Method for preparing ammonium dihydrogen phosphate and by-product special compound fertilizer for pineapple

The invention discloses a method for preparing ammonium dihydrogen phosphate and a by-product a special compound fertilizer for pineapple. The method comprises the following steps: preparation of raw materials, preparation of ammonium dihydrogen phosphate, addition of elements into a filtrate and drying. High-purity ammonium dihydrogen phosphate is prepared by a reaction between phosphoric acid and urea; and simultaneously, remaining slurry undergoes processes such as element addition, drying and the like so as to prepare the special compound fertilizer required by growth of pineapple. Thus, mother liquor is fully utilized; costs are reduced; the prepared compound fertilizer meets growth requirements of pineapple to the maximum; waste of elements is decreased; and the soil pollution problem caused by the residual compound fertilizer is avoided.