Biosorption Process For Removal and Recovery of Heavy and Precious Metals from Aqueous Solutions: Past, Present and Future

Dr J. Paul Chen Department of Chemical & Environmental Engineering

National University of Singapore, Singapore

Presented at International Symposium on Water Resources

Wuhan, China

November 9, 2003

Outline of PresentationMotivationHistorical backgroundCurrent development

ApplicationMechanisms

Future trendsSummary

Major Industries in Singapore

• Originally 7 islands of total area of 900ha

Reclamation efforts: 2,650ha in 2001, to increase to 3,200ha in 2003

• 55 companies on site (e.g. DuPont, Chevron, Celanese, ExxonMobil, Eastman, Sumitomo)

• Target output from chemical industries: S$75 billion by 2010

Chemical Industry

Chemical Cluster Output : S$ 28.9 billion

Chemical Output Share (2001)

Petroleum62%

Petrochemicals23%

Specialty Chemicals15%

Others1%

Major Industry Sectors (2001)

Total Manufacturing Output : S$ 135 billion

Engineering18.3%

Chemicals20.8%

General Industries

1.4%

Biomedical Sciences

9.2%

Electronics50.3%

Jurong Island: Integrated Petrochemical Hub

1S$=

4.75

RM

B

Why do we care about metal contamination ?

Human activities and natural processes inevitably would produce metal wastes.

Typical industries are metal-plating and metal-finishing operations, e.g. semiconductor mining and ore processing operations, metal processing, battery and accumulator manufacturing operations, thermal power generation (coal-fired plants in particular), nuclear power generation, Military practices, e.g. U

Naturally occurring metal wastes include arsenic and arsenite.

Why do we care ... metal ? Cont’d EPAs have become more concerned the impacts. In the USA, important regulations are Cu-Pb and As rule (new

ruling of 10-ppb AS in drinking water in 2001) Searching cost-effective technologies becomes crucial. Technologies:

Precipitation, adsorption, ion exchange, electro-coagulation, electrochemical reduction, membrane filtration

However, the costs and efficiencies still remain as a major concern.

Affinity of metal with organicsL-2-Aminopropanoic Acid (Alanine) with various metal

Log K

Ca2+ 1.30

Co2+ 4.31

Ni2+ 5.36

Cu2+ 8.11

Zn2+ 4.58

Cd2+ 3.98

Pb2+ 4.15

CHCOOHCH

|

NH

3

2

MLLM 22 =+ −+

}}{L{M

{ML}22 −+=K

Metal Ions

1. Immobilization of organics; 2. use of organics in natural biosolids

Historical background: 1980-1995Biosorption by the materials derived directly and/or indirectly by various organisms has long recognized

However, the applications of biosorption started to appear in scientific literatures in early 1980s.

Credit - One of earlier researchers, B. Volesky of McGill Univ., had contributed significantly by publishing a series of papers, mainly on screening of biosorbents and measurement of biosorptive capacities.

What is biosorption ?• Biosorption is a property of certain types of

inactive/active organisms to bind and concentrate heavy metals from even very dilute aqueous solutions.

• Biosorbents can be classified into:a. Inactive organisms (mainly) include algae, fungi and bacteria

b. Their derivatives which are termed as biopolymers.

• Opposite to biosorption is metabolically driven active bioaccumulation by living substances.

What are typical biosorbents ?• Some of the biomass types come as a waste by-product of

large-scale industrial fermentations (the mold Rhizopus, the bacterium Bacillus subtilis and waste activated sludge).

• Other metal-binding biomass types, certain abundant seaweeds (particularly brown algae e.g. Sargassum, Ecklonia ), can be readily collected from the oceans.

• Biopolymers are normally extracted from inactive organisms and processed before use (e.g. Ca-Alginate)

• These biosorbents can accumulate in excess of 25% of their dry weight in deposited metals: Pb, Ag, Au, U, Cu.

Case presents• Raw seaweeds – collected in Singapore

• Ca-alginate beads

• Ca-alginate based ion exchange resin (CABIER)

Examples: Marine Algal collected in Singapore

Padina sp. Sargassum sp.

Why biosorption ?

Cu sorption

Characterization of biosorbents by instrumental analysis

• Fourier transform infrared spectroscopic (FTIR) and X-ray Photoelectron Spectroscopic (XPS) studies show that biosorbents have significant amount of COO, OH, C=O, and C-O.

• These organic functional groups would be responsible for metal uptake onto the biosorbents due to the high affinity for metal ions.

• SEM shows less pore development in bisorbents

Biosorption Equilibrium

Metal biosorptive properties: pH effectSOH + Mm+ = SO-Mm+ + H+

pH

1 2 3 4 5 6 7

Met

al r

emov

al, %

0

20

40

60

80

100

CuPb

[Pb]o=[Cu]o=1x10-4 M

[CABIER]=0.15 g/L

Sargassum Ca-alginate

0

4

8

12

16

20

0 1 2 3 4 5 6 7 8

Final pH

q, m

g/g

Cr3+

CrO4-

Metal biosorptive properties: pH effectEffect of Ionic Strength on Copper Removal

TCu=5x10-5 M, 2mL of 1.5 % alginate

0

20

40

60

80

100

1 2 3 4 5 6pH

Copp

er Re

mova

l,%

I=0.005 M

I=0.050 M

I=0.500 M

Metal biosorptive properties: ionic strength effect

Algae as the biosorbentsBi omass Met al i ons qmax (mmol/g) Ref er encesAscophyl l um spp. Ni , Pb, Cd, Cu 1.03-1.43 Vol esky et al . , 2000Chl or el l a sp. Cd 0.99 Aksu, 2001Cl adophor a sp. Pb 0.35 Jal al i et al . , 2002Cycl ot el l a sp. Cu 0.41 Schmi t t et al . , 2001Cymodocea spp. Cu, Zn 0.71-0.83 Sanchez et al . , 1999Fucus sp. Pb 1.6 Vol esky, 1994Gr aci l ar i a sp. Pb 0.2-0.26 Jal al i et al . , 2002

Padi na spp. Pb, Cu 0.31-1.05 Vol esky, 1994; Jal al i et al . , 2002; Kaewsar n, 2002

Phaeodact yl um sp. Cu 1.67mg/g Schmi t t et al . , 2001Pol ysi phoni a sp. Pb 0.49 Jal al i et al . , 2002Por phyr i di um sp. Cu 0.27mg/g Schmi t t et al . , 2001

Sar gassum spp. Pb, Cu, Cd, Ni 0.71-1.99 Vol esky et al . , 1994, 2000; Jal al i et al . , 2002

Scenedesmus spp. Cu, Cd 0.06-0.21 Schmi t t et al . , 2001Schi zomer i s spp. Pb, Cd 0.31-0.44 Ozer et al . , 1999Spi r ul i na sp. Cd 0.87 Rangsayat or n et al . , 2002Ul va sp. Pb 0.61 Jal al i et al . , 2002

Mechanisms of metal biosorption Instrumental investigations through XPS, FTIR,

titration and equilibrium experiments reveal that the biosorption is a complex chemical phenomenon.

Depended on the types of bisorbents applied, the metal uptake may be due to:metal surface complex formation (MSCF) ion exchange, and elementary coordination

XPS spectra of Pb- and Cu-adsorbed CABIER

137

Binding Energy (eV)

130 135 140 145 150 155

Inte

nsi

ty

0

200

400

600

800

1000

1200

1400

Pb 4f7/2

Binding energy (eV)

920 930 940 950 960

Inte

nsit

y

250

300

350

400

450

500

550

600

932.8

935.0

Cu 2p3/2

-O-M-O-

XPS Analysis

• Note that BE values of 577.2 and 579 represent Cr (III) and Cr (VI)

• Uptake reduction and MSCF

574 578 582

Binding Energy (eV)

574 578 582

Binding Energy (eV)

574 578 582

Binding Energy (eV)

574 578 582

Binding Energy (eV)

Raw Padina Cr(VI): pH 1

Cr(VI): pH 2 Cr(III): pH 4

577.1 578.5577.2 579.2

579.5577.5

biosorption of Metal Ions: Surface Complex Formation Model

_

_

_

_

_

_

_

_

_

_

__

_

__

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+

+ ++

+

+

++

+

Surface PlaneInner Helmholtz PlaneOuter Helmholtz Plane

+

+

+

+

_

_

o d

Distance

Potential

0 d

β

ψο

ψ β

ψ d

β

biosorption results from reactions between functional groups of adsorbents and metal ion species.

Two-pK Triple-Layer Model - MSCF

M=Cu, or Zn, or Co, X=Cl, or NO3, or ClO4

yo=eψo / kT and yβ=eψβ / kT referred to o-layer and β-layer

SOH H y SOHo

KH

+ ( )+ + − ⇔ = +exp1

2 SOH H y SOo

KH

- ( )+ −− − ⇔exp2

-+2

+- )exp()exp(X + XSOHyyHSOHXK

o ⇔−−−++ β

SOH Na H y y SO NaKNa

+ -+ + - +− − + − ⇔exp( ) exp( )ο β

+−++ ⇔−−−−++ 20

2 )(exp)(exp2 MSOyHyMSOHCuK

β

+−++ ⇔−−−−++ MOHSOyHyMSOHCuOHK

)(exp2)(exp 02

β

−−+−+ ⇔−−−−+++ CuClSOyHyClCuSOHCuClK

)(exp2)(exp 02

β

MSCF for Cu biosorption by Ca-alginate beads

0

2 0

4 0

6 0

8 0

1 0 0

1 2 3 4 5 6 7

p H

Copp

er Re

mova

l, %

Chen, J.P., et al., Environmental Science and Technology, Vol. 31, No. 5, pp. 1433-1439, 1997.

Conceptual model for the metal removal by ion exchange.

Ca2+R2-

Ca2+R2-

R2- + M2+

M2+R2- + Ca2+

M = Cu and Pb

Ion exchange in biosorption (e.g. by CABIER)

1. M2+ + Ca-R M-R + Ca2+ (ion exchange) 2. M2+ + R2- M-R (R: unreacted group)

(elementary coordination)3. 2H+ + Ca-R H2-R + Ca2+ (pH effect) and 4. solution and precipitation reactions……..

Chen, J.P. et al., Langmuir, Vol. 18, No. 24, pp. 9413-9421, 2002.

Prediction of pH Effect on Metal Removal by CABIER

pH

1 2 3 4 5 6 7

Rem

ova

l, %

0

20

40

60

80

100

CuPb

[Pb]o= 1.0×10-4 M, m=1 g/L, [Cu]o=1.0×10-4 M, m=0.15 g/L. modeling

Prediction of Competitive Biosorption by CABIER

Resin applied, g/L

0.0 0.2 0.4 0.6 0.8 1.0

Res

idua

l Met

al C

onc.

x10

5 , M

0

4

8

12

16

20

[Pb]o = 1.63x10-4 M

[Cu]o = 1.81x10-4 M

modeling

0 20 40 60 80 100 1200

20

40

60

80

100

Res

idua

l lea

d co

ncen

trat

ion

X 1

05 , M

0

1

2

3

4

Res

idua

l cop

per

conc

entr

atio

n X

10

5 , M

Initial copper concentration X 105, M

Generalized approach for the simulations- MINEQL

Solution Reactions:

Adsorption Reactions:

Precipitation Reactions:

yi = Kiy ck

aiky

k=1

Na∏

sk

biky

k=1

Ns

∏

co

aioy

cβaiβ

y

, i =1,2,..., My

1= Kip ck

aikp

k =1

Na∏ , i = 1,2,..., Mp

xi = Kix ck

aikx

k =1

Na∏ , i = 1,2, ..., Mx

EDL

Solution and Precipitation Reactions in the Modelingn2

n2 )OH(CunOHCu −−+ =+ n2

n2 CuClnClCu −−+ =+

)s()OH(CuOH2Cu 22 =+ −+ OH)s(CuOOH2Cu 2

2 +=+ −+

n2n

2 PbClnClPb −−+ =+n2n

2 )OH(PbnOHPb −−+ =+

)s()OH(PbOH2Pb 22 =+ −+ OH)s(PbOOH2Pb 2

2 +=+ −+

OH)s()OH(OPbOH4Pb2 2222 +=+ −+

……………Chen, J.P. and Lin, M.S. Water Research, Vol. 35, No. 10, pp. 2385-2394, 2001.

How about modeling for metal reduction ?

• NO solution yet !!!

• It is on-going; but we may have hard time !!!

Bisorption Kinetics

Biosorption kinetics: four types of seaweeds vs. “novel” CABIER

[Ca2+]o = 0, [Na+]o = 0

Time (min)

0 30 60 90 120 150 180

q (

mg

/g)

0

20

40

60

80

100

[Pb2+]o = 20 ppm

[Pb2+]o = 36.8 ppm

seaweeds CABIER

time (min)

0 100 200 300 400 500

q (m

mol

/g)

0.0

0.2

0.4

0.6

0.8

1.0

PadinaSargassumUlvaGracillaria

pH=5.0m=1.0g/L, C0=1.0mmol/L

copper

Sorption Kinetics of Metal Ions: Diffusion-Controlled Model

Adsorbent

Liquid Film

Bulk Liquid

Concentration

Porous

ap r, distance measured from adsorbent particle center

ρp, εp

m

kf jCj

c j

qj

qj

c j

c j(r=ap)Dpj

Model Parameters• Rate-controlling mechanism

(i.e., transport-controlled or reaction-controlled cases)

• Rate parameters (i.e., diffusion and mass transfer coefficients or rate constants)

• Characterization of sorbents

Sorption rate results fromeither mass transfer of ionspecies to the surface of sorbents or complexationreactions between functionalgroups of sorbents and ionspecies.

An Intraparticle Diffusion Model for Metal Uptake Kinetics

t

q

r

q

rr

qDe ∂

∂=

∂∂+

∂∂ 2

2

2

0=∂∂

r

q

C*)(Ckρr

qD fpe −=⋅

∂∂

kinetics of metal biosorption

[Ca2+]o = 0, [Na+]o = 0

Time (min)

0 30 60 90 120 150 180

q (

mg

/g)

0

20

40

60

80

100

[Pb2+]o = 20 ppm

[Pb2+]o = 36.8 ppm

pH = 4-5, m = 0.4 g/L, De = 2.95×10-11 m2/s, kf = 2.41×10-4 m/s

Engineering applications

Continuously operated system for metal treatment – an engineered approach

m

V

p Lz

us cin

Kinetics: external mass transfer and internal diffusion

Equilibrium: capacity as function of chemistry and adsorbents

Mixing: dispersion and advection

Batch/CSTR ?

Fixed-bed ?

Fluidized-bed ?

Continuously operated fluidized-bed

02468

101214161820

0 10 20 30 40 50Ti me, hr

Effl

unet

con

cent

rati

on,

ppm

89

1011121314151617

0 10 20 30 40Ti me, hr

Bed

Heig

ht,c

m

Major obstacles and challenges• Reluctance to use by industries

• Organic leaching

• Waste biosorbent disposoal

• Physical properties

• Optimization of specific biosorption process

Prevention of TOC leaching-most recently development

• Organic leaching has been extremely if raw seaweeds are used.

• formaldehyde has been used for surface modification and the resulting TOC significantly reduces to below 5 ppm

• The biosorptive capacity increases and pH becomes more stable.

Summary• Biosorption of metals becomes more attractive due

to high removal capacity, high kinetics, low cost and possibility to recover metals.

• Biosorption is highly depended on pH.• Various mechanisms lead to the metal uptake.• Kinetics is mainly controlled by diffusion.• Various reactor configurations can be used.• Challenges still remain in the way leading to full-

scale industrial application.

acknowledgement Professor Sotira Yiacoumi of Georgia Tech Professor L. Hong of NUS for XPS and FTIR Post-graduate students in NUS:

Dr S.N. WuMs J. PengMs L. WangMr P.X. ShengMr L. YangMs. LH Tan