Sunlight and urine to produce iron

Ferrous metallurgy is a millenary process that requires coal or charcoal to transform iron oxide ore extracted from mines into steel. The carbon contained in these fuels serves a dual purpose, acting both as a chemical and a heater.

In the process developed at the LPCNO, heat is provided directly by concentrated sunlight while the necessary chemicals are derived from urine. This low-carbon process—which requires neither electricity, fossil coal nor wood—is based on resources available everywhere on the planet: sunlight and urine..

The method thus embraces the low-tech philosophy that inspired the scientists behind the study, who are working to develop simple and resilient technologies for a post-growth world.

“We have shown that urine can be a good source of ammonia, which itself acts as a reducing agent for iron oxide. We investigated two different methods of producing ammonia from urea: one involved heating the urea using solar radiation while the other involved stimulating the decomposition of the urea using ground seeds. And both of these methods enabled us to produce iron!” explains Marion Luu, who completed her PhD at the LPCNO working on this topic.

An idea that emerged almost ten years ago

This work is the result of several years of reflection on the way scientific research could be leveraged to develop low-tech solutions.

“This work is the culmination of a project and an idea we had almost ten years ago, when we asked ourselves what scientific research in low-tech might look like. We began by demonstrating that the reduction of iron oxide under a concentrated light beam was possible using hydrogen, then ammonia, and finally, now, urea,” explains Sébastien Lachaize, an INSA lecturer and researcher at the LPCNO and co-author of the study.

The decision to focus on iron metallurgy also stems from a desire to examine an ancient process that is particularly carbon-intensive.

“We wanted to tackle iron smelting because it is a process closely linked to basic human needs. However, its principle has remained unchanged for millennia and relies on the use of carbon. We wanted to show that non-carbon-based, low-tech metallurgy is possible. The process would therefore contribute neither to deforestation nor to the depletion of fossil fuels,” emphasizes Julian Carrey, a lecturer and researcher at INSA’s LPCNO and co-author of the study.

Rethinking metallurgy in a post-growth world

LPCNO scientists have estimated the maximum amount of metal that could be produced using this process, if all human urine was devoted to the process: around 15 kilograms per person per year – a far lower quantity than the current production of steel, which stands at approximately 250 kg per person per year.
The scientists behind the project argue that the large amount of steel currently produced is, in any case, incompatible with the long-term habitability of Earth and that it must, as a matter of urgency, be drastically reduced.
Their research project aims to stimulate discussion on the technical system of a post-growth society that would be sustainable, equitable and convivial and would rely on low-tech solutions. The research team members hope that their findings will encourage other laboratories to approach their research fields from a similar ‘low-tech’ perspective, so as to address the ecological and climate emergency, the consequences of which are becoming increasingly apparent in our daily lives.

“In the face of the climate and ecological emergency, we believe that research questions need to be framed differently. We advocate a new approach to scientific research, one that takes planetary boundaries into account and is relevant to a post-growth world. Scientific research into degrowth has so far been mainly conducted by economists. In this article, we aim to show that the natural and engineering sciences are essential to this new paradigm,” concludes Marie-Hélène Pietraru, a postdoctoral researcher at the LPCNO.

Further reading

The main component of urine is urea, at an average concentration of 20 g/L. Urea breaks down into ammonia when exposed to heat or to an enzyme called urease, which is found in certain plants and bacteria.
In their paper, scientists at the LPCNO demonstrated that it is possible to significantly accelerate the decomposition of urea into ammonia by adding ground soya or watermelon seeds to the urine. The authors of the study also showed that urea can be heated and broken down by exposing it to a concentrated light beam. Regardless of the method, the ammonia thus produced enables iron oxide to be converted into iron.
Currently, the most common metallurgical process, carried out in blast furnaces, relies on the use of coal. This process results in the emission of 2.2 tonnes of CO₂ per tonne of steel produced. More generally, the 2 billion tonnes of steel produced each year account for 8 percent of global CO₂ emissions.

• Scientific article:
  Natural sciences for post-growth in practice: low-tech iron oxide reduction under a concentrated light flux using urine-derived ammonia and hydrogen as reducers
  M.-H. Pietraru, M. Luu, J. P. Smit, S. Lachaize, J. Carrey
  Journal of Cleaner Production, 576, 149114 (2026)

EN 1 Clic