Canada ranks in the top five producing countries for 13 major minerals and metals such as gold and diamonds, uranium and niobium, nickel, cobalt, aluminum, and platinum. Indeed, the mining industry is the largest private sector providing over 16,600 jobs to community members; therefore, it is not far from this projection that the mining industry contributed $97 billion, or 5%, to Canada’s total nominal GDP to this profitable industry. In the gold mining industry, the gold is finely disseminated in a sulphide mineral matrix (pyrite and arsenopyrite). This fraction is not recovered with conventional processes such as cyanidation, pyrometallurgy, roasting, pressure oxidation. Although their efficiency, the gold is still not recovered at high titers.
Therefore, harnessing the abilities of some species of prokaryotic microorganisms to catalyze the oxidative dissolution of sulfide minerals and to facilitate the extraction of metals; is promising. Currently, biooxidation is carried out in:  i) stirred stainless steel tanks or ii) piles of crushed ores, known as heaps, irrigated with oxidizing bacteria and aerated to enhance their microbial growth. Generally, with low-grade sulphide ores, heap biooxidation approach, using chemolithotrophic bacteria, is economically attractive. However, heap biooxidation of low-grade sulphide ore in cold climate of Canada introduces a greater degree of complexity. The complexity of the bacterial community is most pronounced in heaps in which there is a spatial variation of physical, chemical and mineralogical conditions, indicating the necessity of niche adaptation and specialization by microbial communities for different ore types and conditions.
In order to extract the gold with high efficiency, it is strongly required to have full knowledge about the mineralogical properties of ores in combination with minerals particle sizes as well as the formation of alloy in minerals, cyanides consumers’ structures including enargite, carbonaceous materials and clay deposits oxygen consumers as a preg-robbers materials in refractory mineral gold ores. To succeed in the heap bioleaching, many considerations should be taken into account such as: i) transport of aqueous species inside ore particles, ii) transport, attachment, growth, dynamic of populations and catalytic action of microorganisms, iii) oxygen and water transport through the bed, vi) heating and cooling of the bed, associated with exothermic (e.g. between 30 to 70 ̊C), and endothermic reactions and heat transfer to the environment. To overcome these challenges, the conception and the design of heap as well as the development of a hydraulically efficient and cost effective system that provides a better circulation of leaching biosolutions represents a must for different mining industries.
Therefore, the main objective of this research program is to optimize bio-oxidation process from lab to pilot scale through the introduction of new engineered concepts of bio-heaps in nordic climate for the extraction of gold-bearing sulphide ores, optimizing bacterial growth parameters, heat retention, and irrigation and aeration rates. The originality of the work is categorized to the three main scopes including: implementation of effective nutrients and carbon source for efficient bacteria growth and biooxidation rate; reactor and column (as a laboratory sample of heap) tests for the specific sample and process optimization (case study).