Decarbonation Of Carbonate Research Articles

Thermal behaviour of biomass ashes in air and inert atmosphere with respect to their decarbonation

The carbonation/decarbonation of biomass ashes (BAs) is responsible for the CO2 capture and storage (CCS) potential of these waste products. Therefore, the thermal behaviour of eight BAs treated from ambient temperature up to 900 °C in air and inert atmosphere was studied to evaluate the decomposition of carbonates and associated with them minerals. A combination of thermal, mineralogical and chemical analyses was used for that purpose. The chemical composition of BAs is highly variable and their phase-mineral composition consists of diverse inorganic amorphous material, carbonates, sulphates, and silicates, plus some phosphates, chlorides, oxyhydroxides, and char. It was found that there are significant differences in the minerals transformation of BAs thermally treated under oxidizing and pyrolyzing conditions. Most BAs have lower mass loss in air than in inert atmosphere up to 900 °C due to the decomposition of minerals and char with subsequent oxygen uptake during oxidation of their decomposition products. The carbonates in BAs consists of calcite and kalicinite, and to a lesser extent, fairchildite and butschliite. The most important temperature for the decarbonation of carbonates is 600–900 °C and all BAs have higher mass loss under pyrolyzing conditions than under oxidizing environment in this temperature range. The inert atmosphere is more favorable for the decomposition of calcite, K2CO3, fairchildite, and butschliite, and melting of chlorides than air atmosphere. In contrast, the air atmosphere is more favorable for the dehydration, dexydroxylation, and oxidation of minerals and char than inert atmosphere. Hence, the determination of decarbonation for BAs (respectively CCS) is more representative in inert atmosphere because it avoids the oxidation reactions.

Co-production of high quality hydrogen and synthesis gas via sorption-enhanced steam reforming of glycerol coupled with methane reforming of carbonates

The sorption enhanced steam reforming (SESR) produces high-purity hydrogen and capture CO2 in the form of carbonates, allowing for controllable CO2 storage or utilization. However, the decarbonation of carbonates at temperatures high up to 800–900 °C makes the SESR process and the subsequent CO2 utilization energy-intensive. Herein, we report the feasibility coupling the SESR of glycerol with CH4 reforming of carbonates, which combines the decarbonation with CO2 utilization to simplify the technology and avoid the energy-consuming temperature swing. A high-efficiency bi-functional Ni-CaO-Ca12Al14O33 catalyst was proposed to this process. The catalyst was derived from a Ni-Ca-Al hydrotalcite-like (HTl) material to achieve homogeneous mixing of Ni, CaO and Ca12Al14O33 which were active metal, sorbent and a spacer to prevent CaO sintering. Thanks to the high activity and stability of Ni-CaO-Ca12Al14O33 catalysts, 98.53% hydrogen-enriched gas could be obtained in SESR of glycerol, and the high CH4 conversion (95.3%) and H2/CO molar ratio (<2) suitable for further Fisher-Tropsch synthesis were achieved during the CH4 reforming reaction. Meanwhile, Ca12Al14O33 as a spacer had provided a stability for ten cycles. Our results highlight the significance of process intensification and high-efficiency bi-functional catalysts for the hydrogen production with low carbon emissions.

System closure during the combustion metamorphic “Mottled Zone” event, Israel

The Hatrurim Formation (or the “Mottled Zone”) is a unique rock complex in Israel and Jordan, which is composed mainly of high-temperature–low-pressure metamorphic minerals, typical of the sanidinite and pyroxene-hornfels facies. These rocks are the metamorphic product of combustion of the bituminous (“oil shales”) Maastrichtian to Paleocene chalk and marls of the Ghareb and Taqiye Formations.Temperatures of 500–700°C were common during the combustion metamorphic process producing the high-grade gehlenite–larnite, calcite–spurrite and anorthite–diopside fels (“dense-olive” rocks). In order to test the degree of system chemical closure the graphical isocon method was applied. We compared the chemical composition of the metamorphic rocks and their protolith equivalents — Ghareb Formation oil shales and Taqiye Formation rocks, on an outcrop scale. With respect to a set of 8 major, minor as well as 21 trace elements, the chemical composition remained similar during metamorphism and yielded almost no element mobility. The main losses were those of organic matter, which was oxidized during combustion, dehydration, upon heating and decarbonation of carbonates. Combustion resulted in an average mass loss of 30% and some volume loss (derived from the mass loss as well as the formation of denser mineral phases). These suggest that the combustion process was essentially isochemical on a large scale. On the other hand, the common presence of veins in some of the rocks implies that the Hatrurim metamorphism was isochemical on a large scale, whereas on a smaller scale open system fractionation characterized some of the elements, which are enriched in the veins.

New models for the origin of Valles Marineris closed depressions

Current models for the formation of the abundant large closed depressions of Valles Marineris have serious shortcomings. Purely tectonic mechanisms are inconsistent with the morphology of many depressions, and removal of large quantities of ground ice from the canyon walls is inconsistent with the observed strength of the walls. Accordingly, we offer some alternatives. One possibility involves decay of ice‐rich bodies occupying partially sediment‐choked ancient graben that predated the overlying cratered and ridged plains. Other possibilities involve the removal of massive equatorial carbonate deposits storing much of the planet's CO2 inventory, generated during greenhouse conditions on early Mars. Solution by carbonic acid derived from the atmosphere (analogous to terrestrial karst) requires extensive recycling of the available water supply. Solution by various groundwater acids, possibly derived from the Tharsis magmas, requires less water, especially if only the smaller closed depressions are due to carbonate decay. Alternatively, volume loss due to decarbonation of carbonate during early high heat flow or a later Tharsis‐related heat pulse can produce extensive collapse, especially if the carbonates have high silica content.

Mineralization and wall-rock alteration at the Bogala graphite deposit, Bulathkohupitiya, Sri Lanka

The graphite mineralization in the Bulathkohupitiya area was studied with an emphasis on the Bogala deposit.Vein-type mineralization occurs in the zones of deep-seated fractures in supracrustal stratiform metasedimentary rocks resulting from the differential rise of subcrustal migmatites.The mineralization at Bogala comprises several veins of graphite and a large vein of syenite pegmatite. Mineralogical and geochemical study of the wall rocks reveals a well-zoned alteration halo about the deposit. Chemical zoning in the altered wall rock and the relict mineral replacement textures indicate deep-seated hydrothermal activity. Formation of vein graphite by decarbonation of carbonates and reduction of CO 2 formed during the decarbonation reaction is indicated by the available carbon isotope data.Chemical zoning in the alteration halo may be a useful aid in the exploitation of known graphite deposits.