The present contribution details a new numerical model designed for simulation of the potential effeciency of the enhanced weathering techniques. Spreading crushed minerals over agricultural fields has been proposed as a technique able to mitigate the atmospheric CO2 rise due to human activities. But the question of the faith of the spread mineral particles has been simulated with very simple methods, and the present contribution aims at improving this description.

The authors describes a mechanistically-based numerical model built to improve the prediction of the amount of CO2 that will be consumed by enhanced weathering. This model is in the ligneage of the CrunchFlow model, which was implemented by Carl Steefle. The new model (Specter) includes a description of the water-mineral interactions based on kinetic laws, the precipitation of secondary phases, the gas diffusion in soils, and the mixing in the upper layer related to the biological activity. All this seems to me correct, and more accurate than parametric methods. I only have a few  comments, which can be easily included in a slightly revised version of this ms.

1. Similar models have been implemented since about 30 years. I think that the authors forgot a few references. For examples, ref to the SAFE and PROFILE box-models should appear in the text, because these are the first to apply laboratory kinetic laws to the field. The WITCH model has been also developped to simulate weathering reactions mechanistically, and a version of it includes the CO2 diffusion (check Goddéris et al., 2006, in GCA; Roland et al.,  2013 in Biogeosciences; Beaulieu et al. 2012 in Nature Climate Change; Goddéris et al. , 2013 in Biogeosciences). Although not dealing with enhanced weathering, these simpler box-models demonstrate their ability to simulate weathering processes in the field based on a more mechanistic formulation.

2. I found a bit strange to talk about uplift. Is the model really accounting for uplift ? If I understand it correctly, it seems to me that the model is using a referential in which fresh primary minerals are going upwards as weathering proceeds. In the real world, it is the regolith which progressively penetrates the bedrock and thus goes downward. This has nothing to do with uplift ?

The authors report the development of a much-need second model with time-dependent capability for determining CDR from EW that complements that of Beerling et al. published in Nature last year.  I sympathize with the lack of empirical datasets to evaluate the model against.  Nevertheless, I’d urge the authors to consider the (extensive) geochemistry literature on basalt grain dissolution across a wide range of particle sizes, temperatures and pH units as a source of potentially useful information in this regard.  The manuscript is detailed and comprehensive. I have only a few minor comments for the authors to consider.

15. l. 15. Suspect the authors of the Beerling et al. would quibble with the notion it lacked mechanistic detail. Theirs was a 1-D model calibrated against a phreeqC RTM of comparable to detail to the present one. That strategy gave great flexibility both for integrating into a broader EW techno-economic framework and future development in terms of adding geochemistry details and year-to-year particle size treatment.
16. l. 47-48. Agreed. Ensembles of traceable EW models for CDR estimate will be an important advance in this field.
17. l. 480. Treatment of biotic weathering seems to be mainly through the production of SOM and its subsequent decomposition, as it affects the acid-base balance. But there is also the effect of nutrient uptake (base cations) by plant and release of protons by fine roots likely to be in direct contact with silicate rock grains, and production of organic acids by fine and mycorrhizal fungi which also produce a focused release of H+ from explorative hyphae (this is partially noted in the conclusions but the omission might be flagged here too).
18. l. 615. Part of the explanation in the timescale of CDR efficiency between the present model and Beerling et al. may be related to the treatment of particle size distributions in the soil from one year to the next (discrete vs continuous).