Characterizing As(III,V) adsorption by soils surrounding ash disposal facilities

Leachate derived from unlined coal ash disposal facilities is a potential anthropogenic source of arsenic to the environment. To establish a theoretical framework for predicting attenuation of arsenic by soils subject to ash landfill leachate, which is typically enriched in calcium and sulfate, the adsorption of As(V) and As(III) was characterized from 1 mM CaSO₄ for 18 soils obtained down-gradient from three ash landfill sites and representing a wide range in soil properties. As(V) consistently exhibited an order of magnitude greater adsorption than As(III). As(V) adsorption was best described by coupling pH with 15 s DCB-Fe (R² = 0.851,  = 0.001), although pH coupled to clay, DCB-Fe, or DCB-Al also generated strong correlations. For As(III), pH coupled to Ox–Fe (R² = 0.725,  = 0.001) or Ox–Fe/Al (R² = 0.771,  = 0.001) provided the best predictive relationships. Ca²⁺ induced increases in As(V) adsorption whereas sulfate suppressed both As(V) and As(III) adsorption. Attenuation of arsenic from ash leachate agreed well with adsorption measured from 1 mM CaSO₄ suggesting that the use of 1 mM CaSO₄ in laboratory adsorption tests is a reasonable approach for estimating arsenic behavior in soils surrounding ash landfills. We also showed that the impact of leachate-induced changes in soil pH over time may not be significant for As(V) adsorption at pH < 7; however, As(III) adsorption may be impacted over a wider pH range especially if phyllosilicate clays contribute significantly to adsorption. The benefits and limitations of predicting arsenic mobility using linearized adsorption coefficients estimated from nonlinear adsorption isotherms or from the relationships generated in this study are also discussed.     

Summer cover crops reduce atrazine leaching to shallow groundwater in southern Florida

At Florida's southeastern tip, sweet corn (Zea Mays) is grown commercially during winter months. Most fields are treated with atrazine (6-chloro-N-ethyl-N'-[1-methylethyl]-1,3,5-triazine-2,4-diamine). Hydrogeologic conditions indicate a potential for shallow groundwater contamination. This was investigated by measuring the parent compound and three degradates--DEA (6-chloro-N-[1-methylethyl]-1,3,5-triazine-2,4-diamine), DIA (6-chloro-N-ethyl)-1,3,5-triazine-2,4-diamine, and HA (6-hydroxy-N-[1-methylethyl]-1,3,5-triazine-2,4-diamine)--in water samples collected beneath sweet corn plots treated annually with the herbicide. During the study, a potential mitigation measure (i.e., the use of a cover crop, Sunn Hemp [Crotalaria juncea L.], during summer fallow periods followed by chopping and turning the crop into soil before planting the next crop) was evaluated. Over 3.5 yr and production of four corn crops, groundwater monitoring indicated leaching of atrazine, DIA, and DEA, with DEA accounting for more than half of all residues in most samples. Predominance of DEA, which increased after the second atrazine application, was interpreted as an indication of rapid and extensive atrazine degradation in soil and indicated that an adapted community of atrazine degrading organisms had developed. A companion laboratory study found a sixfold increase in atrazine degradation rate in soil after three applications. Groundwater data also revealed that atrazine and degradates concentrations were significantly lower in samples collected beneath cover crop plots when compared with concentrations below fallow plots. Together, these findings demonstrated a relatively small although potentially significant risk for leaching of atrazine and its dealkylated degradates to groundwater and that the use of a cover crop like Sunn Hemp during summer months may be an effective mitigation measure.     

A numerical simulation model of cyclic hardening behavior of AC4C-T6 for LNG cargo pump using finite element analysis

This paper is concerned with the evaluation of cyclic hardening models within the stress–strain behavior of aluminum alloy AC4C-T6 that can be used to LNG cargo pump operating in cryogenic temperature. To insure the strength assessment of LNG cargo pump, material model of cyclic hardening and plasticity for aluminum alloy AC4C-T6 is investigated through FEA (Finite Element Analysis) with various hardening options including linear and non-linear hardening, isotropic and kinematic hardening, and combined hardening model. Monotonic tensile and cyclic tensile experiments for AC4C-T6 alloy were performed at room temperature and temperature of ?165 °C. Parameters of each hardening model are obtained from the experimental data; thus five hardening models are numerically simulated thereafter. Appropriate hardening models which describe the cyclic stress–strain relationship are investigated through the simulations of cyclic hardening behavior by FEA. In order to verify the predicted behavior of cyclic hardening obtained by FEA, the results of FEA and those measured by experiments are compared.     

Ameliorants to immobilize Cd in rice paddy soils contaminated by abandoned metal mines in Korea

The cadmium (Cd) content of rice grain grown in metal-contaminated paddy soils near abandoned metal mines in South Korea was found to exceed safety guidelines (0.2 mg Cd kg?1) set by the Korea Food and Drug Administration (KFDA). However, current remediation technologies for heavy metal-contaminated soils have limited application with respect to rice paddy soils. Laboratory and greenhouse experiments were conducted to assess the effects of amending contaminated rice paddy soils with zerovalent iron (ZVI), lime, humus, compost, and combinations of these compounds to immobilize Cd and inhibit Cd translocation to rice grain. Sequential extraction analysis revealed that treatment with the ameliorants induced a 50-90% decrease in the bioavailable Cd fractions when compared to the untreated control soil. When compared to the control, Cd uptake by rice was decreased in response to treatment with ZVI + humus (69%), lime (65%), ZVI + compost (61%), compost (46%), ZVI (42%), and humus (14%). In addition, ameliorants did not influence rice yield when compared to that of the control. Overall, the results of this study indicated that remediation technologies using ameliorants effectively reduce Cd bioavailability and uptake in contaminated rice paddy soils.     

Application of eggshell waste for the immobilization of cadmium and lead in a contaminated soil

Liming materials have been used to immobilize heavy metals in contaminated soils. However, no studies have evaluated the use of eggshell waste as a source of calcium carbonate (CaCO?) to immobilize both cadmium (Cd) and lead (Pb) in soils. This study was conducted to evaluate the effectiveness of eggshell waste on the immobilization of Cd and Pb and to determine the metal availability following various single extraction techniques. Incubation experiments were conducted by mixing 0-5% powdered eggshell waste and curing the soil (1,246 mg Pb kg?1 soil and 17 mg Cd kg?1 soil) for 30 days. Five extractants, 0.01 M calcium chloride (CaCl?), 1 M CaCl?, 0.1 M hydrochloric acid (HCl), 0.43 M acetic acid (CH?COOH), and 0.05 M ethylendiaminetetraacetic acid (EDTA), were used to determine the extractability of Cd and Pb following treatments with CaCO? and eggshell waste. Generally, the extractability of Cd and Pb in the soils decreased in response to treatments with CaCO? and eggshell waste, regardless of extractant. Using CaCl? extraction, the lowest Cd concentration was achieved upon both CaCO? and eggshell waste treatments, while the lowest Pb concentration was observed using HCl extraction. The highest amount of immobilized Cd and Pb was extracted by CH?COOH or EDTA in soils treated with CaCO? and eggshell waste, indicating that remobilization of Cd and Pb may occur under acidic conditions. Based on the findings obtained, eggshell waste can be used as an alternative to CaCO? for the immobilization of heavy metals in soils.     

Emission of particulate and gaseous pollutants from household laser processing machine

Indoor air quality (IAQ) directly affects the health of occupants. Household manufacturing equipment (HME) used for hobbies or educational purposes is a new and unexplored source of air pollution. In this study, we evaluated the characteristics of particulate and gaseous pollutants produced by a household laser processing equipment (HLPE). Various target materials were tested using a commercial HLPE under various operating conditions of laser power and sheath air flow rate. The mode diameters of the emitted particles gradually decreased as laser power increased, while the particle number concentration (PNC) and particle emission rate (PER) increased. In addition, as the sheath air flow rate quadrupled from 10 to 40 L/min, the mode diameter of the emitted particles decreased by nearly 25%, but the effect on the PNC was insignificant. When the laser induced the target materials at 53 mW, the mode diameters of particles were <150 nm, and PNCs were >2.0 × 10⁴ particles/cm³. Particularly, analyses of sampled aerosols indicated that harmful substances such as sulfur and barium were present in particles emitted from leather. The carcinogenic gaseous pollutants such as acrylonitrile, acetaldehyde, 1,3-butadiene, benzene, and C₈ aromatics (ethylbenzene) were emitted from all target materials. In an actual indoor environment, the PNC of inhalable ultrafine particles (UFPs) was >5 × 10⁴ particles/cm³ during 30 min of HLPE operation. Our results suggest that more meticulous control methods are needed, including the use of less harmful target materials along with filters or adsorbents that prevent emission of pollutants.