21 st Annual Conference
Dec 22, 2015
Chemical-enhanced Soil Washing for
Land Decontamination
Dr. Dan TsangLecturer
Department of Civil and Natural Resources Engineering University of Canterbury
Contaminated Site Remediation Land contamination
human health risks impact on ecosystem
Risk-based land management reduce potential risk to an acceptable level site-specific risk-based treatment objectives
Managerial actions Remedial actions
ReceptorPathwaySource
Key drivers Excavation and landfill disposal (‘dig and dump’)
ease of use, quick, applicable for complex contamination landfill space? transportation? fuel? greenhouse gas? backfill materials?
United States Hazardous Waste Laws Section 121 (b) of the Comprehensive Environmental Response,
Compensation, and Liability Act (CERCLA, or Superfund) prescribes remedial actions that “permanently and significantly reduces the volume, toxicity, or mobility of the hazardous substances, pollutants, and contaminants”
“Superfund Amendments and Reauthorization Act of 1986 (SARA) expressed a preference for permanent remedies (that is, treatment) over containment or removal and disposal in remediation of Superfund sites.” (USEPA, 2007)
U.S. EPA (2007) Treatment Technologies for Site Cleanup: Annual Status Report (Twelfth Edition).
Key drivers European Union (EU) Landfill Directive and Landfill Tax
implementation in summer 2004 reduced the available landfill space for all forms of waste disposal and banned co-disposal of soils from contaminated land and non-hazardous wastes
tightened further in 2005 in that no wastes can be sent to hazardous waste landfills in excess of 6% organic matter and the new Waste Acceptance Criteria require that all wastes sent to hazardous waste landfills have to be pre-treated
prices for disposal to hazardous landfill have risen dramatically, e.g., in the UK, to above £100/m3, and frequently in the region of £150/m3
Excavation and landfill disposal – less economically attractive Remediation industry looking for alternative methods
Council of the European Union (1999) Council Directive 1999/31/EC of 26th April 1999 on the Landfill of Waste
(USEPA, 2001)
Technology Overview Soil washing
ex-situ on-site soil remediation physical–chemical approach
majority of contamination associated with fine soil particles physical separation of large, clean soil particles mineral-processing equipment significant volume reduction
Soil washing project at Elgin in the UK reuse more than 80% (2,770 m3) of excavated soil
otherwise require haulage off-site to landfill and equivalent amount of clean quarried stone imported
minimise truck movements avoid more than 275 return lorry trips, 70,000 vehicle miles,
associated emissions, noise, congestion and health and safety issues
Applicability SVOCs (e.g., PAHs and PCBs), fuels, heavy metals, radionuclides,
and pesticides contaminants sorbed on fine particles, or as surface coatings
and discrete precipitates sufficient space for on-site treatment
Technology Overview
Crude oil (Alberta, Canada)
Creosote (Edmonton, Canada)
Hydrocarbons (Olympic Park, London, UK)
Hydrocarbons; 500,000 tons (East London, UK)
As; 410,000 tons (Vineland Chemical, NJ, USA)
Cr, Cu, Ni; 19,200 tons (King of Prussia, NJ, USA)
TPH; 50,000 tons (Lezo, Spain)
Technology Overview Soil washing
physical separation
Chemical-enhanced soil washing chemical extraction
physical separation and chemical extraction
Physical Separation
clean soil fractions
contaminated soil fractionscontaminated soil
Chemical Extraction
processed, clean soil
contaminated washing solutioncontaminated soil
Physical Separation
clean soil fractions
contaminated soil fractions
contaminated soil
Chemical Extraction
processed, clean soil fractions
contaminated washing solution
Chemical-enhanced soil washing Produce a cleaner sand fraction
that otherwise fails to meet the specified cleanup goals
Or treat the entire soil matrix, including the fines fraction
Rotating Drum Rotating Screwpump
%100)/(
)/(1
(%)
kgmgsoilinionconcentratinitial
kgmgsoilinionconcentratfinal
efficiencyextraction
%100)(
)((%)
tonssoilsfeed
tonsproductscleanreductionvolume
(>2 mm)
(chemical additives)
(<2 mm)
U.S. EPA mobile soil washing system
Chemical-enhanced soil washing
(mineral-processing equipment)
Chemical agents surfactants, cosolvents, chelating
agents, acids
Surfactants reduce surface and interfacial tension,
mobilizing residual organics solubilisation of hydrophobic organics
by surfactant micelles
Cosolvents water-miscible organic solvents increase effective aqueous solubility of
hydrophobic organics e.g., methanol, ethanol, propanols
Surfactant-Enhanced Soil Washing for crude oil contamination (Alberta, Canada)
C12E4 (nonionic)
CTAB (cationic)
SDS (anionic)
Chemical-enhanced soil washing
Chemical agents surfactants, cosolvents, chelating agents, acids
Chelating agents (chelants) enhance metal extraction by forming soluble
complexes non-biodegradable – EDTA, DTPA biodegradable – NTA (carcinogenic), S,S-EDDS
Chemical-enhanced soil washing
EDTA metal-EDTA complexEDDS metal-EDDS complex
Contaminants of Concern
Feed Soil (After Surfactant Flushing)
(mg/kg)
Clean Soil (mg/kg)
Removal Efficiency
Total Petroleum Hydrocarbons (TPH)
3,000 – 15,000 150 – 500 95-97%
former hydrocarbon storage facility in Spain 50,000 tons of soils contaminated with total petroleum hydrocarbon surfactant-enhanced soil washing
higher throughput rate and lower cost compared to thermal treatment
30 to 50 ton-per-hour feed capacity mobile treatment plant
Case Study
Site Overview Free-Phase Product Plant Feed Soil Washing Plant Cleaned Soil
from 1950 to 1994 Vineland Chemical Co. manufactured arsenic-based herbicides in New Jersey
contamination of soil, sediment, and groundwater of the plant site (54 acres), a low-lying nearby marsh, the Blackwater Branch, the Maurice River and Union Lake
National Priority List (Superfund site) USEPA tenured to USACE (US Army Corps of Engineers) and
ART to plan, design, and execute the selected remediation bench-scale treatability and process optimization
studies in late 2001 construction activities included
plant building, soil treatment plant, plant support systems, chemical storage area and outside contaminated and clean soil storage pads
plant construction was completed in the fall of 2003
Case Study
Plant Fabrication
Equipment Assembly
initial remedial design – 180,000 tons of contaminated soil located at the Plant Site (source control) and Blackwater Branch (river areas), with the potential for future treatment of additional volumes)
sandy soils; arsenic concentrations ranged from < 20 to > 10,000 ppm excavation, staging and blending plan – desired feed concentration of arsenic
(60-90 ppm) commissioning and prove-out phase – full-scale operations at original design
rate of 56 tons per hour comprehensive plant optimization in July 2004 – capacity increased from 56
to >70 tons per hour, resulting in savings of US$ 3M
Case Study
Soil Treatment Plant
unit operations: wet screening, hydrocyclones chemical extraction arsenic precipitation, leachate regeneration, water clarification sand dewatering, fines thickening and filter press dewatering
trommel and vibrating wet screens to remove oversize materials (> 2 mm) from the feed soil
hydrocyclones to separate the fines (< 100 m)
Case Study
Soil Feeding Soil Screening
sand slurry – mixed with chemical agents at 130 oF in four in-series leaching tanks
rotating ball mill – remove arsenic coatings from higher-concentration feed materials
clean sand (< 20-ppm cleanup level) only 1.3 percent of treated soils required
retreatment contaminated water – pH adjustment for
arsenic precipitation and flocculation sludge generated and fines –
consolidated and disposed off-site
Case Study
Leaching Tanks
Arsenic Precipitation
Clean Soil
Soil Extraction
operations completed in 2007 a total of 410,000 tons processed – largest of
its kind in the US 94 percent of treated soils returned to the
site as clean backfill 6 percent disposed classified by USACE and USEPA as a “great
success” “Its success offers great promise for use on
other site operable units or for similar efforts within the Superfund program.”
Case Study
Summary Chemical-enhanced soil washing Ex-situ, on-site, physical-chemical process Heavy metals, fuels, SVOCs, pesticides, etc Mineral-processing equipment Volume reduction, contaminant extraction, soil reuse as cleanfill
or construction materials
Thanks for your time – Questions are most welcome([email protected])
Kinetic interactions in soil washing/flushing:Tsang, D.C.W.; Yip, T.C.M.; Lo, I.M.C. (2009). Environ. Sci. Technol., 43, 837-842. Yip, T.C.M.; Tsang, D.C.W.; Ng, K.T.W.; Lo, I.M.C. (2009). Environ. Sci. Technol., 43, 831-836.Zhang, W.; Tsang, D.C.W.; Lo, I.M.C. (2008). J. Hazard. Mater., 155, 433-439.Tsang, D.C.W.; Zhang, W.; Lo, I.M.C. (2007). Chemosphere, 68, 234-243. Zhang, W.; Tsang, D.C.W.; Lo, I.M.C. (2007). Chemosphere, 66, 2025-2034.Modeling extraction:Yip, T.C.M.; Tsang, D.C.W.; Ng, K.T.W.; Lo, I.M.C. (2009). Chemosphere, 74, 301-307. Modeling transport:Tsang, D.C.W.; Lo, I.M.C.; Chan, K.L. (2007). Environ. Sci. Technol., 41, 3660-3667.