Heap-borehole bio-leaching of precious and non-ferrous metals under continental climate conditions: a perforated-tube thermal activation approach

Abstract

A novel heap-borehole bio-leaching method with integrated thermal activation was developed and evaluated for the recovery of copper, nickel, and gold from low-grade ores under continental winter conditions. The method employs a dual perforated-tube system installed in boreholes drilled to a depth of 10 m within the ore heap. An outer acid-resistant tube (diameter 100 mm) and a coaxial inner tube (diameter 50 mm) with graduated perforation sizes (0.5, 1.5, and 2.5 mm per every 3 m segment) distribute oxidising bacterial solutions directly into the ore mass, while a heating cable maintains the internal temperature at 15–20 °C during winter periods with ambient temperatures of −20 to −30 °C. Bench-scale trials were conducted over 120 days under unheated outdoor conditions, simulating sub-zero winter environments. Comparative experiments included a baseline acid-only treatment, an analogue biooxidation prototype, a perforated-tube variant, and the full proposed method combining all factors. The proposed method achieved copper extraction of 86.46 %, nickel extraction of 54.03 %, and gold extraction of 84.29 % — representing improvements of approximately 30–35 percentage points over the prototype for copper and gold, and approximately 28 percentage points for nickel. The results demonstrate that integrated borehole delivery, microbial oxidation, and controlled thermal activation overcome the principal limitations of conventional heap leaching in cold climates, enabling year-round operation and economically viable recovery of precious and non-ferrous metals.