The big difference is that artillery shells are a lot more powerful than land mines, and some of those shells have mustard gas. Using a machine of some sort is a good idea but I bet it wouldn't work the same as the minefield sweeper at all.
There are also the mines that were placed to destroy trenches. Truly colossal quantities of explosives that were placed at the end of tunnels. Not all were exploded.
Yes, these are mines, built by miners (the people that dig tunnels to extract minerals). During the war, they dug mines under enemy lines and filled them with tons of explosives. Not all were used and the location of some unused ones has been lost [1]. One of them blew up from a lightning strike in 1955[2].
As we reduce our coal use, the United States has a lot of absolutely enormous strip mining equipment going surplus. An obsolete 1960's era shovel moves 80m^3 in a scoop and that scoop is WW-1 era bomb proof for all practical purposes, say you want to dig down 4 meters, thats 20m^2 cleared per scoop. About 2 million scoops to clear a square mile. That one shovel should be able to pick up and sift a square mile of Europe in about 2 years. Granted, some of it will need to be run through an incinerator as well and you'd have the same environmental result as a used strip mine, but you can farm that and a square mile of France or Belgium should have resale value.
Edit: The German bucketwheel excavators like the Bagger 293 might do it faster.