1. Key Laboratory of Nonferrous Metals Chemistry and Resources Utilization of Gansu ProvinceState Key Laboratory of, Applied Organic Chemistry and, College of Chemistry and Chemical EngineeringLanzhou University Lanzhou 730000 P. R. China
2. College of Earth and Environmental SciencesLanzhou University Lanzhou 730000 P. R. China
3. School of Physical Science and TechnologyLanzhou University Lanzhou 730000 P. R. China