Use and Misuse of Sorption Kinetic Data: A Common Mistake That Should Be Avoided

Numerical simulation of sorption dynamics showed that the use of data recorded at (or very close to) equilibrium in the search for the kinetic equation that best describes the process frequently leads to incorrect conclusions. Notably, it has been demonstrated that the fit of the adsorption data at equilibrium (t/q t versus t) is a straight line irrespective of the sorption kinetics. In order to distinguish pseudo-first-order from pseudo-second-order sorption kinetics, the data near the equilibrium should be omitted from the least-squares fit and the result confirmed by a different method. A straightforward method based on Δ(q t /q e )/Δt versus 1 – q t /q e and versus (1 – q t /q e ) 2 plots is suggested. Some recent papers reporting incorrect sorption kinetic analyses are discussed

Adsorption of Supranol Yellow 4GL from Aqueous Solution onto Activated Carbons Prepared from Seawater Algae

International audienceAdsorbents prepared from seawater algae, viz. green Ulva lactuca (PGA) and brown Systoceira stricta (PBA), by chemical activation were successfully tested for the removal of Supranol Yellow 4GL dye from aqueous solutions. Impregnation in 20% phosphoric acid for 2 h at 170 °C and subsequent air activation at 600 °C for 3 h significantly enhanced the adsorption capacities of both algae relative to their inactivated states. Parameters influencing the adsorption capacity such as contact time, adsorbent dosage, pH and temperature were studied. Similar experiments were carried out with commercially available Merck activated carbon (MAC) for comparative purposes. Adsorption efficiencies were measured at a pH 2 and dosages of 8 g/l and 12 g/l for PGA and PBA, respectively. Batch adsorption experiments resulted in maximum adsorption capacities determined from Langmuir models of up to 263, 93 and 84 mg/g for PGA, PBA and MAC, respectively. BET, FT-IR analyses, iodine number and Methylene Blue index determination were also performed to characterize the prepared adsorbents. The adsorption kinetics were found to comply with the pseudo-second-order model with intra-particle diffusion being the rate-determining step. Thermodynamic analysis confirmed that the adsorption reaction was spontaneous and endothermic. These studies indicate that these seawater algae could be used as low-cost alternatives for the removal of dyes

Development of a fluidized bed system for adsorption of phenol from aqueous solutions with commercial macroporous resins

This work is related to removal of phenol from wastewaters by adsorption onto polymeric resins, a current alternative to activated carbon. A closed circuit, bench-scale liquid fluidized bed system was developed for this purpose. Phenol aqueous solutions with initial concentrations in the range of 0.084 to 0.451 kg/m³ were used to fluidize small permeable capsules of stainless steel screen containing a commercial resin at 308 K. Experiments were carried out using a fluidizing velocity 20% above that of the minimum fluidization of the capsules. Typically, 30 passages of the liquid volume circulating through the bed were required to reach a quasi-equilibrium concentration of phenol in the treated effluent. A simple batch adsorption model using the Freundlich isotherm successfully predicted final phenol concentrations. Suspended solids, often present in residual waters and a common cause of fixed bed clogging, were simulated with wood sawdust