TESTWORK5.1 IntroductionThe FS test

TESTWORK5.1 IntroductionThe FS testwork programme built on the PFS programme completed by SGS Lakefield in2016. The purpose of the testwork programme was to confirm process design in thebeneficiation and extraction areas of the plant and validate and optimise the process designcriteria. The three main phases of the FS testwork programme were:• PHASE 1: Proof of concept for unit operations in the flow sheet and optimisation ofdesign criteria for equipment design• PHASE 2: Locked Cycle Testwork Program to prove the stability and robustness ofthe flow sheet, with recycle streams incorporated and the flow sheet unit operationsrun sequentially and not in isolation• PHASE 3: Effect of ore variability on the flow sheet.At the end of the PFS, the flow sheet consisted of beneficiation and extraction plants. Thebeneficiation plant was based on scrubbing, followed by upgrading by coarse particlerejection and flotation of mid-size producing a calcite and silica reject stream. The extractionplant was based on a gypsum and limestone roast followed by water leach, solutionpurification and evaporation, and crystallisation to produce lithium carbonate.Several modifications have been made to the PFS flow sheet resulting from the FS testwork.These changes have improved the project economics and plant operability. The mainchanges made are:• A grinding circuit replaced the PFS scrubbing circuit to beneficiate the ROM ore usingenergy more efficiently• Calcite flotation was removed, as it was determined that there would be little to noexcess calcite in the ROM feed• The roast feed material is briquetted which is the most practical way to handle theroast material in a tunnel furnace. This also enables effective heat transfer throughthe mass of briquettes• The roast recipe has been changed to a sodium sulfate and gypsum roast, from thePFS gypsum only roast, to reduce the operating costs associated with gypsumconsumption• The Glauber’s salt step was moved upstream of PLS evaporation to remove the bulkof the sodium sulfate which allowed the lithium tenor to be increased in the evaporatorto maximise the lithium carbonate precipitation yield• Fluoride removal is included in the flow sheet• A bleed stream is included to remove caesium and rubidium from the PLS with alumprecipitation.The final FS flow sheet was established by testwork initially on Trench 4 material. Thistestwork determined that primary grinding with a SAG mill, calcite flotation and grinding thefeed to the extraction plant to -125 μm was the optimum beneficiation circuit. Roasting andleach testwork on Trench 4 material also confirmed the optimum reagent mix and roastingconditions. This Trench 4 testwork was used to confirm the flow sheet to be used for theVariability Testwork in both the beneficiation and extraction circuits, as well as locked cycletestwork.