• Journal of the Mineralogical Society of Korea
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• v.27 no.2
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• pp.73-83
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• 2014

In order to investigate selective phase transformations and to determine the maximum Au leaching factors from microwave treated Au-bearing complex sulfides, a microscope, SEM-EDS analysis, and thiocyanate leaching tests were performed. When the Au-bearing complex sulfides were exposed to microwave heating, increasing the microwave exposure time increased temperature and decreased weight. Arsenopyrite was first selectively transformed to hematite, which formed a concentric rim structure. In this hematite, oxygen and carbon was detected and always showed high iron content and low arsenic content due to arcing and oxidation from microwave heating. The results of the leaching test using microwave treated sample showed that the maximum Au leaching parameters was reached with 0.5 g concentration thiocyanate, 2.0 M hydrochloric acid, 0.3 M copper sulfate and leaching temperature at$60^{\circ}C$. Under the maximum Au leaching conditions, 59% to 96.69% of Au was leached from the microwave treated samples, whereas only 24.53% to 92% of the Au was leached from the untreated samples.

• Journal of the Mineralogical Society of Korea
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• v.31 no.3
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• pp.137-147
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• 2018

The aim of this study was to leach penalty elements, such as Bi and As, effectively through microwave leaching of a gold concentrate sample containing penalty elements with nitric acid solution. For this purpose, the time effect of microwave leaching, nitric acid concentration effect, and sample addition effect in a microwave were examined. The experiment, demonstrated that the leaching rate of penalty elements increased as microwave leaching time and nitric acid concentration increased and concentration addition decreased. When a microwave heating experiment was carried out on the concentrate and ore minerals, Bi was removed by as much as 90%, and the phase of arsenopyrite was transformed in the order of arsenopyrite (FeAsS), pyrrhotite (FeS), and hematite ($Fe_2O_3$). When the X-ray diffraction (XRD) analysis was carried out with solid residue, elemental sulfur and anglesite were identified. The intensity of the XRD peaks of elemental sulfur and anglesite increased, and the peaks were sharper when the microwave leaching time was 12 min instead of 1 min, the nitric acid concentration was 4 M in rather than 0.5 M, and the concentration addition was 30 g rather than 5 g. This was probably because more elemental sulfur and anglesite were generated in the leaching solution as the leaching efficiency increased. Bi can be leached as valuable elements in the leaching solution through microwave leaching processes while they are released to the environment through a microwave heating processes.

• Journal of the Korean Chemical Society
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• v.54 no.4
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• pp.419-428
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• 2010

Here we describe a fast and rapid technique for preparation of amino acid hydrazide as well as peptide hydrazide derivatives using diisopropylcarbodiimide (DIC)/1-hydroxybenzotriazoles (HOXt) (X = A or B) under microwave irradiation employing a multimode reactor (Synthos 3000 Aton Paar, GmbH, 1400 W maximum magnetron). A comparison between conventional and microwave irradiation was described. The microwave methodology is rapid, convenient, proceeds under mild conditions. Diisopropylcarbodiimide (DIC)/7-aza-1-hydroxybenzotriazole (HOAt) always gave much better yield (95 - 98%) and purity than diisopropylcarbodiimide (DIC)/1-hydroxybenzotriazole (HOBt).

• Journal of Applied Tourism Food and Beverage Management and Research
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• v.15 no.1
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• pp.113-125
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• 2004

Effect of microwave radiation on physico-chemical properties of cor'n starches was studied. Waxy com, com and high amylose com starches of varying moisture content(20～35%) were subjected to microwave processing(2450MHz) at $120^{\circ}$ and the experimental starch samples were examined by a X-ray diffractometry, rapid viscosity analyzer(RVA) and. with the samples in temperature was observed and the peaks of high amylose com starches at $2^{\circ}$=5.0, 15.0 and $23.0^{\circ}$, were disappeared indicating the melting of crystallines while those of com and waxy com had not changed. A change in gelatinization pattern was observed in the case of corn starches from type A with nearly no peak-viscosity and breakdown to type C. Except a decreased viscosity, no change was observed in those of waxy com starches.

• Journal of Energy Engineering
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• v.21 no.4
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• pp.325-338
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• 2012

Currently, there are the technologically urgent needs of fabricating the hyper coal (HC) based on the approach to extracting mainly effective organics from low rank coals (LRCs), because some industrial countries pursue global sustainability dealing with hot issues such as local energy supply security as well as global warming. In this study, as of the fabrication of clean HCs via LRCs upgrading, we comprehensively review the R&D status of two solvent extraction technologies, namely, Ohm heating (OH) and microwave irradiation (MI) extraction processes on the basis of the performance indicator such as a HC extraction yield.

• Journal of the Korean Chemical Society
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• v.57 no.4
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• pp.515-519
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• 2013

• Food Science and Preservation
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• v.13 no.2
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• pp.216-222
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• 2006

Microwave energy (2450 MHz) was applied to extract health-effective component (HEC) from grape seed. Three different solvents approved for grape seed extract such as water, ethanol and acetone, were confirmed in their microwave-heating properties and by which extraction efficiencies were determined. Microwave-assisted extraction (MAE) was performed under different parameters; microwave power : (0, 50, 100 and 150), time : (1, 3, 5, 7, and 9 min), the sample to solvent ratio : (1:20, 1:10, 1:5 and 1:2.5), and particle size(whole, 20, 40 and 60 mesh) and the subsequent extracts were used for determining their physicochemical properties, such as total yield : (TY), total phenolics : (TP), catechin content : (CC), electron donating ability : (EDA), and browning color. The heating properties of solvent demonstrated the optimal ranges of microwave and time as 100 W and 2 to 6 min. The TY and HFC content were higher with increasing powers in water and ethanol solvent, while HFC content were lower in acetone at over 100 W. The longer of extraction time up to 5 min, the higher extraction efficiency. Based upon the overall MAE efficiency and solvent recovery, it was found optimal to use 10 times volume of ethanol for 10 mesh of seed particle at 100 W.

• Journal of the Korean Society of Food Science and Nutrition
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• v.32 no.6
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• pp.864-869
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• 2003

In order to expand the acceptability of irradiated foods by public, substantial basic data about the change of nutrient contents during irradiation are needed. The nutrient contents and digestibility of macronutrients such as carbohydrates, proteins and lipids in foods are known to be not significantly influenced by irradiation treatment. However, some of the vitamins among micronutrients are susceptible to irradiation to a large extent depending upon the food composition, food process and storage condition. This study was conducted to investigate change of thiamin in chicken breast, and vitamin C in strawberry and mandarine orange after irradiation. The effects of irradiation at frozen or refrigerated state and the effects of cooking such as heating or micron ave on thiamin contents in chicken breast were observed. Irradiation reduced the thiamin content, however, temperature condition during irradiation was much more important factor to the loss of thiamin contents. In strawberry, vitamin C content was significantly affected by original content or the variety rattler than treatments such as irradiation, heating or microwave. These results indicated that the losses of water-soluble vitamins, especially thiamin or vitamin C, are affected by food temperature during irradiation process and variety or composition of foods rallier than irradiation itself, within an acceptable range of irradiation.

• Journal of the Korean Society of Food Science and Nutrition
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• v.28 no.4
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• pp.954-957
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• 1999

The changes in L ascorbic acid content by processing treatments; gamma irradiation, heating and microwave were investigated using high performance liquid chromatography. The content of L ascorbic acid in standard solutions and citrus fruits decreased from 27.4 to 44.9% and from 6.9 to 21.9%, re spectively, by gamma irradiation doses in the range of 1 to 10 kGy. By heating treatments, L ascorbic acids in standard solutions and citrus fruits were destroyed 22.5 to 36.8% and 4.5 to 18.1%, respectively. By microwave treatment, L ascorbic acid content also decreased from 23.1 to 47.4% and from 6.5 to 22.6%, respectively.

• The Korean Journal of Food And Nutrition
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• v.23 no.3
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• pp.405-410
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• 2010

The effect of microwave treatment on Korean ginseng was studied by measuring the changes in moisture, crude lipid, crude ash, crude protein, total dietary fiber and saponin contents, as well as changes in density, color and microstructure. Korean ginseng was treated with 100 or 200 watts of microwaves for 1 or 3 hrs, respectively, followed by drying using an oven at $60^{\circ}C$ for 96 hrs. The moisture contents decreased to 13.12~10.77% from an initial 76.26%. The amounts of lipid and ash were reduced in proportion to the time of microwave treatment and level of microwave power. The amount of protein in ginseng after microwave treatment did not significantly change. The amount of total dietary fiber increased after microwave treatment and the color of dried ginseng became dark. The amounts of ginsenoside-$Rb_1$, $Rb_2+Rb_3$, Rc, Rd, Re, Rf, $Rg_1$, $Rg_2+Rh_1$ and $Rg_3$ were reduced after treatment with 100 watts of microwave radiation for 1 and 3. The amounts of ginsenoside-$Rb_1$, Rd, Re, Rf, $Rg_1$, $Rg_2+Rh_1$ and $Rg_3$ after treatment with 200 watts of microwave radiation for 1 and 3 hr also reduced. On the other hand, the amounts of ginsenoside-$Rb_2+Rb_3$ and Rc after treatment of ginseng with 200 watts of microwave radiation for 1 and 3 hrs were increased.