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The separation of copper sulfide ore minerals from gangue using magnetic nanoparticles functionalized with peptides selected via phage display : a proof of concept Greene, Robert Crandall


Copper is one of the most important mineral resources. While much unmined copper remains to meet increasing demands, reserve deposit concentrations are dropping while increasing in mineralogical complexity. Porphyry deposits containing the largest reserves have an average grade of 0.25% and often contain elevated concentrations of arsenic in comparison to the deposits that supplied most copper before the 20th century. The current copper porphyry processing scheme first concentrates sulfide ores via froth flotation, then smelts these concentrates. These processes are energy intensive and employ toxic chemical reagents. Low grade deposits must be extensively milled to release ore from gangue. Copper sulfide grains milled to <30 μm in diameter are hard to recover by flotation and an average of 15% of this size fraction is lost to tailings, where it is oxidized, creating acid rock drainage. Copper concentrates containing arsenic at concentrations >2000 ppm cannot be smelted without releasing gaseous arsenic compounds. Common flotation reagents cannot distinguish between arsenic-bearing enargite (Cu₃AsS₄) and chalcopyrite (CuFeS₂). Biotechnology, however, offers a solution to these problems with peptides. Peptides displayed on bacteriophage can be selected for their binding affinity to a specific mineral phase. In this thesis, peptides that bind to chalcopyrite and not to silicate gangue were attached to iron oxide nanoparticles coated with aminopropyl silane via a polyethylene glycol cross-linker. Attachment of the peptides to the nanoparticles was confirmed with FTIR and UV-vis spectroscopy. The nanoparticles were then used to coat and magnetically concentrate chalcopyrite. The nanoparticles preferentially concentrated <38 μm chalcopyrite grains with recoveries near 50%, making them ideally suited to recover the mineral fraction most difficult to float. They were also shown to preferentially coat chalcopyrite over quartz. Concentrates containing 37% chalcopyrite and 13% quartz were collected. Chalcopyrite was concentrated in pure water at pH 7 using non-toxic reagents. Attempts to separate <38 μm enargite and chalcopyrite were met with limited success, though 42% of total copper was recovered from residue otherwise bound for tailings. While this work is still preliminary, these positive results indicate peptide collectors hold great promise. Plans to further explore the potential of peptides are also discussed.

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