BIOMININGlecture # 1

Zygmunt SADOWSKI

Wroclaw University of Technology

Chemical Engineering

Schedule

04.12 Friday Lecture #1 Lecture # 2

07.12 Monday Lab. Lab.

09. 12 Wednes. Lecture # 3 Lab.

10. 12 Thurday Lecture # 4 Lab.

11. 12 Friday Lecture #5 Lab.

14.12 Monday Lecture #6 Lecture #7

15. 12 Tuesday Lecture # 8 Lecture #9

16.12 Wedns. Lecture #10 Exam

Subject of lecture

1. Introduction to biohydrometallurgy2. Microorganisms involved in bioleaching3. Physical chemistry of bacterial leaching4. Mechanism of bacterial oxidation5. Bioleaching kinetics6. Copper ores bioleaching7. BIOXTM process8. Post mining restoration of environment (Acid mine

drainage)9. Biosorption10. Desulferization of coal and oil

Books

1. Giovanni Rossi „Biohydrometallurgy” McGraw-Hill Book Comany GmbH, 1990.

2. D.E.Rawlings (Ed.)„Biomining Theory, Microbes and Industrial Processes” Springer 1997.

3. D.E.Rawling, B.W.Jonson (Eds.) „Biomining”Springer 2007.

4. Edgardo R.Donati, Walfgang Sand „Microbial Processing of Metal Sulfides”, Springer, 2007.

5. Z.Sadowski, „Biogeochemia- wybrane zagadnienia”, Wydawnictwo P.Wroc. 2006

Definition

• Bioleaching is the biological conversion of an insoluble metal compound into a water soluble form.

• For bioleaching Bacteria and Archaea are used.

• Bioleaching involves chemical and biological reactions.

Ancient history of hydro- and biohydrometallurgy

Roman writer Glius Plinus Secundus 23-79 A.D. describes haw copper minerals are obtained using a leaching process.

Hydrometallurgical extraction of copper from ore and the precipitation of copper from the solution by treatment with metallic iron is an ancient technology

History of biohydrometallurgy

History of biohydrometallurgy

• 166A.D. the scientist Galen described „in situ” leaching in old copper and lead mine at Cyprus.

• 1494-1555 Georgius Agricola described roasting pyrite (FeS2) to prepare for leaching and produce FeSO4.

• 1572 Industrial heap leaching of copper sulfides in Rio Tinto (Spain).

• 1879 Bioleaching of low-grade ore at Rio Tinto.• 1947 Thiobacillus ferrooxidns was identified and

isolated from acid mine drainage.• 1965 Discovery of the first iron and sulfur oxidizing

archaea Acidianus Brierlevi from thermal spring in Yellowstone.

What is biohydrometallurgy ?

The recovery of heavy metals from sulfidic ores employing microorganisms

The various branches of science from which the fundamentals of hydrometallurgy are derived

Area of application

• Three main areas of application can be identified:

Metal extraction from minerals and rocksEnvironmental protectionPre-treatment of minerals to make them

amenable to further processing

Biohydrometallurgy

The main application of biohydrometallurgy is bioleaching

The action of bacteria

1. to convert insoluble metal sulfides ( or oxides in the case of uranium) to water soluble metal sulfates.

2. to open up the structure of the sulfides minerals for other chemical better penetration.

Bioleaching

• The mobilization of metal cations from insoluble ores by biological oxidation and complexation process is referred to as bioleaching.

• Metals for which bioleaching is employed: Copper (Cu) Cobalt (Co) Nickel (Ni) Zinc (Zn)

Uranium (U)

Advantages to using bioleaching for the metal extraction

1. The use of naturally occurring components:

microorganisms, water, ore, and air.

2. Simple to operate and maintain (stirred tanks, heap leaching).

3. Low pressure (atmospheric) and temperature process.

4. Dust and SO2 free

Advantages of bioleaching

• The advantages of bacterial leaching technology are agreeable with these requirements:– Moderate capital investment with low

operating costs,– Appropriate recovery of metals from low-

grade ores and waste materials,– Basic equipment and simple operating

procedures.

Advantages

• Miroorganisms are responsible for production of ferric iron (Fe3+) and acid.

• Bioleaching is environmental friendly than many physical metal extraction processes

Disadvantage of biomining

• The main disadvantage of bioleaching of sulfides is that the process is perceived to be slow relative to pyrometallurgical processes

Pyro- and hydrometallurgy

Currently 25 % of all copper worldwide, worth more than $ 1 bilion annually, is produced through bioprocessing

Block diagram showing the factors affecting reactor bioleaching profitability

Microorganisms-mineral interaction

• Acidolysis – formation of organic and inorganic acids (protons).

Sulfuric acid is the main inorganic acid found in bioleaching environments.

• Complexolysis – the extraction of complexing agents.

• Redoxolysis – oxidation and reduction reactions.

Complexolysis and Acidolysis

• Metals in certain non-sulfide minerals may be solubilized by a process of complexation with oxalic, citric or other organic acids.

• These organic acid are typically produced by certain type of fungi.

• Aspergillus niger, Penicillum

Bacteria for biooxidation process

• In the processes that operate from ambient temperature to about 40oC, the most important microorganisms are considered to be a consortium of Gram-negative bacteria.

• These are the iron- and sulfur-oxidizing bacteria (Acidithiobacillus

ferrooxidans). the sulfur-oxidizing (Acidithiobacillus thiooxidans and

Acidithiobacillus caldus) the iron-oxidizing leptospirilli (Leptospirillum ferrooxidans

and Leptospirillum ferriphilum)

Bacteria for biooxidation process

Bacteria Biooxidation reactions

Acidithiobacillus ferrooxidans

Fe2+ Fe3+

S2- or S0 SO42-

Acidithiobacillus

thiooxidans

S2- or S0 SO42-

Leptospirillum ferroxidans

Fe2+Fe3+

Acidophilic metal sulfide oxidizing microorganisms

• All acidophilic metal sulfide oxidizing microorganism oxidize Fe2+ and sulfur compound.

Biooxidtion of Fe2+ ions, Redox potential (Eh)

• The potential Eh is the ratio of dissolved ferric to ferrous ions.

• Eh is used as a bioleaching indicator.

• The best leaching was achieved between 600-750 mV

2

3

log59771Fe

FeEh

Biooxidation process

• The biooxidation conditions typically exhibit a relatively high redox potential around Eh=0.65 – 0.70 V .

• One consequence of the high solution potential is that ferric ion readily precipitates as a basic sulphate , like jarosite .

3Fe3+ + 2SO42- +6H2O + Me+MeFe3(SO4)2(OH)6 +

6H+

where Me = K+,Na+, NH4+

Jarosite precipitation

Experimental equipment for biooxidation

Bioleaching

• The recovery of heavy metals from sulfidic ores employing microorganisms is now an established branch of biotechnology.

• Microorganisms are able to regenerate of the oxidizing reagent which chemically reacts with metal sulfides.

• Bioleaching is currently an economical alternative for treating specific sulfidic ores.

Heap and tank bioleaching

Copper recovery Gold ores pretreatment

There are two ways of applying bioleaching for metal recovery from sulfide ores, namely heap leaching and tank leaching

Tank bioleaching process

• In stirred tank processes highly aerated, continous-flow reactors in series are used to treat the mineral suspension.

• The stirred tank reactors operate at 400C and 500C.

• The suspension density is limited to above 20 %, as the pulp density is > 20% the microbial problems occur.

Application of tank bioleaching

• Stirred tanks are used as a pretreatment process for gold containing arsenopyrite concentrates.

• The first bioleaching instalation has been built at Fairview mine, Barberton, South Africa in 1986.

• The largest is at Sansu in the Ashanti goldfields of Ghana, Wester Africa.

• Cobalt-containing pyrite is leached at Kasese, Uganda

Stirred tank versus bioheap

• The principal disadvantages of aerated, stirred-tank reactors compared to bioheaps are the capital and operating costs.

• In situ bioleaching

In situ bioleaching has been commercially us for extraction uranium and copper from depleted underground mines

Bioheap leaching

• The pregnant leach solution containing:

1.5-6 gL-1 soluble copper and up to 20 gL-1 is collected and sent to a recovery plant

• The common methods for copper recovery: Precipitation with using iron (cementation) Electrowinning Solvent extraction followed by electrowinning

Pirometallurgical methods

• The arsenopyrite flotation concentrate contain gold is roasted at 7000C in the presence of oxygen or digested with acid under pressure in oxygen-enriched atmosphere (autoclaved).

Environmental impact of the acid generation

1.33 moles of sulfuric acid are produced per mole of pyrite

pH = 2.5