(formerly DAVY RESEARCH AND DEVELOPMENT, LIMITED)
(Chemical Treatment)
This treatment employs resin-in-pulp (RIP) or carbon-in-pulp (CIP) technologies to treat soils, sediments, dredgings, and solid residues contaminated with organic and inorganic material. These technologies are based on resin ion exchange and resin or carbon adsorption of contaminants from a leached soil-slurry mixture.
RIP and CIP processes are used on a commercial scale to recover metals from ores. The RIP process recovers uranium and uses anion exchange resins to adsorb uranium ions leached from ore. The CIP process recovers precious metals. In this process, activated carbon adsorbs gold and silver leached as cyanide complexes.
The figure below illustrates a typical process for metals and other inorganically contaminated soils. Incoming material is screened, and over sized material is crushed. The two fractions are then combined and leached in an agitated tank, where the contaminants are extracted. The leached solids are then passed to cyclones that separate coarse and fine material. The coarse material is washed free of contaminants, and the wash liquors containing the contaminants are passed to the contaminant recovery section. The leached fine fraction passes to the RIP or CIP contactor, where ion-exchange resins or activated carbon remove the contaminants. The difficult fines washing step is thereby eliminated.
The resins and carbons are eluted and recycled in the extraction step, and the concentrated contaminants in the effluent pass to the recovery section. In the recovery section, precipitation recovers contaminants from the wash and eluate solutions. The precipitation yields a concentrated solid material and can be disposed of or treated to recover metals or other materials. The liquid effluent from the recovery section can be recycled to the process.
For organically contaminated feeds, the in-pulp or slurry process treats the whole leached solid. Organic contaminants eluted from the resin or carbon must be treated appropriately by a separate technology.
Both the RIP and CIP commercial scale processes operate in multistage, continuous, countercurrent contactors arranged horizontally.
This chemical treatment technology treats soils and other materials contaminated with inorganic and organic wastes. Inorganics include heavy metals such as copper, chromium, zinc, mercury, and arsenic. Treatment of materials containing organics such as chlorinated solvents, pesticides, and polychlorinated biphenyls requires appropriate extractant reagents and sorbent materials.
This technology was accepted into the SITE Emerging Technology Program in July 1991. Laboratory studies have been underway since January 1991. Bench-scale tests have successfully met targets for removal of several heavy metal contaminants.
Arsenic and mercury have proven more difficult to remove; however, laboratory tests have reduced arsenic to below 30 milligrams per kilogram (mg/kg) in soil and mercury to 0.5 mg/kg in soil in the major fraction of the soil. Due to the lack of demand for this technology in the European Market, Davy has decided to withdraw from the SITE Program.
FIGURE...
Chemical Treatment Process
EPA PROJECT MANAGER:
Vince Gallardo
U.S. EPA
National Risk Management Research Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
513-569-7176
Fax: 513-569-7620
TECHNOLOGY DEVELOPER CONTACT:
George Rowden
Davy International Environmental Division
Ashmore House
Richardson Road
Stockton-on-Tees
Cleveland TS18 3RE
England
011-44-1642-602221
Fax: 011-44-1642-341001