The Science of Persulfate Activation - PeroxyChem · The Science of Persulfate Activation ... remediation with a particular emphasis on in situ chemical ... He holds a PhD in civil

The Science of Persulfate

Activation

Philip Block, PhD Director of Technology FMC’s Environmental Solutions Division Brant Smith, PhD Sr. Project Manager XDD

April 24, 2013

Bios

Philip Block is the director of technology for FMC's Environmental Solutions Division. The Environmental Solutions Division provides integrated products and solutions in three major focus areas: soil and groundwater remediation, wastewater and industrial water treatment, and air pollution. He holds a PhD in physical chemistry and a BS in chemical engineering. Dr. Smith specializes in water chemistry and hazardous waste remediation with a particular emphasis on in situ chemical oxidation and reduction technologies. He is the Director of XDD's treatability laboratory in Stratham, NH and has over 12 years experience with remedial technologies. He holds a PhD in civil engineering.

April 24, 2013

Brant Smith, P.E., Ph.D XDD, LLC [email protected] (603) 778-1100

Philip Block, Ph.D FMC Environmental Solutions [email protected] (215) 299-6645

Introduction to

Klozur® Persulfate

• Klozur® Persulfate is a strong oxidant used for in situ and ex situ destruction of contaminants in soil and groundwater

• Provides the strength of “Fenton’s Chemistry” but with extended subsurface lifetime (3 – 4 months) and little to no heat or gas evolution

• Applicable across a broad range of organic contaminants

April 24, 2013

Introduction to

Klozur® Persulfate

Chlorinated Solvents PCE, TCE, DCE TCA, DCA Vinyl chloride Carbon tetrachloride Chloroform Chloroethane Chloromethane Dichloropropane Trichloropropane Methylene chloride

TPH BTEX GRO DRO ORO creosote

Oxygenates MTBE TBA

Chlorobenzenes Chlorobenzene Dichlorobenzene trichlorobenzene

Phenols phenol Pentachlorophenol nitrophenol

Freons

Pesticides DDT Chlordane Heptachlor Lindane Toxaphene MCPA Bromoxynil

PAHs Anthracene Benzopyrene Styrene Naphthalene Pyrene Chrysene trimethylbenzene

Others Carbon disulfide PFOS / PFOA Aniline PVA/ TNT / DNT

Examples of Contaminants Destroyed by Klozur Persulfate

April 24, 2013

Chemistry and Stoichiometry

S2O8

-2 + 2H+ + 2e- 2HSO4-1

Persulfate Oxidation Principles:

Examples 15 S2O8

-2 + C6H6 + 12 H2O 6 CO2 + 30 HSO4-1

2 S2O8-2 + C2Cl4 + 4 H2O 2 CO2 + 4 Cl- + 4 H+ + 4 HSO4

-1

45 lb / lb

3 lb / lb

persulfate anion

benzene

PCE

April 24, 2013

Chemistry and Stoichiometry

However, persulfate anion kinetics are generally too slow for most contaminants. As a result, you must activate persulfate to form the sulfate radical.

Activated Persulfate

produces a radical which is more powerful and kinetically fast

FMC always recommends using an activator

proper activation method is based on contaminant, site lithology, and hydrogeology

S2O8

-2 + activator SO4•- + (SO4•- or SO4-2)

Heat Iron H2O2 High pH

Purchase of FMC’s Klozur® Persulfate includes rights to practice the inventions covered by global patents in the purchase price of the product.

2.6 eV One of strongest oxidants available.

April 24, 2013

Presentation Overview

• Activation Methods of Activated Persulfate

– Overview

– Chemistry

– Discussion

• Bench testing activated persulfate

• Case study

– Industrial site with chlorinated ethanes,

ethenes and 1,4-dioxane

April 24, 2013

Activation Methods of Persulfate

• Persulfate is a peroxygen, and similar to hydrogen peroxide, it can be split at the O-O bond:

-O3S-O-O-SO3- -O3S-O• •O-SO3

-

• Reaction is facilitated by activation methods,

which include: – Reduced metals (Iron and Iron-Chelate)

– Alkaline/high pH

– Heat

– Hydrogen peroxide

– Others (photolysis)

8

Iron/Iron Chelate Activation:

Overview

• Sodium persulfate (2.05 V) is activated by the a reduced iron, Fe(II) is most common, to form the sulfate radical (SO4•; 2.6 V)

• Has been shown to be reactive with: – Reduced organics (PAHs, BTEX, TPH, etc)

– Chlorinated ethenes (PCE, TCE, DCE, and VC)

– Oxygenates (MTBE, 1,4-Dioxane, etc)

– Perfluorinated acids (PFOA, PFBA, etc)

• FMC guidance of 150 mg/L Fe to 600 mg/L Fe

April 24, 2013

Iron/Iron Chelate Activation:

Chemistry

• Iron/Iron Chelate S2O8

2- + Fe(II) Fe(III) + SO4- + SO4•

• Chelate or not to chelate: – At pH >~2.7 Fe (III) will precipitate

– EDTA, citrate, or other chelates help keep iron in solution

• How does Fe(III) cycle back to Fe(II)? – Likely reaction with destabilized organics

10 April 24, 2013

Iron/Iron-Chelate Activation:

Discussion

• Reactivity due to sulfate radical

• Field application is well established

• Minimized health and safety concerns

• Does not react with chlorinated ethanes or methanes such as 1,1,1-TCA or carbon tetrachloride

• Does not typically include anything to neutralize the acid that is formed during the decomposition of persulfate (more of a concern as concentrations increase)

• Formation of halomethanes has been observed if halides are present

April 24, 2013

Alkaline Activation:

Overview

• Sodium persulfate is activated when the solution is raised to pH > 10.5

• Has been shown to be reactive with:

– Reduced organics (PAHs, BTEX, TPH, etc)

– Chlorinated ethenes (PCE, TCE, DCE, and VC)

– Chlorinated methanes or ethanes (CT, 1,1,1-TCA, etc)

– Oxygenates (MTBE, 1,4-Dioxane, etc)

– Perfluorinated acids (PFOA, PFBA, etc)

• Sufficient base needs to be added to account for buffering capacity of the soil plus the acid that is generated during the decomposition of sodium persulfate

April 24, 2013

Alkaline Activation:

Chemistry • Alkaline Activation-simple version:

pH >10.5 S2O82- 2SO4•

• Alkaline Activation-complex version (Furman et al., 2010):

S2O82- + 2H2O HO2

- + 2SO42- + 3 H+

HO2- + S2O8

2- SO4- + SO4

2- + H++ O2-

SO4- + OH- OH + SO4

2-

(note: H2O2 HO2- + H+ pKa = 11.7)

• Complex version of the reaction results in the transient oxygen species of SO4

- , OH , O2- , and HO2

-

• Analogous to the chemistry that has been studied with catalyzed hydrogen peroxide (CHP)

13 April 24, 2013

OH-

Alkaline Activation:

Discussion

• Generates reductive (O2

-), nucleophilic (HO2

-), and oxidative (SO4

-; OH) species to react with broad suite of contaminants

• As a result AAP can treat CT, and 1,1,1-TCA

• Ease of implementation

• Health and safety risk of NaOH or other base.

• Additional cost of NaOH

• Typically has increased non-target demand from soils

• Site pH following application

April 24, 2013

Heat Activation:

Overview

• Heat activated persulfate used in certain TOC analyses

• Subsurface heated to desired temperature

• Persulfate degrades to form different compounds as the temperature increases

April 24, 2013

Block et al, 2004

Activation with Heat:

Chemistry

• Heat (>35°C sulfate radical; >80°C multiple oxidants)

S2O82- 2SO4•

• Two schools of thought:

– Different oxidants formed at elevated

temperatures

– Kinetics (ie. Arrhenius equation)

16 April 24, 2013

Heat Activation:

Discussion

• Arguably the most effective activation method, especially in the lab setting

• Reacts with wide variety of compounds depending upon the temperature

• Can be used as part of a combined remedy with thermal treatments

• Soils/silica are good insulators

• Typically requires dual system to heat the subsurface

• Introduces unique failure mechanisms such as thermal sinks/losses/distribution

• Health and safety associated with heat source

April 24, 2013

Hydrogen Peroxide Activation:

Overview

• “Activation” – Addition of hydrogen peroxide to react with

(donate an electron) sodium persulfate

– Heat

• Combination of two proven ISCO technologies

• Ratio between the two reagents determines application characteristics

April 24, 2013

Hydrogen Peroxide Activation:

Catalyzed Hydrogen Peroxide Chemistry

Fundamental Fenton’s reaction (hydroxyl radical) Fe2+ + H2O2 Fe3+ + OH. + OH-

Perhydroxyl Radical OH• + H2O2 HO2• + H2O

Fe3+ + H2O2 HO2• + Fe2+ + H+

Superoxide

HO2• O2•-+ H+ pKa 4.8

OH• + HO2- O2•

-+ H2O

Hydroperoxide

HO2• + Fe2+ Fe3+ + HO2-

HO2• + O2•- O2+ HO2

-

19 April 24, 2013

Hydrogen Peroxide Activation:

Chemistry

• Hydrogen peroxide can donate electrons going

to oxygen or accept electrons to become water

O2 O2•- H2O2 H2O

• If hydrogen peroxide is present in sufficient

quantities, the reaction should result in the

transient species of SO4- , OH , O2

- , and HO2-

April 24, 2013

e- e- 2e-

April 24, 2013

Hydrogen Peroxide Activation:

Discussion

• Various reactive

species should allow

for the destruction of

a wide variety of site

COCs

• Thermodynamic

energy could be used

to generate heat

activated persulfate

• Design engineers

needs to be

concerned with

overlapping ROIs

• Issues associated

with the application of

hydrogen peroxide

April 24, 2013

Summary of Activation Methods

Several commonly used activation methods

allows the activation method to be selected by

the design engineer on a site specific basis

– Iron/Iron chelate: Less expensive, effective on

petroleum compounds and chlorinated ethenes

– Alkaline: Effective in treating most chlorinated

and petroleum compounds. Proper alkaline dose

should return site to near neutral pH.

April 24, 2013

Summary of Activation Methods

Continued

– Heat: Effective in treating most chlorinated, petroleum compounds and perfluorinated acids. Cost and issues with subsurface heating need to be addressed.

– Hydrogen peroxide: Effective in treating most chlorinated and petroleum compounds. May work via subsurface heating or direct reaction. Design engineer should evaluate overlap in subsurface distribution of each oxidant

April 24, 2013

Bench Scale Tests

• Bench Scale Tests can be used to: – Determine interactions of site specific

geochemistry with the chemistry of activated persulfate

– Generate critical design parameters

• Choosing to not bench test: – Field application design will be based on

assumptions or a “standard approach” without the development of site specific design parameters

– Moves risk to the field

April 24, 2013

Bench Scale Design Parameters

• Each activation method: – Non-target demand

– Degradation ratio/Persulfate efficiency number

• Additional Design Parameters: – Iron/Iron chelate

• Iron:chelate loading or ratios

– Alkaline • Base buffering capacity

– Heat • Treatment temperature

• Soil heat capacity

– Hydrogen peroxide • Stability of hydrogen peroxide

April 24, 2013

Case Study:

AAP at an Active Facility

• Key Points

– Closure goal – 1 mg/L for each compound (1,1,1-TCA, PCE, 1,4-dioxane)

– Active, high security facility – 3rd shift/evening applications

– Bench tested iron activated persulfate, alkaline activated persulfate, ZVI, calcium peroxide, RegenOx as alternatives.

– Focus on safety - recommended alkaline persulfate for indoor application

• Eliminate degassing/vapor issues and pressure concerns

April 24, 2013

• Former Vapor Degreaser

• COCs – TCA (101 mg/L), PCE (20 mg/L) and 1,4 Dioxane (3 mg/L)

• Fill underlying concrete floor and overlying sands and

silts – till layer below – high oxidant demand

Site Overview

XDD identified “transition zone”

between upper and lower zones

contained majority of COC

mass

April 24, 2013

Injection Well Layout

• Well Network: 9 shallow and

9 deep 2” PVC injection

wells to 20 feet bgs

April 24, 2013

Operational Overview

• Two injection

events in 2007

• 100 to 200 g/L

Persulfate

• 1st event:

33,000 lbs

persulfate

• 2nd event:

36,000 lbs

persulfate

April 24, 2013

Long Term COC Monitoring Results

• 2-3 Orders Magnitude Reduction

• Target compounds remain below 1 mg/L (3 yrs post application monitoring)

30

Primary ISCO

Polish ISCO

Primary ISCO

Polish ISCO

Primary ISCO

Polish ISCO

April 24, 2013

Long Term Contaminant Monitoring

• 2-3 Orders Magnitude

Reduction

• Target compounds

remain below 1 mg/L (3 yr post application sampling

round)

April 24, 2013

Primary ISCO

Polish ISCO

Primary ISCO

Polish ISCO

Primary ISCO

Polish ISCO

Metals Mobilization-3 years post

• Monitoring wells in

the source zone

• Data from 3 years

post application

• Metals have

attenuated, typically

in 1 year

April 24, 2013

Downgradient Metals Mobilization

• As and Cr were not

observed to migrate

downgradient in

events 1 yr and 3 yr

post (shown)

application

April 24, 2013

All Concentrations in ug/L

ISCO Area Downgradient

Downgradie

nt Downgradient

ISCO Area

As still at Baseline levels

Cr still at Baseline levels

Summary

• Several successful methods to activate sodium persulfate

• Characteristics of each method lend themselves to site specific engineered designs

• Activated sodium persulfate is a proven technology that has been successfully applied in the field for several years

April 24, 2013

Questions???

April 24, 2013

Brant Smith, P.E., Ph.D XDD, LLC [email protected] (603) 778-1100

Philip Block, Ph.D FMC Environmental Solutions [email protected] (215) 299-6645