• Resources Recycling
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• v.26 no.5
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• pp.3-11
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• 2017

Solvent extraction is an important process to recover pure gold and silver from various leaching solutions. The present work reviews the aqueous chemistry and solvent extraction separation of gold (I, III) and silver (I) from several leaching systems such as cyanide, thiocyanate, thiosulfate, thiourea and chloride medium. The extraction and separation behavior of gold (I, III) and silver (I) by various single and mixtures was compared on the basis of extraction reaction and the selectivity from these mediums. The chloride medium is recommended for the separation of gold and silver by solvent extraction in terms of extraction and stripping efficiency.

• Applied Biological Chemistry
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• v.51 no.4
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• pp.321-328
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• 2008

The research was conducted to identify the antimicrobial effect, anti-oxidative effect and tyrosinase inhibitory effect of MeOH 80% extract and n-hexane, chloroform, ethyl acetate, n-butanol and water fractions from the extract of six kinds of compositae plants, which are naturally grown across the nation. In the antimicrobial effect, the extract and chloroform fraction of Arctium lappa and hexane/ethyl acetate fractions of Taraxacum platycarpum exhibited significant inhibition. In case of antioxidant effect, the extract of Artemisia capillaries showed the highest effect and ethyl acetate/butanol fractions of all plants showed about 90%, which fractions were more polar than the fractions that showed antimicrobial effect. In case of tyrosinase activity, only the MeOH 80% of Arctium lappa among the extracts showed a potent inhibition, and butanol fraction of Chrysanthemum indicum, as well as ethyl acetate/water fractions of Artemisia capillaries showed 48, 38, and 37% respectively, which were higher than control group (arbutin). These active fractions in tyrosinase inhibition also were higher polarity than those that showed antimicrobial effect. In MeOH 80% extracts, only Arctium lappa was found to have antimicrobial, anti-oxidant and tyrosinase inhibitory activity, however there was no fraction to show effects commonly in the three assay system.

• Analytical Science and Technology
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• v.18 no.3
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• pp.194-200
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• 2005

The N hyperfine coupling constants ($a_N$) of di-t-butyl nitroxide (DTBN) radicals in water-solvent system were measured with EPR spectroscopy. Various kinds of the solvents with different polarity such as acetone, dimethylsulfoxide (DMSO), methanol, ethanol and 1-propanol were applied and studied. Equilibrium constants for the solvation equilibrium and the solvent parameters ($E_T$, molar transition energy) of various water-solvent system were obtained from the experimental results and are presented. The $a_N$ values were plotted as a function of mole fraction of the solvent. In case of water-DMSO, water-ethanol and water-1-propanol system, slight negative deviations from the straight line were observed. In water-acetone system, the absorption wavelength (${\lambda}$) due to ${\eta}{\rightarrow}{\pi}^{\ast}$ transition increased linearly with the increase of mole fraction of acetone. The relationship between $a_N$ of DTBN and ${\lambda}$ due to ${\eta}{\rightarrow}{\pi}^{\ast}$ transition in water-acetone and water-DMSO system was examined. It was found that the electronic structure of the nitroxide radicals is stablized from the fact that the N hyperfine coupling constants of DTBN radicals are greatly unaffected in the environment of water-solvent system.

• Membrane Journal
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• v.10 no.1
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• pp.19-29
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• 2000

To estimatc mutual diffusion coefficient for the analysis of mass transfer phenomena in polymer/solvent system, two models are proposed and the equations are derived. The estimates of mutual diffusion coefficients are obtained by two models suggested in this work and compared with and experimental data and Vrentas-Duda's. Vrentas-Duda's self diffusion coefficient was used for the mutual diffusion coefficient. Derivative of chemical potential on solvent was derived and used using original UNIFAC-FV and modified UNIFAC-FV. However, Vrentas-Duda's equation for mutual diffusion coefficient contains Flory-Huggins parameter x. For the derivative of chemical potential term, Vrentas-Duda assumed that parameter x was constant and independent of temperatures and concentrations The assumption is one of shortcoming in vrentas-Duda's mutual diffusion coefficient. New methods proposed in this work do not have such assumptions and simplifications. For the solvent of cyclohexane, n-pentane, and n-hexane in PIB(polyisolbutylene) and PMS-BR (poly(p-methylstyrene-co-isobutylene), new methods well correlate the experimental data at various temperatures and concentrations, and predicted the experimental data much better than Vrentas-Duda's for the PIB/toluene system. It is shown that new methods are excellent tools for correlating mutual diffusion coefficient data in polymer/solvent system over wide ranges of temperature and concentration without any assumptions or simplifications.

• Journal of the Korean Chemical Society
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• v.23 no.6
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• pp.339-348
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• 1979

The kinetics of the solvolysis of 2-furoyl chloride and 2-thenoyl chloride in $MeOH-H_2O,\;EtOH-H_2O,\;(Me)_2CO-H_2O,\;MeCN-H_2O$ and MeCN-MeOH has been investigated. The rates were faster in protic solvents than in aprotic solvents. This was caused by the bond breaking of leaving group through hydrogen-bonding solvation of protic solvents. In MeCN-M$\'{e}$OH the rate in MeOH rich solvents was faster than in MeCN rich solvents by the specific solvation of alcoholic hydrogen and there was a maximum rate of reaction at MeOH mole fraction of 0.8. The reaction rates of solvolysis were considerably slower than those of benzoyl chloride owing to the electron withdrawing effect of thienyl and furyl groups. It was concluded that solvolytic reaction proceeds via a dissociative $S_N2$ mechanism in which bond-breaking precedes bond-formation at the transition state.

• KSBB Journal
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• v.16 no.1
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• pp.66-70
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• 2001

Factors affecting the supercritical carbon dioxide extraction of camptothecin(CPT) and 10-hydroxycamptothecin(HCPT) from the dried powder of Cmptotheca acuminata were studied. Only a few amount of CPT and HCPT was extracted with pure supercritical carbon dioxide. Methanol and ethanol were efficient modifiers to extract CPT and HCPT. At $40^{\circ}C$, 250 bar, 1 mL/min flow rate, 41% of CPT and 35% of HCPT were extracted with supercritical carbon dioxide modified with 16% of methanol. The diffusion effect of HCPT on extraction efficiency was studied in this solid-fluid system. Round matrix hot-ball model assumption revealed that the value of D/$r^2$ was 0.0072 $min^{-1}$ which was higher than that of solvent extraction with methanol.

• Journal of the Korean Wood Science and Technology
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• v.45 no.3
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• pp.268-277
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• 2017

In this study, lignocellulose nanofibrils (LCNFs) were prepared from Pussy willow wood powder by disk-milling after pretreatment using the cosolvent of 1-ethyl-3-methylimidazolium acetate ([EMIM]Ac) and N,N-dimethylformamide (DMF) with different mixing ratios for different time. All pretreated samples showed native cellulose I polymorph and cellulose crystallinity was lowest when cosolvent of DMF with 30% [EMIM]Ac was used. Average crystallite size of raw material and the pretreated product by MDF and its cosolvent with 10% [EMIM]Ac was found to be about 3.2 nm and decreased with increasing pretreatment time at the DMF cosolvent with 30% [EMIM]Ac. Defibrillation efficiency was improved by loosening wood cell wall structure by the pretreatment using co-solvent system of [EMIM]Ac and DMF.

• Polymer(Korea)
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• v.25 no.5
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• pp.665-670
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• 2001

The solvent extraction of polyethylene glycol (PEG) by ethanol has been studied for the powder injection molded compacts of Sr-ferrite/PEG/carnauba wax/HDPE. The extraction rate of PEG is sensitively proportional to the solvent temperature whereas it is inversely proportional to the contents of PEG, the molecular weight of PEG. and the specimen thickness. The high extraction rate of PEG is achieved under the following conditions: solvent temperature of $70^{\circ}C$, PEG contents of 30%, and PEG molecular weight of 400 g/mol. In the early stage of solvent extraction, the non-linear relationship between the extraction rate and the square root of the extraction time indicates that the extraction of PEG does not follow the Fickian behavior. At extraction times longer than 180 min. however, the extraction of PEG follows the Fickian behavior. The extraction fate of PEG by ethanol is about$1.0{ imes}10^{-6}g/cm^2sec$ enough for common applications.

• Polymer(Korea)
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• v.26 no.3
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• pp.307-315
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• 2002

Major factors affecting the impact resistance of high impact polystyrene (HIPS), the rubber-toughened grade of polystyrene, are rubber-phase particle size and size distribution, molecular weight, morphology, and degree of grafting. Accordingly, it is important to control or investigate these factors. In this study, the effect of solvent content was analyzed by the morphology and particle size distribution of rubber phase, and final properties in bulk-solution polymerization of HIPS. The prepolymerization time was, first, determined by measuring the evolution of particle size distribution of dispersed phase to explain the phase inversion with time. As the solvent content increased, the size of rubber particle increased and then gradually decreased. Rubber-phase morphology was likely to have higher degree of grafting as the solvent content increased. Rheological and mechanical properties decreased as the solvent content increased because of the decrease of matrix molecular weight due to the chain transfer reaction to solvent and the existence of residual solvent. Nevertheless, the impact resistance seemed to increase when the rubber particle size increased.

• Korean Chemical Engineering Research
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• v.53 no.6
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• pp.717-722
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• 2015

D-limonene included in citrus fruits is obtainable to extract essential oil as well as separate the oil ingredient. Soxhlet extraction, a type of SDE (Simultaneous steam Distillation and solvent Extraction), was used to extract limonene from tangerine peel. HPLC analysis was performed to quantify extracted d-limonene by using reversed-phase HPLC column. Results of HPLC analysis showed that the optimal extraction time was 2 hours in any solvent, and the extracted amounts of d-limonene in tangerine peel (per g tangerine peel) were 7.77 mg, 0.49 mg, and 0.28 mg in ethyl alcohol, n-hexane, and ether. Because yield was the highest in using ethyl alcohol as a solvent, polarity is stronger factor to effect on yield of extraction than boiling point.