Mining and Microbiology: Biotechnologies for Mineral Processing

Transcription

1 Bangor Acidophil Research Team Mining and Microbiology: Biotechnologies for Mineral Processing David Barrie Johnson College of Natural Sciences, Bangor University, U.K.

2 Bangor Whe al Jane

3 acidophilic microbiology angor cidophile Research Team metal-microbe interactions

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6 What can microbiology offer the mining industry? A different approach for processing ores and concentrates Technologies for remediating waste waters

7 Compost bioreactor Acid rock drainage: Avoca copper mine, Ireland Lab-scale sulfidogenic bioreactor

8 What can microbiology offer the mining industry? A different approach for processing ores and concentrates Technologies for remediating waste waters Novel ways to recover and recycle metals

9 Sulfidogenic plants (Paques bv) Budel zinc refinery, The Netherlands Kennecott Utah copper mine

10 What can microbiology offer the mining industry? A different approach for processing ores and concentrates Technologies for remediating waste waters Novel ways to recover and recycle metals Sustainable (integrated) technologies

11 (new genus & species) Bio-prospecting for acidophiles in a geothermal zone: Yellowstone National Park, U.S.A. Frying Pan Hot Spring Ferrithrix thermotolerans

12 ae Coch S mine, north Wales Pyrite mine, actively worked for S (used in explosives) during the 19 th century and from Abandoned since 1918, apart from exploratory work in 1940 FeS 2 ; fools gold

13 Life underground in Cae Coch Isolated pools Slimes on wall faces Gelatinous stalactites

14 Mynydd Parys Copper Mine, Anglesey, north Wales

15 Cantareras: Iberian Pyrite Belt

16 Two new bacterial species isolated from abandoned mines: 1. Ferrovum myxofaciens Iron-oxidizing chemolithotroph Produces copious amount of EPS

17 Two new bacterial species isolated from abandoned mines: 2. Acidithiobacillus ferrivorans Iron and S-oxidizing chemolithotroph Cold-tolerant

18 Biomining Technology based on the oxidative dissolution of sulfidic minerals by prokaryotic microorganisms that facilitates the recovery of metals

19 The Origins of Biomining: Isolation (in 1947) of the first bacterium that was demonstrated to oxidize Fe 2+ to Fe 3+ and to accelerate the dissolution of sulfide minerals (Thiobacillus ferrooxidans)). The first commercial biomining operations were put in place (in the western USA) in the early 1960 s. Human beings had already been using bacteria to extract metals from copper ores for hundreds of years without being aware of them.

20 19 th century Precipitation Pond for Recovering Copper from the Flooded Parys Mine, Anglesey

21 What metals can (and are) be extracted by biomining? Copper (mostly in heaps and dumps) Uranium (in situ operations) Gold (mostly in tanks) Cobalt (tank leaching: Uganda) Nickel (heap leaching: Finland) Zinc Others

22 Biomining currently accounts for: % global copper production - 5% of global gold production - smaller production of some other metals

23 Advantages of bioprocessing of minerals over competing technologies Costs (where there is a penalty for smelting, e.g. As-containing concentrates) Recovery of by-products Processing of lower-grade ores Processing of complex ores (polymetallics) On-site production of sulfuric acid

24 Biomining: engineering options Irrigation-based processes: - dump leaching - heap leaching - in situ mining Stirred tank processes

25 1. Dump leaching Low-grade run-of-mine ore Large rocks and boulders are not crushed, and are piled into large stacks (up to 35 m high) Stacks are periodically irrigated with acidic raffinate (Fe/sulfate-rich wastewater) Each cycle may extend for ~ a year

26 Kennecott Chino copper mine, New Mexico

27 Kennecott Chino copper mine, New Mexico

28 Kennecott Chino copper mine, New Mexico

29 Kennecott Chino copper mine, New Mexico

30 Kennecott Chino copper mine, New Mexico

31 Copper recovery from pregnant leach solutions by cementation Cu 2+ + Fe 0 Cu 0 + Fe 2+

32 Kennecott Chino copper mine, New Mexico copper recovery by cementation

33 Dexing copper mine, China dump leaching of waste rock

34 2. Heap leaching Low-grade run-of-mine ore (or concentrate) Rocks are generally crushed, and ores may be agglomerated (with acid); ores are constructed to heights of m; several lifts may be used Heaps are constructed on impermeable membranes (or pads ) to avoid loss of leach solutions Heaps are irrigated with acidic raffinate and may be also inoculated

35 Heap leaching: basic design copper metal raffinate acid irrigation electrowinning blowers copper ore heap Pregnant Liquor Solution solvent extraction impermeable membrane

36 Two contrasting sites Talvivaara, Finland Escondida, Chile

37 Talvivaara Mining Company, Finland

38 Sb. acidophilus YTF1 Sb. thermosulfidooxidans Acidicaldus Y008

39 Sb. acidophilus YTF1 Sb. thermosulfidooxidans Acidicaldus Y008

40 Over 300 days, calculations show that nearly 80% of Ni had been recovered After 300 days

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42 Escondida Copper Mine, Chile

43 Largest copper-producing mine in the world operating profit $6 billion (2006) concentrate produced from higher grade ore (~1.7% Cu) copper oxide ores leached with sulfuric acid (in heaps) low-grade copper sulfide ores (~0.5% Cu) bioleached in heaps

44 Bioheap leaching parameters Run of mine ore (uncrushed or graded) 0.5% Cu: - 40% chalcocite (Cu 2 S) - 10% covellite (CuS) - 50% chalcopyrite (CuFeS 2 ) Processing 180,000 tonnes ore/annum

45 Bioheap operation: Escondida, Chile 5 km 2 km

46 Air blowers: Escondida

47 Inoculation pond: Escondida

48 In situ biomining using rock fracture and injection: Idealised scenario overburden ore deposit Impermeable rock injection liquor PLS out

49 Minerals are processed in a matter of days (~3-6) 3. Stirred tank leaching Used for mineral concentrates (chiefly refractory gold) and at pulp densities of ~20% Most stirred tanks operate at between 35 and 45 C; cooling is a major operating cost Tanks are generally constructed of high-grade stainless steel Tanks are actively aerated Agitation (stirring) is another major operational cost

50 First biooxidation plant, Fairview mine, 14t/d, now 55 t/d

51 Sansu plant, Ashanti, Ghana, 960 t/d, 24 X 1000m 3 reactors Impeller Alliance thermophilic stirred tank (Chile)

52 Gold Biomining in Asia Suzdal BIOX plant (Kazakhstan): 192 t gold concentrate/day in subzero temperatures A more recent operation at Kokpatas (Uzbekistan) is designed to process over 160,000 t of refractory gold concentrate/year

53 Biomining environments: characteristics Low ph Elevated concentrations of sulfate and dissolved metals Variable temperature Selects for extremophilic prokaryotes (thermo)acidophiles

54 How do micro-organisms solubilise metals from sulfide minerals? - by a process of oxidative dissolution, involving (primarily) ferric iron

55 Dissolution of pyrite at low ph by ferric iron 2Fe 2+ FeS 2 Fe 3+

56 Dissolution of pyrite at low ph: role of primary* microorganisms 2Fe 2+ Fe 2+ FeS 2 Fe 3+ Fe 3+

57 Dissolution of pyrite at low ph: role of primary* microorganisms 2Fe 2+ Fe 2+ FeS 2 Fe 3+ Fe 3+ Contact leaching Non-contact leaching

58 Dissolution of pyrite at low ph: role of tertiary* microorganisms CO 2 2Fe 2+ Fe 2+ DOC FeS 2 Fe 3+ Fe 3+ Fe 2+ Fe 3+ Polythionates, S 0 S 2 O 3 2- DOC DOC SO 4 2-, H + *heterotrophic acidophile

59 Lithotrophic ( rock eating ) prokaryotes Unexposed rock Pitted rock due to selective dissolution of sulfidic minerals

60 Bioleaching of base metal sulfides Ni 2+ FeS 2 (Fe,Ni) 9 S 8 SiO 2 Fe/S bacteria SiO 2 Fe 3+ SO 4 2- FeS 2

61 Biooxidation of refractory gold ores FeS 2 FeAsS Au Fe/S bacteria FeS 2 Au CN- FeS 2 Au(CN) 4 -

62 Bioleaching of uranium ores UO 2 2+ UO 2 Fe 2+ Fe 3+ At. ferrooxidans Leptospirillum spp. etc. FeS 2

63 Stirred tank operations Generally operate at C Provide a homogeneous environment, with regard to ph, temperature, aeration, dissolved solids etc. Operate as continuous flow (non-sterile) systems Objective is to degrade the minerals as quickly as possible Limited biodiversity generally up to 4/5 prokaryotes

64 asese Cobaltiferous pyrite: single tank operated at 37 o C & ph 1.3 (BRGM, France) Cu-Ni concentrate (Nkomati): single tank operated at 45oC & 10% pulp density (Mintek, South Africa)

65 Extensive biodiversity is advantageous Heap Leaching Operations Highly heterogeneous environments, e.g. temperature can range from ambient to > 80 C Variations are both spatial and temporal Tend to select for acidophiles that attach to the mineral phase Selection for rapid cell growth is less important

66 Copper heap bioleach microbiology: Utah At.ferrooxidans Sb.thermosulfidooxidan a b c d e f unknown At.ferrivorans At.thioooxidans

67 Examples of the application of acidophile microbial ecology and new isolates to existing and evolving biotechologies 2. Bioremediation

68 Abandoned mines and mine spoils generate vast quantities of pollution as run-off drainage streams and pit lakes Mine Impacted Waters (MIWs) These may be acidic (often extremely so) and are frequently enriched in transition metals, and metalloids Cwm Rheidol ARD

69 "Active" systems: aeration and lime addition Abiotic "Passive" systems: e.g. anoxic limestone drains REMEDIATION OPTIONS Biological "Active" systems Off-line sulfidogenic bioreactors Accelerated iron oxidation (immobilized biomass) "Passive" systems Aerobic wetlands Permeable reactive barriers Compost reactors/wetlands

70 There is no perfect solution to ARD remediation Non-sustainable - consumption/transport of chemical alkaline reagents (lime etc.) Inconsistent performance (wetlands and compost reactors)* Produce of hazardous wastes, and do not facilitate the recovery of metals (active and passive treatment)

71 Biological systems can be used to remediate ARD Removal of iron by oxidation and precipitation Biological generation of alkalinity (consumption of acidity)

72 Pilot-scale reactor for removing iron (by oxidation and precipitation) from acid mine drainage water: Lusatia, Germany EPS Microbial community dominated by Ferrovum myxofaciens

73 A new approach for active biological treatment of ARD being developed at Bangor University Targets: Removal of sulfate Amelioration of ph Selective recovery and recycling of metals Simple engineered system with low running costs

74 Mine water treatment using sulfidogenesis*: generation of alkalinity removal/precipitation of many transition metals (and As) as highly insoluble sulfides removal of sulfate *generation of H 2 S

75 Two examples of novel acid-tolerant SRB Desulfosporosinus acidiphilus (M1) (isolated in the late 1990s from the volcanic island of Montserrat, W.I.) Desulfobacillus acidavidus (isolated from anaerobic microbial mat at the abandoned Cantareras copper mine, Spain) Solute concentration (mm) Glycerol Zinc Time (hours) *Both isolates are active in highly acidic liquors (ph 3 and above)

76 Mixed culture system operated as an Upflow Biofilm Reactor (UBR) cost-effective system simple engineering design low operating costs

77 Construction of an Upflow Biofilm Reactor (UBR): Commissioning of Bioreactor eed in Pump ph electrode Effluent out

78 Separation of soluble heavy metals by sulfidogenesis ph 2 ph 4 ph 7 Fe 2+ Fe 2+ Fe 2+ FeS Zn 2+ Zn 2+ ZnS Cu 2+ CuS

79 lycerol (a waste product from biodiesel production) acts as e energy source for SRB: 4 C 3 H 8 O SO H + 12 CO H 2 S + 16 H 2 O hanging glycerol concentration allows control of ph crease, and removal of sulfate/production of H 2 S

80 Bioreactor data

81 Iron is oxidized and precipitated in a downstream UBR (operated as a passive system)

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83 Schematic: Integrated asrb system INFLUENT H 2 S OFF GAS EFFLUENT UBR Zn PPT FOB REACTOR Cu PPT TANK

84 moving from this to this mixed metal sludge copper zinc iron

85 Waste Dumps as Lucrative Resources? $ $ $ $ $ $ $ $ $ $ $ $

86 A new direction for Biomining

87 Not all metal ores occur as reduced minerals, for example, the nickel laterites, which account for 73% of global Ni reserves Ni FeO.OH FeO.OH Ni FeO.OH Ni FeO.OH Ni FeO.OH Ni FeO.OH Ni Ni FeO.OH Ni FeO.OH FeO.OH Ni FeO.OH Ni FeO.OH Ni FeO.OH Ni FeO.OH Ni Ni FeO.OH Ni FeO.OH FeO.OH Ni Ni-laterite ore, Western Australia

88 One possible bioprocessing option is to promote the reductive dissolution of the goethite phase, thereby liberating the nickel Ni FeO.OH FeO.OH Ni FeO.OH Ni FeO.OH Ni FeO.OH Ni FeO.OH Ni Ni FeO.OH Ni FeO.OH FeO.OH Ni FeO.OH Ni FeO.OH Ni FeO.OH Ni FeO.OH Ni Ni FeO.OH Ni FeO.OH FeO.OH Ni reductive dissolution Fe 2+, Ni 2+, OH - Again, doing this is an acidic liquor would maintain metals in solution

89 The iron/sulfur-oxidizer Acidithiobacillus ferrooxidans can also reduce soluble ferric iron*, using sulfur or hydrogen as an electron donor S 0 + 6Fe H 2 O SO Fe H + *no reports of reductive dissolution of ferric iron minerals.

90 Reductive dissolution of Ni-laterite by At. ferrooxidans (S as electron donor)

91 angor cidophile Research Team