Use of surfactant-modified zeolite as fertilizer carriers to control nitrate release

Abstract

Use of soluble N fertilizers is one of the major causes for groundwater contamination in agricultural farmland. Thus, research producing inexpensive slow-releasing fertilizers has drawn great attention recently. In this study, the feasibility of using surfactant-modified zeolite (SMZ) as fertilizer carriers to control nitrate release was investigated. The zeolite was first modified by hexadecyltrimethylammonium, a cationic surfactant, to increase its capacity of nitrate retention. Batch studies revealed that nitrate sorption onto SMZ increased as the surfactant loading on SMZ increased. Nitrate desorption from nitrate-loaded SMZ was almost instantaneous and partially reversible. After desorbed with 100 pore volumes of water, 30–40% of sorbed nitrate still remained on SMZ. Column leaching experiments showed a 20-fold reduction in initial effluent nitrate concentration when nitrate-loaded SMZ was used compared to that when soluble nitrate was mixed with zeolite at the same nitrate loading. The effluent nitrate concentration was quickly reduced to <0.2 mM when a mixture of soluble nitrate and zeolite was leached with less than 2 pore volumes of water. In contrast, the effluent nitrate concentration remained >0.3 mM when nitrate-loaded SMZ was flushed with more than 50 pore volumes of water. Greenhouse tests showed the same growth rate for corns when nitrate-loaded SMZ and water soluble nitrate were used. The results indicate that SMZ is a good sorbent for nitrate, while slow release of nitrate is achievable. These dual properties suggest that SMZ has a great potential as fertilizer carriers to control the release of nitrate and other anions.