Low Cr Concentrations Research Articles

Removal of metals from wastewaters by mineral and biomass-based sorbents applied in continuous-flow continuous stirred tank reactors followed by sedimentation

Numerous studies have examined the performance of mineral and biomass-based sorbents for metal removal under laboratory conditions, but few pilot-scale tests have been performed on possible water purification systems in which these sorbents can be used. This study addressed this issue by evaluating the suitability of selected sorbents for use in continuous-flow continuous stirred tank reactors (CSTR) followed by sedimentation in laboratory and in situ pilot-scale experiments. Acid (HCl)-modified peat (M-Peat), a commercially available mineral sorbent containing mainly magnesium (Mg) carbonates, Mg oxides and Mg silicates (Mineral-P) and a calcium-rich ground granular blast furnace slag (by-product of stainless steel production (Slag) were tested for treatment of metallurgical industry wastewater (laboratory, pilot). Overall, higher metal removal was achieved from samples with higher initial metal concentrations. M-Peat achieved good removal of Zn (50–70%) and Ni (30–50%) in laboratory and pilot experiments. However, the poor settling characteristics of M-Peat can restrict its application in systems where sedimentation is the solid-liquid separation process applied. Mineral-P showed good performance in removing 65–85% of Zn present in the water and it performed similarly in laboratory and pilot tests. However, low concentrations of As and Ni leached from Mineral-P in all tests. Slag achieved good performance in treatment of the industrial wastewater, removing 65–80% of Zn and 60–80% of Pb during pilot tests. However, low concentrations of Cr and Cu were leached from Slag in a few tests. As a by-product of the same (metallurgical) industry, ground granular blast furnace slag is an excellent candidate for reducing Zn concentrations from industrial wastewater flows.

Tectonic setting and metallogenic chronology of the Ashele Cu–Zn deposit in Xinjiang, NW China: Constraints from Re-Os dating of pyrite, U-Pb dating of zircon and Hf isotopes

The Ashele Cu-Zn deposit, an important volcanogenic massive sulfide (VMS) deposit, is located in the centre of the Ashele volcano-sedimentary basin of the Altay metallogenic belt, North Xinjiang, NW China. The No. 1 orebody is located between the roof basalt and the base tuff. The roof basalt yielded a zircon U-Pb age of 342 ± 4.6 Ma (MSWD = 1.5). Four pyrite samples from massive ores sulfides yielded a Re-Os isochron age of 342 ± 11 Ma (MSWD = 9.2), while the vein sulfide has a model age of 315 Ma. This shows that massive sulfide orebodies developed contemporaneously with the emplacement of the roof basalt. The basalts have geochemical characteristics of tholeiitic basalts with relatively high Mg# values (62.7–63.9), Cr and Ni, a slightly negative Eu anomaly (δEu = 0.75–0.87), and relatively low concentrations of Sr, Nb/Ta and (La/Yb)N. The dacite has characteristics similar to those of sanukite, in terms of high concentrations of Mg# values (52.7–53.0), a weakly negative Eu anomaly (δEu = 0.90–1.04), and low concentrations of Cr, Ni, Sr and (La/Yb)N. Hf isotope analysis in the basalt exhibits the εHf(t) value of (+9.68 to + 17.03). The two-stage Hf model age (TDM2) shows 259–727 Ma with an average of 500 Ma. These geochemical characteristics indicate that the deposit formed in the magmatic arc setting, whereas the basalt originated from young (regenerated) mantle material. Re/Os and common Os imply that crust-derived and S-rich sediments also contributed to the ore formation. Accordingly, based on the results of this study and review of the regional magmatic framework, we can conclude that the Ashele deposit is diplogenetic, with VMS epigenetic and hydrothermal mineralization expressed.

Geochemical Characterization of Al-Lith Coastal Sediments, Red Sea, Saudi Arabia

This study investigates the geochemistry of Al-Lith coastal sediments using the spatial distributions of grain size and of some environmentally sensitive chemical elements and their geochemical zonation. The results show that the sediments are characterized by a wide range of grain sizes and consist mainly of terrigenous and biogenic carbonate materials. Statistical analyses of the data show three main factors controlling the distribution of elements. They are grain size, mineralogical composition, and organic carbon content. According to the elemental associations and distributions, four geochemical zones are identified. Zones A and C are dominated by carbonate-rich sediments and high concentrations of Ca and Sr and lesser Mg. Zones B and D consist of sandy and muddy sediments with low carbonate contents and significant concentrations of Fe, Al, Mn, Ni, Co, Zn, Cr, and Cu. Elements show differences in partitioning trends, indicating varied elemental behaviors with environmental and sedimentological significance.

Improved voltammetric methodology for chromium redox speciation in estuarine waters

Chromium is a toxic element naturally present in natural waters whose chemical speciation regulates its cycling, mobility and bioavailability. We present here: 1- an improved analytical method for chromium speciation (Cr(VI) vs Cr(III)) in estuarine samples by catalytic adsorptive cathodic stripping voltammetric (cat-AdCSV) and 2- a study highlighting a significant change of redox speciation during summer and winter. Initial measurements first revealed that surface-active substances (SAS) present in estuarine samples strongly influenced the analytical determination of Cr by partially masking the Cr peak through an increase of the background current. We found that the application of a low negative accumulation potential (−1.65 V) resulted in much better voltammograms compared to those obtained using the usual accumulation potential of −1.0 V. Using humic acid (HA) as a model SAS of natural origin, we show that this negative potential clearly prevents adsorption of SAS on the Hg-electrode surface, which in turns benefits the adsorption of the in-situ formed Cr(III)-DTPA complex and the resulting signal. The optimised method was applied to determine chromium redox speciation and distribution along the 23 km long salinity gradient, well oxygenated, Krka River estuary (Croatia). Cr(VI) was found to be the dominant redox species in both summer and winter, with Cr(III) contribution being lower in summer (up to ∼30%, average of ∼5%) than in winter (up to ∼50%, average of ∼30%). In summer, lower concentrations of Cr(VI) were found in the freshwater end-member (2.5 nM) than in the seawater end-member (4–5 nM), while the opposite trend was found in winter. Hexavalent chromium exhibited a non-conservative behaviour along the salinity gradient for both seasons. Chromium predominantly exists in dissolved phase, and contribution of particles reactive Cr(III) was minor.

Effect of carbon on cryogenic tensile behavior of CoCrFeMnNi-type high entropy alloys

High entropy alloys (HEAs) with a face-centered cubic (fcc) structure are considered as promising structural materials, in particular due to their impressive ductility and toughness at cryogenic temperature; at the same time strength of these HEAs is often quite low. An addition of interstitial elements like carbon substantially increases the strength of the fcc HEAs at room temperature, however the effect of C on cryogenic properties has not been properly studied. Therefore in this work we examined cryogenic tensile behavior of the fcc high entropy alloys with different carbon content (0–2 at.%). The alloys had non-equiatomic proportions of principal elements, i.e. Co1Cr0.25Fe1Mn1Ni1. The lower Cr concentration in comparison with the equiatomic alloy led to the higher solubility of carbon confirmed by both ThermoCalc calculations and experimental results; only in the alloy with 2 at.% C a small (<1%) fraction of Cr-rich M7C3 carbides was found in the as-cast condition. The microstructure of the alloys was not significantly affected by the carbon content and generally consisted of coarse (250–300 μm) fcc phase grains with dendritic segregations. In turn, the carbon content influenced on mechanical behavior substantially: the strength of the alloys progressively increased with the carbon content along with some reduction in ductility. Solid solution strengthening by carbon at 77 K was much stronger than that at room temperature: 67 MPa/at% and 178 MPa/at%, respectively. The increase in solid solution strengthening agreed well with an anticipated increase in lattice friction at lower temperatures. Plastic deformation was associated with dislocations slip both at 293 K and 77 K; a decrease in temperature and an increase in the carbon concentration increased the inclination to planar slip. The obtained results offer new approaches to increase the cryogenic properties of fcc HEAs.

Facile preparation of amine-rich polyamidoamine (PAMAM) gel for highly efficient removal of Cr(VI) ions

The development of high-performance adsorbent towards toxic Cr(VI) ions is highly desired. Herein, we present a polyamidoamine (PAMAM) gel with porous structure and multiple amine groups for highly efficient removal of Cr (VI) ions. The gel is prepared in a single step based on the crosslinking reaction between the PAMAM and the epichlorohydrin. The adsorption property of resulted PAMAM gel towards toxic Cr(VI) ions was evaluated systematically with respect to the solution pH, NaCl, temperature, contact time, and initial concentration of Cr(VI) ions. At relatively low concentration of Cr(VI) ions (≤200 mg/L), the PAMAM gel exhibited very high removal efficiency (≥99.32%) towards Cr(VI) ions. The adsorption rate is fast and could reach equilibrium within about 60 min. The maximum adsorption capacity of PAMAM gel could reach as high as 267.4 mg/g. Furthermore, the adsorption data fitted well with the pseudo-second order kinetic model and Langmuir isotherm. After adsorption, the Cr(VI) ions-adsorbed PAMAM gel could be easily collected by filtration and the PAMAM gel presented nice desorption capability. Moreover, it still showed high adsorption capacity (202.15 mg/g) for Cr(VI) ions even after five cycles.

Correlation between Electrode Reaction and Chromium Deposition in SOFC Cathodes

In this study, Cr-poisoning in a SOFC mixed conducting cathode was investigated. To examine the influence of the electrode reaction systematically, a model patterned thin film electrode was used. La0.6Sr0.4CoO3-δ was chosen as the model cathode material. The LSC model electrode was exposed to Cr-containing oxygen at 973 K under a cathodic polarization. The Cr content in the feed gas was controlled by setting the temperature of a Cr-source at 973 K or 773 K. The degradation of the electrode performance was observed under both conditions. Deposits observed on the electrode surface were SrCrO4 for the higher Cr-concentration in the feed gas. On the other hand, deposits were Sr-compounds without detectable amount of Cr for the lower Cr-concentration. These results may indicate that not only the Cr-deposition but also the decomposition of the electrode material could be considerable causes for the Cr-poisoning in mixed conducting cathodes depending on the Cr-concentration.

Analysis of the effect of Chromium concentration (Cr) in welding electrodes on Carbon diffusion (C) at weld interface of ASTM A213 T22 material using metallographic and hardness testing methods

In joinning superheater pipes ASTM A213 T22 and ASTM A213 T91 by welding there is carbon diffusion from the parent metal ASTM A213 T22 to the weld seam. According to Nemoto’s research, this could occur because the Cr concentration in ASTM A213 T22 metal is lower than the Cr concentration in the electrode. Diffusion of carbon can reduce the mechanical properties of the parent metal so that it can cause the formation of type IV weld crack. This study aims to analyze the effect of Cr concentration in electrodes on the carbon diffusion on the ASTM A213 T22 parent metal interface. The metal is welded using the AWS A5.5 standard electrodes with the difference in Cr content and then followed by post weld heattreatment at a temperature of 750 o C for 5 hours. Metallographic and hardness test results showed that the electrode which have a greater Cr content than the parent metal caused carbon diffusion after heattreatment. Whereas those which have a lower Cr concentration than the parent metal did not cause carbon diffusion. The result proved that the diffusion of carbon on the weld of ASTM A213 T22 metal occured on an uphill basis, namely carbon diffusion occurs from lower Cr concentration to a higher Cr concentration metals. The result of this research are in line with the research of Darken and Nemoto where carbon diffusion occurs uphill due to changes in carbon chemical potential gradients caused by differences in concentration such as Cr or Si

Effects of chironomid larvae and Limnodrilus hoffmeisteri bioturbation on the distribution and flux of chromium at the sediment-water interface

The impacts of chironomid larvae and the tubificid worm Limnodrilus hoffmeisteri on the distribution and flux of the heavy metal chromium (Cr) across the sediment-water interface were investigated with a 21-day laboratory microcosm experiment. The two studied species feature different bioturbation modes involving bioirrigation and upward bioconveyance. The Cr concentrations in the overlying water and pore water were measured and compared using treatments with bioturbation by a single species and by combinations of both species and a treatment with no organisms. The results indicated that both bioturbation modes significantly increased the Cr concentrations in the overlying water and pore water. The overlying water had lower Cr concentrations than the pore water. Little variation in the Cr concentrations was observed in the treatment without organisms. Both species enhanced the Cr flux from the pore water to the overlying water. The worm treatments had a great impact on the Cr concentration in the overlying water through intensive upward conveyance activity, while the chironomid larvae treatments exerted significant effects on the Cr variation in the pore water and Cr flux across the interface via bioirrigation activity. These findings reveal the importance of bioturbation in biogeochemical processes in freshwater ecosystems.

Magneto-transport and magneto-optical properties of Cr-alloyed SnO2 thin films: A correlation between structural and magnetic behaviors

In this work, the tin oxide thin films alloyed with Cr up to 50 at.% were prepared via a spray pyrolysis method on the glass substrates, and their structural, magneto-optical and magneto-transport properties were studied. The results show that all the films are polycrystalline grown in a tetragonal rutile structure. A critical Cr concentration of about 15% was found concerning the lattice volume variations in SnO2:Cr films, as well as their magnetoresistance and magneto-optical properties suggesting a correlation between the structural and magnetic behaviors and indicating to two different mechanisms for Cr addition. For low Cr concentrations (less than 15%), the substitutional doping is the involving mechanism, while for more Cr concentrations, the interstitial one is predominant in the involved films.

Late Carboniferous to Early Permian adakitic rocks and fractionated I‐type granites in the southern West Junggar terrane, NW China: Implications for the final closure of the Junggar–Balkhash Ocean

The final closure of the Junggar–Balkhash Ocean resulted in the amalgamation of the circum‐Balkash–Junggar segments of the south‐western Central Asian Orogenic Belt, but the exact timing of its closure remains uncertain. Here, we use zircon U–Pb and whole‐rock chemical data for the adakitic rocks and fractionated I‐type granitoids in the Alashankou area of the southern West Junggar terrane (WJT) to investigate their petrogenesis and tectonic implications for the closure of the Junggar–Balkhash Ocean. The adakitic rocks were emplaced at 313–295 Ma and exhibit high Sr/Y ratios of 121–229. Their low MgO contents (0.91–2.09 wt%), Co, Cr, and Ni concentrations, initial 87Sr/86Sr ratios, and high εNd(t) values, indicate an origin from partial melting of juvenile lower crust under garnet‐amphibolite‐facies conditions triggered by basaltic underplating. By comparison, the fractionated I‐type granitic plutons (283–273 Ma) are weakly peraluminous and distinctive in terms of their low MgO contents (0.31–0.39 wt%) and strongly negative Nb, Ta, P, Eu, and Ti anomalies. These features, along with their higher initial 87Sr/86Sr ratios and lower εNd(t) values, suggest derivation by partial melting of a depleted mantle source and/or of newly underplated lower crust with crustal contamination. Given the Late Carboniferous depositional hiatus and post‐orogenic strike‐slip faulting and absence of post‐Devonian ophiolites and post‐Palaeozoic magmatic events in the WJT, the widespread occurrence of Late Carboniferous to Permian compositionally diverse granitoids (including the adakitic rocks, high‐Mg dioritic rocks, and I‐ and A‐type granitoids) and coeval mafic dykes can be best explained by a post‐collisional slab breakoff model. Together with other lines of geological evidence in the circum‐Balkash–Junggar area, we propose that the Junggar–Balkhash Ocean should have been closed at the beginning of the Late Carboniferous (~320 Ma), consistent with the closure time (~325–300 Ma) for regional major ocean basins.

The long-term effects of hexavalent chromium on anaerobic ammonium oxidation process: Performance inhibition, hexavalent chromium reduction and unexpected nitrite oxidation

The toxicity of hexavalent chromium (Cr(VI)) is one of the challenges in implementing Anammox process to ammonium-rich wastewater treatment. However, the response of Anammox process to Cr(VI) stress and the inhibition mechanism remain unclear. Here, two Anammox UASB reactors were operated for 285 days under different Cr(VI) stresses. The results showed Anammox performance was not affected at low Cr(VI) concentration (i.e., 0–0.5 mg L−1), but was severely inhibited at 0.8 mg L−1. Attempts to domesticate Anammox process to higher Cr(VI) by lowering nitrogen loading rate were failed. Examination of Cr(VI) fate showed the occurrence of extracellular and intracellular Cr(VI) reduction to Cr(III). The inhibition was ascribed to the significant intracellular Cr(VI) reduction, accounting for 99.78% of the total Cr(VI) reduction. Moreover, under long-term Cr(VI) exposure, most nitrite was oxidized to nitrate. But microbial community showed no enrichment of Cr(VI) reducing bacteria and other nitrogen transformation-related bacteria.

Charge fluctuations of a Cr atom probed in the optical spectra of a quantum dot

We study the emission of individual quantum dots in CdTe/ZnTe samples doped with a low concentration of Cr. In addition to dots with a photoluminescence (PL) split by the exchange interaction with a magnetic Cr atom, we observe another type of dots with a complex PL structure composed of a minimum of six lines on the exciton and biexciton and three lines on the charged excitons. In these dots, the linear polarization dependence and the magnetic field dependence of the PL behave like three similar quantum dots emitting at slightly different energies. Cross-correlation intensity measurements show that these emission lines are not independent but exchange intensities in a time scale of a few hundred nanoseconds depending on the optical excitation power. We attribute this PL structure to charge fluctuations of a Cr atom located in the vicinity the CdTe dots in the ZnTe barrier. We present a model which confirms that the presence of a single charge fluctuating between -e (Cr$^{+}$), 0 (Cr$^{2+}$) and +e (Cr$^{3+}$) and located a few nm away from the dot explains the observation of three emission energies. We finally show that the interaction between the confined carriers and the nearby fluctuating localized charge can be modified by an applied static electric field which modulates the splitting of the emission lines.

Metagenomic analysis of the inhibitory effect of chromium on microbial communities and removal efficiency in A2O sludge.

This is the first study exploring the effects of persistent Cr(VI) treatment on microbial communities and function as well as the process efficiency of an A2O system. The inhibitory effect was clearly higher at a high Cr(VI) concentration than a low Cr(VI) concentration, and different Cr(VI) concentrations had distinct effects on the microbial communities as well as on the performance efficiency of the system. Functional annotation analysis indicated that Cr(VI) stress inhibited most of the metabolic pathway and functional genes of the microbial communities, especially those involved in the denitrification pathway. Network analysis was used to investigate the co-occurrence patterns between denitrification genes and microbial taxa; the results indicated that microorganisms with functional genes had high diversity and were adversely affected by Cr(VI) exposure. This study is the first to establish a relationship between Cr(VI) stress and microbial communities and function as well as to determine the underlying mechanisms and roles of Cr(VI) in A2O sludge.

Iron-based nanoparticles prepared from yerba mate extract. Synthesis, characterization and use on chromium removal

Iron-based nanoparticles were synthesized by a rapid method at room temperature using yerba mate (YM) extracts with FeCl3 in different proportions. Materials prepared from green tea (GT) extracts were also synthesized for comparison. These materials were thoroughly characterized by chemical analyses, XRD, magnetization, SEM-EDS, TEM-SAED, FTIR, UV–Vis, Raman, Mössbauer and XANES spectroscopies, and BET area analysis. It was concluded that the products are nonmagnetic iron complexes of the components of the extracts. The applicability of the materials for Cr(VI) (300 μM) removal from aqueous solutions at pH 3 using two Cr(VI):Fe molar ratios (MR), 1:3 and 1:0.5, has been tested. At Cr(VI):Fe MR = 1:3, the best YM materials gave complete Cr(VI) removal after two minutes of contact, similar to that obtained with commercial nanoscale zerovalent iron (N25), with dissolved Fe(II), and with a likewise prepared GT material. At a lower Cr(VI):Fe MR (1:0.5), although Cr(VI) removal was not complete after 20 min of reaction, the YM nanoparticles were more efficient than N25, GT nanoparticles and Fe(II) in solution. The results suggest that an optimal Cr(VI):Fe MR ratio could be reached when using the new YM nanoparticles, able to achieve a complete Cr(VI) reduction, and leaving very low Cr and Fe concentrations in the treated solutions. The rapid preparation of the nanoparticles would allow their use in removal of pollutants in soils and groundwater by direct injection of the mixture of precursors.

Morphology-controlled fabrication of CNT@MoS2/SnS2 nanotubes for promoting photocatalytic reduction of aqueous Cr(VI) under visible light

Heavy metal pollution has become a global environmental problem. Industrial wastewater containing hexavalent chromium Cr(VI) is particularly harmful to the environment. Effective treatment of industrial wastewater containing Cr(VI) is still difficult. In this study, functionalized hybrid nanotubes, denoted as CNT@MoS2/SnS2, were developed for the photocatalytic reduction of low concentrations of Cr(VI). First, CNT@MoS2 hybrid nanotubes were synthesized by a one-step method. The hybrid nanotubes were coated with a sheet-like structure, which was conducive to the further assembly and growth of SnS2 nanosheets to give CNT@MoS2/SnS2 hybrid nanotubes. The hybrid nanotubes were able to absorb visible light and possessed a high photoelectron transport rate; as a result, they exhibited high photocatalytic activity under visible-light irradiation. The prepared CNT@MoS2/SnS2 hybrid nanotubes displayed higher photocatalytic activity than that of other photocatalytic materials because of their narrow band gap. Degradation of 50-mg/L Cr(VI) solution by CNT@MoS2/SnS2 under visible light showed that nearly 100% of Cr(VI) was removed within 90 min. The removal rate of Cr(VI) by SnS2 was 96.3% under the same conditions, and only 80% was removed by CNT@MoS2. Moreover, CNT@MoS2/SnS2 also completely removed Cr(VI) from 120-mg/L Cr(VI) solution in 90 min. These results indicate that CNT@MoS2/SnS2 shows potential for application in environmental remediation.

Magnetic Fe3O4 assembled on nZVI supported on activated carbon fiber for Cr(VI) and Cu(II) removal from aqueous solution through a permeable reactive column.

Magnetic Fe3O4 assembled on nanoscale zero-valent iron (nZVI) supported on an activated carbon fiber (ACF) to form nanoscale magnetic composites (nZVI-Fe3O4/ACF) for removing Cr(VI) and Cu(II) from aqueous solution through a permeable reactive column was synthesized via an in situ reduction method. The nZVI-Fe3O4/ACF composites and the interaction between nZVI-Fe3O4/ACF and both Cr and Cu ions were characterized by field emission scanning electron microscopy (FESEM) with EDX, TEM, XRD, and XPS. Batch experiments were used to analyze the effects of main factors on Cr(VI) removal and investigate the simultaneous removal of Cr(VI) and Cu(II) through a permeable reactive column. The results indicated that the ACF and Fe3O4 can inhibit the agglomeration and enhance the dispersibility of nZVI, and Fe3O4 and nZVI displayed good synergetic effects. The removal efficiency of Cr(VI) improved with the increase amount of Fe3O4 in the nZVI-Fe3O4/ACF composites. With low initial concentration of Cr(VI) and acidic conditions, ~ 90% of 20.0mg·L-1 Cr(VI) in the solution was removed after 60min. The removal of Cr(VI) was also affected by coexisting ions. The removal efficiency of 10.0mg·L-1 Cu(II) was ~ 100% after 45min of reaction, and the presence of Cu(II) can accelerate the reduction of Cr(VI). The simultaneous removal mechanisms of Cr(VI) and Cu(II) by the nZVI-Fe3O4/ACF composites also were proposed.

Geochemistry of Maastrichtian Clastic Sedimentary Rocks from Western Flank of Anambra Basin, Nigeria: Implications for Provenance, Tectonic Setting, Paleoclimate and Depositional Paleoenvironment

The geochemistry, provenance, tectonic setting, paleoclimate and depositional paleoenvironment of Maastrichtian clastic sedimentary rocks from the western flank of Cretaceous-Tertiary intracratonic Anambra Basin, Nigeria have been studied through major and trace element geochemical analysis. Ten (10) representatives outcrop samples collected from two stratigraphic sections in the study area were analyzed chemically using Inductively Coupled Plasma Atomic Emission Spectroscopy, ICP-AES (Lithium Borate Fusion). The geochemical data shows that the sediments are enriched in major oxides including SiO2, Al2O3, Fe2O3 and TiO2 but depleted in other major element oxides. Also, the sandstones have higher concentrations in SiO2, CaO and Na2O compared to the associated mudrocks whereas the mudrocks are more enriched in Al2O3, Fe2O3, MgO, K2O, TiO2 and P2O5 compared to the sandstones. The mudrock samples have higher concentration of Ba, Ni, Sr, Y, Nb, Sc in comparison to sandstones. However, sandstone samples have higher concentration in Zr (1098.50 ppm) than the mudrocks (1038 ppm). The sandstones are classified as litharenites, sublitharenites, Fe-rich sandstones, while the mudrocks are labeled as shale and Fe-rich shale based on chemical composition. Analysis of the data shows a dominantly felsic igneous to intermediate igneous and quartzose sedimentary provenances of mixed granite and granodiorite composition as indicated by various discriminant plots. The inferred provenance is corroborated by the low concentrations of Cr, Ni and Sc in the samples and other proxies. On the basis of various tectonic setting discriminant function diagrams, the Maastrichtian sediments from the study area were deposited on passive margin tectonic setting that developed consequent to the breakup of Gwandana supercontinent but was later affected by tectonism in Santonian times. The alteration feldspars to smectite and kaolinite as depicted by the A-CN-K ternary diagram alongside the high values of chemical index of alteration (CIA, 87.38 - 98.09) and chemical index of weathering (CIW, 89.22 - 99.90) indicates paleogeographic setting characterized by warm and humid/tropical paleoclimatic condition where there was prevalence of intense chemical weathering. The low values of Sr/Ba ratio (0.31 - 0.70) suggest sediment deposition in continental to deltaic paleoenvironment.

Influence of Cr Content on Cellular Precipitation Behaviour of Ni-38Cr-3.8Al Alloy with Lamellar Structure

Ni-Cr binary alloys containing high amount of Cr demonstrate gamma/alpha-Cr lamellar structure by discontinuous precipitation (DP) reaction from grain boundary. The mechanism of DP reaction is caused by supersaturated Cr in the gamma phase. Supersaturated Cr concentration influences the driving force for the DP reaction and the lamellar spacing. Moreover, the Ni-based alloys with high Cr, containing Al, significantly increase the hardness and strength due to the very narrow lamellar structure. Al addition brings on Ni consumption in the matrix by precipitation of the gamma prime phase. Therefore, Cr supersaturates dramatically in the matrix. The wrought Ni-Cr-Al alloy, Ni-38Cr-3.8Al (mass%) , reaches extremely high tensile strength, which is over 2 GPa, after annealing treatment. Even though chemical composition of Ni-38Cr-3.8Al is simple, the microstructure is complex because it consists of the gamma/alpha Cr lamellar structure with the fine gamma prime particles. Therefore, in this study, we investigated the influence of Cr concentration on the cellular precipitation behaviour. In order to understand the influence of Cr concentration, Ni-34, 36 and 38Cr-3.8Al alloys were prepared. Forged bars were subjected to solution treatment in the gamma single phase region. Subsequently, the alloys were aged from 873K to 1073 K for various times. The cellular precipitation reaction is suppressed by a decrease in Cr concentration, particularly at low temperature annealing treatment condition. The hardness is low in lower Cr concentration alloys in all range of annealing treatment temperature. These results indicate that Cr concentration remarkably affects the driving force for the DP reaction.

Facile Functionalization of Natural Peach Gum Polysaccharide with Multiple Amine Groups for Highly Efficient Removal of Toxic Hexavalent Chromium (Cr(VI)) Ions from Water.

The development of low-cost adsorbent with excellent adsorption property remains a big challenge. Herein, the functionalization of natural peach gum polysaccharide (PGP) with multiple amine groups for the removal of toxic Cr(VI) ions from water was studied. The obtained PGP-NH2 gel exhibited high-removal efficiency (>99.5%) toward Cr(VI) ions, especially with relatively low initial concentration of Cr(VI) ions (≤250 mg/L). The influences of pH, ionic strength, contact time, initial concentration, and temperature on the adsorption of Cr(VI) ions were systematically investigated. The PGP-NH2 gel showed rapid adsorption rate and could reach adsorption equilibrium within about 40 min. The Cr(VI) ion uptake process could be described by pseudo-second-order kinetic and Langmuir isotherm models. The maximum adsorption capacity of PGP-NH2 gel could reach 188.32 mg/g. Thermodynamic investigation results indicated the spontaneous and exothermic characteristic of the uptake process. Moreover, the PGP-NH2 gel also exhibited favorable reusability, and 135.52 mg/g of adsorption capacity was retained even after being reused for five times. Considering its low cost and superior uptake property, the PGP-NH2 gel holds a great promise for employing as an adsorbent to treat Cr(VI) ion-containing wastewater.