Spectral fitting approach for the determination of enrichment and contamination factors in mining sediments using laser-induced breakdown spectroscopy.

Monitoring of pollution index values in sediments is crucial in assessing the environmental impacts of toxic metals in a given location. These indices are typically acquired using elaborate and tedious calibration curve-dependent techniques such as (inductively coupled plasma - optical emission spectroscopy) ICP-OES and (atomic absorption spectroscopy) AAS. In this study, laser-induced breakdown spectroscopy (LIBS) was used as a simple and fast alternative method for estimating enrichment factor (EF) and contamination factor (CF) of the sediment samples obtained from selected mining sites. Quantitative analyses of three metal targets (Cd, Pb, and Zn) were done using a calibration-free LIBS method based on the Boltzmann population distribution. Both the EF and CF values calculated from classical ICP-OES method provided significantly high correspondence with the respective EF (R2 = 0.8862-0.9770, p < 0.01-0.05) and CF (R2 = 0.9454-0.9714, p < 0.01) obtained from the developed LIBS method. The intensity-based LIBS approach identified samples AC2 and CCC as the ones with the highest and lowest pollution index values, respectively. The same observation was seen using the concentration-based ICP-OES technique which showed good correlation between the two methods. The correlation results showed the potential of the curve-fitting LIBS analysis in evaluating the level of metal contamination in an area without the preparation of matrix-matched calibration curves.

Effect of organic matters on CO2 hydrate formation in Ulleung Basin sediment suspensions.

Marine sediment core samples collected from a gas hydrate deposit site (Ulleung Basin (UB), East Sea, Korea) were explored to identify the role of sediment organic matters (SOMs) on the formation of CO(2) hydrate. Two distinct CO(2) hydrate formation regimes (favorable (≤40 min) and unfavorable (>250 min)) were observed from the hydrate formation tests. CO(2) hydrate induction time in UB sediment suspensions was approximately seven times faster than that in UB sediment suspensions without SOMs (baked UB), showing a direct influence of SOMs. Spectrometric and spectroscopic analyses confirmed the existence of different types of SOMs including nonhumic and humic substances in UB sediment samples. We found SOMs with aromatic ring structures in all sediment extracts and SOMs with amine and amide groups and lignin in alkaline extracts. SOMs were extracted from UB sediment core samples (1 g each). Measured CO(2) hydrate induction times were different in baked UB sediment suspensions with different extracts of UB sediments. The experimental results demonstrated that SOMs can play a significant role to accelerate the formation of CO(2) hydrate in UB sediment suspensions, suggesting that the gas hydrate deposit site at UB may be a proper place for CO(2) sequestration as a form of CO(2) hydrate.

Effect of pH on carbon dioxide hydrate formation in mixed soil mineral suspensions.

We investigated the effect of pH on CO2 hydrate formation in the presence of phyllosilicate mixtures. Different pH conditions of phyllosilicate suspensions (Na-montmorillonite-rich and phyllosilicate-rich suspensions) with and without NaCl (3.5%) were prepared and controlled by the addition of an acid or base before the dissolution of CO2. The formation of CO2 hydrates was observed in all phyllosilicate suspensions (30 bar and 273.45 K). The temperature-time plot results showed that hydrate formations were suppressed more in acidic mineral suspensions than in basic suspensions. The fastest hydrate induction time can be observed in Na-montmorillonite-rich and phyllosilicate-rich suspensions with and without NaCl at near neutral conditions (pH 6-8), followed by basic (approximately pH 12.0) and acidic (approximately pH 2.0) pHs. Hydrate induction time can be significantly affected by various chemical species forming under different suspension pHs. The distribution of chemical species in each mineral suspension was estimated by a chemical equilibrium model, PHREEOC, and used for the identification of hydrate formation characteristics in the suspension. Particle-particle and particle-water interactions may possibly contribute to the delay of hydrate formation. NaCl was not an efficient inhibitor but a possible promoter for hydrate formation when pH-dependent solid surfaces were present in the system.

Formation of carbon dioxide hydrate in soil and soil mineral suspensions with electrolytes.

We have identified the effects of solid surface (soil, bentonite, kaolinite, nontronite, and pyrite) and electrolyte (NaCl, KCl, CaCl2, and MgCl2) types on the formation and dissociation of CO2 hydrate in this study. The hydrate formation experiments were conducted by injecting CO2 gas into the soil suspensions with and without electrolytes in a 50 mL pressurized vessel. The formation of CO2 hydrate in deionized water was faster than that in aqueous electrolyte solutions. The addition of soil suspensions accelerated the formation of CO2 hydrate in the electrolyte solutions. The hydrate formation times in the solid suspensions without electrolytes were very similar to that in the deionized water. We did not observe any significant differences between the hydrate dissociation in the solid suspension and that in the deionized water. The pHs of clay mineral suspensions decreased significantly after CO2 hydrate formation and dissociation experiments, while the pH of the soil suspension slightly decreased by less than pH 1 and that of pyrite slightly increased due to the dissolution of CO2 forming carbonic acid. The results obtained from this research could be indirectly applied to the fate of CO2 sequestered into geological formations as well as its storage as a form of CO2 hydrate.

Influence of ozone concentration and temperature on ultra-fine particle and gaseous volatile organic compound formations generated during the ozone-initiated reactions with emitted terpenes from a car air freshener.

Experiments were conducted to identify the emissions from the car air freshener and to identify the formation of ultra-fine particles and secondary gaseous compounds during the ozone-initiated oxidations with emitted volatile organic compounds (VOCs). The identified primary constituents emitted from the car air freshener in this study were alpha-pinene, beta-pinene, p-cymene, and limonene. Formation of ultra-fine particles (4.4-160 nm) was observed when ozone was injected into the chamber containing emitted monoterpenes from the air freshener. Particle number concentrations, particle mass concentrations, and surface concentrations were measured in time dependent experiments to describe the particle formation and growth within the chamber. The irritating secondary gaseous products formed during the ozone-initiated reactions include formaldehyde, acetaldehyde, acrolein, acetone, and propionaldehyde. Ozone concentration (50 and 100 ppb) and temperature (30 and 40 degrees C) significantly affect the formation of particles and gaseous products during the ozone-initiated reactions. The results obtained in this study provided an insight on the potential exposure of particles and irritating secondary products formed during the ozone-initiated reaction to passengers in confined spaces.

The formation of ultra-fine particles during ozone-initiated oxidations with terpenes emitted from natural paint.

The formation of secondary products during the ozone-initiated oxidations with biogenic VOCs emitted from natural paint was investigated in this study. Mass spectrometry and infrared spectroscopy measurements have shown that the major components of gas-phase chemicals emitted from natural paint are monoterpenes including alpha- and beta-pinenes, camphene, p-cymene, and limonene. A significant formation of gaseous carbonyl products and nano-sized particles (4.4-168nm) was observed in the presence of ozone. Carboxylic acids were also observed to form during the reactions (i.e. formic acid at 0.170ppm and acetic acid at 0.260ppm). The formation of particles increased as the volume of paint introduced into a reaction chamber increased. A secondary increase in the particle number concentration was observed after 440min, which suggests further partitioning of oxidation products (i.e. carboxylic acids) into the particles previously existing in the reaction chamber. The growth of particles increased as the mean particle diameter and particle mass concentrations increased during the reaction. The experimental results obtained in this study may provide insight into the potential exposure of occupants to irritating chemical compounds formed during the oxidations of biogenic VOCs emitted from natural paint in indoor environments.