Low Cr Concentrations Research Articles

Green removal of low and high levels of Cu(II) and Cr(III) cations from concentrated saline chloride medium achieved by a mixture of N,N′-bis(salicylidene)-thiocarbohydrazide-TritonX-100 micellar system via cloud point extraction process

Abstract In this work, we performed the cloud point extraction with low and high concentrations of Cu(II) and Cr(III), two particularly toxic metallic pollutants, that have been shown to have adverse effects on human health and the environment. Removal of the metal ions was achieved in the presence of Triton X-100 as a non-ionic surfactant and N,N′-bis(salicylidene)-thiocarbohydrazide as a chelating ligand in concentrated chloride medium. The behavior of the Schiff base was initially investigated in homogeneous DMSO-water and micellar Triton X-100-water media. The obtained values of the acid constants show that the extractant is more acidic in micellar media than in pure aqueous medium. The recorded cloud point temperatures of Triton X-100 are significantly impacted by the sodium chloride concentration, the surfactant concentration, and the Schiff base ligand. Under the optimised experimental conditions, a quantitative extraction of Cu(II) and a maximum extraction rate of 74 % of Cr(III) were obtained. The reduction of the metal concentration from 10−3 mol L−1 to 10−6 mol L−1 resulted in a reduction of the temperature by 10 °C and a reduction of the contact time from 10 h to 3 h.

Chromium isotopic compositions of a reef in the South China Sea: Biological effects and influence from early diagenetic Mn-oxides reduction

Global climate fluctuations have been inextricably linked with changes in the marine environment and ecosystems' evolution during the Cenozoic. The chromium isotopic compositions (δ53Cr) of marine carbonates have been used to study changes in ocean redox conditions. However, whether δ53Cr of carbonates faithfully reflect the information of ambient seawater at the time of deposition remains controversial. Here, we report major and trace element concentrations, as well as the Cr isotopic compositions for samples from a Neogene–Quaternary biogenic reef (Core NK-1) in the South China Sea. The samples exhibit highly variable Cr concentrations and δ53Cr values. The Cr concentrations range from 0.76 μg/g to 8.58 μg/g with an average of 3.96 μg/g, and the δ53Cr values vary from −0.54‰ to 0.68‰ with an average of 0.06‰, which are generally lower than the reported Cr isotopic compositions for global seawater. The fluctuation of δ53Cr values is unlikely to be controlled by changes in the redox conditions of seawater. Biogenic processes may have affected some samples with relatively low Cr concentrations and δ53Cr values. Other samples may have been affected by post-depositional addition of Cr from pore water. Early diagenetic reduction of ferromanganese oxides is likely another significant control factor for the variation of δ53Cr values. The results suggest that the factors influencing the Cr isotopic compositions of biogenic carbonate reefs are complex, and the variation of Cr isotopic compositions should not be directly linked to the redox state of the ocean. After evaluating the potential influences of multiple factors, the inferred Cr isotopic compositions of syn-depositional fluids of the carbonates from Core NK-1 are similar, which may suggest a relatively stable redox environment in the South China Sea during the Neogene to Quaternary period.

How Cr doping influences on the properties of ZnO nanoparticles obtained by aqueous synthesis: Exploring at low Cr concentrations

A detailed physico-chemical study of Cr3+-doped ZnO nanoparticles (NPs) obtained via aqueous synthesis was carried out. The NPs acquire greenish tonality as the Cr concentration increased. High efficiency of Cr incorporation into the ZnO lattice was found up to approximately 1 at% Cr. The ZnO:Cr NPs show wurtzite hexagonal phase with a lattice compressed for low Cr concentration and tensed for higher concentrations. Structural, chemical and optical analyses indicate that for low Cr concentration Cr occupies the Zn vacancy sites, owing to the reduction in acceptor compensation by passivating the Zn vacancies and the contribution of the unpaired electron of Cr3+, which induces an increase of electron concentration, changes in the conductivity, transport of carriers, optical properties and ferromagnetic properties, among others. At higher Cr concentrations, the passivation of Zn vacancies by Cr atoms reduces the acceptor contribution, and substantial substitution of Zn atoms by Cr atoms in the ZnO lattice strengthens the retention of O atoms in the Cr-O bonds. This results in a reduction in O vacancy concentration, donor contribution, strain, electron concentration, and luminescence intensity.

Synergistic Effects of Earthworms and Plants on Chromium Removal from Acidic and Alkaline Soils: Biological Responses and Implications.

Soil heavy metal pollution has become one of the major environmental issues of global concern and solving this problem is a major scientific and technological need for today's socio-economic development. Environmentally friendly bioremediation methods are currently the most commonly used for soil heavy metal pollution remediation. Via controlled experiments, the removal characteristics of chromium from contaminated soil were studied using earthworms (Eisenia fetida and Pheretima guillelmi) and plants (ryegrass and maize) at different chromium concentrations (15 mg/kg and 50 mg/kg) in acidic and alkaline soils. The effects of chromium contamination on biomass, chromium bioaccumulation, and earthworm gut microbial communities were also analyzed. The results showed that E. fetida had a relatively stronger ability to remove chromium from acidic and alkaline soil than P. guillelmi, and ryegrass had a significantly better ability to remove chromium from acidic and alkaline soil than maize. The combined use of E. fetida and ryegrass showed the best effect of removing chromium from contaminated soils, wih the highest removal rate (63.23%) in acidic soil at low Cr concentrations. After soil ingestion by earthworms, the content of stable chromium (residual and oxidizable forms) in the soil decreased significantly, while the content of active chromium (acid-extractable and reducible forms) increased significantly, thus promoting the enrichment of chromium in plants. The diversity in gut bacterial communities in earthworms decreased significantly following the ingestion of chromium-polluted soil, and their composition differences were significantly correlated with soil acidity and alkalinity. Bacillales, Chryseobacterium, and Citrobacter may have strong abilities to resist chromium and enhance chromium activity in acidic and alkaline soils. There was also a significant correlation between changes in enzyme activity in earthworms and their gut bacterial communities. The bacterial communities, including Pseudomonas and Verminephrobacter, were closely related to the bioavailability of chromium in soil and the degree of chromium stress in earthworms. This study provides insights into the differences in bioremediation for chromium-contaminated soils with different properties and its biological responses.

Chromium removal from aqueous solution using bimetallic Bi0/Cu0-based nanocomposite biochar.

Chromium (Cr), due to its greater contamination in aquifers and distinct eco-toxic impacts, is of greater environmental concern. This study aimed to synthesize nanocomposites of almond shells biochar (BC) with zerovalent bismuth and/or copper (Bi0/BC, Cu0/BC, and Bi0-Cu0/BC) for the removal of Cr from aqueous solution. The synthesized nanocomposites were investigated using various characterization techniques such as XRD, FTIR spectroscopy, SEM, and EDX. The Cr removal potential by the nanocomposites was explored under different Cr concentrations (25-100mg/L), adsorbent doses (0.5-2.0g/L), solution pH (2-8), and contact time (10-160min). The above-mentioned advanced techniques verified successful formation of Bi0/Cu0 and their composite with BC. The synthesized nanocomposites were highly effective in the removal of Cr. The Bi0-Cu0/BC nano-biocomposites showed higher Cr removal efficiency (92%) compared to Cu0/BC (85%), Bi0/BC (76%), and BC (67%). The prepared nanocomposites led to effective Cr removal at lower Cr concentrations (25mg/L) and acidic pH (4.0). The Cr solubility changes with pH, resulting in different degrees of Cr removal by Bi0-Cu0/BC, with Cr(VI) being more soluble and easier to adsorb at low pH levels and Cr(III) being less soluble and more difficult to adsorb at high pH levels. The experimental Cr adsorption well fitted with the Freundlich adsorption isotherm model (R2 > 0.99) and pseudo-second-order kinetic model. Among the prepared nanocomposites, the Bi0-Cu0/BC showed greater stability and reusability. It was established that the as-synthesized Bi0-Cu0/BC nano-biocomposite showed excellent adsorption potential for practical Cr removal from contaminated water.

Atomistic investigations of Cr effect on the deformation mechanisms and mechanical properties of CrCoFeNi alloys

The emerging class of multi-principal element alloy (MPEA) processes superior mechanical properties and has great potential for applications in extreme environments. In this work, the synergic effect of the Cr content and crystallographic orientation on the deformation behaviors of single-crystal CrCoFeNi MPEAs has been investigated by atomistic simulations. We have found distinct differences in dislocation activities, deformation microstructures, and mechanical behaviors in the model MPEAs, which depend on crystallographic orientations, Cr concentration, and the number of activated slip systems. When multiple slip systems are triggered along [100] and [111] orientations, Shockley partial activation and their interaction are predominant, leading to the formation of sessile dislocations and a dense dislocation network. When only two slip systems of Shockley partials are favored along the [110] direction, the influence of Cr concentration and planner defect energies emerges. At low Cr concentration, the double planar slip of Shockley partials results in deformation-induced nanotwins. At high Cr concentration, the partial dislocations of a single slip plane become dominant, attaining the highest volume fraction of deformation-induced phase transformation. The results provide a fundamental understanding of deformation mechanisms in MPEAs, elucidating the synergic effect of crystal orientation and composition on tunning the mechanical behaviors.

The exchange rate of creatine CEST in mouse brain.

To estimate the exchange rate of creatine (Cr) CEST and to evaluate the pH sensitivity of guanidinium (Guan) CEST in the mouse brain. Polynomial and Lorentzian line-shape fitting (PLOF) were implemented to extract the amine, amide, and Guan CEST signals from the brain Z-spectrum at 11.7T. Wild-type (WT) and knockout mice with the guanidinoacetate N-methyltransferase deficiency (GAMT-/- ) that have low Cr and phosphocreatine (PCr) concentrations in the brain were used to extract the CrCEST signal. To quantify the CrCEST exchange rate, a two-step Bloch-McConnell (BM) fitting was used to fit the CrCEST line-shape, B1 -dependent CrCEST, and the pH response with different B1 values. The pH in the brain cells was altered by hypercapnia to measure the pH sensitivity of GuanCEST. Comparison between the Z-spectra of WT and GAMT-/- mice suggest that the CrCEST is between 20% and 25% of the GuanCEST in the Z-spectrum at 1.95 ppm between B1 = 0.8 and 2 μT. The CrCEST exchange rate was found to be around 240-480 s-1 in the mouse brain, which is significantly lower than that in solutions (∼1000 s-1 ). The hypercapnia study on the mouse brain revealed that CrCEST at B1 = 2 μT and amineCEST at B1 = 0.8 μT are highly sensitive to pH change in the WT mouse brain. The in vivo CrCEST exchange rate is slow, and the acquisition parameters for the CrCEST should be adjusted accordingly. CrCEST is the major contribution to the opposite pH-dependence of GuanCEST signal under different conditions of B1 in the brain.

Corrosion behavior of a compositionally complex alloy utilizing simultaneous Al, Cr, and Ti passivation

The corrosion behavior of the Al0.3Cr0.5Fe2Mn0.25Mo0.15Ni1.5Ti0.3 compositionally complex dual-phase alloy was explored in a variety of electrolytes. Comparable corrosion resistance to 316L stainless steel and Ni-Cr binaries was observed in NaCl despite lower Cr concentrations. Individual elemental fates during corrosion were identified by combinations of in-situ atomic emission spectroelectrochemistry and ex-situ X-ray photoelectron spectroscopy with high-resolution surface analysis and depth profiling. A potentiostatically grown passive film was enriched in Al(III), Cr(III), Ti(IV), and Mo(VI). Al-Ti and Cr-Ti layers were suggested but significant Al, Cr, and Ti mixing was present. Proposed benefits of Al-Cr-Ti coexistence are addressed.

Geochemical conditions regulating chromium preservation in marine sediments

In the marine sediment record, concentrations and isotope ratios of chromium (Cr) can be used to reconstruct ocean biogeochemical conditions. These reconstructions rely on a detailed understanding of the chemical pathways that Cr undergoes as it is transferred from the water column to the sediment record. We examined Cr concentrations in marine pore fluids and sediments from six continental margin sites, which can be grouped into two basic environments: (1) sites where sediments are oxygenated and rich in solid phase Mn (herein termed oxic), and (2) sites where sediments are organic C (Corg)-rich and oxygen is depleted (anoxic). We found Cr concentrations to be lower (maximum of 12 nM in pore fluids and 124 ppm sediment solid phase) at oxic sites compared with anoxic sites (maximum of 77 nM and 184 ppm). Our findings confirm previously published interpretations of dissolved Cr in pore fluids (Brumsack and Gieskes, 1983; Shaw et al., 1990). In oxic surface sediments, particulate Cr(III) can be oxidised by Mn oxides, which leads to elevated concentrations of dissolved Cr co-occurring at the same depth as elevated Mn concentrations in the sediment. Under these oxidising conditions, down-core sediments contain relatively low solid-phase Cr concentrations. In oxic sediments, Cr speciation reveals that most of the pore fluid Cr is in the Cr(VI) state. At the site where Mn oxide-rich sediments rest below an oxic water column, oxidative loss of Cr from the sediment to the bottom water leads to the lowest estimated Cr burial efficiency of the sites examined here. Under anoxic Corg-rich conditions, both pore fluids and sediment solid phases contain high Cr concentrations, with 40–80% of dissolved pore fluid Cr present as Cr(III). This enrichment of Cr appears to be tightly linked to the presence of high total organic carbon (TOC) content and scavenging of Cr by (organic) particles in the water column. Combined, these data highlight the strong dependence of Cr on both sedimentary redox conditions as well as biological productivity. Based on the data from modern continental margin sediments, we propose that Cr concentrations and isotope compositions of the authigenic sediment fraction may record a combination of redox conditions and biological productivity in the water column. If confirmed by Cr isotope analyses, these findings will add support for the notion that Cr may serve as a proxy for ocean biological and chemical sedimentological conditions. Thus, careful assessment of the impact of organic matter on Cr is required for reconstructions of redox conditions with sedimentary records.

Biopolymer‐Based Nanocomposites for Removal of Cr(VI) from Aqueous Systems: A Review

AbstractHexavalent chromium Cr(VI) has emerged as a contaminant of prime concern for the environmentalists because of its improper disposal by tannery, dye, and electroplating industries. Adsorption is the most exploited method for its removal from industrial wastewater because of its high removal efficiency even at low Cr(VI) concentration, minimal sludge, and ease of regeneration. In recent years, several adsorbents of biological origin such as plants, algae, fungi, and bacteria have been explored for Cr(VI) remediation. This review comprehends the recent studies involving usage of biopolymer‐based nano‐composites with respect to its adsorption mechanisms, adsorption capacities, isotherms, and kinetics. The conventional abiotic and biotic techniques for removal of Cr(VI) are also discussed with a comparative insight of their adsorption capacity and removal efficiency. Nano‐biocomposites integrate the functional properties of both nanoparticles and biopolymers, which make them efficient biosorbents. Nano‐biocomposites offer a large surface area, reduced particle loss, minimal particle agglomeration on the surface, and high stability. Common kinetic models among the nano‐biocomposites, and various equilibrium models are also analyzed to understand the mode of adsorption and associated factors. These materials are mostly found to follow monolayer adsorption with ion exchange, electrostatic interaction, and surface complexation as major players in the process.

Multi-element imaging of urinary stones by LA-ICP-MS with a homogeneous co-precipitation CaC2O4-matrix calibration standard.

Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) studies on trace element concentration and their spatial distribution in CaC2O4-matrix urinary stones are important but powerfully rely on matrix-matched external calibration. In this work, CaC2O4 precipitate CaOx-1 which was doped with Mg, Cr, Mn, Fe, Co, Cu, Zn, and Sr was prepared by the homogeneous co-precipitation method. It had a homogeneous distribution of major (RSD of 0.46%) and trace elements (RSD of 1.83-6.92%) due to thenegligible concentration difference compared with that prepared by the heterogeneous co-precipitation method. Based on this, an analytical method for quantitative determination of elemental concentration in CaC2O4-matrix samples was established using CaOx-1 as a calibration standard, and the accuracy of this method was assessed by calibrating theelemental concentration in another synthetic CaC2O4 precipitate CaOx-2 with relative deviation (Dr) from - 11.43% (Mn) to 9.76% (Mg). Finally, a methodology for quantitative imaging of Mg, Cr, Mn, Fe, Co, Cu, Zn, and Sr in urinary stones via LA-ICP-MS was developed. From the elemental distributional maps, an annular texture can be found for Mg, Cu, Zn, and Sr, which corresponds to the annular white and brown texture in the real urinary stone. A homogeneous distribution of Fe and low concentrations of Cr and Co were found throughout the stone, while Mn was highly concentrated in the margin of the stone. All these results demonstrate that quantitative distribution patterns of Mg, Cr, Mn, Fe, Co, Cu, Zn, and Sr can be obtained by LA-ICP-MS using CaOx-1 as a calibration standard, which can provide potential evidence for urological and other medical studies.

Imidazolium functionalized polysulfone/DTPA-chitosan composite beads for simultaneous removal of Cr(VI) and Cu(II) from aqueous solutions

Simultaneous removal of chromium(VI) oxyanions and heavy metal cations from contaminated water body is of great significance. In this work, a novel and bifunctional sorbent, imidazolium functionalized polysulfone/DTPA-chitosan composite bead (IMPSF/DACS) was successfully constructed by phase inversion method and applied for co-removal of Cr(VI) and Cu(II) from aqueous solutions. The maximum adsorption capacities for Cr(VI) and Cu(II) on IMPSF/DACS in single system at pH 5 were 56.72 and 43.05 mg g−1, respectively. In binary system, the removal of Cr(VI) could be further enhanced by the presence of Cu(II) due to the electrostatic shielding effect, while Cu(II) sorption was not significantly affected by the coexistence of Cr(VI). Moreover, IMPSF/DACS could simultaneously reduce low concentrations of Cu(II) and Cr(VI) in simulated contaminated lake water below the limit, while also showing good reusability in co-removal of Cr(VI) and Cu(II). The order of inhibitory effect of competing anions on Cr(VI) removal was as follows: H2PO4− < Cl− < NO3− < SO42−, while the competing hardness cations had a little effects on the adsorption of Cu(II), implying that the Cr(VI) removal was mainly depended on the electrostatic attraction between Cr(VI) and imidazolium ions modified on IMPSF/DACS, and Cu(II) uptake was associated with chelation of DACS encapsulated in IMPSF/DACS beads. These assumptions were confirmed by XPS, FTIR and EDS-mapping techniques.

Groundwater conceptual pollution model and related human health hazards, the main dilemma of a desert aquifer near ophiolite complex.

Groundwater is a finite resource in Davarzan region which is located between the ophiolite complex mountain in the north and salty playa at the south. The water samples were analyzed to assess the origin of groundwater pollution and explain links between the disturbed heavy metals composition of the earth's surface and the human health risks. The main heavy metal pollutants in the groundwater are Cr, Fe, As and Pb ions. In general, the groundwater salinity and some elements such as Cr and As are increased along with surface topography and groundwater flow directions from the northern ophiolite highlands recharge area to the adjacent desert discharging zone in the south. Despite the ophiolite complexes being the most enriched in Cr element, the lowest Cr concentration in the groundwater was measured near the ophiolite area, which is in the range of its discharged springs. Based on the groundwater conceptual pollution model, bedrock geochemistry controls the composition of soil and hence that of groundwater. The Cr samples show a direct relation with the EC value indicating that intrusion of salinity from the salt pan is probably another reason for the increased Cr concentration. The results of health risk assessment indicated that the groundwater suffered from significant contamination and if used for long-term without pre-treatment may pose serious health risks to human population via drinking water and irrigation of agricultural fields. This is the first attempt to apply hydrogeological setting along with the source of pollution and its health risk in a desert-ophiolitic area.

Regulation of chromium translocation to shoot and physiological, metabolomic, and ionomic adjustments confer chromium stress tolerance in the halophyte Suaeda maritima

Chromium (Cr) is a highly toxic element adversely affecting the environment, cultivable lands, and human populations. The present study investigated the effects of Cr (VI) (100–400 μM) on plant morphology and growth, photosynthetic pigments, organic osmolytes, ionomics, and metabolomic dynamics of the halophyte Suaeda maritima to decipher the Cr tolerance mechanisms. Cr exposure reduced the growth and biomass in S. maritima. The photosynthetic pigments content significantly declined at higher Cr concentrations (400 μM). However, at lower Cr concentrations (100–300 μM), the photosynthetic pigments remained unaffected or increased. The results suggest that a high concentration of Cr exposure might have adverse effects on PS II in S. maritima. The enhanced uptake of Na+ in S. maritima imposed to Cr stress indicates that Na+ might have a pivotal role in osmotic adjustment, thereby maintaining water status under Cr stress. The proline content was significantly upregulated in Cr-treated plants suggesting its role in maintaining osmotic balance and scavenging ROS. The metabolomic analysis of control and 400 μM Cr treated plants led to the identification of 62 metabolites. The fold chain analysis indicated the upregulation of several metabolites, including phytohormones (SA and GA3), polyphenols (cinnamic acid, sinapic acid, coumaric acid, vanillic acid, and syringic acid), and amino acids (alanine, leucine, proline, methionine, and cysteine) under Cr stress. The upregulation of these metabolites suggests the enhanced metal chelation and sequestration in vacuoles, reducing oxidative stress by scavenging ROS and promoting photosynthesis by maintaining the chloroplast membrane structure and photosynthetic pigments. Furthermore, in S. maritima, Cr tolerance index (Ti) was more than 60% in all the treatments, and Cr bio-concentration factor (BCF) and translocation factor (Tf) values were all greater than 1.0, which clearly indicates the Cr-hyperaccumulator characteristics of this halophyte.

Twofold age-hardening mechanism of Al-added high-Cr ODS ferritic steels

Age-hardening of oxide dispersion strengthened (ODS) ferritic steels with various contents of Cr and Al was investigated by Vickers hardness (HV) measurement and tensile test after ageing at 475°C for up to 9000 h. The correlation between age-hardening and the evolution of nanometer-scale structure and chemistry studied by atom probe tomography (APT) reveals that the age-hardening could be interpreted in terms of twofold hardening mechanism involving α–α′ phase separation and/or the precipitation of (Al, Ti)-enriched β′ phases. The results of APT characterization indicate that the Cr concentration and volume fraction of α′ phase increase significantly while the chemical compositions and volume fraction of β′ phases don't changed considerably during ageing from 300 h to 9000 h. At the early stage of ageing, the age-hardening due to α–α′ phase separation is very limited because of the low Cr concentration of α′ phase, which results in very weak modulus strengthening. With the increasing of ageing time, the age-hardening is increased because of the increasing of Cr content in the α′ phase, resulting in considerably enhanced modulus mismatch strengthening. However, age-hardening due to β′ phase precipitation is significant once the β′ phases are formed and, thereafter, it doesn't change apparently. The metal/oxide interfaces in ODS steels provide nucleation sites for α′ and β′ phases. Based on the comprehensive data developed, the roles of Cr and Al in the age-hardening of ODS ferritic steels were elucidated.

A biomimetic porous fibre bundle adsorbent for the rapid and complete removal of multiple low-level heavy metal ions

Improving diffusion and mass transfer kinetics to enhance the synchronous removal efficiency of adsorbents for low concentrations of various heavy metal ions is of great significance for reducing heavy metal removal. Here, a biomimetic porous fibre bundle adsorbent with multiple adsorption sites was constructed by embedding and bonding porous coconut shell biochar on amino and sulfhydryl group-functionalized cellulose nanofibre bundles in the process of fibrogenesis, which was inspired by the principle of spider silk. The high porosity, specific surface area (212.17 m2/g) and swelling rate (184 %) of the porous fibre bundle could effectively improve the diffusion and mass transfer kinetics. Multiple adsorption sites of amino, carboxyl, and sulfhydryl groups endow the adsorbent with a synchronous removal rate for various heavy metal ions in water. Therefore, the porous fibre bundle could remove low concentrations of Pb(II), Cu(II), Cd(II) and Cr(VI) to safe drinking water level standard concentrations (US EPA) within 20 min. This study provided a simple method for designing an effective adsorbent for lowering heavy metal removal.

Association of Plant and Microorganisms on Textile Wastewater Remediation

Phytoremediation of heavy metals containing textile wastewater using vetiver grass (Chrysopogone zizanioides) associated with Bacillus sp. and Pseudomonas aeruginosa has been performed. Two levels of heavy metal in wastewater (<1 and 100 ppm) in two replication were treated using C. Zizanioides associated with Bacillus sp. and C. Zizanioides associated with Pseudomonas aeruginosa. Assessment of C. zizanioides capability was determined by the efficiency of heavy metals (Cu and Cr) removal and its accumulation in both of leaves and roots of the plants. It was obtained that the experiment of low concentration of Cr was totally eliminated from 0.06 to 0.00 ppm and on the other hand, about 42.6 percent (of 118.65 to 66.06 ppm) for high concentration decreased using C. zizanioides with Bacillus sp. The use of C zizanioides associated with P. aeruginosa was also able to eliminate totally low concentration Cr in textile wastewater (0.08 to 0.00 ppm) and about 69.2 percent (158.76 to 48.9 ppm) of the high Cr concentration. Elimination of Cu from wastewater was 74.4% (0.48 to 0.12) and 55.7% (61.34 to 27.16 ppm) for the treatment using C. zizanioides with Bacillus sp. at a low and high level of concentrations respectively. Meanwhile, combined C. zizanioides with Pseudomonas aeruginosa absorb the Cu 100% (0.36 to 0.00 ppm) and 65% (64.93 to 22.77 ppm) for wastewater with low and high concentrations of Cu respectively. Combination of C. zizanioides, Bacillus sp., and Pseudomonas aeruginosa are fruitful in heavy metals containing wastewater remediation.

Ultrafast removal of Cr(VI) by chitosan coated biochar-supported nano zero-valent iron aerogel from aqueous solution: Application performance and reaction mechanism

Chitosan coated biochar-supported nano zero-valent iron aerogel (C-nZVI@BC) was successfully synthesized for the efficient removal of Cr(VI) from aqueous solution. Results showed that the C-nZVI@BC has a 2.1-fold higher adsorption capacity of Cr(VI) than the uncoated sample. Chitosan coating on nZVI@BC and BC support could prevent the oxidation and agglomeration of nZVI. Ultrafast adsorption of Cr(VI) with 61 %, 77 %, and 87 % of the maximum adsorption capacities were achieved within 1 min with the initial concentrations of Cr(VI) at 100 mg/L, 300 mg/L, and 600 mg/L, respectively. The C-nZVI@BC exhibited high adsorption performance under aerobic conditions, and showed high Cr(VI) removal rates (>83 %) in a wide pH range (2–8). Cr(VI) and Cr(III) could be simultaneously removed by C-nZVI@BC, and the key mechanisms were adsorption, reduction, and complexation. The acid and alkali resistance experiment of C-nZVI@BC showed that C-nZVI@BC still has better adsorption capacity of Cr(VI) (96.7 mg/g) in acid environment. The application of C-nZVI@BC in the simulated electroplating wastewater treatment indicated a high removal rate of Cr(VI). C-nZVI@BC could effectively reduce the low concentration of Cr(VI) below the standard of the World Health Organization. The syringe filtration and column adsorption experiments implied the potential of C-nZVI@BC for Cr(VI) removal in groundwater. In addition, C-nZVI@BC could be a direct reducing agent for Cr(VI) and an activator of persulfate (PS) for the degradation of antibiotics, and C-nZVI@BC + PS showed 77 % and 82 % removal of tetracycline and chlortetracycline within 5 min. Overall, C-nZVI@BC was a suitable adsorbent for pollutant removal.

Chromium Removal in the Presence of NOM during Fe(II) Reductive Precipitation for Drinking Water Treatment

Cr(VI) is toxic and carcinogenic, which fuels discussions on reducing existing standards for maximum Cr concentrations in drinking water. Fe(II) reductive precipitation is a common and economical method for achieving very low Cr(tot) concentrations (&lt;5 µg/L). While Cr(VI) is reduced to Cr(III), Fe(II) is oxidized to Fe(III). The resulting Cr(III) and Fe(III) have low solubilities at neutral pH, precipitate as hydroxides, and can be removed by conventional media filtration. The presence of natural organic matter (NOM) in the raw water source can, depending on pH, concentration, type of NOM, and contact time, affect this process in various ways, from promoting Cr(VI) reduction, to re-reducing Fe(III), to forming stable complexes with Cr and Fe, thus, impairing chromium removal. The presented data showed that NOM, whether dominated by terrestrial humic acid, or of aquatic origin, could substantially impair chromium removal at neutral pH conditions. In particular, the ultimate removal of Cr(III) was affected. Soluble complexes and/or colloids of Cr(III), Fe(III) and NOM in the size range of 10 kDa–0.1 µm were formed, that could not be removed by conventional media filtration. Presence of iron sludge (&gt;50 mg/L Fe(III)) mitigated the negative impacts of NOM on Cr(VI) reduction and Cr(III) removal. However, even 100 mg/L Fe(III), the highest applied sludge concentration, did not lead to a decrease in Fe(II) dosing requirements under the given conditions. A molar ratio higher than the given stochiometric ratio of [Fe(II)]:[Cr(VI)] = 3 was necessary for sufficient Cr(VI) removal.

Transparency and room temperature ferromagnetism in diluted magnetic polycrystalline Zn1−xCrxTe non-oxide II-VI semiconductor compounds

Polycrystalline Zn1−xCrxTe samples for x = 0.00, 0.05, 0.10, 0.15, 0.18, and 0.20 were synthesized by solid-state reaction, and their physical properties were studied for the purpose of identifying a novel non-oxide transparent diluted magnetic semiconductor (DMS). Their transport properties exhibit semiconducting behavior for low Cr concentrations and become conductors for higher Cr concentration concentrations. Ferromagnetic behavior was observed in Cr-doped ZnTe with Curie temperature Tc increasing as Cr concentration increases. At x = 0.20 Cr concentration, the system has Tc above room temperature, indicating an interesting II-VI ferromagnetic semiconductor. Furthermore, optical transparency in the visible light range was found to be 30–85 % for different Cr concentration concentrations. Also, according to the electrical transport measurement data in this study, the resistivity doesn’t exhibit any significant change as the temperature increases for x = 0.20. This consistent resistivity exhibits a possible candidacy for further studies of the sample Zn0.80Cr0.20Te for half-metallic ferromagnetic properties.