Study of the physical and chemical mechanisms influencing the long-term environmental stability of natrojarosite waste treated by stabilization/solidification

Abstract

Natrojarosite is a residue of zinc refining generated in large quantities by zinc producers in many parts of the world. Stabilization/solidification (s/s) is currently used to immobilize heavy metals prior to storage of the solidified material as a heap. Our study aimed at assessing the long-term environmental stability of treated natrojarosite waste in the field situation. Flow-through leaching tests were carried out on monolithic samples in a modified triaxial cell and on crushed samples in packed columns. Tests with monolithic samples simulated natural infiltration through treated material containing few cracks and fractures, whereas, packed column tests were more representative of weathered material. The microstructure of leached and unleached materials was characterized by scanning electron microscopy and X-ray energy dispersive spectrometry (SEM–EDX). The results of flow-through leaching tests combined with microscopic characterization and geochemical equilibrium calculations provided valuable insights on the physical and chemical mechanisms influencing the long-term leaching behavior. This information was used to develop a mathematical model for alkalinity depletion in the treated waste. When infiltration of acid rain through the material was considered, the model predicted that the leachate would remain at high pH for many thousands of years in the field.