Copper sulfide precipitation in acidic cobalt solutions: Aggregate growth, fragility, and implications for particle handling

Abstract

Understanding the time-dependent evolution of particle size and aggregate structure remains crucial for selecting appropriate solid-liquid separation equipment and improving the separation efficiency. Literature currently lacks a comprehensive multi-method analysis of particle dynamics in complex, highly acidic multi-metal systems. This study addresses this gap by presenting a novel integrated characteristic analysis of metal sulfide precipitates generated during copper impurity removal from a highly acidic, cobalt-processing solution. Laser diffraction, optical microscopy with Fiji-based image analysis, automated image analysis, surface area measurements, and fractal analysis were integrated to capture complementary aspects of particle size, morphology, structure, and fragility. Rapid and preferential copper removal (> 99%) was achieved within minutes, while the liquid phase was dominated by dissolved cobalt. Mineralogical characterization confirmed the formation of poorly crystalline copper-rich metal sulfide phases, dominated by covellite (CuS) with contributions from carrollite (Co2CuS4). All particle sizing methods revealed a consistent trend: particle size increased up to the one-hour mark, followed by a subsequent decrease, indicating a transition from rapid aggregation to structural restructuring. Laser diffraction consistently revealed the smallest median aggregate sizes compared to image-based methods, reflecting hydrodynamic shear effects on fragile aggregates. This discrepancy was quantified using a relative discrepancy (RD) metric, which revealed up to a 70% size reduction under shear. Fractal analysis further quantified aggregate structural complexity and linked densification, restructuring, and weakening to measurement-dependent discrepancies. The integrated framework developed provides a robust basis for quantifying aggregate stability in metal sulfide precipitation systems and offers practical insights relevant to industrial solid-liquid separation processes.