Nanotechnology with Nanoparticles (NPs) can be highly reactive due - - PowerPoint PPT Presentation

Hong Kong University of Science and Technology

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Hong Kong University of Science and Technology

Nanotechnology with Magnetic Separation Unit for Wastewater Treatment

Professor Irene M. C. Lo, PhD, FHKIE, FASCE Department of Civil and Environmental Engineering Hong Kong University of Science and Technology Drainage Services Department Research & Development Forum 2013

5 December 2013 R&D Forum 2013

Hong Kong University of Science and Technology

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Nanoparticles- widely used nanotechnology

• Nanoparticles (NPs) can be highly reactive due to

– large surface area – greater number of reactive sites

• Rapid removal of contaminant concentrations

(Tratnyek and Johnson, 2006, nanotoday)

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Global Market of Metal Oxide Nanoparticles

• Conservative market estimates for metal oxide

nanoparticles in 2012 are 270, 041 tons, rising to 1,663,168 tons by 2020.

Source: Future Markets, Inc./Nanotech Magazine <info@futuremarketsinc.com>

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Synthesizing Methods

Surfactant Fe2+, Fe3+, NH4OH ( or +Me) Magnetite particle

pH 8.0 (or 10)

Maghemite nanogel Oil bath Maghemite nanoparticles (< 10 nm, ~ 160 m2/g) Ethanol washing Octyl ether

• Sol-gel method

Maghemite (γ-Fe2O3) nanoparticles

Sol-gel method: γ-Fe2O3 magnetic nanoparticles

3 nm 7 nm 11 nm

3nm 7nm 11nm

magnet

US Patent 7622423

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Characterization of Magnetic NPs

• Surface area; microporous:

– BET Analyzer

• Particle dimension:

– TEM, SEM

• Morphology; chemistry; binding:

– XRD, AFM, XRF, XPS

• Magnetic properties:

– Vibrating sample magnetometer (VSM)

– Tendency to be attracted by magnetic fields

Removal Rate and Capacity Removal Mechanisms NPs Recovery

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Application: wastewater treatment

• Iron-based nanoparticles (NPs) for removal of heavy

metals (Ponder et al., 2000, Environ. Sci. Technol.; Mak and Chen, 2004, Dyes Pigments)

• NPs with magnetic properties for wastewater treatment

removing anionic metals (Cr, As), nitrate & phosphate

(Wang and Lo, 2009, Water Res.; Tang et al., 2010, Environ. Eng. Sci.; Tang and Lo, 2013, Water Res.)

Potential advantages Implications for industrial applications Large adsorption capacity Superior removal Short adsorption time Space saving Magnetic separation Recovery/collection of NPs Ease of desorption Regeneration of NPs for reuse

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Metal adsorption by γ-Fe2O3 magnetic NP

Metal removal selectivity due to the changes in surface charges with pH Short equilibrium time (5 min)

(Hu at al. 2005, Water Res.)

10 20 30 40 50 60 70 80 90 100 1 2 3 4 5 6 7 8 9 10 11 pH Removal efficiency(%) Cu(II) Ni(II) Cr(VI)

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Problems/challenges

• Recovery by magnetic field
• Regeneration of magnetic particles

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Recovery by magnetic field

Magnetic separation requirement

• Magnetic behaviour: superparamagnetic
• Although iron-based magnetic NPs can be recovered

by magnetic field, the magnetic force decreases with the particle size decrease (Ngomsik et al., 2005, C. R. Chimie)

• Very strong magnetic field is required for NPs

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Recovery by magnetic field-cont.

(3-acrylamidopropyl)trimethylammonium chloride (APTMCl) (monomer) N,N’-methylenebisa-crylamide (MBA) (crosslinker) N,N,N’,N’- tetramethylethylenediamine

(TEMED) (accelerator)

potassium persulfate

(KPS) (initiator)

Magnetic hydrogels (polymeric microparticles) 10 μm-contain more functional groups- positive surface charges

γ-Fe2O3 embedded polymeric microparticles (10 μm)

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Recovery by magnetic field-cont.

• high removal rate
• Very high Cr removal capacity

(200 mg/g) due to trimethyl ammonium functional group

γ-Fe2O3 embedded polymeric microparticles (10 μm)

20 40 60 80 100 1 2 3 4 5

Cr(VI) removal (%) Time (minutes)

50 100 150 200 250 50 100 150 200

Cr(VI) sorbed (mg/g)

Equilibirum Cr(VI) aqueous concentration (mg/L)

(Tang et al., 2010, Environ. Eng. Sci.)

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Recovery by magnetic field-cont.

50 100 150 200 250 500 1000 1500 2000 NO3- adsorbed (mg/g) Equilibrium NO3- aqueous concentration (mg/L)

50 100 150 200 250 500 1000 1500 2000 2500 3000 3500 4000 PO43- adsorbed (mg/g) Equilibrium PO43- aqueous concentration (mg/L)

The maximum adsorption capacities for NO3

• is found to be 187.73 mg/g and for

PO4

3- to be 226.89 mg/g.

γ-Fe2O3 embedded polymeric microparticles (10 μm)

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Problems/challenges

• Recovery by magnetic field
• Regeneration of magnetic particles

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Regeneration (from batch study)

• Cr(VI) is adsorbed via a weak electrostatic interaction (ion

exchange). So a reversible process.

• High Cr(VI) recovery after 3 consecutive cycles of the

adsorption-desorption process

γ-Fe2O3 embedded polymeric microparticles

(Tang et al., 2010, Environ. Eng. Sci.)

Using NaCl for regeneration

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Regeneration (from batch study) – Cont.

1 g/L magnetic hydrogel in 80 mL = 0.08 g Influent-to-regeneration solution ratio (v:v): 80 + 80 : 2 + 2 = 160 : 4 = 40:1 Process Conc. Vol. (mL) Duration (min) 1st Adsorption 20 mg/L Cr(VI) 80 15 2nd Adsorption 20 mg/L Cr(VI) 80 15 Desorption 3 M NaCl 2+2* 15 + 15*

Batch study

90 92 94 96 98 100 0.5 1 1.5 Cr removal efficiency (%) Effluent Cr conc. (mg/L)

1st adsorption

Effluent Cr conc. Cr removal efficiency 90 92 94 96 98 100 0.5 1 1.5 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Cr removal efficiency (%) Effluent Cr conc. (mg/L)

• No. of cycle of adsorption-desorption

2nd adsorption

Effluent Cr conc. Cr removal efficiency 100 200 300 400 500 600 700 Cr recovery conc. (mg/L)

Desorption

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Prototype Treatment System (5 L)

• 1. Adsorption
• 2. Particle

Separation

• 3. Desorption (regeneration)
• 4. Particle Recovery

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Prototype Treatment Unit (5 L) –

Removal and Separation

• Using magnetic

particles for wastewater treatment

• Removal efficiency

~ 97-96%

• Separation efficiency

~ 98.5%

• Stable performance

maintained for 20 cycles

80 85 90 95 100 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Separation efficiency (%)

• No. of cycle of adsorption-desorption

80 85 90 95 100 0.0 0.5 1.0 1.5 2.0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Cr removal efficiency (%) Effluent Cr conc. (mg/L)

• No. of cycle of adsorption-desorption

Effluent Cr conc. Cr removal efficiency

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Prototype Treatment Unit (5 L) - Regeneration

• 3M NaCl was used for

regeneration

• Cr recovery

concentration maintained at around 180 mg/L

50 100 150 200 250 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Cr recovery conc. (mg/L)

• No. of cycle of adsorption-desorption

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Patent

Filed the Patent (FI-130018-60:66/C) in China in February 2013 for the invention entitled “Magnetic Separation Unit for Separating Magnetic Nano- or Micro-particles from Treated Water in a Water or Wastewater Treatment System” (Ref.: TTC.PA.0582).

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Hong Kong University of Science and Technology