IN SITU CHEMICAL
OXIDATION BY
CATALYZED
PERSULFATE
J. Rossabi
J. S. Haselow
T. Jarosch
J. Chiorazzi, E. Escochea, E. Escochea, Jr., E. Hatcher, G. Meyers, W. Noell, G. Powers
Overview
¾ History (Laundry, bleaching, etching,
polymers, TOC, patents)
¾ In Situ Chemical Oxidation
¾ Free Radicals
¾ Total Oxidant Demand (TOD) test
¾ Subsurface Chemical Injection
¾ Field Results
¾ Future Work
History Persulfate
(peroxydisulfate S2O82-)
•
•
•
•
•
Prior to 1940s - Like many oxidizers (e.g.,
hydrogen peroxide) used initially for laundry and
other bleaching. (ammonium, potassium, sodium)
1950s – Used as an initiator for polymers (e.g.,
teflon, PVC, polystyrene, neoprene)
1970s - Metal Etching (printed circuit boards,
etc. )
Other (cosmetics, chemical prep, photog.)
Environmental (~10%)
Persulfate in TOC Analysis
¾ Usually catalyzed by heat or UV light
¾ Standard Method 5310C, D
¾ ASTM Methods D2579, D4129, D4779,
D4839
¾ EPA Methods 415.1 and 415.2; SW846
9060)
¾ Used because it oxidizes nearly all
organics to CO2
Patents
¾ Chemical Oxidation of VOCs: G. E. Hoag,
P.V. Chheda, B.A. Woody, G. M. Dobbs
(University of Conn, United Technologies
Corp.) 6,019,548 (Feb 2000)
¾ FMC Corporation, Main producer of
persulfate
In situ Chemical Oxidation (ISCO)
¾ Desire to avoid contaminant removal
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Expense
Exposure
Access
¾ Rapid recovery of valuable real estate
¾ Completely “mineralize” contaminant
¾ Ozone, peroxide, permanganate,
persulfate, Cl based, others.
Oxidation
¾ Taking electrons away from a molecule
oxidizes it.
¾ May make the molecule more stable or
less stable and susceptible to further
oxidation.
C(IV)O2
¾ C(-IV)H4 (VCl, DCE, TCE, PCE, etc.)
¾ May need to add energy to system
¾ Oxidants add energy to system
Catalyzed Oxidant Adds More
Energy
¾ S2O82-
+ energy (heat, light, etc.)
2SO4●-
¾ Sulfate Radical has lots of energy,
electrons ready to react.
Free Radical
¾ Unpaired electrons, results from splitting of
covalent bonds by homolytic fission.
¾ Usually short lived
¾ Very reactive
¾ Uncharged
¾ Often an oxygen molecule that has lost an
electron and is looking to rip one from
somebody else.
Free Radical Reactions
¾
Initiation
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Result in net increase of free radicals e.g.,
• Stable species + energy = free radicals
• Free radical + stable species = free radicals
¾
Propagation
z
¾
Results in no change in number of free radicals
Termination
z
Results in net decrease of free radicals e.g.,
• Free radical + free radical = stable species
Radicals we know and love?
¾ Oxygen actually diradical – two unpaired
electrons (combustion-heat, food
digestion-enzymes)
¾ Chlorofluorocarbons solar UV
disassociates to generate free radicals,
react with ozone (consume) and generate
more radicals
Relevant radicals and pseudo
radicals
¾
Superoxide (O2●- ) – can act as oxidant or
reductant), hydroxyl (●OH)(formed under
reducing conditions)
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¾
¾
¾
Decomposes to peroxide (reaction with itself + H2)
Singlet oxygen higher energy than ground state
triplet oxygen – reactive
Persulfate (SO4●-) reactive oxygen species
peroxo anion.
The reactive oxygen species may produce short
lived free radical species.
Radicals
¾ Can produce other radicals including
organic radicals:
¾ SO4●- + H2O
¾ SO4●- +CH3OH
From Bartlett and Cotman, 1949.
HSO4- +●OH
HSO4- +CH2●OH
Oxidation Potential
¾ Hydroxyl radical ●OH
¾ Sulfate radical SO4●¾ Ozone O3
¾ Persulfate anion S2O8¾ Hydrogen peroxide H2O2
¾ Permanganate ion MnO4¾ Peroxymonosulfate anion HSO5-
2.7V
2.6V
2.2V
2.1V
1.8V
1.7V
1.4V
Mineralization of Benzene
¾ 15:1 mol/mol (46:1 g/g) of persulfate to
benzene
¾ For 20m x 10m x 5m contaminated
volume, @1 mg/l benzene (0.35 porosity):
¾ Therefore need 16 kg persulfate to oxidize
contaminant (or 0.01 g oxidant/kg soil)…
¾ but contaminant doesn’t usually
produce the majority of the oxidant
demand
Total Oxidant Demand Tests
¾ Majority of oxidant demand in subsurface
is from rocks (reduced minerals) aqueous
or solid phase
¾ Rest from organic contaminant and natural
organic material and self-demand
¾ Note: NAPL and large amounts of NOM
may produce very large demand.
Generalized TOD Results
Geochem Status
Occurrence
Range of TOD
(g/kg)
Low metals
Limestone or clean
sand
<0.1 to 0.5
Low NOM
Limestone or clean
sand
<0.1 to 0.5
Oxic
Elevated dissolved O2
<0.1 to 1.0
Mildly reducing
Elevated ferrous iron
<0.1 to 2.0
Moderately reducing
Depressed nitrate but
elevated sulfate
<0.1 to 5.0
Strongly reducing
Elevated methane or
ethene (CVOCs)
<0.1 to 15.0
From Haselow et al., Remediation, Autumn 2003.
Injection Considerations
(Well or direct push)
¾ Health and Safety
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handling, compatibility, kinetics
¾ Must contact contaminant
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Trouble with impermeable zones
• (Fracing, diffusion may help a little)
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Preferential flow paths
• Permeability contrasts
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“Daylighting”, “Flow by”
¾ Effectiveness under different conditions
(temperature, pH, eH, etc.)
More Injection Considerations
¾ Fluid characteristics (viscosity, corrosivity,
solubility, reactivity and “hang time”, etc.)
¾ Cost
¾ Ease of Use
¾ Secondary effects (metals mobilization,
etc.)
¾ Rebound?
Persulfate Field Results
Chlorinated Solvents
Location
1,1 DCE
(ug/l)
Scotland Neck, NC 230,000/460
Garner, NC
81,700/0.8
Location
Cobb County, GA
1,1,1 TCA
(ug/l)
390,000/68,000
73,000/987
PCE
TCE
(mg/kg)
(mg/kg)
5,100/<2.6
3.2/<0.05
Petroleum
Location
benzene
(ug/l)
Blackstone, VA
Clayton, DE
1600/78
519/7.4
Location
xylene
(ug/l)
Hagaman, NY
Lexington, NC
MTBE
(ug/l)
1300/360
16,100/233
naphthalene
(ug/l)
2,778/22
>1,000,000/<1,000
1, 4 Dioxane Results
1, 4 dioxane Treatment by Catalyzed Sodium
Persulfate
Monitoring
Dioxane concentration (ug/L)
Wells
Pre Treat
Post Treat
MW-1
50,000
<5
MW-7
3220
<5
MW-14
3020
<5
MW-17
3400
Non Detect
Persulfate Advantages
¾ Strong oxidant
¾ Apparently slower reaction kinetics
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Longer persistence (several weeks)
Easier to handle
Faster injection rates
¾ Little energy wasted on the production of
heat and gas
¾ Works in variety of pH conditions.
Persulfate Disadvantages
¾ Rapidly Corrosive to metals (weak acid,
catalyzed by iron) – need buffer
¾ Produces sulfate (potential secondary
drinking water standard issue) – can buffer
with Ca lime and produce gypsum.
Need more research
¾ Understand mechanism, intermediate
products, effective catalysts, etc.
¾ Maurice Hilleman died 4/11/05
z
z
Developed vaccines for mumps, measles,
rubella chicken pox, bacterial meningitis, flu,
hepatitis B.
“…don’t know a damn thing about how they
(vaccines) work…in the old days we used to
solve problems without having to understand
them.”
Electrical Conductance of Sodium Persulfate Solution
140,000
25 deg C
35 deg C
Conductance (uSiemans/cm)
120,000
45 deg C
100,000
80,000
60,000
40,000
____Seawater (30,000)____
20,000
____Brackish water (1,000)____
0
0%
2%
4%
6%
8%
10%
12%
Sodium Persulfate (wt %)
____Fresh water (500)____
14%
16%
18%
20%