Investigating the Effect of Reaction Temperature on the Extraction of Calcium from Ironmaking Slag: A Kinetics Study

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Abstract
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.

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