[en] Mining and processing plant projects are very capital intensive and as such tend to follow the typical project development route of 1) Scoping Study (SS), 2) Pre-feasibility Study (PFS) and 3) Definitive Feasibility Study (DFS). This is an attempt at mitigating risk at each stage and to identify the development option(s) which will yield the highest probability of financial success. The early phases are an opportunity to evaluate the various options, to define the most viable processing route with the lowest capital and technical risks. The use of metallurgical testing is key to remove risk that can have a negative impact on capital cost as well as ongoing operating costs. Metallurgical testing and piloting are essential to properly assessing the appropriate processing route to produce the desired end-product from variable ores which are potentially mined over many years. This enables the selection of the most appropriate flowsheet and has a direct impact on capital costs. Extended piloting campaigns at the DFS phase are also a way to minimize risks for operating costs. Changes or modifications of the flowsheet at the early stages of the project are much less costly than at later stages. In some cases, it is impossible to change the fundamental process once the project has been given the Notice to Proceed (NTP). Metallurgical testing and piloting is of particular importance for the fast-growing market for lithium ion battery feedstock such as cobalt and nickel sulphate and lithium carbonate and lithium hydroxide. This is due to the fact that the processing methods are not tried-and-tested mature processes. The feed materials are highly complex and variable, and the end-product specifications are very tight and require careful process control and development. This makes metallurgical testing and piloting crucial in the development of a project. Case studies will be presented. (author)