Adsorption Behavior and Mechanism for the Uptake of Fluoride Ions by Reed Residues

Abstract

The adsorption behavior and mechanism for the uptake of fluoride ions by untreated and desugared reed residues (roots, stems and leaves) were studied through adsorption experiments, elemental analysis, infrared spectroscopy and surface area analysis. The results showed that the adsorption capacity of untreated and desugared reeds followed the order: desugared roots 2136 mg/kg > desugared leaves 1825 mg/kg > desugared stems 1551 mg/kg > untreated roots 191 mg/kg > untreated stems 175 mg/kg > untreated leaves 150 mg/kg, so adsorption capacity of desugared reeds was larger than that of the untreated reeds. The adsorption kinetic of fluoride ions followed a pseudo-first-order model. A Langmuir model could be used to fit the isothermal adsorption process which was a spontaneous endothermic reaction involving mainly physical adsorption. The ΔG for the uptake of fluoride by the desugared reeds was more negative, so the degree of spontaneity was higher than for the use of the untreated reeds. After samples were desugared, the specific surface area and aromaticity of the reed increased, while the polarity and hydrophilicity decreased, which explained the adsorption amount of desugared reed was higher than that of the untreated. This study enriches techniques and methods of removing fluoride ions from water.

Monitoring kinetic and thermodynamic parameters of fluoride adsorption from aqueous solution by pks-based anion resins

“…Moreover, summarization of intra-particle parameters for fluoride uptake on to PKS-AR is presented in Table 2. These results demonstrate that intra-particle diffusion increased with corresponding increase in fluoride concentration in the solution that is analogous to research reported in [12,18]. Figure 2.…”

“…(Figure 1). Furthermore, the adsorption capacity of fluoride onto PKS-AR increased by an escalation in temperature that is also reported by [18] in which adsorption behavior of fluoride was studied on adsorbent using reed residues as a precursor. In addition, absorption capacities revealed that PKS-AR posses limited capacities that got exhausted as the initial fluoride concentration increased.…”

“…These results indicate a high probability of chemisorption that largely constitutes the adsorption mechanism of fluoride onto PKS-AR [12,22]. The correlation coefficients (R 2 ) between experimental data and model predictions was almost unity at all concentrations under consideration (Table 1), indicating goodness of fit of the pseudosecond-order model [18]. Moreover, kinetic rate constant (k1) decreased and initial uptake rate (h) increased at higher concentrations of fluoride (Table 1).…”

“…The external mass transfer that can also be referred as boundary diffusion as well as describe rate limiting steps which are imperative regarding the solute-transfer process in solid-liquid adsorption [18]. The rate-limiting step in the adsorption of fluoride by PKS-AR was investigated by plotting ( Figure 2) the amount of fluoride adsorbed against the square root of time ( at all initial concentrations of fluoride under consideration ), based on the Weber and Morris model (Equation 4).…”

“…Also, the change in standard entropy for adsorption process is positive (Table 3) showing increasing degree of freedom of fluoride ions. This phenomenon is associated to change in the structure of PKS-AR that increased the solid-liquid interface [3,18,20].…”