Papers by Keyword: Chromium

Abstract: The present work assess the capability of silicon oxide (SiO₂) nanoparticle and microparticle incorporated in poly (vinyl alcohol)/chitosan/silicon oxide (PVA/CS/SiO₂) beads to reduce chromium (Cr) ions of Cr (VI) to Cr (III). PVA/CS/(nanoand micro)-SiO₂ beads were prepared through a simple drop wise method. The elemental analysis of prepared photocatalytic beads were confirmed by scanning electron microscopy-energy dispersive x-ray spectroscopy (SEM-EDX) and morphology of PVA/CS/SiO₂ beads before and after Cr ions reduction were observed with SEM. The reduction of chromium (Cr (VI)) ions by both of PVA/CS/(nanoand micro)-SiO₂) beads, as evaluated by the reduction duration taken were studied by photocatalytic process in which factors of SiO₂ powders size and pH of reducing environment were varied. Photocatalytic studies revealed better performance of PVA/CS/nanoSiO₂ beads in compared to PVA/CS/micro-SiO₂ beads in Cr (VI) to Cr (III) ions reduction. Reduction Cr (VI) to Cr (III) ions by PVA/CS/nanoSiO₂ beads occurred in 30 minutes and 50 minutes by PVA/CS/micro-SiO₂. Moreover, both PVA/CS/(nanoand micro)-SiO₂ showed excellent reduction of Cr (VI) ions at lower pH environment. It is thus concluded that both of PVA/CS/(nanoand micro)-SiO₂ beads are capable for chromium reduction in highly acidic environment in which PVA/CS/nanoSiO₂ beads showed better performance.

Abstract: The core-nanoshell composite materials with magnetic fly-ash hollow cenosphere as core and nanoLaFeO₃ as shell were synthesized by high-energy ball milling method. The samples were characterized by XRD, SEM and VSM. The results show that the core-nanoshell composite materials were prepared successfully. As the exchange-coupling interaction happens between ferrite of magnetic fly-ash hollow cenosphere and nanosized ferrite coating,the remanence and the coercivity improves, so it is better for core-nanoshell to adsorb heavy metals. The adsorption-magnetic separation processing were used for Cr (VI) of heavy metals in water, by atomic absorption spectrometry to measure ion concentration after adsorption. Batch experiments were carried out to investigate the effect of solution pH on the adsorption as well as adsorption kinetics and adsorption isotherm. The results show that at pH 2, obtain the maximum removal rate. The adsorption data were better fitted for the Freundlich model,indicating that the adsorption of Cr (VI) preferably follows multilayer and heterogeneous adsorption process. Compared with two kinetic models linear fitting parameters, adsorption conforms to pseudo secend-order kinetic model well,revealing chemisorption as the dominant mechanism.

Abstract: ArcGIS analysis was applied to study the concentrations and spatial distribution characteristics of Cr and Ni in surface soil (0~20cm) of corn belt in Dehui—the typical area of black soil in Jilin province. The average concentrations of Cr and Ni were 49.85 mg·kg^-1 and 20.85 mg·kg^-1, which were both lower than the corresponding background value and thus in no pollution level. The trends for soil Cr and Ni were similar with higher concentrations trending N-S across the centre of the study area, while the other hotspots were located in the southwest of Dehui. There was prominent correlation between Cr and Ni in 0.01 level, indicating the close relationship of them. The method based on the geostatistical analysis in ArcGIS can exactly reflect the character of spatial distribution of heavy metals.

Abstract: Adsorption ability of chromium in wastewater by purified diatomite as the adsorbent material was studied. The influence of the diatomite dosage, adsorption time, chromium concentration, pH value and reaction temperature to chromium removal rate was got. The results show that under the condition of the diatomite dosage of 9.0g, adsorption time of 90 min, chromium concentration in wastewater of 5mg/L, wastewater pH of 6, and temperature of 30°C, diatomite adsorption removal rate to hexavalent chromium can reach 91.6%. The main adsorption mechanism is the combination of physical adsorption and chemical adsorption, and the latter is dominant. The cost of diatomite as adsorbent is low, and a good removal rate of chromium can be reached, which provides a solid theoretical basis for the removal of chromium in wastewater.

Abstract: The room-temperature ferromagnetism of Cr-doped cerium oxide (Ce_0.96Cr_0.04O_2δ) nanopowders synthesized using a sol-gel process is reported in this paper. XRD and Raman spectroscopy confirm that the Cr atoms successfully displaced some of the Ce atoms in the CeO₂ lattice without forming any impure phases. The results also confirmed that all calcined samples exhibited a single-phase fluorite structure. The crystallite size (as confirmed by XRD) and the particle size (as confirmed by Raman spectroscopy) increased as the calcination temperature increased. Magnetic measurements indicated that the room-temperature ferromagnetism of the sample was sensitive to the calcination temperature. When the calcination temperature increased, the saturation magnetization decreased while the coercivity increased, which corresponds to less dense and larger particles. The calcined sample at 400°C exhibited superior magnetic properties with the highest saturation magnetization (M_s) of 2.5 × 10^-2 emu/g (H_c ~ 1.27 kOe). The results of the Raman and X-ray photoelectron spectroscopies suggest that the nature of the observed room temperature ferromagnetism in the samples are likely a result of the oxygen vacancies induced by Cr-doping in CeO₂.

Abstract: Reduction and immobilization of Cr (VI) as Cr₂O₇^2- is investigated by using metakaolinite-based geopolymer complexed reductant. Without reductants, the leached Cr concentration from metakaolinite-based geopolymer containing Cr (VI) is very high. Adding reductants as FeCl₂·4H₂O, FeSO₄·7H₂O, and Na₂S·9H₂O respectively during geopolymerization, the leached Cr concentration is below 5 mg L^-1 with high Cr immobilization rate above 99 %. By comparison with the immobilization of Cr (III), the added reductants reduced Cr (VI) to Cr (III) which can be locked successfully in the amorphous structure of geopolymer. Meanwhile, Cr (VI) initial concentration is lower than 0.7 wt. % in metakaolinite-based geopolymer, the above reductants can all meet the requirements. While for Cr (VI) initial concentration larger than 0.7 wt. %, Na₂S·9H₂O is more appropriate. Such a simultaneous reduction and immoboilization process enables the feasibility of using metakaolinite-based geopolymer complexed reductant to implement a one-step procedure for chromite ore processing residue cleanup.

Abstract: Various problems related to pollution of soil and groundwater caused by toxic oxyanion have been actualized in recent years. In particular, the enlargement of the polluted area by diffusion of chromate ions has been a worry in Japan, and arsenic pollution of well water is also a serious problem in South Asia nations. Removal process of chromate and arsenic in aqueous solution using 14CaO·5Al₂O₃·6ZnO, which is an easy-to-use method technically, has been investigated in our laboratory. The results obtained are summarized as follows: 1) Oxyanion of chromium and arsenic such as CrO₄^2-, AsO₃^3- and AsO₄^3- ions are able to be removed from aqueous solution by addition of 14CaO·5Al₂O₃·6ZnO, however, the removal rate of those arsenic ions are much lower than that of CrO₄^2-. 2) Removal of CrO₄^2- from aqueous solution is caused by the immobilization to 3CaO·Al₂O₃·CaCrO₄·12H₂O, on the other hand, both AsO₃^3- and AsO₄^3- mainly occurred by the adsorption to unhydrated 14CaO·5Al₂O₃·6ZnO. 3) Simultaneous use of 14CaO·5Al₂O₃·6ZnO and calcium hydroxide is an effective method in the removal of CrO₄^2-, AsO₃^3- and AsO₄^3- from aqueous solution.

Abstract: The distribution, enrichment, accumulation, and potential ecological risk of chromium (Cr) in the surface sediments of Anping Harbor, Taiwan, were investigated. Sediment samples from ten locations were collected and characterized for Cr, aluminum, water content, organic matter, and grain size. The results show that samples collected at all monitoring points contain 23.3–881.3 mg/kg of Cr with an average of 250.0±265.4 mg/kg. The spatial distribution of Cr reveals that the Cr concentration is relatively high in the Bamboo River mouth region, and gradually diminishes toward the harbor region. This indicates that upstream industrial and municipal wastewater discharges along the river bank are major sources of pollution. Results from the enrichment factor and geo-accumulation index analyses imply that the Bamboo River mouth sediments can be characterized as severe enrichment and moderate to strong accumulation of Cr, respectively. However, results of potential ecological risk index indicate that the sediment has low ecological potential risk. The results can provide valuable information to developing future strategies for the management of river mouth and harbor.

Abstract: Steel alloyed by nickel, chromium and molybdenum reach according to normative standards (EN) yield point about 900 MPa and contraction about 25% after heat treatment. Authors of this paper noticeably increase the strength properties of that steel without changes in plastic properties with using of electroslug remelting refining technology (ESR). Subject of research are forgings of very large mass and dimensions. The forgings are used in special armament technology as (tank gun barrels). Very negative influence on mechanical properties of final product has content of nanodimensioned impurities.

Abstract: In the present study, organic-inorganic hybrid mesoporous material (HMC) were used to optimize the removal rate for Cr (VI) by applying Response Surface Methodological approach. Batch mode experiments were also carried out to assess the adsorption equilibrium in aqueous solution. The effect of three parameters, that is pH of the solution (1.52.5), initial concentration (100500 mg/L) and adsorbent dose (0.050.15 g/ 50 mL) was studied for the removal of Cr (VI) by HMC. BoxBehnken model was used as an experimental design. The optimum pH, adsorbent dose and initial Cr (VI) concentration were found to be 2.0, 0.05 g/L and 500 mg/L, respectively. Under these conditions removal adsorption capacity of Cr (VI) was found to be 337..