Phosphate coating on pyrite to prevent acid mine drainage

Mine Wastes

“…Various chemical reagents such as sodium acetate, sodium metasilicate or potassium orthophosphate have been evaluated for the coating of pure pyrite and pyrrhotite samples and pyritic coal waste (Evangelou 2001;Fytas and Evangelou 1998;Georgopoulou et al 1996;Hodson et al 2000;Huang and Evangelou 1994;Zhang and Evangelou 1998). The techniques allow chemical reactions to take place between reagents and the sulfide minerals.…”

Inhibition of sulfide mineral oxidation by surface coating agents: Batch and field studies

“…Although various concentrations of coating agents (10 −1 -10 −3 M KH 2 PO 4 , MgO, KMnO 4 and 0.3 g apatite, cement and manganite), oxidizing agents (10 −1 -10 −3 M NaClO and H 2 O 2 ), and buffer (10 −1 -10 −3 M NaOAc) were tested, only the best results are presented in Table 3. A buffer was used to keep pH between 5 and 7 and to promote iron oxide formation on the sulfide mineral surface [21]. Previous studies by Zhang and Evangelou [22] reported the use of NaOAc as a buffer to adjust pH and to inhibit pyrite oxidation forming iron oxide coating on the surface of pyrite.…”

Water Management at Abandoned Flooded Underground Mines

“…• surface inactivation by encapsulation or coating (Evangelou 1995;Fytas and Bousquet 2002), • reducing the hydraulic permeability of pollutant bearing rocks (Ziegenbalg 1999;Waring and Taylor 1999;Ziegenbalg 2005), • injection of chemically reducing gas mixtures (Taylor and Waring 2001;Houston et al 2005), and • reactive material ("reactive barriers").…”

“…Encapsulation and coating can be conducted with a range of substances, such as Fe-phosphate, silica, sodium silicates, or "simple" but effective clay caps (Brandberg et al 1993;MEND [Mine Environment Neutral Drainage Program] 1994;Evangelou 1995;Roy and Worral 1999;Fytas and Bousquet 2002;Carlsson 2004). The "oxidation proof silicate surface coating on iron sulfides" method, though still unproven, is patented (U.S. Patent 5,494,703), so it cannot be freely used!…”