Abstract
Enhanced silicate rock weathering for long-term carbon dioxide sequestration has considerable potential, but depends on the availability of suitable rocks coupled with proximity to suitable locations for field application. In this paper, we investigate the established mining industry that extracts basaltic rocks for construction from the Paraná Basin, Sao Paulo State, Brazil. Through a Life Cycle Assessment, we determine the balance of carbon dioxide emissions involved in the use of this material, the relative contribution of soil carbonation and enhanced weathering, and the potential carbon dioxide removal of Sao Paulo agricultural land through enhanced weathering of basalt rock.Our results show that enhanced weathering and carbonation respectively emit around 75 and 135 kg carbon dioxide equivalent per tonne of carbon dioxide equivalent removed (considering a quarry to field distance of 65 km). We underline transportation as the principal process negatively affecting the practice and uncover a limiting road travel distance from the quarry to the field of 540 ± 65 km for carbonation and 990 ± 116 km for enhanced weathering, above which the emissions offset the potential capture. Regarding Sao Paulo State, the application of crushed basalt at 1 t/ha to all of the State's 12 million hectares of agricultural land could capture around 1.3 to 2.4 Mt carbon dioxide equivalent through carbonation and enhanced weathering, respectively.This study suggests a lower sequestration estimate than previous studies and emphasizes the need to consider all process stages through a Life Cycle Assessment methodology, to provide more reliable estimates of the sequestration potential of greenhouse gas removal technologies.
Highlights
Scientists agree that, by 2100, the annual extraction of an average of 3.3 Gt of carbon equivalent per year (>12 Gt carbon dioxide equivalent [CO2eq] per year) from the atmosphere will be necessary to limit the increase in global average temperature to 2 C relative to pre-industrial levels (Fuss et al, 2014; Smith et al, 2016; Williamson, 2016)
Results show that the impacts per hectare increase proportionally with the rate of application while the results per tonne of CO2eq removed occur independently of application rate and are inversely proportional to the sequestration potential of the path (EW & carbonation)
Let us hypothesize that i) the North American production system of 5 mm basalt particles is equivalent to the one represented in this study; ii) that 50% of the material takes the enhanced weathering (EW) path and the other 50% the carbonation path; iii) that all the considered croplands are situated at an average road distance of 65 km from the closest basalt mine; iv) and that the topography and road quality of the area does not affect the emissions of the truck transport
Summary
Scientists agree that, by 2100, the annual extraction of an average of 3.3 Gt of carbon equivalent per year (>12 Gt carbon dioxide equivalent [CO2eq] per year) from the atmosphere will be necessary to limit the increase in global average temperature to 2 C relative to pre-industrial levels (Fuss et al, 2014; Smith et al, 2016; Williamson, 2016). Enhanced weathering (EW) has received increasing interest in the past few years (Martin, 2017; Renforth et al, 2011); its global potential has been addressed by Beerling et al (2018) It is defined as the “process by which CO2 is sequestered from the atmosphere through the dissolution of silicate minerals on the land surface” (Renforth, 2012) and is regarded as a potential GGRT. Rock extraction The basalt quarry and production facilities studied here typically have a production capacity of 167 tonnes of aggregate per hour (Rosado et al, 2017). Rock comminution For this study, we selected a particle size of 5 mm, corresponding to the high end of what is widely referred to as fine aggregate (Mitchell et al, 2008). The process inherently minimises energy consumption, and utilises widely used machinery
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