Biological iron and sulfate control in mining

waters

Jaakko Puhakka

Tampere University of Technology

Comprehensive sulfate management in cold mining waters, Oulu, March 21, 2018

Objectives

• To develop an integrated process comprising

a fluidized-bed reactor (FBR) and a gravity

settler for precipitative removal of iron and

sulfate from bioleach liquors

1. Partial removal from bioleaching circuits

2. Removal from bioleaching effluent streams

FBR configuration

Fluidized-bed reactors for iron

oxidation at TUT

Various biomass carriers used in FBR’s

Various biomass carriers:

• Activated carbon (=AC)

• Diatomaceous earth (Celite)

• Al2O3 (Compalox)

• Jarosite flocculated with

InChem flock D 33

Criteria for carrier selection:

• Biomass hold-up capacity

• Chemical and mechanical

durability

• Iron-oxidation rates

• Material costs

Bacterial communities developing on the

carrier materials (DGGE)

“Ferrimicrobium acidophilum”

(99-100 % similarity)

No readable sequence

data obtained

Leptospirillum ferriphilum

(99-100 % similarity)

Process developed for iron and

sulfate control

1

2

5

6

7

3

4

9

7

8

1: Feed pump

2: FBR

3: Base addition

4: Settling tank

5: Aeration pump

6: Aeration unit

7: Recycle pump

8: System effluent

9: Precipitate removal(Not drawn to the scale)

7

Feed solution:

• Barren heap bioleaching

solution from which

valuable metals (Cu, Zn, Ni

and Co) had been

recovered

• Initial pH ~3

• Initial redox ~200-340 mV

• Initial Fe2+ ~6-8 g/L

Removal of excess iron from

bioleach circuit liquors

0

3

6

9

12

0 25 50 75 100 125

HR

T, h

Time, day

0.7

9

5 5

2.51.5

1 1.5

0

3

6

9

12

0 25 50 75 100 125

Fe

2+, g

/L

Time, day

0

1

2

3

4

5

0 25 50 75 100 125

pH

Time, d

a

b

c

pH

0

3

6

9

12

0 25 50 75 100 125

HR

T, h

Time, day

0.7

9

5 5

2.51.5

1 1.5

0

3

6

9

12

0 25 50 75 100 125

Fe

2+, g

/L

Time, day

0

1

2

3

4

5

0 25 50 75 100 125

pH

Time, d

a

b

c

pH

0 25 50 75 100 125

Time, d

FBR performance at various HRTs

2.5

1.0

0.7

9.0

1.5

5.01.5

5.0

Feed: ○

FBR effluent:

HRT

0

20

40

60

80

100

0

4

8

12

16

20

0 25 50 75 100 125O

xid

atio

n, %

g F

e2+/L

·h

Time, day

0

2

4

6

8

0 25 50 75 100 125

DO

2, m

g/L

Time, day

0

10

20

30

40

0 25 50 75 100 125

kg

O2/m

3. d

ay

Time, day

400

500

600

700

0 25 50 75 100 125

Re

do

x, m

V

Time, d

|

5.0

2.5

1.5 1.0

1.59.0

5.0

0.7

HRT, h

a

b

c

d

| || | | | | |

Iro

n o

xid

atio

n ra

te,

Oxyg

en

tra

nsfe

r ra

te,

Dis

so

lve

d o

xyg

en

,R

ed

ox, m

V

0 25 50 75 100 125

Time, d

FBR performance at various HRTs

● Rate

○ Efficiency (%)

HRT, h

0 25 50 75 100 125Time, day

400

500

600

700

0 25 50 75 100 125

Time, d

Re

do

x, m

V

2.5

1.0

0.7

9.0

1.5

5.01.5

5.0

Precipitation of iron in the gravity settler

at different FBR HRTs

0

5

10

15

20

25

30

0 25 50 75 100 125

Iro

n p

reci

pita

tion

, mg

/L·h

Time, d

5.0 2.5

1.5

1.0

1.5

9.0

5.0

0.7

HRT, h

a

| | || | | | | |

0

20

40

60

0 25 50 75 100 125

Pre

cip

itate

d p

erc

en

t, %

Time, d

b

Partial removal of iron from

bioleach circuits

12

Removal of iron and sulfate from

bioleaching effluent streams

Operational conditions during the

experimental periods with pH adjustment

pH 2.5 pH 3.0 pH 3.5 pH 3.2 pH 3.0 pH 2.8 pH 2.8

pH adjustment with KOH pH adjustment with CaCO3

1 65432 7

6.01.5 g Fe2+/L in the feed

0 30 60 90 120 150

Time, d

140.5 g Fe2+/L in

the feed

HRT = 2 h HRT = 2 hHRT = 5 h

pH 3

Feed and effluent Fe2+ concentrations

during the pH adjustment

Feed

Effluent

Fe2+ , g/L

0

4

8

12

16

0 30 60 90 120 150

KOH

2.5 3.0 3.5 3.2 3.0 2.8 2.8

CaCO3

Time, d

0

4

8

12

16

0 30 60 90 120 150

Fe

2+, g

/L

Time, day

0

200

400

600

800

0 30 60 90 120 150

Re

do

x p

ote

ntia

l, m

V

Time, day

0

2

4

6

8

10

0 30 60 90 120 150

DO

, m

g/L

Time, day

0

20

40

60

80

100

0

2

4

6

8

10

0 30 60 90 120 150

Oxid

atio

n

eff

icie

ncy,

%

Iro

n o

xid

atio

n ra

te,

g F

e2+/L

·h

Time, day

0

20

40

60

80

100

0

10

20

30

40

50

60

0 30 60 90 120 150

Pre

cip

ita

tio

n

eff

icie

ncy,

%

Iro

n p

recip

ita

tio

n ra

te,

g/L

·h

Time, d

KOH

2.5 3.0 3.5 3.2 3.0 2.8 2.8

CaCO3

a

b

d

c

e

Iron oxidation and precipitation rates

and efficiencies

KOH CaCO3

pH 2.5 3.0 3.5 3.2 3.0 2.8 2.8

Rates

Efficiencies

m

Sulfate concentration in the FBR feed, effluent, and

precipitated sulfate, and precipitated mol ratio of

[Fe]:[S]

FBR feed

Effluent

Precipitated sulfate

Theoretical mol ratio of [Fe]:[S] of

pure jarosite with the idealized

formula of XFe3(SO4)2(OH)6,

where X = Na+, K+, NH4+ or H3O

+

0

20

40

60

0 30 60 90 120 150

SO

42- , g

/L

Time, day

KOH CaCO3

a

b

0

1

2

3

4

5

0 30 60 90 120 150

Pre

cip

ita

ted

[Fe

/S]

b

Time, d

KOH CaCO3

pH 2.5 3.0 3.5 3.2 3.0 2.8 2.8

An X-ray diffractogram of precipitate from

gravity settler without pH adjustment

All peaks with labeled d-values (in Å) represent Na- and H3O-jarosites

18

Precipitates - pH adjustment with KOH

pH 2 2.5 2.5-3.0 3.0 3.0-3.5 3.5

Jarosite, hydronian

(K,H3O) Fe3(SO4)2(OH)6

Natro jarosite,

NaFe3(SO4)2(OH)6

Goethite (a-FeOOH)

19

Precipitates - pH adjustment with CaCO3

Brushite CaPO3(OH)2H2OJarosite, hydronian

(K,H3O) Fe3(SO4)2(OH)6

Jarosite synthetic

KFe3(SO4)2(OH)6

pH 3.2 3.0 2.8 2.8

15 g Fe2+ / L

Gypsum

(CaSO4·2H2O)

Conclusions

The integrated process consisting of an FBR combined with

a gravity settler in the recycle line can be applied for:

1) Iron control (partial removal) in bioleaching applications

to prevent the accumulation of dissolved iron in leaching

circuits. The process can be optimized for efficient and

high-rate iron regeneration

2) Treatment of bioleaching effluents for high-rate and

high-efficiency iron and sulfate removal as stable end

products