Can a liquid barium drink for ct scan prep irritate the colon after a recent case of diverticulitis?

Barium is a laxative: What do you mean by "irritation"? Abdominal pain? Increased output? Blood? Barium, for all its use in imaging, is also a laxative & often used as an enema. It will force the stool out of the intestines & colon as it makes its way out. Therefore, "irritation" of the colon (depending on how you define it) isn't uncommon after a barium-contrast CT. It shouldn't cause bleeding nor pain, however. TTYD