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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

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Outline of Presentation Motivation Historical background Current development Application Mechanisms Future trends Summary

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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$75 billion by 2010 Jurong Island: Integrated Petrochemical Hub 1S$=4.75 RMB

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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.

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Why do we care... metal ? Contd 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.

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Affinity of metal with organics L-2-Aminopropanoic Acid (Alanine) with various metal Log K Ca 2+ 1.30 Co 2+ 4.31 Ni 2+ 5.36 Cu 2+ 8.11 Zn 2+ 4.58 Cd 2+ 3.98 Pb 2+ 4.15 Metal Ions 1. Immobilization of organics; 2. use of organics in natural biosolids

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Historical background: 1980-1995 Biosorption 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.

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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.

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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.

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Case presents Raw seaweeds collected in Singapore Ca-alginate beads Ca-alginate based ion exchange resin (CABIER)

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Examples: Marine Algal collected in Singapore Padina sp. Sargassum sp.

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Why biosorption ? Cu sorption

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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

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Biosorption Equilibrium

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Metal biosorptive properties: pH effect SOH + M m+ = SO-M m+ + H + Sargassum Ca-alginate

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Metal biosorptive properties: pH effect Metal biosorptive properties: ionic strength effect

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Algae as the biosorbents

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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

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XPS spectra of Pb- and Cu-adsorbed CABIER -O-M-O-

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XPS Analysis Note that BE values of 577.2 and 579 represent Cr (III) and Cr (VI) Uptake reduction and MSCF Raw Padina Cr(VI): pH 1 Cr(VI): pH 2Cr(III): pH 4 577.1 578.5 577.2 579.2 579.5 577.5

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biosorption of Metal Ions: Surface Complex Formation Model biosorption results from reactions between functional groups of adsorbents and metal ion species.

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Two-pK Triple-Layer Model - MSCF M=Cu, or Zn, or Co, X=Cl, or NO 3, or ClO 4 y o =e o / kT and y =e / kT referred to o-layer and -layer

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MSCF for Cu biosorption by Ca-alginate beads Chen, J.P., et al., Environmental Science and Technology, Vol. 31, No. 5, pp. 1433-1439, 1997.

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Conceptual model for the metal removal by ion exchange. + Ca 2+ M = Cu and Pb

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Ion exchange in biosorption (e.g. by CABIER) 1. M 2+ + Ca-R M-R + Ca 2+ (ion exchange) 2. M 2+ + R 2- M-R (R: unreacted group) (elementary coordination) 3. 2H + + Ca-R H 2 -R + Ca 2+ (pH effect) and 4. solution and precipitation reactions.. Chen, J.P. et al., Langmuir, Vol. 18, No. 24, pp. 9413-9421, 2002.

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Prediction of pH Effect on Metal Removal by CABIER [Pb] o = 1.0 10 -4 M, m=1 g/L, [Cu] o =1.0 10 -4 M, m=0.15 g/L. modeling

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Prediction of Competitive Biosorption by CABIER

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Generalized approach for the simulations- MINEQL Solution Reactions: Adsorption Reactions: Precipitation Reactions: EDL

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Solution and Precipitation Reactions in the Modeling Chen, J.P. and Lin, M.S. Water Research, Vol. 35, No. 10, pp. 2385-2394, 2001.

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How about modeling for metal reduction ? NO solution yet !!! It is on-going; but we may have hard time !!!

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Bisorption Kinetics

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

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Sorption Kinetics of Metal Ions: Diffusion-Controlled Model 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 from either mass transfer of ion species to the surface of sorbents or complexation reactions between functional groups of sorbents and ion species.

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An Intraparticle Diffusion Model for Metal Uptake Kinetics

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kinetics of metal biosorption

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Engineering applications

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Continuously operated system for metal treatment an engineered approach 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 ?

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Continuously operated fluidized-bed

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Major obstacles and challenges Reluctance to use by industries Organic leaching Waste biosorbent disposoal Physical properties Optimization of specific biosorption process

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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.

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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.

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acknowledgement Professor Sotira Yiacoumi of Georgia Tech Professor L. Hong of NUS for XPS and FTIR Post-graduate students in NUS: Dr S.N. Wu Ms J. Peng Ms L. Wang Mr P.X. Sheng Mr L. Yang Ms. LH Tan