Influence of granulating factor at variable humidity on granulation of partially acidulated phosphate rocks

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Unstable situation on fertilizer raw material market emerges the need to find substitute for superphosphate fertilizers. PAPR-type phosphate fertilizers (partially acidulated phosphate rock) constitute the most relevant alternative. PAPR-type fertilizers are formed by reaction of phosphate rock with nonstoichiometric, in relation to reaction during superphosphate production process, portion of mineral acid. The resulting product contains an available (soluble in water and/or in neutral ammonium citrate) and less available (soluble in mineral acids) forms of phosphorus. Possibility of using low-grade phosphate rock represents a great advantage of PAPR-type over superphosphatic manufacturing process, where applying phosphate rock of high P2O5 at low impurities content is highly recommended. Granulation process is an essential stage of PAPR-type fertilizers production. Granulation significantly reduces the dust emissions during the fertilizers application furthermore limits the regression of fertilizers in soil to unavailable forms (so-called the aging processes of fertilizers). Optimization of process parameters is very important for economic and ecological reasons because this process is one of the most energy consuming in whole cycle of PAPR-type fertilizers production. PAPR-type fertilizer preparations obtained under laboratory conditions were subjected to examinations. Products were characterized by a variable humidity, which was achieved by altering the concentration of mineral acid used for investigations. The second variable factor was the type of liquid used for granulation. Both, the sieve analysis and determination of resistance were carried out for classification of obtained granules.