High-Pressure Acid Leaching (HPAL) : Présentation structurée pour un ingénieur métallurgiste

This document presents a comprehensive technical overview of the High-Pressure Acid Leaching (HPAL) process for the treatment of nickel laterite ores, with a focus on limonitic feeds. Its primary objective is to provide a structured guide for metallurgical engineers by integrating thermodynamic and kinetic principles, flowsheet design, operating parameters, equipment selection, and industrial feedback. The text explains how HPAL operates at 240–270 °C and 35–60 bar in sulfuric acid to achieve rapid nickel and cobalt extraction (>90% in 30–90 min), while simultaneously regenerating part of the acid through iron hydrolysis to hematite, thereby improving impurity rejection relative to atmospheric and heap leaching. The document details mineralogical constraints (limonite vs saprolite), key dissolution and hydrolysis reactions, and the influence of temperature, acid concentration, and pulp density on leaching kinetics. A full HPAL flowsheet is described, from ore preparation and autoclave operation to downstream production of MSP, MHP, or battery-grade NiSO₄ via SX. Major operational bottlenecks—including acid consumption, silica gelation, scaling, corrosion, and valve reliability—are analyzed with practical mitigation strategies. Comparative assessment with atmospheric leaching and pyrometallurgy clarifies HPAL’s techno-economic positioning. Industrial case studies (Taganito, Ambatovy, Ramu) illustrate scale-up and performance benchmarks. Finally, the document proposes R&D avenues in dynamic acid staging, Fe–Si coprecipitation, HPAL–AL integration, and specialized severe-service materials, providing a coherent framework from pilot testing to industrial design.