Controlled release of nitrate from hydrotalcite modified formulations

Different nitrate controlled release systems based on modified hydrotalcite-like LDH (LDH) have been investigated to reduce environmental pollution derived from nitrogen-fertilizer use. A synthesized nitrate-hydrotalcite was modified with hydroxypropyl methylcellulose (HPMC) in different proportions and two types of systems were prepared: a) granules with a LDH/HPMC 5/1 proportion and three different sizes (200 mu m, 500 urn and 1 mm) and b) tablets with three different proportions of LDH/HPMC (5/1, 5/0.5 and 5/0.25). In order to determine the release rate of the active ingredient, we carried out the release experiments as a function of time in water and in a simulated soil solution. In both experimental conditions (decarbonated water and simulated soil solution), the LDH/HPMC 5/0.5 system produces the slowest release rate of nitrate than the other two systems. Using the Ritger and Peppas equation, the T-50 parameter was calculated. The average values ranged from 8.7 x 10(-4) h and 12.3 h for the granules system in simulated soil solution and decarbonated water respectively, up to 17.6 and 54.5 h for the tablet system, in simulated soil solution and decarbonated water, also respectively. From the analysis of these data, it could be deducted that the release rate of nitrate can be controlled mainly through the shape of the formulations, the tablets being more effective than the granules. (C) 2011 Elsevier B.V. All rights reserved.