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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.

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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.