Scrap gold can be any kind of gold that you no longer desire, but it is normally not located in large amounts. For instance, old gold jewelry and gold coins may be considered scrap gold since they are not worth a great deal on their own.

Gold bullion refers to a bulk capacity of gold. Gold bullion is traded in commodity markets in the shape of ingots, bars, or coins. Unlike money, gold bullion is appreciated by its purity and its mass.

That is the difference between both of them. Hope that helps.