1. a Centre for Environmental Policy, Imperial College , London , SW7 2AZ , UK
2. b Environmental Division, Zijin Mining and Metallurgy Research Institute , Fujian , 364200 , China
3. c Consulting Earth Scientists Pty Ltd , Sydney , Australia
4. d Technology Department , Paques BV , P.O. Box 52, 8560 AB Balk, The Netherlands