escribe the processes used to extract copper and gold from their ores using bacterial leaching. In each case, explain how the micro-organisms liberate the metal from its ores and describe how the metal is then extracted from the mixture. Bacterial Leaching of ores and other Materials Bacterial leaching is a process in which bacteria is used to extract heavy metals from low grade ores and tailings (left from an earlier traditional mining).
In mining industry, bioleaching is a new technique used to extract minerals such copper and Gold from their low grade ores. The main agents used in bioleaching process are micro organisms such as Chemolithoautotrophs; they capture carbon for the synthesis of cellular components not from organic nutrients but from carbon dioxide (CO2) in the atmosphere. These bacteria are Thiobacillus Ferrooxidans and
Thiobacillus Thiooxidans. Thiobacilli grow in acidic environment because they are acidophilic (acid loving). They drive energy by the oxidation of the Ferrous iron and Sulphur part of the mineral for their survival. They grow at PH value from 1 to 4 and strictly under aerobic conditions. Bacterial Leaching has been divided into two mechanisms: Direct Mechanism: – Direct mechanism is that in which bacteria is physically attached to the mineral surface.
In this reaction, the electron passes into the bacterial cell which produces ATP (Adenotriphosphate), is the energy currency of the cell which reduces oxygen molecules to water.Discuss the advantages and disadvantages of using bacterial leaching rather than traditional extraction methods and suggest why bacterial leaching is used only as a secondary extraction process for copper but as a primary extraction process for Gold?
Advantages and Disadvantages:- Bacterial leaching process is simple to operate, mild operation conditions. It uses naturally occurring resources such as micro-organisms, Water and air. It is very friendly towards environment but in smelting and roasting process, emissions of SO2 are released. It requires low energy input, low pressure and temperature process rather than traditional extraction methods. Traditional method is expensive as bioleaching involves low capital costs. Bioleaching is a slow process as it takes decades rather than years to extract metals but as traditional method is expensive but it is faster. As facts had revealed that bacterial leaching is the cause of acid mine drainage.
Secondary extraction process for copper but as a primary extraction process for Gold: Bacterial leaching is considered as secondary process for copper for the fact that it is not able to perform on a large scale and copper is present in large amounts in their ores. It is also an extremely slow process and uneconomic. For gold however it proved to be cost effective as it recovered almost all the gold. Summarise the development stages that a new mining process (such as bacterial leaching) must pass through before it can operate commercially?