Papers by Keyword: Adsorption Thermodynamics

Abstract: A novel composite material, calcium/chitosan/fly ash (Ca/CTS/FA) adsorbent prepared by adding a small amount of chitosan (CTS) and calcium ion(Ca) on fly ash (FA) was applied to the adsorption of three direct dyes including direct orange S (DO-S), direct green BE (DG-BE) and direct bordeaux BE (DB-BE). Adsorption equilibrium, isotherms and adsorption thermodynamics were studied . The results show that the adsorption rates of three direct dyes to Ca/CTS/FA are high and the adsorption equilibrium can be reached within 60 minutes. isothermal adsorption data agree with Langmuir model, and the saturated adsorption capacities are 1667mg/g for DO-S, 1111mg/g for DG-BE and 1111mg/g for DB-BE respectively at 298K. Dubinin-Radushkevich (D-R) model is used to investigate the adsorption behavior of direct dyes, and theaverage adsorption energy is in the range of 17.2 ~ 23.6kJ/mol at different temperatures. the thermodynamic parameters indicate that the adsorption processes of direct dyes to Ca/CTS/FA are spontaneous and endothermic from 298K to 328K. Characterization results by FT-IR indicate that Ca/CTS/FA composite is successfully prepared. As a low-value composite adsorbent, Ca/CTS/FA has very high adsorption capacity for direct dyes.

Abstract: This study intends to explore the application of treating Methylene Blue dyeing wastewater with an inexpensive adsorbent compounded with . It studied the adsorption kinetics and adsorption thermodynamics of MB-Mold/Bentonite system. And single factor investigation were also conducted, including dosage, initial concentration, pH, stirring time and standing time. The results showed that the Methylene Blue system fitted second-order kinetics with 62.11mg/g saturated adsorption capacity. While the adsorption isotherms fitted Freundlich equation well(monolayer adsorption), with 61.49mg/g adsorption capacity. And the removal was above 99%, when the dosage of composite absorbent was 8g/L, pH was nature (5.6), stirring time was 15min and standing time was 1h .

Abstract: This study intends to explore the application of treating Acid Purplish Red dyeing wastewater with an inexpensive adsorbent compounded with Mold/Bentonite. It discussed the adsorption conditions and mechanism of Acid Purplish Red through single factor experiments (including dosage, initial concentration, and pH, stirring time and standing time). It also studied the adsorption kinetics and adsorption thermodynamics of this system. The results showed that the removing rate was above 94%, when the dosage of composite absorbent was 10 g/L, pH was nature (5.8), stirring time was 20min and standing time was 1h.The Acid Purplish Red system accorded with Langmuir and Freundlich absorption model, and it fitted Langmuir thermostatic adsorption equation better. And the saturated adsorption capacity can be obtained as 17.63mg/g. The sorption parameters showed that the adsorption of composite absorbent on Acid Purplish Red was easy, the system was monolayer adsorption. While the adsorption kinetic of Acid Purplish Red system fitted second-order kinetics with 78.15mg/g saturated adsorption capacity of Acid Purplish Red, and the adsorption was chemic-sorption.

Abstract: The form distribution of phosphorus (P) in ten surface sediments from the upper reaches of the Yellow River, China, was studied using the sequential chemical extraction procedure－the standards, measurements and testing harmonized procedure. The equilibrium and thermodynamics of P adsorption onto sediments were evaluated. Five fractions of sedimentary P, including metal oxide bound P (NaOH-P), calcium bound P (HCl-P), inorganic P (IP), organic P (OP) and concentrated HCl P (total P, TP), were separately quantified. The results indicated that the contents of different P fractions in sediments varied greatly. The mean of TP content was 657.57 mg/kg, and averages of NaOH-P, OP, HCl-P and IP contents represented 4.03%, 8.85%, 82.10% and 88.69% of TP, respectively. HCl-P was the major component of IP and TP. the amount of potential bioavailable P was approximately estimated 12.88% of TP. The equilibrium data of P adsorption on different sediments fitted perfectly for Langmuir and Freundlich models. the adsorption amounts of P decreased with increasing temperature. The negative values of thermodynamic parameters ΔG and ΔH indicated the spontaneous and exothermic nature of the sorption.

Abstract: Alizarin Red (AR) has been shown to be effectively removed from aqueous solution using the ultrafine fly ash (UFA) prepared by ball milling from raw fly ash (FA), a low-cost industrial solid waste. The maximum removal rate was 91.04% in a solution of initial AR concentration of 700 mg/L, adsorption time of 60 min at pH 5.0 and temperature of 25°C. Compared with FA, the adsorption capacity of UFA is higher for AR removal. Effects of important parameters, contact time, adsorbate concentration, pH and temperature, were investigated. The UFA and AR-loaded UFA were characterized by FT-IR. The equilibrium, kinetics and thermodynamics of AR adsorption onto UFA were evaluated. The AR uptake process followed the pseudo-second-order rate equation well, but the pseudo-first-order rate equation and intra-particle diffusion equation could only be applied to describe the initial stage of adsorption, furthermore, intra-particle diffusion might be the rate-controlling step of fast adsorption process. The sorption decreased with increasing temperature and the adsorption apparent activation energy was 8.28kJ/mol. Langmuir isotherm equation could better describe the adsorption equilibrium at different temperatures, compared with Freundlich model. Thermodynamic parameters, ΔG, ΔH and ΔS, were also calculated. The results inferred that the adsorption of AR/UFA system was feasible, spontaneous and exothermic nature of the process which was mainly controlled by physical adsorption.

Abstract: Monte Carlo simulations and finite-size scaling analysis have been carried out to study the critical behavior in a submonolayer lattice-gas, which mimics a nanoporous environment. In this model, one-dimensional chains of atoms were arranged in a triangular cross-sectional structure. Two kinds of lateral interaction energies have been considered: (1) wL, interaction energy between nearest-neighbor particles adsorbed along a single channel and (2) wT, interaction energy between particles adsorbed across nearest-neighbor channels. We focus on the case of repulsive transverse interactions (wT > 0), where a rich variety of structural orderings are observed in the adlayer, depending on the value of the parameters kBT/wT (kB being the Boltzmann constant) and wL /wT. For wL /wT = 0, successive planes are uncorrelated, the system is equivalent to the triangular lattice, and the well-known [ ] ordered phase is found at low temperatures and a coverage, , of 1/3 [2/3]. In the more general case (wL /wT  0), the competition between interactions along a single channel and the transverse coupling between sites in neighboring channels leads to a three-dimensional adsorbed layer. Consequently, the and structures “propagate” along the channels and new ordered phases appear in the adlayer. The influence of each ordered phase on adsorption isotherms, differential heat of adsorption and configurational entropy of the adlayer has been analyzed and discussed in the context of the lattice-gas theory. Finally, the Monte Carlo technique was combined with the recently reported free energy minimization criterion approach (FEMCA) [F. Romá et al.: Phys. Rev. B Vol. 68 (2003), art. no. 205407] to predict the critical temperatures of the surface-phase transformations occurring in the adsorbate. The excellent qualitative agreement between simulated data and FEMCA results allows us to interpret the physical meaning of the mechanisms underlying the observed transitions.