Impurity Control in Copper Metallurgical Plants with Special Focus on Arsenic

George P. Demopoulos*Department of Mining and Materials Engineering, McGill University*george.demopoulos@mcgill.cahttps://www.mcgill.ca/materials/people/faculty/george-p-demopoulos

P1resented at the Int’l Seminar on Impurities in Copper Raw Materials, Tokyo, Japan, October 2018

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Towards Sustainable Metallurgical Processes

• Impurity control- a must in making the Copper metallurgical industry sustainable!

• Development of sustainable processes means innovation

• Meet economic and environmental goals simultaneously

• Innovation needs research collaborations

• This series of seminars is an excellent initiative…

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Sustainability Aspects of Impurity Control Technologies-1

• Consider deportment of impurities throughout the whole process flowsheet for best intervention strategy

• 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.

• Equally important to get enrichment-concentration to facilitate economic recovery and/or disposal

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Sustainability Aspects of Impurity Control Technologies-2• Consider recovery if there is demand of the

impurity as by-product; 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 compact stable matrix (unleachable)!

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Minor Impurities-Removal• As, Sb, Bi

• Cu refineries mostly• Electrolytic stripping• SX for As• IX for Sb and Bi

• Se, Te• Cu, Zn plants

• Oxidation state (VI vs IV)• Cementation with Cu or Ag• Sulphide precipitation• Reduction (Se)

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IBC Bi removal as bisulfate salt (picture above)>200 TPY Bi

Impurity control studies at McGill• Arsenic immobilization as scorodite etc (last 25

years) PLUS

• 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- )

• Ni recovery from spent Cu electrolyte by solvent displacement crystallization (1998-2003)

• Mn removal by SO2/O2-patented process (1998-2001)• Impurity control by cementation in Zn plants (Co, Cd) (1996-2002)

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Arsenic in the Non-ferrousIndustry

It reports in flue dusts, acid bleed streams, various wastes, autoclave discharge solutions, process solutions-effluents/residues and ultimately tailingsSafe disposal (residue stability) much more

challenging than its removal from plant streams

Leachability/pore water limit: <1 mg/L As

But TCLP-type testing not necessarily the appropriate measure when it comes to long term stability!

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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;

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

Scorodite (FeAsO4.2H2O)

Other stabilization methods?

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Neutralization

Long-term storage

SolidsS/L Separation

Arsenic-laden effluent

Arsenic-bearing solids

CaO Fe2(SO4)3

Picture from http://www.kiggavik.ca/wp-content/uploads/2010/06/McClean_Mine_02.jpg

(Fe/As ≥ 3)

Arsenic-bearing phases:• AsO4-FeOOH• CaSO4·2H2O• FeAsO4·xH20, x = 2-3

Arsenic Fixation Methods: Co-precipitation with Fe(III)*

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McGill staged Co-precipitation Circuit: 10 yrsresearch*

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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 Precipitate rather poorly crystalline and difficult to

separate; difficult to handle reagentNot satisfactory for disposal!

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)*

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*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 <T<180°C)#

• McGill research led to the development of The Atmospheric Process; this became a commercial reality in Chile in 2012 by 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)

Also it can be produced by conversion of amFA to scorodite* the Outotec Scorodite Process

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12*J.F. Le Berre, R. Gauvin and G.P. Demopoulos, 2008, Colloids andSurfaces A,, 315, 117–129.

#M.A. Gomez, G.P. Demopoulos, 2011, Hydrometallurgy, 107, 74–90.

Scorodite Production - The Atmospheric Process

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8 Supersaturation-controlled process concept*

Work within “heterogeneous” zone

Self-seeded in continuous reactors

“Self-corrected” in case of pH overshooting

*Demopoulos, Hydrometallurgy 96 (2009) 199–214

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Laboratory Crystallization

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82H3AsO4 + Fe2(SO4)3 + 4H2O 2FeAsO4·2H2O + 3H2SO4

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NEW-GEN SCORODITE*FREE of GYPSUM! 14

*Patent application pending

Atmospheric Precipitation of Scorodite

Well grown solids (20-30 μm)Excellent S/L separation & washing

characteristics Oct

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Polishing

Arsenic Sludge

CaO

Arsenic-FreeSolution(As < 0.1 mg/L)

SL

Atmospheric Scorodite Process Flowsheet*(implemented by Ecometales in Chile)

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As2O3

Dissolution and As(III)(Fe(II))Oxidation

FumeDust

Weak Acid

Iron Source

SO2/O2

CaCO3

CaCO3

Atmospheric ScoroditePrecipitation

ScoroditeGypsumto disposal

Recycle of Seed

LS

Leach Residue (optional)

LS

Recovery of Metal Value

CopperCathode

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*Demopoulos et al., paper in Copper 2003 16

Arsenic stabilization via ScoroditeProduction 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

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Ecometales Product: scorodite(1/3)/gypsum (2/3) mixture*

*F. Lagno, G. P. Demopoulos, et al., paper presented at the HYDROCOPPER 2009

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*Kubo et al, paper in Proceedings of Copper 2010, Vol 7-2.

Dowa Scorodite Process*

18The process was tested at a demonstration plant (30 t/month of As fixed as scorodite) in Dowa’s copper smelter site in Kosaka--refer to Dowa presentation.

Scorodite Stability

Scorodite passes EPA’s new TCLP test limit of 1 mg/L As involving testing @ pH 5 for

20 hr

What about its long term dissolution kinetics over a

wider range of pH and ORP?

Note that not all scorodites are equal!

Figure from Bluteau & Demopoulos, Hydrometallurgy, 2007.

Scorodite solubility data as a f(pH)

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0 7 14 21 28 35 42 49 56 63 70 77 84

As C

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250 mV

400 mV

DI Water

As release from atmospheric scorodite as a function of redox potential*

• pH 7 CaO and gypsum saturated• Significant release when Eh< 150mV

*Cesar Verdugo, Gustavo Lagos, Levente Becze, Mario Gómez and George Demopoulos, Submitted to Hydrometallurgy

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Development of scorodite encapsulation technology-the next generation!

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• Scorodite’s stability is a function of pH;• Scorodite unstable under reducing conditions;• Enhance its stability by encapsulation with inert

materials;• Stabilization/solidification (S/S) of mineral-derived

arsenical residues (including scorodite) using cement as in “Jarofix”) not appropriate

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PERFECT FOR INTEGRATION WITH OUR NEW GYPSUM-FREE SCORODITE PROCESS! 21

• Metal phosphates (AlPO4·1.5H2O, and Ca5(PO4)3OH,F)• Aluminum hydroxyl gels

ScoroditeSubstrate

Encapsulation Matrix

Encapsulation materials

Stabilization technology based on encapsulation*

Aluminum Salt

Solution Base

Aluminum hydroxyl

gels

Aluminum hydroxyl gels

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22*Fuqiang Guo and G.P. Demopoulos, 2018, Development of an Encapsulation Process for Scorodite, in Extraction 2018, TMS, 1411-1420.

Naked scorodite Blending Ageing Mineralization

Al-gelpH Eh

pH Eh

pH E

h

Stabilizing scorodite by mineral coating!

After blending

After ageingScorodite GEL Mineralized

AlOOH coated SCORO

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• Enhanced stability!• Mineralized coatings: Gibbsite, bayerite,

and boehmite

Oxic condition

Anoxic condition

Before aging

STABILITY OF GEL MINERALIZED SCORODITE: 33 times reduced As release!

167 days at 22 °C

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Process flow diagram for industrial application

Atmospheric production of crystalline scorodite

Preparation of amorphous aluminum hydroxyl gel

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Final words

Process selection and design is linked to stability

Pay equal attention to method of removal and disposal

Encapsulation is expected to provide an additional layer of protection-stability to disposed hazardous impurity compounds

Intensify efforts for recovery of impurities that can be sold to other industries (re. Bi, Se, Te etc.)

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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

research • JOGMEC for the invitation!• Special thank you to Professor Nakamura of Tohoku

University!

THANK YOU!

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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

Better stability than even that of hydrothermal scorodite (10 vs. 100 ppm As release)!

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0 50 100 150 200 2500

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Time (days)

As C

onc

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Scorodite naked

Oxic

Anox

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Time (days)

OR

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Exp. 14: Scorodite naked Anox

ORP initial

ORP after pH

ORP adjusted

pH initial

pH adjusted

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