• Membrane and Water Treatment
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• v.10 no.4
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• pp.259-264
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• 2019

Cost effective clay adsorptive microfiltration membranes were synthesized to remove Cr (III) from high polluted water. Raw and calcined bentonite were mixed in order to decrease the shrinkage and also increase the porosity; then, 20 wt% of carbonate was added and the samples, named B (without carbonate) and B-Ca20 (with 20 wt% calcium carbonate) were uniaxially pressed and after sufficient drying, fired at $1100^{\circ}C$ for 3 hours. Then, physical and mechanical properties of the samples, their phase analyses and microstructure and also their ability for Cr(III) removal from high polluted water (including 1000 ppm Cr (III) ions) were studied. Results showed that the addition of calcium carbonate lead the porosity to increase to 33.5% while contrary to organic pore formers like starch, due to the formation of wollastonite, the mechanical strength not only didn't collapse but also improved to 36.77 MPa. Besides, sample B-Ca20, due to the presence of wollastonite and anorthite, could remove 99.97% of Cr (III) ions. Hence, a very economic and cost effective combination of membrane filtration and adsorption technology was achieved for water treatment which made microfiltration membranes act even better than nanofiltration ones without using any adsorptive nano particles.

• Analytical Science and Technology
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• v.8 no.3
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• pp.299-304
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• 1995

The adsorption behaviors of Ba(II), Cr(II), Fe(II) and Cu(II) on the N, N'-bispalmtoyl 1, 12-diaza-3, 4:9, 10-dibenzo-5, 8-cyclopentadecane (hexadecyl $NtnOenH_4$)-octadecylsilanized silicas(ODS) were investigated with water as the mobile phase. Binding constants for metal ions were measured in aqueous solution. The order of binding constants(K) and the degree of sorption(E) were Ba(II)$NtnOenH_4$-octadecyisiianized silicas(ODS) increased with concentration of metal ions, and the degree of adsorption was found to be affected by the cation-chelation mechanism. The experimental results showed good efficiency for separation of Cu(II) from mixtures of Ba(II), Cr(II), Fe(II) and Cu(II) in aqueous solution.

• Journal of the Korean Chemical Society
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• v.25 no.4
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• pp.270-274
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• 1981

Al(III) and Cr(III) were determined selectively by colorimetry of Bismark Brown R {4,4'[(4-methyl-1,3-phenylene)bis(azo)]-bis(6-methyl-1,3-benzenediamine) dihydrochloride} in the presence of the various cations and anions without the using of any masking agents, but tartrate and citrate ions were interfered. The ligand of Bismark Brown R and complexes of Al(III) and Cr(III) were shown the maximum absorbance at the same wavelength together and both metallic ion were interfered to determine each other, but Al(III) were able to determine after oxidation of Cr(III) to Cr(VI).

• Journal of the Mineralogical Society of Korea
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• v.26 no.3
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• pp.151-160
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• 2013

A column experiment was carried out to study the reaction of Cr(VI) with organic carbon. Chemical analysis for the effluent collected at different times after the reaction of Cr(VI) with organic carbon in compost and SEM observation for the solid samples remaining after the reaction were conducted. Cr(VI) supplied to the column was not detected in the effluent from column at initial stage, but the concentration of Cr(VI) increased abruptly and maintained the initial supplied concentration (20 mg/kg), indicating that Cr(VI) was effectively removed from the solution at the first state. In general, the concentrations of cations and anions with the exception of $PO_4$ increased and decreased again. Considering that most of these ions were not detected or showed very low concentration, these ions are considered to originate from the organic carbon in the column. SEM observation showed that Cr was coprecipitated with Fe on the surface of organic carbon with small amount of other metals such as Mn, No, and Co. This indicated that on the reduction condition on the organic carbon, Cr(VI) was reduced to $Cr(OH)_3$ and coprecipitated with $Fe(OH)_3$, and that Fe is very important in the precipitation of Cr. After the soluble Fe and Mn are not dissolved any more, $Cr(OH)_3$ is not precipitated. Different from other ions, the concentrations of $PO_4$ decreased and increased, which was thought to be the result of the release of $PO_4$ from organic carbon and sorption on the precipitates. After the maximum sorption on the precipitates and no further release of Fe, the concentration of $PO_4$ returns to its original value measured for the ones released from the organic carbon.

• Journal of Environmental Science International
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• v.5 no.6
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• pp.779-783
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• 1996

Cation exchange distribution coefficients of poly(dithiocarbamate) were presented for $Cd^{2+}$, $Cr^{3+}$, and $Pb^{2+}$ in HCI. The distribution coefficients were determined tv using the batch method. Based on these distribution data, the separation possibilities of the heavy metal ions were discussed. The distribution coefficients of three heavy metal ions on dithiocarbamate resin were decreased as HCI concentrations were increased. The selective separation of $Cr^{3+}$ and $Cd^{2+}$ was possible by using 0.1M HCl in dithiocarbamate resin and the reproducibility test showed that the average absorptivity of resin was 90% in the case of $Cd^{2+}$ ion by the column method.

• Bulletin of the Korean Chemical Society
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• v.28 no.11
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• pp.1985-1992
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• 2007

Ordered mesoporous silica (MCM-41) materials with different textural properties were prepared using alkyl (dodecyl, cetyl, eicosane) trimethyl ammonium bromide (DTAB, CTAB, ETAB, respectively) as structure directing surfactants, functionalized with amine groups and used as adsorbent for the toxic metal ions, Cr (VI), As (V), Pb (II) and Hg (II). Amino functionalization of mesoporous MCM-41 was achieved by cocondensation of N-[3-(trimethoxysilyl)-propyl] aniline with tetraethyl orthosilicate. Adsorption isotherm and adsorption capacity of the amine functionalized materials for Cr (VI), As (V), Pb (II) and Hg (II) ions were followed by inductively coupled plasma mass spectrometry (ICP-MS). Results demonstrate that amine functionalized MCM-41 prepared with ETAB showed higher adsorption capacity for Cr (VI), As (V), Pb (II) and Hg (II) ions in comparison to MCM-41 prepared with CTAB and DTAB. The higher adsorption capacity for MCM-41(ETAB) was correlated with amine content in the material (determined by CHN analysis) and relative decrease in pore volume and pore diameter. X-ray diffraction (XRD) analysis, nitrogen adsorptiondesorption measurements and Fourier Transform infrared spectrometry (FTIR) were used to follow the changes in the textural parameters and surface properties of the mesoporous materials as a result of amine functionalization to correlate with the adsorption characteristics. The adsorption process was found to depend on the pH of the medium.

• Korean Journal of Materials Research
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• v.12 no.3
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• pp.220-224
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• 2002

The oxide scales formed on $Ni_3Al$-7.8%Cr-1.3%Zr-0.8%Mo-0.025%B after oxidation at 900, 1000 and 110$0^{\circ}C$ in air were studied using XRD, SEM, EPMA and TEM. The oxide scales consisted primarily of $NiO,\; NiAl_2O_4,\;{\alpha}-Al_2O_3,\; monoclinic-ZrO_2,\; and \;tetragonal-ZrO_2$. The outer layer of the oxide scale was rich in Ni-oxides, whereas the internal oxide stringers were rich in Al-oxides and $ZrO_2$. Within the above oxide scales, Cr and Mo tended to exist as dissolved ions.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.218-218
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• 2012

Recently, hexagonal manganites have attracted much attention because of the coexistence of ferroelectricity and antiferromagnetic (AFM) order. The crystal structure of hexagonal manganites consists of $MnO_5$ polyhedra in which $Mn^{3+}$ ion is surrounded by three oxygen atoms in plane and two apical oxygen ions. The Mn ions within Mn-O plane form a triangular lattice and couple the spins through the AFM superexchange interaction. Due to incomplete AFM coupling between neighboring Mn ions in the triangular lattice, the system forms a geometrically-frustrated magnetic state. Among hexagonal manganites, $YMnO_3$, in particular, is the best known experimentally since the f states are empty. In addition, for applications, $YMnO_3$ thin films have been known as promising candidates for non-volatile ferroelectric random access memories. However, $YMnO_3$ has low magnetic order temperature (~70 K) and A-type AFM structure, which hinders its applications. We have synthesized $YMn1_{-x}Cr_xO_3$ (x = 0, 0.05 and 0.1) samples by the conventional solid-state reaction. The powders of stoichiometric proportions were mixed, and calcined at $900^{\circ}C$ for $YMn1_{-x}Cr_xO_3$ for 24 h. The obtained powders were ground, and pressed into 5-mm-thick disks of 1/2-inch diameter. The disks were directly put into the oven, and heated up to $1,300^{\circ}C$ and sintered in air for 24 h. The phase of samples was checked at room temperature by powder x-ray diffraction using a Rigaku Miniflex diffractometer with Cu $K{\alpha}$ radiation. All the magnetization measurements were carried out with a superconducting quantum-interference-device magnetometer. Our experiments point out that the Cr-doped samples show the characteristics of a spin-glass state at low temperatures.

• Journal of Magnetics
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• v.12 no.4
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• pp.137-140
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• 2007

We have studied the temperature dependent magnetic properties and crystalline phase transitionn in small amount Fe doped nickel chromite. The Crystalline structure of $NiCr_{1.7}Fe_{0.3}O_4$ is spinel cubic (Fd-3m) structure with a lattice constant $a_0=8.317\AA$ at room temperature. The magnetic $N\acute{e}el$ temperature $(T_N)$ of the Fe doped nickel chromite sample is determined to be 250 K. The $M\ddot{o}ssbauer$ spectra exhibit that there are two magnetic phases with the two different sites for the $Cr^{3+}$ ions. The spectrum at 4.2 K is fitted to two magnetic components of the magnetic hyperfine fields $H_{hf}=496$ and 485 kOe. From the spectrum at 295 K, the electric quadrupole splittings are observed with large values of 0.49 and 0.50 mm/s, respectively. The values of the isomer shifts at all temperature ranges show that the Fe ions are ferric states. We are suggested that the dynamic Jahn-Teller distortion and anisotropic magnetic relaxation effects due to the crystalline phase transition.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2014.11a
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• pp.214-214
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• 2014

Computational analysis of aqueous solution stability of Fe-Cr-Ni system to find an electroplating condition of Fe-Cr-Ni layer. Aqueous sulfate solution with iron, chromium and nickel ions was selected by using a numerical S/W with which aqueous solution stability was analyzed. Several possible conditions to perform electro-forming of Fe-Cr-Ni were selected with thermo-dynamical data. The Fe-Cr-Ni system was electro-formed which composition and microstructure of the electroplated Fe-Cr-Ni significantly depended on the solution temperature and electro-potential. The final composition of Fe-3%Cr-48%Ni with less than $30{\mu}m$ thick was well electroplated.