Enhanced phosphate removal from aqueous solution by ferric-modified laterites: Equilibrium, kinetics and thermodynamic studies

Abstract

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Abstract:The phosphate removal performances of a series of ferric-modified laterites (ML) were tested and compared with raw laterite (RL) in this study. After the modification with 0.5 MFeCl 3 solution, the resulting adsorbent ML-C exhibited 90.12 % of phosphate removal, which was 37.47 % higher than that of RL under the same experimental condition. This may be attributed to the significant increase of BET surface area and total pore volume for ML-C, arising from the formation of akaganeite. The effects of contact time, initial phosphate concentration, temperature, pH, and co-existing ions on the adsorption capacity of ML-C were investigated in detail. The equilibrium data of ML-C were fitted better by the Freundlich model than the Langmuir model, suggesting the heterogeneity of the adsorbent surface. The maximum adsorption capacity was estimated to be 31.53 mg P/g at 25 °C, which decreased with increasing temperatures. The negative change in free energy (∆G°) and in enthalpy (∆H°) indicated that the adsorption was a spontaneous and 2 exothermic process. The phosphate adsorption kinetics was better described by the pseudo-second-order model, which indicated the adsorption process was chemisorption.Phosphate removal capacities decreased with increasing pH. The presence of 0.001 M and 0.01M completive ions, e.g. Cl − , NO 3 − , SO 4 2− and HCO 3 − , had neglectable effects on the phosphate adsorption. In the reusability study, the adsorbent showed no significant loss in their adsorption performance after four adsorption-desorption cycles, indicating that ML-C was able to be utilized as a potential cost-effective phosphate adsorbent for practical applications.

Adsorption of phosphate from water on lake sediments amended with zirconium-modified zeolites in batch mode

“…In order to gain an insight into the mechanism involved in the adsorption process, thermodynamic parameters for the adsorption of phosphate on the raw and ZrMZ-amended sediments, including the free energy change of adsorption ( G • , kJ/mol), the heat of adsorption ( H • , kJ/mol) and the entropy change of adsorption ( S • , J/mol K) were calculated using the data of Fig. 5 and the following equations (Huang et al, 2013;Jin et al, 2005;Lǔ et al, 2013):…”

Porous Pr(OH)3 nanowires as novel high-performance adsorbents for phosphate removal

“…Table 3 summarizes the values of ∆G°, ∆H° and ∆S°, which are obtained by using the thermodynamic analysis. The negative values of ∆G° increase when the temperature is elevated from 25 °C to 45 °C; that reveals the nature of adsorption is spontaneous and the spontaneity is reduced at higher temperatures [18,26]. The negative value of ∆H° confirms the phosphate adsorption on Pr(OH) 3 NWs is an exothermic process [44].…”

“…This conclusion is consistent with the aforementioned isotherm results; that the adsorption capacities decline by increasing temperatures. The negative ∆S° suggests the reduction in randomness during phosphate adsorption [18,26].…”

“…As known, various inorganic anions are present in natural water bodies or wastewater, which may compete with phosphate anions for active sites on the adsorbent and in turn affect its phosphate removal [18,26]. Fig.…”

“…Motivated by our previous work in the field of phosphate adsorption [18,[25][26][27], we reported the phosphate removal with the utilization of porous 1D Pr(OH) 3 NWs, which were fabricated via electrochemical deposition, for the first time herein. Their phosphate adsorption isotherms and kinetics were investigated in detail.…”