Brownfield Remediation with Phosphates: A Nature‑Based and Circular Economy Approach

Soil contamination by heavy metals (HMs) [or potential toxic elements (PTEs)] poses serious risks to ecosystems and human health. Metals persist in the environment and can reach groundwater and freshwater as the food-chain. In soils, anthropogenic inputs dominate over geogenic sources; unfortunately, HMs cannot be easily destroyed by biogeochemical processes as other contaminants. Metal mobility is strongly controlled by factors such as pH, mineralogy, and erosion processes that transport metal‑bearing clay fractions. Erosion due to wind and water can transport soil clay component, clay can usually bind contaminants such as HMs. Remediation technologies are broadly classified as ex-situ and in-situ, with trade‑offs in cost, duration, and site disruption; the optimal choice depends on contaminant speciation, concentration, soil properties, and climate. In-situ remediation using phosphates are among Nature based Solutions (NbS), waste from phosphatic rock mine activity and/or from fertilizer industry is a way to apply the circular economy principle; it is a cost-effective stabilization strategy for mobile and exchangeable fraction of metals. Using waste material is a tool suggested from the circular economy, so waste is becoming a valuable resource. This study evaluates the immobilization efficiency and mechanisms of four phosphate materials applied to a brownfield site, combining chemical speciation analyses and leaching tests to assess reductions in metal mobility and potential for safe site reuse. Results clarify which phosphate amendments most effectively stabilize target HMs and inform practical, circular remediation strategies for contaminated urban soils.