Direct Precipitation for a Continuous Synthesis of Nanoiron Phosphate with High Purity

Abstract

A microreactor competent to control the microprecipitation environment is exploited to investigate the direct precipitation process between iron and phosphorus sources. The dependency of the reaction species on the purity of the final products is revealed. The Fe 3+ hydrolysis and the pH of the mixture are confirmed to have decisive influences on the generation of byproducts. The addition of phosphoric acid in the iron source is verified to be an effective method to simultaneously inhibit Fe 3+ hydrolysis and adjust the pH of the mixture. By optimizing the amount of phosphoric acid addition, pure nanoiron phosphate with an average size of ca. 20 nm is successfully prepared by a continuous precipitation process. Assuming instantaneous mixing and fast precipitation reactions, Fe 3+ and HPO 4 2− are indicated as the main species during the pure iron phosphate precipitation. The criteria would lay a practical guidance for achieving a continuous synthesis of nanoiron phosphate with high purity.

FePO4 nanoparticles produced by an industrially scalable continuous-flow method are an available form of P and Fe for cucumber and maize plants

“…A pilot plant for the continuous-flow synthesis of FePO 4 NPs was set up, after modifications of the method described by Zhang et al . 35 . The system could produce 15 L·h −1 of raw 0.05 M FePO 4 NPs suspension, for a productivity of approximately 140 g FePO 4 /h.…”

“…Among various chemical methods for synthesis of different types of NPs, the co-precipitation process has several advantages, including low cost, good homogeneity, high purity of product and not requiring organic solvents and heat treatment 27 . For this reason, co-precipitation is widely used for the synthesis of metal oxides NPs 28–30 but also for the synthesis of NPs made of insoluble salts such as FeCO 3 18 , Ca 5 (PO 4 ) 3 (OH) 19 , CaF 2 31 and FePO 4 32–35 .…”

“…Co-precipitation methods are often carried out in batch, as shown in the examples cited above. However, this method can also be carried out in continuous flow, and continuous flow synthesis was demonstrated for FePO 4 NPs 33–35 . NPs are thermodynamically unstable due to their very high surface energy.…”

Continuous Synthesis of Nanocrystals via Flow Chemistry Technology

“…Based on these effects, a series of nanoparticles, including CaCO 3 , Li 2 CO 3 , FePO 4 , Li 3 PO 4 , and Ca 3 (PO 4 ) 2 was successfully prepared 85,86,87b,88,100. An example of the Li 2 CO 3 particles proposed by Lu et al is shown in Figure d …”

“…Copyright 2018, Elsevier. d) Schematic and picture of membrane dispersion reactor and Li 2 CO 3 nanoparticles prepared by the reactor, reproduced with permission . Copyright 2014, American Chemical Society.…”