Effects of Organic Matter and pH on Chromium Oxidation Potential of Soil

Chung, Jong-Bae,Eum, Jin-Sup 한국환경농학회 2001 한국환경농학회지 Vol.20 No.5

Oxidation of Cr(III) to Cr(VI) can increase availability and toxicity of chromium. In this study, possible mechanisms by which pH and organic matter can control the chromium oxidation and reduction in soil system were examined using four soils of different pHs and organic matter contents. Reduction of Mn-oxides occurred in the soils of higher organic matter content (4.0%), but Mn-oxide was quite stable during the incubation in the soil of pH 7.0 and 0.5% organic matter content. Manganese oxides can be reductively dissolved at lower pH and higher organic matter conditions. The soil of pH 7.0 and 4.0% organic matter content showed the highest Cr-oxidation potential. Reduction of soluble Cr(VI) was observed in all the soils examined. The most rapid reduction was found in soil of pH 5.5 and 4.0% organic matter content, but the reduction was slow in soil of pH 7.0 and 0.5% organic matter content. Thus, the reductive capacity of organic matter added soils was much higher as compared to other two soils of lower organic matter content. In all the soils examined, the reductive capacity of soluble chromium was much higher than the oxidative capacity. Organic matter was found to be the most important controlling factor in the chromium oxidation and reduction. Reduction of Cr(VI) to Cr(III) could be a potentially useful remediation or detoxification process, and availability and toxicity of chromium in soil would be controlled by controlling organic matter content and pH of the soils.

A Kinetics of Hydrogen Reduction of Nickel Oxide at Moderate Temperature

Dong Soo Lee,Dong Joon Min 대한금속·재료학회 2019 METALS AND MATERIALS International Vol.25 No.4

Nano-metallic nickel powders are highly-valued materials applied in energy, electronic devices and aerospace, which isknown to be produced by the gaseous phase reduction method of NiCl 2 . In the case of a gaseous reduction method, sizecontrol is diffi cult due to the agglomeration of nickel powders. Therefore, a method of producing highly-valued nickel nanopowdersfrom Ni(OH) 2 has been proposed. Considering the reduction behavior of bulk nickel oxide has been reported tofollow the topo-chemical model. However, reduction behavior of nano-particle is expected to be unknown state. It is necessaryto clarify the mechanism of nickel oxide nano-particle reduction. Therefore, in this study, the temperature dependence andparticle size dependence on the reduction behavior of from micro scale to nano scale particle was confi rmed through TGAexperiment. Also, the reduction mechanism of nickel oxide powder was also investigated based on kinetic considerationsusing the grain topo-chemical model. It was confi rmed that the reduction reaction of nickel oxide powder undergoes throughthe 2nd Avrami model and reduction rate can be expressed by function of temperature and particle size of the powder. Dueto the part of the diff usion, the particle size of the powder also aff ects the rate constant of the reduction reaction. g(x) = k ⋅ f(d) ⋅ t

Study on the structure of reduced graphene oxide prepared by different reduction methods

Xiang Xu,Zhu Ying,Gao Changqin,Du Han,Guo Chunwen 한국탄소학회 2022 Carbon Letters Vol.32 No.2

The reduced graphene oxide (rGO) has attracted more and more attention in recent years. How to choose a suitable reduction method to prepare rGO is a critical problem in the preparation of graphene composites. In this work, the differences of rGO reduced by thermal, microwave, Ultraviolet (UV) and reducing agent were studied. The reduction degree and functional groups of rGO were compared by SEM, XPS, Raman, FTIR and TGA. Thermal can remove most of the oxygen-containing groups of graphene oxide (GO) and the thermal reduction is the most effective reduction method. UV light can directly act on the unstable oxygen-containing groups, and its reduction efficiency is second only to thermal reduction. The efficiency of chemical reduction is not as good as that of UV reduction, because the reducing agent only act on the surface of GO. Microwave reduction is a mild thermal reduction with the lowest efficiency, but the residual oxygen-containing groups increase the hydrophilicity of rGO. To sum up, this work studies that rGO prepared by different reduction methods has different characteristics, which provides a reference for selecting appropriate reduction methods to prepare graphene composites with better properties.

Electrochemical Cr(VI) reduction using a sacrificial Fe anode: Impacts of solution chemistry and stoichiometry

Chuang, Sheng-Ming,Ya, Vinh,Feng, Chiao-Lin,Lee, Shou-Jen,Choo, Kwang-Ho,Li, Chi-Wang Elsevier 2018 Separation and purification technology Vol.191 No.-

<P><B>Abstract</B></P> <P>A systematic investigation of Cr(VI) reduction using electrochemical reduction revealed that the Cr(VI) reduction was extremely fast with reaction kinetics limited by the anodic generation of Fe(II). The Cr(VI) reduction rate increased with decreasing pH at the initial stage of reaction but the time to reach complete Cr(VI) reduction is pH independent. The amount of Fe(II) generated per mole of Cr(VI) reduced was calculated and compared with the stoichiometric value, i.e., 3mole of Fe(II) needed per mole of Cr(VI) reduced. The values are 11.1% higher than the stoichiometric value for pH 7 and 9, but are 32.0% less for pH 3 and 5. The spontaneous reduction of Cr(VI) by Fe<SUP>0</SUP> and adsorption of Cr(VI) to Fe(OH)<SUB>3</SUB> precipitates might contribute the additional Cr(VI) removal. Effect of DO was investigated under various mixing schemes. Under N<SUB>2</SUB> purging, Fe(II) generated for one mole of Cr(VI) reduced is 3.67% higher than the stoichiometric value, while mechanic mixing and aeration mixing show 15% and 19%, respectively, higher than stoichiometric value, indicating that DO does impact Cr(VI) reduction. The electrochemical Cr(VI) reduction process was also employed to treat electroplating wastewater with and without pH pre-adjustment, achieving 100% total Cr and Ni removal for both cases. ORP can be used as a controlling parameter when electrochemical reduction is implemented for Cr(VI) reduction.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Effect of current on Cr(VI) reduction under same current density was studied. </LI> <LI> Effects of initial and fixed pH on Cr(VI) reduction were investigated. </LI> <LI> Effect of DO on Cr(VI) reduction was explored. </LI> <LI> Electrochemical reduction was applied for treating electroplating wastewater. </LI> <LI> ORP is an ideal parameter for controlling electrochemical Cr(VI) reduction. </LI> </UL> </P>

Effects of Oxygen Partial Pressure on Oxidation Behavior of CMnSi TRIP Steel in an Oxidation-Reduction Scheme

( Seong-hwan Kim ),( Joo-youl Huh ),( Myung-soo Kim ),( Jong-sang Kim ) 한국부식방식학회(구 한국부식학회) 2017 Corrosion Science and Technology Vol.16 No.1

An oxidation-reduction scheme is an alternative approach for improving the galvanizability of advanced high-strength steel in the continuous hot-dip galvanizing process. Here, we investigated the effect of oxygen partial pressure (PO₂) on the oxidation behavior of a transformation-induced plasticity steel containing 1.5 wt% Si and 1.6 wt% Mn during heating to and holding for 60 s at 700 °C under atmospheres with various PO₂ values. Irrespective of PO₂, a thin amorphous Si-rich layer of Si-Mn-O was formed underneath the Fe oxide scale (a Fe₂O₃/Fe₃O₄ bilayer) in the heating stage. In contrast to Si, Mn tended to segregate at the scale surface as (Fe,Mn)₂O₃. The multilayered structure of (Fe,Mn)₂O₃/Fe₂O₃/Fe₃O₄/amorphous Si-Mn-O remained even after extended oxidizing at 700 °C for 60 s. Fe₂O₃ was the dominantly growing oxide phase in the scale. The enhanced growth rate of Fe₂O₃ with increasing PO₂ resulted in the formation of more Kirkendall voids in the amorphous Si-rich layer and a less Mn segregation at the scale surface. The mechanisms underlying the absence of FeO and the formation of Kirkendall voids are discussed.

Effect of Palladium and Nickel on the Temperature Programmed Reduction of Metal Oxides and Metal Oxide Layers

Kim, Jong Pal 한국화학공학회 2004 Korean Journal of Chemical Engineering Vol.21 No.2

A new binary oxide support was suggested as being useful in many commercial reactions. Our study was focused on the reduction effect of metal oxide layer on alumina during reaction. Hence temperature programmed reduction of both bulk metal oxide and metal oxide layer on alumina was studied first and the effect of palladium and nickel on the reduction of the oxide support was also investigated. Vanadium oxide was mainly studied and niobium oxide, tantalum oxide, titanium oxide and zirconium oxide were also compared. Some metal oxides were reduced in a hydrogen stream at elevated temperature. In these cases both the bulk metal oxide and metal oxide layer were reduced. A tiny amount of palladium or nickel affected the reduction by decreasing the reduction temperature. The decrease of the reduction temperature was explained by means of increased adsorption of hydrogen on the transition metal and ability of the metal to spillover of the hydrogen to the oxides.

Effect of Palladium and Nickel on the Temperature Programmed Reduction of Metal Oxides and Metal Oxide Layers

김종팔 한국화학공학회 2004 Korean Journal of Chemical Engineering Vol.21 No.2

A new binary oxide support was suggested as being useful in many commercial reactions. Our study wasfocused on the reduction effect of metal oxide layer on alumina during reaction. Hence temperature programmedreduction of both bulk metal oxide and metal oxide layer on alumina was studied first and the effect of palladium andnickel on the reduction of the oxide support was also investigated. Vanadium oxide was mainly studied and niobiumoxide, tantalum oxide, titanium oxide and zirconium oxide were also compared. Some metal oxides were reduced ina hydrogen stream at elevated temperature. In these cases both the bulk metal oxide and metal oxide layer werereduced. A tiny amount of palladium or nickel afected the reduction by decreasing the reduction temperature. Thedecrease of the reduction temperature was explained by means of increased adsorption of hydrogen on the transitionmetal and ability of the metal to spillover of the hydrogen to the oxides.

$UO_2$ 소결체의 산화/환원에 의해 제조된 분말 특성

김봉구,송근우,이정원,배기광,양명승,박현수 한국세라믹학회 1995 한국세라믹학회지 Vol.32 No.4

Unirradiated UO2 pellets were pulverized by oxidation in air at 40$0^{\circ}C$, and the oxidized powders were reduced in H2 and CO atmospheres at $600^{\circ}C$. During the oxidation of UO2 at 40$0^{\circ}C$, intergranular cracks which caused the spallation were mainly developed by the volume contraction due to the formation of intermediate phase (U4O9 or U3O7). As oxidation proceeded, U3O8 finally formed. As the oxidation/reduction cycles were repeated, the powder surface became coarser, specific surface area was increased and average particle size was decreased. The sintered densities of the powder were increased by the oxidation/reduction cycle due to the characteristic changes of the powder.

Relationship Between Tyrosinase Inhibitory Action and Oxidation-Reduction Potential of Cosmetic Whitening Ingredients and Phenol Derivatives

Sakuma, Katsuya,Ogawa, Masayuki,Sugibayashi, Kenji,Yamada, Koh-ichi,Yamamoto, Katsumi The Pharmaceutical Society of Korea 1999 Archives of Pharmacal Research Vol.22 No.4

The oxidation-reduction potentials of cosmetic raw materials, showing tyrosinase inhibitory action, and phenolic compounds structurally similar to L-tyrosine were determined by cylcic voltammetry. The voltammograms obtained could be classified ito 4 patterns (patterns 1-4). Patterns 1, characterized by oxidation and reduction peaks as a pair, was observed with catechol, hydroquinone or phenol, and pattern 2 exhibiting another oxidation peak in addition to oxidation and reduction peaks as a pair was found with arbutin, kojic acid, resorcinol, methyl p-hydroxybenzoate and L-tyrosine as the substrate of tyrosinase. Pattern 3 with an independent oxidation peak only was expressed by L-ascorbic acid, and pattern 4 with a reduction peak only at high potentials, by hinokitiol. The tyrosinase inhibitory activity of these compounds was also evaluated using the 50% inhibitory concentration ($IC_{50}$) and the inhibition constant (Ki) as parameters. Hinokitiol, classified as patterns 4, showed the highest inhibitory activity (lowest $IC_{50}$ and Ki). Hydroquinone showing the second highest activity belonged to pattern 1, which also included compounds exhibiting pattern 2 was relatively low with Ki values being in the order of 10-4 M. Although there was no consistent relationship between oxidation-reduction potentials and tyrosinase inhibitory action, the voltammetry data can be used as an additional index to establish the relationship between the structure and the tyrosine inhibitory activity.

용융 전기로 슬래그의 환원반응에 관한 연구

주성웅 ( Seong Woong Joo ),신종대 ( Jong Dae Shin ),신동경 ( Dong Kyung Shin ),홍성훈 ( Seong Hun Hong ),기준성 ( Jun Sung Ki ),황진일 ( Jin Ii Hwang ),유병돈 ( Byung Don You ) 대한금속재료학회(구 대한금속학회) 2012 대한금속·재료학회지 Vol.50 No.10

The reduction behavior of low level oxides such as (T.Fe), (MnO) and (P2O5) in molten EAF slag was investigated using commercial reductants. In an air atmosphere, the slag volume increased and the reduction rate of the slag was very low due to the oxidation loss of reductants by oxygen in the air. The reduction rate of the slag was also low when a commercial reductant was used alone in an Ar gas atmosphere. The reason is probably because the material transfer through the interface between the slag and reductant is difficult due to the formation of high melting point oxide. When reductants were mixed with burnt lime in order to form low melting point reaction products, the reduction rate of the slag increased up to the range of 45-70%. By using the mixtures of reductants and burnt lime so as to form a low melting point slag at the reaction end, the reduction rate of the slag was improved up to 60-85%.