The global transition to renewable energy technologies is driving rapid growth in demand for critical minerals and rare earth elements. The International Energy Agency reports a 50 per cent increase in the mineral intensity of power generation over the past decade, with demand forecast to increase significantly as deployment of wind, solar, battery storage, and electric vehicle technologies accelerates. Meeting this demand requires the successful scale‑up of critical minerals processing, particularly in jurisdictions seeking to develop domestic processing capability and secure supply chains. Scaling critical minerals processing presents challenges distinct from those associated with bulk commodities. Many critical minerals have historically been produced at relatively small volumes, and processing routes developed at laboratory scale may not perform reliably when scaled directly to commercial operations. Large, single‑step scale‑ups introduce technical, financial, and environmental risks, with the potential for process instability, cost escalation, and schedule delays. Demonstration plants provide an essential intermediate step between laboratory testing and full‑scale commercial production. Operating at a representative scale, they enable validation of processing technologies, materials of construction, and operating conditions under realistic conditions, while allowing incremental scale‑up and controlled optimisation. The development of a high‑purity alumina demonstration plant in Brisbane demonstrates how bespoke equipment design and staged scaling can improve confidence in process performance and economic viability. In addition to de‑risking initial scale‑up, demonstration plants deliver ongoing value by supporting process refinement, operator training, and adaptation to changing market requirements. As demand for critical minerals continues to grow, demonstration plants will play a key role in enabling technically robust, economically viable, and environmentally responsible processing solutions.