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

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.

Keywords: hydrotalcite, phosphorus, slow-release, sorption-desorption

为减缓土壤中磷的释放并防止其向环境中的流失，已研发出采用层状双氢氧化物（LDH）的新技术。然而，无机基质中的缓释机制在文献中鲜有讨论，且释放后的吸附-解吸过程亦未予以充分考虑。因此，本研究采用改良的LDH对土壤中磷的动力学和吸附过程进行了探究。该改良通过在磷溶液中采用重构方法进行。材料（HTCP）经傅里叶变换红外光谱（FT-IR）和X射线衍射（XRD）进行表征。磷向土壤溶液的释放过程较为缓慢。在45天（1080小时）内，LDH中引入的磷约11%释放至粘土土壤溶液中，5.5%释放至沙质土壤溶液中。本研究应用了一阶和二阶动力学模型、Elovich模型、颗粒内扩散模型和幂函数模型。颗粒内扩散模型最佳地描述了粘土土壤中的磷释放过程，并表征了离子交换作用，而二阶模型则更优地调整了沙质土壤中的磷释放。双模式Langmuir-Freundlich模型适当地描述了土壤样品中磷的吸附过程，其解吸几乎可以忽略不计。尽管部分磷被吸附，但吸附后的pH值仍保持在植物可利用磷的有效范围内，揭示了使用HTCP作为缓释肥料的益处。

关键词：水滑石，磷，缓释，吸附-解吸