Phosphoric acid spill cleanup
The product you were using is very likely a &quot;rust converter&quot;. Used to convert rust to a stable products before painting . I have used it several times , usually I just rinse the  surface , let it dry and paint . It is also used for industrial maintenance coating of poorly prepared surfaces ( those not sand blasted). That is ;it is commonly used and when I worked with coatings I never heard of a problem. Baking soda will neutralize it . I once inspected super phos storage tanks : it starts as 107 % phosphoric acid used to blend liquid fertilizers. When I stepped out of the tank and walked across the limestone gravel ,each step of the rubber boots left some jelly-like acid which foamed on the gravel. The people that worked at the facility thought nothing of it; from that I conclude neutralized phos acid it not a problem . Sorry this is all anecdotal ,but I have never needed to research the situation.