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BacTech Mentioned - BioMetMine

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Types of Bioleaching Technologies Available

Bioleaching can broadly be categorized into two segments, whole ore and concentrate systems. Whole ore can be further subdivided into in situ or ex situ systems. Concentrate systems are always ex situ processes.

Whole Ore Processes

In Situ

• In situ bioleaching – in-situ treatment refers to the process where ore is treated without mining to remove the rock to a treatment process on the surface. This process relies on fracturing the ore by blasting or natural processes thus, producing voids and porosity to allow free solution flow. The solution is collected, generally at the bottom of the mine processed for metals recovery. The biological system receives its oxygen from the solution. The application of this process has not been wide spread as it requires very specific ore body characteristics, high permeability ore with low permeability host rock. Additionally, the recoveries are typically low and the time required is long.

Ex Situ

• Stirred tank bioleaching – bacterial oxidation of ground mineral slurry can be carried out in aerated agitated vessels, when the value of the metal is sufficient to justify the cost of installing and operating the equipment. The reaction vessel can be either a mechanically stirred tank with a means of introducing oxygen into the slurry or an air agitated pachuca reactor where the introduction of the air provides not only the oxygen but the agitation of the slurry. The application of this process to ores has been fairly limited due to the large size of the vessels, thus often making it cost prohibitive. However, oxidation kinetics are much higher than in situ or heap systems.
  
• Biooxidation heaps – heaps are formed by stacking crushed rock into constructed piles on prepared impervious pads that have a sloped base to allow solution to flow by gravity into collection drains. Oxygen can be added to the system to enhance the rate of oxidation by blowing low pressure air into the heap base. This system was first employed for secondary copper minerals in large dumps using run of mine ores. Acidic solutions carry away the biooxidized products such as copper or iron. Recent advances in whole ore heap leaching have seen the use of closely sized ore particles to aid the oxidation rate, under heap piping for better air distribution and agglomeration, and preinoculation to aid in permeability and oxidation rate. Additionally, whole ore systems are now applied to a wide range of ore types including refractory gold ores, copper sulphides, nickel sulphides, cobaltiferrous ores and zinc sulphides. Companies such as GeoBiotics, Newmont and Titan Resources all have various technologies for whole ore biooxidation.
  
• Vats – vat leaching refers to the method of treatment where the sulphide mineral is immersed in the solution for all or part of the treatment process. This is a highbred process that is a combination of whole heap leaching and stirred tank. The vats provide for better control of the biooxidation environment while not having the requirement of expensive agitation and air distribution. This system is not commonly employed as the biooxidation rate is often slow and the extent of biooxidation low.

Concentrate

• Stirred tank bioleaching – bacterial oxidation of ground mineral slurry can be carried out in aerated agitated vessels, when the value of the metal is sufficient to justify the cost of installing and operating the equipment. The reaction vessel can be either a mechanically stirred tank with a means of introducing oxygen into the slurry, or an air agitated pachuca reactor where the introduction of the air provides not only the oxygen but the agitation of the slurry. The application of this process to ores has been fairly limited as the size of the vessels and thus the costs is often prohibitive. The oxidation kinetics are much higher than in situ or heap systems. Concentrate systems require smaller tankage and therefore are less expensive but do require a concentration circuit and generally more cooling. Systems have been successfully commercialized using a wide range of temperatures ranging from mesophiles at 35-40oC, moderate extreme thermophiles at 45-55oC and extreme thermophiles at 60-75oC. Companies such as Bactech/Minteck, Goldfields, and BHPBilliton have all successfully developed stirred tank systems for a variety of concentrates including refractory gold, copper sulphides, nickel sulphides, and cobaltiferrous concentrates.
  
• Biooxidation heaps – forming a heap from a concentrate is impossible but GeoBiotics’ patented GEOCOAT® technology allows the low cost of a heap system to be employed for concentrate biooxidation by coating the concentrate onto a suitable substrate. The heaps are formed in a similar manner to conventional heaps, by stacking crushed rock into constructed piles on prepared impervious pads that have a sloped base to allow solution to flow by gravity into collection drains. The difference is that as the rock passes off the end of the stacker concentrate is sprayed onto it. Oxygen is be added to the system to enhance the rate of oxidation by blowing low pressure air into the heap base. The heap is irrigated with low pH solution containing nutrients to promote bacterial growth. For base metal sulphides the valuable metal is recovered in the solution while for refractory gold treatment the biooxidized residue is removed for treatment by conventional processing. This system also allows ore to be treated simultaneously as the substrate can be oxidized in unison. The advantages of this system are that is has a much lower capital and operating cost, while the main disadvantages are the slower oxidation rates and difficulty operating in extremely cold environments.

https://technology.infomine.com/biometmine/biopapers/biomet_types.asp