Remediation of Copper from Copper Mine Wastes and Contaminated Soils Using (S,S)-Ethylenediaminedisuccinic Acid and Acidophilic Bacteria

The biodegradable chelating agent (S,S)-Ehylenediaminedisuccinic acid (EDDS), autochthonous acidophilic bacteria, and a combination of the two means were investigated for the removal of pseudo-total and ethylenediaminetetraacetic acid (EDTA)-available content of Cu from surface layers of three soil categories in the Bor copper mining area. Their efficiencies were compared at mine overburden, flotation tailings, and agricultural land sites in order to determine the potential role of these approaches in the soil remediation process. The most effective removal of Cu was achieved on flotation tailings, where combined treatment showed significant reduction of pseudo-total and EDTA-available concentrations of Cu (40.5?±?27.3% and 99.6?±?0.2%, respectively). Acidophilic bacteria treatment showed high efficiency on flotation tailings, removing 94.1?±?1.2% of EDTA-available Cu. EDDS treatment showed discernible results in the removal of EDTA-available Cu from agricultural land soil (44.4?±?13.9%). In the case of overburden soil material, selected agents did not have statistically significant results in the removal of pseudo-total or EDTA-available fraction of Cu. Chosen remediation approaches showed diverse efficiency for soil categories on investigated sites. Combined approach showed synergistic results in the case of EDTA-available Cu removal from flotation tailings soils, suggesting that this combination deserves further attention as a potentially promising environmentally friendly remediation option.     

Carbon storage in relation to soil size-fractions under tropical tree-based land-use systems

The extent of carbon (C) sequestration in soils under agroforestry systems in relation to soil types (fraction sizes) and vegetation structure remains largely unexplored. This study examined soil C storage, an indicator of C sequestration potential, in homegardens (HGs), natural forest, and single-species stands of coconut (Cocos nucifera), rice (Oryza sativa)-paddy, and rubber (Hevea brasiliensis), in Thrissur district, Kerala, India. Soil samples collected from four depth zones up to 1 m were fractionated to three size classes (250 – 2000 µm, 53 – 250 µm, ?<?53 µm) and their total C content determined. Total C stock (Mg ha^?1) was highest in forests (176.6), followed by managed tree-based systems, and lowest in rice-paddy field (55.6). The results show storage of higher amounts of C in the ?<?53 µm fraction, the most stable form of C in soil, up to one- meter depth, in land-use systems with high stand density of trees such as forests and small-sized HG. Although the results do not allow comparison of changes in soil C stock in different land-use systems, they show higher C storage in soils under tree-based land-use systems compared with the treeless (rice-paddy) system, especially in lower soil depths, suggesting the higher soil C sequestration potential of tree-based systems, and thereby their role in reducing atmospheric concentration of carbon dioxide.     

Soil Ingestion Estimates for Children in Anaconda Using Trace Element Concentrations in Different Particle Size Fractions

This investigation assessed the effect of soil particle size on soil ingestion estimates of children residing at a superfund site. Earlier research indicated that wide intertracer variability in soil ingestion estimates are based on soil concentrations with a soil particle size of 0 to 2?µm was markedly reduced when the estimates were based on soil tracer concentrations for a soil particle size of 0-250?µm. The reduced intertracer variation was principally attributed to changes in soil concentrations of only three of the soil tracers (i.e., Ce, La, Nd) which became concentrated in the finer particle size by approximately 2.5 to 4.0-fold. It was hypothesized that the intertracer agreement in soil ingestion estimates may continue to improve if the estimates are based on concentrations of tracers at finer particle sizes assuming that children ingest finer particles and that the above three tracers would continue to be further concentrated in the finer sized soil particles. The principal findings indicate: 1. The soil concentrations of Al, Si, and Ti do not increase at the two finer particle size ranges measured. 2. The soil concentrations of Ce, La, and Nd increased by a factor 2.5 to 4.0 in the 100 to 250?µm particle size range when compared with the 0 to 2?µm particle size range. No further substantial increase in concentration was observed in the 53 to 100 |jm particle size range. 3. The soil ingestion estimates are consistently and markedly changed only between the estimates based in 0 to 2?µm and 100 to 250?µm for Ce, La, and Nd. These changes reduced the intertracer variability in estimating soil ingestion, suggesting that the children eat finer soil particle sizes. 4. Because the particle sizes for all tracers (except Zr) were only modestly affected at the 53 to 100?µm range, it was not possible to confidently resolve the particle size of soil ingested by the children. 5. Residual intertracer variability in soil ingestion estimates based on Ce, La, Nd are likely to be significantly affected by non-food, non-soil sources of these tracers (i.e., source error). 6. Soil ingestion estimates of this study will be more reliable when derived from the finer-sized particles.     

Removal of Anionic Surfactants from Wastewater Using a Constructed Wetland

Removal of anionic surfactants from municipal wastewater using a constructed wetland with a horizontal subsurface flow was studied in 2007 and 2008. Extraction spectrophotometry with methylene blue served to determine the analyte concentrations in individual samples. The anionic surfactant‐removal efficiency depended on actual conditions, mostly the treated water flow intensity, its temperature, and a redox‐potential gradient in the longitudinal profile of the wetland bed. It increased with decreasing inflow and increasing temperature. The average efficiency was 83.7% in 2007 and 81.7% in 2008; however, values higher than 85% were often determined during the summer period. On the other hand, the efficiencies were usually lower than 80% in winter, especially in periods with intensive precipitation and inflows. The average concentration of anionic surfactants in water taken at the outflow was lower than 0.65 mg/l (expressed as sodium dodecyl sulfate). The most significant fraction of anionic surfactants (almost 50%) was degraded at the beginning (1 m from the inflow zone) of the wetland bed. The rhizosphere aeration via the vegetation roots strongly supported the anionic‐surfactant removal.     

Remediation of Contaminated Dredged Sediments Using Physical Separation Techniques

Physical separation processes constitute a cost-effective approach to remediate contaminated sediments. A laboratory-scale physical separation process using froth flotation, Wilfley table (WT), and physical separation column (PSC) as the key unit operations was studied using Sandy Beach sediments (Gaspé, Canada) contaminated with metals, mainly copper (Cu), and polycyclic aromatic hydrocarbons (PAHs). Copper was distributed (89-96%) mainly in the fractions <250 μm, whereas PAHs were mainly in the sand, coarse particles, and gravel. Froth flotation was found to be effective for separating both Cu and PAHs simultaneously from fractions < 250 μm. WT (0.25-2 mm) and PSC (> 2 mm) were more effective for PAH removal than Cu removal. Overall, the treatment process resulted in a cleaned sediment recovery of 74-75% (w/w) with the following pollutants removed: 71-80% PAHs, 61-65% Cu, 27-33% Zn, and 36-40% Pb.     

Remediation of Arsenic-Contaminated Soil Using Alkaline Extractable Organic Carbon Solution Prepared from Wine-Processing Waste Sludge

Past studies have shown that dissolved organic carbon (DOC) washing can effectively remove heavy metals from contaminated soil. In this study, we used alkaline DOC solutions for remediation of arsenic (As)-contaminated soil (with an initial As concentration in the topsoil of 390 mg kg^?1). The removal of As and the change in soil nutrients during DOC washing were studied for 60 min at pH 10 with a 60:1 liquid/soil ratio (v/m). Approximately 88% of As was removed by washing the soil twice using a 3000 mg L^?1 DOC solution at 25°C. Following this treatment, the pH of the soil had increased from 5.6 to 9.2; organic carbon content had increased from 3.5% to 4.1%; cation exchange capacity, ammonium-N, and available phosphorus had increased to 2.3, 1.4, and 6.6 times their original levels, respectively; and exchangeable K, Na, Ca, and Mg had increased to 91, 6.1, 4.2, and 2.2 times their original levels, respectively. A sequential extraction investigation revealed that residual As and easily exchangeable As in the fraction were initially 10.2% and 9.2%, respectively, but that the former became the maximum remainder (64%) after the ultimate DOC washing.     

Cryoprotectant removal temperature as a factor in the survival of frozen rice and sugarcane cells

Removal of cryoprotective additives through use of a room temperature (22 °C) washing step, instead of 0 °C, was found to improve the recovery of sugarcane suspension culture and rice callus tissues. Cultured cells were cryoprotected by gradual addition of a mixture of polyethylene glycol, glucose, and DMSO (PGD) to a final concentration of 10%-8%-10%, w/v, respectively, added at either 0 or 22 °C. After a programmed slow freezing of the cells, they were thawed rapidly and the cryoprotectants were gradually diluted and washed out using a 22 or 0 °C washing medium. Viability of suspension cultured sugarcane cells protected with PGD was greatly diminished when a cold washing solution was used, whether the cells had been frozen (?23 °C) or not. Two mutant lines of rice callus when frozen to ?196 °C in PGD and thawed showed less growth than unfrozen cells, but their growth was improved by washing the thawed cells with a 22 °C solution. With all cultures tested, the addition of PGD at 0 °C and post-thaw washing out at 22 °C gave improved survival. Particularly with the rice lines, optimizing the addition and washing procedures allowed culture survival of liquid nitrogen freezing not otherwise attained.     

The Removal of Pb and Cd from Heavily Contaminated Soil in Kayseri,Turkey by a Combined Process of Soil Washing and Electrodeposition

In this study, a combined system of soil washing and electrodeposition was designed to remove Pb (16381±643 mg/kg) and Cd (34347±1310 mg/kg) from contaminated soil. 0.05 M Na₂EDTA was used as a chelating agent for the remediation of soil, taken from the nearby city Kayseri, Turkey. As a result of the batch extraction tests, maximum removals were determined as; at the 20:1 liquid: soil ratio for Pb is 60.7%, for Cd at the 30:1 liquid: soil ratio is 67.4%. An electrochemical treatment was applied to the waste washing solution which appeared to be the second pollutant after the Na₂EDTA extraction from the soil. With extraction tests of Pb and Cd, being transformed from the solid phase to the liquid phase. The electrochemical treatment (electrodeposition), performed in three different potential (6 V, 8 V and 10 V) and maximum removal efficiencies, were found 99.7% and 80.3% at 10 V for Pb and Cd, respectively.

Speciation tests (BCR) were carried out, both before and after the soil washing process, to evaluate the redistribution of metal fraction in the soil. The fraction, associated with the organic substance, was found as 10.67% for Pb and 1.81% for Cd. The metal bioavailability factor increased after soil washing, which indicates that EDTA could enhance the mobility of Pb and Cd.     

Treatment of phenolic wastes in an aerated submerged fixed-film (ASFF) bioreactor

The biological removal of phenol was studied in a multi-stage fixed-film reactor at phenol concentrations in the range of 190–900 mg l⁻¹, hydraulic loadings of 0.02–0.22 m³ m⁻² day⁻¹ and temperatures of 20–35°C. Phenol removals up to 99.9% were obtained at 20°C but the efficiency decreased as the loading rate or phenol concentration was increased. The reactor coped with organic overloads better than with hydraulic overloads. Removal efficiencies increased as temperature was increased. Reactor performance was stable under extreme loadings and the reactor was capable of handling a ten-fold increase in loading with less than 20% loss in phenol removal efficiency. A large amount of attached biomass was retained in the reactor and was mostly present in the first stage where the majority of organic removal occurred.     

In Situ emulsification and mobilization of gasoline range hydrocarbons using surfactants

In this article the conditions that govern surfactant‐enhanced emulsification and mobilization of petroleum hydrocarbons in soil are reviewed. The effect of soil properties, groundwater constituents, and differing surfactant solutions on the emulsification process is discussed. A constant head soil flushing apparatus used to characterize surfactant‐enhanced mobilization of m‐xylene is described. Data showing the effect of surfactant‐enhanced mobilization on m‐xylene removal efficiency in washed sand is presented. Flushing solutions were used at concentrations from below to well above the critical micelle concentration (CMC) of the surfactants used. Removal efficiencies are shown to vary with surfactant concentration and with surfactant type. Flushing solutions of anionic, nonionic, and anionic/nonionic surfactant mixtures were evaluated.     

Efficacy of lipase from Aspergillus niger as an additive in detergent formulations: a statistical approach

The efficacy of lipase from Aspergillus niger MTCC 2594 as an additive in laundry detergent formulations was assessed using response surface methodology (RSM). A five-level four-factorial central composite design was chosen to explain the washing protocol with four critical factors, viz. detergent concentration, lipase concentration, buffer pH and washing temperature. The model suggested that all the factors chosen had a significant impact on oil removal and the optimal conditions for the removal of olive oil from cotton fabric were 1.0% detergent, 75 U of lipase, buffer pH of 9.5 and washing temperature of 25°C. Under optimal conditions, the removal of olive oil from cotton fabric was 33 and 17.1% at 25 and 49°C, respectively, in the presence of lipase over treatment with detergent alone. Hence, lipase from A. niger could be effectively used as an additive in detergent formulation for the removal of triglyceride soil both in cold and warm wash conditions.     

Enhanced Soil Washing for the Remediation of a Brownfield Polluted by Pyrite Ash

Soil from an abandoned/disused fertilizer plant polluted with pyrite ash containing heavy metal(loid)s (As, Cu, Pb, and Zn) was treated by means of physical and chemical washing. We first performed an exhaustive characterization of the soil-pollutant interaction, which allowed us to determine the chemical nature (complex oxyhydroxides), potential mobility and bioavailability of the pollutants (very low), as well as the grain size fractions of preferential accumulation (silt-clay fraction comprises more than 60% of the material and revealed contents well above 2.000 ppm of Cu, Zn and Pb). Soil/ash samples were subjected to a number of chemical washing trials, including leaching with 2 M HCl, 2 M NaOH and acidic process water (pH around 0). The fraction below 63 µm was mechanically separated and exposed to additional leaching tests e.g. chloridizing roasting with NaCl plus water leaching. Of all the tested procedures, the latter proved the most effective, particularly with regard to Cu and Zn recovery (recoveries up to 40% and 34%, respectively). The information gathered offers an insight into the modes and rates at which metals can be leached from pyrite ashes after chloridizing roasting as a prelude to more extensive soil washing feasibility studies focused on potential metal recovery.     

Mineral colloids mediate organic carbon accumulation in a temperate forest Spodosol: depth-wise changes in pore water chemistry

Mobile submicron mineral phases within soil pore waters are presumed to play a major role in the transport and availability of organic carbon (OC) in subsurface horizons. This work reports on the composition of the?<?0.45 µm and 0.45–1.2 µm size fractions of extracted soil pore waters from horizons of a well-drained-Spodosol-soil to reveal conditions favorable for carbon mobility and accumulation. These operationally defined quantities are abbreviated SF-S (size fraction small) and SF-L (size fraction large) to identify the?<?0.45 µm and the 0.45–1.2 µm size fraction filtrates, respectively. It is found that in the SF-S fraction, OC mass concentrations are more than 30–50 times higher than metal (M?=?Fe?+?Al) mass concentrations in all Spodosol horizons, with metal-to-carbon (M/C) atomic ratios of 0.15–0.03. Chemical equilibrium modeling calculations estimate?>?95% of the total Fe and Al in SF-S are complexed with OC in all Spodosol horizons. In contrast with the SF-S, the SF-L had much greater OC concentrations and even lower M/C (<?0.01), except in the Bh horizon (M/C?=?0.05). In Bh, major accumulation of organic matter occurred above the lesser-accumulating Bhs, the latter having higher pH, but much lower OC in all forms (soil, colloidal). Infrared spectroscopy indicates the SF-L fraction of soil pore waters contains both organic and inorganic constituents, including amorphous silica, the second-most abundant component after OC. Mineral-organic associations such as mineral crystallites embedded in OC are observed in the SF-L fraction by transmission electron microscopy (TEM). Transmission electron microscopy also reveal carbon-rich amorphous structures containing traces of Fe, Al and Si, and small (~?100 nm) spherical amorphous SiO₂ particles. These observations provide support for the main mechanism of OC accumulation in Spodosols being the downward movement of colloids (organic, OC-sorbed mineral and organo-mineral), followed by colloid immobilization due to a combination of increases in pH and M/C ratio. The occurrence of these three types of colloidal structures in pore waters seems to depend on the pH and the relative supply of OC and Fe?+?Al to pore waters. Similar colloidal structures might also contribute to the transport and availability of OC in subsurface horizons of soils that range in the accumulation of organic and organo-metallic compounds, that is, in the expression of spodic properties.     

Effects of young Artemisia rothrockii shrubs on soil moisture,soil nitrogen cycling,and resident herbs

Questions: How do young sagebrush shrubs (Artemisia rothrockii, Asteraceae) affect soil moisture availability? How do young sagebrush shrubs affect soil nitrogen cycling? How does the resident herb community respond to shrub removal in the early stages of sagebrush encroachment? Location: Mulkey and Bullfrog Meadows on the Kern Plateau in the Golden Trout Wilderness, Sierra Nevada Mountains, Inyo National Forest, Inyo County, California, USA. Methods: We removed young encroaching sagebrush shrubs from 3.5 m × 3.5 m plots and compared soil moisture, net mineralization, net nitrification, and herb cover with paired control plots over four growing seasons. Results: On average throughout the experiment, the difference between removal plots and control plots in soil moisture was small. Removal plots were wetter by 1.3 ± 2.0% at 0–30 cm depth, 2.1 ± 3.1% at 30–60 cm depth and 3.1 ± 5.8% at 60–90 cm depth. By contrast, after four years, net mineralization was 32 ± 26% (mean ± 95% CI) lower in sagebrush removal plots, suggesting that sagebrush encroachment increases rates of N‐cycling. Total herb cover was 13.0 ± 6.4% (mean ± 95% CI) higher in plots where young sagebrush shrubs were removed. This difference in cover appeared during the first season in which sagebrush shrubs were removed. Conclusions: Our results suggest that while young sagebrush shrubs do not contribute substantially to meadow drying, they alter N cycling rates, and may indirectly increase the rate of their own encroachment by competitively reducing resident herbs.     

Biosorption of lead by cotton shells powder: Characterization and equilibrium modeling study

Lead (Pb) is a toxic heavy metal causing serious health risks to humans and animals. In the present study, cotton (Gossypium hirsutum L.) shells powder was used as adsorbent for the treatment of synthetic Pb-contaminated water. The batch scale biosorption capacity of cotton shells powder was evaluated to study the effects of Pb concentrations, adsorbent doses and contact time at constant pH (6) and temperature (25?°C). Results revealed that sorption of Pb increased (q?=?0.09–9.60?mg/g) with increasing Pb concentration (1–15?mg/L) and contact time (15–90?min) while decreasing adsorbent dose (1–0.1?g/100?mL). The maximum Pb removal (90%) was achieved at Pb concentration (1?mg/L), contact time (90?min) and adsorbent dose (1?g/100?mL). Freundlich isotherm model proved best fit for Pb sorption (R²?=?0.99). The cotton shells powder has microporous structure confirmed by SEM, and has BET surface area (45 m²/g) and pore size (2.3 µm). These surface moieties along with various functional groups (C-H, C-O, C=O, O-H, S=O) confirmed by FTIR analysis might involve in Pb removal by complexation and ion exchange mechanisms. The cotton shells powder biomass could be considered as promising adsorbent for the removal of Pb from contaminated water.     

The Interactive Effect of Selenium and Farmyard Manure on Soil Microbial Activities,Yield and Selenium Accumulation by Wheat (Triticum aestivum L.) Grains

This study assessed the interactive effect of selenium (Se) and farmyard manure (FYM) on soil microbial activities, growth, yield, and Se accumulation by wheat grains. Preliminarily, the effect of Se (0–250 µg kg^?1 soil) and FYM (0–12.5 g kg^?1 soil) was assessed on soil microflora. Selenium exhibited an adverse impact on soil microflora; respiration was decreased at?≥?10 µg kg^?1 soil while dehydrogenase and urease activities were decreased at?≥?125 µg kg^?1 soil. At 250 µg Se kg^?1 soil, respiration, dehydrogenase and urease activities were decreased by 81, 40 and 35%, respectively, on unamended soil, and by 9, 47 and 22%, respectively, on FYM-amended soil. The subsequent plant experiments were conducted with same Se and FYM rates; one was harvested 42 days after sowing and other at crop maturity. The application of 125 µg Se kg^?1 and 12.5 g FYM kg^?1 soil improved seedling biomass by 12.6 and 22%, respectively, while their combined use lacked synergistic effect. Similarly, at maturity Se and FYM increased grain yield while their combined effect was not synergistic. The Se-induced suppression in microbial activities was not related to yield which was improved (11% at the highest rate in unamended soil) by Se application. Selenium application increased grain Se content in a rate-dependent manner, it increased from 0 to 1025 µg kg^?1 by applying 250 µg Se kg^?1 soil. Moreover, FYM application decreased Se accumulation in grains. It is concluded that FYM application increased soil microbial activities and yield but reduced grain Se accumulation in wheat on Se-applied soil.

     

Organic matter contributed to soil by plant roots during the growth and decomposition of maize

Maize (Zea mays var. Caldera) plants were grown under sterile and not sterile conditions in soil in an atmosphere continuously enriched with ¹⁴CO₂ for 36 days. At harvest the above ground parts of the maize were cut off and the roots were separated from the soil by washing with water. The soil was dispersed using ultrasonics and separated into soluble clay silt and sand fraction. Roots were included in the coarse sand fraction. 25% of the total label present in the soil 5.5% of that in the soil-plant system, was water soluble. Very little label was present in the clay and silt fractions (5% in each) and most (65%) was in the sand fraction as root material.Rapid extraction of soil after the removal of roots without ultrasonic treatment released soluble matter which amounted to <0.5% of the total activity in the soil-plant system.Isolated roots steeped in water released about 18% of their activity. Much of the soluble fraction may therefore be root lysate.The soil and roots accounted for 22% of the total activity in the soil-plant system. Glucose accounted for 89% of the sugars in the soluble fraction of the soil.78% or more of the ¹⁴C present in glucose, arabinose and xylose constituents of the root-soil mixture occurred in the coarse and fine sand fractions, which also included root material. For mannose and galactose the value was 70% and for rhamnose, 50%.After reinoculation of the soil-root mixture and decomposition for 56 weeks, the water soluble material obtained on fractionation of the soil decreased to less than 1% of the total activity. A much greater proportion, 25%, was present in the clay fraction as a result of decomposition.     

Removal of nonionic surfactants from wastewater using a constructed wetland

Removal of nonionic surfactants from municipal wastewater using a constructed wetland with a horizontal subsurface flow was studied in 2009 and 2010. Extraction spectrophotometry with 3′,3″,5′,5″‐tetrabromophenolphthalein ethyl ester and KCl served to determine the analyte concentrations. Triton^® X‐100 was used as a standard to express the nonionic‐surfactant concentrations. Anionic and cationic surfactants were shown not to interfere during the determination. Nonionic surfactants were degraded (to products undeterminable by the method) with a high average efficiency that reached 98.1% in 2009 and 99.1% in 2010, respectively. The average concentration of nonionic surfactants at the inflow was 0.978 mg/l, while it was close to the limit of quantification at the outflow (0.014 mg/l). A significant fraction of nonionic surfactants (38.7%) was already degraded during the pretreatment, and only 14.0% of the nonionic surfactants remained in the interstitial H₂O taken in the vegetation bed at a distance of 1 m from the inflow zone at a 50‐cm depth. Nonionic surfactants were degraded both under aerobic and anaerobic conditions.     

Phosphorus removal in pilot plant using biofilm filter process from farm wastewater

Various environmental conditions affecting total phosphorus removal from farm wastewater in a biofilm filter, process were investigated using loess balls andChromobacterium LEE-38 at a pilot plant. WhenChromobacterium LEE-38 was used, the removal efficiency of total phosphorous was approximately 10- or 5-fold higher than that ofAcinetobacter CHA-2-14 orAcinetobacter CHA-4-5, respectively. When a loess ball of 11–14 mm manufactured at a 960°C calcining temperature was used, the removal efficiency of total phosphorous was 90.0%. When 70% of the volume fraction was used, the maximum efficiency of total phosphorus removal was 93.1%. Notably, when the initial pH was in the range of 6.0 to 8.0, the maximum removal efficiency of total phosphorus was obtained after 30 days. When the operating temperature was in the range of 30 to 55°C, the maximum removal efficiencies of total phosphorus, 95.6 to 94.6%, were obtained. On the other hand, at operating temperatures below 20°C or above 40°C, the removal efficiency of total phosphorous decreased. Among the various processes, biofilm filter process A gave the highest removal efficiency of 96.4%. Pilot tests of total phosphorus removal using farm wastewater from the biofilm filter process A were carried out for 60 days under optimal condition. WhenAcinetobacters sp. Lee-11 was used, the average removal efficiency in thep-adsorption area was only 32.5%, and the removal efficiencies of chemical oxygen demand (COD) and biological oxygen demand (BOD) were 56.7 and 62.5%, respectively. On the other hand, whenChromobacterium LEE-38 was used, the average removal efficiency was 95.1%, and the removal efficiencies of COD and BOD were 91.3 and 93.2%, respectively. The first two authors contributed equally to this work.     

Chemical Extraction of Arsenic from Contaminated Soils in the Vicinity of Abandoned Mines and a Smelting Plant Under Subcritical Conditions

Under subcritical conditions, we studied the chemical extraction of arsenic (As) from contaminated soils that were sampled from the vicinity of abandoned mines and a smelting plant in South Korea. The total initial concentrations of As in the soil samples from the Myungbong and Cheongyang mines and the Janghang smelting plant were 298.6, 145.6, and 103.7 mg/kg, respectively. X-ray photoelectron spectroscopy analysis showed that the species of As identified in the soil was As(+V), including As₂O₅ and AsO₄ ^3? _. At 20°C, only 27.4, 26.5, and 40.1% of the total As was extracted from the Myungbong, Cheongyang, and Janghang soil samples, respectively, with 100 mM of NaOH. As the temperature was increased to 300°C, the extraction efficiencies remarkably increased. However, to achieve the complete extraction of As from the soils, 100 mM of citric acid, EDTA, or NaOH was needed at 200, 250, or 300°C. Extraction with subcritical water at 300°C resulted in incomplete extraction of As from the soils. The results of these experiments indicate that extraction mechanisms other than oxidative dissolution of As(+III) species may be responsible for the enhancement of As extraction. Our results suggest that subcritical water extraction combined with extracting reagents can effectively remediate As-contaminated soil regardless of the As species.