Using a food processor or blender, puree pineapple chunks with juice until smooth. Mix puree with juice, coconut, rum, lemon juice, and coconut extract in a large bowl.
Spoon mixture into a baking dish, wrap with plastic wrap and place in freezer for at least 8 hours. Take mixture out of freezer and scrape with a fork until fluffy. Spoon the mixture into a freezer safe container, wrap, and freeze up to 1 month. When ready to serve, spoon into a glass and top with mint.