• Journal of Wetlands Research
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• v.19 no.2
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• pp.246-251
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• 2017

This study was carried out to evaluate the possibility of Chromium removal by 3 different kinds of adsorbents, where activated carbon(AC), carbon nanotube(CNT) and layered double hydroxides(LDHs) were employed. The highest surface area was shown in AC and pore volume was in CNT which were $1028.1m^2{\cdot}g^{-1}$ and $0.829cm^2{\cdot}g^{-1}$, respectively. AC and CNT are composed of more than 99% carbon. AC has shown the possibility of chromium removal more than 80.2% under the acidic pH condition.

• Clean Technology
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• v.7 no.1
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• pp.75-80
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• 2001

In this study, hexavalent chromium (Cr(VI)) plating wastewater in strong acidic condition was treated by reduction and alkalization. Ferrous sulfate ($FeSO_4$), known to reduce Cr(VI) to Cr(III) rapidly at acidic pH, was used as a reductant of Cr(VI). The optimum reduction condition of Cr(VI) was observed at iron to chromium dose ratio of 3:1 by mole concentration. The precipitation of Cr(III) as $Cr(OH)_3$, was achieved by the pH adjustment in the limestone aeration bed. The precipitates were removed less than the upper limit of chromium for effluent at pH over 5.0. The continuous removal of Cr(VI) was performed using the process consisting of reduction vessel, limestone aeration bed, and sedimentation tank coupled with metal screen membrane. As pH was maintained around 5.0 in the limestone aeration bed, insoluble chromic hydroxide flocs was formed continuously. Most chromic hydroxide flocs were filtered by the metal screen membrane with 1450 mesh size, and the treated water to meet the upper limits of chromium for effluent (Cr Conc. 0.25~0.90 mg/l) was obtained in 30 minutes. Periodic backwashing decreased the fouling on the membrane rapidly.

• Resources Recycling
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• v.1 no.1
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• pp.23-28
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• 1992

The process for recovery of acids and valuable metals such as nickel and chromium from the stainless-steel pickling acids has been developed vased on the use of solvent extraction technique. Until now, several processes for the treatment of waste acids were already developed in such countries as Japan, Swden and Canada. Those methods are, however, forcussed on the recovery of acids from them discarding the metals included in them as the hydroxides sludge. In the present work, the recovery of nickel and chromium in addition to nitric acid and hydrofluoric acid has been aimed so as to recycle them to the stainless-steel pickling lines and also to minimize the amount of sludge generated during the treatment of waste acids. The establishment of the process to recover the acids has been carried out based on the solvent extraction with TBP. The iron was eliminated from the waste solutions by precipitating in the form of hydroxide through the adjustment of pH with calcined limestone and the selective extration of chromium and nickel from the resultant solutions has been conducted by using D2EHPA as extractant.

• Journal of the Korean Solar Energy Society
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• v.33 no.4
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• pp.31-38
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• 2013

The chemical composition of the black Cr solar selective coatings electrodeposited were investigated for property analysis by using a XPS(X-ray photoelectron spectroscopy) before and after annealing in air at $300^{\circ}C{\sim}500^{\circ}C$ for 120 hours. Black Cr selective coating exposed by solar radiation for 5 months was compared with annealed sample. In addition, The Cu solar selective coatings were prepared by thermal oxidation method for low temperature application. The samples obtained were characterized by using the optical reflectance measurements by using a spectrometer. Optical properties of oxidized Cu solar coatings were solar absorptance $({\alpha}){\simeq}0.62$ and thermal emittance $({\epsilon}){\simeq}0.41(100^{\circ}C)$. In the as-prepared Cr black selective coating, the surface of the coating was found to have Cr hydroxide and Cr. The Cr hydroxide of the major component was converted to $Cr_2O_3$ or $CrO_3$ form after annealing at $500^{\circ}C$ with the desorption of water molecules. The black Cr selective coating was degraded significantly at temperature of $500^{\circ}C$. The main optical degradation modes of this coating were diffusion of Cu substrate materials.

• Journal of the Korean Applied Science and Technology
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• v.33 no.3
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• pp.441-448
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• 2016

Heavy metal removal study is conducted from synthetic waste water by reduction and oxidation(redox) reaction of Cu-Zn metal alloy and adsorption reaction of aluminium silicate. Heavy metal whose ionization tendency is smaller than zinc are reducted in an aqueous solution, and the concentration of ionized zinc is reduced by adsorption reaction. The average diameter of metal alloy micro fiber is about $200{\mu}m$, and the surface area is wide enough to get equilibrium in a single cycle treatment. A single cycle treatment of redox reaction of Cu-Zn metal alloy, could remove 100.0 % of Cr(III), 98.0 % of Hg, 92.0 % of Sn and 91.4 % of Cu respectively. An ionization tendency of chromium is very close to zinc, but removal efficiency of chromium by redox reaction is significant. This result shows that trivalent chromium ion is expected to generate hydroxide precipitation with $OH^-$ ion generated by redox reaction. Zinc ion generated by redox reaction is readily removed by adsorption reaction of aluminium silicate in a single cycle treatment. Other heavy metal components which are not perfectly removed by redox reaction also showed very high removal efficiency of 98.0 % or more by adsorption reaction. Aluminium ion is not increased by adsorption reaction of aluminium silicate. That means heavy metal ion removal mechanism by adsorption reaction is turned out to be not an ion exchange reaction, but an adsorption reaction.

• Journal of Korean Society of Environmental Engineers
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• v.29 no.12
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• pp.1381-1389
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• 2007

Wastewater discharged by industrial activities of metal finishing and electroplating units is often contaminated by a variety of toxic or otherwise harmful substances which have a negative effects on the water environment. The treatment method of heavy metal-cyanide complexes wastewater by alkaline chlorination have already well-known($1^{st}$ Oxidation: pH 10, reaction time 30 min, ORP 350 mV, $2^{nd}$ Oxidation: ORP 650 mV). In this case, the efficiency for the removal of ferro/ferri cyanide by this general alkaline chlorination is very high as 99%. But the permissible limit of Korean waste-water discharge couldn't be satisfied. The initial concentration of cyanide was 374 mg/L(the Korean permissible limit of cyanide is 1.0 mg/L max.). So a particular focus was given to the treatment of heavy metal-cyanide complexes wastewater by $Zn^{+2}/Fe^{+2}$ ion and coprecipitation after alkaline chlorination. And we could meet the Korean permissible limit of cyanide(the final concentration of cyanide: 0.30 mg/L) by $Zn^{+2}/Fe^{+2}$ ion and coprecipitation(reaction time: 30 min, pH: 8.0, rpm: 240). The removal of Chromium ion by reduction(pH: 2.0 max, ORP: 250 mV) and the precipitation of metal hydroxide(pH: 9.5) is treated as 99% of removal efficiency. The removal of Copper and Nickel ion has been treated by $Na_2S$ coagulation-flocculation as 99% min of the efficiency(pH: $9.09\sim10.0$, dosage of $Na_2S:0.5\sim3.0$ mol). It is important to note that the removal of ferro/ferri cyanide of heavy metal-cyanide complexes wastewater should be employed by $Zn^{+2}/Fe^{+2}$ ion and coprecipitation as well as the alkaline chlorination for the Korean permissible limit of waste-water discharge.

• Journal of the Korean Society of Food Culture
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• v.19 no.6
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• pp.691-700
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• 2004

This study was conducted to examine the proximate composition, alginic acid and mineral contents and the types of calcium and magnesium in the parts(frond, stipe, sporophyll) of sea mustards. Carbohydrates and the crude fat was the highest in sporophyll. The contents of alginic acid were $25.9{\sim}32.2%$. Total alginic acid(32.2%) and insoluble alginic acid in water(27.7%) was e highest in sporophyll. Calcium and magnesium was the highest in frond. Phosphorous, potassium and sulfur was the highest in sporophyll. Iron, zinc and mangane was the highest in frond. Ca/P ratio in frond and stipe was about $1.7{\sim}1.8:1$ levels. Calcium and magnesium soluble in sodium chloride was the highest in sea mustards. Calcium and magnesium soluble in water was the highest in frond. Calcium and magnesium soluble in hydrochloric acid was the highest in sporophyll.

• Clean Technology
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• v.8 no.3
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• pp.151-165
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• 2002

In the treatment of the wastewater containing metals($Cu^{2+}$, $Zn^{2+}$, $Ni^{2+}$, $Cr^{3+}$) by using batch precipitation and flocculation followed by membrane filtration, permeate flux and removal efficiency were investigated according to by the effect of pH and coagulants, and the type of membranes used and pore size. It was found that it is most effective to use $0.45{\mu}m$-polysulfone membrane and coagulant(PAC) at the conditions of the pH of 10.0~10.5 for the case of copper containing wastewater, $0.1{\mu}m$-PVDF membrane and coagulant(PAC) at the conditions of the pH of 10.0~10.5 for the case of zinc containing wastewater, $0.1{\mu}m$-PVDF membrane and coagulant at the conditions of the pH of 11.0~11.5 for the case of nickel containing wastewater, $0.2{\mu}m$ membrane and coagulant at the conditions of the pH of 8.0~8.5 for the case of chromic containing wastewater, and $0.2{\mu}m{\sim}0.45{\mu}m$ membrane and coagulant at the conditions of the pH of 11.0~11.5 for the case mixture wastewater. The permeate flux could higher as to be used coagulants except for the case of copper containing wastewater.