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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. Adsorption. Aqueous Phase.

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adsorption
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

slide2

Adsorption

Aqueous Phase

Napthalene dissolved in aqueous phase

Solid Surface

Reactive surface site

Adapted from Fundamentals of Environmental Engineering, Mihelcic

terms
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
physical adsorption
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)
physical cont
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
another way to look at adsorption
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
equilibrium
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
adsorb ates of interest
Adsorbates of Interest
  • Taste and Odor (major interest)
  • Synthetic Organic Compounds (SOC)
    • Aromatic solvents (benzene, toluene)
    • Chlorinated aromatics
    • Pesticides, herbicides
    • Many more
adsorbates of interest cont

H

H

C

H

H

  • Halomethanes can be formed when water containing humic substances is chlorinated.
    • Methane molecule with halogens (Cl, Br,...) substituted for H’s. Some are carcinogens.
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.
adsorbates of interest cont1
Adsorbates of Interest (cont.)
  • Some metals
    • antimony, arsenic, silver, mercury,...
  • Viruses
  • Other inorganics
    • Chlorine, Bromine
adsorb ents
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
history of activated carbon
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.

what is activated carbon
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
activated carbon picture
Activated Carbon Picture

Source: solomon.bond.okstate.edu/thinkchem97/experiments/lab7.html

types
Types
  • PAC: Powdered activated carbon
    • A fine powder, < 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
how do we use pac
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
how do we use gac
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

gac use cont
GAC Use (cont.)
  • Clean contaminated groundwater
    • Counter flow
      • dirtiest GAC contacts dirtiest water
      • continuous or batch addition of fresh GAC & removal of dirty GAC
gas station site
Gas Station Site

Clean Water

Dirty Water

Drums of Activated Carbon

Groundwater

Pumping

Well

Contaminated Aquifer

gas station site1
Gas Station Site

First Drum gets dirty fastest

Drums of Activated Carbon

Groundwater

Pumping

Well

Contaminated Aquifer

gas station site2
Gas Station Site

Add clean drum at end

Pull first drum

Drums of Activated Carbon

Groundwater

Pumping

Well

Contaminated Aquifer

single tank

Dirty Water

Dirty GAC

Clean GAC

Clean Water

Single Tank
design
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
terms1
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.
experiment
Experiment

SP1

Column 1

Column 2

Column 3

2.3 m

SP3

SP4

SP2