“Are there any valid reasons for divorce or separation beyond what the Bible specifically identifies?”
Matthew records that the Lord Jesus told his disciples, “Everyone who divorces his wife, except on the ground of sexual immorality, makes her commit adultery, and whoever marries a divorced woman commits adultery.” God hates divorce and forbids it between his children. The linked phrase above beginning with “except” constitutes what most Bible students today feel is the only possible circumstance under which that general principle does not apply.
Separation is a little more nebulous.