Thermodynamic and experimental studies on condensation behavior of low-boiling-point elements volatilized in the melting process

To study the volatilization and condensation behaviors of low-boiling-point elements in the waste melting process, experiments were conducted to collect the dust from a coke-type incineration residue melting furnace. Then, a comparison was made between the experimental results and the calculated values obtained from a thermodynamic equilibrium model in terms of the chemical composition of the dust. The composition of the dust collected from a cylindrical filter in the exhaust gas duct was determined by chemical methods, scanning electron microscopy/energy-dispersive X-ray spectroscopy, and X-ray analysis. As a result, the sampled dust was classified into two different types: fine particles mainly containing Na, K, Pb, and Zn collected from the side face of the cylindrical filter, and large particles containing Ca, Si, and Al collected from the bottom face of the cylindrical filter. From X-ray analysis of the sampled dust, NaCl, KCl, PbS, and ZnS were identified in the fine-particle dust, while CaO, SiO₂, Al₂O₃ were detected in the large-particle dust. From the results of the thermodynamic equilibrium calculation in the gas cooling process from 2000 to 600 K, it was found that Na, K, Pb, and Zn volatilized as metals in the melting furnace were condensed as alkali chlorides such as NaCl and KCl and heavy metal sulfides such as PbS and ZnS. These computational results were in good agreement with the X-ray diffraction results of the sampled dust at a gas temperature of 823 K for the formation of NaCl, KCl, PbS, and ZnS.     

Effect of chlorine on volatilization of Na, K, Pb, and Zn compounds from municipal solid waste during gasification and melting in a shaft-type furnace

In the present work, a shaft-type furnace model in which the furnace column is divided into multiple cells was proposed and equilibrium reaction calculation software was used to describe the model. The model was used to study the effects of gasification and melting conditions such as temperature, oxygen partial pressure, and chlorine content on the volatilization behaviors of the low-boiling-point metals Na, K, Pb, and Zn during the gasification and melting process of municipal solid waste in a shaft-type furnace. Consequently, the volatilization ratios of Na, K, Pb, and Zn compounds in the exhaust gas from a pilot plant shaft-type furnace were found to be in good agreement with the calculation results, and the Na, K, Pb, and Zn compounds were volatilized mainly as metal chlorides in the temperature range up to approximately 1173 K. With a further rise in temperature, these low-boiling point metals were volatilized as metallic forms. It was found that almost 100% of Pb and Zn compounds were volatilized regardless of the chlorine content in municipal solid waste; in contrast, the volatilization rates of Na and K increased when the chlorine content increased. Finally, Na, K, Pb, and Zn compounds were converted from reduced metals to metal chlorides such as NaCl, KCl, PbCl₂, and ZnCl₂ with an increase in the ratio of chlorine to each metal.     

Mathematical prediction of imidacloprid persistence in two Croatian soils with different texture,organic matter content and acidity under laboratory conditions

In the present laboratory study, persistence of imidacloprid (IMI) as a function of initial insecticide concentration and soil properties in two Croatian soils (Krk sandy clay and Istria clay soils) was studied and described mathematically. Upon fitting the obtained experimental data for the higher concentration level (5 mg/kg) to mathematical models, statistical parameters (R ², scaled root mean squared error and χ ² error) indicated that the single first-order kinetics model provided the best prediction of IMI degradation in the Krk sandy clay soil, while in the Istria clay soil biphasic degradation was observed. At the lower concentration level (0.5 mg/kg), the biphasic models Gustafson and Holden models as well as the first-order double exponential model fitted the best experimental data in both soils. The disappearance time (DT₅₀) values estimated by the single first-order double exponential model (from 50 to 132 days) proved that IMI can be categorized as a moderately persistent pesticide. In the Krk sandy clay soil, resulting DT₅₀ values tended to increase with an increase of initial IMI concentration, while in the Istria clay soil, IMI persistence did not depend on the concentration. Organic matter of both experimental soils provided an accelerating effect on the degradation rate. The logistic model demonstrated that the effect of microbial activity was not the most important parameter for the biodegradation of IMI in the Istria clay soil, where IMI degradation could be dominated by chemical processes, such as chemical hydrolysis. The results pointed that mathematical modeling could be considered as the most convenient tool for predicting IMI persistence and contributes to the establishment of adequate monitoring of IMI residues in contaminated soil. Furthermore, IMI usage should be strictly controlled, especially in soils with low organic matter content where the risk of soil and groundwater contamination is much higher due to its longer persistence and consequent leaching and/or moving from soil surface prior to its degradation.     

Volatilization behavior of lead from molten slag under conditions simulating municipal solid waste melting

To reutilize molten slag derived from an ash melting process, the lead volatilization mechanism under reducing conditions was investigated. Reducing conditions were established by introducing a CO-CO₂-N₂ gas mixture to the reactor or by adding graphite to the molten slag prior to the experiments. As samples, two types of simulated molten slag composed of CaO-SiO₂-Al₂O₃ mixed with PbO were used and the lead volatilization behavior was studied at 1773 K. It was found that the lead volatilization rate increased on increasing the amount of reducing agent for both graphite and the CO-CO₂ gas mixture. For the CO-CO₂ reducing gas mixture, this increase was mainly attributed to PbO conversion to Pb. For the addition of graphite, the increase in lead volatilization ratio was considered to partially result from PbO conversion to Pb and partially from a reaction of graphite with SiO₂ yielding volatile SiO. The volatile SiO gas was then emitted from the furnace, which brought about a reduction in the SiO₂ content of the slag. As a result, the slag viscosity decreased, which led to an enhancement of the lead volatilization ratio.     

Paramagnetic antibody-modified microparticles coupled with voltammetry as a tool for isolation and detection of metallothionen as a bioindicator of metal pollution

Low-molecular mass proteins rich in cysteines called metallothioneins (MT) can be considered as markers for the pollution of the environment by metals. Here, we report on suggestion for an automated procedure for the isolation of MT followed by voltammetric analysis. Primarily, we optimized the automated detection of MT using an electrochemical analyser. It was found that the most sensitive and repeatable analyses are obtained at a temperature of 4 °C for the supporting electrolyte. Further, we optimized experimental conditions for the isolation of MT by using antibody-linked paramagnetic microparticles. Under the optimal conditions (4 h long interaction between the microparticles and MT), the microparticles were tested on isolation of various amounts of MT. The lowest isolated amount of MT by antibody-linked paramagnetic microparticles was 5 μg ml(-1) of MT (50 ng). The automated procedure of MT isolation was further tested on isolation of MT from guppy fish (Poecilia reticulata) treated with silver(i) ions (50 μM AgNO(3)). The whole process lasted less than five hours and was fully automated. We attempted to correlate these results with the standard method for MT isolation. The correlation coefficient is 0.9901, which confirms that results are in good agreement. Moreover, the concentration of silver ions in tissues of fish treated with Ag(i) ions was determined by high performance liquid chromatography with electrochemical detection.     

Reductive decomposition of waste gypsum with SiO<Subscript>2</Subscript>, Al<Subscript>2</Subscript>O<Subscript>3</Subscript>, and Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> additives

From the point of view of a sustainable and environment-friendly society based on the recycling of material resources, it is preferable to utilize waste gypsum as a substitute for lime, which is currently produced by the calcination of limestone. In the present work, the reductive decomposition of CaSO₄ was investigated under an atmosphere of CO: 2 vol%, CO₂: 30 vol%, with N₂ as a carrier gas without and with the addition of SiO₂, Al₂O₃, or Fe₂O₃. It was found that the decomposition temperature of CaSO₄ was significantly reduced from 1673 K to 1223 K when only 5 wt% Fe₂O₃ was added to CaSO₄. In the case of the addition of SiO₂ or Al₂O₃ to CaSO₄, the decomposition temperature was reduced from 1673 K to 1623 K. This was due to the formation of composite oxides (calcium ferrite, calcium silicate, or calcium aluminate) during the reaction of CaSO₄ with the additives at a lower temperature. In addition, the formation of unfavorable product CaS was inhibited in the presence of 5 wt% Fe₂O₃, and this inhibition effect further increased as the addition of Fe₂O₃ was increased. In contrast, no significant effect on the inhibition of CaS formation was observed on the addition of SiO₂ or Al₂O₃.     

Ozone flux over a Norway spruce forest and correlation with net ecosystem production

Daily ozone deposition flux to a Norway spruce forest in Czech Republic was measured using the gradient method in July and August 2008. Results were in good agreement with a deposition flux model. The mean daily stomatal uptake of ozone was around 47% of total deposition. Average deposition velocity was 0.39 cm s⁻¹ and 0.36 cm s⁻¹ by the gradient method and the deposition model, respectively. Measured and modelled non-stomatal uptake was around 0.2 cm s⁻¹. In addition, net ecosystem production (NEP) was measured by using Eddy Covariance and correlations with O₃ concentrations at 15 m a.g.l., total deposition and stomatal uptake were tested. Total deposition and stomatal uptake of ozone significantly decreased NEP, especially by high intensities of solar radiation.     

Study on reaction kinetics and selective precipitation of Cu, Zn, Ni and Sn with H₂S in single-metal and multi-metal systems

Determination of reaction kinetics and selective precipitation of Cu, Zn, Ni and Sn with H(2)S in single-metal and multi-metal systems were studied to develop a process of metal recovery from plating wastewater. As samples, single-metal model wastewaters containing Cu, Sn, Zn or Ni, and multi-metal model wastewater containing Cu-Zn-Ni or Sn-Zn mixtures were used. In both single-metal and multi-metal systems, the pH value was precisely controlled at a value of 1.5 for CuS and SnS precipitation, 4.5 for ZnS precipitation and 6.5-7.0 for NiS precipitation. Subsequently, the sulfidation of Cu, Sn, Zn and Ni was evaluated. It was found that an amount of H(2)S equimolar to a given metal was sufficient to achieve almost complete precipitation of the particular metal. Further, the selectivity of metal precipitation was found to be higher than 95% in the Cu-Zn-Ni multi-metal system and higher than 91% in the Sn-Zn system. It was also found that the sulfidation reaction proceeded in accordance with Higbie's penetration theory and reaction rate constants and mass-transfer coefficients under various experimental conditions were determined. Finally, the reaction rate constants obtained in single-metal and multi-metal systems were found to be almost the same indicating that the precipitation of a particular metal was not significantly affected by the presence of other components.     

Lead,cadmium and mercury contents and bioaccumulation potential of wild edible saprophytic and ectomycorrhizal mushrooms,Croatia

ABSTRACT

Lead (Pb), cadmium (Cd), and mercury (Hg) contents in ten species of edible mushrooms in Trako??an, Croatia were determined. In addition, the similarity between the studied species was determined by cluster analysis. The caps and stipes of the fruiting bodies were analysed separately. The analyses were carried out by inductively coupled plasma - optical emission spectrometry (ICP-OES). The greatest mean lead concentrations of 1.91 and 1.60 mg kg ^?1 were determined in caps and stipes of Macrolepiota procera. The greatest mean concentrations of cadmium (3.23 and 2.24 mg kg^?1) were determined in caps and stipes of Agaricus campestris and of mercury (2.56 and 2.35 mg kg^?1) in Boletus edulis. In terms of the anatomical parts of the fruiting body (cap-stipe), a considerably greater concentration of the analysed elements was found in the cap for all mushroom species. According to calculated bio-concentration factors, all the examined species were found to be bio-accumulators of Cd and Hg. On the basis of the accumulation of the studied metals, great similarity of mushroom species belonging to the same genus and partial similarity of species of the same ecological affiliation was obtained by cluster analysis.