Sintering Preparation and Release Properties of K2MgSi3O8 Slow-Release Fertilizer Using Biotite Acid-Leaching Residues as Silicon Source

Abstract

The sintering preparation of K2MgSi3O8 at 700–950 °C for 2 h using biotite acid-leaching residues, K2CO3, and Mg(OH)2 as the starting materials was investigated in this research. The sintered samples were characterized by X-ray diffraction, X-ray fluorescence, Fourier transformation infrared spectrometry, and scanning electron microscopy. The results indicated that the hexagonal kalsilite-like K2MgSi3O8 with an irregular blocky morphology was prepared at 900 °C for 2 h. The solubility of K2MgSi3O8 in HCl and citric acid solution shows that the extraction of K2O is 38.94% in 0.50 M HCl and 23.58% in 0.10 M citric acid solution, respectively. For the optimal sample dispersed in distilled water, the accumulative release of K2O is 6.06% in the first day and 44.90% in 28 days, which reaches the Chinese national standard of slow-release fertilizer. All the results indicate that the as-prepared K2MgSi3O8 is appropriate for application as slow-release fertilizers supplying nutritional components K, Mg, and Si for...