Adsorption of nitrogen and phosphorus into layered double hydroxides for production of slow-release fertilizers
2014
Nguyen Quang Hai; Nguyen Ba Kien; Pham Thi Nhung
Layered double hydroxides (LDHs) are of high-tech nanostructurcd materials promising application in many potential areas, including slow-rclcasc fertilizers production. In the present study, 10 LDHs were used to examine their adsorption capacity of nitrogcn (N, in NO3' form) and phosphorus (P, in H2P04'form) by three adsorption methods, namely: shaking interchange, bottom-up interchange, and top-down interchange. The results showed that the N adsorption capacity of LDHs was very low (less than 4%), while the P adsorption capacity was quite high. Among 10 tested LDHs, ore having a high adsorplion capacity of P was selected for trial production of slow-release phosphorus fertilizer, LDH-P. The form of LDM chosen was [Mg/Al]-CO3 with molecular ratio of Mg/AI = 2/1. It was found that the most suitable method for adsorption of P into LDH was the top-down interchange method. The appropriate conditions for production of LDH-P slow-rclease fertilizer from LDH and KH2PO4 were determined as follows: concentration of KH2PO4 solution = 1.0 M with pH = 5.0: solution volume (V, liter) needed for absorbing a maximum amount of P into m (kg) LDH accounting from equation: V = 26.814 m - 1.2381. The trial production created a LDH-P with P content of 21% or P2O5 content of 48%. The slow-relense phosphorus fertilizer had a P (%) content 2.7 times higher than single super phosphate and are considered a promising phosphorus source for crops.
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