Potential sustainable slow-release fertilizers obtained by mechanochemical activation of MgAl and MgFe layered double hydroxides and K 2 HPO 4

Abstract

This study describes the behavior of potential slow-release fertilizers (SRF), prepared by the mechanochemical activation of calcined Mg 2 Al-CO 3 or Mg 2 Fe-CO 3 layered double hydroxides (LDH) mixed with dipotassium hydrogen phosphate (K 2 HPO 4 ). The effects of LDH thermal treatment on P/K release behavior were investigated. Characterizations of the inorganic composites before and after release experiments combined X-Ray diffraction (XRD), Fourier-transform infra-red spectroscopy (FTIR), solid-state nuclear magnetic resonance (NMR), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The best release profile (< 75% in 28 days and at least 75% release) was obtained for MgAl/K 2 HPO 4 (9 h milling, 2: 1 molar ratio, MR). Compared to readily used K 2 HPO 4 , milling orthophosphate into LDH matrices decreases its solubility and slows down its release, with 60% and 5.4% release after 168 h for MgAl/K 2 HPO 4 and MgFe/K 2 HPO 4 composites, respectively. Mechanochemical addition of carboxymethylcellulose to the LDH/K 2 HPO 4 composites leads to a noticeable improvement of P release properties.