Liquid and Solid Compound Granulated Diurea Sulfate-Based Fertilizers for Sustainable Sulfur Source

Abstract

Design and manufacture of high nitrogen content sulfur-containing fertilizers is of crucial importance in sustainable food and energy crop production. The availability of large elemental sulfur amounts in oil refining and natural gas processing facilities, in combination with decreasing sulfur deposition into soil from natural and anthropogenic sources in a bioavailable sulfate form, calls for innovative engineering solutions that bridge this gap via sustainable sulfur processing. Diurea sulfate-based liquid and compound solid granulated fertilizers were synthesized in this work, and their resulting physicochemical properties were determined. First, phase compositional information on the 2CO(NH2)2·H2SO4–CO(NH2)2–H2O ternary system was measured, and high nitrogen content, ∼15:1 N:S ratio liquid fertilizer grades, were established. Next, diurea sulfate granulation experiments using (i) dolomite, (ii) byproduct material after the phosphoric acid extractive production, CaSO4·0.5H2O, and (iii) dolomite combined with diammonium phosphate, (NH4)2HPO4, and potassium chloride, KCl, were performed. Using diurea sulfate, 16–16–16–5.5(S)–0.4(MgO)–0.6(CaO) compound granulated fertilizers were successfully obtained, and time-resolved changes in their crystalline phase composition during granule curing were monitored using XRD. The granule crushing strength measured increased to 3.800 MPa within the 30 day storage thus resulting in high quality fertilizer material.