Fate and transport of phosphorus mining waste

Abstract:

This project investigates innovative strategies to enhance the efficiency of resource recovery during thermal treatment of phosphate acid sludge, focusing on the interplay between speciation, composition, and recoverability of phosphorus and REEs. 

The first stage involved a comprehensive literature review of phosphorus mining and waste management practices. Data from the Florida Industrial and Phosphate Research Institute (FIPR) highlighted the underexplored potential of acid sludge and phosphogypsum among 54 documented waste streams, with only a fraction of studies targeting recovery strategies. This gap underscores the urgent need for systematic evaluation of waste valorization pathways. Second stage includes experimental work progressed through sequential extraction tests. Results demonstrated that a significant fraction of phosphorus in acid sludge is readily extractable, confirming the feasibility of recovery under mild conditions. Parallel sequential extraction of REEs revealed concentration profiles across different operational steps, with recovery rates varying according to mineral phase associations. These results illustrate the heterogeneous binding environments of REEs, informing process optimization for selective leaching. The understanding of REE speciation was from a complementary X-ray diffraction (XRD) analysis to monitor mineralogical changes during stepwise extraction and treatment. This characterization provided insights into the transformation of crystalline phases and their influence on the availability of phosphorus and REEs. Together, these findings strengthen mechanistic understanding of how acid sludge mineralogy governs recovery efficiency. A critical advancement was achieved through hydrothermal treatment trials, where preliminary results indicated promising REE recovery. This pathway, combined with the use of cost-effective adsorbents, offers dual benefits: (i) lowering the conductivity and contaminant levels of lime-treated process waters, and (ii) concentrating valuable resources for downstream recovery. Such integrated approaches align with circular economy principles, simultaneously mitigating waste burdens and generating new value streams.