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 PO43-
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.
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