- Title
- Synthesis and application of mineral carbonation by-products as portland cement substitutes
- Creator
- Benhelal, Emad
- Resource Type
- thesis
- Date
- 2018
- Description
- Professional Doctorate - Doctor of Philosophy (PhD)
- Description
- This thesis presented the results of investigations on single and two stage mineral carbonation processes (using heat activated serpentine as feed stock) aimed at producing reactive materials as cement substitutes from mineral carbonation by-products. This study examined the effect of different sample preparation techniques (wet grinding, wet sieving, and heat activation), single and two stage carbonation processes at laboratory and pilot scale and cement substitution studies at a commercial cement manufacturer R&D facility. Chemical and physical characterisation of feed and by-product samples were performed employing a variety of analytical techniques including Thermal Gravimetric Analysis Mass Spectrometry (TGA-MS), Inductively Coupled Plasma Atomic Emission Spectroscopy (ICPAES), Qualitative and semi-quantitative Powder X-ray diffraction (XRD), Malvern Mastersizer PSD analyser, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), Surface area and porosity measurement (BET), Fourier-Transform Infrared Spectroscopy (FTIR), Transmission Electronic Microscopy (TEM),29Si Solid State Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) and Matrix Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS). Undesired side reactions occurring during single stage aqueous mineral carbonation process using heat activated serpentine (antigorite and lizardite) were investigated. It was found that when heat activated antigorite was used as feed, crystalline serpentine and a silica-rich passivating layer were formed on the surface of reacting particles. In contrast, when using heat activated lizardite as feed, crystalline serpentine was absent and a silica-rich passivating layer was the only undesired side product formed during the carbonation process. These findings disclosed a possible explanation for the relatively low magnesite yields often observed in the aqueous mineral carbonation process using heat activated serpentine as feed. Quiescent soaking of heat activated lizardite under aqueous conditions at ambient temperature and pressure was found to be a very simple and promising approach to increase magnesite yields of single stage carbonation process. Results showed that soaking produced coral shaped nano-structure on the surface of heat activated lizardite. The coral-shaped nanostructure was found to be an amorphous magnesium silicate hydroxide phase with 1:1 mole ratio of magnesium and silicon, which is suggested to be formed in a dissolution/precipitation process. By-products of single and two stage mineral carbonation processes using heat activated lizardite were characterised, to investigate their potentials as cement substitutes. It was found that all samples contained at least 40 wt% of an amorphous silica phase. Experiments were performed to increase the concentration of amorphous silica by magnesium extraction in two stage and acid treatment processes. Treating the solid residue of the two stage process with nitric acid was effective in the quantitative extraction of magnesium and produced a very reactive silica product. The experimental data obtained from a 30 L pilot batch reactor, used for single stage aqueous carbonation and for the dissolution of heat activated lizardite was compared to laboratory scale data obtained under similar reaction conditions. The results of aqueous carbonation experiments in the pilot and the laboratory scale reactors showed less than 5% scatter in repeat experiments. Results indicated that the magnesite yield obtained in the pilot batch reactor were 35±2% higher than that produced in the laboratory scale reactor. The higher yield was attributed to improved mixing and in consequence, removal of passivating phases from the surface of the reacting particles in the pilot reactor compared to the laboratory reactor. The yield of magnesite in mineral carbonation experiments using distilled water and tap water were almost identical. Undertaking reaction in 1 M NaCl solution did not have a significant effect, but adding 0.64 M sodium bicarbonate had a notable effect on magnesite yield. Regrinding of the solid residue remaining after dissolution stage of two stage process and performing a second dissolution step resulted in a 50% increase in the amount of magnesium extracted. The feasibility of utilising feed and by-products of mineral carbonation technology as cement substitutes was investigated. These materials, with and without pre-treatment, were used to substitute 5, 10 and 20 wt% of Portland cement in mortars. Pozzolanic activity tests indicated that acid treated silica-enriched residue from two stage process displayed pozzolanic activity. At 5 wt% cement replacement, all materials showed compressive strengths comparable to the control. When 10 wt% of cement was replaced, only heat activated lizardite showed strength results similar to the control. The compressive strength of mortars containing other samples with 10 wt% or greater cement replacement showed that the extra water demand outweighed any pozzolanic contribution of mineral carbonation materials and resulted in lowering the compressive strength of these mortars compared to controls. Therefore our study showed that replacing up to 5 wt% of Portland cement with mineral carbonation by-products was feasible.
- Subject
- mineral carbonation; heat activated serpentine; silica-rich passivating layer; serpentinisation; mineral carbonation pilot plant; cement substitution; pozzolanic activity; silica -enriched material
- Identifier
- http://hdl.handle.net/1959.13/1388344
- Identifier
- uon:32744
- Rights
- Copyright 2018 Emad Benhelal
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
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| View Details Download | ATTACHMENT01 | Thesis | 14 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 920 KB | Adobe Acrobat PDF | View Details Download |