Comparing the removal of perchlorate when using single-walled carbon nanotubes (SWCNTs) or granular activated carbon: Adsorption kinetics and thermodynamics

Abstract

This study aims to remove perchlorate using single-walled carbon nanotubes (SWCNTs) or granular activated carbon (GAC). Dynamic and equilibrium adsorption experiments were performed to evaluate the thermodynamic behavior of perchlorate on SWCNTs and GAC. Key parameters affecting the adsorption, such as pH, ionic strength, and temperature were studied. The experimental results showed that the dynamic adsorption experiment achieved equilibrium in approximately eight hours. The adsorption capacity increased as the concentration of perchlorate increased or as the ionic strength decreased. The selected adsorption models were the modified Freundlich, the pseudo-1st-order, and the pseudo-2nd-order equations. The results showed that the modified Freundlich equation best described the kinetic adsorption processes. The maximal adsorption capacities of GAC and SWCNTs were 33.87-28.21 mg/g and 13.64 - 10.03 mg/g, respectively, at a constant temperature between 5°C and 45°C. The thermodynamic parameters, such as the equilibrium constant (K0 ), the standard free energy changes (ΔG°), the standard enthalpy change (ΔH°) and the standard entropy change (ΔS°), were obtained. The results of the isothermal equilibrium adsorption experiment showed that low pH levels, low ionic strength, and low-temperature conditions facilitated the perchlorate adsorption, indicating that GAC and SWCNTs are potential absorbents for water treatment.

A thermodynamic and kinetic study of trace iron removal from aqueous cobalt sulfate solutions using Monophos resin

“…During an ion exchange process, there are three main steps: (1) diffusion of species through a liquid film around resin particles (liquid film diffusion); (2) transfer of species through resin pores to places of ion exchange (particle diffusion); and (3) chemical reaction between species and resin functional groups (chemical reaction). Equations (8), (9), and (10), respectively can describe these three steps: 12–14…”

“…The Lagergren equation (see equation 7a) is one of the commonly used first-order kinetic equations, whereas the McKay equation (see equation 7b) is often used as second-order kinetic equation. [12][13][14] In addition, other kinetic models, such as the Elovich equation (see equation (7c)), Webber-Morris equation (see equation 7d Figure 7 shows fitting plots for these five models. From the fitting results (see Figure 7 and Correlation factor other equations.…”

Functionalized activated carbon for the adsorptive removal of perchlorate from water solutions

“…The extensive use of activated carbon for enhancing perchlorate removal has been reported. Mahmudov and Huang have showed that pristine activated carbon has moderate perchlorate uptake capacity compared with other major competing anions such as nitrate, sulfate and bicarbonates [33][34][35]. Increase in positive surface charge promotes the removal of anions while negatively charge surface enhances the removal of cations.…”