Improving Filterability of Hydroxide Precipitates in Hydrometallurgical Hydrolysis Processes: A Critical Review

Hydrolysis-based precipitation is widely used in hydrometallurgy for impurity removal and metal recovery; however, the resulting hydroxide precipitates frequently exhibit poor filterability, leading to low filtration rates, high cake moisture, and significant operational constraints. Despite extensive research on precipitation chemistry, the link between formation mechanisms and solid–liquid separation performance remains insufficiently addressed. This review critically examines how supersaturation, nucleation and growth kinetics, solution chemistry, and hydrodynamic conditions govern the evolution of hydroxide structure—from primary particles to aggregated networks—and ultimately determine cake permeability and compressibility. Evidence from both laboratory and industrial systems shows that filterability is not an intrinsic property of the solid but a consequence of its formation history and structural organization. Strategies such as controlled supersaturation, seeded precipitation, temperature optimization, and selective flocculation are evaluated, highlighting trade-offs between filtration performance, product purity, and process stability. The review identifies key gaps, including the lack of standardized metrics, limited coupling between precipitation and filtration studies, and insufficient scale-up validation. A process-integrated framework is proposed to connect reaction pathways with filtration behavior, providing a basis for designing hydrolysis systems with improved solid–liquid separation performance.