The content of selected phosphorus forms in partially acidulated phosphate rocks enriched with sulfur

Sulfur enrichment becomes emerging issue in fertilizer production as levels of available compounds decrease over the years. Companies are in need of exact parameters and methods of enrichment. In this group PAPR-type fertilizers with this element are interesting solution. Specific technology of PAPRs production consists of phosphate rock acidulation with non-stoichiometric, in relation to production of superphosphates, amount of mineral acid (mainly orthophosphoric or sulfuric acids). Additional function of S after applying fertilizer to soil can be used in this. S in product made that way can be, after the process of mineralization, used by plants as a nutrient in form of sulfate ion SO4 , additionally it can act as an increasing factor in the phosphorus availability from PAPRs. In an optimal conditions (pH ~6.0–6.8) SO4 2– ions can activate conversion of undissolved part of fluorapatite (Ca5(PO4)3F), contained in phosphate rock, to available H2PO4 – and HPO4 2– phosphate ions. The aim of this research was the evaluation of contents of selected phosphorus forms in PAPR-type fertilizer enriched with S depending on a various methods of enrichment. The obtained products were characterized by constant ratio of S : P2O5 (1 : 1 w/w), value of degree of PAPR stoichiometric norm ( PAPR = 0.5), constant amount of surfactant (5 cm ) and variable humidity, which was achieved by different amounts of water introduced into the system (0, 15, 35 % w/w). Method with less additional H2O (~15 % m/m) and surfactant added to slurry was selected for further studies. Although the best solution for industrial manufacturing might be the method with melted S, where usage of this medium and temperatures of 140 C are easily achievable and facilitates production without adding dispensable water, which has a negative influence on granulation process. Next step was to study sulfur effect on PAPRs based on phosphoric acid enriched with sulfur using chosen method. Results revealed that PAPR = 0.5 is unaffected by addition of sulfur and might be best for mixing with sulfur-based fertilizers. Furthermore PAPR = 0.7 indicated decreases in P forms with addition of excessive amounts of elemental sulfur.