Reydick D. Balucan

Thermal activation of antigorite for mineralization of CO2.

This contribution demonstrates the sensitivity of antigorite dehydroxylation to treatment conditions and discusses the implications of the observations for scientific (i.e., dehydroxylation kinetics) and technological (i.e., energy efficient conditions and design of practical activation reactors) applications. At present, the energy cost of dehydroxylation of serpentinite ores represent the most important impediment for a large scale implementation of sequestering CO(2) by mineralization. We have analyzed changes in antigorites derivative thermogravimetric curves (DTG) and deduced factors affecting the mass loss profiles. The imposed heating rate, type of purge gas, type of comminution and sample mass all influence the dehydroxylation curve. However, the results show no influence of material of construction of the heating vessel and flow rate of the purge gas. We report an important effect of oxidation of Fe(2+) under air purge gas that occurs prior to dehydroxylation and leads to formation of hematite skins on serpentinite particles, slowing down subsequent mass transfer and increasing the treatment temperature. From the process perspective, 75 μm particles afford optimal conditions of temperature and rate of dehydroxylation. Overall, the practical considerations, in thermally activating serpentinite ores for storing CO(2) by carbonation, comprise rapid heating, proper size reduction, prior demagnetisation, and fluidization of the powder bed.

The influence of cleat demineralisation on the compressibility of coal

The natural fracture system of coal is the primary conduit for gas flow. Low permeability is in many cases attributed to low fracture porosity and/or connectivity. Mineral occluded coal cleats are known to considerably reduce coal permeability. Whilst cleat demineralisation has been found to increase coal permeability, its influence on compressibility is poorly understood. In this study, we investigated the influence of mineral dissolution and secondary mineralisation on the compressibility of coal (Cf) following acidification with hydrochloric and hydrofluoric acid (HCl-HF). In-situ HCl core flooding and core immersion in 3% and 15% HF yielded a less compressible core (Cf 0.006 from 0.020 bar-1) with sustained, enhanced permeability to brine (k 0.40 from 0.10 mD). We attribute improved stress resilience and better fluid flow characteristics to the dissolution and subsequent secondary mineralisation of the cores circumferential periphery. Predictive geochemical speciation using OLI Analyzer 9.1, for surveying mineral solubilities and precipitation tendencies, identified the formation of radio-dense neofluoride salts K2SiF6 and CaF2 Structural modifications and mineralogical changes detected from scanning electron microscopy-electron diffraction spectroscopy (SEM-EDS), confirmed the presence of these salts. Results suggest that mineral alteration and subsequent secondary mineralisation of the core periphery following HCl-HF acidisation yielded well-formed crystalline salts, apparently serving as in-situ generated proppants buttressing newly created void spaces for enhanced fluid flow and improved resistance to increasing confining stress.