Identification of the Major Constituents of Fused Potassium Silicate Fertilizer

Abstract

The major component of fused potassium silicate (FPS) fertilizers, produced from steel-making slag, was studied. FPS compounds have received considerable attention as slow-release potassium fertilizers beneficial for crops. This major component was found to be a single phase compound, K₂Ca₂Si₂O₇, which had not been previously identified. In order to confirm the presence of the newly identified compound, we synthesized a potassium calcium silicate mixture, K₂O–2CaO–2SiO₂, by fusing a mixture of K₂CO₃, CaCO₃, and SiO₂. The X-ray diffraction patterns of the synthesized K₂O–2CaO–2SiO₂ were largely consistent with those of FPS fertilizer, and Energy Dispersive X-ray Spectroscopy indicated that this compound was a single phase with a K:Ca:Si molar ratio of 1:1:1. It is concluded that the major component of FPS fertilizer is a compound of K₂O–2CaO–2SiO₂, newly identified as K₂Ca₂Si₂O₇. FPS fertilizers exhibit the characteristic, controlled by their K₂Ca₂Si₂O₇ content, of slowly releasing potassium into water and soil.