• Journal of the Korea Institute of Building Construction
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• v.17 no.3
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• pp.211-217
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• 2017

The objective of this study is to seek a reliable mixture proportion for magnesium potassium phosphate composite(MKPC) mortars with a near-neutral pH value (below 9.5) and a relatively good compressive strength exceeding 30MPa. The main parameter selected was the molar ratios($M_{mp}$) of $MgO-to-KH_2PO_4$ which varied from 30.4 to 3.4. The setting time of the MKPC mortars tended to shorten with a decrease in $M_{mp}$ value. With regard to the strength development ratio normalized by the 28-day strength, the ranges measured in the mortars with an $M_{mp}$ below 7.9 were 50~61% at 1 day and 60~73% at 3 days, indicating a highly rapid early-strength development. With a decrease in $M_{mp}$, the formation of struvite-K crystal identified as a primary hydration product increased, which led to the decrease of the macro-capillary pores in micro-structures. For achieving the targeted requirements for pH value and compressive strength, the $M_{mp}$ needs to be selected as below 5.1.

• Resources Recycling
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• v.25 no.1
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• pp.40-47
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• 2016

Nickel laterite ore is classified into two principal ore types: saprolite (silicate ore) and limonite (oxide ore). Saprolite-type ore characterized by high magnesia and silica contents is treated by pyrometallurgy process. On the other hand, limonite-type ore is subjected to hydrometallurgy process to produce nickel products. Hydrometallurgy process requires that a raw material to meet the demands that Si+Mg contents lower than 10% and Fe content over than 40%. It is therefore required that separation of saprilite-type ore to use nickel laterite ore as a raw material for hydrometallurgy process. In this study, separation of sparolite-type ore and limonite-type ore from nickel laterite ore from New Caledonia has been tried by dry classification. The results show that -5 mm size fraction and +5 mm size fraction of the nickel laterite ore contains mainly limonite-type ore and saprolite-type ore, respectively. To understand the moisture content of the raw ore on the dry classification, nickel laterite ore with different moisture contents of 23.0% and 9.1% were subjected to the dry classification. The results show that drying of the ore makes the separation more efficient as the amount of the fine product, that can be subjected to hydrometallurgy process without further separation or drying operations, was increased.

• Korean Journal of Materials Research
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• v.4 no.7
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• pp.775-782
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• 1994

Influence of $TiO_{2}$ addition on sintering behavior and microstructure of MgO-$ZrO_{2}$ composites was studied. $ZrO_{2}$ containing 3mol%Y203 was existed as a c-$ZrO_{2}$ phase due to the formation of solubility of MgO, $TiO_{2}$ and $ZrO_{2}$ when sintered $1400^{\circ}C$ for 2h. All the compositions employed exhibited a similar shrinkage behavior with an end-point shrinkage between 8.58 and 11.00%. The additlon of $TiO_{2}$ promoted densification and the bulk density of specimen containing 1.67wt% $TiO_{2}$ was 3.75g/$\textrm{cm}^3$(98% TD) when $1600^{\circ}C$ for 2h. The amount of solubilities of MgO and TiOz in $ZrO_{2}$ were 5.ti7wt% and 2.62wt%,respectively. They were partially segregated near $ZrO_{2}$ grain boundary in the form of Ti-compounds during cooling. This segregation resulted in the formation microcracks which decreased the bending strength.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.3
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• pp.103-110
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• 2019

Damage to the pavement system due to various causes will be required rapid repair work for reopening the vehicle traffic. The magnesium oxide phosphate composite(MPC) has a short curing time and is capable of early compressive strength development, is suitable for rapid repair materials. The aim of this study was to evaluate the hardening and compressive strength characteristics of MPC according to the water-binder (W / B) ratio and magnesium-phosphate(M / P) ratio in order to develop repair materials consisted with light burned magnesia and potassium dihydrogen phosphate. In order to ensure the workability in the field application, the difference of mechanical properties according to standard sand and ordinary sand and performance of retards were evaluated. The mix proportion with W/B ratio was about 35% and the M/P ratio was about 1.0 ~ 1.2 has a superior perfomance with strength and hardening condition. Especially, the strength of composite at only 1 day curing with W/B ratio of 0.35 and the M/P ratio of 1.2 was shown the higher than 25.0 MPa. Boric acid as a retarder was found to be suitable for ensuring the working time, and the purity of magnesium oxide was about 90 ~ 95%, which is effective for ensuring curing time and strength.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.4
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• pp.440-448
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• 2023

Utilizing admixture, which is one of the raw material replacement method in the cement industry, is expected to be easily and quickly put to practical use as it is relatively more accessible than other methods. Among cement admixtures, limestone powder is reported to be able to improve cement performance through nucleation effects, chemical effects, and filler effects, so it is a material expected to be suitable as a cement admixture. Meanwhile, as high-quality limestone is depleted around the world, the use of limestone with clay or high magnesia (MgO) content is becoming increasingly inevitable. Therefore, in this study, we attempted to evaluate the suitability of limestone cement as a admixture by measuring the basic properties of limestone cement mixed with limestone of different qualities commonly used in Korea. As a result, the effect of alite reaction promotion was confirmed regardless of the chemical composition of the limestone binder. However, the dilution effect depending on the substitution amount was greater than the chemical composition. It is believed that normal-grade limestone can be used as a mixture as long as the limestone content in cement is within 15 % in this scope of study. In the future, we plan to evaluate the impact of the chemical composition of the limestone mixture through additional experiments depending on the chemical composition of cement.

• Journal of Life Science
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• v.21 no.10
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• pp.1460-1465
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• 2011

This study was conducted to determine the effects of total mixed fermentation (TMF) with bean curd dregs on body weight gain, feed intake and body size of growing Hanwoo heifers. Thirty Hanwoo heifers, 6 months of age and weighing $125.9{\pm}12.0$ kg, were randomly allocated to 3 experimental groups of 10 animals each for a 6-month feeding trial. The groups were T1 (rice straw offered ad libitum with restricted (1.7% BW/day) concentrate), T2 (TMF only offered ad libitum) and T3 (TMF and rice straw offered ad libitum with restricted (1.0% BW/day) concentrate). TMF feeds were composed of 60% bean curd dregs, 16.5% corn meal, 10.4% wheat bran, 5% rice straw, 7% rice hulls, 0.5% urea matter, 0.5% magnesia lime and 0.1% lactic acid bacteria. The chemical composition and pH value of TMF feeds were measured at 0, 24, 48 and 72 hr after storage. In TMF with bean curd dregs, there were no differences in concentrations of DM, EE, and CF according to storage periouds. The ADF and NDF at 72 hr of storage time showed a significant decrease (9.52 and 3.15 %, respectively) compared to 0h of storage time (p<0.05). The value of pH was gradually decreased during the storage periods. Body weight gain, feed intake and average daily gain were higher in the TMF groups (T2, T3) compared to the T1 group (p<0.05). Changes in body size were also higher in the TMF groups compared to the T1 group (p<0.05). Thus, the present results indicate that TMF with bean curd dregs may help improve growth performance in growing Hanwoo heifers.

• Korean Journal of Environmental Agriculture
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• v.42 no.1
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• pp.52-62
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• 2023

This study focused on determining the specific causes and prevention methods of mass fish deaths occurred in five reservoirs (Gagugi, Neupgokgi, Danggokgi, Sagokji, and Hangokji) in Andong-si. For this purpose, a survey of agricultural land and livestock in the upper part of the reservoirs and analysis of water quality in the reservoir irrespective of whether it rains or not were conducted. We attempted to examine the changes in dissolved oxygen (DO) in the surface and bottom layers of reservoirs and changes in DO depending on the amount of livestock compost and time. Based on the above investigations, treatment plans were established to efficiently control the inflow of contaminated water into reservoirs. The rainfall and farmland areas in the upper part of the reservoir were investigated using Google and aviation data provided by the Ministry of Land, Infrastructure, and Transport. The current status of livestock farms distributed around the reservoirs was also examined because compost from these farms can flow into the reservoir when it rains. Various water quality parameters, such as phosphate phosphorus (PO₄-P) and ammonium nitrogen (NH₃-N), were analyzed and compared for each reservoir during the rainy season. Changes in the DO concentration and electrical conductivity (EC) were also observed at the inlet of the reservoir during raining using an automated instrument. In addition, DO was measured until the concentration reached 0 ppm in 10 min by adding livestock compost at various concentrations (0.05%, 0.1%, 0.3%, and 0.5% by wt.), where the concentration of the livestock compost represents the relative weight of rainwater. The DO concentration in the surface layer of reservoirs was 3.7 to 5.3 ppm, which is sufficient for fish survival. However, the fish could not survive at the bottom layer with DO concentration of 0.0-2.1 ppm. When the livestock compost was 0.3%, DO required 10-19 h to reach 0 ppm. Considering these results, it was confirmed that the DO in the bottom layer of the reservoir could easily change to an anaerobic state within 24 h when the livestock compost in the rainwater exceeds 0.3%. The results show that the direct cause of fish mortality is the inflow of excessive livestock compost into reservoirs during the first rainfall in spring. All the surveyed reservoirs had relatively good topographical features for the inflow of compost generated from livestock farms. This keeps the bottom layer of the reservoir free of oxygen. Therefore, to prevent fish death due to insufficient DO in the reservoir, measures should be undertaken to limit the amount of livestock compost flowing into the reservoir within 0.3%, which has been experimentally determined. As a basic countermeasure, minerals such as limestone, dolomite, and magnesia containing calcium and magnesium should be added to the compost of livestock farms around the reservoir. These minerals have excellent pollutant removal capabilities when sprayed onto the compost. In addition, measures should be taken to prevent fish death according to the characteristics of each reservoir.

• Korean Journal of Environmental Biology
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• v.40 no.3
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• pp.267-274
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• 2022

Excess nitrogen (N) flowing from livestock manure to water systems poses a serious threat to the natural environment. Thus, livestock wastewater management has recently drawn attention to this related field. This study first attempted to obtain the optimal conditions for the further volatilization of NH₃ gas generated from pig wastewater by adjusting the amount of injected magnesia (MgO). At 0.8 wt.% of MgO (by pig wastewater weight), the volatility rate of NH₃ increased to 75.5% after a day of aeration compared to untreated samples (pig wastewater itself). This phenomenon was attributed to increases in the pH of pig wastewater as MgO dissolved in it, increasing the volatilization efficiency of NH₃. The initial pH of pig wastewater was 8.4, and the pH was 9.2 when MgO was added up to 0.8 wt.%. Second, the residual ammonia nitrogen (NH₄⁺-N) in pig wastewater was removed by precipitation in the form of struvite (NH₄MgPO₄·6H₂O) by adjusting the pH after adding MgO and H₃PO₄. Struvite produced in the pig wastewater was identified by field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) analysis. White precipitates began to form at pH 6, and the higher the pH, the lower the concentration of NH₄⁺-N in pig wastewater. Of the total 86.1% of NH₄⁺-N removed, 62.4% was achieved at pH 6, which was the highest removal rate. Furthermore, how struvite changes with pH was investigated. Under conditions of pH 11 or higher, the synthesized struvite was completely decomposed. The yield of struvite in the precipitate was determined to be between 68% and 84% through a variety of analyses.