In the mining of gold, cyanide has been the preferable lixiviant globally since the year 1887. Even though, cyanide can be spiflicated and reclaimed by a number of processes, it is still extensively discussed and analyzed because of its possible toxicity as well as impacts on the environmental. Biological cyanide treatment is a well-set up procedure and has been commercially applied at gold mining procedures in various parts of the world. Biological treatment procedures alleviate microbial growth that is necessary for the treatment (Akcil & Mudder, 2003).
In biological cyanide treatment, bacteria change free as well as metal complexed cyanides to ammonia and bicarbonate while the freed metals are either precipitated from solution or adsorbed in the biofilm. The easiness with which the metal complexes of cyanide are broken down usually follows their order of chemical constancy with free cyanide being the mainly readily degradable and iron cyanide the least. The ability of the other metal cyanide complexes to be degraded like Ni, Zn, and Cu lie in between (Mudder, Botz, & Smith, 2001).
Iron cyanides have been demonstrated to break down to a minor degree as well as be adsorbed in the biomass. The first stage, in biological treatment procedure, is the oxidative degradation of cyanides, and following sorption, as well as precipitation of free metals into the biofilm. Cyanide is broken down to a combination of carbonate, sulfate, and ammonia. The next step involves conversion of ammonia to nitrate via the conventional two-step process of nitrification with nitrite as the intermediate. A variety of Pseudomonas species are known to completely oxidation of cyanide (Akcil, 2003).
Gold is among the most uncommon metals on earth, and its value has been known since ancient times. From the raised demand for gold in nanotechnology and industry, examination for new deposits of gold in the natural surroundings has turned to be very crucial. From another point of view, gold in waste solutions from a number of industrial procedures, for example, gold electroplating and gold mining effluents could be retrieved and recycled. Thus, there is a crucial call for development of alternative, cost effectual and environmentally healthy methods for retrieving gold from waste solutions.
The chemical procedures that exist are not frugal for treatment of a large amount of water bodies of dilute concentration of metal. In this attempt, biomass of microbes has come out as an alternative for rising economic and eco friendly processes for treatment of wastewater. Dead and non-living microbial biomass may inertly confiscate metal by the biosorption process from dilute solutions. The algae like Chlorella and Anabaena are employed for extraction of cadmium, copper, zinc and lead. A procedure, which could selectively retrieve the noble metals from old dumps of mining, mineral leach procedures, and industrial procedures using them would distinctly have marvelous commercial potentiality (Kiruthika & Shrinithya, 2008).
The Pseudomonas fluorescens is a microorganism that destroys cyanide through bio degradation. Thus, this bacterium provides new positions in the treatment of industrial wastewaters polluted with cyanide since its enzymes are able to break down cyanide, stable iron cyanide complexes and metal cyanide complexes into less poisonous compounds such as formic acid, formamide and ammonia (Akcil, Karahan, Ciftci, & Sagdic, 2003). Degradation of Cyanide by Pseudomonas fluorescens appears to be an assimilative procedure as cyanide elimination coincides with the exponential growth stage as well as with the maximum oxygen consumption rate. It is, therefore, clear that cyanide can be generally broken down by this bacterium and may also utilize cyano-metal complexes, based on the high amount of complexes of heavy metal-cyanide available in the remains from the jewellery industry, on top of free cyanide (Kiruthika & Shrinithya, 2008).
Akcil, A. (2003). Destruction of cyanide in gold mill effluents: biological versus chemical treatments. Biotechnology Advances, 21, 501–511.
Akcil, A., & Mudder, T. (2003). Microbial destruction of cyanide wastes in gold mining: process review. Biotechnol Lett, 25, 450–455.
Akcil, A., Karahan, A. G., Ciftci, H., & Sagdic, O. (2003). Biological treatment of cyanide by natural isolated bacteria (Pseudomonassp.). Mineral Engineerin, 16(7), 643-649.
Kiruthika, A. J., & Shrinithya. (2008). Cyanide Detoxification and Recovery of Gold from Gold Effluent. Advanced Biotech, 20-26.
Mudder, T., Botz, M., & Smith, A. (2001). The chemistry and treatment of cyanidation wastes. London: Mining Journal Books.