Erika Padilla-Ortega

Removal of Toxic Pollutants from Aqueous Solutions by Adsorption onto an Organobentonite

An organobentonite was prepared by adsorbing the cationic surfactant hexadecyltrimethylammonium bromide (HDTMA) onto the surface of a calcium bentonite. The adsorption capacity of the organobentonite towards 2,4-dichlorophenoxyacetic acid (2,4-D), phenol and the dichromate ion (HCrO−4) from aqueous solutions was investigated. The Langmuir isotherm gave a reasonable fit to the experimental data for the sorption of 2,4-D, phenol and the HCrO−4 ion onto the organobentonite. The adsorption equilibrium data for 2,4-D demonstrated bimodal adsorption for equilibrium concentrations of 2,4-D greater than 650 mg/l. The capacity of the organobentonite for sorbing 2,4-D, phenol and the HCrO−4 ion was considerably higher than that of the bentonite. This capacity was compared to that of a commercial activated carbon (F-400), from which it was concluded that modification of the bentonite substantially enhanced its adsorption capacity whereas the capacity of the organobentonite was lower than that of the F-400 carbon.

Adsorption of Heavy Metal Ions from Aqueous Solution onto Sepiolite

The adsorption capacity of sepiolite towards the removal of heavy metal ions from aqueous solution was studied in this work, with adsorption equilibrium data being obtained with a bath adsorber. The sepiolite sample was chemically stable over the pH range 2–12, but dissolved in acidic solutions with pH values less than 2. The Langmuir isotherm gave a better fit of the experimental adsorption equilibrium data, since the average absolute percentage deviation of the Langmuir isotherm was lower than that of the Freundlich isotherm. The adsorption capacity of sepiolite towards metal ions decreased in the following order: Cr(III) > Cd(II) > Cu(II) > Zn(II) > Ni(II) > Ag(I). Increasing the temperature from 15 °C to 35 °C led to an increase in the adsorption capacity. The capacity of sepiolite towards the adsorption of Cd(II) ions was diminished considerably on reducing the solution pH from 7 to 3. The effect of the solution pH was attributed to electrostatic interaction between the negatively charged sepiolite surface and the positively charged Cd(II) ions in the aqueous solution. The surface charge of sepiolite became less negative when Cd(II) ions were adsorbed onto the sepiolite surface. This result indicates that electrostatic interaction between the sepiolite surface and the Cd(II) ions in the aqueous solution played a very important role in determining the adsorption capacity of sepiolite. The adsorption of Cd(II) ions onto sepiolite at pH 7 was reversible when desorption was undertaken at pH 3, but not when desorption was undertaken at pH 7.

Adsorption of Heavy Metals on Diatomite: Mechanism and Effect of Operating Variables

The adsorption capacity of diatomite towards heavy metals as well as the adsorption mechanism was investigated in the present study. The chemical and X-ray diffraction analyses revealed that the diatomite was mainly composed of SiO2 (95.91%) as cristobalite and quartz. The maximum uptake of Cd(II), Zn(II), Pb(II) and Cr(III) were 0.734, 0.232, 0.169 and 0.162 meq/g at pH of 7, 6, 4 and 4, respectively. The adsorption capacity of diatomite was enhanced by increasing the temperature because the adsorption process was endothermic. The effect of the pH on the capacity was studied, and the maximum capacity augmented 6.3 times while increasing the pH from 4 to 7. This trend was due to the electrostatic interactions between the metal cations in solution and the negatively charged surface of the diatomite. The predominant adsorption mechanism of Cd(II) on diatomite was chemisorption, while ion exchange was responsible for 10% to 50% of the adsorption.

Comparison between diffusional and first-order kinetic model, and modeling the adsorption kinetics of pyridine onto granular activated carbon

AbstractIn this work, a surface diffusion model (SDM) obtained in a previous work was verified in a wide range of experimental conditions to predict the adsorption kinetics of pyridine on activated carbon. Moreover, the predictions of SDM model were compared with that obtained by using the first-order kinetic model. The results showed that the first-order model adjusted satisfactorily the experimental data. The effect of the stirring speed, mass of pyridine adsorbed, (qe), and temperature on the rate constant of the first-order model, (k1), was analyzed and equations were proposed to correlate k1 as functions of qe and temperature. Nevertheless, the dependence of k1 regarding the temperature, stirring speed, and qe cannot be accurately correlated, indicating that the overall adsorption rate of pyridine on activated carbon is controlled by the intraparticle diffusion. Moreover, it was shown that the rate of adsorption on active site is not controlling the overall adsorption rate. On the other hand, the SDM...

Equilibrium and Kinetic Adsorption of Organic Compounds onto Organobentonite: Application of a Surface Diffusion Model

The equilibrium and kinetic adsorption of Methylene Blue (MB), Methyl Blue (MTB) and 1-naphthalene sulphonic acid (NSA) onto organobentonite was investigated. The effect of pH on the adsorption capacity was studied by determining the adsorption isotherm over the pH range 3–12. The results showed that the maximum adsorption capacity at 25 °C of the organobentonite towards the removal of the compounds studied occurred at pH = 3 for MTB and NSA and at pH = 11 for MB. The experimental adsorption rate data were interpreted via a diffusional model that considered the external mass transport, intra-particle diffusion and adsorption onto an active site, intra-particle diffusion being considered as both pore volume and surface diffusion. The surface diffusion model fitted the experimental data quite well, thereby indicating that the overall rate of adsorption was controlled by surface diffusion. Furthermore, the surface diffusion coefficient increased by augmenting the mass of MB, MTB and NSA adsorbed at equilibrium. In addition, the surface diffusion model was used to interpret experimental data cited in the literature, thereby showing that surface diffusion plays an important role in the adsorption of organic compounds onto organoclays.

Antagonistic, synergistic and non-interactive competitive sorption of sulfamethoxazole-trimethoprim and sulfamethoxazole‑cadmium (ii) on a hybrid clay nanosorbent

The competitive sorption of the antibiotics sulfamethoxazole (SMX) and trimethoprim (TMP) and SMX-Cd(II) on a hybrid clay nanosorbent (NanoSorb) was investigated in detail in this work. NanoSorb was synthesized by sorbing a surfactant on bentonite. Besides, the sorption of SMX on the NanoSorb was confirmed by FTIR analysis, and SMX was mainly sorbed on NanoSorb by a partition mechanism due to hydrophobic interactions. Otherwise, the single adsorption of Cd(II) and TMP onto NanoSorb were due to electrostatic interaction and hydrophobic partition, respectively. The capacity of NanoSorb for sorbing single SMX was very similar to that for single Cd(II), but more than 10 times higher than that for single TMP. The competitive sorption of SMX-TMP was antagonistic because the sorption of one antibiotic on NanoSorb was decreased by the presence of the other antibiotic. The uptake of SMX was reduced up to 43.4% by the presence of TMP, whereas the presence of SMX decreased the uptake of TMP up to 29.6%. The non-modified Langmuir multicomponent isotherm (NLMI) interpreted quite well the experimental competitive sorption data of SMX-TMP. On the other hand, the competitive sorption of SMX-Cd(II) on NanoSorb revealed that the sorption of SMX was non-interactive because it was not influenced by the presence of Cd(II). Whereas, the sorption of Cd(II) was synergistic or cooperative since the uptake of Cd(II) sorbed increased considerably with the uptake of SMX sorbed on NanoSorb. The two-site Langmuir model fitted the experimental competitive sorption data of Cd(II) on NanoSorb saturated with SMX. The application of this isotherm was based on the fact that Cd(II) sorbed on two types of sites: a) cationic sites of the NanoSorb and b) Pi-cation interactions between the aromatic ring of the SMX sorbed on NanoSorb and Cd2+.