Battery-Grade Nickel Sulfate & HPAL Refining Finance Lab

1. Mass Balance & Sizing

2. Capital Expenditure (CapEx)

3. Unit Cash OPEX ($/t Ni eq)

4. Project Finance Returns

1. Autoclave Metallurgy and Iron Hydrolysis Thermodynamics

Nickel laterite ore deposits consist of upper iron-rich limonite ($1.0\%\text{--}1.5\%\text{ Ni}$, $40\%\text{--}50\%\text{ Fe}$, $<3\%\text{ Mg}$) and lower magnesium-rich saprolite. High-Pressure Acid Leach (HPAL) selectively leaches limonite in titanium-clad autoclaves at extreme temperatures ($250^\circ\text{C}\text{--}255^\circ\text{C}$) and vapor-saturated pressures ($4.2\text{--}4.8\text{ MPa}$):

While ferric iron initially dissolves, at temperatures above $240^\circ\text{C}$ the precipitation of insoluble crystalline hematite ($\text{Fe}_2\text{O}_3$) is thermodynamically favored. Hematite precipitation regenerates free sulfuric acid within the slurry, ensuring over 94% of nickel and 92% of cobalt are extracted into solution while iron is rejected as an easily filterable solid precipitate.

2. Exothermic Sulfur-Burning Acid Plant Co-Generation

Sulfuric acid cannot be economically transported in millions of tonnes to remote mining concessions. HPAL complexes operate on-site sulfur-burning Double Contact Double Absorption (DCDA) acid plants:

The massive exothermic heat of sulfur oxidation is captured in waste-heat boilers producing superheated steam at 6.0 MPa and 450°C. This steam expands through multi-stage condensing turbine generators, delivering 45%–60% of the entire industrial complex's electricity requirement, significantly lowering plant operating cash costs.

3. Environmental Tailings Management: DSTP vs. Dry Stacking

Tailings management is the single largest ESG differentiator for project financing:

• Deep Sea Tailings Placement (DSTP): Slurry is piped into deep ocean submarine canyons (>800m depth below the thermocline). While CapEx is lower, DSTP faces fierce resistance from environmental bodies, commercial fisheries, and Western electric vehicle automakers.
• Dry Stacking: High-pressure plate-and-frame filter presses dewater neutralized gypsum and hematite tailings to <18% moisture. The dry cakes are compacted into engineered dry stacks with synthetic geomembrane liners, preventing groundwater contamination and qualifying supply for Western automotive offtakers under strict IRA §30D traceability audits.