In blender or food processor, place orange liqueur, lime juice, powdered sugar and ice. Cover; blend until smooth. Spoon into nonmetal freezer container. Cover; freeze until almost firm, 2 to 2 1/2 hours.
To serve, if mixture freezes completely, let stand at room temperature about 30 minutes. Rub rims of glasses with lime wedges; dip in salt to coat.
Into blender or food processor, spoon orange liqueur mixture; blend until slushy. Place 1/2 cup slush in each salt-rimmed glass; add 1 to 2 tablespoons tequila. Garnish with lime wedges.