Zero-valent irons effectiveness at dehalogenating chlorobenzenes and - - PowerPoint PPT Presentation

▶

Dec 16, 2023 344 likes •557 views

Zero-valent irons effectiveness at dehalogenating chlorobenzenes and its feasibility as a reactive cap Shawn Moderow and Danny Reible University of Texas at Austin Department of Civil, Architectural and Environmental Engineering

SLIDE 1

Zero-valent iron’s effectiveness at dehalogenating chlorobenzenes and its feasibility as a reactive cap

Shawn Moderow and Danny Reible University of Texas at Austin Department of Civil, Architectural and Environmental Engineering

SLIDE 2

Used in the

manufacturing of pesticides, herbicides, dyestuff and rubbers

Range of chemical

and physical properties.

High MW CBs

strongly sorbing.

Low MW CBs are

very volatile.

Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl Cl

Hexachlorobenzene, HCB Pentachlorobenzene, PeCB

1,2,3,4-Tetrachlorobenzene 1,2,3,5-Tetrachlorobenzene 1,2,4,5-Tetrachlorobenzene 1,2,3-Trichlorobenzene 1,2,4-Trichlorobenzene 1,3,5-Trichlorobenzene

1,2-Dichlorobenzene 1,3-Dichlorobenzene 1,4-Dichlorobenzene

Monochlorobenzene

Benzene

Chlorobenzenes, CBs

SLIDE 3

Bayou d’Inde (Bayou Den)

Tributary of the Calcasieu

River (Calc-a-shoe) outside Lake Charles, Louisiana that has received discharge of metals, PAH, PCBs, CBs, and

ther chlorinated organics.

Primarily contaminated with

HCB.

Natural attenuation has been

ineffective at reducing HCB contamination (Yeh and Pavlostathis, 2004).

response.restoration.noaa.gov

SLIDE 4

Sediment Capping

Improve quality of aquatic

habitat

Stabilize sediments Physically isolate sediment

contaminants from benthic

rganisms

Reduce contaminant flux to

benthos and water column

Improve surficial substrate

SLIDE 5

Sand caps

Majority of existing caps Effective for contaminants strongly sorbed to

solid phase of underlying sediment

Easy to place with minimal intermixing Generally erosion resistant compared to

existing bottom but, if necessary, can be supplemented with armoring layer

Often provides much-needed diversity to

bottom substrate

Drives sediment layer anaerobic

SLIDE 6

Active Capping

Provides an opportunity for treatment in addition to passive containment

Sorption and sequestration
Chemical and biological treatment

From a variety of materials, Zero-Valent Iron (ZVI) was chosen for investigation as an active capping material for the use in the Bayou d’Inde. Why?

ZVI has been shown to be effective at reducing chlorinated aliphatics

and PCBs

Can HCB be reduced to less chlorinated benzenes?
Results of literature review inconclusive
Iron is an relatively inexpensive and nontoxic material.

SLIDE 7

Goals

Assess ZVI potential for reducing

chlorobenzenes.

Published reports have shown mixed results
n the reactivity of ZVI and CBs.

SLIDE 8

Zero-valent Iron

MicroScale ZVI - 0.14

m2/g, 70% < 44 μm diameter.

Reactive Nanoscale

Iron Particles (RNIP) – 33.1 m2/g, ~ 70 nm

Low Permeability Cap Low Permeability Cap Contaminated Sediment Layer

Funnel and Gate design for ZVI active capping

Reactive Zone, ZVI

Sand Layer Sand Layer

Ground water flow

SLIDE 9

Zero-Valent Iron Chemistry

Fe0 = Fe2+ + 2e- RCl + 2e- + H+ = RH + Cl- Fe0 + RCl + H+ = RH + Cl- + Fe2+

(A) Reduction by zero-valent

iron.

(B) Reduction by Fe2+. (C) Catalyzed hydrogenolysis.

A. Fe2+ RCl + H+ RH + Cl- B C Fe3+ Fe2+ Fe2+ H2O OH- + H2 RCl + H+ RH + Cl- H2O OH- + H2 RCl RH + Cl- Catalysis e- e- e- e-

SLIDE 10

Preliminary Experiments

Batch tests

20 ml aqueous solution in 40 ml vials pH ~7 ~8 grams of acid pretreated MicroScale Fe0 Anaerobic Environment ~3.2 μM Chlorobenzene isomer Run over 24- 48 hrs CB recovery with injection of Hexane, 10 - 20 min Continuously shaken using Shaker table

SLIDE 11

Preliminary Results (Trichlorobenzene)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 5 10 15 20 25 30 Time, Hours C/Co 1,2,4-Trichlorobenzene 1,2,4-Trichlorobenzene control

SLIDE 12

Preliminary Results (Hexchlorobenzene)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 10 20 30 40 50 60 Time, Hours HCB C/Co 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10 PeCB C/Co HCB HCB Control PeCB

SLIDE 13

Experimental Adjustments

Ensure iron activity Longer extraction times to recover reactant

sorbed to iron

Enhance mixing throughout with tumbler

(relative to shaker table)

Lower pH (2.7) to maximize potential for

reductive dechlorination

SLIDE 14

Hexachloroethane

0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Time, Hours

m ic r o M

5000 10000 15000 20000 25000 G C /E C D A re a o f D e c h lo rin a tio n b y p ro d u c t

Expected at pH 7 Observed pH 2.7 Control

SLIDE 15

Results - pH 2.7

0.000 0.010 0.020 0.030 0.040 0.050 0.060 0.070 10 20 30 40 50 Tim e, hours H C B M icro M o les 0.000 0.001 0.002 0.003 0.004 0.005 0.006 0.007 PeC B M icro M o les HCB Total Moles Control, no ZVI HCB Total Moles w / ZVI Theoretical Mass injected PeCB Total Moles w / ZVI 0.000 0.005 0.010 0.015 0.020 0.025 0.030 0.035 0.040 10 20 30 40 50 60 Tim e, Hours m icro m o le PeC B 0.0000 0.0005 0.0010 0.0015 0.0020 0.0025 0.0030 0.0035 0.0040 m icro m o le T eC B Pentachlorobenzene Control Pentachlorobenzene 1,2,3,4-Tetrachlorobenzene 1,2,3,5-Tetrachlorobenzene and 1,2,4,5-Tetrachlorobenzene

Observed reductions in HCB and PeCB were 0.8% and 0.7 %.
Observed reductions in 1,2,3,4-TeCB, 1,2,3,5-TeCB and 1,2,4,5-TeCB

were negligible (0.04, 0.05 and 0 %, respectively)

SLIDE 16

Micro vs Nano Iron

Nanoscale iron requires much lower iron loading

rate compared with microscale to achieve equivalent surface areas per gram.

209 56 SA conc m2/L 33.1 0.14 Surface Area m2/g 6.3 400 Iron loading g/L Nanoscale Microscale

SLIDE 17

Nanoscale Iron Reduction of PCB

0.0 0.5 1.0 1.5 2.0 2.5 3.0 10 20 30 40 50 60 Time, Hours PeCB micro M 0.00 0.05 0.10 0.15 0.20 0.25 0.30 TeCB micro M PeCB 1,2,3,4-TeCB 1,2,3,5-TeCB 1,2,4,5-TeCB

Cl Cl C l Cl Cl Cl Cl Cl Cl Cl Cl C l Cl Cl C l Cl Cl

3.12 % , 59 % 0.73 % , 15 % 1.26 % , 27 %

SLIDE 18

Nanoscale Iron Reduction of HCB

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 10 20 30 40 50 60 Tim e, Hours HCB uM 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 PeCB uM HCB PeCB

SLIDE 19

Summary

1,2,4-TCB
0.04
1,2,3,4-TeCB
1,2,4,5-TeCB
0.05
1,2,3,5-TeCB

2.70 / 5.11

0.34 / 0.69
PeCB

2.22 / 3.33 0.30 / 0.36 0.50 / 0.80 0.61 / 0.78 HCB 24 / 48 hrs 24 / 48 hrs 24 / 48 hrs 24 / 48 hrs pH 2.7 pH 7 pH 2.7 pH 7 NanoScale Fe Microscale Fe Percent Reduction

SLIDE 20

Conclusions

ZVI has shown limited reactivity with CBs ZVI cannot be recommended as a reactive

capping material for the purpose of reducing CBs.

Larger MW CBs have greater reactivity with