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Adsorption of Bipyridylium Herbicides by Humic Acid¹

ABSTRACT

The adsorption of paraquat (1,1'-dimethyl-4,4'-bipyridylium dichloride) and diquat (1,1'-ethylene-2,2'-bipyridylium dibromide) by various cation-saturated humic acids was investigated. The cation order for increasing adsorption for the two herbicides was nearly the same and followed the sequence: Al³⁺ < Fe³⁺ < Cu²⁺ < Ni²⁺ < Zn²⁺ < Co²⁺ < Mn²⁺ < H⁺ < Ca²⁺ < Mg²⁺. It was suggested that the colloid geometry of humic material and the shape, size and nature of bipyridylium cation would influence the adsorption of the herbicide. By infrared spectroscopic and potentiometric techniques evidence was procured for the involvement of ion-exchange and charge transfer mechanisms in the adsorption of bipyridylium herbicides by humic acid.

Key Words: herbicide-humic acid complex • paraquat • diquat • infrared spectra • potentiometric titration

¹ Contribution from the Research Station, Canada Dept. Agr., Regina (Sask.), Canada.

² Research Scientist. Chemistry and Biology Research Institute, Canada Dept. Agr., Ottawa (Ontario), Canada K1A OC6.

Received for publication July 3, 1973.