Description of Organoclays

Organically modified clays, also called organoclays, consist of bentonite,
modified with quaternary amine salts, such as di-methyl di-hydrogenated
tallow ammonium chlorides. The major constituent of the bentonite, a
chemically altered volcanic ash, is the clay mineral montmorillonite. It has a cation exchange capacity of 70-95 meq/100 gm. The ammonium functional group, a nitrogen atom on the quaternary amine, which has a positive charge, is exchanged onto the clay surface for sodium and calcium (11). The replaced sodium and calcium ions and the free chloride ions from the amines are washed out. The modified clay acts as a non-ionic surfactant. As mechanically emulsified, non-polar oil molecules and dissolved organic compounds encounter organoclay particles whose alkyl chains extend into the water, these chains attract the oil molecules. Since this partitioning activity takes place off the surface of the clay particles, no blinding occurs.

During the ion exchange of the quaternary amine with the sodium and
calcium ions, only a part of the total number of ions are replaced. The
remainder are still present, and give the clay the ability to also remove
inorganic metal cations such as lead, zinc, copper and others. While the
removal capacity is hard to predict, it nevertheless is a side benefit for
the end user to have a product that has the capability to remove organics
and inorganics simultaneously.

If the removal of oil is the main purpose of using the organoclay, and if
it is placed into a carbon vessel, the clay is granulated and then blended
with anthracite to keep the pore spaces open. Batch systems use powdered organoclay.

Laboratory Methods

The Mini-Column Technique (12)
This method consists of pumping a contaminated solution through a small sorbent sample. For example, 1 gram organoclay sorbent is packed into a small column, and spiked water is passed through this column until the influent concentration of the contaminant equals that of the effluent. Using small particles accelerates the time to obtain equilibration between the particles and contaminated water, i.e. the aqueous phase. The pump is a high-pressure pump, which delivers 2000 lb/inch square (psi) of pressure. Target compounds are measured periodically in the influent and effluent water samples. Breakthrough point is achieved when contaminant is detected in the effluent. The shape of the breakthrough curve describes the "Mass Transfer Zone (MTZ )" (12). The solid is a fine powder, in this case organoclay and/or activated carbon powder (PAC). In our case, synthetic water solutions spiked with: benzene, toluene, xylene and naphthalene, were prepared and passed through the mini-columns to determine the effectiveness of each sorbent, organoclay and PAC. A reservoir with contaminated water is placed near the top of the column, and the contaminated water is passed through the column until the effluent concentration of the contaminant is the same as the influent concentration, i.e. a steady state exists. This technique is more practical than the construction of isotherms. Replications were not performed due to financial restraints.

Preparation of Emulsions for Oil Removal Capacity Testing

499.50 grams of tap water (softened) were weighed into a clean glass
blender container. 0.50 grams of a commercial oil to be tested were added and the mixture blended in a blender at high speed for five minutes. Eight 500-gram batches were subsequently combined together to form a composite suspension. The composite batch was continuously stirred with an overhead mixer.

Organoclay Testing for Oil Removal Using the Jar Test

The "Jar Test" was designed by the author for this study as a quick and
economic method to achieve preliminary results. It is basically a single
point isotherm. It is performed by contacting a known weight of sorbent with the contaminated water. A water sample with no sorbent is also tested and used as control, so that the adsorbent performance can be determined. This test provides a quick performance evaluation, without having to perform a ten point ASTM Isotherm Test (12). Due to financial constraints, replication was not conducted.

349.72 grams of a composite oil/water solution (emulsion) were weighed out into a clean mechanical mixer and mixed for four minutes at low speed. Then 0.28 grams of organoclay were added to the agitating composite, for four minutes. This amount had been pre-determined in separate tests as representative of maximum adsorption with the minimum amount of clay. A portion of the treated emulsion was then pipetted out. The author determined to add a drop of an anionic surfactant to flocculate the organoclay out of the solution, thus allowing testing of a sample that was not contaminated
with solids. The oil content (in milligram per liter) was determined with a
portable Horiba oil detection instrument.

Results and Discussion

Laboratory Results

When testing the removal capacity of the sorbents for benzene,
toluene, o-xylene and naphtalene, the organoclay performs nearly as well as carbon, improving in performance as the solubility of the compound
decreases. Surprisingly, organoclay removes methylene chloride much more effectively than does activated carbon. The reasons for this phenomenon are not clearly understood.

These tests were followed by a set of mini column tests using a ternary influent. The influent was spiked with benzene, toluene and naphthalene. The activated carbon industry has long been aware that there is competition amongst some contaminants for sorption sites. The less soluble ones seem to keep the more soluble ones such as benzene, off the sorption sites. Often the more soluble ones such as benzene are removed from sorption sites by less soluble compounds such as xylene or toluene. This knowledge is important to the design engineer for determining the amount of organoclay and carbon that is required for maximum economy of the pump and treat system.

900 mg/l of each compound was added to water. It was possible to add that much naphthalene because the benzene and toluene helped dissolve it. Usually its solubility is 10 mg/l. This concentrate was pumped at a constant rate, separately through an organoclay and a carbon column. The effluent was tested for each solvent to determine the break through, i.e. which compound broke through earlier and at what levels. The last column was filled first with 0.5 gram of organoclay, followed by 0.5 gram of activated carbon, to determine if the organoclay/carbon combination (not mixture) was indeed more effective than each of them alone.

Benzene broke through first, followed by toluene and naphthalene. The most important conclusion is that the organoclay/carbon system is much more effective than either sorbent alone, even though the amount of sorbent in each case is double than that in the combined column.

Field Results

A test was conducted to determine the
suitability of organoclay, activated carbon, or a combination of the two,
for the removal of gasoline (measured as TOC) from groundwater at an
underground storage tank (UST) site. A standard permeability test was
performed. Three columns were set up, three inches wide, 30 inches long, and filled with a fixed amount of filtration media. The first column contained organoclay, the second contained activated carbon, the third one was a combined sample consisting of one half (upper portion) granular organoclay (blended with anthracite at a 30%/70% blend), and one half (lower portion) granular activated carbon. The influent is pumped through the column with a small peristaltic pump, simulating about three gallons per minute per ft2, which is a standard accepted flow rate in the field. The organoclay removed the gasoline completely, as well as a significant amount of other solvents, increasing the activated carbon's effectiveness for the removal of the volatile organic carbons.

Results of Jar Tests

It was observed that refined oils are removed much more efficiently than crude oils. The reason is that crude oils contain many polar substances, which the non-polar organoclay removes with lower effectiveness. As long as mineral oils are non-polar, the non-ionic organoclay is an excellent adsorber. The effect of polarity is even more pronounced in the removal of plant oils from water. As long as the oil is refined, the results are good. The cationic organoclay is much better at removing crude oil compounds than non-ionic organoclay. The crude oil compounds tend to be slightly polar due to the presence of lipids, increasing the effectiveness of a cationic organoclay for removal of these compounds from water.

Case Histories

1. 3 million gallons of wastewater were stored in a gas holder at a former
manufactured gas plant. The tank is made out of steel, and placed onto a
concrete slab. The bottom of the tank was covered with coal tar.
Contaminated water sat on top of the tar. The water was part of the original seal that contained the gas in the telescoping tank. The purpose of removing the water was to facilitate the removal of the tar. An oily sheen was found floating on top of the water and adhering to the tank walls. The water was contaminated with polycyclic aromatic hydrocarbons, oil, benzene, toluene, ethyl benzene, xylene and heavy metals. Only benzene and xylene needed to be removed, according to local discharge standards, to levels of 134 ppb and 74 ppb, respectively.

The treatment system that was installed initially included an oil/water separator, bag filters to remove suspended solids, and two granular activated carbon vessels that could each hold 6000 lb of carbon. The flow rate was 150 gallons per minute, about four gallons per minute per foot square, which gives a retention time of about eight minutes. The activated carbon was spent within three days due to blinding of the pores by oil. Then the 6000 lb carbon in the first vessel was replaced by 9,000 lb of organoclay/anthracite. The organoclay lasted six weeks, then was changed out once, while the carbon was replaced twice. Discharge limits were met at all times.

The concentration of contaminants was:

The organoclay, after it was spent, was landfilled in the nearest
landfill. It was found to be non-hazardous. The activated carbon was
regenerated by the supplier. The savings for the tank owner, generated by
using the organoclay/carbon combination, instead of carbon alone or hauling of the water to a hazardous waste water treatment plant, amounted to $990,000.

Facet Superfund Site

At Facet Superfund site in New York, PCB had to be removed from
groundwater to meet discharge standards. Since transformer oil was also
present in the water, an organoclay/activated carbon system was utilized for cleanup of the groundwater. The following results where reported:

The quantity of PCB detected on the surface of the organoclay after all
the water was cleaned was about 40 ppm. Since this amount was less than the 50 ppm maximum permitted for landfill disposal of the media, the spent organoclay was disposed of in a landfill. These data show the capability of the organoclay to remove heavy metals.

Conclusions

The laboratory tests show that a combination of organoclay and activated
carbon, in series, produces more efficient results, namely, the combination lasts longer until breakthrough is reached, than if either media alone is used. The case history above backs up this conclusion. Interestingly, we find that large systems show this improved performance due to the organoclay/carbon combination more drastically than the lab results would suggest. This is reported to us by field personnel.
The obvious conclusion is that the costs of water treatment, be that
industrial wastewater, or "pump and treat" groundwater cleanup systems, can be significantly lowered by using the organoclay/carbon approach.
Pre-polishing with organoclay to remove oils, greases and PCBs lowers
activated carbon consumption by 700%. Secondly, the organoclay removes a substantial amount of less soluble solvents such as chlorophenols, toluene, xylene, ethyl benzene, PNAs and others chlorinated hydrocarbons, improving the effectiveness of activated carbon for the removal of more soluble solvents even more. These data and case histories show that organoclays can be used to improve the efficiency, and thus lower the costs affiliated with carbon, even if there is no oil, or only a very small amount (1 ppm), present in the water. Therefore, the recommendation to the design engineer is that he/she considers using a clay/carbon system for improved water clean up efficiency.

References

1. Jordan, J.W., 1949. Organophilic Bentonites, I, Swelling in Organic
Liquids. Jour. Phys. Colloid Chem., 53: pp. 294-306.

2. Cowen, C.T., and D. White, 1962. Adsorption by Organoclay Complexes, I, Proceedings of the 9th National Clay Conference, Pergamon Press (Elsevier), NY. Pg. 4509-467.

3. Street, G.B., and D. White, 1963. Adsorption by Organoclay Derivatives. J. Appl. Chem., pp.288-291.

4. Slabough, W.H., and D.B. Hanson, 1969. Solvent Selectivity by an
Organoclay Complex. Jour. Of Colloid & Interface Science, Vol. 29, No. 3, pp. 460-463.

5. Mortland, M.M., 1970. Clay-Organic Complexes and Interactions. Adv.
Agronomy 22., pp. 75.

6. Wolfe, T.A., Demiral, T., and E.R. Bowman, 1985. Interaction of Aliphatic Amines with Montmorillonite to enhance Adsorption of Organic Pollutants. Clays and Clay Minerals, Vol.33, pp. 301.

7. Smith, J.A., and P.R. Jaffe, 1994. Benzene Transport through a Landfill
Liner containing Organophilic Bentonite. J. of Environmental Engineering,
120, 1559-1577.

8. Alther, G.R., 1995. Organically Modified Clay removes Oil from Water.
Waste Management, Vol. 15, No.8, pp. 623-628. Pergamon Press (Now Elsevier Sciences), Amsterdam.

9. Alther, G.R., 1999. Organoclays remove Oil, Grease, Solvents, and
Surfactants from Water. CleanTech 99, Proceedings, Witter Publishing Co., Flemington, NJ. Pp. 72-79.

10. Faschan, A., Tittlebaum, M., and F. Cartledge, 1993. Nonionic Organic Partitioning onto Organoclays. Hazardous Waste and Hazardous Materials, Vol. 10, No.3, pp. 313-322. Mary Ann Liebert Publ.

11. Lagaly, G., 1984. Clay-Organic Reactions, Interactions. Phil. Trans. R. Soc. London, A-311. pp. 315-332.

12. Novicki, H.G., and W. Schuliger, 2000. Sorbent Performance Evaluation ASTM Aqueous Phase Isotherm Program. Water Conditioning and Purification, Oct. 2000. pp. 102-106.
   

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