CrVI Removal Research Articles

Magnetic Chitosan–Iron(III) Hydrogel as a Fast and Reusable Adsorbent for Chromium(VI) Removal

The magnetic chitosan–iron(III) hydrogel (MCh-Fe) was synthesized and characterized by SEM, TG, XRD, and FT-IR and used to remove toxic chromium(VI) (CrVI) from aqueous solution. The adsorption of CrVI onto the MCh-Fe adsorbent was fast and could reach equilibrium in less than 30 min. The adsorption was well described by the pseudo-second-order rate model. The equilibrium isotherm was better matched with the Langmuir model. The adsorption of CrVI onto MCh-Fe was an endothermic and spontaneous process. The loading capacity of CrVI on the adsorbent remained at a high level even after five cycles, showing that MCh-Fe can be used for repeated CrVI removal. Column adsorption results indicated that below 0.5 mg L–1 CrVI was found in the effluent up to about 30 and 350 bed volumes for two wastewaters containing 115.0 and 5.6 mg L–1 CrVI, respectively. The CrVI removal mechanism of MCh-Fe was also investigated.

Low-Cost Synthesis of Flowerlike α-Fe2O3 Nanostructures for Heavy Metal Ion Removal: Adsorption Property and Mechanism

Flowerlike α-Fe(2)O(3) nanostructures were synthesized via a template-free microwave-assisted solvothermal method. All chemicals used were low-cost compounds and environmentally benign. These flowerlike α-Fe(2)O(3) nanostructures had high surface area and abundant hydroxyl on their surface. When tested as an adsorbent for arsenic and chromium removal, the flowerlike α-Fe(2)O(3) nanostructures showed excellent adsorption properties. The adsorption mechanism for As(V) and Cr(VI) onto flowerlike α-Fe(2)O(3) nanostructures was elucidated by X-ray photoelectron spectroscopy and synchrotron-based X-ray absorption near edge structure analysis. The results suggested that ion exchange between surface hydroxyl groups and As(V) or Cr(VI) species was accounted for by the adsorption. With maximum capacities of 51 and 30 mg g(-1) for As(V) and Cr(VI), respectively, these low-cost flowerlike α-Fe(2)O(3) nanostructures are an attractive adsorbent for the removal of As(V) and Cr(VI) from water.

Adsorption of Cr VI on commercially available ash powder - A kinetic approach

Among heavy metal pollutants, chromium plays a major role in polluting environment. Several techniques are available and among these, adsorption process is found suitable for the removal of Cr VI species from wastewater. In the present work, the investigator has chosen the commercially available ash powder (CAP), which is being used as a sacred material by Hindus called Vibhoothi or Thiruneeru as the adsorbent. The adsorbent was characterized according to the Bureau of Indian Standards. It has also been planned to determine the adsorption potential of the adsorbent to assess the suitability of the material for the removal of Cr VI from waste waters. Batch mode adsorption experiments were carried out to study the effect of initial concentration of chromium solution, effect of the dose of the adsorbent, and pH of the solution. Various models such as Lagergren, Bhattacharya and Venkobachar were tested and the results are interpreted.

Reduction of aqueous chromate by Fe(II)/Fe(III) carbonate green rust: kinetic and mechanistic studies.

This work describes the heterogeneous reaction between FeII in carbonate green rust and aqueous chromate, in NaHCO3 solutions at 25 degrees C, and at pH values of 9.3-9.6. Evidence for reduction of CrVI to CrIII and concomitant solid-state oxidation of lattice FeII to FeIII was found from FeII titration and from structural analysis of the solids using FTIR, XRD, SEM, and XPS methods. Results indicate the formation of ferric oxyhydroxycarbonate and the concomitant precipitation of CrIII monolayers at the surface of the iron compound that induce passivation effects and progressive rate limitations. The number of CrIII monolayers formed at the completion of the reaction depends on [FeII]t=0, the molar concentration of FeII(solid) at t=0; on [n(o)]t=0, the molar concentration of reaction sites present at the surface of the solid phase at t=0; and on [CrVI]t=0, the molar concentration of CrVI at t=0. Kinetic data were modeled using a model based on the formation of successive CrIII monolayers, -(d[CrVI]/dt) = sigma(1)j k(i)[S] [CrVI]([n(i - 1)] - [n(i)]) with k(i)[S] (in s(-1) L mol(-1)), the rate coefficient of formation of CrIII monolayer i, and [n(i)] and [n(i - 1)], the molar concentration of CrIII precipitated in monolayer i and monolayer i - 1, respectively. Good matching curves were obtained with kinetic coefficients: k(1)[S] = 5-8 x 10(-4), k(2)[S] = 0.5-3 x 10(-5), and k(3)[S] about 1.7 x 10(-6) s(-1) m(-2) L. The CrVI removal efficiency progressively decreases along with the accumulation of CrIII monolayers at the surface of carbonate green rust particles. In the case of thick green rust particles resulting from the corrosion of iron in permeable reactive barriers, the quantity of FeII readily accessible for efficient CrVI removal should be rather low.

Removal of hexavalent chromium by nanofiltration

Removal of chromate CrO 4 2− from water was investigated using nanofiltration as a possible alternative to the conventional methods of CrVI removal from aqueous solution. Retention measurements with single reference salt revealed that Donnan exclusion plays an important role. The phenomenological parameters σ and P were calculated using the Spiegler-Kedem equation. The rejection rate depends on the ionic strength and pH. The increasing of ionic strength decreases the retention. The effect of pH was clarified by using a stable diagram of the CrVIH 2O system. Better retention was obtained at basic pH.