Phosphorus recovery by clay: thermodynamics and reuse

Phosphorus is an essential nutrient for all living organisms, but its production and use create serious environmental challenges. On farmland, phosphorus is necessary for crop growth, while in rivers and lakes even small excess amounts can trigger eutrophication, a process that causes uncontrolled algae growth. When these algae die and decompose, the oxygen in the water drops, threatening fish and other aquatic life. Because of this, removing phosphorus from wastewater is crucial for protecting water quality and keeping ecosystems healthy. At the same time, global supplies of phosphorus are limited, and its industrial production consumes large amounts of energy. These issues make it increasingly important to find smarter and more sustainable ways to recover phosphorus and return it to agricultural use. This project aims to develop an environmentally friendly, low-cost method that solves both problems at once: removing phosphorus from water and reusing it as a slow-release fertilizer. The approach relies on natural, iron-rich clays and iron-carbonates that can capture phosphorus from water and later be transformed into solid materials, known as geopolymers. These geopolymers can gradually release the captured phosphorus back into soil, providing nutrients to plants without causing pollution. This research will first examine how different clay-based materials bind phosphorus, and how this process can be made more effective. By carefully studying both the materials and the water in which they are used, the project will identify the key factors that control phosphorus removal. A major part of the work focuses on understanding the energy changes and other fundamental principles that govern this binding process. This deeper insight will allow for the design of more selective and efficient materials. A new scientific method will be developed to precisely determine the thermodynamic parameters that describe how and why phosphorus adsorbs to the materials. This method combines advanced modeling tools and will lead to a database that can support future upgrade studies on water purification and pollutant removal. In the final phase, the project will test how the newly obtained geopolymers release phosphorus and whether they are safe for use in agriculture. Their environmental impact will also be carefully examined, ensuring that the materials provide benefits without introducing new risks. By linking water treatment with sustainable fertilizer production, this project offers an innovative path toward cleaner water, reduced pollution, and more efficient use of natural resources. It brings together fundamental scientific understanding and practical solutions that support a circular approach to phosphorus use, recovering it from water and returning it to the soil where it is needed most.