A flight to Rio from Newark is full of fuel.
They circled to burn and dump fuel, making the plane much lighter before emergency landing. Reduce risk of fire on landing less stress on the plane.
Plus if it was a hydraulic problem possible landing gear or flaps/ speed brakes won’t work properly on landing.
6 gallons of gas per mile or 150 gallons per passenger so maybe 18000 gallons of fuel or slightly more than 100.000 pounds of fuel which is the weight of a fully loaded freight truck, cargo, truck and everything.
Circling the Atlantic must have taken 2 whole days