• Resources Recycling
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• v.31 no.5
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• pp.26-33
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• 2022

Molybdenum is widely used in many materials; thus, its recovery from ores and secondary resources has attracted considerable attention. In this study, the leaching of molybdenite ore using hydrochloric acid containing sodium chlorate as an oxidizing agent was studied. The effects of several variables, such as the concentrations of HCl and NaClO₃, reaction temperature and time, and pulp density, on the leaching of the ore were investigated. Under strong acidic and oxidizing conditions, the sulfide in the ore was dissolved as a sulfate ion, which formed gypsum with Ca(II), leading to a decrease in the leaching percentage of Mo(VI) from the ore. The leaching percentage of molybdenum was greater than 90%, while those of iron, calcium, and silicon were 38, 29, and 67%, respectively, under the optimum conditions: 2.0 M HCl, 0.5 M NaClO₃, pulp density of 5 g/L, temperature of 90 ℃, and treatment time of 60 min.

• Journal of the Korean Recycled Construction Resources Institute
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• v.1 no.2
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• pp.136-143
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• 2013

In the sewage structures and wastewater facilities, concrete is exposed to hydrogen sulfide ($H_2S$) which acts as an acid material in a solution, and a strongly acidic sulfate ion ($SO{_4}^{-2}$) is generated by a sulfuric bacteria. Hence, a degradation of concrete with biochemical corrosion would be accelerated. Finally, durability of concrete and concrete structures may be greatly reduced. In this study, in order to remove the hydrogen sulfide which is used by the sulfuric bacteria organic-biologically, the antibiotic metal and metallic salt powders were mixed to concrete, and a suppressing performance of the sulfate ion was assessed. For the sulfuric acid bacteria, a comparative evaluation of antimicrobial performance on neutralized concrete specimens were carried out, also by a rapid chloride penetration test, chloride penetration depths and diffusion coefficients were measured for antibiotic concrete in accordance with the amount of metal and metallic salt-based antibacterial agents. Eventually, by an observation of the biochemical state of the surface of concrete specimens exposed outdoors, the performance and applicability of antibiotic concrete were confirmed.

• Journal of Conservation Science
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• v.32 no.3
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• pp.299-312
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• 2016

The Daehan Uiwon (Historic Site No. 248) in which the predecessor of Seoul National University Hospital is a crucial medical institution that built in the Korean Empire period. One of them, East 1 Affiliated Ward that attached to Daehan Uiwon was built with concrete foundation in 1908 and extended two times in 1935 and 1954. As a result of material scientific analysis for concrete foundation, all of the foundation is composed of mortar and stone aggregates, however, the mixing proportions between the aggregate and the mortar were confirmed to be different with construction periods. To determine the mixing proportion, and physical properties by ultrasonic velocity and rebound hardness, the concrete foundations by construction period were obtained. In result, 1954's mixing proportion of concrete between mortar and stone aggregate indicated the highest ratio of aggregates with 1 : 35, mean value of ultrasonic velocity and unconfined compressive strength were calculated with 450 m/s and 18.92 MPa in 1954's constructions that is the lowest values compared with other times. As a result, the difference characteristics of physical properties by construction periods are possible interpreted with porosities and mixing ratios of stone aggregates.

• Journal of the Korean Chemical Society
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• v.20 no.6
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• pp.469-478
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• 1976

Clinoptilolite zeolite samples were treated with hydrochloric acid, sulfuric acid and phosphoric acid of different strength and the adsorption characteristics and crystal structures of the original and acid-treated clinoptilolites were studied. By treating with hydrochloric acid, the adsorbed amount increased to 5-fold for nitrogen, to 3-fold for benzene, but for methanol no significant change was observed. As acid strength increased further, there were declines both in adsorption capacity and crystallinity. The results showed that the increase of adsorbed amount was caused by the rearrangement of the pore entrance and cation exchange. A method for determination of clinoptilolite content in natural mineral based on benzene adsorption on acid-treated sample is proposed. By this method, the original sample used in this study was found to contain approximately 40% of clinoptilolite. Using pulse technique in micro-catalytic reactor system, the catalytic activities of hydrochloric acid-treated clinoptilolites in cumene cracking and toluene disproportionation reactions were measured. For cumene cracking reaction, the maximum conversion was observed for the 0.5 N hydrochloric acid-treated sample. It is instructive to note that the maximum benzene adsorption was also observed for the sample treated with 0.5 N HCl. This suggest that the conversion rate was determined mainly by the rate of transport of reactants and the products through the pore structure. In the toluene disproportionation reaction, the same trend was observed. But the rate of deactivation was high for samples with strong acid sites. Since catalyst having higher activity was deactivated more easily, the conversion maximum was shifted to the sample treated with higher concentration of acid, -1N. The catalytic activity of $Ca^{2+} and La^{3+} ion exchanged samples for the toluene disproportion was much lower than that of acid-treated samples. Introduction of Ca^{2+} and La^{3+}$ into the pore structure apparently decreases the effective pore diameter of acid-treated clinoptilolite thus limiting the diffusion of reactants and products.

• Journal of the Korean Chemical Society
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• v.32 no.4
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• pp.358-370
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• 1988

Several new ion exchange resins have been synthesized from chloromethyl styrene-1,4-divinylbenzene(DVB) with 1%, 2%, 4%, and 10%-crosslinking and macrocyclic ligands of cryptand type by interpolymerization method. The adsorption characteristics and the pH, time, solvents and concentration dependence of the adsorption of metal ions by this resin were studied. The correlation between the separation characteristics of uranium, rare earths and transition metal on the resins and the stability constants of complexes with macrocyclic ligands have been examined. The resins were very stable in both acidic and basic media and have good resistance to heat at $280^{\circ}C$. The $UO_2^{+2}$ aqueous solution are not adsorbed on the resins below pH 3.0, but the power of adsorption of $UO_2^{2+}$ increased rapidly above pH 4.0. The optimum equilibrium time for adsorption of metallic ions was twenty minutes and adsorptive power decreased in proportion to crosslinking size of the resins and order of dielectric constants of solvents used and the selective sequence for metal cations is in the order of $UO_2^{2+},\;Cu^{2+}\;and\;Nd^{3+}$.

• Journal of Chest Surgery
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• v.31 no.9
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• pp.893-898
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• 1998

Material and Method: Esophageal reconstruction by the hypopharyngointestinal anastomosis was done in 7 patients of corrosive upper esophageal stricture at St. Mary's Hospital from August 1995 to January 1997. Result: There were one male and six female patients ranging from 20 to 63 years of age. The causative agents were acid in 6 patients and alkali in 1 patient. The esophageal reconstruction was made by hypopharyngcolojejunostomy in 4 patients and hypopharyngocologastrostomy in 3 patients. There were no operative mortalities. One patient developed anastomotic stenosis but others were free from dysphagia. All gained 4 kg to 13 kg of body weight during the follow-up period. Conclusion: In this experience right colon and terminal ileum including ileocecal valve was revealed as a good substitute for the esophagus and the esophageal reconstruction by hypopharyngocologastro (jejuno)stomy seems to be a satisfactory method with acceptable morbidity and mortality in corrosive upper esophageal stricture patient.

• Food Science and Industry
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• v.53 no.1
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• pp.69-83
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• 2020

For the development of the chitosan industry in Korea, the catch of red snow crabs caught on the east coast is rapidly decreasing. Therefore, it is urgent to develop raw materials that can replace the red snow crab as the top priority to solve the supply and demand problems, as well as wastewater treatment costs account for a large proportion of the cost of chitosan. In order to solve the problems, continuous research on biological extraction methods such as enzymatic extraction and microbial fermentation will increase production efficiency and lower unit cost as well as chemical extraction methods. Further efficient manufacturing method can be established. Establishing of novel techniques is indispensable for production of high-purity chitosan and the ability to regulate and separate the molecular weight, as well as joint research with industry, academia and research institute for the research and development of high-functional chitosan derivatives.

• Economic and Environmental Geology
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• v.39 no.6 s.181
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• pp.699-710
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• 2006

Batch scale experiments to investigate the efficiency of the solidification process for metal mine tailing treatment were performed. Portland and MSG (micro silica pouting) cements were used as solidifier and three kinds of mine tailings (located at Gishi, Daeryang, and Aujeon mine) were mixed with cements to paste solidified matrices. Single axis com-pressible strengths of solidified matrices were measured and their heavy metal extraction ratios were calculated to investigate the solidification efficiency of solidified matrices created in experiments. Solidified matrices ($5cm{\times}5cm{\times}5cm$) were molded from the paste of tailing and cements at various conditions such as different tailing/cement ratio, cement/water ratio, and different cement or tailing types. Compressible strengths of solidified matrices after 7, 14, and 28 day cementation were measured and their strengths ranged from 1 to $2kgf/mm^2$, which were higher than Korean limit of compressible strength for the inside wall of the isolated landfill facility ($0.21kgf/mm^2$). Heavy metal extractions from intact tailings and powdered matrices by using the weak acidic solution were performed. As concentration of extraction solution for the powdered solidified matrix (Portland cement + Gishi tailing at 1:1 w.t. ratio) decreased down to 9.7 mg/L, which was one fifth of As extraction concentration for intact Gishi tailings. Pb extraction concentration of the solidified matrix also decreased to lower than one fourth of intact tailing extraction concentration. Heavy metal extraction batch experiments by using various pH conditions of solution were also performed to investigate the solidification efficiency reducing heavy metal extraction rate from the solidified matrix. With pH 1 and 13 of solution, Zn and Pb concentration of solution were over the groundwater tolerance limit, but at pH $1{\sim}13$ of solution, heavy metal concentrations dramatically decreased and were lower than the groundwater tolerance limit. While the solidified matrix was immerged Into very acidic or basic solution (pH 1 and 13), pH of solution changed to $9{\sim}10$ because of the buffering effect of the matrix. It was suggested that the continuous extraction of heavy metals from the solidified matrix is limited even in the extremely high or low pH of contact water. Results of experiments suggested that the solidification process by using Portland and MSG cements has a great possibility to treat heavy metal contaminated mine tailing.

• Journal of Ginseng Research
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• v.24 no.3
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• pp.107-112
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• 2000

One of the physiologically important ginseng diseases is red-colored phenomena (RCP) that is caused by accumulation of red-colored substances on the epidermis of ginseng roots. Although RCP severely deteriorates the quality of ginseng products, there has been little information on what red-colored substance is and how RCP occurs. Therefore, the heavy losses of cultivators and ginseng industry are suffering by RCP, For this reason, we have investigated with the morphochernical characteristics of RCP to find out main cause of it. The red-colored substances (RS) on the epidermis of red-colored ginseng (RCG) were examined using inverted light microscope, confocal laser scanning microscope (CLSM)and furier transform infrared (FT/IR) spectrometer. Red brown substances were accumulated in the cell wall of the epidermis from early stage to late stage of RCC. Especially, cell wall of the late stage of RCG was covered with the sub-stances with 80~ 130 fm thick. Therefore, the cell wall of RCG cannot protect the ginseng root cells from the mechanical damages, bacteria and fungi. To analyse red substances of roots, RS were isolated from epidermis of RCG and extracted using various solvents. RS is strongly insoluble but it was bleached by oxidizing agents including 12% (v/v) NaOCl. Therefore, RS was Presumed to make up of high chelation power. The proriles of FT/IR spectra or both healthy ginseng (HEG) and RCG showed a significant difference at two wavelength,2857 cm$\^$-1/(C-H) and 1032 cm$\^$-1/(S=O), respectively. Furthermore, absorption peak of 2857cm$\^$-l/ appears on the only epidermis of RCG. The other peak is shown lower absorption rate on the epidermis of RCG than that of healthy ginseng. Also, FT/IR spectra of the mixture of carboxym-ethylcellulose (CMC) and iron (Fe$\^$3+/) were very similar to RCG spectrum profiles. One of a interesting fact is that the contents of phenolic compounds at the epidermis of healthy ginseng were highest. The results of these experiments sup-port the RCP was closely related with the chemical interaction between inorganic elements (Fe) of rhizosphere and organic matters (cellulose, cellobiose, cell sap, etc.) of ginseng roots.

• Korean Journal of Poultry Science
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• v.28 no.3
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• pp.215-224
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• 2001

Since nitrogen(N) is a volatile compound affected by many environmental factors, determining the N content of manure tends to be difficult. Upon arrival in the laboratory, the manure should be moist and refrigerated. Manure samples will have variable N contents due to drying temperature, and the presence of soil in the sample will affect N content. Acidification of the sample prevents ammonia volatilization and should be done before drying. It is recommended that manure samples be pretreated with a strong oxidizing agent, KMnO$_4$, followed by digestion under reduced conditions (reduced Fe-$H_{2}$ $SO_{4}$ ), which achieves a complete recovery of both $NO_{3}$ -N and $NO_{2}$ -N without a low recovery of $NH_{4}$ -N, resulting in a more accurate determination of N content. Accuracy of results for N content determined by recently developed rapid analysis techniques in the field should be tested by comparison with results obtained at laboratories using approved standard methods. Most commonly, the Kjeldahl system is used to determine manure N content. More research is needed on the effects of species, breed, age and individuals on the nutrient contents of manure. The procedures for manure sampling on the farm, shipping and handling of the sample until it reaches the laboratory, and the methods of sampling of the manure at the laboratory must be studied. Development of animal agricultural laboratories where feed, manure, soil, and water are all analyzed by appropriate specialists is needed.