• Korean Journal of Soil Science and Fertilizer
• /
• v.40 no.5
• /
• pp.412-417
• /
• 2007

This study was to elucidate the effects of layered double hydroxides(LDHs) application on the chemical properties of the soils along with the fate of the applied LDHs. The effects of LDHs application were compared with those of calcium carbonate widely used for the neutralization of acidic soils. Incorporation of LDHs into the soil resulted in higher pH value and $Mg^{2+}$ content in soil leachate than that of $CaCO_3$ treatment. There was no significant difference in water-soluble P content in both the treatments. However, $Al^{3+}$ and $Si^{4+}$ contents were decreased by LDHs and $CaCO_3$ treatment, even though a large amount of $Al^{3+}$ was released into soil solution with the disintegration of LDHs framework. LDHs structure in soil was gradually disintegrated from the its original layered structure under acidic condition of soil. Therefore, this study suggests that LDHs could be utilized as a carrier of functional substances to enhance the efficiency of various ago-chemicals without any ill effects on the soil environments.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.48 no.2
• /
• pp.168-175
• /
• 2021

This study compared the microleakages and compressive strengths of various base materials. To evaluate microleakages, 50 extracted permanent premolars were prepared. The teeth divided into 5 groups of 10 each according to the base materials. Cavities with a 5.0 mm width, 3.0 mm length, and 3.0 mm depth were formed on the buccal surfaces of the teeth. After filling the cavities with different base materials, a composite resin was used for final restoration. Each specimen was immersed in 2% methylene blue solution and then observed under a stereoscopic microscope (× 30). To evaluate the compressive strength, 5 cylindrical specimens were prepared for each base material. A universal testing machine was used to measure the compressive strength. The microleakage was highest in the Riva light cure^TM group and lowest in the Biodentine^TM and Well-Root^TM PT groups. For the compressive strengths, in all groups, acceptable strength values for base materials were found. The highest compressive strength was observed in the Fuji II LC^TM group and the lowest strength in the Well-Root^TM PT group.

• Korean Journal of Soil Science and Fertilizer
• /
• v.29 no.2
• /
• pp.113-123
• /
• 1996

This experiment was carried out to compare with the physico-chemical properties of granular fused magnesium phosphates which were two domestic products(Pungnong Biryo Industrial Co., LTD and Kyunggi Chemical Industrial Co., LTD) and a imported Chinese product. The changes of pH, distribution of particle size, disintegration in water and in soil, hardness in soil, chemical composition, and dissolution rates in water, in soil and in 2% citric acid solution were investigated. The changes in pH were bigger in Jungmun series(black volcanic soil), in the imported chinese product, and in Jungmun series with the larger quantities applied. The domestic products were lower in pH, calcium, alkalinity and 1/2N-HCl soluble silicate than the Chinese product but total(Aqua regia) soluble phosphate, 2% citric acid soluble phosphate, 1/2N-HCl soluble and 2% citric acid soluble magnesium, and 2% citric acid soluble manganese concentration were similar among the domestic products and the imported product. In particle sizes, Chinese product was the biggest, Kyunggi product was the next, and Pungnong product was the smallest. The changes of disintegration rate in water and in soil were smaller in Pungnong and Kyunggi products at the early days of dissolution, and there were decreased with the order of Kyunggi product> Chinese product> Pungnong product at the latter days. The hardness of the products in soil was the strongest in Kyunggi product, the next was Pungnong product and Chinese product was the weakest so as to hardly measurable. The changing dissolution rates of 2% citric acid soluble phosphate concentration of granular fused magnesium phosphate products were the highest in Kyunggi product and the lowest in Pungnong product at the early days, the three products were dissolved over 90% within 50 days, and there were no clear difference among the products after 70 days of dissolution. The dissolution rates of 2% citric acid soluble phosphate concentration of granular fused magnesium phosphate products in soil were the highest in Pungnong product and Chinese product was the lowest, but they were less than 60% in 100 days of dissolution.

• Korean Journal of Soil Science and Fertilizer
• /
• v.16 no.2
• /
• pp.131-155
• /
• 1983

Though it has been widely known the nitrogen effects are influenced by soils, varieties, and mineral nutrients in the rice culture, few analyses in relation to the factors increasing nitrogen effect have been studied in Korea. The effects of potassium and silica on the factors increasing nitrogen effects in paddy soils were investigated in accordance with soil improvement practices and nitrogen application methods for the cultivated varieties. The results obtained are as follows. 1. For 413 paddy fields, the yield from soils without nitrogen application ranged from 200 to 850kg/10a and that from nitrogen application did 350 to 1,051kg/10a. The yield increament by nitrogen application varied 50 to 650kg/10a depending on soils. 2. Soil chemical characteristics for high yield were different between with nitrogen and without nitrogen application. In the without nitrogen application, however, contents of organic matter, phosphorous, potassium and calcium of high yield soils were lower than those of low yield, while the available silica content was higher in the former. 3. The yield increased with nitrogen application up to 22.4kg/10a and thereafter it decreased. These phenomena were supposed to be not be decrease of nitrogen uptake but by lowered silica uptake. 4. Clay soil incorporation, deep plough, and inorganic constituents control such as Ca, Mg, and $Sio_2$ were effective as soil improvement praitices. It was appeared that increases of silica content and Ca/Mg ratio were important to increase nitrogen effects. 5. For the correlation between yield and yield components, it was high between yield and panicle in low nitrogen level and so was it between grain yield and ripening rate in high nitrogen. 6. In the urea and super granule urea application plot, recovery rate of nitrogen by plant and soil was high and yield was remarkable high. 7. Regardless of fertilizer types such as ammonium sulfate and urea, the residual nitrogen was about 4kg/10a in both plots of 5.8 and 11.6kg/10a. N applied. 8. The potassium application to soil enhanced the nitrogen efficiency. It was more effective in low potassium soil. 9. Optimum pH value for gel formation in the 4% sodium silicate solution was approximately 6.6. 10. It was suggested that silica could affect to rice plant growth as the inorganic and organic chemical components.

• Korean Journal of Mineralogy and Petrology
• /
• v.33 no.1
• /
• pp.41-51
• /
• 2020

The purpose of this study was to investigate the possibility of eco-friendly/efficient recovery of valuable resources, such as Au from mine tailings, which are environmental pollutants in the Mongolian mine sector. For this purpose, this study selected 4 place of mine tailings of the Mongolian mines sector and carried out mineralogy evaluation of the valuable resources in the tailings. In this study, flotation was performed to separate and concentrate valuable resources in the tailings. Microwave nitric acid leaching was used to leach the valuable resources contained in the sample and to improve the Au grade. Chloride leaching attempted to leach Au from the leaching residues. XRD analysis of the tailings samples showed that most of the samples consisted of silicate minerals. As a result of confirming the content of the element through XRF analysis, the SiO₂ content was very high, the Fe₂O₃ content was 2.32-4.23%, and the content of PbO, CuO and ZnO components were all within 2%. As a result of flotation for the tailings samples, the recovery of Au was the highest in Bayanairag sample (95.38%). As a result of microwave nitric solution experiment on Au concentrate sample obtained by flotation, the content of Au in the microwave nitrate leaching residue increased by 12.15% from 192.72 g/ton to 216.14g/ton in Khamo sample, the highest increase was 57.58% in Bayanairag sample. TCLP tests on tailings generated after flotation showed dissolution characteristics within EPA. Chloride leaching test was performed to recover Au from solid residues. The leaching rate was 87.43-89.35% within 10 minutes. For Khamo sample, 100% Au was leached after 60 minutes of leaching time. Therefore, in order to process the tailings continuously generated in Mongolia, applying the same process as the present study is expected to effectively recover the valuable resources contained in the tailings.