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Retardance of Rainwater-Retardance of Rainwater-Leached Metals in Amended Leached Metals in Amended
Soil Systems:Soil Systems:
A Case Study A Case Study
John D. Harden, P.G., Ph.D.John D. Harden, P.G., Ph.D.Robert E. Pitt, P.E., Ph.D., BCEE, D.WRERobert E. Pitt, P.E., Ph.D., BCEE, D.WRE
Department of Civil, Construction & Environmental Department of Civil, Construction & Environmental EngineeringEngineering
The University of AlabamaThe University of AlabamaTuscaloosa, AlabamaTuscaloosa, Alabama
Presentation OverviewPresentation Overview
Goal and Scope of ResearchGoal and Scope of Research BackgroundBackground Ash and Soil ClassificationAsh and Soil Classification Batch StudiesBatch Studies Column StudiesColumn Studies ConclusionsConclusions Future WorkFuture Work
Research GoalResearch Goal
Identify a readily available agricultural Identify a readily available agricultural soil amendment to reduce the mobility soil amendment to reduce the mobility
of metals at Chromated Copper of metals at Chromated Copper Arsenate (CCA)-treated wood burn sites.Arsenate (CCA)-treated wood burn sites.
Iron sulfate, agricultural lime, and gypsum Iron sulfate, agricultural lime, and gypsum were studied. The results for gypsum were studied. The results for gypsum
(CaSO(CaSO44·2H·2H22O) are presented. O) are presented.
Scope of ResearchScope of Research
What are the potential environmental What are the potential environmental effects on soil and water resulting effects on soil and water resulting from the burning of CCA-wood?from the burning of CCA-wood?– What is the composition of the ash?What is the composition of the ash?– What is the fate of the ash in soil?What is the fate of the ash in soil?– How effectively are metals leached from How effectively are metals leached from
the soil/ash by rainwater?the soil/ash by rainwater?
Can the leaching rates be reduced by Can the leaching rates be reduced by the addition of soil amendments?the addition of soil amendments?
BackgroundBackgroundWhat is CCA?What is CCA?
Chromated Copper Arsenate (CCA) Chromated Copper Arsenate (CCA) wood preservativewood preservative
Designed for the humid Southeastern Designed for the humid Southeastern U.S. where wood is prone to insect and U.S. where wood is prone to insect and fungal attack fungal attack – CuCu - serves as a fungicide - serves as a fungicide– AsAs - serves as an insecticide - serves as an insecticide– CrCr - a fixing agent for bonding Cu & As - a fixing agent for bonding Cu & As
to woodto wood
Used in residential-use wood until 2004Used in residential-use wood until 2004
Very large amounts of wood were Very large amounts of wood were treatedtreated
Pictures: www.google.com/search?q=pictures+of+CCA+wood
Statistics on CCA Production Statistics on CCA Production ~1lb CCA preservative/3 ft~1lb CCA preservative/3 ft33 treated wood treated wood
1997: 450 x 101997: 450 x 1066 ft ft33 of CCA-wood products of CCA-wood products
Service life of CCA-wood 20-50 yearsService life of CCA-wood 20-50 years
CCA-treated wood waste will increase fromCCA-treated wood waste will increase from 5 to 32 x 105 to 32 x 1066 ft ft33/yr by 2015/yr by 2015
AsAs in CCA-wood waste: 31,000 metric tons in CCA-wood waste: 31,000 metric tons introduced into Florida environment over the introduced into Florida environment over the past 30 yearspast 30 years
Burning of waste/old CCA-treated wood has Burning of waste/old CCA-treated wood has been common practicebeen common practice
Metal Species in Metal Species in CCA-Wood/AshCCA-Wood/Ash
NameName
SymbolSymbol
OxidatioOxidationn
StateState
Cation/Cation/
AnionAnionSpeciesSpecies CharacteristicsCharacteristics
CopperCopper
CuCuCu(II)Cu(II) CationCation
CuCu+2+2
CuOHCuOH++
CuCu22(OH)(OH)44--
varying toxicityvarying toxicity
varying solubilityvarying solubility
varying mobilityvarying mobility
ChromiuChromiumm
CrCr
Cr(III)Cr(III) AnionAnionCr HydroxidesCr Hydroxides
Cr(OH)Cr(OH)44--
less toxicless toxicless solubleless solubleless mobileless mobile
Cr(VI)Cr(VI) AnionAnion
ChromateChromate
CrOCrO44-2-2
DichromateDichromate
CrCr22OO77-2-2
more toxicmore toxicmore solublemore solublemore mobilemore mobile
ArsenicArsenic
AsAs
As(III)As(III) AnionAnionArseniteArsenite
AsOAsO33-3-3
more toxic (25-60 more toxic (25-60 times)times)
more solublemore solublemore mobilemore mobile
As(V)As(V) AnionAnionArsenateArsenate
AsOAsO44-3-3
less toxicless toxicless solubleless solubleless mobileless mobile
Investigations to Quantify Investigations to Quantify Metals and Evaluate MobilityMetals and Evaluate Mobility
Produce ash & Quantify metals in CCA-ashProduce ash & Quantify metals in CCA-ash
How mobile are the metals?How mobile are the metals?– Batch Leaching ExperimentsBatch Leaching Experiments
Accelerated leach studiesAccelerated leach studies Regulatory classification of CCA-ashRegulatory classification of CCA-ash Leaching of CCA-ash & a soil/CCA-ash mixtureLeaching of CCA-ash & a soil/CCA-ash mixture Potential contamination of water by CCA-metalsPotential contamination of water by CCA-metals
Effect of CaSOEffect of CaSO44 on metals mobility on metals mobility– Optimization StudyOptimization Study
Column Leaching ExperimentsColumn Leaching Experiments Evaluate CaSOEvaluate CaSO44 performance versus natural soil performance versus natural soil Measure the pH range of the leach eventsMeasure the pH range of the leach events
Burn Site
Down-gradient 10’ & 16’
Sample pointsScale
1ft
Upgradient Sampling:
200’ (baseline) & 10’
CCA-metals at Burn SiteAs (12.2±1.2)Cr (17.4±1.4)Cu (14.5±0.5)
mg g-1 site soil ± 95% CI
LakeTuscaloosa
Sampling Points & CCA-Sampling Points & CCA-metals Concentration at metals Concentration at
Burn SiteBurn Site
Alabama
Burn Site
Soil & CCA-ash Soil & CCA-ash
Soils in US & Proportions of Major Adsorbed Cations on Surface Layers
Soil Order Typical location H+ and Al+3 Ca+2 Mg+2 K+ Na+
Oxisols Hawaii 85 10 3 2 trace
Spodosols New England 80 15 3 2 trace
Ultisols Southeast U.S. 65 25 6 3 1Alfisols PA to WI 45 35 13 5 2
Vertisols AL to TX 40 38 15 5 2
Mollisols Midwest U.S. 30 43 18 6 3
Aridisols Southwest U.S. 65 20 10 5
Adapted from Brady, 1990
Cr, 76mg 33%
Cu, 86mg 37%
As, 70mg 30%
Total CCA-metals in 1g CCA-Total CCA-metals in 1g CCA-ashash
1000mg CCA-ash contains 232mg (23%) CCA-1000mg CCA-ash contains 232mg (23%) CCA-metalsmetals
Microwave digestion & ICP
CCA-metals
As Cu
Cr
Batch LeachingBatch Leaching
Establish preliminary leaching trends for column design
Metals Present and Metals Present and Leached from Soil/Ash Mixture (mg gLeached from Soil/Ash Mixture (mg g-1-1 & &
%)%)
0.01
0.1
1
10
100
1000
1 2 3 4
Mass % Leached
Log
Met
als
(mg
g-1
Ash
)
Total Metal (mg) Leached Metal (mg)
232
6.9
86
0.03
76
4.2
70
2.6
3.0% 0.03% 5.5% 3.7%
Cu Cr As
Leaching Trend : Cr>As>Cu
Regulatory Classification ofRegulatory Classification ofCCA-ash by RCRA-TCLPCCA-ash by RCRA-TCLP
As - Regulated Haz. Waste (RCRA) As - Regulated Haz. Waste (RCRA) TCLP Limit:TCLP Limit: 5.0 mg L 5.0 mg L-1-1 CCA-ash by TCLP: CCA-ash by TCLP: 578578±44.7 mg L±44.7 mg L-1-1
Cr - Regulated Haz. Waste (RCRA) Cr - Regulated Haz. Waste (RCRA) TCLP Limit Cr(VI): TCLP Limit Cr(VI): 5.0 mg L 5.0 mg L-1-1 CCA-ash Cr(VI+III) by TCLP:CCA-ash Cr(VI+III) by TCLP: 0.7190.719±0.057 mg L±0.057 mg L--
11
Cu - Not regulated under RCRACu - Not regulated under RCRA CCA-ash Cu by TCLP:CCA-ash Cu by TCLP: 6.726.72±0.713 mg ±0.713 mg
LL-1 -1
Results reported in mg LResults reported in mg L-1-1 ± 95% CI± 95% CI
Therefore CCA-ash is classified as a regulatedTherefore CCA-ash is classified as a regulated
RCRA Haz. WasteRCRA Haz. Waste due to Asdue to As
0.446
17.1
0.0290.010
4.23
0.369
2.60
10.1
1.02
0.0
0.1
1.0
10.0
100.0
1 2 3
Leach Samples
Log
Leac
hed
Met
al m
g g
-1 A
sh Cu LeachedCr LeachedAs Leached
Cu
As
Cr
Ash-Only Leach
Ash-Soil Leach
Ash-Soil Releach
Batch Leaching of Batch Leaching of CCA-ash & Soil/CCA-ash CCA-ash & Soil/CCA-ash
MixtureMixture
Therefore natural soil retards Cr & As mobilityTherefore natural soil retards Cr & As mobility
75% Lower
74% Lower
280% Higher
250% Decrease
1150% Decrease1550% Increase0.01
0.1
1.0
10
100
Potential Contamination of WaterPotential Contamination of Water by CCA-metals by CCA-metals
MetalMetal LeachedLeached (µg g(µg g-1-1ash)ash)
Regulatory Regulatory Level (µg LLevel (µg L--
11))L gL g-1-1 ash ash
CuCu 11301130 10*10* 113***113***
CrCr 29002900 100**100** 29***29***
AsAs 47004700 10**10** 469***469***
Batch Leach (5 Leachings)1.45 g CCA-ash, 8.25 g Test Soil, 465 mL Total Rainwater
* Cu based on toxicity to freshwater clams, Harrison, et al. 1984** SDWA-MCL*** Volume of Water Contaminated to Regulatory Level
CaSOCaSO44 Optimization Batch Optimization Batch StudyStudy
A 1:1 to 3:1 ratio of CaSO4:CCA-ash was acceptable
1.90
0.1640.0470.0470.023
1.77
2.53
3.213.11
1.241.57
2.83
0
1
2
3
4
-50 0 50 100 150 200 250 300 350 400 450
Gypsum Addition (mg)
Le
ac
he
d C
CA
-me
tal (m
g g
-1 C
CA
-
as
h)
Cu
Cr
As
1:1 4:1 16:1
ash
)
Column Leaching Column Leaching ObjectivesObjectives
Evaluation of CaSOEvaluation of CaSO44 performance performance
Accelerated leaching equivalent to annual rainfall at Accelerated leaching equivalent to annual rainfall at the burn sitethe burn site - 19 Rainfall events = 130 cm yr- 19 Rainfall events = 130 cm yr-1-1
Evaluation of metals leached mass determined for Evaluation of metals leached mass determined for each rainfall eventeach rainfall event
- 49 g CCA-ash, 68 g CaSO- 49 g CCA-ash, 68 g CaSO44, 231 g soil, 231 g soil - 1.6:1 Ratio of Ca- 1.6:1 Ratio of Ca+2+2 to CCA-metals to CCA-metals
Measure leachate pH for each rainfall eventMeasure leachate pH for each rainfall event - pH Range: 7.3 to 8.0- pH Range: 7.3 to 8.0
Mobility Reducing Mobility Reducing MechanismsMechanisms
Negative Surface Charge on Soil Particle
Inner-Sphere Complex
Outer-Sphere Complex Diffuse Ion
- - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - - -
Soil/CCA-ash/CaSOSoil/CCA-ash/CaSO44 System System Ultisol SoilUltisol Soil
– Low Cation Exchange Capacity (CEC), 35% efficiencyLow Cation Exchange Capacity (CEC), 35% efficiency– Low to moderate Anion Exchange Capacity (AEC)Low to moderate Anion Exchange Capacity (AEC)
CCA-ashCCA-ash
– XO => X(OH)XO => X(OH)22 => XCO => XCO3 3 , where X = Ca, Mg, Cu, Cr, As, where X = Ca, Mg, Cu, Cr, As
General Mechanisms from CaSOGeneral Mechanisms from CaSO44 Amendment Amendment
– CaCa+2+2 replaces Al replaces Al+3+3, increases CEC efficiency, increases CEC efficiency
– Increased Al(OH)Increased Al(OH)33 and Cr(OH) and Cr(OH)33 precipitation precipitation
– Increased CaIncreased Ca+2+2 concentration and negative surface concentration and negative surface charge produces greater adsorption and coprecipitation charge produces greater adsorption and coprecipitation of As and Cr. Increased Cu mobility due to competition of As and Cr. Increased Cu mobility due to competition with Cawith Ca+2+2 for adsorption sites and increased mobility of for adsorption sites and increased mobility of Cu-bound organic compoundsCu-bound organic compounds
Accelerated One-Year Mass Leach of Accelerated One-Year Mass Leach of MetalsMetals
Accelerated One-Year Mass LeachAccelerated One-Year Mass LeachControl vs CaSOControl vs CaSO4 4
MetaMetall
CombinationCombination MassMass(mg g(mg g-1-1))
±± %%
AsAsControl Control 2.532.53
-77%-77%CaSOCaSO44 0.5780.578
CrCrControlControl 4.314.31
-72%-72%CaSOCaSO44 1.201.20
CuCuControl Control 0.0120.012
400%400%CaSOCaSO44 0.0480.048
• CaSO4 reduces mobility of As by a further 77% and Cr by 72% over soil alone
• Cu mobility increases by a small mass compared to the large reduction in As and Cr mobility
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
0 500 1000 1500 2000
Cumulative Leach Volume (mL)
Lea
ched
Cr
mg
g-1
Ash
Control
CaSO4
Cr
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0 500 1000 1500 2000
Cumulative Leach Volume (mL)
Leac
hed
As
mg
g-1
Ash
Control
CaSO4As
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0 500 1000 1500 2000
Cumulative Leach Volume (mL)
Lea
ched
Cu
mg
g-1
Ash
Control
CaSO4
Cu
ConclusionsConclusions Unamended soil retards leaching of As & Cr from Unamended soil retards leaching of As & Cr from
CCA-ash while increasing Cu mobilityCCA-ash while increasing Cu mobility
CaSOCaSO44 amendment of soil further reduces mobility amendment of soil further reduces mobility of As by 77% and Cr by 72%of As by 77% and Cr by 72%
Optimization study revealed 3:1 ratio of CaSOOptimization study revealed 3:1 ratio of CaSO44
to CCA-ash mass is recommendedto CCA-ash mass is recommended
A higher ratio of CaSOA higher ratio of CaSO44 to CCA-ash mass would to CCA-ash mass would serve as a continued source of Caserve as a continued source of Ca+2+2 cations for cations for long-term stabilization of As & Crlong-term stabilization of As & Cr
CaSOCaSO44/Soil/CCA-ash system: 7.3 to 8.0 pH/Soil/CCA-ash system: 7.3 to 8.0 pH
Ongoing Work & Future Ongoing Work & Future PotentialPotential
Soil and Sediment ContaminationSoil and Sediment Contamination journal journal has published two articles from this research has published two articles from this research on CCA- metals adsorption/desorption on CCA- metals adsorption/desorption mechanisms in amended soil systems and a mechanisms in amended soil systems and a third article is under review in another third article is under review in another journaljournal
The future of metals immobilization in soil The future of metals immobilization in soil by the use of common soil amendments by the use of common soil amendments could involve the manufacture of could involve the manufacture of “enhanced” soil amendments to improve “enhanced” soil amendments to improve the performance of immobilization the performance of immobilization mechanismsmechanisms
Presentations
Parts of the research results have been presented at the following:
EWRI-World Environmental & Water Resources Congress 2008
Honolulu, HI American Water Resources
Association 2010 Annual Conference Philadelphia, PA
Questions ?