Abstract
A mechanistic study of citric acid leaching of rare earth metals in sulfate and chloride media
José Eric Ortiz Castilloa,1, Wenying Liub,1, David Dreisingerc,1
1Department of Materials Engineering, The University of British Columbia, Vancouver, Canada
ajeortiz@student.ubc.ca, bwenying.liu@ubc.ca, cdavid.dreisinger@ubc.ca
Abstract
Developing environmentally sustainable separation and recycling strategies for rare earth elements (REEs) requires a deeper understanding of their aqueous speciation under realistic chemical conditions. Citric acid is a promising green complexant, however its interaction with individual and mixed REEs is not fully characterized. This project aims to determine the stability constants and speciation behavior of 2 light REE (LREE), Nd, Ce, and 2 heavy REE (HREE) Dy, and Y in the presence of citrate and to assess how complex matrices influence these equilibria. In addition to single-metal systems, a comprehensive evaluation of binary LREE–HREE combinations (e.g., Ce–Dy, Nd–Y, Ce–Nd, Y–Dy) is conducted to quantify competitive complexation effects. The study also examines how common impurity ions (e.g., Al, Fe, Mg, Ca) and varying chloride and sulfate concentrations modify REE–citrate binding, reflecting industrial leaching and recycling environments. A key component of the project is the generation of pH–Eh (Pourbaix) diagrams incorporating measured stability constants to map predominance regions and redox-dependent speciation. These diagrams provide a predictive tool for understanding REE behavior across environmental and process-relevant conditions. Overall, this work establishes a comprehensive framework for modeling REE–citrate systems in complex, multi-ion matrices, supporting the design of cleaner and more selective hydrometallurgical recovery processes.