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TEMPLATE DESIGN © 2008
DEVELOPMENT OF NOVEL ADSORBENTS FOR WASTEWATER TREATMENT
Supervisor: Dr. E.P.L Roberts
School of Chemical Engineering and Analytical Sciences, The University of Manchester
Introduction and Project Background
Wastewater treatment using
adsorbents is increasingly gaining
dominance owing to their
environment friendliness and cost-
effectiveness. After adsorbing
pollutants to their saturation
capacity, they lose their ability to
adsorb further and consequently
have to be regenerated.
Adsorbent Synthesis, Properties and Kinetics
The adsorbent (CEG) was prepared using the following scheme:
Stability of Nyex®Regeneration Characteristics
Electrochemical regeneration was performed in a Y-cell (Figure 9):
Conclusions and Future Work
Using a Sieve Tower to get
particles in the range of
250 – 425 microns
Heating Nyex particles to
800 – 850 °C for 60
Compression in a hydraulic
press at 2500 kgf using a 4
Crushing using a blender
at 18000 rpm
Figure 8: Adsorbate loading over time for Nyex and compressed expanded graphite (CEG).
The initial concentration of AV 17 was taken as 100 mg l-1 in both cases with 20 gm Nyex and
10 gm CEG. It can be seen that steady equilibrium is reached after 60 minutes for both the
adsorbents with about 50 – 60 % adsorption taking place within 20 minutes in both cases.
Figure 4: Surface morphology of Nyex® particles (left) at 100 times magnification. The non-
porous structure of Nyex® particles can be seen which leads to a low adsorption capacity. A
schematic (right) of the intercalated structure showing low inter-planar Van der Waals forces.
Figure 6: Procedure for adsorbent synthesis
1. Brown, N.W., et al., (2004). Electrochemical regeneration of a carbon-based adsorbent loaded with crystal violet
dye. Electro Acta, 49: 3269-3281.
2. Celzard, A., et al., (2002). Preparation, electrical and elastic properties of new anisotropic expanded graphite-
based composites. Carbon, 40: 557-566.
Figure 9: Y-cell equipment used for regeneration. Regeneration was performed for 40 minutes
at 1 A current for adsorbents (110 gm Nyex and 50 gm CEG) over 4 adsorption/regeneration
cycles. In each cycle, a fresh batch of AV 17 dye (500 mg l-1 for Nyex and 800 mg l-1 for CEG)
was taken and replaced after every adsorption cycle which lasted for 1 hour.
Adsorption experiments were performed in flasks using Acid Violet
17 (AV 17) dye solutions as the adsorbate loading. The saturation
adsorption capacity (Figure 8) for CEG (8 mg g-1) was found to be
twice that of Nyex® particles (4 mg g-1) due to a higher surface
area and pore volume of CEG particles (17 m2 g-1 and 0.07 cm3
g-1 respectively) as compared to Nyex particles (1 m2 g-1 and
0.004 cm3 g-1 respectively). This finding marked a significant
breakthrough in improving the adsorption properties of Nyex®.
The regeneration efficiencies (ratio of loaded capacity to fresh
capacity) for both CEG and Nyex® particles (Figure 10) were
found to be around 100%, suggesting that the synthesised
adsorbent (CEG) displayed good regeneration behaviour.
Figure 10: Regeneration efficiencies for both Nyex and CEG were found to be similar and
above 100% for theoretical charge passes (21.8 C g-1 for 110 gm Nyex and 48 C g-1 for 50 gm
CEG, implying 1 A for 40 minutes in each case) calculated using Faraday’s Laws. Marginal
decrease in efficiencies below 100% can be attributed to inefficient current passage through
CEG bed required half the cell voltage (Figure 11) for the same
treatment time (40 minutes) over 4 cycles, leading to a lower
power consumption due to a higher electrical conductivity (1.6 S
cm-1) than Nyex® particles (0.8 S cm-1).
Figure 11: Cell potentials for the two adsorbent beds over 4 cycles. Values were recorded over
40 minutes and the error bars show the standard deviation of multiple readings from mean.
Nyex® particles have been observed to break down in solution
during adsorption. To characterise this breakdown, turbidity
measurements were taken to account for the generation of fines.
Figure 12: Turbidimeter (left) used to assess Nyex® attrition and its working principle (right)
Figure 13: Turbidity values after adsorption/regeneration cycles (left) and with/without current
passage (right). Error bars show standard deviation of multiple readings from mean.
Adsorption and regeneration cycles were mimicked with Nyex®
and water solution in a Y-cell to study the fines generation upon
current passage (Figure 13). During regeneration, more fines
were produced and when current was passed, turbidity was
observed to be 30% higher.
The expanded graphite particles can be impregnated and
polymerised with a conductive furan based resin to obtain
composites (Figure 14) with a higher adsorption capacity, which
can be subsequently, carbonised and activated to increase micro-
porosity – a feature lacking in both Nyex® and CEG particles.
Figure 7: Surface morphology of expanded graphite (left) and compressed expanded graphite
(CEG, right) at 200 and 100 times magnification respectively. The expansion of the graphite
layers can be observed in the morphology (SEM) of expanded graphite. The roughness of
edges which lead to enhanced adsorption can be observed on the surface of CEG particles.
Property Nyex® CEG
BET Surface Area 1 m2 g-1 17 m2 g-1 2000 m2 g-1
Specific Pore Volume 0.004 cm3 g-1 0.07 cm3 g-1 0.70 cm3 g-1
Bulk Density 0.80 g cm-3 0.19 g cm-3 0.30 g cm-3
Electrical Conductivity 0.8 S cm-1 1.6 S cm-1 0.012 S cm-1
d) Crushing of
Figure 2: Thermal regeneration drawbacks
Industrially, thermal regeneration is commonly practised but has
its drawbacks (Figure 2) whereas electrochemical regeneration is
an alternative technique which offers many advantages (Figure 3)
Figure 1: Activated Carbon, common
adsorbents for wastewater treatment
5 – 10%
Figure 3: Electrochemical regeneration advantages
Earlier methods of electrochemical regeneration were less
efficient, made use of high charge passes and required long
treatment times. In 2004, using a non-porous graphite intercalated
compound called Nyex® (Figure 4), Brown et al. achieved over
100% regeneration efficiencies within 20 minutes of treatment and
complete adsorption equilibrium within 60 minutes
Idea is to expand the Nyex structure by lowering the Van der Waals
forces between the layered structure, develop expanded graphite
and compress it to form compressed expanded graphite (CEG).
Characterise the attrition behaviour of Nyex® particles as they have been
found to breakdown in solution during regeneration.
Increase the adsorption capacity of Nyex® particles whilst maintaining
similar regeneration efficiencies.
Figure 5: Scheme for the development of compressed expanded graphite
The synthesised adsorbent showed an increased adsorption
capacity due to a higher surface area and consumed lesser power
during regeneration due to a higher electrical conductivity.
Figure 14: Composite synthesis process
Many options for the synthesis of composites can be screened
and explored by building a framework for material modelling of
intercalated compounds at a molecular level using molecular
dynamics (MD) and Monte-Carlo simulations.
Número de incorporações