Kirkwood was at the bank for 31 years and was latterly UK country head and chairman before departing in 2008.
He is currently a non-executive director of AngloGold Ashanti (SJ:ANG) and chairman of financial advisory firm Ondra LLP.
Bushveld chairman Ian Watson said Kirkwood's expertise in mining and finance would prove "invaluable to the company as we continue to deliver our strategy of further developing Bushveld as a global leading integrated vanadium player".