Zimbabwe secured a $500-million loan from the African Export-Import Bank to try and stabilize its currency market by offering platinum production as collateral, a person familiar with the details of the agreement said. The Reserve Bank of Zimbabwe on Saturday announced on Twitter that the money would be released into the foreign-exchange market from Monday, without saying where it came from. Finance Minister Mthuli Ncube later said in a separate tweet that the funds were secured from “international banks,” without identifying them. The loan is of four years duration, the person said.