Processing of carbonatite-hosted niobium (Nb) ores are not only energy-intensive (~24 GJ t-1 Nb2O5) but also often results in incomplete recovery of associated critical elements such as tantalum (Ta). This study develops an integrated modelling and optimisation approach for the recovery of niobium and tantalum as oxide products (Nb2O5 and Ta2O5) from low-grade carbonatite ores with the objective to improve the overall process efficiency and resource utilisation. A steady-state process model was developed for a 1000 t/h carbonatite ore containing 2.1 per cent Nb2O5 to carry out a detailed mass and energy balance for the process. The flow sheet incorporates all of the important unit operations, including comminution, classification, magnetic separation, flotation, acid leaching, solvent extraction using methyl isobutyl ketone (MIBK), stripping, precipitation, and calcination. The model enables quantitative tracking of metal distribution, reagent consumption, and energy demand across all unit operations. Unlike conventional flow sheet studies, this work establishes a fully integrated mass energy recovery framework that directly links unit-level improvements to overall process performance. The optimised flow sheet achieves approximately 80 per cent recovery of both Nb and Ta from a low-grade feed (2.1 per cent Nb2O5), while reducing overall energy intensity from approximately 24 to 19 GJ t-1 Nb2O5 (20 per cent reduction). These improvements are attributed to reduced circulating loads, enhanced phase separation efficiency, and improved reagent utilisation.