Division of Soil and Water Management, Department of Earth and Environmental Science, KU Leuven, Kasteelpark Arenberg 20, B-3001 Heverlee, Belgium.
School of Agriculture, Food and Wine, The University of Adelaide, PMB 1, Waite Campus, Glen Osmond, SA 5064, Australia.
J Colloid Interface Sci. 2022 Dec 15;628(Pt A):519-529. doi: 10.1016/j.jcis.2022.07.149. Epub 2022 Jul 27.
Layered double hydroxide (LDH) loaded with orthophosphate (PO) are suggested as slow-release P fertilizers. However, PO-LDHs have a low maximal P content, related to high charge HPO/PO anions occupying the anion exchange capacity (AEC) of LDHs. We postulate that the P content of LDHs can be enhanced by exchanging them with polymeric-P (i.e. trimetaphosphate, PO), which has a lower molar charge/P ratio than its monomer.
Adsorption capacities were compared between PO and PO for as-synthesized and calcined MgAl LDHs with Mg/Al ratio of 2, 3, or 4; the P-LDHs were characterized (XRD, FTIR). Dialysis and soil incubation experiments were performed with POLDHs, POLDHs, and corresponding soluble fertilizers to compare their P release and P solubility (CaCl extract).
The P adsorption capacities were 1.25-1.60 fold larger for PO compared to PO, yet the high theoretical P contents with PO were not achieved (incomplete loading, PO depolymerization). PO-MgAl released polymeric-P whereas PO-MgAl released depolymerized PO, and P release from PO-LDHs was slower than that of PO-LDHs. With soil incubation, soluble P from PO-LDH was initially lower but later converged to that of PO-LDH as result of continued hydrolysis, yet did not exceed that of the soluble PO and PO fertilizers.
层状双氢氧化物（LDH）负载正磷酸盐（PO）被认为是缓慢释放的 P 肥料。然而，PO-LDH 的最大 P 含量较低，这与高电荷 HPO/PO 阴离子占据 LDH 的阴离子交换容量（AEC）有关。我们假设通过用聚合-P（即三偏磷酸盐，PO）交换 LDH 可以提高 P 含量，因为聚合-P 的摩尔电荷/P 比低于其单体。
比较了合成和煅烧的 MgAl LDH 与 Mg/Al 比为 2、3 或 4 时，PO 和 PO 之间的吸附能力；用 XRD、FTIR 对 P-LDHs 进行了表征。用 POLDHs、POLDHs 和相应的可溶性肥料进行了透析和土壤培养实验，以比较它们的 P 释放和 P 溶解度（CaCl 提取物）。
与 PO 相比，PO 的 P 吸附能力提高了 1.25-1.60 倍，但 PO 的理论 P 含量并没有达到（不完全负载，PO 解聚）。PO-MgAl 释放出聚合-P，而 PO-MgAl 释放出解聚的 PO，PO-LDHs 的 P 释放速度比 PO-LDHs 慢。随着土壤培养，PO-LDH 中的可溶性 P 最初较低，但由于持续水解，后来与 PO-LDH 的可溶性 P 趋同，但仍未超过可溶性 PO 和 PO 肥料的 P 释放量。
