• Journal of Soil and Groundwater Environment
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• v.9 no.1
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• pp.63-69
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• 2004

Hematite-coated sand was examined for the application of the PRB (permeable reactive barrier) to the arsenic-contaminated subsurface in the metal mining areas. The removal efficiency of As in a batch and a flow system was investigated through the adsorption isotherm, removal kinetics and column experiments. Hematite-coated sand followed a linear adsorption isotherm with high adsorption capacity at low level concentrations of As (＜1.0 mg/L). In the column experiments, high content of hematite-coated sand enhanced the removal efficiency, but the amount of the As removal decreased due to the higher affinity of As (V) than As (III) and reduced adsorption kinetics in the flow system. Therefore. the amount of hematite-coated sand, the adsorption affinity of As species and removal kinetics determined the removal efficiency of As in a flow system.

• Economic and Environmental Geology
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• v.42 no.2
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• pp.95-105
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• 2009

Systematic studies are performed for arsenic adsorption on synthesized lepidocrocite. The synthesized lepidocrocite with high surface area of $94.8\;g/m^2$ has shown that the point of zero charge(PZC) is 6.57 determined by potentiometric titration, suggestive of high capacity of arsenic removal. Results show that arsenite[As(III)] uptake by synthesized lepidocrocite is greater than that of arsenate[As(V)] at pH $2{\sim}12$, indicating that the lepidocrocite has high affinity toward arsenite rather than arsenate. Adsorption of arsenate decreases with increasing pH from 2 to 12, whereas arsenite sorption increases until pH 8.0, and then decreases dramatically with increasing pH, suggesting that changes in surface charge of the lepidocrocite as a function of pH playa important role in aresinc uptake by the lepidocrocite. Upon kinetic experiments, our results demonstrate that both arsenite and arsenate sorption on the lepidocrocite increases rapidly for the first 4 h followed by little changes during the duration of the experiment, showing that adsorption plays a key role in aresenic uptake by the lepidocrocite. Our results also show that power function and elovich models are the best fit for the adsorption kinetics of arsenite and aesenate on the lepidocrocite.

• Journal of the Mineralogical Society of Korea
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• v.21 no.4
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• pp.425-434
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• 2008

Arsenic contamination in soil and groundwater has recently been one of the most serious environmental concerns. This arsenic contamination can be originated from natural or anthropogenic sources. It has been well known that arsenic behavior in geo-environmental is controlled by various oxides or hydroxides, such as those of iron, manganese, and aluminum, and clay minerals. Among those, particularly, iron (oxy)hydroxides are the most effective scavengers for arsenic. For this reason, this study characterized arsenic adsorption of magnetite which is a kind of iron oxide in nature. The physicochemcial features of the magnetite were investigated to evaluate adsorption of arsenite [As(III)] and arsenate [As(V)] onto magnetite. In addition to experiments on adsorption equilibria, kinetic experiments were also conducted. The point of zero charge (PZC) and specific surface area of the laboratory-synthesized magnetite used as an arsenic adsorbent were measured 6.56 and $16.6\;g/m^2$, which values seem to be relatively smaller than those of the other iron (oxy)hydroxides. From the results of equilibria experiments, arsenite was much more adsorbed onto magnetite than arsenate, indicating the affinity of arsenite on magnetite is larger than arsenate. Arsenite and arsenate showed adsorption maxima at pHs 7 and 2, respectively. In particular, adsorption of arsenate decreased with increase in pH as a result of electrical repulsion caused by anionic arsenate and negatively-charged surface of magnetite. These results indicate that the surface charge of magnetite and the chemical speciation of arsenic should be considered as the most crucial factors in controlling arsenic. The results of kinetic experiments show that arsenate was adsorbed more quickly than arsenite and adsorption of arsenic was investigated to be mostly completed within the duration of 4 hours, regardless of chemical speciation of arsenic. When the results of kinetic experiments were fitted to a variety of kinetic models proposed so far, power function and elovich model were evaluated to be the most suitable ones which can simulate adsorption kinetics of two kinds of arsenic species onto magnetite.

• Journal of the Mineralogical Society of Korea
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• v.21 no.3
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• pp.227-237
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• 2008

Arsenic has recently become of the most serious environmental concerns, and the worldwide regulation of arsenic fur drinking water has been reinforced. Arsenic contaminated groundwater and soil have been frequently revealed as well, and arsenic contamination and its treatment and measures have been domestically raised as one of the most important environmental issues. Arsenic behavior in geo-environment is principally affected by oxides and clay minerals, and particularly iron (oxy)hydroxides have been well known to be most effective in controlling arsenic. Among a number of iron (oxy)hydroxides, for this reason, 2-line ferrihydrite was selected in this study to investigate its effect on arsenic behavior. Adsorption of 2-line ferrihydrite was characterized and compared between As(III) and As(V) which are known to be the most ubiquitous species among arsenic forms in natural environment. Two-line ferrihydrite synthesized in the lab as the adsorbent of arsenic had $10\sim200$ nm for diameter, $247m^{2}/g$ for specific surface area, and 8.2 for pH of zero charge, and those representative properties of 2-line ferrihydrite appeared to be greatly suitable to be used as adsorbent of arsenic. The experimental results on equilibrium adsorption indicate that As(III) showed much stronger adsorption affinity onto 2-line ferrihydrite than As(V). In addition, the maximum adsorptions of As(III) and As(V) were observed at pH 7.0 and 2.0, respectively. In particular, the adsorption of As(III) did not show any difference between pH conditions, except for pH 12.2. On the contrary, the As(V) adsorption was remarkably decreased with increase in pH. The results obtained from the detailed experiments investigating pH effect on arsenic adsorption show that As(III) adsorption increased up to pH 8.0 and dramatically decreased above pH 9.2. In case of As(V), its adsorption steadily decreased with increase in pH. The reason the adsorption characteristics became totally different depending on arsenic species is attributed to the fact that chemical speciation of arsenic and surface charge of 2-line ferrihydrite are significantly affected by pH, and it is speculated that those composite phenomena cause the difference in adsorption between As(III) and As(V). From the view point of adsorption kinetics, adsorption of arsenic species onto 2-line ferrihydrite was investigated to be mostly completed within the duration of 2 hours. Among the kinetic models proposed so for, power function and elovich model were evaluated to be the most suitable ones which can simulate adsorption kinetics of two kinds of arsenic species onto 2-line ferrihydrite.

• Journal of the Mineralogical Society of Korea
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• v.22 no.3
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• pp.177-189
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• 2009

Iron (oxyhydr)oxides commonly form as secondary minerals of high reactivity and large surface area resulting from alteration and weathering of primary minerals, and they are efficient sorbents for inorganic and organic contaminants. Accordingly, they have a great potential in industrial applications and are also of substantial interest in environmental sciences. Goethite (${\alpha}$-FeOOH) is one of the most ubiquitous and stable forms of iron (oxyhydr)oxides in terrestrial soils, sediments, and ore deposits, as well as a common weathering product in rocks of all types. This study focused on adsorption reaction as a main mechanism in scavenging arsenic using goethite. Goethite was synthesized in the laboratory to get high purity, and a variety of mineralogical and physicochemical features of goethite were measured and related to adsorption characteristics of arsenic. To compare differences in adsorption reactions between arsenic species, in addition, a variety of experiments to acquire adsorption isotherm, adsorption edges, and adsorption kinetics were accomplished. The point of zero charge (PZC) of the laboratory-synthesized goethite was measured to be 7.6, which value seems to be relatively higher, compared to those of other iron (oxyhydr)oxides. Its specific surface area appeared to be $29.2\;m^2/g$ and it is relatively smaller than those of other (oxyhydr)oxides. As a result, it was speculated that goethite shows a smaller adsorption capacity. It is likely that the affinity of goethite is much more larger for As(III) (arsenite) than for As(V) (arsenate), because As(III) was observed to be much more adsorbed on goethite than As(V) in equivalent pH conditions. When the adsorption of each arsenic species onto goethite was characterized in various of pH, the adsorption of As(III) was largest in neutral pH range (7.0~9.0) and decreased in both acidic and alkaline pH conditions. In the case of As(V), the adsorption appeared to be highest in the lowest pH condition, and then decreased with an increase of pH. This peculiarity of arsenic adsorption onto goethite might be caused by macroscopic electrostatic interactions due to variation in chemical speciation of arsenic and surface charge of goethite, and also it is significantly affected by change in pH. Parabolic diffusion model was adequate to effectively evaluate arsenic adsorption on goethite, and the regression results show that the kinetic constant of As(V) is larger than that of As(III).

• Korean Journal of Soil Science and Fertilizer
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• v.41 no.6
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• pp.369-373
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• 2008

Special concern has been given to the elevated arsenic content in soils because of its high mobility and toxicity. Layered double hydroxide (LDH) which has a high anionic exchange capacity is another potential anion adsorbent for toxic anions such as arsenic, chromate and selenium etc. The uptake of arsenate from aqueous solutions by the calcined Mg-Al LDH has been investigated. The sorption capacity was about 530 mmol/kg. Sorption isotherm was defined as L-type in which arsenate was removed by LDH through anion uptake reaction. Arsenate sorption by the calcined Mg-Al LDH was occurred by reconstruction of LDH's framework. Competitive adsorption revealed that Mg-Al LDH had higher selectivity for arsenate than for sulfate. These results strongly suggest that calcined Mg-Al LDH has a promising potential for efficient removal of toxic metal oxides like arsenates from aqueous environments.

• Journal of the Mineralogical Society of Korea
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• v.25 no.4
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• pp.197-210
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• 2012

Hematite has been known to be the most stable form of various iron (oxyhydr)oxides in the surface environments. In this study, its properties as an adsorbent were examined and also adsorption of arsenic onto hematite was characterized as well. The specific surface area of hematite synthesized in our laboratory appeared to be $31.8g\;m^2/g$ and its point of zero salt effect, (PZSE) determined by potentiometric titration was observed 8.5. These features of hematite may contribute to high capacity of arsenic adsorption. From several adsorption experiments undertaken at the identical solution concentrations over pH 2~12, the adsorption of As(III) (arsenite) was greater than that of As(V) (arsenate). As of pH-dependent adsorption patterns, in addition, arsenite adsorption gradually increased until pH 9.2 and then sharply decreased with pH, whereas adsorption of arsenate was greatest at pH 2.0 and steadily decreased with the increasing pH from 2 to 12. The characteristics of these pH-dependent adsorption patterns might be caused by combined effects of the variation in the chemical speciation of arsenic and the surface charge of hematite. The experimental results on adsorption kinetics show that adsorption of both arsenic species onto hematite approached equilibrium within 20 h. Additionally, the pseudo-second-order model was evaluated to be the best fit for the adsorption kinetics of arsenic onto hematite, regardless of arsenic species, and the rate constant of As(V) adsorption was investigated to be larger than that of As(III).

• Journal of Korean Society of Environmental Engineers
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• v.31 no.8
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• pp.619-626
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• 2009

The objective of this study was to evaluate the efficiency of Fe and Mn oxides coated granular activated carbons (FMOCGs) for the removal of arsenite and arsenate by oxidation and adsorption mechanisms using surface characterization and batch adsorption experiments. Within four manufactured adsorbents, Fe and Mn contents of FMOCG-1 was the highest (178.12 mg Fe/g and 11.25 mg Mn/g). In kinetic results, As(III) was removed by oxidation and adsorption with FMOCGs. Removal of arsenic by FMOCGs increased as pH value of the solution decreased. The adsorption isotherm results were well fitted with Langmuir isotherm. Adsorption amount of As(V) onto FMOCGs was higher than that of As(III) and the maximum adsorption capacities of FMOCGs for As(III) and As(V) were 1.38~8.44 mg/g and 2.91~9.63 mg/g, respectively.

• Economic and Environmental Geology
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• v.38 no.5 s.174
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• pp.579-585
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• 2005

Cheap and environmental sound biosorbent was made for the adsorption of arsenate using an waste activated sludge. The biosorbents were methylated in 9hours and 24 hours respectively for the better adsorption of arsenate. The amount adsorbed of arsenate(V) increased with increasing methylation time. The specific arsenate adsorption was 0.06mmol As(V)/g biomass when the biosorbent was methylated in 24 hours. The methylated biosorbents were also studied with pH 5, 7 and 9. The pH of the solution affect the amount of adsorption of arsenate of the biosorbent even though it was methylated. The specific arsenate adsorption of the biosorbent at pH 5 was best and it was three times greater than the amount of arsenate adsorbed at pH 9.

• Applied Chemistry for Engineering
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• v.30 no.3
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• pp.345-351
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• 2019

In this study, the hollow fibers from $TiO_2$ and various metal oxides additives were fabricated and characterized in order to remove the arsenic substance from a contaminated water. Experimental results showed the best arsenic adsorption performance from pristine $TiO_2$ hollow fibers. When metal oxides were added, the metal oxides reduced the acid sites on the surface of $TiO_2$ and the arsenic adsorption performance decreased. However, the long term arsenic adsorption performance was enhanced and showed better performance than that of using pristine $TiO_2$ hollow fibers when $Al_2O_3$ was added during the hollow fiber fabrication. In addition, the arsenic adsorption performance showed a high dependency on the specific surface area of hollow fibers. It was confirmed that the abundancy of Lewis and Bronsted acid sites provided was favorable for the arsenic adsorption. It was also demonstrated that commercially available $TiO_2$ powders can be an attractive candidate material for manufacturing hollow fibers for a small scale water treatment plant.