• Journal of the Mineralogical Society of Korea
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• v.26 no.3
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• pp.139-150
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• 2013

In order to effectively leach Fe from pyrite, the application of microwave energy and ammonia solution has been conducted. Pyrite transforms into hematite and pyrrhotite when treated with microwave radiation for 60 minutes, and in this time the highest amount of Fe was leached by the ammonia solution. Up to 99% of the Fe was leached when the experimental conditions were: 325-400 mesh particle size for the pyrite and 60 min. was the microwave exposure time. The ammonia leaching conditions were 0.3 M sulfuric acid, 2.0 M ammonium sulfate and 0.1 M hydrogen peroxide concentration. The pyrite, hematite, and pyrrhotite were not detected using XRD analysis from the solid-residues treated by the ammonia solution except for quartz.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.2
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• pp.504-521
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• 2016

Recently, energy harvesting technology has been integrated into wireless sensor networks to ameliorate the nodes' energy limitation problem. In theory, the wireless sensor node equipped with an energy harvesting module can work permanently until hardware failures happen. However, due to the change of power supply, the traditional hierarchical network routing protocol can not be effectively adopted in energy harvesting wireless sensor networks. In this paper, we improve the Low-Energy Adaptive Clustering Hierarchy (LEACH) protocol to make it suitable for the energy harvesting wireless sensor networks. Specifically, the cluster heads are selected according to the estimation of nodes' harvested energy and consumed energy. Preference is given to the nodes with high harvested energy while taking the energy consumption rate into account. The utilization of harvested energy is mathematically formulated as a max-min optimization problem which maximizes the minimum energy conservation of each node. We have proved that maximizing the minimum energy conservation is an NP-hard problem theoretically. Thus, a polynomial time algorithm has been proposed to derive the near-optimal performance. Extensive simulation results show that our proposed routing scheme outperforms previous works in terms of energy conservation and balanced distribution.

• Nuclear Engineering and Technology
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• v.23 no.4
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• pp.374-386
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• 1991

Various factors affecting the teachability of Cs-137 in cement matrix have been investigated. Factors investigated include such as pressure curing, vibration curing, pressure leaching, the effect of the clay addition, ion-exchange resin(IRN-77) addition, and $CO_2$or air injection. Leaching experiments were conducted by the method recommended by IAEA. To analyze the experimental results, pore structure analysis of cement matrices was carried out by BET method. Cement matrices may not contact directly with underground water in real repository, since the surroundings of disposed drums are filled with backfill. Thus, the effect of backfill to the teachability has been investigated. The well-known diffusion theory was utilized to predict long term leach rate and cumulative fraction leached of Cs-137 or non-radioactive species.

• Journal of Korean Society of Water and Wastewater
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• v.30 no.5
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• pp.571-577
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• 2016

Phosphorus is an essential and irreplaceable element for all living organisms and its resource is limited. Significant amount of used phosphorus is collected in sewage treatment plant as sludge. Sludge ash after incineration contains about 10% of phosphorus in dry mass basis, which is comparable to phosphate rocks, and it is an important source of phosphorus recovery. Acid and alkali were used to leach phosphorus from sludge ash and compared for their leaching kinetics and performance. Phosphorus leaching by NaOH was fast and 0.2 N and 2 N NaOH leached 49% and 56% of the total phosphorus in the sludge ash at the L/S ratio of 100. Phosphorus leaching by sulphuric acid and hydrochloric were very fast and most of the phosphorus was leached in 5 minutes. In case of sulphuric acid 95% of the total phosphorus in the sludge ash was leached by 0.2 N at the L/S ratio of 100 and 93% was leached by 1 N at the L/S ratio of 10. 1 N hydrochloric acid leached 99% of the total phosphorus at the L/S ratio of 10. The results showed acids were more effective than alkali for phosphorus leaching from sludge ash and hydrochloric acid leached more phosphorus than sulphuric acid.

• Journal of Powder Materials
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• v.20 no.3
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• pp.197-202
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• 2013

A novel route to prepare Nd-Fe-B magnetic particles by utilizing both spray drying and reduction/diffusion processes was investigated in this study. Precursors were prepared by spray drying method using the aqueous solutions containing Nd salt, Fe salt and boric acid with stoichiometric ratios. Precursor particles could be obtained with various sizes from 2 to $10{\mu}m$ by controlling concentrations of the solutions and the average size of $2{\mu}m$ of precursors were selected for further steps. After heat treatment of precursors in air, Nd and Fe oxides were formed through desalting procedure, followed by reduction processes in Hydrogen ($H_2$) atmosphere and with Calcium (Ca) granules in Argon (Ar) successively. Moreover, diffusion between Nd and Fe occurred during Ca reduction and $Nd_2Fe_{14}B$ particles were formed. With Ca amount added to particles after $H_2$ reduction, intrinsic coercivity was changed from 1 to 10 kOe. In order to remove and leach CaO and residual Ca, de-ionized water and dilute acid were used. Acidic solutions were more effective to eliminate impurities, but Fe and Nd were dissolved out from the particles. Finally, $Nd_2Fe_{14}B$ magnetic particles were synthesized after washing in de-ionized water with a mean size of $2{\mu}m$ and their maximum energy product showed 9.23 MGOe.

• Resources Recycling
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• v.17 no.3
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• pp.3-9
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• 2008

The measurement of physicochemical properties and chemical composition of SSA(sewage sludge ash) has been carried out and the preparation of lightweight material has also been performed using SSA for reuse as building or construction materials. For this aim, lightweight material has been prepared by forming the mixture of SSA, lightweight filler and inorganic binder followed by calcination at elevated temperature and characterized in terms of density and compressive strength. The pH of fly ash was found to be slightly alkaline, pH 8.69, due to the addition of caustic soda in order to neutralize the acidic gas while the pH of bottom ash was 6.48 Heavy metal leachability based on the standard leach test was also found to be below the detection limit for Cd, Cu, Pb, As and Cr of SSA. As far as the compressive strength of lightweight material was concerned, the compressive strength of lightweight material using fly ash was higher than that of lightweight material using bottom ash.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.9
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• pp.1-7
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• 2008

The efficient node energy utilization in wireless sensor networks has been studied because sensor nodes operate with limited power based on battery. Since a large number of sensor nodes are densely deployed and collect data by cooperation in wireless sensor network, keeping more sensor nodes alive as possible is important to extend the lifetime of the sensor network. Energy efficiency is an important factor of researches that efficient routing algorithm is needed in wireless sensor network. In this research, I consider some methods to utilize more efficiently the limited power resource of wireless sensor networks. The proposed algorithm is the sink first divides the network into several areas with hop counts and data transmission based on cluster ID. The performance of the proposed algorithm has been examined and evaluated with NS-2 simulator in terms of lifetime, amount of data and overhead.

• Journal of the Mineralogical Society of Korea
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• v.23 no.4
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• pp.331-346
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• 2010

This study was carried out to leach valuable metals from galena using indigenous bacteria with no optimum pH conditions at room temperature. Even in these conditions, the rod-shaped indigenous bacteria, ranging from $0.4{\times}0.2{\mu}m$ to $0.5{\times}1.7{\mu}m$, were attached to the surface of the galena. For the 19 days of the bioleaching experiment, the content of Ph, Fe, Zn ions was found to be 347, 222 and 1.7 times higher than that of the control leaching agent, respectively. Numerous hexagonal column crystals were observed on the surface of galena. Those crystals may be formed from the biooxidation of galena by the indigenous bacteria. XRD analysis showed the peaks of anglesite observed in the bioleached galena. It is expected that more valuable elements can be leached out of the galena, if the bacteria is used under optimum pH and temperature conditions in future bioleaching experiments.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.11
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• pp.7541-7548
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• 2015

Wireless Sensor Networks is the technology which is used in explore role for military purposes, as well as various fields such as industrial equipment management, process management, and leverage available technologies by distributing node into various areas. but there are some limitations about energy, processing power, and memory storage capacity in wireless sensor networks environment, because of tiny hardware, so various routing protocols are proposed to overcome it. however existing routing protocols are very vulnerable in the intercommunication, because they focus on energy efficiency, and they can't use existing encryption for it, Because of sensor's limitations such like processing power and memory. Therefore, this paper propose mutual authentication scheme that prevent various security threats by using mutual authentication techniques and, Key generation and updating system as taking into account energy efficiency.

• Economic and Environmental Geology
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• v.46 no.1
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• pp.29-37
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• 2013

In order to apply the silver cementation method using Fe powder from pregnant thiourea leaching solution. Parameters such as the amount of Fe powder addition, agitation speed, and temperature were investigated. The silver cementation rate was increased by the increasing of Fe powder addition, agitation speed, and temperature. The highest silver cementation rate was found when the addition of Fe powder was 50 g/L at the agitation speed of 500 rpm. The silver cementation rate increase with increasing temperature according to the Arrhenius equation and obeys $1^{st}$ order kinetics. The activation energy from the kinetics data was found to be between 13.73 KJ/mol and 17.02 KJ/mol. In the XRD analysis, goethite was detected in the precipitate of the thiourea leach solution. This indicates that an oxidation-reduction reaction had occurred in the thiourea solution due to the addition of the Fe powder.