Extraction Of Chromium Research Articles

Characterization and prevention of interfacial crud produced during the extraction of vanadium and chromium by primary amine

In this study, the interfacial crud produced during the extraction of vanadium and chromium by primary amine N 1923 was investigated from the leaching solution containing heavy metals. Effect of pH values of the leaching solution on the percentage of the crud produced and the emulsion type of the crud were studied. X-Ray Fluorescence (XRF), Fourier Transform Infrared Spectroscopy (FT-IR) and X-Ray Diffraction (XRD) and Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) have been employed for the physiochemical characterizations of the crud. Our results indicate that the percentage of the crud produced is greatly affected by the pH value of the real leaching solution, and the crud is more stable in the acidic solution. The crud is an oil-in-water emulsion with many fine solid particles in the water phase. The particles, which are from the real leaching solution, have been proved to be the main cause for the crud formation. Particles in the cruds are normally composed of a large number of the crystals of Na 2SO 4, a few SiO 2 and oxides or hydroxids of Fe and Al. However, component proportions of the solids are dependent on the pH values. Possible mechanism of the crud formation is put forward. The solids present in the real leaching solution exert a stabilizing effect on the emulsion, based on which Na 2SO 4 crystallizes at the interface of the emulsion. Furthermore, the Na 2SO 4 crystals strengthen the stability of the emulsion, and thereafter the interfacial crud forms. Three effective methods to prevent the crud formation are proposed, i.e. clearing the real leaching solution by membrane filtration, increasing of the amount of the modifier, and applying of hexane as the diluent.

Extraction of chromium (VI) from multicomponent acidic solutions by emulsion liquid membranes using TOPO as extractant

Experimental results for the extraction of chromium (VI) from multicomponent acidic solutions by emulsion liquid membrane (ELM) using trioctylphosphine oxide (TOPO) as extractant are presented. The membrane phase consists of kerosene as diluent, TOPO as extractant, ECA 4360J (a nonionic polyamine) as surfactant and (NH 4) 2CO 3 solution as stripping phase. Effects of various parameters such as mixing speed, type and concentration of stripping solution, surfactant and extractant concentrations, and volume ratio of the membrane phase to internal stripping phase on Cr (VI) extraction were studied and optimum conditions were determined. Results show that with proper adjustment of experimental conditions for the extraction of Cr (VI) can be enhanced to a great extent. This study also examined the effects of concentrations of acid and metal ions in the feed phase for the extraction of Cr (VI) ions. The results also showed that by appropriate selection of the extraction and stability conditions, nearly all of the Cr (VI) ions (100–500 mg/L) present in the acidic feed solution containing 1000 mg/L from each of Cu (II), Zn (II), Co (II), Ni (II) and Cd (II) ions were extracted within a few minutes. Concentration variations of Cr (VI) and other ions in the acidic solutions were determined by atomic absorption spectrophotometry.

Removal of chromium (III) by two-aqueous phases extraction

Two-aqueous phase extraction of chromium (III) as a solute from their aqueous solutions was investigated using polyethoxylated alcohols (CiEj) as a biodegradable non-ionic surfactant in the presence of anionic sodium dodecylbenzene sulfonate (SDBS). First, the combined effects of chromium and surfactants mixture (anionic and non-ionic) on the cloud point temperature were determined. After this, the phase diagrams of binary systems water–surfactant (NW342 and C 10E 3) were traced. According to the given surfactants concentration, the extracted solute reached 98.5% and 60% for NW342 and C 10E 3, respectively at pH equal to 3. The addition of sodium chloride lowers the cloud point temperature of surfactant where the phenomenon of salting-out was pronounced. Under the optimal extraction conditions, the suggested extraction mechanism is based on chromium species-NW342 non-ionic surfactant micelles solvatation. Since, the prevalence species (93.82%) were Cr(III) 4(OH) 6 6+, given by a theoretical calculation using CHEAQS V. L20.1. The first stage regeneration of NW342 surfactant was 27.82% at pH equal to 4. 2 3 factorial designs were employed for screening the factors that would influence the overall optimization of a batch procedure of sorption.

The use of microemulsions to remove chromium from industrial sludge

In this work microemulsion systems were used to remove chromium from leather tannery sediments. The sludge was treated by a solid–liquid extraction process (acid digestion). The effects of particle size, digestion temperature and digestion time with regards to the efficiency of chromium removal were considered. The raw sludge (3 Mesh) was dried, grounded and sieved. Particles with 3, 14, 65, 100, 200, and 325 Mesh were evaluated. Sludge digestion solutions were prepared using each studied granule size at 25 °C, 70 °C, and 95 °C. Microemulsion extraction experiments to remove chromium III from the acid digestion solution were made according to a Scheffé Net experimental design methodology, using microemulsion systems inside the Winsor II region (System I) and inside the microemulsion region (Winsor IV – System II). A statistical treatment was used to obtain the isoresponse plots. Chromium extraction percentages were up to 73.3% for System I and up to 93.4% for System II.

Statistical optimization of process parameters for the extraction of chromium(VI) from pharmaceutical wastewater by emulsion liquid membrane

Response surface methodology (RSM) is used to optimize the process parameters for the extraction of chromium from aqueous solution of waste sodium dichromate recovered from the pharmaceutical industry wastewater using emulsion liquid membrane technique. The liquid membrane used was composed of kerosene oil as the solvent, Span-80 as the surfactant and potassium hydroxide as internal reagent and Aliquat-336 as carrier. The process parameters, namely feed concentration, pH, internal reagent concentration and surfactant concentration on the extraction of chromium were optimized using Box-Behnken design. The optimum conditions for the extraction of chromium(VI) were: feed concentration (223.55 ppm), pH (2.73), internal reagent concentration (0.72 N) and surfactant concentration (1.91%, w/w). At the optimized condition the maximum chromium extraction was found to be 97.57%.

Zincon-modified activated carbon for solid-phase extraction and preconcentration of trace lead and chromium from environmental samples

A new method that utilizes zincon-modified activated carbon (AC-ZCN) as a solid-phase extractant has been developed for simultaneous preconcentration of trace Cr(III) and Pb(II) prior to the measurement by inductively coupled plasma optical emission spectrometry (ICP-OES). The separation/preconcentration conditions of analytes were investigated, including effects of pH, the shaking time, the sample flow rate and volume, the elution condition and the interfering ions. At pH 4, the maximum adsorption capacity of Cr(III) and Pb(II) onto the AC-ZCN were 17.9 and 26.7 mg g −1, respectively. The adsorbed metal ions were quantitatively eluted by 1 mL of 0.1 mol L −1 HCl. Common coexisting ions did not interfere with the separation. According to the definition of IUPAC, the detection limits (3 σ) of this method for Cr(III) and Pb(II) were 0.91 and 0.65 ng mL −1, respectively. The relative standard deviation under optimum condition is less than 3.5% ( n = 8). The method has been applied for the determination of Cr(III) and Pb(II) in biological materials and water samples with satisfactory results.

Determination of extractable chromium from leather

People are exposed to chromium ions from leather materials due to everyday contact with different textile objects. The problem is that Cr(VI) is extremely toxic and may cause contact allergic dermatitis on the skin and may also be a trigger for many diseases. Huge amounts of chromium ions are released by waste waters to rivers after chromium-tanning processes in the leather industry; the presence of chromium is not only a problem for human health, but also for the environment. For this reason it is extremely important to monitor the presence of chromium as Cr(VI) and as total chromium. This study aims to present an appropriate analytical method for monitoring Cr(VI) and the total chromium present on leather materials. Applying this method to chromium-tanned leather samples, it was observed that the amounts of total chromium as well as of Cr(VI) are higher than prescribed and recommended by different regulations. Chromium(VI) exceeded the limit of 3 mg/kg in the majority of tested materials, while the total chromium exceeded the limit of 50 mg/kg in all tested samples. For this reason, it is recommended to avoid direct and prolonged contact of those materials with the skin.

Studies on extraction of chromium (VI) from acidic solutions containing various metal ions by emulsion liquid membrane using Alamine 336 as extractant

The extraction of chromium (VI) ions from acidic solutions containing various metal ions by emulsion liquid membrane (ELM) was studied. Liquid membrane consists of a diluent, a surfactant, and an extractant. 0.5 M ammonium carbonate solution was used as stripping solution. Effects of acid concentration in feed solution, type and concentration of stripping solution, mixing speed, surfactant concentration, phase ratio and the influence of membrane characteristics were studied and optimum conditions were determined. Under the optimum conditions, extraction of chromium (VI) was tested and it was possible to selectively extract 99% of chromium from the acidic feed solution. This study also examined the effect of extractant concentration and acid type in the feed solution on the extraction of Cr (VI) ions and almost all of Cr (VI) from the acidic feed solution containing 500 mg/L from each of Co (II), Ni (II), Cd (II), Zn (II), and Cu (II) ions, and 100–500 mg/L Cr (VI) was extracted within 5–10 min.

Silica gel-immobilized-vanillin derivatives as selective solid-phase extractants for determination of chromium (III) in environmental samples by ICP-OES

A method is described for the selective extraction of chromium(III) from aqueous solutions and natural water samples, based on the use of two newly synthesized solid-phase extractors via silica gel-immobilized-vanillin derivatives (I,II). Experimental conditions for effective adsorption of trace levels of Cr(III) were optimized with respect to different experimental parameters using batch and column procedures in detail. The optimum pH values for the separation of Cr(III) simultaneously on the newly sorbents were both 4.0 and complete elution of Cr(III) from the sorbents surface was carried out using 2.0 mL of 0.5 mol L − 1 HCl. The sorption capacity of phase I towards Cr(III) was found to be 0.700 mmol g − 1 where the sorption capacity of phase II was 0.538 mmol g − 1 . The detection limits (3 σ) of the method defined by IUPAC were found to be 0.87 and 0.64 ng mL − 1 with enrichment factors of 100 and 75 for phases I and II, respectively. The method has been applied for the determination of Cr(III) in biological materials and water samples with satisfactory results.

Hydrogen sulfide removal from coal gas by the metal-ferrite sorbents made from the heavy metal wastewater sludge

The metal-ferrite (chromium-ferrite and zinc-ferrite) sorbents made from the heavy metal wastewater sludge have been developed for the hydrogen sulfide removal from coal gas. The high temperature absorption of hydrogen sulfide from coal gas with the metal-ferrite sorbent in a fixed bed reactor was conducted in this study. The metal-ferrite powders were the products of the ferrite process for the heavy metal wastewater treatment. The porosity analysis results show that the number of micropores of the sorbents after sulfidation and regeneration process decreases and the average pore size increases due to the acute endothermic and exothermic reactions during the sulfidation–regeneration process. The FeS, ZnS, and MnS peaks are observed on the sulfided sorbents, and the chromium extraction of the CFR6 can fulfill the emission standard of Taiwan EPA. The suitable sulfidation temperature range for chromium-ferrite sorbent is at 500–600 °C. In addition, effects of various concentrations of H 2 and CO were also conducted in the present work at different temperatures. By increasing the H 2 concentration, the sulfur sorption capacity of the sorbent decreases and an adverse result is observed in the case of increasing CO concentration. This can be explained via water-shift reaction.

Extractive removal of chromium (VI) from industrial waste solution

Extractive removal of Cr (VI) was carried out from chloride solutions using cyanex 923 mixed with kerosene. The efficiency of this extractant was studied under various experimental conditions, such as concentration of different mineral acids in the aqueous phase, concentration of cyanex 923 and Cr (VI) present in the initial aqueous feed, temperature and time of extraction, organic to aqueous (O/A) phase ratio. Percentage Cr (VI) extraction decreases with the increase in temperature at varying concentration of cyanex 923. The interference of the impurities usually associated with Cr (VI) such as Cr (III), Cu, Ni, Fe (II), Zn, Chloride and sulphate, etc., were examined under the optimized conditions and only Zn was found to interfere. Under the optimum experimental conditions 98.6–99.9% of Cr (VI) was extracted in 3–5 min at O/A of 2 with the initial feed concentration of 1 g/L of Cr (VI). The extracted Cr (VI) was quantitatively stripped with 1 M NaOH and the organic phase obtained after the stripping of Cr (VI) was washed with dilute HCl solution to neutralize any NaOH trapped/adhered to the solvent and then with distilled water. This regenerated solvent was reused in succeeding extraction of chromium (VI). Finally a few experiments were performed with the synthetic effluent from an electroplating industry.

Utilização de resíduos da indústria de couro como fonte nitrogenada para o capim-elefante

Uma grande variedade de produtos tóxicos é emitida durante o processo de tratamento do couro nos curtumes que usam o cromo III para obter o couro wet blue. O resíduo sólido (raspas e aparas) contém cerca de 3 % de Cr III, que representa um sério problema ambiental e não tem, atualmente, destino adequado. O resíduo de couro após extração de Cr (colágeno) foi utilizado como fonte nitrogenada para o capim-elefante (Pennisetum purpureum Schum cv. Napier), em um Latossolo Vermelho-Amarelo, aplicando-se quatro doses do colágeno (4, 8, 16 e 32 t ha-1) e três tratamentos adicionais (testemunha; adubação com N mineral e resíduo de couro wet blue- sem a extração do Cr). O colágeno é uma boa fonte nitrogenada alternativa para crescimento do capim-elefante até a dose de 16 t ha-1. O resíduo de couro wet blue não disponibilizou N durante o cultivo de capim-elefante. Isso mostra que a extração do Cr utilizando-se o ácido fosfórico é fundamental para uso do rejeito de couro como fonte nitrogenada na agricultura. A aplicação do colágeno supriu a necessidade de N para plantas de capim-elefante, semelhantemente à adubação com N mineral.

Solid phase extraction of chromium (VI) from aqueous solutions by adsorption of its diphenylcarbazide complex on an alumina column

Abstract A simple method has been developed for the solid phase extraction of chromium (VI) based on the adsorption of its diphenylcarbazide (DPC) complex on an alumina column. The effect of various parameters such as acidity, stability of the column, sample volume, and interfering ions have been studied in detail. The adsorbed complex could be easily desorbed using sulphuric acid and the concentration of chromium has been established using atomic absorption spectrophotometry and visible spectrophotometry. The calibration graph was linear in the range of 0–1 µg/mL chromium (VI) with a detection limit of 4 µg/L. A highest preconcentration factor of 125 could be obtained for 5000 mL sample volume using glass wool as support for alumina. Chromium (VI) could be effectively separated from other ions such as zinc, nickel, copper, chloride, sulphate, and nitrate and the method has been successfully applied to study the recovery of chromium in spiked well water and tap water samples.

Extraction of Chromium(III) and Chromium(VI) Species from Solid Matrices Using Green Solvent Supercritical Carbon Dioxide

Supercritical fluid extraction (SFE) provides an environmentally green technique to decontaminate chromium species from solid matrices using supercritical fluid carbon dioxide (ScCO2). Methanol and a small amount of water were found to significantly improve the extraction efficiency. The fluorinated chelating agent lithium bis(trifluoroethyl)-dithiocarbamate (LiFDDC) was effective in removing Cr ions in methanol-modified CO2 via in situ chelation/SFE technique. This paper indicates that the extraction efficiencies of Cr(III) and Cr(VI) from solid matrices can be greatly increased to more than 92% in the presence of a small amount of water, using 5% methanol-modified CO2 containing LiFDDC as an extractant. Chromium species in a wood waste sample in the form of chromated copper arsenate (CCA) can be extracted, but the extraction efficiency is not as good as expected, possibly due to the complications of the chemistry of Cr species in different oxidation states and to matrix effects.

Solvent Extraction of Chromium(VI) with Tri-n-butyl Phosphate from Aqueous Acidic Solutions

The solvent extraction of Cr(VI) from aqueous acidic solutions by tri-n-butyl phosphate (TBP) in kerosene was investigated. HCl, H2SO4, and H3PO4 were used for the pH adjustment of the aqueous phase. The results show that the distribution coefficient exhibited a maximum when HCl was used. The distribution coefficient increased with increasing TBP concentration (from (0.2 to 3.0) mol·L-1) and decreasing pH (from 2.0 to 0). The results also show that one molecule of Cr(VI) was approximately coordinated to three TBPs in the complex. The enthalpy change of −17.4 kJ·mol-1 was determined using the van't Hoff equation, suggesting that the extraction of Cr(VI) from a HCl medium is an exothermic process. The presence of NaCl in the feed phase improved the extraction efficiency, whereas the presence of Na2SO4 or KH2PO4 has no benefit. The stripping of loaded organic and the reuse of the extractant are also discussed in this paper.

Chelating Extraction for Removal of Chromium, Copper, and Arsenic from Treated Wood with Bioxalate

The present paper describes a novel extractant for chromated copper arsenate (CCA)-treated western hemlock (Tsuga heterophylla). Because the disposal of CCA-treated waste wood is becoming a serious problem in many countries, it is necessary to develop proper remediation technique. Extraction of CCA-treated wood with bioxalate (BO) solvent was evaluated at various solvent pH levels, BO concentrations, extraction temperatures, and liquid-to-solid ratios, as well as with different alkaline metal hydroxides as pH-adjusting reagents. It was clarified that approximately 90% of the chromium, copper or arsenic could be extracted effectively under particular pH conditions (2.2–3.2). Extraction efficiency was also improved by increasing solvent concentration from 0.0125 M to 0.125 M. In addition, increasing BO solution temperature from 25 to 75°C promoted the extraction of chromium and arsenic; however, that of copper was higher than these metals, irrespective of temperature. The optimum conditions for extraction of chromium, copper, and arsenic from treated wood using BO solution were determined to be as follows: pH of 2.2–3.2, solvent concentration of 0.065–0.125 M, solvent temperature of 75°C, and solvent to CCA-treated wood mixture ratio of 20:1 (mL:g). Under these conditions, the extraction efficiencies for chromium, copper, and arsenic were maximized at 89.4, 88.2, and 94.1%, respectively, thus demonstrating the applicability of BO chelation for the remediation of metal contaminated solid waste.

Kinetics of Chromium(VI) Transport from Mineral Acids across Cellulose Triacetate (CTA) Plasticized Membranes Immobilized by Tri-n-octylamine

The extraction of chromium(VI) from an aqueous acidic solution into a coexisting organic phase that contained tri-n-octylamine (TOA) and solvent (o-nitrophenyl pentyl ether) was studied. The calculated logarithm of the extraction constant (log Kex) value for this extraction system was 6.03 ± 0.03. For transport experiments, the polymer inclusion membranes (PIMs) were prepared by physical immobilization of TOA as the carrier and o-nitrophenyl pentyl ether in cellulose triacetate as the polymer matrix. The competitive transport of Cr(VI) ions from mineral acid solutions (chloride, sulfate, nitrate) media through a PIM with TOA was investigated. The selectivity of the process is described by the sequence of ions removed from the source phase: HCrO4- > NO3- > Cl- > SO42-. This order of permeability limits seems to correlate with the molar Gibbs energy of hydration of transported anions. An activation energy of 30.5 kJ/mol was also determined for Cr(VI) permeability across a PIM with TOA, which suggests that the transport of Cr(VI) ions is controlled by a membrane diffusion mechanism. A presented model describes the transport mechanism, which involves diffusion via a fast interfacial chemical reaction, as well as diffusion of a carrier and its metal complex through the plasticized membrane. The diffusion coefficients of the Cr(VI) complex were calculated as a function of the carrier concentration and membrane thickness; their values were 2.34 × 10-9 and 1.22 × 10-10 cm2/s, respectively.

Effects of leachant temperature and pH on leachability of metals from fly ash. A case study: Can thermal power plant, province of Canakkale, Turkey

Lignite powered electric generation plants result in increasing environmental problems associated with gaseous emissions and the disposal of ash residues. Especially, low quality coals with high ash content cause enormous quantities of both gaseous and solid fly ash emissions. The main problem is related to the disposal of fly ash, which, in many cases, contains heavy metals. It is known that toxic trace metals may leach when fly ash is in contact with water. In this study, fly ash samples obtained from the thermal power plant in the town of Can in Turkey were investigated for leachability of metals under different acidic and temperature conditions. The experimental results show that a decrease in pH of the leachant favors the extraction of metal ions from fly ash. A significant increase in the extraction of arsenic, cadmium, chromium, zinc, lead, mercury, and selenium ions from the ash is attributed to the instability of the mineral phases. These heavy metals concentrations increase with respect to increasing acidic conditions and temperature. Peak concentrations, in general, were found at around 30 degrees C.

Solid phase extraction of chromium(VI) from aqueous solutions by adsorption of its diphenylcarbazide complex on an Amberlite XAD-4 resin column

A method has been developed for the solid phase extraction of chromium(VI) based on the adsorption of its diphenylcarbazide complex on an Amberlite XAD-4 resin column. The influence of acidity, stability of the column, sample volume, flow rate and interfering ions were studied in detail. The adsorbed complex could be eluted using acetone–sulfuric acid mixture and the concentration of chromium was determined using visible spectrophotometry. A detection limit of 6 μg L −1 could be achieved. A preconcentration factor of 27 could be obtained for 400 mL sample volume. The validity of the method was checked in spiked water samples and electroplating wastewater.

Solid phase extraction of chromium(VI) from aqueous solutions by adsorption of its diphenylcarbazide complex on a mixed bed adsorbent (acid activated montmorillonite–silica gel) column

A novel approach has been developed for the solid phase extraction of chromium(VI) based on the adsorption of its diphenylcarbazide complex on a mixture of acid activated montmorillonite (AAM)–silica gel column. The effect of various parameters such as acidity, stability of the column, sample volume, interfering ions, etc., were studied in detail. The adsorbed complex could be easily eluted using polyethylene glycol–sulfuric acid mixture and the concentration of chromium has been determined using visible spectrophotometry. The calibration graph was linear in the range 0–1 μg mL −1 chromium(VI) with a detection limit of 6 μg L −1. A highest preconcentration factor of 25 could be obtained for 250 mL sample volume using glass wool as support for the mixed bed adsorbent. Chromium(VI) could be effectively separated from other ions such as nickel, copper, zinc, chloride, sulfate, nitrate, etc., and the method has been successfully applied to study the recovery of chromium in electroplating waste water and spiked water samples.