21st Annual Conference

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(daniel.tsang@canterbury.ac.nz)

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.

21st Annual Conference