Impurity Control in Copper Metallurgical Plants with Special Focus on Arsenic Oct 2018 17,
George P. Demopoulos* Department of Mining and Materials Engineering, McGill University *[email protected] https://www.mcgill.ca/materials/people/faculty/george-p- Seminar Impurity JOGMEC demopoulos P1resented at the Int’l Seminar on Impurities in Copper 1 Raw Materials, Tokyo, Japan, October 2018 Towards Sustainable Metallurgical Processes
• Impurity control- a must in making the Copper metallurgical industry sustainable!
• Development of sustainable processes means Oct Oct 2018 17, innovation
• Meet economic and environmental goals simultaneously
• Innovation needs research collaborations Seminar Impurity JOGMEC
• This series of seminars is an excellent initiative… 2 Sustainability Aspects of Impurity Control Technologies-1 • Consider deportment of impurities throughout the whole process flowsheet for best intervention strategy Oct Oct 2018 17, • Work towards clean impurity-specific separation approaches to minimize valuable metal loss, reagent usage, or intro of new pollutants: SX (residual organics?), IX, Molecular Recognition Technology (MRT), magnetic resins, selective precipitation, Sorption/Adsorption etc. Seminar Impurity JOGMEC
• Equally important to get enrichment-concentration to 3 facilitate economic recovery and/or disposal Sustainability Aspects of Impurity Control Technologies-2
• Consider recovery if there is demand of the
impurity as by-product; Oct 2018 17, Example: Se, Te, Sb, Bi in Cu industry: Can be sold as feedstock for electronic/PV applications
• Disposal: sustainable approach; not only removal
from solution but also economic disposal in Seminar Impurity JOGMEC compact stable matrix (unleachable)!
4 Minor Impurities-Removal • As, Sb, Bi • Cu refineries mostly • Electrolytic stripping • SX for As Oct Oct 2018 17, • IX for Sb and Bi • Se, Te Cu, Zn plants • IBC Bi removal as bisulfate • Oxidation state (VI vs IV) salt (picture above) >200 TPY Bi
• Cementation with Cu or Ag Seminar Impurity JOGMEC • Sulphide precipitation
• Reduction (Se) 5 Impurity control studies at McGill • Arsenic immobilization as scorodite etc (last 25 years) PLUS Oct Oct 2018 17, • Antimony removal from acidic solutions by precipitation as stable ferric antimonate (2012-2015) • Selenium(IV) elimination from acid plant effluents by reduction (2007-2011) • New project on Se(VI) reduction/removal via designing of a photocatalytic-assisted nanocomposite filtration material (2017- ) JOGMEC Impurity Seminar Impurity JOGMEC • Ni recovery from spent Cu electrolyte by solvent displacement crystallization (1998-2003) • Mn removal by SO2/O2-patented process (1998-2001) 6 • Impurity control by cementation in Zn plants (Co, Cd) (1996-2002) Arsenic in the Non-ferrous Industry
It reports in flue dusts, acid bleed streams, various wastes, autoclave discharge solutions, process Oct Oct 2018 17, solutions-effluents/residues and ultimately tailings Safe disposal (residue stability) much more challenging than its removal from plant streams
Leachability/pore water limit: <1 mg/L As JOGMEC Impurity Impurity JOGMEC Seminar
But TCLP-type testing not necessarily the appropriate measure when it comes to long term 7 stability! Hydrometallurgical Arsenic Fixation-which method to use?
Depends on arsenic oxidation state and concentration
• Arsenic retention is favoured when in its V state • Various methods available to oxidise AsIII (not reviewed here; Oct Oct 2018 17, at McGill we have worked with H2O2 and SO2/O2; see new Barrick work with O2/C)
Low concentration (<3 g/L As) sources in plant effluents Ambient T co-precipitation with Fe(III) Arsenic-rich industrial solutions and solid wastes JOGMEC Impurity Impurity JOGMEC Seminar Scorodite (FeAsO4.2H2O)
Other stabilization methods? 8 Arsenic* Fixation Methods: Co-precipitation with Fe(III) Arsenic-laden effluent
CaO Neutralization Fe2(SO4)3 (Fe/As ≥ 3) Oct Oct 2018 17,
Solids S/L Separation
Long-term storage Arsenic-bearing phases: • AsO -FeOOH 4 Seminar Impurity JOGMEC
• CaSO4·2H2O
• FeAsO4·xH20, x = 2-3
Arsenic-bearing solids 9
Picture from http://www.kiggavik.ca/wp-content/uploads/2010/06/McClean_Mine_02.jpg McGill staged Co-precipitation Circuit: 10 yrs research* Oct Oct 2018 17, JOGMEC Impurity Seminar Impurity JOGMEC
10 *See McGill papers in Chemosphere, 151:318-323 (2016) and138 (2015) 239–246; Hydrometallurgy, 151 (2015) 42–50 and 111-112 (2012) 65–72 Arsenic Fixation Methods Arsenic sulphide precipitation from solution
It can work as bulk As removal method with further treatment, but not as direct viable disposal option Oct 2018 17, Precipitate rather poorly crystalline and difficult to separate; difficult to handle reagent Not satisfactory for disposal! JOGMEC Impurity Impurity JOGMEC Seminar But As-S from pyrometallurgical processing/inert roasting and subsequent melting (@250○C) is reported by JX Nippon MM to be stable (TCLP < 0.2 ppm As)* 11 *Akira Yoshimura, presentation at CESCO Impurity Seminar, April 2017 in Santiago, Chile Arsenic Fixation Methods
Production of scorodite (FeAsO4.2H2O) • Production in autoclaves (i.e. 140°C • McGill research led to the development of The Atmospheric Process; this became a commercial reality in Chile in 2012 by Oct 2018 17, ECOMETALES A variation of atmospheric precipitation based on oxidation forms the basis of the Dowa Metal Scorodite Process (High As solution) and Bioscorodite Process (Dilute As solution) JOGMEC Impurity Impurity JOGMEC Seminar Also it can be produced by conversion of amFA to scorodite* the Outotec Scorodite Process #M.A. Gomez, G.P. Demopoulos, 2011, Hydrometallurgy, 107, 74–90. 12 *J.F. Le Berre, R. Gauvin and G.P. Demopoulos, 2008, Colloids and Surfaces A,, 315, 117–129. Scorodite Production - The Atmospheric Process Supersaturation- controlled process concept* Work within Oct 2018 17, “heterogeneous” zone Self-seeded in continuous reactors “Self-corrected” in case of pH overshooting JOGMEC Impurity Seminar Impurity JOGMEC *Demopoulos, Hydrometallurgy 96 (2009) 199–214 13 Laboratory Crystallization 2H3AsO4 + Fe2(SO4)3 + 4H2O 2FeAsO4·2H2O + Oct Oct 2018 17, 3H2SO4 JOGMEC Impurity Seminar Impurity JOGMEC NEW-GEN SCORODITE* 14 FREE of GYPSUM! *Patent application pending Atmospheric Precipitation of Scorodite Well grown solids (20-30 μm) Excellent S/L separation & washing characteristics Oct 2018 17, JOGMEC Impurity Seminar Impurity JOGMEC 15 Atmospheric Scorodite Process Flowsheet* (implemented by Ecometales in Chile) Arsenic Sludge CaCO3 Weak Acid CaCO3 CaO Fume Oct 2018 17, Dust Recovery S L L of Metal L Iron Source S S Value As O 2 3 Recycle of Seed Dissolution Polishing and As(III) Atmospheric Scorodite Seminar Impurity JOGMEC (Fe(II)) SO /O Precipitation Oxidation 2 2 *Demopoulos et al., paper in Copper 2003 16 Copper Arsenic-Free Leach Scorodite Cathode Solution Residue Gypsum (As < 0.1 mg/L) (optional) to disposal Arsenic stabilization via Scorodite Production in CHILE! • The atmospheric scorodite process became an industrial reality after 20 yrs research in 2012! • ECOMETALES – a subsidiary of Codelco – operates a 5,000 TPY As fixation plant in Northern Chile Oct 2018 17, JOGMEC Impurity Seminar Impurity JOGMEC Ecometales Product: scorodite (1/3)/gypsum (2/3) mixture* 17 *F. Lagno, G. P. Demopoulos, et al., paper presented at the HYDROCOPPER 2009 Dowa presentation. as fixed The process was tested at a demonstration plant (30 t/month of of t/month (30 plant As ademonstration at tested was process The Dowa Dowa scorodite Scorodite ) in Dowa’s copper smelter site in site Dowa’s in ) smelter copper * Kubo et al, paper in Proceedings of Copper 2010, 2010, Copper of Proceedings inpaper etKubo al, Process* Kosaka -- refer to to refer Vol 7- 2. 18 JOGMEC Impurity Seminar Oct 17, 2018 Scorodite Stability Scorodite solubility data as a f(pH) Scorodite passes EPA’s new TCLP test limit of 1 mg/L As involving testing @ pH 5 for Oct 2018 17, 20 hr What about its long term dissolution kinetics over a wider range of pH and ORP? JOGMEC Impurity Seminar Impurity JOGMEC Note that not all scorodites are equal! Figure from Bluteau & Demopoulos, 2219 Hydrometallurgy, 2007. As release from atmospheric scorodite as a function of redox potential* • pH 7 CaO and gypsum saturated • Significant release when Eh< 150mV 7 70 Oct Oct 2018 17, 6 100 mV 60 5 50 250 mV 4 400 mV 40 DI Water 3 30 As Concentration (mg/L) 2 20 JOGMEC Impurity Seminar Impurity JOGMEC As Concentration for Eh = 100 mV(mg/L) 1 10 0 0 0 7 14 21 28 35 42 49 56 63 70 77 84 20 Days *Cesar Verdugo, Gustavo Lagos, Levente Becze, Mario Gómez and George Demopoulos, Submitted to Hydrometallurgy Development of scorodite encapsulation technology-the next generation! • Scorodite’s stability is a function of pH; • Scorodite unstable under reducing conditions; • Enhance its stability by encapsulation with inert materials; Oct 2018 17, • Stabilization/solidification (S/S) of mineral-derived arsenical residues (including scorodite) using cement as in “Jarofix”) not appropriate JOGMEC Impurity Impurity JOGMEC Seminar PERFECT FOR INTEGRATION WITH OUR NEW GYPSUM-FREE SCORODITE PROCESS! 21 Stabilization technology based on encapsulation* Encapsulation materials Encapsulation Scorodite Matrix Substrate • Metal phosphates (AlPO4·1.5H2O, and Ca5(PO4)3OH,F) • Aluminum hydroxyl gels Oct 2018 17, Aluminum hydroxyl gels Aluminum Aluminum Salt hydroxyl Solution Base gels Seminar Impurity JOGMEC *Fuqiang Guo and G.P. Demopoulos, 2018, Development of 22 an Encapsulation Process for Scorodite, in Extraction 2018, TMS, 1411-1420. Stabilizing scorodite by mineral coating! pH Eh Al-gel pH Eh pH pH Eh Oct Oct 2018 17, Naked scorodite Blending Ageing Mineralization JOGMEC Impurity Seminar Impurity JOGMEC After After Mineralized Scorodite GEL 23 blending ageing AlOOH coated SCORO • Enhanced stability! • Mineralized coatings: Gibbsite, bayerite, and boehmite Anoxic condition Oct Oct 2018 17, Oxic condition Before aging 167 days at 22 °C JOGMEC Impurity Seminar Impurity JOGMEC STABILITY OF GEL MINERALIZED SCORODITE: 33 times reduced As release! 24 Process flow diagram for industrial application Atmospheric production of crystalline scorodite Oct Oct 2018 17, Preparation of amorphous aluminum hydroxyl gel JOGMEC Impurity Seminar Impurity JOGMEC 25 Final words Process selection and design is linked to stability Pay equal attention to method of removal and Oct 2018 17, disposal Encapsulation is expected to provide an additional layer of protection-stability to disposed hazardous impurity compounds Impurity JOGMEC Seminar Intensify efforts for recovery of impurities that can be sold to other industries (re. Bi, Se, Te etc.) 26 Acknowledgments • All past and current graduate students and postdocs whose work was highlighted here • NSERC: The Canadian Research Funding Agency • The many companies over the years that supported our Oct 2018 17, research • JOGMEC for the invitation! • Special thank you to Professor Nakamura of Tohoku University! JOGMEC Impurity Seminar Impurity JOGMEC THANK YOU! 27 Atmospheric scorodite stability- recent data • Scorodite produced at 85°C from 40 g/L As(V) solution • pH adjusted at 9 with 0.5 M Ca(OH)2 (avoid NaOH!) • ORP adjusted (anoxic70mV vs. SHE or -150mV ORP) with 0.125 M Na2S Oct 2018 17, Scorodite naked Exp. 14: Scorodite naked Anox 12 11 350 10 10 250 9 ORP initial 8 150 Oxic 8 ORP after pH 6 7 50 Anox pH ORP adjusted 6 4 -50 ORP (mV) As Conc (mg/L) 5 pH initial 2 -150 Seminar Impurity JOGMEC 4 pH adjusted 0 3 -250 0 50 100 150 200 250 0 50 100 150 200 250 Time (days) Time (days) Better stability than even that of hydrothermal scorodite (10 28 vs. 100 ppm As release)!