- Title
- Experimental and modelling studies on direct aqueous carbonation of thermally activated lizardite
- Creator
- Abu Fara, Ammar
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2019
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- A lack of understanding of the mechanism of the mineral carbonation process and the difficulty of leaching 100% of Mg from the mineral represent an obstacle for commercial progression in this technology. Furthermore, slow overall reaction rates and relatively low product yields are the main challenges which inhibiting the commercial development of the process and are still far below industry expectations. The major aim of this research is to understand the mechanism of the direct aqueous mineral carbonation of heat activated lizardite by tracking the evolution of aqueous and solid species produced throughout the course of the reaction. The analysis methodology of solid and liquid samples was performed based on different analytical techniques, including Thermal Gravimetric Analysis Mass Spectrometry (TGA-MS), Inductively coupled plasma - optical emission spectrometry (ICP-OES), Qualitative and semi-quantitative X-ray diffraction (XRD), Malvern Mastersizer 2000, Scanning Electron Microscopy (SEM) combined with Energy Dispersive X-ray Spectroscopy (EDS). Carbonation experiments conducted with controlled feed particle size distributions provided insight into the effect of particle size on overall carbonate yield, reaction rate and the formation of passivating silica layers. Reaction kinetics displayed two-step behaviour, with rapid reaction initially, resulting in carbonate product yields ranging from 20 to 50%, when subsequently the reaction rate decreased dramatically. The results indicate that precipitation of MgCO3 is relatively rapid and the dissolution of Mg from the mineral is the rate limiting reaction step. The observed reaction kinetics could be explained by the formation of a silica-rich layer and Mg-silicate phase form a skin layer around the reacting particle which appears to inhibit the rate of the reaction. Some factors which influence the formation of magnesium carbonate phases produced during direct aqueous carbonation; hydromagnesite and the targeted magnesite phase, were investigated. Different stirring speeds (100, 450 and 600 rpm) were tested under ARC standard conditions. Two Mg-carbonate phases were observed (hydromagnesite and magnesite). The position of the impeller was another factor which was examined. In contrast, the influence of sodium bicarbonate was studied to examine its effect on the Mg carbonation yield and the phases thus formed. In order to understand the mechanism of the dissolution, it was important to study the reaction under conditions where the rate of carbonate precipitation, so that the dissolution process can be studied in isolation, dissolution experiments were performed at high pressures (100 bar) and low temperatures (40 ᵒC) to explore the effect of the enhanced solubility of CO2, and how this influences the extent of Mg extraction under these conditions. An important aspect of the investigation was to examine the effect of particle size and solid ratio on the dissolution rate of Mg and Si, in the absence of NaHCO3. The dissolution kinetics disclosed two distinct dissolution regimes, with a rapid initial rate of Mg extraction, resulting the fraction of Mg extracted ranging from 30 to 65 % during the first 20 minutes of the experiment, following which the dissolution rate decreases dramatically. The rapid decrease in rate of Mg extraction may be a result of the formation of a silica-rich layer around a core of un-leached particle, which presents a diffusion barrier and inhibits the rate of further dissolution. Carbonation experiments were conducted under different reaction conditions (temperature, pressure and presence/absence of NaHCO3) using heat activated lizardite to study the effect of each variable on the reaction rate and overall yield. The on-line sampling was employed to track reaction progress and mineral speciation over time, to provide new insights into the reaction mechanism the detailed effect of the optimum conditions proposed by ARC. A novel dosing system was developed to identify the reaction starting point (time zero) by injecting heat-activated lizardite into the reactor.
- Subject
- aqueous mineral carbonation; lizardite; Thermal Gravimetric Analysis Mass Spectrometry (TGA-MS); inductively coupled plasma - optical emission spectrometry (ICP-OES); heat-activated lizardite
- Identifier
- http://hdl.handle.net/1959.13/1397853
- Identifier
- uon:34362
- Rights
- Copyright 2019 Ammar Abu Fara
- Language
- eng
- Full Text
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| View Details Download | ATTACHMENT01 | Thesis | 12 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 238 KB | Adobe Acrobat PDF | View Details Download |