NOTES
Adsorption of Mercury from Aqueous Solutions by Polyethylenimine-Modified Wool Fibers Graeme N. Freeland, Ronald M. Hoskinson,* and Robert J. Mayfield CSIRO, Division of Textile Industry, P.O. Box 21, Belmont, Victoria, 3216, Australia was the amount of mercury adsorbed by the bed when its When used in a packed column or a standing bath, polyconcentration in the column effluent reached 1% of the ethylenimine-modified wool (PEI-wool) had a substaninfluent concentration. For adsorption onto wool in standtially greater ability to adsorb mercury (Hg2) from aqueing baths it was the amount adsorbed from the liquors ous solution than unmodified keratin. A capacity of 3.3 after the prescribed period, and the value was calculated meq/g was achieved within 30 min using solutions of 1000 from the decrease in mercury concentration of the bath ppm (Hg2). Sorption from liquours passing through a colliquor. All adsorption measurements were made a t 20°C. umn was rapid and effective a t the 1-ppm level. The Mercury Analysis. This was by atomic absorption sorbed mercury was readily desorbed and the PEI-wool spectrophotometry. Separate procedures used for solutions used repeatedly. containing 1-1000 ppm ( 1 0 ) and up to 1 ppm Hg2 ( 1 2 ) were essentially as described. ~
There have been several recent reports of the ability of protein fibers to adsorb mercury from aqueous solution (1-4), and the possibility of using them in effluent purification processes or for clinical purposes ( 5 ) has been discussed. Likewise, amine-modified cotton could adsorb mercury from solutions (6, 7 ) . Here we report that the adsorptive capacity of wool for mercury (Hgz) is substantially increased by polymerization of ethylenimine onto the fibers. Experimental
PEI-Wool. Commercially scoured 64’s quality Australian merino wool fibers (40 grams) were immersed (2 hr) in a 0.2% solution of ferrous ammonium sulfate (800 ml) and then squeezed before allowing to dry (48 hr) at 20°C. To the wool was added 0.25% hydrogen peroxide solution (600 ml) and ethylenimine (30 ml) ( 8 ) . [Because of potential hazards from exposure to ethylenimine, it has been recommended (9)that protective gloves and goggles be used and that all operations be performed in a fume hood.] The fibers were heated (19 hr) at 50°C under nitrogen, rinsed under running tap water (2 hr), dried as before, and choppcd to 1-3 mm lengths in a rotary mill. The uptake of ethylenimine (as bound PEI) was 10%w/w. PEI-Reduced Wool. Unmodified wool (10 grams) was chemically reduced with 0.5M thioglycollic acid (300 ml) a t 50°C for 3 hr, washed with distilled water, dried (lOO”C, 5 min), and converted to PEI-reduced wool as above. The uptake of ethylenimine (as bound PEI) was 20.2% (w/w). Adsorption onto Columns of Chopped Wool Fibers. The wool ( 5 grams) was wet out in water containing 0.01% Antarox C0630 (a polyoxyethylated nonylphenol, GAF Corp.) and the resulting slurry poured into a glass column fitted with a porous plug and stopcock. When the fibers had settled they were equilibrated with solutions a t the pH of the test solutions. The test solutions contained 1000 ppm Hg2 (as IIgClz or a combination of HgC12-NaC1, Table I) and adjusted to various pH values with NaOH or HC1. Test solutions were admitted a t the rate of one bed volume,’min. The column effluent was collected in fractions and their mercury concentration measured. Adsorption onto Wool in Standing Bath. The wool (5 grams) was stirred in a glass beaker with a solution (1 liter) adjusted to the required pH, containing 1000 ppm Hg2 (as HgClz or HgC12-NaCl, Table I) for prescribed periods. Capacity of Wool Fiber Beds. Here the capacity of the beds has been expressed as milliequivalents of mercury per gram of wool (meqlg). For adsorption onto columns it
Results and Discussion
PEI-Wool. Protein fibers will bind approximately 1%of polyethylenimine irreversibly (12). This quantity will increase slightly if the fibers are pretreated with chlorine. By polymerization of ethylenimine monomer onto wool fibers, as reported here, irreversible binding of 10-2070 PEI can be achieved. It is not known whether the PEI-wool composite so formed contains the PEI as a physically occluded or chemically grafted component. In the present work, wool treated by the last method has been used as packed beds in columns and in stirred standing baths to examine its potential in both continuous and batchwise mercury recovery processes. Table I shows that maximum adsorption occurred in standing baths where, within 30 min, equilibrium was established. The capacity of 3.3 meq,’g is of the same order as that of many granular ion exchangers. Even in solutions containing 10% NaC1, the adsorption of 1 meq Hg2/g was still significant and may indicate that PEI-wool could Table I. Mercury Adsorption by PolyethylenimineModified Wool Liquor pH
Ex peri rnen ta I rnethodo
NaCl concn
PEl-Wool
6 6 6 6
830
860
10 10
6 6 2
8
5
25
860
25
7 6
860
sl5
C C C 25 PEl-Reduced Wool
6 6 6 6
S80
S80
3 10
6 7 6
830
25
C C 3 Unmodified Wool*
6
s60
2 7
C C
Capacity, rneq Hgl/g wool
3.3 3.3 1.0 1.1 0.6 0.6 1.4 2.4 0.2
3.6 3.6
860
Sk
,% ’
25
2.0 1.1 0.9 2.8
1.6 0 0.58 0.29
a 8 with a numerical subscript refers to adsorption in a standing b a t h for the indicated period (rnin), C refers t o a column adsorption. From ( I ) .
b
Volume 8,Number 10, October 1974 943
have practical advantages in adsorbing mercury from electrolyte solutions ( 1 3 ) . In column adsorption tests, where the contact time was 1 min, the capacity was lowered slightly to 2.4 meq Hg2/g a t pH 7 , indicating that adsorption was a rapid process. Sorbed mercury was quantitatively recovered by extracting the PEI-wool with N HC1 (50°C, 15 min) or with citric acid solution (l%,pH2, 40”C, 15 min). The wool that was stripped in this way could be reused, an adsorption capacity of 2 meq/g persisting after 15 cycles. Adsorption onto columns was effective when low concentrations of mercury were used. When 500-bed volumes of liquor containing 1 ppm Hg2 (pH 6) were passed through the column (1 bed vol/min), the concentration in the effluent did not exceed 0.02 ppm. Greater efficiency could be expected from longer contact times in the column. When we consider the pH range 2-7, we note that modification of wool with PEI changes the pH of maximum adsorption from 2 to 7 ; corresponding differences in the adsorption mechanisms might be inferred. Probably, at pH 2, the association of protonated amino groups with anionic mercuric complexes such as HgC13- or HgCLi2- occurs (1). At pH 7 , the adsorption probably involves chelation of Hg2 with ligands located in both the PEI ( 1 4 ) and the wool. PEI-wool appears to have a mercury adsorbing capacity exceeding cross-linked PEI-cotton (6) by a factor of 100. Although strict comparisons have not been made its rate of adsorbing mercury seems substantially greater than that reported for the modified cotton ( 7 ) . PEI-Reduced Wool. Ethylenimine was polymerized onto thioglycollate-reduced wool in the expectation that the chemically modified fibers, released from the restraint
of protein disulfide bonds, would swell more readily in aqueous media. An increased PEI add-on and correspondingly improved mercury adsorption might then have resulted. Practically, the amount of PEI formed in reduced wool was double that formed in native wool. Only minor increases were observed in the mercury-adsorbing capacity of PEI-reduced wool, consequently no advantage can be seen in using wool in the reduced form. Literature Cited (1) Brady, P. R., Freeland, G. N., Hine, R. J., Hoskinson, R. M., Textile Res. J., in press (1973). (2) Friedman, M., Masri, M. S., J. Appl. Polymer Sci., 17, 2183 (1973). (3) Friedman, M., Waiss, A. C., Enuiron. Sci. Technol., 6, 457 (1972). (4) Friedman, M., Harrison, C . S., Ward, W. H., Lundgren, H. P., J . Appl. Polymer Sei., 17, 377 (1973). (5) Takahashi, H., Hirayama, K., Nature, 232,201 (1971). (6) Roberts, E . J., Rowland, S. P., Textile Res. J., 41, 864 (1971). (7) Roberts, E . J., Rowland, S. P., EnGiron. Sei. Technol., 7, 552 (1973). (8) Lipson, M., Speakman, J. B., J . SOC.Dyers Colour., 65, 390 (1949). (9) Dermer, 0. C., Ham. G. E., “Ethylenimine and Other Aziridines, p 453, Academic Press, New York, S . Y . , 1969. (10) Elwell, W. T., Gidley, J . A. F., “Atomic Absorption Spectrophotometry,” 2nd ed., p 105, Pergamon, London, 1966. (11) Hatch, W. R., Ott, W. L., Anal. Chem., 40, 2085 (1968). (12) Chow, C. D., Textile Res. J., 41,444 (1971). (13) Tarkovskava. I. A.. Strazhesko. D. N.. Andreev. Yu. V.. Kostyuchenko, P . I., Glushankova, Z . I., Khim Tekhnol (Kiev), 3 , 3 (1971). (14) Dermer. 0. C.. Ham. G. E.. “Ethvlenimine and Other Aziridines,” p 335, Academic Press, S e w Ybrk, N.Y., 1969.
Received for recieu’ November 6, 1973. Accepted May 3, 1974.
Removal of Mercury from Aqueous Solutions by A/-( 2-Aminoethyl)aminodeoxycelluloseCotton Stephen L. Snyder and Tyrone L. Vigo Southern Regional Research Center, Agricultural Research Service. U.S. Department of Agriculture, New Orleans, La. 701 79
N-(2-Aminoethyl)aminodeoxycellulose cotton (AEAC) was prepared in yarn form by reaction of ethylenediamine with chlorodeoxycellulose. The adsorption of mercuric ion by AEAC (degree of substitution 0.4) was studied over a wide range of concentrations. In the concentration range 0.5-43 g/l., the adsorption of mercuric chloride follows the Freundlich relationship, loglo x = 0.21 loglo C + 2.7, where x is the mg of mercuric chloride bound per gram of AEAC and C is the residual concentration in g/l. At concentrations in the range of 3.1-0.6 ppm, 100 mg of AEAC removed about 90% of the mercury present in 200 ml of solution, in a single equilibration. The results of this study suggest the possible use of AEAC as an agent for the collection of mercury in industrial processes. The possibility of employing ion exchange or chelating resins as a means of removing heavy metal ions from solution has been explored by a number of workers ( 1 - 5 ) . However, cost considerations have prohibited the widespread application of this technique on an industrial scale. A possible solution to the cost problem might be to use naturally occurring polymers or agricultural by-prod944
Environmental Science & Technology
ucts as the basis for the exchange resin. In this regard, Friedman and coworkers (6, 7 ) have shown that mercuric ion is bound in large amounts by certain agricultural byproducts and polyamine derivatives. This investigation concerns the use of cotton cellulose as the insoluble support matrix; however, the same techniques could be readily applied to other celluloses or synthetic polyalcohols. In the study reported here, we have attached an ethylenediamine group to the anhydroglucose unit of the cellulose backbone via chlorodeoxycellulose (CDC) cotton yarn to give N-(2-aminoethy1)aminocellulose cotton (AEAC). AEAC very efficiently adsorbs mercury over a broad range of concentrations. Suprisingly, we observed that a t very low concentrations (approximately 100 ppb), untreated cotton yarn also removes significant amounts of mercury. This adsorption may be due to carboxyl end groups and trace materials present in native cotton. Experimental
Materials. Cotton was loose twist 12/3 (tex-151) Pima kier-boiled yarn unless otherwise specified. The phosphorus oxychloride (POC13), dimethylformamide (DMF), and
