Whenever the department shall have reason to doubt the solvency of any surety whose name appears upon any bond executed for the purpose of securing the payment of the phosphate royalty by any person digging, mining and removing phosphate rock or phosphatic deposits in any of the territory, the property of the State, under any grant or license, the department shall forthwith notify the person giving such bond and the sureties thereon and require that one or more sureties, as the case may be, shall be added to the bond, such surety or sureties to be approved by the department.