The selective dissolution of pyrolusite (MnO₂) in presence of goethite (FeO.OH) in aqueous ammoniacal ammonium carbamate solution has been investigated; various reducing agents were studied, in particular sodium sulfite (Na₂SO₃) and hydrazine hydrate (N₂H₄.H₂O). Sodium sulfite was found to be an unsatisfactory reducing agent for both goethite and pyrolusite, for the leaching rate decreased steadily with time to an impractical level because of the limited solubility of the reactions products. Hydrazine hydrate was an effective reducing agent for pyrolusite even at low temperature, whereas goethite required much higher temperatures for any appreciable dissolution. A one hour leach at 35°C dissolved 90 per cent of the pyrolusite but only 0.1 per cent of the goethite. Additions of ammonium phosphate had no effect on the rates, there being no phosphate detected in the leach liquor. An activation energy of 17.0 K cal/mole was found for the dissolution of pyrolusite with hydrazine. A reaction mechanism for the leaching of pyrolusite with hydrazine was proposed in which a reduction reaction on the surface of the mineral was the rate-determining step. It was possible to recover manganese from solution with oxygen as an amorphous MnO₂ precipitate. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

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Thallium (Tl) is a rare heavy metal in drinking water, but its extreme toxicity makes its removal crucial to consumer health. Traditional treatment methods do not work for Tl in sources with high concentrations of ions like calcium (Ca+2) and potassium (K+), as they are removed preferentially to Tl. A treatment method that specifically targets Tl must be applied. Pilot studies conducted in Park City Utah found that pyrolusite, a manganese oxide ore, will remove Tl to very low concentrations in the presence of competing ions but because this method is not common, further study was required. This study investigated the mineral composition of the pyrolusite and where, within the material, Tl was held. Calcite is known to accumulate Tl so tests were done looking at Tl accumulation onto pyrolusite with and without calcite on the surface in three water qualities: one with high pH and chlorine (Cl2) and low concentrations of the interfering ions Ca, K, chloride (Cl-) predicted to promote Tl removal, one with low pH and Cl2 and high concentrations of interfering ions predicted to limit Tl removal, and one with a moderate pH used for comparison. The likelihood of this Tl to stay on the media surface with changes in water chemistry was also tested. It was seen that Tl does accumulate in calcite on the media surface. Both pyrolusite media showed a high capacity for Tl and media without calcite exhibited a preference for Tl over K. Calcite dissolved with changes in pH which led to the conclusion that its formation on the media surface must be closely monitored as it may increase the risk Tl release into the drinking water system.