Vat Design and Bed Hydrodynamics in Nickel Laterite Leaching: A Critical Review of Solution Distribution, Permeability Evolution, Process Control, and Scale-Up

Abstract

Vat leaching can provide stronger solution containment and cycle control than heap leaching while avoiding the mechanical intensity of agitated reactors, but its performance is commonly interpreted through nominal residence time and chemical extraction alone. This critical review reframes the vat as a reactive porous-bed reactor whose effective capacity depends on solution distribution, pore connectivity, saturation, permeability evolution, and the fraction of ore actually contacted. A structured corpus of 105 publications was examined, with evidence differentiated among nickel-laterite applications, industrial or pilot heap studies, column experiments, imaging studies, and reactive-transport analogues from copper, uranium, and ion-adsorption rare-earth systems. The review integrates feed preparation, vat geometry, top- and bottom-distribution, drainage, saturated and unsaturated flow, preferential pathways, residence-time distribution, dissolution–precipitation feedback, fines migration, monitoring, modeling, and scale-up. The main critical finding is that no single hydraulic equation or laboratory column is sufficient to represent the full cycle: bed structure and liquid properties evolve as reactions proceed, so the operating window must be defined by coupled hydraulic and metallurgical indicators. A design framework is proposed that combines physical characterization, permeability and tracer testing, pilot-vat validation, zoned instrumentation, liquid-inventory reconciliation, and multi-cycle assessment. Failure modes are linked to observable symptoms and corrective actions, and a hierarchy of models is matched to data availability and decision purpose. The review concludes that reliable scale-up requires preservation or quantitative accounting of the dominant bed-formation, hydraulic, reaction, and mechanical controls—particularly superficial flux, saturation, hydraulic response, residence-time distribution, and permeability evolution—rather than geometric capacity alone.