Atmospheric carbon capture performance of legacy iron and steel waste

Legacy iron (Fe) and steel wastes have been identified as a significant source of silicate minerals, which can undergo carbonation reactions and thus sequester carbon dioxide (CO2). In reactor experiments, i.e., at elevated temperatures, pressures, or CO2 concentrations, these wastes have high silicate to carbonate conversion rates. However, what is less understood is whether a more “passive” approach to carbonation can work, i.e., whether a traditional slag emplacement method (heaped and then buried) promotes or hinders CO2 sequestration. In this paper, the results of characterization of material retrieved from a first of its kind drilling program on a historical blast furnace slag heap at Consett, U.K., are reported. The mineralogy of the slag material was near uniform, consisting mainly of melilite group minerals with only minor amounts of carbonate minerals detected. Further analysis established that total carbon levels were on average only 0.4% while average calcium (Ca) levels exceeded 30%. It was calculated that only ∼3% of the CO2 sequestration potential of the >30 Mt slag heap has been utilized. It is suggested that limited water and gas interaction and the mineralogy and particle size of the slag are the main factors that have hindered carbonation reactions in the slag heap

Atmospheric CO2 sequestration in iron and steel slag: Consett, Co. Durham, UK

Carbonate formation in waste from the steel industry could constitute a non-trivial proportion of global requirements to remove carbon dioxide from the atmosphere at potentially low cost. To constrain this potential, we examined atmospheric carbon dioxide sequestration in a >20 million tonne legacy slag deposit in northern England, UK. Carbonates formed from the drainage water of the heap had stable carbon and oxygen isotope values between -12 and -25 ‰ and -5 and -18 ‰ for δ13C and δ18O respectively, suggesting atmospheric carbon dioxide sequestration in high pH solutions. From the analyses of solution saturation states, we estimate that between 280 and 2,900 tCO2 have precipitated from the drainage waters. However, by combining a thirty-seven-year dataset of the drainage water chemistry with geospatial analysis, we estimate that <1 % of the maximum carbon capture potential of the deposit may have been realised. This implies that uncontrolled deposition of slag is insufficient to maximise carbon sequestration, and there may be considerable quantities of unreacted legacy deposits available for atmospheric carbon sequestration

The effects of coal rank, temperature and residence time on the chemical composition of tar condensates

Experiments involving coal pyrolysis with subsequent capture and analysis of the devolatilised ‘tar’ products is presented, with the aim of providing information pertinent to developing groundwater risk assessments for underground coal gasification (and similar in-situ thermal process). Different coals were pyrolysed at different temperatures and for different lengths of time within a reactor, and the resultant volatilised components were captured by condensation and analysed by GC-MS for PAHs and phenols. Whilst a clear correlation was found between temperature and amounts of potential contaminants in the condensates, there was no clear correlation with the residence time of the parent coal within the furnace

Potential of enhanced weathering of calcite in packed bubble columns with seawater for carbon dioxide removal

Enhanced weathering of minerals is one option being considered for removing CO2 from the atmosphere to help combat climate change. In this work, we consider the weathering of calcite with seawater in a reactor using air enriched with CO2. A mathematical model of the packed bubble column reactor was constructed with the key mass transfer and chemical reaction components validated with experimental data. The modelling results for a continuous process reveal the performance in terms of the specific energy consumption and the CO2 capture rate, which are affected by parameters including particle size, superficial velocities of gas and liquid, reactor bed height and feed CO2 concentration. The major energy requirements are for pumping liquid and compressing gas, and for CO2 enrichment; energy needed for supplying solid particles (mining operations, transport and comminution) was found to be comparatively minor. A trade-off was possible between ground area requirement (determined by CO2 capture rate) and energy requirement. To capture 1 tonne of CO2 at the reactor, optimal designs were predicted to consume 2.1-2.3 GJ of electricity and occupy 1.8-5.2 m2 year of space, depending on the feed CO2 concentration. These would increase to 5.7-8.2 GJ and 7.1-13.1 m2 year per tonne of CO2 captured, after allowing for degassing of the weathering product in the ocean. This increased energy intensity is still within the range of the CO2 removal options previously reported, while the space requirement quantification provides essential information for future feasibility assessment of this scheme