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Adsorption

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Acknowledgement: Some of these s were prepared by Dr. J. W. Everett ... antimony, arsenic, silver, mercury,... Viruses. Other inorganics. Chlorine, Bromine ... – PowerPoint PPT presentation

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Title: Adsorption


1
Adsorption
  • Adsorption
  • Process by which a solute accumulates at a
    solid-liquid interface

Acknowledgement Some of these slides were
prepared by Dr. J. W. Everett Professor
of Civil and Environmental Engineering
Rowan University
2
Aqueous Phase
Napthalene dissolved in aqueous phase
Solid Surface
Reactive surface site
Adapted from Fundamentals of Environmental
Engineering, Mihelcic
3
Adsorption to a pore
4
Terms
  • Adsorbate
  • Substance removed from liquid phase
  • Adsorbent
  • Solid phase on which accumulation occurs
  • Example
  • color can be removed from water using activated
    carbon. Color is the adsorbate, activated carbon
    is the adsorbent

5
Physical Adsorption
  • Electrostatic attraction
  • oppositely charged particles
  • Dipole-Dipole Interaction
  • Attraction of two Polar Compounds
  • Polar compounds have an unequal distribution of
    charge (e.g., one end of molecule has slight
    charge, the other a - charge)

6
Physical (cont.)
  • Hydrogen Bonding
  • special case of dipole-dipole interaction,
    involves hydrogen atom with slightly positive
    charge
  • Vander Waals Force
  • Weak attraction caused when close proximity of
    two non-polar molecules causes change in
    distribution of charges, setting up a slight
    dipole-dipole attraction

7
Another way to look at adsorption
  • Molecules prefer to be in lower energy state
  • If molecule can attain lower energy state by
    sticking to a solid surface, it will.
  • E.g., hydrophobic compounds

8
Equilibrium
  • At equilibrium, the chemical of concern will be
    found
  • Dissolved in aqueous phase AND
  • Adsorbed to solid phase adsorbent
  • Adsorption is Reversable
  • add more to aqueous phase - get more adsorption
  • reduce concentration in aqueous phase, get
    desorption

9
Adsorbates of Interest
  • Taste and Odor (major interest)
  • Synthetic Organic Compounds (SOC)
  • Aromatic solvents (benzene, toluene)
  • Chlorinated aromatics
  • Pesticides, herbicides
  • Many more

10
Adsorbates of Interest (cont.)
  • Humic substances
  • large natural organics, often color forming, with
    molecular weights ranging from few hundred to
    hundred thousands. Adsorption properties vary
    widely.

11
Adsorbates of Interest (cont.)
  • Some metals
  • antimony, arsenic, silver, mercury,...
  • Viruses
  • Other inorganics
  • Chlorine, Bromine

12
Adsorbents
  • Activated Carbon
  • Will remove all of the adsorbates mentioned above
    (to varying degrees)
  • by far most popular adsorbent
  • Synthetic resins
  • Zeolites
  • Clays with adsorptive properties

13
History of Activated Carbon
  • Adsorption on porous carbons was described as
    early as 1550 B.C. in an ancient Egyptian papyrus
    and later by Hippocrates and Pliny the Elder,
    mainly for medicinal purposes. In the 18th
    century, carbons made from blood, wood and
    animals were used for the purification of
    liquids.
  • What about the role of Rosalind Franklin?
  • Her work focused on a wartime problem the
    nature of coal and charcoal and how to use them
    most efficiently. She published five papers on
    the subject before she was 26 years old. Her work
    is still quoted today, and helped launch the
    field of high-strength carbon fibers. At 26,
    Franklin had her PhD and began working in x-ray
    diffraction.

14
What is Activated Carbon?
  • Carbon that has been pyrolyzed (heated in a low
    oxygen environment)
  • Burns off tar, volatizes off gases
  • Creates material with lots of pores, thus lots of
    surface area
  • 500 - 1000 m2/g
  • Creates active adsorption sites
  • carbon is non-polar, good for adsorbing non-polar
    compounds

15
Activated Carbon Picture
Source solomon.bond.okstate.edu/thinkchem97/exper
iments/lab7.html
16
Types
  • PAC Powdered activated carbon
  • A fine powder, lt 0.05 mm dia.
  • As much as 100 acres of surface area / lb
  • Pore sizes down to 10 x10-7 m.
  • GAC Granular activated carbon
  • 0.3 - 3 mm
  • Not as much surface area as PAC

17
How do we use PAC?
  • Water Treatment
  • Add it to rapid mix unit, remove in filter
  • do not regenerate
  • Typical dose 5 mg/L
  • Used to remove taste and color

18
How do we use GAC?
  • Water Treatment
  • As filter media to assist in taste and odor
    removal

Water Head
Activated Carbon Bed
Sand Bed
Under drain
19
GAC Use (cont.)
  • Clean contaminated groundwater
  • Counter flow
  • dirtiest GAC contacts dirtiest water
  • continuous or batch addition of fresh GAC
    removal of dirty GAC

20
Gas Station Site
Clean Water
Dirty Water
Drums of Activated Carbon
Groundwater Pumping Well
Contaminated Aquifer
21
Gas Station Site
First Drum gets dirty fastest
Drums of Activated Carbon
Groundwater Pumping Well
Contaminated Aquifer
22
Gas Station Site
Add clean drum at end Pull first drum
Drums of Activated Carbon
Groundwater Pumping Well
Contaminated Aquifer
23
Single Tank
24
Design
  • Pass contaminated water through single or series
    of columns
  • Use constant Loading Rate (flow/area) and
    Influent Concentration
  • Record concentration at difference points along
    column(s) over time
  • Plot Breakthrough Bed Service Time Curves
  • Determine width velocity of Adsorption Zone
  • determine of columns needed, amount of
    adsorbant needed

25
Terms
  • Loading Rate
  • Flux through column, Flow / Area
  • Co
  • Concentration in influent to 1st column
  • Adsorption Zone
  • Zone where majority of adsorption is occurring
  • Defined as zone where concentration is between 10
    and 90 of Co.

26
Experiment
SP1
Column 1
Column 2
Column 3
2.3 m
SP3
SP4
SP2
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