514 ABSTRACTS

Supercritical Fluid Extraction Of Organic Pollutants From Soil Combined With Adsorption Onto Activated Carbon

C. Erkey, G. Madras, M. Orejuela and A. Akgerman Chemical Engineering Department, Texas A&M University, College Station, TX 77843

A novel process was developed on laboratory scale for remediation of soils contaminated with organic pollut- ants. In this process, the organics are continuously ex- tracted using supercritical carbon dioxide (SCCO2) and then deposited onto activated carbon. Clean CO2 is cir- culated back to the extractor, and the cycle continues un- til the desired level of decontamination is achieved. In order to investigate the feasibility of the process, the ad- sorption isotherms of naphthalene, phenanthrene, hex- achlorobenzene, and pentachlorophenol on standard EPA soil and on activated carbon were determined in the pres- ence of SCCO2 using frontal analysis chromatography. All the adsorption isotherms were modelled based on the Freundlich isotherm. The amount of organic adsorbed on carbon was found to be dependent on the surface area rather than on the nature of the organic; whereas, the ad- sorbed amounts on soil were found to be strong function of the type of contaminant. The heats of adsorption of the organics were also extracted from the temperature de- pendency of the initial slopes of the isotherms. The desorptive behavior of these organics from soil using SCCO2 were also investigated, and the local equilibrium theory was found to predict the desorption profiles fairly accurately. An economical analysis indicates that the op- erational costs for the process compare favorably with existing technologies.

I N V E S T I G A T I O N O F A D S O R P T I O N

C H A R A C T E R I S T I C S O F V O L A T I L E

O R G A N I C C O M P O U N D S O N D R Y A N D

H U M I D S O I L

Catherine Thibaud, Can Erkey and Aydin Akgerman Chemical Engineering Department Texas A&M University College Station, TX 77843-3122

Volatile organic compounds (VOCs) are one of the major types of chemicals found in contaminated soils be- cause of their wide use as solvents and their presence in leaking underground storage tanks. The remediation techniques available for decontamination of VOC-con- taminated soils involve the desorption process of the con- taminant from the soil particles. Assessing the importance of this process necessitates the investigation of the adsorption/desorption characteristics of the con- taminant in soil. The results to be presented were ob- tained using a dynamic response technique based on frontal analysis chromatography. The adsorption capaci- ties corresponding to monolayer coverage were found to

be very well correlated with the adsorbent surface area, whether individual soil constituents (clay, sand, silt) or natural soil (mixture of individual constituents) were considered. The effect of moisture on organic adsorp- tion/desorption was studied, and it was found that or- ganic uptake by soil was drastically reduced in the presence of moisture. The adsorption isotherms of chlo- robenzene and toluene on soil were obtained at different relative humidities. As relative humidity increased, the isotherms became progressively type Ill isotherms which is characteristic of weaker adsorbent/adsorbate interac- tions. The adsorption reduction was especially important at low organic partial pressure and high relative humid- ity. The investigation of the effect of moisture on the desorption process showed that desorption rates were much higher when a moist gas stream was used as strip- ping fluid.

S O I L R E M E D I A T I O N A N D W A S T E O I L

T R E A T M E N T B Y A G G L O M E R A T I O N

W I T H C O A L

David W. Arnold Department of Chemical Engineering, University of Alabama, Tuscaloosa, AL 35487

The coal processing industry first used oil agglomeration to commercially clean and recover coal in 1922 in

Alexandria, Virginia. Agglomeration never enjoyed popularity because of the prohibitively high cost of the

bridging liquid, oil. As a result of the demand for higher

quality coal, there is renewed interest in this technique

because of its ability to clean fine coal. Agglomeration works by sticking the finely ground organic coal particles together with the oil in a dilute coal-water slurry. Intense

mixing is required to accomplish this. The agglomerates (organic + oil) float to the top and are skimmed off, while the organic-free ash-forming mineral fraction sinks

and is rejected. Our laboratory has been working on oil agglomeration

since 1989. This work focused on recovery of waste coal from impoundment ponds, coal washing plant reject streams and from inplant fine coal that is not recovered by present-day coal preparation plants.

Recovery, transportation, and processing of petroleum and other hydrocarbon fuels generate soil contaminated with oil, tar, and other heavy organic. This project treats the oily soil with fine coal. The bridging liquid (oil) is supplied by the contaminated oil. The agglomerated fine coal and contaminant oil is bloated and removed, leaving an oil-free soil.

Our studies to date have shown this method capable of treating soils saturated with heavy hydrocarbons (crude oil) with oil recoveries as high as 99.98%. The coal and oil are recovered as a high-grade fuel.