Peter Mendonidis

In recent years, technical processes for the sequestration of CO₂ through industrial waste mineral carbonation have been explored and developed. There is a large portfolio of carbon capture, utilisation, and storage (CCUS) techniques that have been employed in laboratories and at pilot scale. These include geological storage, ocean storage, and mineralisation by carbonate ores. In view of this, the main purpose of this research was to investigate and explore chemical variables, particularly ammonium salts as lixiviants for calcium mineral extraction from iron-making slag. The slag in use was acquired from a steel mill in the Vaal Triangle Region in Gauteng, South Africa. The experimental test work was conducted using different ammonium lixiviants, namely, NH₄NO₃, NH₄Cl, and CH₃COONH₄, to understand the influence of anion type as well as possible differences in mechanisms of interactions. Lixiviant concentration as well as reaction time were varied in this research study. The three selected ammonium-based lixiviants showed different extents of calcium extraction owing to differences in the anion groups. NH₄NO₃, NH₄Cl, and CH₃COONH₄ were found to be capable of dissolving 50% to 80% of the calcium from the selected slag for different molar concentrations. Anion type and leaching time also had significant influences on the leaching of calcium from the slag. Rapid pH degradation resulted in better calcium extraction capabilities. This work has shown that the selected ammonium salts have the potential to be lixiviants for calcium dissolution from iron-making blast furnace slags. These lixiviants would, therefore, be important to consider during calcium mineral carbonation for CO₂ sequestration.

In recent years, technical processes for the sequestration of CO2 through industrial waste mineral carbonation have been explored and developed. There is a large portfolio of Carbon Capture, Uti-lisation and Storage (CCUS) techniques that have been employed on a laboratory and at pilot scale. These include geological storage, ocean storage and mineralisation by carbonate ores. In view of this, the main purpose of this research was to investigate and explore chemical variables, particularly ammonium salts as lixiviants for calcium mineral extraction from iron making slag. The slag in use was acquired from a Steel Mill in the Vaal Triangle Region in Gauteng, South Af-rica. The experimental test work was conducted using different ammonium lixiviants, namely, NH4NO3, NH4Cl and CH3COONH4 to understand the influence of anion type as well as possible differences in mechanisms of interactions. Lixiviant concentration as well as the reaction time were varied in this research study. The three selected ammonium based lixiviants showed different extents of calcium extraction owing to differences in the anion groups. NH4NO3, NH4Cl and CH3COONH4 were found capable of dissolving 50% to 80% of calcium from the selected slag for different molar concentrations. Anion type and leaching time also had significant influences on the leaching of calcium from the slag. Rapid pH degradation resulted in better calcium extraction ca-pabilities. This work has shown that the selected ammonium salts have a potential as lixiviants for calcium dissolution from iron making blast furnace slags. These lixiviants would therefore be important to consider during calcium mineral carbonation for CO2 sequestration.

Beneficiation of iron and steel slags have a great potential in mitigating high levels of anthropogenic carbon dioxide (CO₂) gas emissions owing to their high contents of calcium and magnesium. Carbonation of calcium and magnesium leaching solutions produce precipitates that promise to act as fluxing agents in various industries. There is also a need to study the physico-chemical factors affecting the extraction of these elements and their kinetic behaviour. A calcium-rich blast furnace ironmaking slag milled to 80%—75 µm was used in an experiment to study the effect of reaction temperature on the dissolution of calcium. An orbital shaking incubator was used by applying the one-factor-at-a-time method for a 2 h leaching test. Reaction temperature was controlled at 30 °C, 50 °C, 70 °C, and 100 °C at constant agitation speed of 200 rpm, 0.5 M of lixiviant concentration and solid-to-liquid ratio kept at 200 g/L. CH3COOH, (NH₄)₂SO₄, and NH₄Cl were tested individually as lixiviants. AAS, XRD and EDX were used to analyse the leach filtrate and residue. Consequently, the findings showed that temperature is the critical operating parameter that yielded exceptionally high calcium extraction. CH₃COOH yielded 80–90% of calcium extracted under high reaction temperatures. The kinetic data for the effect of reaction temperature leaching data fitted one shrinking core model equation, which described diffusion-controlled leaching reactions. The diffusion controlled by a product layer model was fitted and the activation energy were calculated as 19.4930 kJ/mol for NH4Cl solvent. (NH₄)₂SO₄ and CH₃COOH did not fit into any model because of undefined kinetic data and formation of gelatinous silica layer during leaching process.

The Portobello granite, which crops out along the littoral in southern Natal is an S-type, red-coloured, foliated, chlorite-biotite granite that preserves evidence of low-temperature alteration. It intruded the 1091 ± 7 Ma Munster Suite quartz monzonorites and has distinctive 1.0 to 1.5 m wide charnockitic margins adjacent to the contacts with the quartz monzonoritic country rock. SHRIMP geochronology on zircon grains from two samples, one taken from the charnockitic margins and the other from the main body of chlorite-biotite granite, produced two statistically distinct ages: 1057 ± 27 Ma for the chlorite-biotite granite and 1093 ± 7 Ma for the charnockitic margin. The age for the charnockitic margins is identical to that of the country rock and, given the previously proposed origin for the margins by way of partial assimilation of the country rock, it is interpreted that the zircons sampled from the charnockitic margins are xenocrystic. The low-precision age of 1057 ± 27 Ma for the chlorite-biotite granite was produced from milky, metamict zircon grains suggestive of low temperature alteration, which may have affected the accuracy of the age. Nevertheless, the age of 1057 ± 27 Ma for the chlorite-biotite granite is statistically similar to the intrusive ages of the Oribi Gorge Suite and to ages recorded by metamorphic overgrowths on zircon grains from the Munster Suite. The ages produced by this study fall within the range of ages thus far acquired for the Margate Terrane of the Natal Metamorphic Belt, and further corroborate the previously proposed continuation of the terrane into the Vardeklettane Terrane of Dronning Maud Land in Antarctica. A zircon core from the charnockitic margins recorded an age of 1800 ± 12 Ma, which is the oldest age thus far recorded in the Margate Terrane.