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Removal of Paraquat, Diquat, and Amitrole from Aqueous Solution by Chemically Modified Peat¹

ABSTRACT

The presence of organic pesticides in aquatic systems has been reported for more than 40 yr. Various methods, such as sorption by clays, activated C, or synthetic resins, have been used to remove these pesticides from water. Certain pesticides, such as the cationic species paraquat (C₁₂H₁₄N₂Ch₂; 1,1'-dimethyl-4,4'-bipyridinium dichloride), diquat (C₁₂H₁₂N₂Br₂; 6,7-dihydrodipyrido[1,2-a:2',1'-c]pyrazinediium dibromide), and the basic species amitrole (C₂H₄N₄; 3-amino-s-triazole), are sorbed by peat. However, the use of raw peat as a sorption medium for the removal of pesticides is hampered by the relative impermeability of peat, the leaching of organic matter from peat into the effluent, and by the disaggregation of peat at pH values greater than ca. 6.0. Treatment of peat with concentrated sulfuric acid at elevated temperatures yields a granular product that has an enhanced cation exchange capacity, that is resistant to leaching, and is permeable to water flow. The objective of this research was to evaluate the use of such chemically-modified peat for removing paraquat, diquat, and amitrole from aqueous solution under a variety of experimental conditions. Using isotherm and column experiments, it was shown that the treated peat is very effective in removing these pesticides from aqueous solution. Treated peat has a capacity of about 1 mol (+) kg^–1 for these three pesticides. The effects of pH, ionic strength, and flow rate on the efficiency of pesticide removal were found to be relatively small. Peats from two different localities behaved similarly in these experiments.

Key Words: peat • cationic pesticides • basic pesticides • pesticide removal

¹ Contribution from the Dep. of Chemistry and Geochemistry, Colorado School of Mines, Golden, CO 80401.

² Professor and former Graduate Student, respectively, Dep. of Chemistry and Geochemistry, Colorado School of Mines, Golden, CO 80401.

Received for publication February 14, 1985.