Extractive soil washing

ENSR International Group soil cleaning process is an ex situ treatment for soils contaminated with petroleum hydrocarbons. The process uses a combination of soil washing and solvent extraction. Soil washing removes heavy metals and hydrocarbons from coarse soil particles, resulting in a reduced volume of material to be treated by solvent extraction. Solvent extraction uses a chemical additive that enhances the extraction of hydrocarbons from soil particles in an aqueous slurry. 

Thermal desorption systems can be broken into three key components pretreatment, the TDU, and posttreatment (Fig. 1) as discussed below. Additionally, thermal desorption systems are often used in conjunction with other treatment technologies as part of a treatment train. At previous RCRA and Superfund sites, thermal desorption has been used in conjunction with bioremediation, dechlorination, incineration, soil vapor extraction, soil washing, and solidification/ stabilization. " In these cases, the combination of technologies was required to meet the site s cleanup goals. 

In a collection of synopses innovative site remediation technologies (43), technologies are categorized into bioremediation, chemical treatment, thermal treatment, vapor extraction, soil washing, solidification/stabilization, and other physical treatments. Here separation technologies are contained in the thermal treatment, vapor extraction, soil washing, and other physical treatment sections. Key technologies addressed are ... 

All ex situ soil treatment methods involve a two-step approach soil excavation and aboveground treatment of the excavated soil. The differences in the various ex situ excavation/treatment methods for soil remediation lie only in the methods of soil treatment aboveground, such as soil washing plus extraction, and slurry biodegradation. 

A soil sample is placed in a centrifuge tube, mixed with 0.5 M HC1 for 1 hour, and centrifuged. The HC1 solution is removed and the soil washed with water to remove the acid. The soil is then extracted with 0.5 M NaOH for 18 hours with shaking, followed by centrifuging to remove dissolved organic matter from soil (adapted and condensed from Reference 21). 

Newer and more complex humus extractions have been developed. These typically involve more steps such as both physical separation on the basis of density and particle size (related to the size of soil inorganic components), and chemical separation based on extractions and washings with hydrofluoric acid (HF), hydrochloric acid (HC1), and sodium hydroxide (NaOH). The products of such separations are then subjected to spectroscopic analysis and interpretation [22,23],... 

Fig. 4.3. Ultrasonic soil washing, pilot scale equipment giving a 15% improvement in PCB extraction using a Vibrating Tray .

TOOOl 3M Company, 3M Empore Extraction Disk T0124 BioTrol, Inc., Soil Washing Technology T0161 Chemical Oxidation—General... 

T0756 Supercritical Water Oxidation—General T0769 Terra Resources, Ltd., Terra Wash Soil Washing T0779 Terra Vac, Inc., Vacuum Extraction... 

T0755 Supercritical Carbon Dioxide Extraction—General T0757 Surbec Environmental, L.L.C., Soil Washing Technology T0763 Tallon, Inc., Virtokele... 

T0762 Syracuse University, Supercritical Fluid Extraction T0769 Terra Resources, Ltd., Terra Wash Soil Washing T0775 Terra Vac, Inc., Dual-Vacuum Extraction T0776 Terra Vac, Inc., Oxy Vac T0777 Terra Vac, Inc., Pneumatic Soil Fracturing (PSF)... 

The aqueous soil washing system is used to classify the particles into a coarse and fine fraction. The coarse fraction is cleaned by the use of heat, chemicals, and mechanical energy. This material can be returned to the site as clean backfill. The fine fraction is thickened and sent to the solvent extraction unit. 

The treatment costs for the GHEA Associates process depend on the soil matrix, properties, chemical composition of the contaminants, and other site-specific factors. The commercial-scale, integrated process, consists of the extraction and wash liquor purification steps. The estimated costs for the process range from 50 to 80 per ton of soil treated. Other separation processes have estimated treatment costs ranging from 90 to 200 per ton (D13377H, pp. 793, 799). 

TVIES has developed and patented an ex situ, transportable soil washing technology that uses the principle of countercurrent extraction in augers, hydrosizers, flotation cells, and clarifiers. The technology removes contaminants by using a combination of high-pressure water spray, chemical washing, and dissolved air flotation with appropriate acids, bases, and oxidation or reduction conditions. 

The transportable Calocroma soil washing technology is an ex sitn process that nses continnons extraction with an unspecified extraction fluid to extract hydrocarbons and solvents from soils. 

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