1. Adsorption Capacity and Mechanism of Cadmium on Orange Peel-Derived Biochar Produced at Different Pyrolysis Temperatures and Times
Chung
Yuan
Christian
University,
Taiwan
Tran Nguyen Hai
Sheng-Jie You
Huan-Ping  Chao
The 3st International Conference on Solid Waste Technology and Management
Philadelphia, PA, U.S.A
April 3-6, 2016

2. INTRODUCTION

3. Cadmium into water environment
Mining
industry
Metallurgical
industry
Cadmium into water environment
Battery
industry
Alloy
industry
Metal plating
industry

4.  1912 in Japan
Cd replaces Ca in human bone
 Itai – Itai
disease

5. Water drinking Criteria
*WHO: World Health Organization

6. Techniques for Cd removal
Sludge
Disposal
Low concentration
Cd removal
Ultrafiltration
/reverse osmosis
Lime precipitation
Ion exchange
Adsorption
Low cost
Recovery/reuse
Activated carbon
Biochar
Bio-sorbent

7. + Estimated cost: biochar (~ US$ 246/ ton) << AC (~ US$ 1500 per/ton) biochar requires less energy than AC and can be used without further activation or modification +Biochar ~ synthesized using biomass produced via thermal carbonization under O2 limited, N2 atmosphere, or vacuum condition ~ a potential candidate for wastewater treatment because of its porous structure, high surface area, large pore volumes and the availability of abundant functional groups

8. Pyrolysis temperatures (oC) The highest adsorption capacity
Pyrolysis temperatures Adsorption capacity
Biochar
Adsorbate
Pyrolysis temperatures (oC)
The highest adsorption capacity
Orange peel
Naphthalene,
1-naphthol
High to (700 oC)
Municipal sewage sludge
Cd2+
High to (900 oC)
Broiler-litter
Pb2+
Low to (350 oC)
Giant Miscanthus
No effect
No study effect of pyrolytic conditions (temperatures and heating times) on Cd2+ adsorption capacity on OP-derived biochar

9. Research Objectives
(1) To investigate the effects of pyrolysis temperature and heating time on the adsorption capacity of Cd2+ onto biochar derived from orange peel
(2) To publish potential adsorption mechanisms

10. Materials and Methods

11. Orange peel
Biochar

12. Biochar Batch experiments Characterizations
Biochar/Cd2+ solution = 2 g/L
30 oC
150 rpm
Effect of pH (4 - 8)
Adsorption kinetics
Adsorption isotherms
Batch experiments
Adsorption
mechanisms
Biochar
Proximate analysis (i.e. moisture, volatile, …)
pH at point zero charge (pzc)
FTIR
XRD
SEM + EDX
Characterizations

13. OP: orange peel ~ biosorbent
B500-2: biochar produced at 500 oC for 2h
Biochar
Pyrolysis time
Pyrolysis temperature

14. Results and discussion

15. Proximate analysis (wt. % by dry basis)
+ Release of alkali salts from OP during pyrolysis
+ Carbonate formation (i.e. CaCO3)

16. Proximate analysis (wt. % by dry basis)
Destruction:
+ Hemicellulose
+ Cellulose
+ Lignin

17. Proximate analysis (wt. % by dry basis)
Low moisture
and volatile
High quality of biochar

18. Proximate analysis (wt. % by dry basis)
Pyrolysis
temperature and time
Fixed carbon

19. Point of zero charge and effect of pH value (1/2)
pHPZC ~ 9.5
Orange peel
(+) charge
(-) charge
Surface charge
of biochar
will be positive when pH of solution < 9.5

20. Point of zero charge and Electrostatic attraction
effect of pH value (2/2)
Adsorption mechanism:
Electrostatic attraction
pH ~ 7.0
C0 = 100 mg/L
Chemical interaction with sufficient energy to overcome the surface-ion repulsion
Biochar
Cd2+ +
pHpzc ~ 9.5

21. Adsorption kinetics (1/2)
C0 = 100 mg/L
Adsorption occurred rapidly;
80.6– 96.9% of the total Cd2+ in the solutions was removed within the first minute.
Pseudo-first-order:
Non-linear
method
Pseudo-second-order:

22. Adsorption kinetics (2/2)
C0 = 100 mg/L
Cd2+ adsorption onto biochar is chemisorption

23. Adsorption isotherms (1/4)
+ The Langmuir model
+ The Freundlich model
A dimensionless constant separation factor
Adsorption system is:
+ 0<RL<1: favourable
+ RL > 1: unfavourable
+ RL= l: linear
+ RL= 0: irreversible

24. R2 - Langmuir >> Freundlich χ2 - Langmuir << Freundlich
Langmuir region
R2 - Langmuir >> Freundlich
χ2 - Langmuir << Freundlich
Adsorption characteristics of Cd2+ on biochar were described by Langmuir model.

25. Qomax values slightly increased with an increase in pyrolysis temperature and time.
However, this increase did not indicate a statistically significant difference (p>0.01)

26. favourable (0<RL<l),
The effect of the isotherm shape was used to predict whether an adsorption system is
favourable (0<RL<l),
linear (RL=l), or
irreversible (RL=0)

27. Adsorption mechanisms (1/4)
1. Cπ–cation interactions
The Fourier Transform Infrared Spectroscopy (FTIR)
The peaks corresponding to C=C and C=O form indicated surface complexation of heavy metal through delocalized π electrons.
(Rivera-Utrilla and SánchezPolo, 2011; Xu et al., 2013b)

28. Adsorption mechanisms (2/4)
Cd3CO3
Surface precipitation or/and
ion exchange ???
(Cd, Ca)CO3
CaCO3
The X-ray diffraction spectrum (XRD)

29. Adsorption mechanisms (3/4)
2. Surface precipitation
Before
After Cd Ca Ca
Scanning electron microscopy (SEM) and X-ray spectroscopy (EDX )

30. SEM of biochar after adsorption of Cd2+
X 10,000
Precipitation of (Ca,Cd) CO3 on biochar’s surface
X 2,000
SEM of biochar after adsorption of Cd2+

31. Adsorption mechanisms (2/4)
528 m2/g
548 m2/g
Pore filling ~ negligible

32. Comparison
Biochar derived from OP is a favourable alternative for Cd2+ removal from an aqueous solution.

33. Conclusions

34. Conclusions (1/4)
The surface charge of biochar was independent of the carbonization of OP, with the pHpzc of biochar approaching 9.5
Equilibrium can be reached rapid (within 1 min) in kinetic experiments and a removal rate of 81-97% can be generated.
The results fitted the pseudo-second-order model closely

35. Conclusions (2/4)
The adsorption capacity was estimated using Langmuir model.
The maximum adsorption capacity of Cd2+ onto biochar was independent of the pyrolysis temperature and heating time (p>0.01).
The maximum adsorption capacity of Cd2+ was mg/g.

36. Conclusions (3/4)
The SBET of biochar is 548 m2/g, total pore volume (0.236 cm3/g), and micropore volume (0.105 cm3/g)
The primary adsorption mechanisms were regarded
(1) Cπ–cation interactions
(2) surface precipitation in form of (Ca,Cd)CO3

37. Conclusions (4/4) Acknowledgements
This study suggests that OP-derived biochar might be used as an effective, low- cost and environmentally friendly adsorbent for Cd removal in an aqueous solution.
Acknowledgements
This current work was financially supported by Chung Yuan Christian University (CYCU) in Taiwan. First author would like to thank CYCU for the Distinguished International Graduate Students (DIGS) scholarship to pursue his doctoral studies.
Tran, H.N., S.-J. You, and H.-P. Chao, Effect of pyrolysis temperatures and times on the adsorption of cadmium onto orange peel derived biochar. Waste Management & Research, (2): p