Technology of Alkaline Thermophosphates Based on Low-Quality Phosphate Raw Materials and Evaluation of Their Agrochemical Efficiency

Phosphorites with a low phosphorus content (Р2О5»20 %) can be used to obtain phosphoric fertilizers by acid processing only in the presence of a small amount of impurities of «one and a half oxides» - R2О3 (R2О3:Р2О5<0,12 wt.). Low-quality phosphorites with a high content of R2О3 impurities can be processed into alkaline phosphorous fertilizer (thermophosphate) by sintering them with alkali metal salts (Na2CO3, Na2SO4). The results of studies on the production of thermophosphates by sintering phosphorites with various wastes of some industries (sulfate-soda mixture - waste from alumina production, alkaline sludge from petrochemical synthesis) instead of alkaline salts are presented. It is shown that the total phosphorus content in the thermophosphate Р2О5 TOTAL » 20-30 %) is determined by the content of Р2О5 in the initial phosphorite, and the assimilable «lemon-soluble» form of phosphorus (Р2О5 LS » 19-25 %) depends on the firing conditions and the ratio of raw components. It has been established that in order to convert phosphorus into a digestible form, in the case of using Na2SO4, an excess of it in significant quantities is required. The agrochemical efficiency of various types of thermophosphates was evaluated in vegetation experiments with wheat on slightly acidic sandy loam soil. It was found that the use of alkaline thermophosphate against the background of NК-fertilizers ( NН4NO3, К2SO4 ) , in contrast to simple superphosphate with a similar content of Р2О5 LS , contributes to a significant increase in yield (grain weight gain +30%). This is most likely due to the combined influence of 2 major factors: the high content of the digestible «lemon-soluble» form of phosphorus in the thermophosphate, as well as the neutralization of the acidity of the added NН4NO3 and the soil itself.