No description available.

No description available.

No description available.

The removal of many metal ions from solution with bases by precipitation and filtration is well known. Due to it's limited solubility, Mg(OH)(_2) gives many benefits over the other commonly used bases in terms of safety and post-treatment processes such as residual mass and volume. The use of Mg(OH)(_2) as the base in these reactions, however, does not give satisfactory results in many cases, the levels of metal ions in solution after treatment remaining too high to allow discharge into public waterways. In order to aid these reactions, the use of extra reagents along with the base has been studied. These additives take the form of either donor ligands, e.g. PPh(_3), TMEDA, or other metal solutions, typically trivalent metals i.e. Fe(^3+), Al(^3+) or metal oxides i.e. Fe(_2)O(_3), Al(_2)O(_3).Following previous studies where P- and N-donor ligands, used in catalytic quantities had shown great increases in the %age of metal ions removed from complicated, multiple metal ion effluent systems, the reactions of individual metal ion solutions with these ligands showed disappointing results. After testing separate solutions of Cu(^2+) Fe(^2+) Ni(^2+), Zn(^2+), Pb(^2+) and Al(^3+), only Fe(^2+) showed the same improvements seen in the mixed ion systems. Decreases in %age of Cu(^2+) removed were observed for reactions including these ligands .Decreasing removal was seen with increasing ligand addition. This is due to the formation of soluble complexes which are unaffected by the pHs achieved in the reactions. The other metal ions tested showed little change for any addition of these ligand reagents. Addition of equivalent amounts of an easily precipitated metal ion, i.e. Al(^3+) or Fe(^3+), to a more difficult to treat metal ion solution, i.e. Ni(^2+) or Zn(^2+), gave large improvements on the removal of the ions by treatment with Mg(OH)(_2). Tenfold increases in removal of the ions were seen in the reactions, allowing dischargable concentrations to be achieved in far lower times than previously obtained. Addition of the M(III) solutions, while improving the metal ion removal, increased the amount of Mg(OH)(_2) required for treatment. An industrially available additive, containing Al and Fe sulphates, was tested in a similar fashion giving the same beneficial results. The use of identical amounts of base, with and without this additive showed that improvements in removal of metal ions were obtained even over increasing the relative amount of base added. To overcome this problem, the M(III) species were added in the form of oxides, e.g. Al(_2)O(_3). This removed the need for extra base but the results were disappointing compared to the addition of the M(III) ions as solutions, only ~10% increase in precipitation with a tenfold addition of oxide. None of these reactions achieved the Mg(OH)(_2) buffer pH of 10.5 even when large excesses were added. This has been attributed to coating of the solid Mg(OH)(_2) particles by precipitating M(II) hydroxides which prevented dissolution and kept the majority of the hydroxide from taking part in the reaction. The addition of the extra M(III) species provided preferential sites for the M(II) hydroxides to form on and thus allowed the reaction of all of the Mg(OH)(_2) added. The use of ultrasound to improve these reactions, both instead of and as well as the use of additives, was studied and was seen to give further improvement in these reactions. The ultrasound not only provided an increase in the energy of the systems through a general heating of the solution, but the physical forces created aided the break-up of both the solid Mg(OH)(_2) particles and any coatings that may have built up on them. The use of a 16kHz ultrasound probe produced large improvements in the removal of metal ions and when used in conjunction with M(III) additives dischargable concentrations were achieved in only 30 minutes. Through the use of various additives and conditions, Mg(OH)(_2) has been shown to be a viable option in the effluent treatment industry. The reactions were performed mainly on laboratory prepared solutions of the relevant metal ions, with commercially available Mg(OH)(_2) suspensions. The results were obtained from observation of the pH of the reaction mixtures and concentrations of the metal ions remaining in solution after filtration, determined by atomic absorption spectrophotometry.

No description available.

Barytes (the naturally occurring BaSO4) is used as the standard densification agent in drilling fluids world-wide. It increases the density of the drilling fluids for control of formation pressures. It has been highlighted as a major source of toxic heavy metals input in the oil and gas industry. Large scale use in the offshore oil well drilling operations and subsequent discharges of spent drilling fluids containing barytes to the marine environment have raised concerns regarding the potential for bioaccumulation in marine biota of the toxic heavy metals and the possible human health risks. Various analytical and biological aspects of barytes regarding chemistry, analytical methodology, toxicity and heavy metal bioavailability have been thoroughly investigated in this study. Electron probe microanalysis (EPMA) confirms the presence of a number of minerals including barite, galena, anglesite, pyrite, sphalerite, zincite, quartz, barium feldspar, hematite, anhydrite, orthoclase, silicates, mixed minerals in barytes. Quantitative strontium and calcium as part of the crystal lattice whereas other trace heavy metals occur as associated minerals. Image analysis shows that the bulk of barium in barytes corresponds to the mineral barite (BaSO4), however, a small quantity of barium was found to be associated with silicon which confirmed the presence of barium feldspar. The presence of toxic heavy metals such as Cu, Ni, V, Co, Cr, Cd, Bi, Ti, Hg, Te, Sn, Sb, As etc. in barytes is likely to be as inclusions or substitutions in sulphide minerals associated with barite. Mineralogical studies suggest that barytes is not the traditionally inert BaSO4 but, rather, a potentially toxic substance due to its associated toxic heavy metal impurities. Comparative studies on the performance of chemical dissolution procedures such as sodium carbonate fusion, aqua regia digestion, aqua regia /HF digestion and a non-destructive technique, X-ray fluorescence spectrometry shows that sodium carbonate fusion procedure is the best method for the determination of barium in different types of barytes. DTPA and EDTA extractibilities for barium at pHs 12.6 and 10.8 respectively (25oC) were found to be low even though predictions based on thermodynamic data had suggested that BaSO4 should be soluble.

Thesis (M.Sc. Agric)(Soil Science))--University of Pretoria, 2009. / Includes summary. Includes bibliographical references.

This research project examines the application of mineral magnetic techniques to the characterisation of particulates and their sources in the urban highway environment and in stormwater runoff. A review of previous investigations into sources, levels and pathways of metals through the urban highway environment is presented. The principles upon which the mineral magnetic techniques are based and those parameters employed in this study are described. Previous environmental applications are reviewed. A representative sampling scheme was established in a small well-defined sub-catchment. Copper, Fe, Pb and Zn concentrations in highway associated sediments increased with proximity to the road centre and seasonal maxima occurred in summer. Heavy metal loadings were dominated by the sediment loadings. Strong linear relationships between the metals, Cu, Fe, Pb and Zn, and magnetic mineral concentration related parameters, X and IRM3oomT, were observed. Mineral magnetic characterisation achieved complete discrimination between highway associated sediments and roof sediments allowing the derivation of equations defining the sediment groupings. Variations in metal-magnetic properties of sediments with particle size ,were investigated. Primary source materials and particulates were analysed. Metallic and magnetic mineral parameters indicated that atmospheric and vehicle derived· particulates were probably the dominant origins of source particulates. The variation of particulate associated heavy metals in stormwater runoff at the sub-catchment is discussed. Mineral magnetic parameters characterised the majority of stormwater particulates with the roof sediment grouping. The implications of these investigations is discussed. The study was expanded to encompass the parent c~tchment. The characterisation of source sediments from land use and road types other than that· represented by the sub-catchment was carried out. Stormwater particulates collected at the main catchment'· outfall were found to be generally characterised with soil and roof sediment groupings. The further application and use of mineral magnetic parameters in similar research is discussed.

No description available.

Discharge of untreated industrial effluents containing heavy metals is hazardous to the environment as they are highly toxic, accumulates in the food chain and persistent in nature. Because of these adverse effects, their removal from wastewater is a substantial step in the protection of the environment and human health. Biosorption is found to be an eco-friendly, economical and lucrative separation technique in the removal of metal ions from effluent. This study explores the seperation potential of a new sorbent, fibroin (constituent of natural silk spun by Bombyx mori) for the removal of lead, chromium, copper and cobalt ions from effluent water. The biosorbent was prepared by the separation of cocoon into its constituents, fibroin and sericin. The removal of sericin from fibroin, called silk degumming, was carried out by water extraction method. Effect of temperature (55-95oC) on the kinetics and quantity of sericin removed was studied. The separation kinetics was approximated by the intraparticle diffusion model and the pseudo-second-order equation. Biosorption characteristics of fibroin for the removal of lead, chromium, copper, and cobalt ions from aqueous solution were investigated through a batch study. The effect of initial solution concentration, contact time and temperature on the sorption process was investigated. The adsorption equilibrium was described by the Langmuir isotherm. The thermodynamic parameters, the change in enthalpy (∆H) and change in entropy (∆S), were calculated by using Van’t Hoff plot. An accurate mathematical expression was used to calculate Gibbs free energy (∆G), for the adsorption of all metals on fibroin. For the kinetic data analysis, pseudo-second-order equation was modified based on the fact that the term qe in the kinetic equation should be the equilibrium uptake corresponding to the instantaneous metal concentration in the solution. In order to evaluate the rate constant k2, sorption kinetic data was fitted to the modified pseudo-second-order equation. The calculated values of rate constant k2, for the adsorption of all metals on fibroin, were used to the modified pseudo-second-order model to predict the kinetic data. A good comparison was observed between the experimental data and model calculations. The kinetic data was also fitted to the intraparticle diffusion model which showed a multi linear trend. The metal ions were desorbed from fibroin up to ten cycles of adsorption and desorption by using 0.05M ethylenediaminetetraacetic acid (EDTA). The removal of metal ions from fibroin was found to be rapid since complete desorption occurred within 15min. The uptake capacity of fibroin and adsorption/desorption kinetics remained almost the same even after ten cycles. The rate constants for both adsorption and desorption were also calculated by fitting the kinetic data to the modified pseudo-second-order model. The dynamic adsorption was studied in a flow-through column packed with fibroin for the removal of all metals. Experiments were performed in order to study the effect of influent concentration (12-75ppm), influent flow rate (0.15-0.24ml/min) and regeneration of fibroin bed (upto 4 cycles). Whereas the bed height, column diameter and amount of adsorbent packed were kept constant during this study. Fibroin bed saturated with metal ions was regenerated effectively by using 0.5M EDTA solution. After four consecutive cycles of adsorption and desorption, no change in the uptake capacity was observed. The bed depth service time model, the Thomas model and the Yoon-Nelson model were used to analyze the breakthrough data. The calculated values of Yoon-Nelson constants were used to predict the breakthrough curves. A good comparison was observed between experimental data and the Yoon-Nelson model calculations. An investigation was conducted to check if the adsorption of metal ions was carried out either by the surface of the fibroin or they were adsorbed deep inside its polymer network, and bulk was used. For this study, silk fibroin was transformed into thin films of three different thicknesses having same surface area. Batch experiments were conducted to study the thickness effect of fibroin films for the adsorption of metal ions. A constant amount of metal uptake for all three fibroin films showed that the adsorption was not a surface phenomenon, but the bulk body of the fibroin was used for this separation. Kinetic data was fitted to the modified pseudo-second-order model. The kinetic rate constant k2 was not significantly affected by the film thickness which abrogated the possibility of simple diffusion mechanism for metal sorption into fibroin. Fibroin films loaded with metal ions were desorbed once dipped in deionized water. The desorption kinetics was again described by the modified pseudo-kinetic-model. The calculated values of desorption rate constant kd were used to predict the kinetics of film desorption. A good comparison was observed between the modified pseudo-second-order model calculations and experimental desorption data of fibroin films.