Adsorption l Adsorption Process by which a solute

Adsorption l 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 1

Aqueous Phase Napthalene dissolved in aqueous phase Adsorption Reactive surface site Solid Surface Adapted from Fundamentals of Environmental Engineering, Mihelcic 2

Adsorption to a pore 3

Terms l Adsorbate » Substance removed from liquid phase l Adsorbent » Solid phase on which accumulation occurs l Example » color can be removed from water using activated carbon. Color is the adsorbate, activated carbon is the adsorbent 4

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

Physical (cont. ) l Hydrogen Bonding » special case of dipole-dipole interaction, involves hydrogen atom with slightly positive charge l 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 6

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

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

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

Adsorbates of Interest (cont. ) l Humic substances » large natural organics, often color forming, with molecular weights ranging from few hundred to hundred thousands. Adsorption properties vary widely. Halomethanes can be formed when water containing humic substances is chlorinated. H Methane molecule with halogens (Cl, Br, . . . ) H C H substituted for H’s. Some are carcinogens. H 10

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

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

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 18 th century, carbons made from blood, wood 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 Ph. D and began working in x-ray diffraction. 13

What is Activated Carbon? l 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 ü 500 - 1000 m 2/g » Creates active adsorption sites ücarbon is non-polar, good for adsorbing nonpolar compounds 14

Activated Carbon Picture Source: solomon. bond. okstate. edu/thinkchem 97/experiments/lab 7. html 15

Types l PAC: Powdered activated carbon » A fine powder, < 0. 05 mm dia. » As much as 100 acres of surface area / lb üPore sizes down to 10 x 10 -7 m. l GAC: Granular activated carbon » 0. 3 - 3 mm » Not as much surface area as PAC 16

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

How do we use GAC? l Water Treatment » As filter media to assist in taste and odor removal Water Head Activated Carbon Bed Sand Bed Under drain 18

GAC Use (cont. ) l Clean contaminated groundwater » Counter flow üdirtiest GAC contacts dirtiest water ücontinuous or batch addition of fresh GAC & removal of dirty GAC 19

Gas Station Site Clean Water Dirty Water Drums of Activated Carbon Contaminated Aquifer Groundwater Pumping Well 20

Gas Station Site First Drum gets dirty fastest Drums of Activated Carbon Contaminated Aquifer Groundwater Pumping Well 21

Gas Station Site Add clean drum at end Pull first drum Drums of Activated Carbon Contaminated Aquifer Groundwater Pumping Well 22

Single Tank Dirty GAC Clean GAC Dirty Water Clean Water 23

Design l Pass contaminated water through single or series of columns » Use constant Loading Rate (flow/area) and Influent Concentration l Record concentration at difference points along column(s) over time l Plot Breakthrough & Bed Service Time Curves l Determine width & velocity of Adsorption Zone » determine # of columns needed, amount of adsorbant needed 24

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

Experiment SP 2 Column 3 Column 2 Column 1 SP 3 2. 3 m SP 4 26