Abstract
The increasing accumulation of stale tailings from mining operations poses both environmental risks and opportunities for the recovery of valuable metals. This study focuses on the development, additive manufacturing, and experimental validation of a small-scale continuous reactor system for the extraction of nickel, cobalt, and iron from stale pyrite tailings at the Sokolovsko-Sarbaisky Mining and Processing Plant (Kazakhstan). The reactor system was fabricated using additive manufacturing (3D printing) with PET-G polymer, allowing for rapid prototyping, modular assembly, chemical resistance, and cost-effective production. The system comprises three sequentially connected reactors operating in continuous flow. Reagent and slurry feeding were conducted using peristaltic pumps, while a stepper-motor-driven mechanical stirrer ensured homogeneous mixing. Temperature was controlled by circulating a heat-transfer fluid through integrated heat-exchange channels, enabling stable operation over 20-120°C. Before leaching, stale tailings were subjected to oxidative roasting in a fluidized-bed furnace at 650-700°C for 1 hour, which facilitated the decomposition of sulfides into oxides. Subsequent leaching experiments were conducted with sulfuric acid concentrations ranging from 25 to 175 g/dm3, varying residence times, and controlled thermal conditions. Optimal parameters were established as 100 g/dm3 H2SO4, 100°C, and 120 minutes, resulting in recoveries of 93.01% for Ni and 91.49% for Co, with moderate Fe dissolution of 64.4%. The results confirm that the designed continuous reactor system provides reproducible hydrometallurgical performance, stable process control, and scalability potential. This approach highlights the combined advantages of continuous-flow chemistry and additive manufacturing in processing low-grade, environmentally challenging raw materials.