Who was Keturah?
Keturah was the second wife of Abraham (Genesis 25:1; 1 Ch 1:32 f). According to the Biblical tradition, he contracted this second marriage after the death of Sarah (compare Gen 23), and very likely after the marriage of Isaac (compare Gen 24).
It is not improbable that, as some writers have suggested, this change in the life of his son prompted Abraham to remarry in order to overcome the feeling of lonesomeness caused by Isaac's entering the state of matrimony.
1 Ch 1:32 (and also Gen 25:6) shows us that Keturah was not considered to be of the same dignity as Sarah who, indeed, was the mother of the son of promise, and, for obvious reasons, the sons of Abraham's concubines were separated from Isaac.
She was the mother of 6 sons representing Arab tribes South and East of Palestine (Gen 25:1-6), so that through the offspring of Keturah Abraham became "the father of many nations."
IBSE, "Keturah" (in the public domain) with minor edits.