial concentration of chromium (mg/l). RL = 1 represents linear adsorption, while RL = 0 stands for the irreversible adsorption process. RL < 1 is for favorable adsorption, while RL > 1 represents unfavorable adsorption. In this case, the value of RL was found to be 0.975, suggesting that the adsorption process was less than 1 but it was nearly equal to 1 so it was linear adsorption.
Adsorption kinetic In order to define the adsorption kinetics of heavy metal ions, the kinetics parameters for the adsorption process were studied for contact times ranging from to 70 min by monitoring the removal percentage of the Cr(VI). The data were then regressed against the Lagergren equation (Eq. (5)), which represents a first order kinetics equation and against a pseudo-second-order kinetics equation (Eq. (6)).
Fixed bed studies The fixed bed column study for the removal of Cr (VI) from wastewater by dolochar was conducted by using a column of 4.5 cm diameter and 55 cm length. The column was packed with dolochar between two supporting layers of pre-equilibrated glass wool. The schematic diagram of column study is shown in Fig. 7. The column experiments were conducted with distilled water spiked with 10 mg/l metal solutions for dolochar with particle size 75 micron having a bulk density of 1.203 g/cm3, at bed depth of 2.5 cm and maintaining a constant flow rate of 10 ml/min (∼2.10 m3/m2/h) for Cr(VI). The studies were conducted at the room temperature of 30 ± 2 °C. The breakthrough point was considered when the ratio of effluent to influent concentration (C/C) reaches at 0.1. The breakthrough plots for ratio of effluent to influent concentration in the column versus time at bed depths 2.5 cm are shown in Fig. 8 for Cr (VI). It was observed that the time to achieve breakthrough was increased with the increase of bed depths. The breakthrough and exhaust time were found to be 19.5 and 90 h respectively. Treated water volume within beak through and exhaust time were 5.3 and 23 L respectively. The percentage of the total column saturated at breakthrough was found to be 95.68%.
Conclusion
Introduction At present, carbon-based fossil fuels provide ∼80% of the world\'s energy needs (ECOWORLD, 2008) and CO2 is generated by the energy producing processes. Due to increasing anthropogenic emissions of CO2 and other greenhouse gases, climate change has become a major concern. Many solutions can be given to the question: how to reduce CO2 emissions? But an efficient solution requires special attention for specific approaches. Adsorption is classed among practicable separation methods for purification or bulk separation in newly developed material production processes of, for example, high-tech materials and biochemical and biomedical products (Suzuki, 1990). Adsorption is usually described through isotherms, that is, the amount of adsorbate on the adsorbent as a function of its pressure (if gas) or concentration (if liquid) at constant temperature. The quantity adsorbed is nearly always normalized by the mass of the adsorbent to allow comparison of different materials (Foo and Hameed, 2010).