Kitae Baek

Adsorption characteristics of As(V) on iron-coated zeolite

The sorption characteristics of arsenic(As(V)) on iron-coated zeolite (ICZ) were investigated through batch and column studies. As(V) was completely removed within 30 min in a concentration of 2mg/l, with a 100g/l dose of ICZ. Optimum dose of ICZ was 33.3g/l at a concentration of 20.12 mg/l and the effect of solution pH was negligible at a pH range of 3.0<pH<10.0. Langmuir Isotherm Model was suitable to explain the sorption characteristics of As(V) onto ICZ. The co-presence of sulfate ions inhibited sorption of As(V) because of competitive adsorption. The adsorption capacity of ICZ for As(V) was 0.68 mg/g. Based on the result, ICZ is a suitable material to treat the mine drainage or wastewater bearing As(V).

Electrokinetic remediation of Zn and Ni-contaminated soil.

The feasibility of catholyte conditioning with the acidic solution and pre-treatment of soil with acidic solution was investigated with the electrokinetic remediation of Zn and Ni contaminated field soil. The extraction of Zn and Ni from soil increased with the decrease in pH of the extracting solution and nitric acid was very effective to extract Zn and Ni from the soil. Conventional electrokinetic treatment and acetate buffer circulation method were not effective to remove Zn and Ni from the soil. Pre-treatment of the soil with acidic solution enhanced the desorption of Zn and Ni and catholyte conditioning with this solution was effective in maintaining the overall soil pH within the electrokinetic cell. The catholyte conditioning and pre-treatment method enhanced the removal of Zn and Ni up to 41% and 40% after operation for 4 weeks. More than 96% of Zn and Ni removed by electrokinetic remediation were due to the electromigration. Catholyte conditioning and the pre-treatment method is effective in enhancing metal removal in electrokinetic remediation.

Adsorption of Cr(VI) onto cationic surfactant-modified activated carbon

Highly toxic oxyanions, such as hexavalent chromium (Cr(VI)), have caused adverse effects on human health. This study evaluated the feasibility of using cationic surfactant-modified activated carbon (AC) to remove Cr(VI). To modify activated carbon using a cationic surfactant, AC was mixed with a surfactant solution of 0.5 critical micelle concentration (CMC), at which concentration the surfactant molecules exist as mono-molecules. Adsorption kinetics and an isotherm model were used to study the adsorption characteristics of Cr(VI) onto MAC. The adsorption capacity of MAC for Cr(V) was enhanced compared to that of AC. MAC modified by hexadecyltrimethylammonium had a higher adsorption capacity for the removal of Cr(VI) than that modified by cetylpyridinium. The modification of AC by a cationic surfactant enhanced both its Cr(VI) adsorption rate and its Cr(VI) adsorption capacity. The breakthrough point of MAC for Cr(VI) was 100 times greater than for the raw AC. As a result, MAC is a promising adsorbent to treat Cr(VI) in an aqueous stream.

Electrolyte conditioning-enhanced electrokinetic remediation of arsenic-contaminated mine tailing.

Feasibility of electrolyte conditioning with strong acidic or alkaline solution on electrokinetic remediation of arsenic-contaminated mine tailing was investigated in the laboratory. The mine tailing contained calcium oxide of more than 50%. At alkaline condition, arsenic was precipitated with calcium, and formed calcium arsenate which is very stable solid. Catholyte conditioning with strong acidic solution and anolyte conditioning with strong alkaline solution showed similar efficiency to remove arsenic. At 4mAcm(-2) of current density, the removal efficiency of arsenic was 62% after 28 days operation with catholyte conditioning with 0.1M nitric acid.

Extraction behavior of As, Pb, and Zn from mine tailings with acid and base solutions.

The aim of this study was to investigate the extraction behavior of As, Pb, and Zn from mine tailings for considering the feasibility of soil washing. Extraction of metals was studied for different extractant doses, solid/liquid ratios, and equilibrium times. Generally, high extraction efficiency was achieved with HCl, H(3)PO(4), and H(2)SO(4), while H(2)SO(4) proved to be problematic with respect to Pb. NaOH was found to be favorable in removing As, while it was not effective at extracting Pb and Zn. With optimum conditions, which were a 1:5 solid-liquid ratio and 2h of extraction time, 0.5M of HCl extracted 21.1-72.5%, 9.9-86.5%, and 6.1-74.1% of As, Pb, and Zn, respectively. The power and Elovich function were adequate to describe adsorption kinetics. These results suggest that HCl and NaOH could be used to effectively extract all metals without selectivity and As with selectivity, respectively, in mine tailings and could be used for the design of soil washing process.

Removal characteristics of anionic metals by micellar-enhanced ultrafiltration.

Surfactant-based separation of Fe(CN)(6)(3-) and CrO(4)(2-) using regenerated cellulose membrane was studied in order to assess the potential of micellar-enhanced ultrafiltration for the remediation of wastewater or groundwater polluted with ferriccyanide and chromate. In the ferriccyanide/octadecylamine acetate (ODA) and chromate/ODA systems, removal of ferriccyanide increased from 73 to 92% and to 98%, and that of chromate from 64 to 97% and to >99.9% as the molar ratio of ODA to ferriccyanide and to chromate increased from 1 to 2 and to 3, respectively. In the ferriccyanide/chromate/ODA system, while the removal of ferriccyanide increased from 62 to 72% and to 93%, the removal of chromate from 20 to 38% and to 68% as the molar ratio of ferriccyanide:chromate:ODA increased from 1:1:1 to 1:1:2 and to 1:1:4, respectively. With the molar ratio of 1:1:6, the removal was >99.9 and 98% for chromate and ferriccyanide, respectively. Ferriccyanide ions were more easily bound to ODA micelles because the binding power of ferriccyanide was greater than that of chromate.

Electrokinetic remediation of fluorine-contaminated soil: Conditioning of anolyte

The feasibility of anolyte conditioning on electrokinetic remediation of fluorine-contaminated soil was investigated with a field soil. The initial concentration of fluorine, pH and water content in the soil were 414mg/kg, 8.91 and 15%, respectively. Because the extraction of fluorine generally increased with the soil pH, the pH of the anode compartment was controlled by circulating strong alkaline solution to enhance the extraction of fluorine during electrokinetic remediation. The removal of fluorine increased with the concentration of the alkaline solution and applied current density and fluorine removed up to 75.6% within 14 days. Additionally, anolyte conditioning sharply increased the electro-osmotic flow, which enhanced the removal of fluorine in this study. In many respects, anolyte conditioning in electrokinetic remediation of fluorine-contaminated soil will be a promising technology.

Assessment of metals contamination of soils in Ulaanbaatar, Mongolia.

The purpose of this survey is to investigate the current status of metal pollution of the soil in Ulaanbaatar, the capital city of Mongolia. During the last decade, the city has been rapidly urbanized. Twenty-two soil samples were collected from different parts of the city and analyzed by aqua regia extraction. Generally, metal pollution was not a serious problem in the city and there was no significant evidence of infiltration of metal solutions into subsoil (at a depth of 30 cm). However, it was recently found that the arsenic(As) concentration in the soil was higher than the guideline value and the lead(Pb) content in some samples was higher than normal. The source of As pollution appears to be the coal combustion in three power plants in the city. The sources of the increase in Pb pollution might be the remarkable increase in the number of used vehicles and the increase in the use of leaded fuel in the last few years. To evaluate the leaching potential of heavy metals, sequential extraction was conducted. The quantity of the easily extractable fraction of metals was lower than that of the hardly extractable (residual) fraction. As a result, the leaching potential of heavy metals in Ulaanbaatar was found to be quite low.

Electrokinetic remediation of contaminated soil with waste-lubricant oils and zinc.

The feasibility of electrokinetic technology on the remediation of mixed-waste-contaminated railroad soil, contaminated by lubricant oil and zinc, was investigated. To enhance the removal efficiency, catholyte purging with 0.1M HNO(3) and a supply of non-ionic surfactant, secondary alcohol ethoxylate, was applied to the anode to remove Zn and to solubilize the lubricant oil. The catholyte purging maintained the soil pH as acidic and enhanced desorption of zinc from the soil, where the zeta potential of the acidic soil became positive. Thereafter, the direction of electro-osmotic flow was changed from the cathode to anode and the flow rate was reduced. The lesser in magnitude reverse electro-osmotic flow inhibited the migration of zinc and the lubricant oil was removed by the electro-osmotic flow. The removal of zinc and lubricant oil was enhanced with an increase in voltage gradient; however, a higher voltage gradient resulted in higher energy expenditure. After electrokinetic operation over 17 days, the removal efficiency of zinc was 22.1-24.3%, and that of lubricant oil was 45.1-55.0%. Although the removal of lubricant oil was quite high, the residual concentration did not meet Korean regulation levels.

Arsenic speciation and bioaccessibility in arsenic-contaminated soils: sequential extraction and mineralogical investigation.

In this study, a combination of sequential extraction and mineralogical investigation by X-ray diffraction and X-ray photoelectron spectroscopy was employed in order to evaluate arsenic solid-state speciation and bioaccessibility in soils highly contaminated with arsenic from mining and smelting. Combination of these techniques indicated that iron oxides and the weathering products of sulfide minerals played an important role in regulating the arsenic retention in the soils. Higher bioaccessibility of arsenic was observed in the following order; i) arsenic bound to amorphous iron oxides (smelter-2), ii) arsenic associated with crystalline iron oxides and arsenic sulfide phase (smelter-1), and iii) arsenic associated with the weathering products of arsenic sulfide minerals, such as scorodite, orpiment, jarosite, and pyrite (mine). Even though the bioaccessibility of arsenic was very low in the mine soil, its environmental impact could be significant due to its high arsenic concentration and mobility.