Browsing by Subject "Cadmium"
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Item Kinetics and mechanisms of adsorption of heavy metal ions on activated carbon(Texas Tech University, 1979-08) Lin, Chieh-ChienNot availableItem Mechanisms of Organic-inorganic Interactions in Soils and Aqueous Environments Elucidated using Calorimetric Techniques(2011-08-08) Harvey, Omar R.Organic matter is ubiquitous in the environment and exists in many different forms. Reactions involving organic matter are diverse and many have significant economic and environmental implications. In this research, calorimetric techniques were used to study organic- inorganic reactions in two different systems. The primary objectives were to elucidate potential mechanism(s) by which: (i) natural organic matter (NOM) influences strength development in lime-stabilized soils, and; (ii) plant-derived biochars reacts with cations in aqueous environments. Natural organic matter influenced strength development in lime-stabilized soils through the direct inhibition of the formation of pozzolanic reaction products. The degree of inhibition was dependent mainly on the type of pozzolanic reaction product, and the amount and source of organic matter. The formation of the pozzolanic reaction product, calcium silicate hydrate II (CSH2) was less affected by NOM, than was the formation of CSH1. For a given pozzolanic product, the inhibition increased with NOM content. The effect of organic matter source followed the order fulvic acid> humic acid> lignite. Formation of CSH pozzolanic reaction products decreased by 50-100%, 20-80% and 20-40% in the presence of ?2% fulvic acid, humic acid and lignite, respectively. Cation interactions with plant-derived biochars were complex and depended both on the nature of the cation and biochar surface properties. Reactions involving the alkali cation, K+; occurred via electrostatic ion exchange, on deprotonated functional groups located on the biochar surface and; were exothermic with molar heats of reaction (?Hads) between -3 and -8 kJ mol-1. In contrast, reactions involving the transition metal cation, Cd2+ were endothermic with delta Hads between +10 and +30 kJ mol-1. Reaction mechanism(s) for Cd2+ varied from ion exchange/surface complexation in biochars formed at <350 oC, to an ion exchange/surface complexation/diffusion-controlled mechanism in biochars formed at >/=350 oC. For a given cation, differences in sorption characteristics were attributable to temperature-dependent or plant species dependent variations in the properties of the biochars.Item Predicting ion adsorption onto the iron hydroxide goethite in single and multi-solute systems(2013-12) Mangold, Jeremiah Edward; Katz, Lynn EllenSurface complexation models (SCMs) have proven to be a useful tool in predicting ion adsorption at the mineral – water interface. In particular, previous research has shown that the Diffuse Layer Model (DLM), Constant Capacitance Model (CCM), and Triple Layer Model (TLM), are all capable of predicting ion adsorption in relatively simple single solute systems. To better simulate the environmental conditions experienced by groundwater sources present in the Earth’s subsurface, experimental adsorption studies have been conducted for more complex multi-solute systems. Under these conditions, SCMs have not proven to be reliable in consistently predicting ion adsorption behavior for the adsorbates of interest. This inability of these SCMs to predict ion adsorption for more complex, multi-solute systems is thought to stem from the variable site density (NS) values utilized in these models. In this research, a methodology was developed for characterizing mineral surface heterogeneity that allows for the different site density values predicted from crystallography, microscopic imaging, tritium exchange, surface saturation data, and surface charging data to all be explained using a single unified theory. This methodology was applied to a goethite mineral sample used in performing batch adsorption studies in single and bi-solute systems with Cd(II), Pb(II), and Se(IV). The adsorption behavior of these adsorbates onto the goethite sample was successfully predicted using the Charge Distribution Multi-Site Complexation (CD-MUSIC) Model and surface complexes consistent with spectroscopic data and computational molecular modeling simulations. A second, separate modeling study was performed using CD-MUSIC to predict Hg(II) adsorption onto different goethite samples of varying size and crystal morphology in single and multi-solute systems. In this study, site density values were predicted for the mineral samples studied utilizing a linear relationship observed for goethite between specific surface area and proton reactive site density. The CD-MUSIC model proved successful in predicting Hg(II) adsorption over all conditions studied while employing only surface complexes consistent with molecular scale analyses. In addition, a novel method for quantifying carbonate’s presence in experimental systems was developed.Item Switchgrass tolerance to cadmium: uptake and translocation(Texas Tech University, 1997-08) Reed, Roderick LynnRecent efforts have been initiated to develop switchgrass (Panicum virgatum L.) as a bioenergy crop. Switchgrass requires input of nitrogen (N) to be productive. Alternatives to inorganic fertilizers are needed to reduce input costs and maintain a positive energy balance. Municipal sludge may be an economical source of N and other nutrients for biomass production; however, the response of switchgrass to heavy metals in the sludge is not known. Two greenhouse studies and a 2-yr field study were conducted to determine the interaction of (1) cultivar and cadmium (Cd)application, (2) soil pH and Cd application, and (3) soil moisture and Cd application on biomass accumulation and Cd allocation of switchgrass. In the first experiment, 'Alamo', 'Blackweir, 'Cave-in-Rock', and 'Trailblazer' switchgrass were grown in sand culture and were watered twice weekly with nutrient solution containing 0, 1,2, 4, 8, or 16 mg Cd L^-1. Cultivars differed (P<0.05) by less than 15% for biomass accumulation and allocation. Cadmium levels of 16 mg L' reduced biomass yields by 31% for roots, 39% for leaf blades, and 47% for shoots (culm + leaf sheath) as compared to no added Cd. At 16 mg Cd L', Cd concentration in leaf blades was 9.9 mg kg"'. The highest levels of Cd (329 mg kg^-1) were found in roots of Blackwell and Trailblazer grown at the high Cd level. In the second experiment. Alamo switchgrass was grovm in pots at five soil pH levels (4.0, 5.1, 5.8, 6.6, and 7.3) and four soil Cd levels (0, 50, 100, and 200 mg Cd kg^-1). Two hundred mg Cd kg^-1 decreased biomass accumulation of all plant components by 95%. Cadmium concentrations of 900 mg kg' were found in root tissue of plants grown in soil with 200 mg Cd L ' and a pH of 4.0. In the third experiment. Alamo switchgrass was grown in the field at three irrigation levels (0, 50, and 100%) of weekly pan evaporation) and four soil Cd levels (0, 25, 50, and 100 kg ha^-1). Biomass yield, tiller mass, and mass of tiller components were not significantly (P>0.05) affected by either irrigation or Cd level in 1995 or 1996. Concentrations of Cd in aboveground tissue ranged from 0.36 to 0.87 mg kg"'. Alamo switchgrass translocated little Cd to the aboveground portion of the plant at all Cd application levels and tolerated 100 kg ha^-1 of applied Cd. However, in different environments and management systems, Cd concentrations in aboveground tissue may increase to levels above suggested maximum tolerance levels. Producers should maintain soil pH near neutral to minimize Cd accumulation by switchgrass.Item Toxicity of cadmium quantum dots compared to cadmium and zinc ions in zebrafish (Danio rerio) and water flea (Daphnia pulex)(2013-05) Tang, SongRecent advances in the ability to manufacture and manipulate materials at the nanoscale have led to increased production and use of many types of nanomaterials in diverse areas. Nanocrystaline semiconductors (Quantum dots; QDs) are small, long-lived fluorescent nanocrystals composed of a core of semiconductor material (e.g. cadmium selenide, zinc sulfide) and shells or dopants of other elements. Often, the continuously increased uses of QDs come increased appearance of in the aqueous environments, and then can be toxic to aquatic organisms and poses significant ecological risks. However, the toxicological impacts of heavy metal constituted QDs on aquatic species are largely unknown, especially at the molecular level. Moreover, it is crucial to determine whether the toxicity of metallic QDs is quantitative or mechanistically different than that of soluble metal components. The aim of this study was to compare the toxicities of ionic cadmium (Cd) and zinc (Zn) and Cd- and Zn-containing QDs at both in vitro via zebrafish liver cells (ZFL) and in vivo through Daphnia pulex. Our results revealed that (1) ionic Cd2+ was more toxic than Zn2+, and the general trend of toxicity of QDs was determined to be CdTe > CdSe/ZnS or InP/ZnS; (2) smaller QDs showed greater toxicity than larger QDs; (3) both Cd2+ and CdTe QDs exposure led to an accumulation of Cd, an increased formation of intracellular reactive oxygen species (ROS), and an induction of DNA strand breaks; (4) CdTe QDs exposure induced expression patterns of metal response, stress defense, and DNA repair genes in a manner similar to that of Cd2+ exposure, while CdSe/ZnS or InP/ZnS QDs altered gene expression in a manner very different from that of the corresponding Cd or Zn salts; and (5) nucleotide excision repair (NER) repair capacity were inhibited with Cd2+ but not with CdTe. The adverse cellular effects caused by acute exposure of QDs might be mediated through differing mechanisms than those resulting from Cd2+ toxicity, and studying the effects of the ionic form may be not enough to explain QD toxicities in aquatic organisms.Item Ultrasonic attenuation in superconducting cadmium(Texas Tech University, 1973-08) Robbins, Roger AlanNot available