Lime and copper sulfate powders are used frequently on open wounds in horses. They have value in treating wounds with excessive granulation tissue (proud flesh). They should not be used on fresh wounds and should never be applied to wounds that may be sutured.
Wonder Dust® is a combination of lime, copper sulfate, activated charcoal and a variety of other ingredients. I have seen this product (and lime powder, table salt, copper sulfate granules and others) used successfully by horse owners on simple open wounds with proud flesh, that do not involve critical structures and are otherwise uncomplicated.
I have also seen these materials used for months on infected joint and tendon sheath wounds that should have been evaluated by a veterinarian. In several cases, the delay in appropriate treatment cost the horse its life. Some topical products that destroy proud flesh also cause damage to healing tissue and delay healing.