Modified hydrotalcite for phosphorus slow-release: Kinetic and sorption-desorption processes in clayey and sandy soils from North of Paraná state (Brazil)

Abstract New technologies have been developed to slow down the phosphorus release in the soil and prevent the loss to the environment by using layered double hydroxides (LDH). However, slow-releasing mechanisms in inorganic matrices are not often discussed in the literature, and post-release sorption-desorption processes have also not been taken into account. Thus, kinetic and sorption processes of P in soils were herein investigated employing a modified LDH. The modification was carried out by the reconstruction method in the P solution. The material (HTCP) was characterized by FT-IR and XRD. The release of P to the soil solution was slow. Around 11% of the P introduced in the LDH was released to the clayey soil solution, and 5.5% to the sandy soil solution over 45 days (1080 h). Kinetic models of first-order and second-order, Elovich, intraparticle diffusion, and power function were applied. The intraparticle diffusion model best described the P release in clayey soil, characterizing ion exchange, while the second-order model better adjusted the release in sandy soil. The dual-mode Langmuir-Freundlich model appropriately described the sorption of P in the soil samples, being the desorption almost null. Although some of the P was sorbed, the post-sorption pH remained in a viable range for making P available to the plants, revealing the benefits of using HTCP for slow-release fertilizers.