Any lands so received and patented from the United States shall be held as a part of the educational lands of this state, and shall be subject to all existing laws pertaining to such lands; Provided, that such lands, so received in exchange, shall only be subject to lease for terms not exceeding twelve years, with the privilege of renewing for a like term in the option of the board. Such leases may also include the right to the lessee of removing all improvements he may have erected on the land.