Flue dusts accumulating within the gas cleaning units of copper smelting plants establish a critical recycling loop that cannot be directly reintegrated into the mainstream flash furnace due to capacity degradation and operational constraints. This study investigates the hydrometallurgical extraction of valuable base metals from cyclone (CD), boiler (BD), and electrostatic precipitator (ESP) dusts collected from an industrial smelting facility. Direct atmospheric sulfuric acid leaching tests conducted without prior thermal treatment yielded suboptimal zinc extractions of 40%–52%, and copper extractions ranging from 71% to 73%. These restricted dissolution rates are fundamentally attributed to the complex mineralogical nature of the feed material, which is dominated by amorphous phases and highly acid-resistant crystalline structures, such as franklinite, that act as a refractory barrier. To overcome these structural limitations, thermal roasting pretreatment was systematically executed on homogenized composite dust samples across a temperature spectrum of 600 °C to 900 °C. The experimental results revealed that increasing the roasting temperature above 600 °C induces thermal sintering and severe particle agglomeration, which substantially reduces the active surface area and degrades downstream leaching kinetics. Under leaching conditions of 90 °C, 8 hours and 1.0 M sulfuric acid, the optimum roasting pretreatment was determined to be 600 °C. This optimized route elevated copper and zinc extraction efficiencies to their peak values of 93.07% and 88.74%, respectively. Ultimately, this process demonstrates a viable industrial flowsheet for breaking the impurity accumulation cycle and shifting smelter waste into a sustainable circular economy model.