Try miratic acid it's used for balancing pool water (weak mix) or prepping concrete for paint (stronger mix) use extreme caution and rubber gloves( it's pretty powerful at full strengh)

If you live in a community (or State?) where, unfortunately,  meth labs are always in the news, Muriatic acid would be a bad thing to buy as it is a chemical commonly used in the cooking process.  Yet another reason why drugs are bad!  A whole list of common, useful stuff that, when purchased, draws the attention of the "Man".  (sorry, been watching Dharma and Greg too much lately)

My vote is for Simple Green straight and directly poured onto the spill.  worked on my driveway and I hope it will work on the back patio where I have been rebuilding the '93 Tracker...