Thinly slice white and light green parts of scallions. Thinly slice dark green parts to equal ¼ cup. Melt 2 tablespoons of the butter in a saucepan over medium-high. Add white and light green scallions, and cook, stirring often, 1 minute. Add rice. Cook, stirring constantly, until fragrant and toasted, 2 minutes. Add wine. Cook, stirring constantly, until absorbed, about 30 seconds. Stir in broth and 1 teaspoon of the salt; bring to a boil. Reduce heat to low; cover and simmer until liquid is absorbed, 15 to 17 minutes. Remove from heat; cover until ready to use.

While rice cooks, cut remaining 4 tablespoons butter into pieces. Place butter and lemon slices in a microwavable bowl. Microwave on HIGH until butter is almost melted, 30 to 40 seconds. Stir until melted; remove and discard lemons. Cover lemon butter to keep warm.

Rinse scallops; pat dry. Remove muscle from side of scallops; discard. Season with pepper and remaining ½ teaspoon salt.

Heat 1 tablespoon oil in a large cast-iron skillet over medium-high. Add 8 scallops; press gently with a spatula. Cook until bottom side is deep golden brown, about 4 minutes. Turn scallops over; cook until slightly opaque in center, 3 to 4 more minutes. (Don't overcook.) Transfer to a plate lined with paper towels. Wipe skillet; repeat with remaining oil and scallops.

Fluff rice with a fork; stir in parsley and zest. Serve scallops with rice; sprinkle with dark green scallion slices and additional parsley. Spoon lemon butter evenly over scallops before serving.