Determining the cost of recovering rare earth metals from Indonesian fumed tin slag: a techno-economic study

Abstract

This study evaluates the techno-economic feasibility of recovering rare earth elements (REEs) from Indonesian fumed tin slag and examines how carrier-phase distribution controls process performance. Size-resolved chemical data, correlation analysis, stoichiometric constraints, mass and energy balances, discounted cash-flow modelling, sensitivity analysis, and Monte Carlo simulation were integrated to assess an alkali-fusion flowsheet with caustic regeneration. The results reject the conventional monazite–xenotime host hypothesis: phosphorus correlates strongly with zirconium (r=0.98) but not with REEs (r=-0.14), while the available phosphorus could host only 71% of the REE inventory as orthophosphate. The REEs are therefore interpreted as dispersed in the aluminosilicate matrix, which consumes 90.4% of the stoichiometric NaOH requirement. At 8,500 t/y feed, the process requires USD 15.06 million capital and USD 4.51 million/y operating cost, yielding a base-case NPV of −USD 6.18 million and a 13.4% probability of positive NPV. Economic viability requires regional-scale feed aggregation, favourable offtake terms, and improved recovery. Size classification and magnetic pre-rejection provide no robust benefit, whereas sulphuric acid baking merits experimental comparison with alkali fusion.