Preparation of Fertilizers with Rosin and Tricalcium Phosphate Coated Zinc Chelates. Laboratory Characterization

Abstract

Zinc fertilizers were obtained by adhering Zn-EDTA or Zn-lignosulfonate over urea pellets of 1.6-2 mm diameter, to give a span of zinc weight percentages between 0.60 and 1.40. Some of these pellets were also coated. The materials used as adhesives and coatings were mixtures of rosins (natural, dismutated, and esterified) and tricalcium phosphate. The weight percentages of coatings ranged from 0 to 47%. Water solubility kinetics showed that zinc solubilization in the base products (uncoated) were almost immediate, while the percentage released in the coated products diminished as the coating thicknesses were increased, up to 63 and 14% for the more heavily coated products of Zn-EDTA and Zn-lignosulfonate, respectively. Equations were established that enabled the behavior of products with the same percentage of coating in the two series to be predicted and compared. The tested products comply with national and international standards for commercial fertilizers with regard to their chemical composition. Their physical properties were within the limits found with commercial fertilizers. A scanning electron microscopy study showed that the rosin coatings were fairly compact and homogeneous.