Controlling Co-precipitation in Hydrometallurgy: From Physicochemical Parameters to Process Design and Technology Readiness

Co-precipitation is a major challenge in hydrometallurgical processing because it directly affects metal recovery, product purity, reagent consumption, solid–liquid separation, and environmental performance. Although precipitation reactions are widely used for impurity removal and selective metal recovery, co-precipitation phenomena remain insufficiently understood due to the complex interactions between thermodynamic, kinetic, hydrodynamic, and interfacial parameters. This critical review examines how physicochemical variables—including pH, supersaturation, redox potential, temperature, ionic strength, solution composition, and colloidal effects—govern the mechanisms of adsorption, structural incorporation, occlusion, and gel-mediated entrapment in multicomponent hydrometallurgical systems. The review further evaluates the influence of operational factors, including mixing intensity, residence time, reagent addition strategy, and reactor design, on precipitation selectivity and process stability. Industrial case studies of zinc, nickel, copper, rare earth, and battery recycling systems are critically analyzed alongside the technology readiness level (TRL) of conventional and emerging control strategies. The analysis demonstrates that effective co-precipitation control requires integrated process design rather than isolated parameter optimization. Current limitations in predictive modeling, real-time monitoring, and industrial multivariable control are identified as key barriers for the development of selective and sustainable hydrometallurgical processes.