Mechanochemical Route for Synthesizing KMgPO4 and NH4MgPO4 for Application as Slow-Release Fertilizers

This article introduces a mechanochemical (MC) process for the synthesis of KMgPO4 and NH4MgPO4 by milling starting materials in a planetary ball mill. First, KMgPO4 was prepared my milling KHPO4 and Mg(OH)(2) at a molar ratio of 1:1 for 120 min at mill rotational speeds of 500-600 rpm. Washing of KMgPO4 in water for 700 h released only up to 20-25% of K+ and PO42- ions into solution. Second, NH4MgPO4 was prepared by milling NH4HPO4 and Mg(OH)(2) at a molar ratio of 1:1 for 120 mill rotational speeds of 300-700 rpm. Washing of NH4MgPO4 in water for 500 h released only up to 10-20% of NH4+ and PO42- ions into solution. The MC process could be developed to synthesize KMgPO4 and NH4MgPO4 for possible application as slow-release fertilizers.