Maximum Sorption Efficiency Research Articles

Extraction of Fe(III) from hydrochloric acid solutions using Amberlite XAD-7 resin impregnated with trioctylphosphine oxide (Cyanex 921)

Ferric ions were efficiently removed from HCl solutions using Amberlite XAD-7 resin impregnated with trioctylphosphine oxide (Cyanex 921). Iron was removed under the form HFeCl 4 through direct binding on the resin or by extraction with Cyanex 921 involving a solvation mechanism. High concentrations of HCl and intermediary extractant loadings were required for maximum sorption efficiency and rationale use of the extractant. At intermediary extractant loading (in the range 300–450 mg Cyanex 921 g − 1 ) the maximum sorption capacity increased with extractant loading. Maximum sorption capacity slightly increased with temperature, the reaction is endothermic and the enthalpy change was found close to − 30.8 kJ mol − 1 . Sorption isotherms were fitted with the Langmuir equation and maximum sorption capacity reached values as high as 20–22 mg Fe g − 1 in 3 M HCl solutions. Despite the good fit of experimental data with the pseudo second-order rate equation, sorption kinetics was controlled by the resistance to intraparticle diffusion. The intraparticle diffusion coefficient ( D e) varying in the range 1.2 × 10 − 11 –4.7 × 10 − 10 m 2 min − 1 was found to increase with metal concentration and with temperature, while varying the extractant loading it reached a maximum at a loading close to 453 mg Cyanex 921 g − 1 . The desorption of Fe(III) can be achieved using 0.1 M solutions of nitric acid, sulfuric acid, sodium sulfate and even water, maintaining high efficiencies for sorption and desorption for at least 5 cycles.

High‐temperature sequestration of elemental mercury by noncarbon based sorbents

AbstractThis work is concerned with sequestration of elemental Hg at high temperatures (900–1100 °C) on a sorbent that is mineral based, rather than carbon based. This sorbent consists of an intimate mixture of CaO, CaCO3, and Al2O3–2SiO2, and is manufactured in industrially relevant quantities (metric tons) from residues produced in paper recycling processes. In contrast to activated carbon (AC), this noncarbon based sorbent has special advantages in that, it can actually enhance fly ash utilization for cement manufacture, rather than diminish it, as is the case for AC.Disperse phase experiments have been conducted, using an externally heated quartz tube reactor, with sorbent feeding rates ranging from 1 to 6 g/h. Preliminary results indicate that Hg removal efficiency is sensitive to sorbent feed rates and to furnace temperature. The Hg removal percentage increased with both these variables. Two mechanisms come into play: an in‐flight Hg sorption mechanism, and an Hg sorption mechanism related to sorbent deposits on the reactor wall. A maximum total (in‐flight plus deposit‐related) Hg removal efficiency of 83–90% was obtained at temperatures of 900–1100 °C. There was negligible sorption by either mechanism at temperatures below 600 °C. Results for the in‐flight mechanism alone showed a maximum sorption efficiency at ∼900 °C, whereas that on the reactor surface increased monotonically with temperature. This suggests that sorbent deactivation can occur in‐flight at high temperatures, which is in agreement with other fixed bed results obtained in this laboratory. Deactivation was not apparent for the sorbent‐related substance formed on the reactor wall. Raw and spent sorbents were analyzed by X‐ray diffraction (XRD) and scanning electron microscopy with energy dispersive spectrophotometer (SEM‐EDS) to identify the sorbent mineral transitions that seem to activate the process. The in‐flight mechanisms appear to involve (1) activation of the sorbent, caused most probably by an internal solid–solid reaction, followed by (2) Hg sorption, and (3) possible deactivation, if the temperatures are too high for longer period. Reactor surface mechanisms still remain to be elucidated. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd.

A critical examination of sorbent extraction pre-concentration with spectrophotometric sensing in flowing systems

In this paper, the solid-phase spectrophotometric concept is critically examined in flow systems exploiting a dedicated microcolumn-based optical sensor packed with octadecyl chemically-modified silica gel. The flow configuration integrates matrix separation with pre-concentration and on-column sensing of non-polar complexes resulting from analyte derivatization. The design criteria for optimum performance of both the sorbent-packed microcolumn and optosensing instrumentation are for the first time discussed in detail. Practical considerations required to warrant the maximum sorption efficiency of the reversed-phase material by avoiding chain collapse, and avenues to overcome the effects derived from its transparency changes upon solvation with solutions of different polarity are also addressed. The noteworthy features of the flow-through enrichment system involve the sensitivity enhancement with respect to common spectrophotometric procedures in the liquid-phase, as well as the capture of a large amount of scattered light, which is the most severe pitfall of conventional solid-phase absorptiometric approaches using commercially available flow-through cells. Several common spectrophotometric assays for monitoring key inorganic and organic parameters (viz. oxidized nitrogen, ammonium, sulfite, phosphate, iron(II)/total iron, chromium(VI), nickel(II) and phenol index) in environmental samples are taken as practical examples. Plausible sorption mechanisms together with discussions for proper performance of the different investigated reversed-phase extraction optosensing methods are presented in the bulk of the text. Special emphasis is paid to problems arising in real sample analysis due to unspecific sorption of matrix constituents and potential means to circumvent them are thoroughly explored.

Removal of chlorophenols from groundwater by chitosan sorption

The equilibrium and kinetics of chlorophenol (CP) sorption by chitosan, poly D-glucosamine, were studied under simulated groundwater conditions. Lower temperature, from 25°C to 15°C and then 5°C, markedly decreased the adsorption rates by a factor of 30–53% and 7–22%. Comparison between two types of chitosan, flakes and highly swollen beads, demonstrated that the maximum pentachlorophenol (PCP) uptake capacities in Langmuir and Freundlich models depend on the specific surface area of the particle. Low temperature (5°C) significantly increased the PCP uptake capacity in comparison to higher temperatures (15°C and 25°C). PCP uptake capacity was halved at pH levels higher than 6.5, and NaCl concentrations greater than 1% blocked PCP sorption almost completely. Of five kinds of chlorophenols, i.e. 2,4,6-trichlorophenol (2,4,6-TCP), 3,4-dichlorophenol (3,4-DCP), 2,3-dichlorophenol (2,3-DCP), 2,6-dichlorophenol (2,6-DCP), 3-monochlorophenol (3-MCP), TCP had the maximum sorption efficiency on flake-type chitosan, followed by DCPs, and finally MCP (the three kinds of DCP, with the same elemental compositions, achieved similar sorption performances).

Removal of chlorophenols from groundwater by chitosan sorption

The equilibrium and kinetics of chlorophenol (CP) sorption by chitosan, poly D-glucosamine, were studied under simulated groundwater conditions. Lower temperature, from 25°C to 15°C and then 5°C, markedly decreased the adsorption rates by a factor of 30–53% and 7–22%. Comparison between two types of chitosan, flakes and highly swollen beads, demonstrated that the maximum pentachlorophenol (PCP) uptake capacities in Langmuir and Freundlich models depend on the specific surface area of the particle. Low temperature (5°C) significantly increased the PCP uptake capacity in comparison to higher temperatures (15°C and 25°C). PCP uptake capacity was halved at pH levels higher than 6.5, and NaCl concentrations greater than 1% blocked PCP sorption almost completely. Of five kinds of chlorophenols, i.e. 2,4,6-trichlorophenol (2,4,6-TCP), 3,4-dichlorophenol (3,4-DCP), 2,3-dichlorophenol (2,3-DCP), 2,6-dichlorophenol (2,6-DCP), 3-monochlorophenol (3-MCP), TCP had the maximum sorption efficiency on flake-type chitosan, followed by DCPs, and finally MCP (the three kinds of DCP, with the same elemental compositions, achieved similar sorption performances).

Soaps, shampoos, and detergents

Heavy metals are pollutants that are naturally produced by human activities. Due to heavy metals' amount and toxicity in aqueous media, they are considered extremely harmful to human life. Therefore, it is necessary to find effective and efficient methods, as a severe challenge for reducing these pollutants to a permissible level. Among the various removal methods, the adsorption process has received much attention due to its benefits like low cost, ease of operation, high selectivity, and high removal efficiency. So far, various adsorbents such as activated carbon, agricultural waste, minerals, nanoparticles, and other inexpensive adsorbents have been used. Surface modification of these adsorbents by surfactants improves the adsorption properties, and as a result, enhances the adsorption capacity of adsorbents. This research has tried to discuss the use of surfactant-modified adsorbents to remove metal ions from aqueous media. In this study, heavy metals and various methods for removing them will also be studied. Also, isotherm, thermodynamic and kinetic behaviors of the sorption process are considered. The addition of anionic and cationic surfactants to the adsorbents can strongly alter the adsorbent's surface charge and directly affect the optimal pH value. Also, the maximum sorption efficiency using surfactant-modified adsorbents has been obtained at low temperatures (25 °C), which can be economically viable. According to previous studies, two surfactants such as SDS and CTAB, have shown a high ability to improve the adsorption efficiency and adsorption capacity of adsorbents. To this end, DNPH/SDS/Fe3O4 and CTAB/yeast adsorbents showed the highest removal efficiency (99.5%), which were able to remove Cr(VI) and CrO42− ions, respectively. Moreover, both adsorbents showed significant adsorption capacity.