Using Enhanced Rock Weathering in the Sahel Region of Africa
OK I did a paper on mitigating climate change by enhanced weathering of rock on agricultural land for my masters (2014) it's not brilliant, but it does include some useful references if you want to research this further.
I would imagine the main limiting factor in the Sahel region would be that the process needs to be wet. So you're possibly only talking about being able to add material to irrigated areas. There are also the limitations you've already discussed of getting the material on site. In terms of crop yield, I would suggest that it will only increase plant growth in areas which do not already have alkaline geology (and I have no idea what the geology looks like in the Sahel, I'm afraid) and adding too much to soils may well actually decrease site fertility without the addition of something else (manure is the traditional amendment)
As far as I'm aware, enhanced weathering is perfectly technologically feasible, but it does have a limited application - due to the sheer quantity of it we'd need.
Hope this helps.