Sub-topics Chemical characterization Sorption-Desorption - - PowerPoint PPT Presentation

SLIDE 1

Sub-topics

• Chemical characterization

Sorption-Desorption Characteristics Determination of kd (The Distribution coefficient)

• Thermal Characterization
• Electrical Characterization

SLIDE 2

z C R v z C R D t C

s 2 2

               

i

η K ρ 1 R

dry d

  

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

SLIDE 3

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 4

Partitioning Relationships

• Solid ↔ water

Water L / mg Solid Kg / mg K C C

d W S

 

• Water ↔ vapor

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 = SaturationPorosity ()

b



= bulk density of porous medium Cs: Sorbate sorbed per unit mass of solids Cw: Sorbate remaining in the solution, at equilibrium.

SLIDE 5

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

• 2. Column Tests

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 6

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 7

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 8

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 9

1000 2000 3000 4000 5000 0.0 0.7 1.4 2.1 2.8 10

• 2

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

• 1

d s

  

Freundlich Isotherm(FH)

Sorption Characteristics (Isotherms)

SLIDE 10

(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

• 1

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 11

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 12

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 13

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

• 1

10 10

1

10

2

10

3

10

4

10

1

10

2

10

3

10

4

10

5

10

• 2

10

• 1

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 14

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 15

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

      

SLIDE 16

Example Analysis No1

c0 hL LCCL

Transit Time Analysis

Transit time, t: time required for solute concentration at the bottom of the barrier [e.g. c(LGCL, t) to reach a specified value relative to the source concentration [e.g., c(LGCL,t)/c0 = 0.5]

SLIDE 17

Advective Analysis Where: KCCL= hydraulic conductivity of compacted clay iCCL = hydraulic gradient across compacted clay n = porosity of compacted clay

ta = L/Vs = neL / K i

SLIDE 18

Porosity: Use ne = n = 0.30 (case 1) ne = 0.01 (case 2) Use LCCL = 600 mm = 60 cm Typically: 10-10 m/s < KCCL < 10-8 m/s Use KCCL = 10-9 m/s Hydraulic gradient considerations: For LCCL = 60 cm & hL = 30 cm, i = 1.5

i = (hL + LCCL)/LCCL ta = 0.3 x 0.6/ 10-9 x 1.5 = 4 years = 0.01 x 0.6/10-9 x 1.5 = 0.13 years

SLIDE 19

Example Analysis No2

• A chemical waste is being discharged into a

shallow injection well

• Surrounding soil is sand with K = 6 x 10-4 m/s

and e = 0.9, i=0.006

• Water well 3 km downstream

t required for the contaminants to travel from the source to the water well?

SLIDE 20

Porosity : n = e/(1+e) x 100% = (0.91/1.91) x 100 = 48 % Vs = K i/n = 6 x 10-4 x 0.006/0.48 = 0.075 10-4 m/s t = L/Vs = 3000/0.075 = 13 years

SLIDE 21

Example analysis No3

Landfill is leaking leachate with a chloride concentration of 725 mg/l which enters an aquifer with the following properties: K = 3 x 10-5 m/s, i=0.002, ne=0.23, D*=1 x 10-9 m2/s Calculate the concentration of chloride in 1 year at a distance 15 m from the source

SLIDE 22

• Seepage velocity

Vs = K i/ne = 2.6 10-7 m/s

• Coefficient of longitudinal hydrodynamic

dispersion aL = 0.00175 L1.46 = 0.91 m

• Coefficient of hydrodynamic dispersion DL

DL = 0.91 x 2.6 10-7 + 1 x 10-9 = 2.4 10-7 m2/s

• Concentration

C= 362.5 =[erfc (1.24) + exp (16.25) x erfc (4.22) = 30 mg/l