Karel As

Hello, if you are interested in sustainability, geochemistry and phosphate please read on.

Phosphate mineral rock (Apatite Ca₅(PO₄)₃) is mined to produce fertilizers used in agriculture. Fertilizers are applied to increase crop yield to unprecented heights. It has been estimated that up to 50% of the global population would not be alive if not for fertilizers. In this respect it is a daunting perspective that phosphate rock is becoming increasingly scarce due to its continuous extraction. Within 50 to 150 years economic and true scarcity is predicted to occur. Eventhough this is the case, phosphorus is generally not treated as a limited resource. On the contrary, most of the phosphorus applied in agriculture is not taken-up by plants but runs off into lakes and streams. Here it stimulates the growth of nuisance algal blooms with strong economic and ecological consequences. Phosphate therefore presents a paradoxal situation: being at the same time scarce and in excess. To alleviate these troubles, the Europe-wide P-trap project was started in 2019. Goal is to uncover new trapping technologies to immobilize phosphates in eutrophic waters as well as recycling mechanism to reduce pressure on rock mining. I am working on the immobilization of phosphorus in lakes using iron oxide coated sands (ICOS).

In lakes iron is a major actor in the availability of phosphate. Under oxic conditions, iron is present as iron oxide onto which phosphate can adsorb as a ligand. However, when a lake becomes anoxic due to biomass input from the surface water, iron is reduced and concomitantly phosphate is released.  Thus in anoxic lakes sediments can serve as a source of phosphorus and effectively contribute to algae production. Furthermore, this means decreasing external input of phosphorus alone is not enough!!

Light microscope image of sand coated with iron oxides

To immobilize phosphorus ICOS addition to lakes could prove an effective measure. Fortunately enough, they are an abundant and cheap waste materials from sand filters which are used in water purification. As part of the P-Trap project I will perform the following investigations: 1) determine the efficiency of iron oxide addition in reducing p-release from the sediment, 2) further knowlegde on the intertwined chemical pathways of Fe:P:S:DOC and 3) apply fundamental knowledge to improve p-immobilization and recycling of phosphate.

To understand the changes occuring in lake sediments as a result of ICOS addition it is required to monitor the stability and transformation of the iron-phosphate bond. The interaction between Fe and P is altered due to dynamic lake redox conditions and the presence of a mixture of chemical species. To determine the Fe:P dynamics in these conditions we will: 1) mimick mineral transformations in the lab 2) incubate lake sediments to which ICOS can be added and scenario`s tested and 3) field work will be performed to determine relevance of the observed phenomena in real lakes.

If you are interested in talking about iron-oxides, phosphate recovery and recycling techniques or have experimental ideas, please let me know.