Antifreeze in any form is considered a hazardous material and is very poisonous. Dogs and other animals will lap the stuff up like mana, because of its sweet odor.
I’m lucky enough to be a few minutes from a facility that accepts used oil, antifreeze, oil filters, AND oil containers. If there isn’t such a place near you (perhaps by the local landfill?), most auto parts stores or shops will accept it for disposal.