Ball Milling Preparation And Slow-Releasing Technology Research Of Phosphogypsum-Based Sulphur-Nitrogen Fertilizer

Phosphogypsum-based sulphur-nitrogen fertilizer, which could control the nitrogen release according to the crop nutrient requirement, was prepared from phosphogypsum and general fertilizer (ammonium bicarbonate and urea) as the material. At first, phosphogypsum was reacted with ammonium bicarbonate and urea by solid-phase ball milling respectively to prepare ammonium sulfate and urea-gypsum used as fertilizer. Then, though the adjustment of proportion of above two products, the amount of additives and granulation diameter, phosphogypsum-based sulphur-nitrogen fertilizer with good controlled release property was prepared. At last, the controlled release property was evaluated and a rapid method to test and predict the fertilizer longevity was established. The results showed that the optimum solid-phase ball milling parameters to prepare ammonium sulfate were as follows: the molar ratio of CaSO₄·2H₂O to NH₄HCO₃ was 0.55, the milling time was 15min, the ball-feed ratio was 3︰1 and the rotational speed rate was 600r·min^-1, and the average conversion of reaction is 98.02% under this condition. The optimum technical condition to prepare urea-gypsum were as follows: reaction temperature was 55℃, reaction time was 40min, ball-feed ratio was 6︰ 1, rotational speed rate was 600r·min^-1, and the average conversion of reaction can reach 89.38% in this condition. Regularity of nitrogen release could be controlled by adjustment of the proportion of ammonium sulfate masterbatch and urea-gypsum masterbatch according to the crop nutrient requirement. And the optimal preparation condition were as follows: the amount of bentonite was 4%, the amount of starch adhesive was 6%, the amount of hemihydrate gypsum was 6% and the granulation diameter was 5～6mm. Contrasted with common ammonium bicarbonate and common urea, phosphogypsum-based sulphur-nitrogen fertilizer had a superior performance on slowing down and controlling the nitrogen release rate, and fertilizer longevity was 105 days predicted by quartz sand leaching method replacing still water cultivation method.