Hexavalent Chromium

Hexavalent chromium (Cr(VI)) contamination has gained interest from regulatory authorities due to its high toxicity and carcinogenicity. Different approaches have been applied for the remediation of Cr(VI) from aquatic media, with adsorption being the most common method. Biochar has gained popularity in recent years as a costeffective and greener adsorbent for remediation of heavy metals (HMs) via different mechanisms, including complexation, electrostatic or ionic interactions, and precipitation. Owing to its facile synthesis methods and excellent physico-chemical properties, biochar has been applied extensively for the removal of Cr(VI) from different matrices. However, very few studies have targeted the elimination of Cr(VI) from real polluted environmental matrices, such as soil or water. Therefore, this review comprehensively discussed the potential application of modified biochar in remediation of Cr(VI) from different environmental matrices, starting with its toxicology impacts on flora and fauna. Furthermore, this review has provided a comprehensive state-of-the-art analysis of biochar tailoring technology, modification methods, various adsorption mechanisms, and factors which influence the adsorption of Cr(VI) from different environmental matrices, along with regeneration and reuse of spent adsorbents. Finally, current work focuses on the major gaps in the literature and areas in which further research should be pursued in addition to the effective application of biochar as adsorbent for the remediation of Cr(VI).

Aspergillus niger isolated from soil of leather tanning effluent had higher activity to remove chromium then the other fungal isolates. The potency of A. niger was evaluated in shake flask culture by absorption of chromium at pH 6, temperature 30°C. The toxicity of chromium evaluated in petriplates and soil microcosm seed bioassay test had indicated increase in toxicity with the

Sludge, soil and leachate samples collected from a chromium-contaminated tannery waste dumping site in Kanpur, India, were found to contain considerable amounts of Cr(VI), despite the fresh tannery sludge containing little or no Cr(VI). Literature reports suggested that dry Cr(III) ...

ABSTRACT Although many heavy metals acts as micro-nutrients playing essential roles for all living organisms, most of them, when bioavailable in high concentrations, have to be considered potentially toxic. Some of them, such as Cr, and Ni are generally highly concentrated in all ultramafic rocks as well as in serpentines and their weathering products (soils and sediments), that largely outcrop in ophiolite belts, such as those of Central Italy. High Cr (VI) concentrations have been found in some spring waters associated with serpentinite outcrops and in Cecina Valley (Western Tuscany) soils, sediments and ground waters. Thus, we set up a multidisciplinary research program (RESPIRA) financed by Tuscany Region and by European Union, aimed to enhance the understanding of the weathering processes of serpentinite rocks in order to assess the mobility and hence the bioavailability of heavy and toxic metals such Ni and Cr in soils and namely to study the release and mobility of Cr with in the "critical zone" where rocks, soils, meteoric waters and atmospheric gasses interact. Sr-Pb isotopes of serpentinites suggest an interaction with recent, low-T, waters. Three isotopic end-members are identified in soils and sediments: serpentinites, marine limestones and tertiary siliciclastic rocks. Sr isotopic values of ground waters match with the higher values (87Sr/86Sr ≈ 0.7089 - 0.7092) of soils and sediments compositional range. Cr (VI) free and Cr (VI) bearing spring waters, spilling out from the serpentinite outcrops (Santa Luce, Querceto, Montecastelli), display Mg-HCO3 chemical composition 87Sr/86Sr from 0.7074 to 0.7084 (in the serpentinite range). Petrographic and minero-chemical analyses of both rocks and soil samples from the same sites, highlight the occurrence of secondary minerals containing significant Cr contents, such as chlorites (Cr2O3 from 2 to 8 wt%) that can easily release Cr(III). Nerveless the absence of Mn-oxides, considered the more common electron acceptors, able to rapid oxidise Cr(III) into Cr (VI ), implies that local presence of Cr (VI) in waters have to be ascribed to other processes. Some serpentinites contain significant amount of Fe-rich brucite and show evidences of its dissolution during surface weathering. This process could lead to the formation of both of hydrous magnesium carbonates and of Mg-rich members of "layered double hydroxide" group, which can contain high contents of Cr(III) that can be easily oxidized and mobilized during weathering reactions (Langone et al., in press). Cr isotopes analyses, able to record any occurrence of Cr redox reactions, are analysed in order to better understand which are the mineralogical, chemical and thermodynamic parameters responsible for Cr(III)-Cr(VI) oxidation during water-rock interactions. Langone A., Baneschi I., Boschi C., Dini A., Guidi M, and Cavallo A., (in press), Serpentinite-water interaction and chromium (VI) release in spring waters: examples from Tuscan ophiolites, Ofioliti.

Amount of waste water containing heavy metals is increasing in the environment due to industrialization. Heavy metals treatment of waste water should be done due to increase in pollution and scarcity of water. Hexavalent Chromium is one of the heavy metal emitted from textile dye, tannery, nuclear power plants, and battery making steel and electroplating industries which cause chronic disorders in human. It is one of the most common metal present in the effluents. So it is necessary to remove heavy metals from waste water as it is very toxic. The study was carried out to increase the percentage removal of hexavalent chromium, characteristics, efficiency and economy of waste water by low cost adsorbent.

Quantification of Cr(VI) in an aqueous solution is conducted by direct UV/visible spec-trophotometry based on the yellow coloring of the chromate ion. Measurements show that absorption follows the Beer-Lambert law over a wide range of concentrations. At pH below the pK a of 6.4 (HCrO4/CrO4), the absorption maximum lies at 350 nm wavelength and the linear range spans from 0.5 to 100 mg Cr(VI)/L; above the pK a (pH 6.4), the absorption maximum is 373 nm and linearity occurs in the range of 0.5-25 mg/L. The wide range of validity of the Beer-Lambert law is advantageous for the measurement of concentrated samples. The standard method of analysis of aqueous Cr(VI) is by colorimetry with the 1,5-diphenylcarbazide (DPC)-Cr(VI) complex. This method, although very sensitive, bears a narrow range of linearity from 0 to 0.8 mg Cr(VI)/L. It is shown that when analyzing Cr(VI) solutions with concentrations in the range of 30-500 mg/L, the DPC method gives inaccurate results and relative standard deviations of 20-50%. This is due to high dilution factors. On the contrary, the direct method performs with high accuracy. Relative standard deviation is only 0.5% at 500 mg Cr(VI)/L. The direct method is fast, reliable, and nondestructive for the sample. The direct method is recommended for the quantification of Cr(VI) at concentrations greater than 1 mg/L.

Phytoremediation is a method that uses plants to remediate site that contaminated with organic and inorganic pollutants. This method has several advantage than others conventional methods. It's a green technology, no need of expensive equipment and specialized expert person, easy and low cost application, and has aesthetic value. Although this methods has some limitation and some ecological adverse effect, with carefully-planned phytoremediation using fast growing, high biomass, deep rooted and native chromium-hyperaccumulator species, it is the best alternative for remediating chromium-contaminated bodies of soils and water in developing countries.
Phytoremediation adalah metode yang menggunakan tanaman untuk menangani lingkungan yang terkontaminasi polutan organik maupun anorganik. Metode ini dibandingkan metode lain mempunyai kelebihan yaitu ramah lingkungan, tidak memerlukan alat yang mahal maupun orang yang sangat ahli, mudah diaplikasikan dan berbiaya rendah, serta lebih mempunyai nilai estetika. Sekalipun terdapat beberapa keterbatasan serta kekhawatiran menyangkut aspek ekologi, dengan phytoremediation yang dirancang seksama menggunakan tanaman asli yang tumbuh cepat, tinggi biomasanya, berakar sampai ke dalam tanah dan bersifat hyperaccumulator terhadap krom, metode ini berpotensi besar dalam pengolahan lingkungan terkontaminasi krom di negara-negara berkembang.

The biosorption potential of six brown macroalgae viz. Nizamuddina zanardinii, Stoechospermum marginatum, Cystoseira indica, Dictyota cervicornis, Padina australis, and Sargassum glaucescens, for the removal of hexavalent chromium (Cr(VI)) was investigated in the present study. Optimum conditions were determined by studying the effect of initial solution pH, biomass dosage, initial Cr(VI) concentration, and contact time on Cr(VI) removal by the macroalgae. Cr(VI) sorp-tion was found to be highly pH dependent and maximum sorption was obtained at pH 1.0. Freundlich isotherm model showed the best fit with the equilibrium data. The removal rate of Cr(VI) was relatively rapid during the first 30 min, although the rate decreased gradually and the sorption reached equilibrium in about 70 min for S. marginatum, 90 min for N. zanardinii, and 150 min for D. cervicornis, P. australis, S. glaucescens, and C. indica. Different kinetic models such as pseudo-first-order, pseudo-second-order, and intra-particle diffusion model were tested, and the experimental data was in agreement with the pseudo-second-order model. The results of the present study suggest that brown macroalgae could be used as effective biosor-bents for Cr(VI) removal from aqueous solution.

Adsorption is one of the method that is in use for remediation of contaminated water. The experimental factors affecting the batch mode of adsorption of various metals and inorganic anions are discussed in this book. The elemental contaminants have been categorized into four major categories i.e. major toxic elements; essential elements having toxicity on excessive exposure; miscellaneous elements having undetermined effects; non-toxic elements having trivial or unidentified significance. In addition, anions like nitrate, perchlorate and sulphate as water contaminants are considered. This unique volume fills a niche in the area of water treatment. Key Features: Provides practitioners with the background they need to understand and apply batch adsorption processes to the purification of water Describes the actions of adsorption capacity or percentage removal with respect to factors affecting the adsorption process Excellent source of information for those working in the industry for remediation of metals and anions Discusses the current era of Anthropocene which is highly dependent on the anthropogenic mineral sources for its sustenance

In the present work, the trivalent and hexavalent chromium phytoaccumulation by three living free floating aquatic macrophytes Salvinia auriculata, Pistia stratiotes, and Eicchornia crassipes was investigated in greenhouse. These plants were grown in hydroponic solutions supplied with non-toxic Cr3+ and Cr6+ chromium concentrations, performing six collections of nutrient media and plants in time from a batch system. The total chromium concentrations into Cr-doped hydroponic media and dry roots and aerial parts were assayed, by using the Synchrotron radiation X-ray fluorescence technique. The aquatic plant-based chromium removal data were described by using a nonstructural kinetic model, obtaining different bioaccumulation rate, ranging from 0.015 to 0.837 l mg−1 d−1. The Cr3+ removal efficiency was about 90%, 50%, and 90% for the E. crassipes, P. stratiotes, and S. auriculata, respectively; while it was rather different for Cr6+ one, with values about 50%, 70%, and 90% for the E. crassipes, P. stratiotes, and S. auriculata.

One of the better options to remove chromium VI (Cr(VI)) from wastewaters is the electrochemical continuous reactor. This process can be used to clean rinse waters from the plating industry. A mathematical model of the reactor is developed by classical application of mass balances for Cr(VI) and Fe, both corroborated in a bench scale electrochemical reactor. The reactor model is employed as the real process where the proposed controller is implemented. For the controller synthesis a reduced order uncertainty estimator is employed to infer the reaction rate, which is assumed unknown and an input/output linearising controller is designed, using the input flow to the reactor as control input and the Cr(VI) concentration in the wastewater as controlled variable. This procedure yields a nonlinear PI controller; where new tuning rules are given. Stability analysis of the closed loop behaviour of the reactor under the proposed methodology is done via mathematical analysis of the equations that describe the dynamic behaviour of the estimation and regulation errors. The performance of the controlled reactor is illustrated with numerical simulations.

Se estudio la remoción de cromo hexavalente utilizando arcillas funcionalizadas mediante tratamientos ácidos (HNO3, H2SO4, H3PO4 y C4H7OOH) buscando incrementar su capacidad de adsorción para potenciar su uso en la remoción de cromo hexavalente. Se realizó el estudio de la adsorción en un sistema batch a un pH constante de 2 y a una temperatura de 25oC, siguiendo un diseño de experimentos factorial. En este diseño se consideró como variable de análisis la proporción Cr6+/arcilla. Se generaron las isotermas de adsorción obteniendo que la máxima remoción fue del 80% para la arcilla funcionalizada con H3PO4 (AAF). Posteriormente se realizó el estudio de las arcillas utilizadas en la adsorción mediante espectroscopia de infrarrojo (FTIR) y microscopía de transmisión electrónica (TEM) para identificar la interacción arcilla-Cr6+, mediante lo cual se presume que el Cr6+ fue removido tanto por adsorción como por reducción de este a Cr3+.