Dr J. Paul Chen Department of Chemical & Environmental Engineering

1. 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

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

3. Major Industries in Singapore Jurong Island: Integrated Petrochemical Hub 1S$=4.75 RMB • 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

4. 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.

5. 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.

6. Log K Ca2+ 1.30 Co2+ 4.31 Ni2+ 5.36 Cu2+ 8.11 Zn2+ 4.58 Cd2+ 3.98 Pb2+ 4.15 Affinity of metal with organics • L-2-Aminopropanoic Acid (Alanine) with various metal Metal Ions 1. Immobilization of organics; 2. use of organics in natural biosolids

7. 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.

8. 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.  

9. 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. 

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

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

12. Why biosorption ? Cu sorption

13. 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

14. Biosorption Equilibrium

15. Metal biosorptive properties: pH effectSOH + Mm+ = SO-Mm+ + H+ Sargassum Ca-alginate

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

17. Algae as the biosorbents

18. 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

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

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

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

22. Two-pK Triple-Layer Model - MSCF M=Cu, or Zn, or Co, X=Cl, or NO3, or ClO4 yo=eyo / kT and yb=eyb/kT referred to o-layer and b-layer

23. 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.

24. Conceptual model for the metal removal by ion exchange. + Ca2+ M = Cu and Pb

25. 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.

26. 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

27. Prediction of Competitive Biosorption by CABIER

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

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

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

31. Bisorption Kinetics

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

33. C o n c e n t r a t i o n m P o r o u s A d s o r b e n t r e , B u l k L i q u i d p p C j k f j L i q u i d F i l m c ( r = a ) j p D p j c j c j q j q j a p r , d i s t a n c e m e a s u r e d f r o m a d s o r b e n t p a r t i c l e c e n t e r Sorption Kinetics of Metal Ions: Diffusion-Controlled Model 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. 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

34. An Intraparticle Diffusion Model for Metal Uptake Kinetics

35. kinetics of metal biosorption

36. Engineering applications

37. Continuously operated system for metal treatment – an engineered approach Fixed-bed ? Batch/CSTR ? Kinetics: external mass transfer and internal diffusion Equilibrium: capacity as function of chemistry and adsorbents Mixing: dispersion and advection Fluidized-bed ?

38. Continuously operated fluidized-bed

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

40. 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.

41. 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.

42. 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