Thesis
"Nickel precipitation by ozone oxidation in a semi-batch bubble reactor
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- Abstract
- The research aims to develop the use of ozone in nickel oxidation-precipitation from dilute solutions. The process presents three main steps: ozone transfer from gas to liquid, ozone decomposition by hydroxyl ions, and nickel oxidation-precipitation. Each step was studied using a semi-batch bubble reactor. For ozone gas-liquid transfer, a methodology to calculate the volumetric mass transfer coefficient ("kLa") was developed. Parameters evaluated included: diffuser porosity, volume of liquid and superficial gas velocity. To calculate the mass transfer coefficient ("kL") interfacial area ("a") is estimated from gas holdup and bubble size measurements. Ozone decomposition by OH" was examined as a function of pH and two ranges were identified, above and below pH 7.2. A kinetic equation for pH > 7.2 is proposed. Decomposition rate below pH 7.2 is low and considered negligible. Ozone oxidation-precipitation of nickel (II) in aqueous sulfate solution was determined as a function of pH, ozone and nickel concentration. Xray diffraction (XRD) analysis determined that the products comprised Ni(OH)2, NiOOH, Ni302(OH)4 and Ni202(OH)4. From the pattern of ozone consumption and the XRD results the proposed reaction sequence is hydrolysis - precipitation - oxidation rather than oxidation - hydrolysis - precipitation suggested in the literature.
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- 2022-03-18
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2021323.pdf | 2019-10-12 | Public | Download |