(1) The proceeds from the sale of any bonds issued under this act shall be applied only for the purpose for which the bonds were issued. However, any premium or secured interest received in a sale shall be applied to the payment of the principal of or the interest on the bonds sold. If for any reason a portion of the proceeds shall not be needed for the purpose for which the bonds were issued, the unneeded portion of the proceeds shall be applied to the payment of the principal of or the interest on the bonds.

    (2) The proceeds of bonds issued under this act shall be kept in a separate fund to be known as the export development bond fund, which separate fund is created in the state treasury. All other money received by the authority also shall be deposited in this fund. With the approval of the board, the state treasurer may invest and reinvest all money in the fund from time to time in such obligations of the United States or of such other governmental or corporate issuers as the state treasurer, with the approval of the board, considers appropriate. All earnings upon the investments shall be added to the fund.