Download to read offline
More Related Content
Similar to Management of Minor Elements
Management of Minor Elements
- 1. Management of MinorManagementof Minor Elements in theElements in the Production of Base MetalsProduction of Base Metals Sharif Jahanshahi, Warren Bruckard, Chunlin Chen and Frank Jorgensen Mission: To progressively eliminate waste and emissions in the minerals cycle, while enhancing business performance and meeting community expectations
- 2. Presentation by SharifJahanshahi PhD, FAusIMM Sharif Jahanshahi has over 30 years experience in R&D across; high temperature processing of ferrous and base metals, thermodynamics and kinetics of high temperature systems, melt chemistry, process modelling, simulation and development Currently consulting for leading global players in the metallurgical industry through Meta-Logical Solutions Pty Ltd. Website: http://www.metalogical.solutions Email: sharif@metalogical.solutions
- 3. Green Processing 2006:5-6 June 3 BackgroundBackground Australia exports ~ 3 millions of tpa of copper, nickel, lead and zinc in form of concentrate and refined metals. Base metal ores contain low levels (1- 104 ppm) of toxic/ hazardous elements (As, Sb, Bi, Cd, Hg, Se, Te…, Th, U) Clean, coarsely-grained ore bodies becoming depleted Ore bodies of future becoming more complex, finer-grained and containing higher amount of minor/toxic elements. Worldwide industry mines and process 100s million tonnes of base metal ores each year Accumulated mass of minor elements in biosphere is large and could have a significant environmental impact
- 4. Green Processing 2006:5-6 June 4 Industry ContextIndustry Context Minor elements present technical and environmental problems as well as being costly Smelters impose treatment charges and penalty payment on minor elements in concentrates Governments becoming increasingly sensitive to emissions Community pressure for more sustainable processing Smelters setting tighter penalty specifications for minor elements Imperative to develop alternative treatments for selective removal of toxic elements at the mine site before despatch of concentrate to smelters
- 5. Green Processing 2006:5-6 June 5 Options for Dealing with ToxicOptions for Dealing with Toxic Elements in OresElements in Ores Primarily determined by mineralogy and grain size Occurrence - association with other elements Distribution between phases For widely and uniformly dispersed minor elements in mineral phases treatment option is limited Separation and removal in waste/residue streams produced in metal extraction If concentrated in discrete phases, options exists for early removal by physical and chemical means Having separated and concentrated the toxic elements, consideration has to be given to their use or safe disposal
- 6. Green Processing 2006:5-6 June 6 ArsenicArsenic Is one impurity element found in most base metal ores and concentrates Lowers metal quality, if not removed from product metal Contributes to health concerns during metallurgical processing Causes environmental concerns during disposal of tailings and wastes High arsenic levels in an ore can make the deposit economically unviable Blending of high and low arsenic concentrates has been practiced by industry. Can we continue this in the future?
- 7. Green Processing 2006:5-6 June 7 Mineralogy ConsiderationMineralogy Consideration In copper ores arsenic occurs as Enargite (Cu3AsS4) Tennanite (3Cu2S.As2S3) Arsenopyrite (FeAsS) Cobaltite (CoAsS) In nickel systems Gersdorffite (NiAsS) Niccolite (NiAs) Arsenopyrite (FeAsS) Cobaltite (CoAsS) Physical separation of arsenic bearing minerals from non- arsenic bearing minerals is difficult Similar specific gravity, non-magnetic, strongly floatable with conventional collectors etc. Some As minerals contain high concentration of copper and nickel e.g. enargite (Cu3AsS4) has 48% Cu
- 8. Green Processing 2006:5-6 June 8 Mineral Recovery in 1 minuteMineral Recovery in 1 minute 0 10 20 30 40 50 60 70 80 90 100 -500 -400 -300 -200 -100 0 100 200 300 400 500 Pulp potential (mV vs SHE) Mineralrecoveryat1min(%) Enargite (pH 8) Chalcopyrite (pH 8) 0 10 20 30 40 50 60 70 80 90 100 -500 -400 -300 -200 -100 0 100 200 300 400 500 Pulp potential (mV vs SHE) Mineralrecoveryat1min(%) Enargite (pH 8) Chalcopyrite (pH 8) Senior et al J. Min Eng. Int, In press
- 9. Green Processing 2006:5-6 June 9 Selective RoastingSelective Roasting Roasting has been used to remove arsenic from ores and concentrates A number of treatment options have been developed and reviewed in literature Operating windows for selective removal of arsenic from copper concentrates identified through thermodynamic modelling
- 10. Green Processing 2006:5-6 June 10 Effect of Roasting TemperatureEffect of Roasting Temperature 100 80 60 40 20 0 500 600 700 800 900 Temp. (°C) RemovalofArsenic(%) 0.055%As 0.54%As 5.3%As O2:Chalcopyrite = 2 CuFeS2:FeS2: FeS ~ 10:1.7:1 58% desulfurisation 100 80 60 40 20 0 500 600 700 800 900 Temp. (°C) RemovalofArsenic(%) 0.055%As 0.54%As 5.3%As O2:Chalcopyrite = 2 CuFeS2:FeS2: FeS ~ 10:1.7:1 58% desulfurisation Nakazawa, Yazawa & Jorgensen Met Trans 30B, 1999
- 11. Green Processing 2006:5-6 June 11 Effect of Oxygen Supply at 700 CEffect of Oxygen Supply at 700 C 100 80 40 60 20 0 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 O2 : chalcopyrite (mol:mol) RemovalofArsenic(%) 5.3% As 0.54% As 0.055% As 700 ° C FeAsO4 100 80 40 60 20 0 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 O2 : chalcopyrite (mol:mol) RemovalofArsenic(%) 5.3% As 0.54% As 0.055% As 700 ° C FeAsO4 Nakazawa, Yazawa & Jorgensen Met Trans 30B, 1999
- 12. Green Processing 2006:5-6 June 12 Effect of Oxygen Supply at 900 CEffect of Oxygen Supply at 900 C 100 80 40 60 20 0 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 O2 : chalcopyrite (mol:mol) RemovalofArsenic(%) 5.3% As 0.54% 0.055% 900 °C 100 80 40 60 20 0 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 O2 : chalcopyrite (mol:mol) RemovalofArsenic(%) 5.3% As 0.54% 0.055% 900 °C Nakazawa, Yazawa & Jorgensen Met Trans 30B, 1999
- 13. Green Processing 2006:5-6 June 13 Arsenic Removal from CopperArsenic Removal from Copper Concentrate during RoastingConcentrate during Roasting Smelter Roaster* Temp. (°C) Arsenic in feed (wt %) Arsenic removal (%) Sulphur removal (%) US EPA MH 540 0.2 27 - US EPA FB 540 to 620 0.02 15 - El Indio MH 720 max. 6.4 >90 56 Saganoseki FB 685 to 705 5 to 6 85 to 90 60 to 70 Lepanto FB 700 1.3 82 60 Oroya MH 700 2.6 76 53 Boliden FB 700 to 720 2 92 56 *MH = multi-hearth and FB = fluidized bed
- 14. Green Processing 2006:5-6 June 14 Distribution of As, Bi, Pb duringDistribution of As, Bi, Pb during SmeltingSmelting 40 45 50 55 60 0 25 50 75 100 T=1573 K PSO2 =0.1 atm Iron silicate slag bBi Gas Matte 40 45 50 55 60 0 25 50 75 100 T=1573 K PSO2 =0.1 atm Calcium ferrite slag T=1573 K PSO2 =0.1 atm Calcium ferrite slag eBi Gas Matte wt% Cu in matte 40 45 50 55 60 0 25 50 75 100 T=1573 K PSO2 =0.1 atm Iron silicate slag aAs Slag Gas Matte Distribution(%) 40 45 50 55 60 0 25 50 75 100 T=1573 K PSO2 =0.1 atm Calcium ferrite slag d Matte As Slag Gas Distribution(%) wt% Cu in matte 40 45 50 55 60 0 25 50 75 100 cT=1573 K PSO2 =0.1 atm Iron silicate slag Pb Gas Matte 40 45 50 55 60 0 20 40 60 80 100 fPb Gas Matte wt% Cu in matte Chen et al Sohn Intl Symp , 2006
- 15. Green Processing 2006:5-6 June 15 Simulated FlowsheetSimulated Flowsheet Converting 1st & 2nd Stages Smelting Fire-refining 1st & 2nd Stages Copper Conc Slag Slag Matte Blister Copper Anode Copper Gas Gas Gas Air + Flux Air + Flux Air/Methane
- 16. Green Processing 2006:5-6 June 16 Arsenic DistributionArsenic Distribution -- From Concentrate to Anode CopperFrom Concentrate to Anode Copper 0 25 50 75 100 Smelting Convert 1 Convert 2 Fire-ref 1 Fire-ref 2 Processing Step ArsenicDistribution(%) Gas Slag Matte/ Copper 0.1 wt% As in Conc Iron silicate slag
- 17. Green Processing 2006:5-6 June 17 Arsenic DeportmentArsenic Deportment - From Concentrate to Anode Copper- From Concentrate to Anode Copper 0 25 50 75 100 Smelting Convert 1 Convert 2 Fire-ref 1 Fire-ref 2 Processing Step ArsenicDeportment(wt%) Gas Slag Matte/Copper 0.1 wt % As in Conc Iron silicate slag
- 18. Green Processing 2006:5-6 June 18 Copper Production from SulfideCopper Production from Sulfide OresOres Ore Tailing Dam Anode Slimes Smelting Air, Flux, Coal Air, Flux Acid Plant Concentrate Matte Blister Anode Copperr Copper 99.99% Anode Slimes Air, Natural Gas Air, Flux Slag SlagSlagSlag Acid Dore Metal (Ag- Au) Tailings Gypsum Tailing Dam Tailing Dam Flotation Smelting 2-stage Converting Fire-refining Electro- refining
- 19. Green Processing 2006:5-6 June 19 Safe Disposal of Toxic ElementsSafe Disposal of Toxic Elements Production of arsenic and other toxic elements is well in excess of market demand Typically concentrated in form of fumes, dross, precipitates and slags Disposal of surplus in a safe and environmentally acceptable manner Thus conversion to a less hazardous form and longer term solutions are required conversion into calcium arsenate, ferric arsenate etc. encapsulation in concrete or locking in silicate slags Careful assessment of these options is required
- 20. Green Processing 2006:5-6 June 20 The Early Removal OptionsThe Early Removal Options Tailing Dam Flotation Roaster Smelter Low As Conc High As Conc Low As Conc Safe Disposal e.g mine backfill Ore Arsenic Fumes
- 21. Green Processing 2006:5-6 June 21 ConclusionsConclusions Increasing pressure on metal producers to reduce emissions and manage toxic elements deportment Challenge - orebodies with higher levels of minor elements, which are difficult to process Early removal option offers competitive advantage Several options for safe disposal of low volume highly toxic streams, which could be linked with the early removal We believe, it is time to put current capability into practice by examining the integrated flowsheets to deal with the management of the minor elements in a more sustainable way.
- 22. Green Processing 2006:5-6 June 22 AcknowledgementAcknowledgement Some of the work and findings presented were generated through a project carried out under the auspice and financial support of the Cooperative Research Centre for Sustainable Resource Processing, which was established and is supported under the Australian Government's Cooperative Research Centres Program
Editor's Notes
- #4 Each year Australia exports ~ 3 millions of tonnes of copper, nickel, lead and zinc in form of concentrate and refined metals. Base metal ores contain low levels of toxic/hazardous elements e.g: As, Sb, Bi, Cd, Hg, Se, Te …, Th, U. Clean, coarsely-grained ore bodies becoming depleted Ore bodies of future becoming more complex, finer-grained and containing higher amount of minor/toxic elements. Worldwide industry mines and process 100s million tpa of base metal ores Accumulated mass of minor elements in biosphere is large and could have a significant environmental impact.
- #5 Removal and safe disposal of minor elements present technical and environmental problems as well as being costly Smelters impose treatment charges and penalty payment on minor elements in concentrates, because of difficulties in their removal and safe disposal Governments are becoming increasingly sensitive to emissions from smelters, Pressure is building from the community for more sustainable processing Smelter are setting tighter penalty specifications, With increasing demand for base metals and increasing levels of minor elements in ores, there is an imperative to develop alternative treatments that allow removal of toxic elements at the mine site before despatch of concentrate to smelters
- #6 Primarily determined by mineralogy and grain size Occurrence - association with other elements Distribution between phases If minor elements are widely and uniformly dispersed in mineral phases (as in a solid solution) treatment option is limited to separation and removal in waste or residue streams produced during smelting to recover valuable components If toxic elements are concentrated in in discrete phases, options exists for early removal by physical and chemical means. Physical means include separation based on differences in grain size or density, flotation characteristics, while chemical means include selective roasting or leaching Having separated and concentrated the toxic elements, consideration has to be given to their use or safe disposal.
- #7 Is a good example of impurity element found in most base metal ores and concentrates Lowers metal quality, if not removed from product metal Contributes to health concerns during metallurgical processing Causes environmental concerns during disposal of tailings and wastes High arsenic levels in an ore can make the deposit economically unviable Blending of high and low arsenic concentrates has been practiced by industry. Can we continue this in the future? Given the depleting clean and coarse-grained ore bodies, then the answer is NO. We will use arsenic as an example to illustrate and compare the current processing options with alternative treatment options, namely early removal and safe disposal, that could offer a number of benefits.
- #8 In copper ores arsenic occurs as Enargite (Cu3AsS4)Tennanite (3Cu2S.As2S3) Arsenopyrite (FeAsS)Cobaltite (CoAsS) In nickel systems Gersdorffite (NiAsS)Niccolite (NiAs) Arsenopyrite (FeAsS)Cobaltite (CoAsS) Physical separation of As bearing minerals from non-arsenic bearing minerals is difficult As they have similar specific gravity, non-magnetic, strongly floatable with conventional collectors etc. Second important point is that some As minerals contain high concentration of copper and nickel e.g. enargite (Cu3AsS4) has 48% Cu
- #9 Recently, CSIRO has made advances in physical separation of arsenic-containing minerals from valuable minerals by floatation. Given that the flotation behaviour of sulphide minerals depends on the oxidation-reduction state of pulp, then one can exploit this pulp potential effects to promote separation of arsenic-bearing sulphides such as enargite from non-arsenic sulphides. A good example of applying this to separation of Enargite from Chalcopyrite is shown in this figure, where through controlling the pulp potential (between -25 and 50 mv at a pH of 8) selective flotation and separation of enargite should be possible. Furthermore, according to the database developed at CSIRO, other copper-iron sulphide minerlas including birnite (Cu5FeS4) should be similar to that of Chalcopyrite.
- #10 Roasting has been used to remove arsenic from ores and concentrates Elemental arsenic and its sulfides, chlorides and oxides are volatile at roasting temperatures and a number of treatment options have been developed and reviewed in literature. Nakazawa, Yazawa and Jorgensen applied thermodynamics to simulate the removal of arsenic from copper concentrates in presence of oxygen More recently Jorgensen and co-workers applied roasting technique to remove arsenic from nickel concentrate
- #11 Roasting has been used to remove arsenic from ores and concentrates Elemental arsenic and its sulfides, chlorides and oxides are volatile at roasting temperatures and a number of treatment options have been developed and reviewed in literature. Nakazawa, Yazawa and Jorgensen applied thermodynamics to simulate the removal of arsenic from copper concentrates in presence of oxygen This figure shows some of the results from Nakazawa et al’s work on the effects of temperature and initial arsenic content on the degree of removal via roasting the concentrate with oxygen. It is evident that the effect of temperature becomes more pronounced for low Arsenic containing concentrate, where vapour pressure of As bearing species is too low at lower temperatures for the set oxygen supply rate.
- #12 The effect of oxygen supply is shown in this figure, where maximum arsenic removal is achieved at Oxygen to chalcopyrite ratios between 2.5 and 3.5. At higher oxygen supply rate, oxidation of concentrate to non-volatile ferric arsenate occurs and results in sharp drop in the arsenic removal.
- #13 At higher temperature of 900 C, similar behaviour was predicted, but with some sudden dip in the extent of removal caused by the formation of non-volatile Cu3As as well as As2O3. According to these results the ratio of 2.4 moles of oxygen per mole of chalcopyrite seems to be the optimum at 900 C.
- #14 This table compares results obtained from a number laboratory and plant scale practices. These results confirm the predictions by thermodynamic modelling i.e: Low degree of arsenic removal at temperatures below 700 C and/or low initial arsenic content Very high degree of arsenic removal from concentrates with > 1% initial arsenic and at temperatures close to 700 C. Recent work at CSIRO has shown high degree of arsenic removal from nickel concentrates. We may thus conclude that selective roasting can convert the high arsenic-bearing concentrates into very low arsenic concentrate for smelters.
- #15 If toxic elements are dispersed at low levels through the valuable mineral component of concentrate, their removal is accomplished during smelting, converting and refining steps. During smelting copper concentrate is reacted with air to oxidise and remove some of the sulphur and iron from the molten matte phase CSIRO’s MPE package covers thermodynamic behaviour of several minor elements in slags, mattes, alloys and gas phases. In this figure the predicted behaviour of As, Bi and Pb are shown during the smelting of copper concentrate to high grade mattes. Arsenic and antimony report predominantly to gas phase Bismuth and lead tends to concentrate in the gas phase while Selenium and tellurium report to the matte phase The predicted behaviour have been shown to be in close agreement with laboratory data as well as plant data.
- #16 Calculations were carried out for converting of matte produced by smelting, using a 2-stage Pierce Smith converter, followed by fire-refining of the blister copper to produce anode copper. For each stage of the flowsheet, the distribution of minor elements between condensed and gas phases was calculated.
- #17 The results for arsenic through these thermodynamic calculations are presented in this Figure. It is evident that in the smelting step over 70% of the input arsenic reports to the gas phase with the remainder being distributed between the matte and slag. The conversion of matte to blister copper results in further removal of the arsenic by the gas phase, but it is predominantly dispersed in the while metal and blister copper phase. During the fire-refining very little of the remaining arsenic reports to the gas phase.
- #18 In this figure the overall deportment of arsenic between the phases is presented, where about 70% of the input arsenic is captured by the gas phase. About 20% of the input arsenic reports to the slag phase and only 10% finds its way to the electro-refining. Results for bismuth and lead show that these elements mostly report to the gas phase, with the residual concentration in the metal being extremely low. On the other hand nearly all the Se and Te reported to the fire-refined anode copper.
- #19 While 70% of input arsenic and a portion of other toxic elements report to the gas streams, effective collection and safe disposal of these toxic elements is a significant issue, particularly when dirty concentrates are being treated. Generally a portion of arsenic and other volatile species condense in the bag-houses with small portion reporting to the acid plant. The portion that reports to acid plant is generally converted into gypsum and stored or disposed in tailing dams. The condense fumes, which contain arsenic and other volatile elements, are sometimes recycled through the smelter for recovery of valuable components such as copper.
- #20 The production of arsenic and other toxic elements is well in excess of market demand Typically these elements are produced by-products of smelting operations and are concentrated in form of fumes, dross, precipitates and slags Consideration has to be given to the disposal of surplus in a safe and environmentally acceptable manner This requires conversion to a less hazardous form and if the volume is small storage as a temporary solution Longer term solutions are required Arsenic trioxide is water soluble and requires conversion to more stable compounds before disposal A number of options have been proposed in the past. These include; conversion into calcium arsenate, ferric arsenate or scorodite, encapsulation in concrete and locking the arsenic in silicate slags. Each option has some merits and limitations. A careful assessment of these options is required.
- #21 The treatment options for managing the minor elements are determined b y their level and mineralogy in the primary flotation concentrate. Low levels <0.5% may be acceptable to a smelter without further treatment and subsequent processing involves conventional smelting and refining However for higher levels additional processing may be required. For cases where the arsenic is present as discrete grains and the gangue can be rejected to produce a clean concentrate then the flowsheet shown here could be considered. Here through combination of early removal by floatation and selective roasting of high arsenic portion the feed material to the smelter will be low arsenic concentrate. If on the other hand the arsenic minerals are not amendable to differential floatation, it would be necessary to roast all the primary concentrate in order to produce a clean concentrate.
- #22 There is increasing community and government pressure on metal producers to reduce emissions and manage toxic elements deportment in an environmentally acceptable and sustainable way. Metal producers are facing the challenge of orebodies with higher levels of minor elements, which are difficult to process There is now an increased focus on minor element deportment in flowsheet development for base metals ores The early removal option offers competitive advantage in respect to minor elements dispersion and management issues, as well as maintaining overall valuable metal recovery There are several options for safe disposal of low volume highly toxic streams which could be generated with the early removal in processing We believe it is time to put current capability into practice by examining the integrated flowsheets that deal with the management of the minor elements in a more sustainable way. This will involve, modelling, rigorous testing at laboratory and pilot scale followed by techno-economic evaluation and life cycle assessment.