• Resources Recycling
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• v.28 no.3
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• pp.26-34
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• 2019

Due to the increasing demand of rare earth magnet for various application, it is predicted that the amount of waste rare earth magnet will increase sharply. The process of waste rare earth magnet recycling is mainly consisted of leaching and separation of rare earth element contained in the magnet. However, there is no study on the breakage characteristics of the waste rare earth magnet for production of magnet powder. Therefore, in this study, effective crushing/grinding process and breakage characteristics were investigated for waste rare earth magnet. In the case of jaw crusher, the particle size of magnet was effectively reduced without rapid oxidation. In ball mill grinding test, it was found that the grinding process was not performed properly at the early stage of grinding. Moreover, waste rare earth magnet showed very low specific rate of breakage(S) and high fraction of fine particle breakage distribution(B) compared to ordinary minerals. These results can be used as a basic data for developing crushing/grinding circuit of waste rare earth magnet.

• Journal of Korean Society of Environmental Engineers
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• v.31 no.4
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• pp.287-293
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• 2009

This study investigated the influence of ionic strength on the adhesion and release of bacteria (Escherichia coli, Bacillus subtilis, and Staphylococcus aureus) in quartz and iron-coated sands using column experiments. Results show that the mass recovery remained constant (E. coli = 13.7${\pm}$0.5%, B. subtilis = 9.8${\pm}$1.3%, S. aureus = 13.0${\pm}$2.1%) in iron-coated sand while it decreased from 80.7 to 45.3% (S. aureus) in quartz sand with increasing ionic concentrations from 1 to 100 mM. As the ionic concentrations of leaching solution was lowered from 100 to 0.1 mM, average 39.1% of bacterial detachment was quantified from quartz sand, but no bacterial release was observed in iron-coated sand. The phenomenon observed in iron-coated sand can be attributed to the inner-sphere complexes between bacteria and coated sand, which have minimal effect from ionic strength. This study improves our knowledge regarding the bacterial interaction with surface-modified porous media.

• KSBB Journal
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• v.16 no.1
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• pp.54-60
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• 2001

The activity of microorganisms is an important factor that determines the efficiency of the bacterial recovery of precious metals from low-grade ore. Metal-leaching microorganisms must have a tolerance, within the concentration levels encountered to leached metals. In this study, the tolerance levels of Thiobacillus ferroxidans to the single and mixed metal ions systems, composed of $Zn^{2+}$, $Cu^{2+}$, $Ni^{2+}$, and $Cd^{2+}$ were investigated. When single metal ions of $Zn^{2+}$ (10~60 g/L), $Cu^{2+}$ (1~6 g/L), $Ni^{2+}$ (1~6 g/L), or $Cd^{2+}$ (1~6 g/L) were added to the growth medium of T. ferrooxidans, the iron oxidation rate of this bacterium was not significantly inhibited. The maximum inhibition percentage observed on the iron oxidation rate of T. ferrooxidans was approximately 50% in the medium supplemented with two or three mixed metal ions of $Cu^{2+}$, $Ni^{2+}$, and $Cd^{2+}$. However, when $Zn^{2+}$ was also added to the medium with the other metal ions, the inhibitory effect on the iron oxidation activity of T. ferroxidans was remarkably increased.

• Resources Recycling
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• v.32 no.1
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• pp.50-59
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• 2023

The amount of dust generated during the dissolution of scrap in an electric arc furnace is approximately 1.5% of the scrap metal input, and it is primarily collected in a bag filter. Electric arc furnace dust primarily consists of zinc and ion. The processing of zinc starts with its conversion into pellet form by the addition of a carbon-based reducing agent(coke, anthracite) and limestone (C/S control). These pellets then undergo reduction, volatilization, and re-oxidation in rotary kiln or RHF reactor to recover crude zinc oxide (60%w/w). Next, iron is discharged from the electric arc furnace dust as a solid called Fe clinker (secondary by-product of the Fe-base). Several methods are then used to treat the Fe clinker, which vary depending on the country, including landfilling and recycling (e.g., subbase course material, aggregate for concrete, Fe-source for cement manufacturing). However, landfilling has several drawbacks, including environmental pollution due to leaching, high landfill costs, and wastage of iron resources. To improve Fe recovery in the clinker, we pulverized it into optimal -sized particles and employed specific gravity and magnetic force selection methods to isolate this metal. A carbon-based reducing agent and a binding material were added to the separated coarse powder (>10㎛) to prepare briquette clinker. A small amount (1-3%w/w) of the briquette clinker was charged with the scrap in an electric arc furnace to evaluate its feasibility as an additives (carbonaceous material, heat-generating material, and Fe source).

• Korean Journal of Soil Science and Fertilizer
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• v.18 no.2
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• pp.140-147
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• 1985

This experiment was conducted in the field to investigate the effects of mulched condition on nutrient's mineralization and its mobility as affected by environmental changes (soil moisture and soil temperature) in the plow layer. 1. Nitrogen mineralization was faster owing to the prevention of evaporation and the increase of soil temperature in the poly ethylene mulched plot. As a result, nitrate form of nitrogen was much earlier available for plant in mulched plot than in non mulched plot. 2. Available $P_2O_5$ content in the plow layer was kept highest in the fertilized zone (10-20 cm depth) regardless of difference between mulched and non mulched condition, and was nearly constant without showing difference between planting and non planting of tobacco due to the lower availability of phosphorus by tobacco. 3. Potassium applied in the plow layer was remained a large quantity until the latter growth stage resulting in the lower recovery of potassium by tobacco. 4. Mineralized nutrients such as $NH_4-N$, $NO_3-N$, and K in the plow layer of mulched plot were transported from the fertilized layer (10-20 cm depth) and accumulated to the surface layer (0-10 cm depth) as the growing time goes by, but those in non mulched plot were distributed to the deeper layer. 5. Mobility of available nutrients in the plow layer was If order as $NO_3-N$ $$\geq_-$$ $NH_4-N$ > K > available $P_2O_5$. 6. Leaching degree of mineralized nutrients in the mulched plot was much lower than in the non mulched plot.

• Journal of the Korean Electrochemical Society
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• v.17 no.2
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• pp.111-118
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• 2014

The electrochemical properties using the cells assembled with the synthesized $LiCoO_2$(LCO) were evaluated in this study. The LCO was synthesized from high-purity cobalt sulfate($CoSO_4$) which is recovered from the cathode scrap in the wastes lithium ion secondary battery(LIB). The leaching process for dissolving the metallic elements from the LCO scrap was controlled by the quantities of the sulfuric acid and hydrogen peroxide. The metal precipitation to remove the impurities was controlled by the pH value using the caustic soda. And also, D2EHPA and $CYANEX^{(R)}272$ were used in the solvent extraction process in order to remove the impurities again. The high-purity $CoSO_4$ solution was recovered by the processes mentioned above. We made the 6 wt.% $CoSO_4$ solution mixed with distilled water. And the 6 wt.% $CoSO_4$ solution was mixed with oxalic acid by the stirring method and dried in oven. $LiCoO_2$ as a cathode material for LIB was formed by the calcination after the drying and synthesis with the $Li_2CO_3$ powder. We assembled the cells using the $LiCoO_2$ powders and evaluated the electrochemical properties. And then, we confirmed possibility of the recyclability about the cathode materials for LIBs.