Suppressive effects of ferric-catecholate complexes on pyrite oxidation.

Abstract: Pyrite, a common gangue mineral in complex sulfide ores and coals, is rapidly oxidized in water by ferric ions and dissolved oxygen to form a very acidic and heavy metal-laden leachate called acid mine drainage (AMD). Carrier-microencapsulation (CME) using Ti4+, Si4+, and Al3+ was reported as a promising new approach to prevent pyrite oxidation by forming a passivating barrier on the pyrite surface. In CME, the presence of Fe3+-catecholate complexes is unavoidable but their effects on pyrite oxidation remain unclear. In this study, the effects of Fe3+-catecholate complexes on pyrite oxidation were investigated. Formations of mono-, bis-, and tris-catecholate complexes of Fe3+ were verified by UV–Vis spectrophotometry and their speciation with pH was consistent with thermodynamic considerations. Linear sweep voltammetry was conducted to evaluate the redox properties of Fe3+-catecholate complexes, and the results indicate that ligands in the three complexes were sequentially oxidized until Fe3+ is released. Coating formation on pyrite was confirmed after treatment with mono- and bis-catecholate complexes. Results of SEM-EDX and ATR-FTIR indicate that the coating is composed primarily of iron oxyhydroxide phases. The results of leaching experiments showed that pyrite oxidation was suppressed by Fe3+-catecholate complexes via two mechanisms: (1) electron donating effects of the complexes, and (2) formation of a protective coating on pyrite. The results provide not only a better understanding of the effects of Fe3+-catecholate complexes on pyrite oxidation but also some possible applications of Fe3+-based CME such as the suppression of pyrite oxidation to prevent AMD formation and depression of pyrite floatability in mineral processing. Graphical abstract Image 1 Highlights • Fe3+-catecholate complexes were oxidatively decomposed to release Fe3+ on pyrite surface. • Fe3+ was precipitated as an iron oxyhydroxide coating on pyrite surface. • Iron-based CME suppressed pyrite oxidation and could depress its floatability in mineral processing. [ABSTRACT FROM AUTHOR]