A milling process to reduce kaolin to amorphous phase in the presence of KH2PO4 or NH4H2PO4 and allow mechanochemical (MC) reaction for incorporation of KH2PO4 and NH4H2PO4 into the kaolin structure was investigated in this work. Mixtures of kaolin and KH2PO4 and NH4H2PO4 in separate systems were prepared by milling in a planetary ball mill. Tests with kaolin contents ranging from 25 to 75 wt.% and mill rotational speeds from 200 to 700 rpm were performed to evaluate incorporation of KH2PO4 and NH4H2PO4 and release of K+, NH4+ and PO43- ions into solution. Analyses by XRD, DTA and ion chromatography indicated that the MC process was successfully applied to incorporate both KH2PO4 and NH4H2PO4 into the amorphous kaolin structure. Release of K+ and PO43- ions from the system (kaolin-KH2PO4) when dispersed in water for 24 h reached only up to 10%. Under similar conditions for the system (kaolin-NH4H2PO4). release of NH4+ and PO43- ions reached between 25 and 40%. These results indicated that the MC process can be developed to allow amorphous kaolin to act as a carrier of K+, NH4+ and PO43- nutrients to be released slowly for use as fertilizer. (C) 2011 Elsevier B.V. All rights reserved.