Mechanochemical Synthesis of Slow-release Fertilizers: A Review

Solvent-free ball milling was used to activate kaolin, a trioctahedral clay material, with diammonium phosphate[(NH ₄ ) ₂ HPO ₄ ] to serve as a fast-acting phosphorus and nitrogen releasing fertilizer. Different tests on a mixture of 3:1 weight ratio of kaolin: (NH ₄ ) ₂ HPO ₄ were performed to analyze the level of incorporation of (NH ₄ ) ₂ HPO ₄ in the kaolin and the degree of liberation of NH 4 + {\rm{NH}}_4^ + and PO 4 3 − {\rm{PO}}_4^{3 - } ions into solution. The experimental mill speeds were varied from 200 to 700 rpm rotational rates for a fixed period of 2 hours. Several milling periods of 1, 2, and 3 h. were studied at the fixed milling speed of 600 rpm. To explain the properties of activated materials and to understand the purpose behind the simpler disintegration of phosphorus, several analytical methods such as FT-IR, TGA-DTG and Ion chromatography (IC) were used. The proposed procedure was environmentally friendly, and it helped to maintain a balanced supply of nitrogen and phosphorus fertilizer for agriculture's long-term development by offsetting some of the existing high-cost chemical fertilizer. The results demonstrated that the mechanochemical reaction could yield an intercalated form of kaolin that is a transmitter of N and P sources in fertilizers.

This study investigated a mechanochemical (MC) process for synthesizing a slow-release urea fertilizer by co-grinding the starting materials of (NH2)2CO and amorphous kaolinite in a planetary ball mill. The tests with kaolinite contents ranging from 25 to 75 wt. %, milling time ranging from 1 (h)...

In this study, a novel slow-release fertilizer (SRF) consisting of kaolinite and K₂SO₄ was prepared, employing the process of mechanochemical milling in a planetary ball mill. To obtain the optimum milling time and speed, several samples were made at fixed mass ratios of kaolinite: K₂SO₄ (3:1). The milling rotational speed ranged from 200 to 700 rpm for 120 min. Different milling times ranging from 60 to 180 min at fixed 600 rpm milling speed were also investigated to evaluate the incorporation of K₂SO₄ and to measure the liberation of K⁺ and SO₄²⁻ ions into solution. The properties of the studied samples were analyzed by Fourier transformation infrared spectrometry (FTIR), thermal gravimetric analysis (TGA), and ion chromatography (IC). The mechanochemical process is a green chemistry procedure that is successfully applied to incorporate K₂SO₄ into the amorphous kaolinite structure. The slow-release performance was evaluated by determining the K⁺ and SO₄²⁻ content in the aqueous solution upon leaching. The optimum released amount of K⁺ after 24 h was 32 mg L⁻¹ for the milling conditions of 180 min and 700 rpm, indicating that K₂SO₄-kaolinite has good slow-release properties. The novel SRF is cost-effective, environmentally friendly, and improves the fertilizer’s efficiency in many agricultural applications.