OBTAINING NPK FERTILIZERS USING DECOMPOSITION OF PHOSPHATE ROCK BY SULFURIC-ACID

In this study a method for obtaining granular NPK fertilizers of vario us grades has been established. Kola apatite or Baltic phosphorites we re dissolved in 57% H2SO4; the resulting slurries were then ammoniated , evaporated and mixed with urea or ammonium nitrate and potassium sal ts. In some experiments micronutrients (B, Cu, Mo, Co or Mn) were adde d. The mixtures were dried and granulated. When using urea, granulatio n was carried out by heating the mixture until partial melting occurre d, but the mixtures with ammonium nitrate had to be granulated with th e addition of water. The products contained 29-38% fertilizer nutrient s (N soluble in water, P2O5 soluble in citric acid and K2O soluble in water) and had a ratio of over 90% of P2O5 soluble in citric acid to t he P2O5 total. The granules were hygroscopic, but little caking occurr ed. The urea-containing materials produced better granules. Adding mic ronutrients usually resulted in an improvement in the product quality (an increase in the granule hardness and phosphorus solubility).