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

INTRODUCTION

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

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

Water drinking Criteria *WHO: World Health Organization

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

+ 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

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 150-700 High to (700 oC) Municipal sewage sludge Cd2+ 500 - 900 High to (900 oC) Broiler-litter Pb2+ 350-650 Low to (350 oC) Giant Miscanthus 300-600 No effect No study effect of pyrolytic conditions (temperatures and heating times) on Cd2+ adsorption capacity on OP-derived biochar

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

Materials and Methods

Orange peel Biochar

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

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

Results and discussion

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

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

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

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

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

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

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:

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

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

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.

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)

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)

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)

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

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

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+

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

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

Conclusions

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

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 114.69 mg/g.

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

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, 2016. 34(2): p. 129-138.