Improving Copper Recovery from Production Slags by

EMC 2011, June 2011 Düsseldorf

Improving Copper Recovery from Production Slags by Advanced Stirring Methods M. Zander , B. Friedrich J. Schmidl, M. Hoppe J. Kleinschmidt, R. Degel IME Process Metallurgy and Metal Recycling RWTH Aachen Prof. Dr.-Ing. Bernd Friedrich

Table of Contents  Slag cleaning as an established step in modern pyrometallurgical copper processes  Lab-scale experiments using different stirring modes

 Technology of and trial campaigns in a technical and demonstrational-scale slag cleaning stirring reactor

Anode (+)

Off gas

Slag Coke

Slag Slag

Matte

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(–) Cathode Recycling

Source: SMS Siemag

The Pyrometallurgical Copper Process Route Dried Concentrate (25-35 % Cu) Fluxes Air/O2

Matte smelting Copper Matte (60-70 % Cu)

Slag (~ 1-8 % Cu) Slag cleaning Valuable Metals

Converting

Blister Copper (98-99 % Cu)

Slag (0.8-1.3 % Cu) Intensive slag cleaning

Saleable Slag

Focus of Investigations

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Electrolytic refining

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Design of a Submerged Arc Furnace (SAF)

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Source: SMS Siemag Recycling

Basic of Inclusion´s Settling – Stoke´s Equation

u

d  g  ( p  ) 2 p

18

Source: Kumar, N., 2008: Comprehensive physics XI, ISBN: 8131801969 pp. 1043.

u dp g p  

relative velocity of the particle in the fluid media m/s particle size in mm gravitation in m/s2 density droplets in kg/m3 density slag kg/m3 viscosity of the fluid Ns/m2



Crucial parameter is the viscosity (strong temperature dependence)



Inclusion size and level of melt bath influence the settling of inclusions

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Source: SMS Siemag

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wt [%]

FexOy

40-43

SiO2

31-33

Al2O3

2.5

CaO

3-5

Zn

1.5

Cu

0.8

Pb

0.3

Mo

0.3

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ch n ik

Element/ Compound

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Characterisation of Treated Fayalite Slag

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Primarily, copper inclusions are chemical bonds with sulfur

Motivation: Why is Slag Cleaning a Growing Concern ? Background:  The metal contents are decreasing in the available ore deposits

 Increasing demand for copper – focus on improving process efficiency  Decreasing the heavy metal content in slags generates a high quality mineral product Source: Aurubis AG

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Intensive slag cleaning leads to economic and ecological benefits

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Source: Peute Baustoff AG

Concept of First Lab-Scale Experiments at the IME Goal: Get a first impression of the influence of bath movement on the copper inclusion settling Concept: Testing different stirring modes by using different types of lab-scale furnaces Submerged arc furnace

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1) high temperature moderate stirring Recycling

Induction furnace with purging gas

2) marginal and intensive stirring

Resistance heated furnace

3) no slag stirring

Measurement of the Slag Cleaning Rate (Pb and Cu) Sampling of the slag after each trial solidified melt

Derivation of the cleaning degree A Me 

m Slag, Me,P mSlag, Me,R

* 1 00

AMe, cleaning  1  AMe

top layer 40 wt.-%

middle layer 35 wt.-%

cuts

bottom layer 25 wt.-%

where: AMe = percentage metal yield, mSlag,Me = mass of each metal in slag phase, index R = Reactant; index P = Product, AMe,cleaning = Percentage of metal in treated slag compared to the metal content in the feed slag.

Content of the feedstock Cu: 0.68 wt.-% Pb: 0.21 wt.-%

 By each stirring mode all experiments are carried out with and without the addition 5 wt.-% of the reducing agent CaC2.  Each trial is repeated once ch n ik ss te P ro ze

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The following results are all average values Recycling

First Trials: Experiments in Lab-Scale SAF Parameters  Feedstock: 2 kg / Holding time: 20 min  Temperature: ~1500 °C – 1600 °C  Slag has to be casted after the trials Observations  Bath movement by arc displacement and thermal convection  Visible evaporation Results Cu-content in slag feedstock

Cu [wt. %]

Pb [wt. %]

Mo [wt. %]

Ni [ppm]

0.68

0.21

0.19

340

54 %

94.5 %

86 %

83.5 %

With adding 5 % of CaC2

52 %

96.5 %

92.5 %

92 %

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ch n ik

Without additives

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Degree of slag cleaning (top and middle layer)

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Trials Using Different Stirring Conditions Parameters of the trials under no, marginal and intensive melt bath stirring:

Induction furnace

 Holding temperature: 1300 °C  Feedstock: 1 kg slag + 20 g coal top-layer  Holding time at 1300°C: 60 min

Source: INDUGA GmbH & Co. KG, Köln

Additional purging gas treatment  Heating rate: approx. 400 °C/h

Inert gas Lance

 Crucible is cooled down under atmosphere (no casting)

Slag

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Crucible

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Melt flow Gas bubbles

Results of Induction Furnace Trials  Higher cleaning rate by using CaC2  No significant improvement on Cu cleaning by using intensive stirring conditions (induction furnace + purging gas)

Degree of Cu, Pb cleaning in the top and middle layer

CaC2

60% 50%

2

40% 30% 20% Without PG, Additive

10% 0%

CaC2PG

PG: Purging Gas

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 Improved Pb cleaning by using purging gas

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Cu PG: Purging Gas PG

Pb

Results of Experiments without Stirring Conditions Assumption Bath stirring due to convection is negligible

cold (atmosphere)

hot (liquid slag)

Results w/o stirring Cu-content in slag feedstock

Cu [wt. %]

Pb [wt. %]

Mo [wt. %]

0.68

0.21

0.19

28 %

no significant influence

9%

With adding 5 % of CaC2

27 %

no significant influence

13 %

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Without additives

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Degree of slag cleaning after the trials:

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Conclusion of the Results

2

marginal and intensive (PG) stirring

2

no stirring

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Significant slag cleaning degree in all trials Recycling

2

high temperature marginal stirring

Conclusion of the Results

2

marginal and intensive (PG) stirring

2

no stirring

2

high temperature marginal stirring

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By heating up the slag to a level of > 1500 °C with moderate stirring, maximum decrease of the copper content of 50 % was achieved in SAF trials. Strong temperature influence on the viscosity. Recycling

Conclusion of the Results

2

marginal and intensive (PG) stirring

2

no stirring

2

high temperature marginal stirring

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No improved copper cleaning with marginal stirring compared to the trials without bath movement Recycling

Conclusion of the Results

2

marginal and intensive (PG) stirring

2

no stirring

2

high temperature marginal stirring

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Strong turbulence leads to no significant influence on the Cu cleaning rate. flushing gas inhibits the settling of the copper particle in the molten slag. Recycling

Conclusion of the Results

22

marginal and intensive (PG) stirring

22

no stirring

22

high temperature marginal stirring

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Stirring of the melt improved the influence of the CaC2 on the cleaning degree. Recycling

Slag Cleaning Stirring Reactor  Slag cleaning as an established step in modern pyrometallurgical copper processes  Lab-scale experiments under different stirring modes  Technology of and trial campaigns in the technical and demonstrational-scale slag cleaning stirring reactor

Anode (+)

Off gas

Motivation: Preliminary Results:(*)  The DC magnetic field

improves the copper yield Coke

Slag Slag

(–) Cathode Source: SMS Siemag

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Matte

 First trials reduced the copper content in the slag from 4.4 wt.-% to 1.0 wt.-%

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(*)Source: Warzok, A., Degel, R. et al.: Latest Results of the Intensive Slag Cleaning Reactor for Metal Recovery on the Basis of Copper, Proceedings of the Copper 2010

Principle of Electrodynamic Slag Cleaning Principles of the stirring reactor: (*)  Stirring due to electromagnet  Reduction on the reducing surface  Cathodic and anodic reactions due to DC operation forced migration of metal/matte droplets under electric field leads to coalescence, coalescence leads to a settling

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Stirring enhances reduction and coalescence

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Settling of inclusions after coalescence

(*)Source: Warzok, A., Degel, R. et al.: Latest Results of the Intensive Slag Cleaning Reactor for Metal Recovery on the Basis of Copper, Proceedings of the Copper 2010

The Aurubis Demonstrational-Scale Stirring Reactor  Slag is tapped from the SAF into a ladle and transported by a forklift  Cleaned slag flows via an overflow into a ladle and is allowed to cool down.

 In the field of the first electrode, the magnetic field is applied into the slag.

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 First continuous campaigns in the demoscale stirring reactor in Hamburg with a mass flow of 4 t/h

Source: SMS Siemag

Source: Aurubis

New 1 MW SAF at IME Recycling Research Center (IRRC)

 AC (3- phase) and DC current mode possible  Melt volume 1.5 m³, outer height 3.2 m, hearth diameter 1.6 m ch n ik ss te P ro ze

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 More than 200 sensors and actuators Recycling

The IME technical-scale stirring reactor  Melt volume ~ 300 liter

 Using 1 DC electrode  Slag is charged by a ladle  Cleaned slag is taken out by an overflow

 Settled copper matte is taken out by a metal tap

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 Flexible magnet and electrode position

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Slag cleaning in the IME Research recycling centre (IRRC)

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Slag cleaning in the IME Research Recycling Centre (IRRC)

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Start-up of the IME electric smelter (Vmelt: 1500 l) in combination with a technical scale stirring reactor is expected in the end of 2011

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Outlook – Next Project Steps  Investigating the influence of different magnetic field strengths on the inclusion settling behaviour in the Aurubis Hamburg demo-scale stirring reactor  Start-Up of the IME electric smelter and the technical-scale stirring reactor  Construction of a water fluid model of the technical-scale stirring reactor  Lab-scale experiments with the aim to describe and understand the reactions of additives

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 Transferring the results to other production slag systems (Pb, Ni, Co, PGM)

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EMC 2011, June, Düsseldorf

Thank you very much for your attention Thanks especially to BMBF for financing the „Copper-Slag“ Project

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(BMBF 033R006)

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Principle of Electrodynamic Slag Cleaning (1) Situation: Small copper (matte) inclusions can not be separated physically – Stokes equation - Too small Aim:

Increase of copper recovery by intensified slag cleaning

Equipment: DC electric furnace with superimposed magnetic field, optional: reducing agents

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Parameters: Using different degrees of electric power, magnetic field strength, retention time of the slag in the „mixer“

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(*)Source: Warzok, A., Degel, R. et al., 2010: Latest Results of the Intensive Slag Cleaning Reactor for Metal Recovery on the Basis of Copper, Proceedings of the Copper 2010, pp. 1213-1231 and Warzok, A., Riveros, G., 2007: Slag reducing and cleaning with calcium carbide, Cu 2007 – Volume 3 (Book 2), The Carlos Díaz Symposium on Pyrometallurgy, Toronto, Canada, pp. 379-390.

Principle of Electrodynamic Slag Cleaning (2) Situation Small copper (matte) inclusions can not be separated physically – Stokes equation - Too small

Principles of the stirring reactor (*)  Stirring due to electromagnete  Reduction on the reducing surface  Cathodic and anodic reactions due to DC operation

Forced migation of metal/matte droplets under electric field leads to coalescence, coalescence leads to a settling

First Results(*)  The DC magnetic field improves the copper yield

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 First trials reduced the copper content in the slag from 4,4% to 1,0% Recycling

(*)Source: Warzok, A., Degel, R. et al., 2010: Latest Results of the Intensive Slag Cleaning Reactor for Metal Recovery on the Basis of Copper, Proceedings of the Copper 2010, pp. 1213-1231 and Warzok, A., Riveros, G., 2007: Slag reducing and cleaning with calcium carbide, Cu 2007 – Volume 3 (Book 2), The Carlos Díaz Symposium on Pyrometallurgy, Toronto, Canada, pp. 379-390.

2. Summary of the IME lab-scale trials  Significant degree of slag cleaning in all trials  By heating up the slag to a level of > 1500 °C with moderate stirring, maximum decrease of the copper content of 50 % was achieved in SAF trials. Strong temperature influence on the viscosity  No significant differences in the degree of cleaning by the trials with no bath movement compared to the trials with a marginal bath movement were observed.  Strong turbulence leads to no significant cleaning rate. Flushing gas inhibits the settling of the copper particle in

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the molten slag Recycling