Pyrogenic Carbon and Carbonating Minerals for Carbon Capture and Storage (PyMiCCS) Part I: Production, Physico-Chemical Characterization and C-Sink Potential

Johannes Meyer zu Drewer^1,2,3*Maria-Elena Vorrath⁴Thorben Amann⁴Jens Hartmann⁴José María De La Rosa⁵Jens Möllmer⁶Sara Maria Pérez-Dalí⁵William Meredith⁷Clement Uguna⁷Colin Snape⁷Claudia Irene Kammann⁸Hans-Peter Schmidt⁹Nikolas Hagemann^1,3*

• ¹Ithaka Institute (Germany), Goldbach, Germany
• ²Institute for Sustainable Energy Systems (INES), Offenburg University, Offenburg, Germany
• ³Agroscope, Zurich, Switzerland
• ⁴Institute for Geology, University Hamburg, Hamburg, Germany
• ⁵Instituto de Recursos Naturales y Agrobiología de Sevilla, Seville, Spain
• ⁶Institute for Non-Classical Chemistry eV (INC), Leipzig, Lower Saxony, Germany
• ⁷University of Nottingham, Faculty of Engineering, Nottingham, United Kingdom
• ⁸Department of Applied Ecology, Geisenheim University, Geisenheim, Germany
• ⁹Ithaka Institute (Switzerland), Arbaz, Switzerland

Carbon dioxide removal (CDR) at gigaton-scale is essential to meet the Paris climate goals.Relevant CDR rates can only be achieved through the co-deployment of multiple CDR approaches. However, synergisms between different CDR methods and joint co-benefits beyond CDR have seldom been investigated. The combination of pyrogenic carbon (PyC) and enhanced weathering of minerals (Mi) for carbon capture and storage (CCS), in short PyMiCCS, presents a potentially synergetic and multifunctional approach that may be achieved by either co-application of biochar and rock powder to soils or the co-pyrolysis of biomass and rock powder before soil use. Here, we mixed biomass (wood; straw) with 10 to 50 wt% silicate rock powder (namely basanite or diabase) for co-pyrolysis to produce twelve different rockenhanced (RE-) biochars. Products were subject to physico-chemical characterization, including an assessment of carbon yield and proxies for biochar persistence. Rock-enriched biochars showed higher nutrient content, liming-and C-sink potential but lower solid-state electrical conductivity and porosity compared to pure biochars. Co-pyrolysis resulted in a coating of rock particles with secondary char but did not affect the net carbon yield. The thermal stability of wood-based RE-biochars (+10 wt% rock) was higher than that of pure woody biochars. However, the underlying mechanism and implications for biochar persistence in the environment need further investigation. Despite the addition of rock powder, the short-term release of ions from the ash fraction remains dominated by cations and anions of biogenic (biochar) origin. Therefore, it is still unclear whether the pyrogenic coating influences rock weathering. Co-pyrolysis with rock dust opens further options for designing biochar properties and to produce novel composite materials catering for multifunctional CDR.