• Journal of Korean Society of Environmental Engineers
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• v.31 no.1
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• pp.29-34
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• 2009

This study was performed under four operational conditions for nitrogen removal in metal finishing wastewater. The conditions include electrode gap, reducing agent, the recycling of treated wastewater in 1st step and the simultaneous treatment of nitrate and other materials. Result showed that the removal efficiency of $NO_3{^-}-N$ was highest at the electrode gap of 10 mm. As the electrode gap was shorter than 10 mm, the removal efficiency of $NO_3{^-}-N$ decreased due to increasing in concentration polarization on electrode. And, in case that the electrode gap was longer than 10 mm, the removal efficiency of $NO_3{^-}-N$ increased with an increase in energy consumption. Because hydrogen ions are consumed when nitrate is reduced, reducing reaction of nitrate was effected more in acid solution. As 1.2 excess amount of zinc was injected, the removal efficiency of $NO_3{^-}-N$ increased due to increasing in amount of reaction with nitrate. As the effluent from 1st step in the reactor was recycled into the 1st step, the removal efficiency of $NO_3{^-}-N$ increased. Because the zinc were detached from the cathode and concentration-polarization was decreased due to formation of turbulence in the reactor. The presence of $NH_4{^+}-N$ did not affect the removal efficiency of $NO_3{^-}-N$ but the addition of heavy metal decreased the removal efficiency of $NO_3{^-}-N$. As chlorine is enough in wastewater, the simultaneous treatment of nitrate and ammonia nitrogen may be possible. The problem that heavy metal decrease the removal efficiency of $NO_3{^-}-N$ may be solved by increasing current density or using front step of electrochemical process for heavy metal removal.

• Journal of Wetlands Research
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• v.12 no.1
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• pp.23-31
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• 2010

Chlorinated aliphatic hydrocarbons (CAHs) such as tetrachloroethylene (PCE), 1,1,1-trichloroethane (1,1,1-TCA) are the contaminants most frequently found in soil and groundwater. They have a potential to be toxic to and persistent in environment. This study is focused on selection of zero-valent metal and ores for the removal of high concentration PCE or 1,1,1-TCA and mixture of two compound. For the screening of suitable metals, we measured dechlorination rate, removal capacities and economics by using batch reactor test. This results suggest that removal rate and dechlorination of high quality iron and zinc are higher than slag and nature ores like zinc and manganese. Among nature ores, zinc ores(64% purity) have highest removal capacities. And in economics zinc ores is 10 times better than high quality metal tested. We conclude zinc ore is most suitable metal for the removal of PCE or 1,1,1-TCA.

• Journal of Environmental Science International
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• v.13 no.1
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• pp.61-68
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• 2004

Three kinds of toxic heavy metals, such as lead, copper, and cadmium, existing abundantly in contaminated soils were selected to investigate pH change, electroosmotic flow, and the removal rate in the application of electrokinetic process. In the change of pHs, they reached to about 12 and 2 at each cathodic and anodic region, respectively, and maintained for reaction being proceeded. Electroosmotic flow rates were not influenced by the kind of metal species but by electropotential gradient. On the soils contaminated by each metal, the removal rate of Cd was the fastest among three as in the order of Cd>Pb>Cu. While on the soils contaminated by mixed metal species, Cu was the fastest. Metal species transported by electrokinetic processes were distributed in between 0.9 and 1.0 of normalized region. In the case of soils contaminated by one kind of metal. the relative concentrations of Pb and Cd estimated in between normalized region 0.9 and 1.0 were 5.2 and 5.7, respectively.

• Journal of Environmental Science International
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• v.9 no.4
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• pp.325-330
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• 2000

The hydroxyapatite (HAp) for the present study was prepared by precipitation method in semiconductor fabrication and the crystallized at ambient to 95$0^{\circ}C$ for 30min in electric furnace. The ion-exchange characteristics of HAp for various heavy metal ions such as $Cd^{2+}, Cu^{2+}, Mn^{2+}, Zn^{2+}, Fe^{2+}, Pb^{2+}, Al^{3+}, and Cr^{6+}$ in aqueous solution has been investigated. The removal ratio of various metal ions for HAp were investigated with regard to reaction time, concentration of standard solution, amount of HAp and pH of solution. The order of the ions exchanged amount was as follws: $Pb^{2+}, Fe^{3+}>Cu^{2+}>Zn^{2+}>Al^{3+}>Cd^{2+}>Mn^{2+}>Cr^{6+}. The Pb^{2+}$ ion was readily removed by the Hap, even in the strongly acidic region. The maximum amount of the ion-exchange equilibrium for $Pb^{2+}$ ion was about 45 mg/gram of HAp. The HAp would seem to be possible agent for the removal of heavy metal ions in waste water by recycling of waste sludge in semiconductor fabrication.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.7 no.3
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• pp.67-74
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• 2008

Polycrystalline diamonds(PCD) tools are widely used in machining a large variety of advanced materials. However, the manufacture of PCD tool blanks is not an economical process. The shaping of PCD blanks with conventional machining methods(such a grinding) is long, labor-intensive process. This paper reports experimental investigation of the influence of electrical machining conditions on the metal removal rate of WEDM of PCD. Experimental results show that the longer pulse-on time and the shorter pulse-off time increase the metal removal rate and worsen the surface quality. The smaller grain size of diamond yields the metal removal rate and shows the better surface quality. Higher electrical conductivity of water yields worse surface roughness.

• Analytical Science and Technology
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• v.19 no.4
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• pp.280-284
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• 2006

The objective of this study is to investigate the removal of heavy metal by using the coprecipitation of barium sulfate. Several parameters governing the efficiency of the coprecipitation method were evaluated by the pH of sample solution, amount of coprecipitant, and addition of sulfide for the removal of As(V), Cd(II), Cr(III), Cr(VI), Cu(II), Hg(II) and Pb(II) metal ions ($10{\mu}g/ml$ each). The coprecipitation was about 80% - 95% only for lead at low pH but under 10% for other ions. The amount of removal was about 95% - 100% for Cd, Hg, Pb, Cu in the all pH range by the addition of sulfide with barium sulfate but As(V) and Cr(III, VI) ions were not affected by the same conditions.

• Resources Recycling
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• v.31 no.4
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• pp.49-55
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• 2022

In this study, the heavy metal ions (of Pb, Cd, Cr, and Hg) in wastewater were removed using a spent Li₂O-Al₂O₃-SiO₂-based crystallized glass previously used as an induction top plate material. Changes in the removal efficiency of heavy metals according to different reaction parameters, such as the amount of zeolite used as a heavy-metal adsorbent, adsorption time, initial concentration of the heavy metals, and pH of the initial solution, were investigated. As the amount of zeolite added increased, the heavy-metal removal efficiency also increased. Adsorption time had a considerable influence on adsorption characteristics, and the removal efficiency of all heavy metals increased with increasing adsorption time. In the case of Cd, the removal efficiency was greatly improved depending on the adsorption time. The initial concentration of the heavy-metal solution did not affect the removal efficiency; however, the initial pH of the heavy-metal solution affected the removal efficiency. More specifically, the removal efficiency of Cd increased while that of Pb and Cr decreased with increasing pH. The adsorption characteristics of Hg were not significantly affected by pH.

• Journal of the Korean Wood Science and Technology
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• v.12 no.3
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• pp.9-14
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• 1984

The removal and readsorption effects of pine and oak bark grown in Korea on water pollution caused by heavy metal ions have been investigated. Bark saturated with heavy metal ions is refleshed with 0.1 N ammonium acetate and then its readsorption has been done. The results obtained are as follows: 1. Adsorption effect of pine bark is similiar to that of oak bark, and 20-40 meshed bark gives the best results. 2. 0.1 N amonium acetate of pH 7 shows more elutriative than the others such as pH 3 hydrochloric acid, pH 10 ammonium hydroxide and pH 7 water. 3 Pine bark refleshed with 0.1 N ammonium acetate gets two times as effective in adsorption as raw bark, and shows more effective than oak bark.

• Journal of Mechanical Science and Technology
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• v.15 no.12
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• pp.1676-1682
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• 2001

This work deals with the electrical conductivity of dielectric and cobalts percentage on output parameters such as metal removal rate and surface roughness value of sintered carbides cut by wire-electrical discharge machining (WEDM). To obtain a precise workpiece with good quality, some extra repetitive finish cuts along the rough cutting contour are necessary, Experimental results show that increases of cobalt amount in carbides affects the metal removal rate and worsens the surface quality as a greater quantity of solidified metal deposits on the eroded surface. Lower electrical conductivity of the dielectric results in a higher metal removal rare as the gap between wire electrode and workpiece reduced. Especially, the surface characteristics of rough-cut workpiece and wire electrode were analyzed too. To obtain a good surface equality without crack, 4 finish-cuts were necessary reducing fille electrical energy and the offset value.

• Journal of Environmental Health Sciences
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• v.22 no.3
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• pp.81-87
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• 1996

The purpose of this research is to examine the utilization of oyster shells for neutralization and removal of heavy metal ions in plating wastewater, because oyster shells have been known to be very porous, to have high specific surface area and to have alkaline minerals such as calcium and magnesium. The results obtianed from this research showed that oyster shells had a buffer capacity to neutralize an acidic.alkali system in plating wastewater. Generally, it could be showed that the removal efficiencies of heavy metal ions were very influenced by reaction times and oyster shell dosages. In point of ocean waste, if oyster shells substituted for a valuable adsorbent such as actviated carbon, they could look forward to an expected economical effect.