Study of aplication of Layered Double Hydroxides in removal and slow release of pesticides

Author(s)

Lucelena Patricio Cardoso

• Document type: Doctoral Thesis
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto (PCARP/BC)
• Defense date: 2006-09-13

Examining board members

Joao Barros Valim; Vera Regina Leopoldo Constantino; Fergus Gessner; Herenilton Paulino Oliveira; Fernando Wypych

• Advisor: Joao Barros Valim

Abstract

The extensive use of pesticides in modern agriculture has been contributing to an increase in environmental contamination. Layered Double Hydroxides (LDHs), or anionic clays, bear a layered structure, and a variety of anions can be intercalated between these layers through electrostatic interactions. These layered materials can be used in adsorption/sorption processes and in the slow release of chemical compounds. So this work aims at studing the sorption of the acid herbicides bearing organic anions 2,4-D, MCPA and Picloram, used in national agriculture, through regeneration of calcined Mg-Al-CO3 LDH and anion exchange of Mg-Al-Cl ? LDH. For this purpose, the kinetics of the sorption process was investigated, and the determination of isotherms in two different pH values was carried out. The herbicides were intercalated in Mg-Al ? LDH using two indirect synthesis methods: regeneration of the calcined material and anion exchange in solution; besides the direct synthesis method by coprecipitation. The obtained materials were properly characterized. All the obtained materials, intercalated with each of the herbicides, were used in a kinetic release study in water. The materials obtained by regeneration were also used in a leaching and in a bioassay study, to test the efficiency of LDHs as supports for the slow release of herbicides. From the kinetic sorption process of the organic anions in solution using Mg-Al ? LDH containing chloride or carbonate after calcination, it was observed that the removal of anions occurred through an anionic exchange process in the case of the LDH containing chloride, or through regeneration of the layered structure in the case of the calcined LDH. The intercalation of organic anions in a vertical position was observed in the adsorption/sorption process, and it was shown to be dependent on the herbicide concentration in solution. The calcined LDH was the most efficient for removal of anions in solution. The herbicides supported on LDHs, presented a slower release in water than the same compounds in their free form, and the release behavior was not dependent on the methodology used for the preparation of the matrix. Leaching study results using the LDH obtained by regeneration as matrix demonstrated a slow release of the active ingredient, mainly for the Picloram herbicide. The bioassay showed that the release behavior of the supported herbicides was efficient in the control of plant seeds germination at preemergence applications. (AU)