Concentration Of Chromium In Solution Research Articles

Study of the Adsorption Efficacy of Cr(III) on a Metal Oxide-Based Material Derived from the Quartz Sand Enrichment Process

In the present study, the efficacy of chromium removal from water media was studied. For this purpose, a metal oxide based material, derived from the enrichment process of quartz coastal sand was used as possible adsorbent of chromium (III) ions. Following additional modification of the adsorbent, the effect of operational parameters including pH, contact time and Cr(III) concentration were studied according to one-factor-at-a-time procedure. Adsorption efficacy was assessed by the measurement of the remaining chromium concentration in solution, after adsorption. Atomic absorption spectroscopy technique, with flame atomization was used for the determination of chromium concentration in solution. Obtained results revealed that selected material exhibited higher adsorption efficacy in alkaline solution (pH = 6-9). The maximum removal efficacy (>93%) was achieved after 180 minutes of contact time, with an adsorbent dosage of 5 g/L and initial chromium concentration 20 mg/L. The adsorption process for Cr(III) follow the Freundlich isotherm and gives high correlation coefficient R². Calculations performed based on the Langmuir isotherm showed that the maximum adsorption efficiency of Cr³⁺ in the natural metal-oxide material has resulted 10 mg/g or 10000 μg/g. Pseudo second order reaction kinetics has provided a realistic description for removal of Cr(III) from solution with high correlation coefficient R² of (0.999). The adsorption isotherms were better described by the Freundlich equation (R² = 0.934). Adsorption of trivalent chromium ions onto selected material followed the pseudo second order model (R² = 0.996). Hence, the residual materials derived from the enrichment processes of quartz sand can be used as alternative adsorbent for the removal of trivalent chromium ions from aqueous solutions.

A clean metallurgical process for vanadium precipitation from chromium-containing vanadate solution

The conventional process of sodium carbonate roasting-water leaching for vanadium extraction cannot be applied to high chromium bearing vanadium slag, and the production process will produce a large amount of V-Cr-bearing reducing slag and wastewater containing sulfate and ammonium salt. To avoid these questions, this work proposes a novel process for the extraction of vanadium and chromium from vanadium slag. In the current research, the vanadium precipitation part of the novel process was studied in detail. The experiment results show that weak basic ammonium bicarbonate precipitation method can realize the selective precipitation of vanadium from chromium-containing vanadate solution. The presence of Cr(VI) in the solution has a great influence on precipitation, crystallization as well as product purity of NH4VO3. Chromium can increase the solubility of NH4VO3 and reduce the supersaturation degree of NH4VO3. Furthermore, it can change the crystal morphology of NH4VO3 and affect the precipitation of NH4VO3. The precipitation of NH4VO3 increased with the increase of N/V molar ratio, but decreased with the increase of chromium concentration in the solution. The content of chromium in V2O5 increased with the increase of N/V molar ratio as well as the chromium concentration in solution. For vanadate solutions containing 2.0, 5.0, 10, 20 and 25 g/L Cr, under the most suitable vanadium precipitation conditions, the precipitation of vanadium is 83.5%, 80.1%,73.8%, 61.2% and 60.3%, respectively.

Ectodermis of paddle cactus (Opuntia spp.) as biosorbent of chromium (VI) from aqueous solutions

The adsorption behaviour of chromium ( and/or ) from aqueous solutions on ectodermis of Opuntia in a batch system is presented. Modification of the biosorbent, contact time, concentration of chromium in solution and pH and temperature of the aqueous media were the studied parameters. Chromium anion uptake was higher at pH 2 for biosorbents treated with formaldehyde or HCl. The adsorption data were fitted to the Freundlich and Langmuir isotherms. The thermodynamic parameters Δ H 0, Δ G 0 and Δ S 0 were estimated and the obtained results showed that the adsorption reaction was endothermic and spontaneous for both biomaterials.

Separation, preconcentration and speciation of chromium by solid phase extraction on immobilised ferron

A sensitive and simple method for determination of chromium species after separation and preconcentration by solid phase extraction (SPE) has been developed. For the determination of the total concentration of chromium in solution, Cr(VI) was efficiently reduced to Cr(III) by addition of hydroxylamine and Cr(III) was preconcentrated on a column of immobilised ferron on alumina. The adsorbed analyte was then eluted with 5 mL of hydrochloric acid and was determined by flame atomic absorption spectrometery. The speciation of chromium was affected by first passing the solution through an acidic alumina column which retained Cr(VI) and then Cr(III) was preconcentrated by immobilised ferron column and determined by FAAS. The concentration of Cr(VI) was determined from the difference of concentration of total chromium and Cr(III). The effect of pH, concentration of eluent, flow rate of sample and eluent solution, and foreign ions on the sorption of chromium (III) by immobilised ferron column was investigated. Under the optimised conditions the calibration curve was linear over the range of 2–400 µg L−1 for 1000 mL preconcentration volume. The detection limit was 0.32 µg L−1, the preconcentration factor was 400, and the relative standard deviation (%RSD) was 1.9% (at 10 µg L−1; n = 7). The method was successfully applied to the determination of chromium species in water samples and total chromium in standard alloys.

Factors Influencing on the Surface Properties of Chromia-Pillared α-Zirconium Phosphate Materials

A new method for preparing colloidal suspensions of α-zirconium phosphate (α-ZrP), based on the use of a phase swelled with n-propylamine vapors, is described and applied to the synthesis of new chromia-pillared materials. The colloidal phase was obtained by contacting the n-propylamine intercalate with a dilute aqueous solution of acetic acid. For comparison, a conventional procedure of colloidization, based on the addition of a n-propylamine aqueous solution to the pure phosphate, was also employed. The intercalation of polyhydroxoacetato CrIII clusters was accomplished by refluxing chromium acetate solutions with each colloidal phosphate suspension. The new method gave rise to chromium oligomer intercalates with higher basal expansions, and moreover, larger oligomeric species seemed to be intercalated with a high chromium concentration in solution. Two series of chromia-pillared materials were obtained by calcination of the intercalated precursors at 673 K under N2. In both series, the acidity, as determined by TPD-NH3 and pyridine adsorption, increased with chromium content. The chromia-pillared materials prepared by the new method displayed a high porosity and catalytic activity for the decomposition of isopropyl alcohol. Under the experimental conditions used, all catalysts behaved exclusively as dehydrating catalysts.

Chromium adsorption by plant roots and formation of long-lived Cr(V) species: An ecological hazard?

The adsorption of either chromium(III) or chromate(VI) by plants has been investigated by means of ESR spectroscopy. Cr(III) absorption yielded complexes, in part immobilized, of 0-donor ligands in the roots. The adsorption of chromium(VI) produced first mobile Cr(V) species, where the metal ion was bound to low-molecular weight ligands, and then also Cr(III) species. The intensity ratio between the ESR signals of Cr(V) and Cr(III) species became almost constant with elapsing contact time, but decreased as the Cr(VI) concentration in solution was lowered. Noticeably, Cr(V) species were detected even at chromium concentration in solution as low as 1 ppm. The formation of stable Cr(V) species in plants, could produce dangerous effects to ecological cycles, because, according to literature data, Cr(V) may be involved in the mutagenic and carcinogenic properties of the element.

Coprecipitation of chromic ion with titanium(IV) hydroxide

Experimental testing of a previously proposed model for the adsorption of chromic ions onto freshly precipitated titanium hydroxide was carried out. The model represents by a Langmuir-type equation the relationship between the concentrations of adsorbed chromic ions and of chromium remaining in solution for a given proton activity. Two examples are given: batch neutralization of a dilute laboratory solution and continuous neutralization of an industrial spent acid. In spite of very different experimental conditions, the experimental results, given as the concentration of chromium in solution as a function of pH, are in very good agreement with the predictions given by the model. Temperature and ionic strength appear to have little influence on the adsorption of chromic ions onto the titanium hydroxide. The model should be useful for the study of practical industrial systems.

Isothermes d'adsorption de l'ion chromique sur l'hydroxyde de titane fraîchement précipité

AbstractA laboratory experiment has been made on the adsorption of the Cr3+ ion on freshly‐precipitated titanium dioxide, in order to determine the effect of the concentrations of the Cr3+ and H+ ions in solution on the amount of the adsorbed chromium. The adsorption isotherms have been determined at 5 pH's (3.25 to 4.25). The adsorption at each pH is well shown by the Langmuir isotherm; it could be generalized by expressing the two parameters of the equation in function of the H+ proton activity: the maximum adsorption capacity may be represented by a second‐degree polynomial (1/verbar;Hverbar;) and the adsorption constant by a power law.The general model proposed is the following: where X and C represent the adsorbed chromium concentration and the chromium concentration in solution, respectively.The aforesaid study has permitted to explain the coprecipitation of chromium (III) and titanium (IV) during the continuous neutralization of an industrial effluent containing both metals.

Méthode de dopage au chrome dans la préparation du rubis hydrothermal

Hydrothermal growth of ruby single crystals, on {1¯22} oriented seeds, has been carried out, using silver cans in a 150 cm3 autoclave. Chromium doping using potassium dichromate in an aqueous solution of potassium carbonate with sapphire as source material, caused inhomogeneous chromium distribution with unequally colored bands in the crystal. The use of ruby both as nutrient and doping reagent yielded a more regular chromium distribution. Both the two preceding methods generally produced heavy chronium accumulation at the seed-crystal interfaces and chromium rich green deposits on seeds have often been observed; in the latter case no further growth occured. In order to greatly reduce the initial chromium concentration in solution during the warm-up period, gibbsite was added to the ruby nutrient; in the same way, an experiment performed with sapphire instead of gibbsite was not satisfactory. First, the starting crystallisation temperature of ruby was determined, then the gibbsite solubility was determined, so that the useful amount of gibbsite could be correctly estimated. With the use of an appropriate gibbsite-ruby nutrient mixture, optically clear and uniformally doped ruby single crystals have been prepared.