L10- Adsorption Flashcards
Adsorption & methods
Removal of substances in a solution by accumulation on a solid phase
Methods:
passing liquid through bed of adsorbent;
blending adsorbent material with water followed by sedimentation/filtration
Type of adsorbents & evaluate each
Activated carbon: remove chlorine and organics (VOCs), odour- low cost but regeneration issues
Granular Ferric Hydroxide (GFH): remove arsenic, chromium etc. - high cost but disposal at end rather than regeneration
Activated Alumina: from naturally occuring bauxite, removal of arsenic and chlorides - regeneration with base/acids, but waste management issues
Suspended and dissolved particles
Suspended- do not dissolve, stay suspended - inc. organic colloids, insoluble metal hydroxides
Dissolved- remain dissolved- inc. pesticides, heavy metal ions
Adsorbate and adsorbent
Adsorbate - substance being removed
Absorbent- surface which adsorbate accumulates (activated carbon and synthetic materials used for adsorption)
Stages of adsorption (kinetics)
Bulk solution transport
FIlm diffusion transport
Pore and surface transport
Adsorption
Mass balance of adsorption - define variables
Initial adsorbate - final adsorbate = amount adsorbed
VC0 - VCe = qe*M
-> qe = [V*(C0-Ce)/M]
qe = equilibrium adsorption capacity (mg/g)
V = total volume of solution (L)
C0 = initial concentraion of solute (mg/L)
Ce = equilibrium concentration of solute (mg/L)
M = mass of adsorbent (g)
Isotherm & factors affecting adsorption
Plot of adsorption capacity (qe) against equilibrium concentration (Ce)
Factors: Adsorbent does, size, size distribution, surface charge, pH, temp, pressure, contact time, presence of contaminants
Freundlich equation - define variables
x/m = Kf*Ce^(1/n)
x/m = mass of adsorbent adsorbed per unit mass of adsorbent (mg adsorbate/ g adsorbent)
1/n = Freundlich intensity parameter
Kf = Freundlich capacity factor [(mg adsorbate/g activated carbon)*(L water/mg adsorbate)^(1/n)] [(mg/g)(L/mg)^(1/n)]
Ce = equilibrium concentration of adsorbate in solution after adsorption has occurred (mg/L)
Langmuir equation - define variables
x/m = [(abCe)/(1+ b*Ce)]
x/m = mass of adsorbent adsorbed per unit mass of adsorbent (mg adsorbate/ g adsorbent)
a,b = empirical constants
Ce = equilibrium concentration of adsorbate in solution after adsorption has occurred (mg/L)
Graphically finding Freundlich constant
log(x/m) = logKf + (1/n)*logCe
Plot log(x/m) against logCe
Mass Transfer Zone (MTZ) & describe the process of the breakthrough and exhaustion volume related to MTZ
Area of bed in which sorption is occurring.
No further adsorption occur within bed below MTZ.
As top layers of carbon granules become saturated with organic material, MTZ move down bed until breakthrough
Volume of given water processed until breakthrough and exhaustion - VBT and VE
Breakthrough curve description and phases
Relationship between the effluent concentration of a particular pollutant and the volume of water that has passed through an adsorbent bed over time.
Used to evaluate the performance of an adsorbent system and to determine when the system is no longer effective in removing the target pollutant.
Process limitations of adsorption
Logistics involved with transporting large volumes of adsorbent materials
Area requirements for carbon contactors
Production of waste adsorbent
Graphically finding Langmuir constant
Ce/(x/m) = 1/ab + (1/a)*Ce
Plot Ce/(x/m) against Ce
Breakthrough curve effect of using different compounds (nonadsorbable, biodegradable)
Shape depends on whether applied liquid contains nonadsorbable and biodegradable constituents
Nonadsorbable constituents may reduce the effectiveness of the system by competing for adsorption sites or causing fouling
Biodegradable constituents may have a variable effect on the performance of the system, depending on the specific constituents and the presence of beneficial microorganisms.
