Abstract

Flow Synthesis of Phosphorus Composites for Enhancing P Availability in Soil

Volker Hessel, Professor, The University of Adelaide

Microfluidic devices operated in continuous-flow, due to their high surface-to-volume ratio, good mixing, etc. enhance the mass transfer coefficient, reduce waste, and provide more benefits. The complexity of the synthesis of composite nanomaterials makes it a good test case for such advanced engineering. In this context, a composite P fertilizer is prepared by a coiled flow inverter (CFI).
The reaction was based on the precipitation of Ca²⁺ and PO₄^3- in an alkaline media with the presence of citrate ions and was conducted as 1-stage synthesis with all solutions injected simultaneously into the CFI. Downstream, a feed containing a chitosan solution was incorporated to form the chitosan-phosphorus-citrate composite. The prepared composites were tested for enhancing the chosen performance parameters: available P in soil and P nutrient use efficiency, including practical glasshouse tests with a wheat variety used by Australian farmers. We also test with industrial flow reactors (Corning Advanced Flow) and with industrial continuous-flow stirred reactors (StoliChem).

Citrate ions play an important role in the fertiliser efficiency of the composite, which motivates to increase the citrate capacity in the final product. The presence of chitosan improves the citrate capacity up to 3 times compared to that without chitosan. At the application rate of 25 kg P/ha, after 14 days of incubation in soil, the prepared material increased the available P in soil by 3 times compared to the control (no fertilizer). Also, the P nutrient use efficiency was 63% while that of a chosen commercial product was 55%. In the soil column experiment, the presence of chitosan in the prepared material allowed the phosphate ion to be released in a more stable manner and reduced nutrient leaking by 50% compared to the commercial product after 23 days.