I flagged three of more egregious examples: they have been deleted. But I wonder what is the procedure for closing an account.
If you see a pattern of problematic behavior of a user, flag a post by that user as "in need of moderator intervention" and describe the problem.
This applies to essentially any pattern of problematic behavior. (It's best to flag a post related to the pattern, but if this is impossible just flag any post by that user. Please, do flag a post though, and not a comment.)
Consistently, low-quality contributions indeed can be a reason for suspension of an account. When made aware of it moderators will investigate and evaluate the situation.