Study On Preparation And Properties Of Novel Slow Release Fertilizers Based On Superabsorbent

To improve the utilization of fertilizer and water resources at the same time, and reduce the contamination caused by illogical fertilization, several types of novel superabsorbent-based slow release fertilizers were prepared in this thesis. Acrylic acid (AA), itaconic acid (IA), sodium carboxymethylcellulose (CMC), K-Carrageenan (kC), sodium alginate (SA), celite, and activated carbon (PAC) were used as the main materials. The agrochemicals used in this thesis were urea, K2HPO4, and NH4Cl. The superabsorbents and fertilizer samples were characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and thermogravimetric analysis (TG/DTA). Major factors affecting on the water absorbency of the superabsorbents were investigated and optimized systematically. Element analysis and ICP were used to determine the contents of nitrogen, phosphorus, and potassium. The largest water-holding ratio, the water-retention property of soil as well as the slow release behavior of fertilizers in soil was explored, and a possible slow-release mechanism was proposed. The main results were shown as follows:1. A new slow-release PK compound fertilizer (SRCF) with the function of water retention was prepared by grafting crosslinked P(AA-co-IA) chains onto CMC via a free radical polymerization. Element analysis results showed that the product contained20.46%potassium (shown by K2O) and15.45%phosphorus (shown by P2O5), which were trapped in the matrix of CMC-g-P(AA-co-IA) superabsorbent polymer. The SRCF effectively improved the water retention capacity of soil, even though at a low application rate. The release rates of potassium and phosphorus were slower for higher crosslinker content of SRCF. After degradation in soil for3months, the surface of the SRCF was rugged and there were many irregular apertures on it.2. A multifunctional slow-release nitrogen fertilizer (SRNF) has been developed in a pan granulator. kC-SA and crosslinked KC-g-PAA/celite superabsorbent were used as inner and outer coating materials, which were coated consecutively on the granule core urea. Elemental analysis showed that the nitrogen content of SRNF was22.6%. The average crushing strength of SRNF was about10%higher than the uncoated urea. The addition of SRNF into soil could significantly improve the water-holding capacity and water-retention property of soil. Meanwhile, it can prevent soil from becoming harder. Moreover, the product had good slow-release property: nutrient N had release value of94.2%after being incubated in the soil for25days.3. The coal-based powdered activated carbon (PAC) was used as the starting material, which was oxidized using concentrated nitric acid to obtain the oxidized activated carbon (OAC). A series of OAC/PAA superabsorbent composites were prepared by free radical polymerization in the presence of OAC and AA. Adsorption measurements were carried out by batch experiment of the OAC/PAA composite and NH4C1solutions to load the nitrogen. When the adsorption equilibrium was achieved, the nitrogen content of the composite was found to be12.29%. The OAC/PAA composite could adjust pH value of soil solution as a kind of soil amendment. Meanwhile, the OAC/PAA composite had good slow-release property:loaded nitrogen had release value of97.4%after being incubated in the soil for20days.