Biosorbents for hexavalent chromium elimination from industrial and municipal effluents

The presence of hexavalent chromium in wastewater is a potential hazard to aquatic animals and humans. There are various mechanisms proposed, kinetic models used and adsorption isotherms employed for the efficient removal of hexavalent chromium from industrial and municipal wastewaters using biosorbents. Biosorption of heavy metals is a most promising technology involved in the removal of toxic metals from industrial waste streams and natural waters. Metal removal treatment systems using microorganisms are cheap because of the low cost of sorbent materials used and may represent a practical replacement to conventional processes. The present review discusses hexavalent chromium biosorption properties of algae, bacteria, fungi, and agricultural products, as well as adsorption properties of non-living substances. Cell walls are responsible for biosorption of dead biomaterial; compositions of cell walls are discussed. Chemical modification of biosorbents, optimization of biosorption parameters, mixtures of different biosorbents and the study of biosorption mechanisms are the main keys to transfer the biosorption process from lab to industry.     

Sources and toxicity of hexavalent chromium

Chromium exists in oxidation states ranging from ?IV to +VI, inclusively. The compounds exhibit a wide range of geometries including square planar, tetrahedral, octahedral, and various distorted geometries. Ore refining, chemical and refractory processing, cement-producing plants, automobile brake lining, catalytic converters for automobiles, leather tanneries, and chrome pigments contribute to the atmospheric burden of chromium. Hexavalent chromium is known to have 100-fold more toxicity than trivalent chromium, for both acute and chronic exposures because of its high water solubility and mobility, as well as easy reduction. The respiratory tract is the major target organ for hexavalent chromium following the inhalation exposure in humans. Chronic inhalation exposure to hexavalent chromium results in effects on the respiratory tract, with perforations and ulcerations of the septum, bronchitis, decreased pulmonary function, pneumonia, and nasal itching and soreness as reported. Chronic human exposure to high levels of hexavalent chromium by inhalation or oral exposure may produce effects on the liver, kidney, gastrointestinal, and immune systems, and possibly the blood. Dermal exposure to hexavalent chromium may cause contact dermatitis, sensitivity, and ulceration of the skin.     

Simultaneous determination of hexavalent and total chromium in water and plating baths by spectrophotometry

A new spectrophotometric determination method of hexavalent chromium in waste water and plating baths is described based on the oxidation of beryllon III by chromium(VI) in 0.02M sulphuric acid medium. The decrease in the absorbance of beryllon III was measured at 482 nm with an apparent molar absorptivity of 5.15 x 10(4)1.mole(-1).cm(-1). Beer's law was obeyed for chromium(VI) over the range 0-25 mug/25 ml. After the oxidation of Cr(III) to Cr(VI) by ammonium persulphate, total chromium can be determined. Therefore, chromium(III) can be calculated by subtracting chromium(VI) from total chromium. The detection limit is 0.015 and 0.020 mug/25 ml for chromium(VI) and total chromium, respectively. A sensitive spectrophotometric method for trace Cr(III) and Cr(VI) in waste water and plating baths was developed with good precision and accuracy. The reaction is also discussed.     

Hexavalent chromium recovery by liquid-liquid extraction with tributylphosphate from acidic chloride media.

A method is introduced for recuperation of chromium(VI) in water samples by liquid-liquid extraction with tributylphosphate PO(C4H9O)3 (TBP) from acidic chloride media. The optimum conditions for quantitative extraction of Cr(VI) were evaluated by varying the experimental parameters, such as the shaking period, the pH of the aqueous phase, the hydrochloric acid concentration, the hydrogen and chloride ion concentrations, the extractant concentration and the ratio of aqueous-to-organic phase. The probable extracted species of hexavalent chromium in organic phase, deduced from log-log plots, were H2CrO4 in acid media in absence of chloride and HCrO3Cl in acidic chloride media. Chromium(VI) was found to be extracted with tributylphosphate from acidic chloride media according to the following reaction: HCrO4-(aq), + 2H+(aq) + Cl-(aq) + 2TBP(org) <==> [HCrO3Cl, 2TBP](org) + H2O(aq). Since the tributylphosphate (TBP) exhibited a high selectivity for chromium(VI), this method can be applicable to the extraction and the determination of chromium in both oxidation states [Cr(VI) and Cr(III)] in water samples.     

水溶液中六价铬在碳纳米管上的吸附

针对用碳纳米管对水溶液中六价铬的吸附净化进行了研究, 考察了溶液浓度、溶液pH值、共存的三价铬离子等因素对吸附行为的影响. 实验结果表明, 碳纳米管在室温下对于六价铬的吸附量随着平衡浓度的增大而升高, 在铬浓度为493.557 mg•L−1时碳纳米管吸附量达到最大值为532.215 mg•g−1; 六价铬的浓度在300~700 mg•L−1的范围内, 碳纳米管对铬的吸附量变化不大；大于700 mg•L−1时, 随着铬的平衡浓度的升高碳纳米管对铬的吸附量降低, 铬浓度为961.074 mg•L−1时, 碳纳米管吸附量降至194.631 mg•g−1. 在pH值为2~7的范围内, 碳纳米管对六价铬的吸附量随着溶液pH值的减小而增大; 而在碱性条件下, pH值对碳纳米管吸附六价铬的影响不大. 溶液中存在三价铬时, 碳纳米管对六价铬的吸附量明显降低, 表明三价铬与六价铬有竞争吸附. 此外, 活性炭的对比吸附实验表明, 在低浓度时, 譬如在六价铬浓度为190 mg•L−1吸附时, 碳纳米管对铬的吸附量约为活性炭的6倍；而在高浓度下, 譬如六价铬浓度为493 mg•L−1时, 碳纳米管对铬的吸附量约为活性炭的2倍.     

Coprecipitation as a means of separation in substoichiometric isotope dilution analysis

Chromium has been determined by isotope dilution in artificial standards and in standard alloys using the substoichiometric principle. As a substoichiometric reaction the reduction of Cr(VI) to Cr(III) was used, followed by separation of these species by coprecipitation of the trivalent chromium on a Ti(OH)₄ precipitate. For amounts smaller than 1 μg the standard method had to be modified owing to spontaneous reduction of hexavalent chromium in the solution. Interferences from other metals, if they occur, can be easily overcome. The method is simple and inexpensive.     

Electroanalytical Detection of Cr(VI) and Cr(III) Ions Using a Novel Microbial Sensor

A microbial sensor, namely carbon paste electrode (CPE) modified with Citrobacter freundii (Cf–CPE) has been developed for the detection of hexavalent (Cr(VI)) and trivalent (Cr(III)) chromium present in aqueous samples using voltammetry, an electroanalytical technique. The biosensor developed, demonstrated about a twofold higher performance as compared to the bare CPE for the chosen ions. Using cyclic voltammetry and by employing the fabricated Cf–CPE, the lowest limit of detection (LLOD) of 1x10⁻⁴ M and 5x10⁻⁴ M for Cr(VI) and Cr(III) ions respectively could be achieved. By adopting the Differential Pulse Cathodic Stripping Voltammetric technique, the LLOD could be further improved to 1x10⁻⁹ M and 1x10⁻⁷ M for Cr(VI) and Cr(III) ions respectively using the biomodified electrodes. The reactions occurring at the electrode surface‐chromium solution interface and the mechanisms of biosorption of chromium species onto the biosensor are discussed. The stability and utility of the developed biosensor for the analysis of Cr(VI) and Cr(III) ions in chromite mine water samples has been evaluated.     

Determination of dissolved hexavalent chromium in industrial wastewater effluents by ion chromatography and post-column derivatization with diphenylcarbazide

A proposed EPA method for the determination of dissolved hexavalent chromium in drinking water, groundwater and industrial wastewater effluents was developed using existing ion chromatographic techniques. Two solid waste matrices were briefly investigated. Aqueous samples were passed through a 0.45-micron filter and the filtrate was either (1) left unadjusted, (2) adjusted to pH 8 or (3) adjusted to pH 10 prior to analysis by ion chromatography. The method detection limits were 0.3-0.4 micrograms/l. When analyzed within 24 h, the two pH levels and the unadjusted sample yielded ca. 100% recovery of spikes. No oxidation of trivalent chromium to hexavalent chromium was observed at pH 7, 8 or 10 when aqueous samples were spiked with 50 mg/l Cr(III).     

Use of analytical microscopy to analyze the speciation of copper and chromium ions onto a low-cost biomaterial

In this paper, we present our study of the speciation of copper and hexavalent chromium sorbed onto a lignocellulosic substrate, using analytical microscopy. The lignocellulosic substrate constitutes a low-cost biomaterial that can be used in wastewater treatment. Transmission electron microscopy (TEM) coupled with energy-dispersive X-ray spectroscopy (EDXS) was used to determine the speciation of the two metal ions on the constitutive moieties of the lignocellulosic substrate. The use of a staining agent sensitive to carbon unsaturation allowed us to differentiate between the microstructures rich in lignin entities and those rich in cellulose entities. The EDX analysis showed that metal ions are preferentially sorbed onto microstructures rich in lignin moieties. The energy electron loss spectroscopy (EELS) was used to determine the oxidation states of chromium in association with lignocellulosic moieties. We showed that the sorption process of hexavalent chromium requires the reduction of Cr(VI) into Cr(III) and the probable oxidation of lignin moieties.     

Surfactant-assisted bioremediation of hexavalent chromium by use of an aqueous extract of sugarcane bagasse

Agricultural products and by-products are now widely used for removal of hexavalent chromium from waste water. This option is more efficient and less expensive than conventional physicochemical treatments. The purpose of this study was reduction of carcinogenic hexavalent chromium to non-toxic trivalent chromium by use of aqueous extracts of sugar cane bagasse, which contains a variety of reducing components, for example sugar. The rate of this process is accelerated by use of surfactant as catalyst.     

Separation and speciation of Cr(III) and Cr(VI) with Saccharomyces cerevisiae immobilized on sepiolite and determination of both species in water by FAAS

A rapid, sensitive and accurate method for the separation, preconcentration and determination of Cr(III) and Cr(VI) in water samples is described. Chromium species can be separated by biosorption on Saccharomyces cerevisiae immobilized on sepiolite and determined by flame atomic absorption spectrometry (FAAS). The optimum conditions for separation and preconcentration (pH, bed height, flow rate and volume of sample solution) were evaluated. Recovery of the chromium was 96.3+/-0.2% at 95% confidence level. The breakthrough capacity of the adsorbent was found as 228 mumol g(-1) for Cr(III). The proposed method was applied successfully to the determination of Cr(III) and Cr(VI) in spiked and river water samples.     

Capillary electrophoresis hyphenated to inductively coupled plasma-sector field-mass spectrometry for the detection of chromium species after incubation of chromium in simulated sweat

The presence of chromium in chromium-tanned leather represents a considerable health problem since it can lead to chronic allergic contact dermatitis. Apart from trivalent chromium (Cr(III)), which is used for tanning, leather often contains hexavalent chromium (Cr(VI)), resulting from the oxidation of Cr(III) during the tanning process. This study deals with the chromium compounds in simulated sweat when brought into contact with Cr(III) or Cr(VI) and with chromium-tanned leathers. A capillary electrophoresis (CE) method was developed, with inductively coupled plasma-sector field-mass spectrometry (ICP-SF-MS) for element-specific detection. Two different electrophoretic runs, applying once the positive and once the negative polarity mode, were necessary for the detection of positively and negatively charged chromium species. Although sometimes described in the literature, a pre-run derivatization of the chromium-species was not performed here to prevent species transformation. 50 mmol.L(-1) sodium phosphate at a pH of 2.5 was used as CE separation buffer and as make-up liquid for the CE-ICP-SF-MS interface. When applied to simulated sweat samples incubated with Cr(VI), this method showed that methionine is responsible for the reduction of Cr(VI) into Cr(III), which, at its turn, forms a complex with lactic acid. In the case of sweat plus Cr(III), the latter step was also seen. Applied to simulated sweat in contact with leather samples, the method developed showed the presence of the former species among a much more complex pattern.     

Preconcentration of chromium(III) and chromium(VI) in sea water by complexation with quinolin-8-ol and adsorption on macroporous resin

Chromium(III) is a sea water at the nanomole level was selectively collected using a column packed with macroporous polystyrene-divinylbenzene resin after complexation with quinolin-8-ol. Complex formation between ligand and inert hydrated chromium(III) ions was achieved by heating a sample solution containing a small amount of quinolin-8-ol for a short time in a microwave oven. Chromium(VI) was collected by a similar method after reducing it to chromium(III) with hydroxylamine. The effect of co-existing organic materials on the collection of chromium(III) and chromium(VI) was examined. This method was successfully applied to the determination of chromium(III) and chromium(VI) in sea water by graphite furnace AAS.     

Combination of electroreduction with biosorption for enhancement for removal of hexavalent chromium

Hexavalent chromium is one of the most toxic heavy metals in aqueous solutions. It has been well documented that the brown seaweed can be used as a promising biosorbent for the sequestration of this heavy metal from wastewater. However, the uptake of Cr(VI) is reportedly a rather slower process; the sorption equilibrium can only be established after a few days, much slower than a few hours for the trivalent chromium ion. In this study, we developed a novel technology of electrochemically assisted biosorption (ECAB) system for the enhancement of the treatment efficiency. It was found through our study that the removal efficiencies of Cr(VI) and total chromium were greatly enhanced by 48.1% and 51.3%, respectively, with the application of -1.0V in the ECAB system. The conversion of Cr(III) due to the electroreduction of Cr(VI) and the higher pH due to the cathodic H(2) evolution created a favorable condition for the uptake of chromium onto the modified seaweed (MSW). The reduction and adsorption of Cr(VI) by MSW was proved to play a minor role in the removal. Both direct electroreduction and indirect electroreduction by atomic H(*) contributed to the reduction of Cr(VI).     

Diffusion Mechanisms of Biosorption of Cr(VI) onto Powdered Cotton Stalk

The present study investigates biosorption diffusion mechanism for the removal of toxic hexavalent chromium from aqueous solution using powdered cotton stalk an agricultural waste biomass. The effects of pH, temperature, adsorption isotherms, adsorption kinetics, and thermodynamic on chromium biosorption were investigated. The results showed that a maximum removal efficiency of 95% was achieved at pH 2. The pH at zero point charge (pH_zpc) on biosorbent surface was 4.3. The adsorption kinetics showed that the pseudo-second order rate expression fitted well the biosrption process. The equilibrium isotherm was measured experimentally and results were analyzed by Langmuir, Freundlich, and Temkin isotherms using linearized correlation coefficients. The significant parameters for isotherms were determined. The Langmuir adsorption isotherm relative to two other isotherms was found to fit the equilibrium data best for chromium adsorption. Thermodynamic studies reveal that the biosorption of Cr(VI) on cotton stalk was endothermic, spontaneous and occurs with increase in disorder at solid-liquid interface. Adsorption diffusion kinetic was further analyzed and showed that biosorption mechanism was totally controlled by intraparticle diffusion mechanism.     

Speciation of Chromium in Natural Waters,Tea, and Soil with Membrane Filtration Flame Atomic Absorption Spectrometry

A sensitive and selective method was developed for the speciation of chromium(III) and chromium(VI) in environmental samples based on membrane filtration and determination by flame atomic absorption spectrometry. Chromium(III) reacts with cochineal red A, yielding a complex that is adsorbed on a cellulose acetate membrane filter, whereas chromium(VI) remains in aqueous solution, permitting separation. After reduction of chromium(VI) to chromium(III) with hydroxylamine hydrochloride, the total concentration of chromium was determined, and the concentration of chromium(VI) was calculated by subtraction. The pH, amount of cochineal red A, and sample volume were optimized on the basis of the recovery of Cr(III). The influence of matrix ions was also investigated. The preconcentration factor was 94. The detection limit (3 sigma) for Cr(III) was 1.4 micrograms per liter. The method was validated using environmental certified reference materials. The method was successfully employed for the speciation of chromium in wastewater and lake water.     

Preconcentration and spectrophotometric determination of chromium(vi) in natural waters by coprecipitation with barium sulfate

A selective preconcentration of chromium(VI) is proposed for analysis of natural waters. Chromium(VI) is quantitatively separated from chromium(III) by coprecipitation with barium sulfate; salicylic acid is used as a masking agent for iron(III), aluminum(III) and chromium(III). The precipitate is fused with alkali carbonate, and the chromium(VI) in the melt is isolated with hot water and determined spectrophotometrically with diphenylcarbazide. The detection limit is 0.02 μg l^-1 the relative standard deviation for chromium(VI) in river water is less than 5%.     

超痕量六价铬分析仪检测制革场地中六价铬

为解决制革等污染场地中Cr(III)-有机络合物会干扰六价铬测定的问题,通过优化仪器色谱条件、在现有行标基础上改进前处理方式,使用超痕量六价铬分析仪检测六价铬,并通过在土壤中投加低、中、高浓度的三价铬、六价铬以及Cr(III)-有机络合物考察三价铬、色度和Cr(III)-有机络合物对六价铬测定的影响。结果表明仪器的最佳色谱条件为：流动相浓度为0.1 mol/L、流动相pH为9、浓硫酸用量为5 mL、流动相流速为1.2 mL/min,衍生试剂流速为0.7 mL/min。样品预处理方式由抽滤提取改进为离心提取,上机前样品pH无需调节,可提高检测效率;该方法与现行行标相比操作简便、耗时短且不受三价铬、样品色度及Cr(III)-有机络合物的干扰。方法精密度和正确度均显著提高,相对标准偏差为1.7%~5.2%,回收率均在94.6%~103%之间。通过与液相色谱-电感耦合等离子体质谱仪对实际样品测定结果的统计学检验发现,结果无显著性差异。该方法适用于制革、电镀等富含Cr(III)-有机络合物场地中六价铬的测定。     

Preconcentration procedures for the determination of chromium using atomic spectrometric techniques: A review

Chromium is one of the regulated toxic metals in the environment. Naturally, this element exists mainly in two oxidation: Cr(III) and Cr(VI). In general, Cr(VI) is more toxic than Cr(III). Cr(VI) affects human physiology, accumulates in the food chain and causes severe health problems ranging from simple skin irritation to lung carcinoma. Hence, the determination of chromium traces as well as its speciation in environmental samples is a very important task. In recent years, several preconcentration methods such as coprecipitation, liquid-liquid extraction, dispersive liquid-liquid microextraction, cloud point extraction, and solid phase extraction have been developed and widely used. The aim of this study is to review the recent literature (mainly last 5 years) on the preconcentration technologies those have been used in chromium removal before the determination step by atomic spectrometric techniques. Their advantages and limitations in application are also evaluated.     

Application of ionizing radiation to environmental protection: removal of toxic Cr(VI) metal ion in industrial wastewater: preliminary study

Hexavalent chromium, a major contaminant in most wastewater sites, is a potential health threat inducing cancer to humans while trivalent chromium is an essential element for the metabolism of sugar. The radiation-induced reduction of Cr(VI) metal ion to Cr(III) by the perhydroxyl radical (HO₂ ^?) and carboxyl radical anion (CO₂ ^??) produced by continuous radiolysis of water was investigated by steady state radiolysis of O₂, Ar and N₂O-saturated pH 3 solutions in the presence of formate. In all cases the removed Cr(VI) was a linear function of the absorbed dose. The added formate was favorable for removing Cr(VI). Its presence protects the solution from reverse radiolytic oxidation of Cr(III) to Cr(VI). The measured and calculated yield of removal of Cr(VI) do agree quite well at low formate concentration but at high formate concentration the measured yield was higher than the expected. When all formate is exhausted no recovery of Cr(VI) from Cr(III) was observed in case of O₂- and Ar-saturated solutions whilst in the case of N₂O-saturated solutions Cr(VI) recovers. The results obtained in this study highlight the potential of this technology for industrial wastewater treatment.