Could soaking a foot in sodium borate (borax/bopeep) help rid a bone spur?

Bone spur soak. There are no soaks that can reduce a skeletal problem. It is too deep.
Its an astringent. You cannot dissolve a bone spur by soaking your foot. A spur is a calcification, typically of a ligamentous attachment. You can't access it from the surface of the skin.
No. A bone spur is a growth of bone which is located under the skin. It is hard and may reduce in size if all the pressure is removed from it. The only other way to reduce it is size is by surgery. Depending on where it is located a minimal incision approach might work.
No. This will relieve symptoms for a time but a cure will require more treatment.I usually recommend an insert into your shoe with the sore spot cut out of the insert.My dpm (drs of podiatry medicine) friends cringe;they expect to do a surgical procedure which may be required at some time.I delay this as long as possible.
No. Bone spurs are not going to go away without surgery. The pain associated with bone spurs may feel better with soaking.