Carbon sequestration in unmineable coal seams has been proposed as one of the most attractive technologies to mitigate carbon dioxide (CO2) emissions in which CO2 is stored in the microporous structure of the coal matrix in an adsorbed state. The CO2 adsorption process is hence considered one of the more effective methodologies in environmental sciences. Thus, adsorption isotherm measurements and modelling are key important scientific measures required in understanding the adsorption system, mechanism, and process optimization in coalbeds. In this paper, three renowned and reliable adsorption isotherm models were employed including Langmuir, Freundlich, and Temkin for pure CO2 adsorption data, and the extended-Langmuir model for multicomponent, such as flue gas mixture-adsorption data as investigated in this research work. Also, significant thermodynamics properties including the standard enthalpy change ($$\Delta H^\circ$$ Δ H ∘ ), entropy change ($$\Delta S^\circ$$ Δ S ∘ ), and Gibbs free energy ($$\Delta G^\circ$$ Δ G ∘ ) were assessed using the van’t Hoff equation. The statistical evaluation of the goodness-of-fit was done using three (3) statistical data analysis methods including correlation coefficient (R2), standard deviation (σ), and standard error (SE). The Langmuir isotherm model accurately represent the pure CO2 adsorption on the coals than Freundlich and Temkin. The extended Langmuir gives best experimental data fit for the flue gas. The thermodynamic evaluations revealed that CO2 adsorption on the South African coals is feasible, spontaneous, and exothermic; and the adsorption mechanism is a combined physical and chemical interaction between the adsorbate and the adsorbent.

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Numerous studies have been carried out recently on the sequestration of carbon dioxide (CO 2 ), a greenhouse gas, produced due to human activities. Consequently, storage of CO 2 in storage sites, such as unmineable coal seams, has been identified as one of the promising options with the advantage of recovering coal-bed methane (CH 4 ). However, CO 2 injected into coal seams contains additional gases that may reduce storage capacity, cause changes in sorption behaviour and physicochemical properties of coal. This research was aimed at investigating the sorption behaviour of three South African coals (sorbents) upon pure CO 2 and flue gas (sorbates) sorption. Measurements were conducted on 10 g samples with a grain size <2 mm. A synthetic industrial flue gas containing 12% CO 2 , 5.5% O 2 , 82% N 2 , 0.38% SO 2 and 0.12% NO 2 was used in the study. Sorption isotherms were measured at a temperature ranging from 30 to 60°C and pressures up to 9 MPa using a high-pressure CO 2 volumetric adsorption system (HPCVAS). Sorption of CO 2 by coal was highly reduced in the presence of additional gases due to competition for sorption sites. The reduction in CO 2 (in flue gas) sorption capacity of coal was up to 63% compared to sorption of pure CO 2 .

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Purpose -The effect of chlorides on corrosion of reinforcing steel is well documented in the literature. However, few studies have focused attention on the effect of sulphates on the corrosion of low carbon steel in alkaline media. This paper aims to address this issue. Design/methodology/approach -This paper describes the results of the investigation into the corrosion behaviour of low carbon steel (typically used as reinforcing steel), exposed to alkaline media at a pH of 9 and 12 with varying concentrations of sulphate and chloride ions, as well as, in sulphate only solutions. An attempt was made to inhibit corrosion of steel exposed to the corrosive media using laser surface treatment of the steel specimens. Mass loss tests and electrochemical tests were conducted to evaluate the effect of sulphate only and the combined effect of sulphate and chloride ions in an alkaline media on steel. Findings -It was found that sulphate ions could cause corrosion of steel in alkaline media. The severity of the attack increased with increasing sulphate ion concentrations, as well as with combinations of sulphate and chloride ions. The pH 12 conditions seem to show much more critical attack with evidence of pitting corrosion as compared to uniform corrosion for test conditions at a pH of 9. The attempt to inhibit the observed corrosion of steel exposed to the corrosive high alkaline media containing sulphate ions on their own and in combination of chloride ions by laser surface treatment proved to be successful. Originality/value -The research undertaken here adds to the body of knowledge relating to the effect of sulphate ions on reinforcing steel corrosion in highly alkaline media. Most literature points out that sulphate ions on their own do not have a corrosive effect, but rather, a passivating effect!