1. Department of Chemical Engineering, University of Pretoria, Pretoria 0002, South Africa
2. Department of Chemical and Geological Sciences, Università degli Studi di Cagliari, 09124 Cagliari, Italy
3. National Mining Agency of Brazil (ANM), São Paulo 04040-033, Brazil
4. Istituto di Geoscienze e Georisorse (UOS Firenze), Consiglio Nazionale delle Ricerche, 50121 Firenze, Italy