SLIDE 1 15.10.2018 Lecture No. 21 Lecture Name: Geomaterial Characterization
Sub-topics
- Chemical characterization
Sorption-Desorption Characteristics Determination of kd (The Distribution coefficient)
- Thermal Characterization
- Electrical Characterization
SLIDE 2
Sorption Absorption Adsorption atoms or molecules move into the bulk of a porous material, e.g. the absorption of water by a sponge Atoms or molecules move from the bulk phase (that is, solid, liquid, or gas) onto a solid or liquid surface.
Incorporation, Assimilation, Inclusion Accumulation of substance on surface
e.g. purification by adsorption where impurities are filtered from liquids or gases by their adsorption onto the surface of a high-surface-area solid such as activated charcoal The adhesion of a thin layer of molecules of some substance to the surface of a solid or liquid
SLIDE 3 Terms related to Sorption
- Adsorbates - molecules that have been adsorbed onto solid surfaces
- Substrate or Adsorbent - the surface to which adsorbates are adsorbed
- e.g. in case of adsorbed cations tightly held on surfaces of negatively
charged dry clay particles, clay particle is substrate and cations are adorbates. Clay particle
cations
SLIDE 4 Desorption
- a phenomenon whereby a substance is released from or through a
surface
- process is the opposite of sorption
- ccurs in a system being in the state of sorption equilibrium between
bulk phase (fluid, i.e. gas or liquid solution) and an adsorbing surface (solid or boundary separating two fluids)
- When the concentration (or pressure) of substance in the bulk phase
is lowered, some of the sorbed substance moves to the bulk state
SLIDE 5
- Soil washing
- Soil flushing
- Vitrification
- Solidification
- Immobilization
Important to determine Sorption and Desorption Characteristics of Geomaterial and Immobilizing Agents
SORPTION & DESORPTION CHARACTERISTICS
Strategies for Remediation of Contaminated Soils/Geomaterials (Site cleanup/Site remediation) Excellent philosophy to simulate geomaterial-contaminant interaction Sorption and Desorption are opposite interaction mechanisms
SLIDE 6 Importance of Sorption and Desorption Characteristics
- Fate and Transport of Reactive Contaminant(s)
- Efficiency of Environmental Cleanup Strategies
- Selection of Suitable Geological Formations and Backfill Materials
- Design of Barrier Layers of Waste Containment System
- Accumulation of Heavy Metals and Pesticides in Subsoil
Challenge Precise Determination of these Characteristics (kd & kdl) in a short duration kd : the coefficient describing sorption process kdl : the coefficient describing desorption process (subscript l corresponds to leaching process)
SLIDE 7 Also known as the partition(ing) or distribution coefficient Is a measure of sorption of contaminants to soils/rocks/admixtures (geomaterials). Defined as the ratio of the quantity of the sorbate sorbed per unit mass
- f solids (Cs) to the amount of the sorbate remaining in solution (Cw), at
equilibrium. The reverse is true for desorption (leaching) process
The coefficient kd
Kd measurement, some issues Experimental conditions Measurement methodology Contaminant chemical characteristics Sorbents (particle size, geochemistry) Type (active/passive) and concentration of the sorbate
SLIDE 8 Partitioning Relationships
Water L / mg Solid Kg / mg K C C
d W S
water m / mg air m / mol (H) constant law s Henry' C C
3 3 w g
Contaminant Concentration in geomaterials Total mass in unit volume of geomaterial
CT =
b
.Cs + θw.CW + θg.Cg
If soil is saturated, θg = 0 and θw =
b T
C
Cs + Cw
θw
: Volumetric water content
θg
: Volumetric vapour content
θ = SaturationPorosity ()
b
= bulk density of porous medium Cs: Sorbate sorbed per unit mass of solids Cw: Sorbate remaining in the solution, at equilibrium.
SLIDE 9 Determination of Sorption and Desoprtion Characteristics
- f Geomaterials
- 1. Batch Tests
Fail to simulate “Geomaterial-Contaminant- immobilizing agent Interaction” in a realistic manner Fail to come up with recommendations regarding Generalized Isotherm
Quite Time and Cost Intensive “Low Hydraulic Conductivity” Accelerated Physical Modeling Using a Geotechnical Centrifuge seems to be a viable option In situ field batch tests Field modelling tests koc method koc = kd.(100/OC) koc = organic carbon normalized adsorption coefficient OC = percentage of organic carbon in the sample (g/g)
SLIDE 10
Available Methodologies
ASTM (American Society of Testing and Materials). 1987. “24-hour Batch- Type Measurement of Contaminant Sorption by Soils and Sediments.” In Annual Book of ASTM Standards, Water and Environmental Technology, Volume 11.04, pp. 163-167, Philadelphia, Pennsylvania. ASTM 1988. “Determining a Sorption Constant (koc) for an Organic Chemical in Soil and Sediments.” In Annual Book of ASTM Standards, Water and Environmental Technology. Volume 11.04, pp. 731-737, Philadelphia, Pennsylvania. OCED TG 106, 2000, Determination of Soil Adsorption/Desorption Using a Batch Equilibrium Method.
OECD: Organization for Economic Co-operation and Development
SLIDE 11 Factors Influencing Sorption and Desorption Characteristics
- Specific-surface Area
- Pozzolanic Activity (Lime Reactivity)
- CEC Value
- Liquid to Solid Ratio
- pH of the Soil Solution
- Buffer Capacity of the Sorbent
- Temperature
- Grain Size
- Presence of other Ions
- Ionic Strength
- Organic Content & Fe- Mn Oxides
- Carbonate Content
SLIDE 12 Factors Influencing
- Liquid to solid ratio (L/S = 10, 20, 50, 100, 200)
Interaction time
Batch Sorption Tests
Geomaterial (in powder form) + Contaminant (in solution form) is allowed to interact for certain duration (with continuous stirring)
Ci Initial concentration of contaminant Ce Concentration of contaminant in solution after time interaction time is to be recorded by sampling the solution frequently Cs Concentration of the contaminant sorbed
(L/S) C C C
e i s
0.01 0.1 1 10 100 20 40 60 80 100
Ce (mg/l)
ts (h)
L/S 10 20 50 100 200
24 h
Variation of Ce with interaction time
SLIDE 13 1000 2000 3000 4000 5000 0.0 0.7 1.4 2.1 2.8 10
10 10
2
10
4
10
1
10
3
10
5
1000 2000 3000 4000 5000 0.00 0.25 0.50 0.75 1.00
Ce (mg/l) L/S 10 20 50 100 200 Cs (10
4 mg/kg)
LR FH
Cs (mg/kg)
LM
Ce/Cs (kg/l)
Linear Isotherm (LR) Cs = Kd· Ce
b b
e s e
C K 1 C C
d
Langmuir Isotherm (LM)
) log(C n ) log(K ) log(C
e
d s
Freundlich Isotherm(FH)
Sorption Characteristics (Isotherms)
SLIDE 14 (L/S) C C C
el s l s
Desorption Characteristics (Isotherms)
el dl sl
C K C
Linear Isotherm (LR)
l el l l d sl el
C K 1 C C b b
Langmuir Isotherm (LM)
) log(C n ) log(K ) log(C
el
l dl sl
Freundlich Isotherm (FH) Csl : the amount of contaminants present in the sorbate after desorption phenomena Cel : the equilibrium concentration of contaminants present in the solution after equilibration time Cs : Concentration of the contaminant sorbed
0.01 0.1 1 10 100 0.1 1 10 100
L/S 10 20 50 100 200
Cel(mg/l) tl (h)
2 h
Variation of Cel with leaching time
SLIDE 15 Principal minerals CEC (meq/100 g) Kd (ml/g)
Quartz, Montmorillonite 49-57 3347-3580 Quartz, Orthoclase 6.4-6.6 1497-1530
Relationship between CEC and Kd
20 40 60 80 100
100 1000 10000
L/S
Kd(ml/g)
SLIDE 16 Some Important Relationships
5 10 15 20 25 2400 2800 3200 3600
kd (ml/g) t (h)
3 4 5 6 7 8 9 2000 4000 6000 8000 10000 12000
Kd (ml/g) pH
SLIDE 17 10 10
1
10
2
10
3
10
1
10
2
10
3
10
4
10
5
Material CS WC IC RSS BSS FA-I FA-II EC (mS/cm)
L/S
10
10 10
1
10
2
10
3
10
4
10
1
10
2
10
3
10
4
10
5
10
10
10 10
1
10
2
10
3
EC (mS/cm) Kd (l/kg)
89
1000
Material
CS WC IC RSS BSS FA-I FA-II
Kdl (l/kg)
9.8
“Accelerated Physical Modeling of Sorption and Desorption Characteristics
- f Geomaterials and Immobilizing Agents”
Dali Naidu (2006)
SLIDE 18 Column Tests
PV= Vsol[L(d2/4)]-1
Vsol is the volume of the solute passing through the sample L is the length of the sample, is the porosity
sample
55
L
Porous disc
h1
100 10 140
Inner cylinder Middle cylinder Outer cylinder Base plate
20 40 60 80 100 120 140 160 0.0 0.2 0.4 0.6 0.8 1.0 Sorption
Desorption starts @ 62 h
Ct/C0 t (h)
The BTC
SLIDE 19 z C R v z C R D t C
s 2 2
i
η K ρ 1 R
dry d
ysorption = 1 Ydesorption = 0.5
A C mC mA AC B C mC mB BC A B mB mA AB
N N ln t t ln y and N N ln t t ln y , N N ln t t ln y
y A mA p
N t t
t C . η K . ρ z C v z C D t C
d dry s. 2 2 i.
1-D ADE R = Retardation factor Centrifuge Modeling of Sorption/Desorption mechanisms . ......... N t N t N t t
y C mC y B mB y A mA p
