BIOLEACHING AND BIOMINING PDF

PDF version Biomining is mineral processing with microbes. Biomining is the process of using microorganisms microbes to extract metals of economic interest from rock ores or mine waste. Biomining techniques may also be used to clean up sites that have been polluted with metals. Valuable metals are commonly bound up in solid minerals. Some microbes can oxidize those metals, allowing them to dissolve in water.

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Bioleaching of non-sulfidic ores such as pitchblende also uses ferric iron as an oxidant e. Sulfidic iron ores can be added to speed up the process and provide a source of iron. Bioleaching of non-sulfidic ores by layering of waste sulfides and elemental sulfur, colonized by Acidithiobacillus spp.

The copper is removed by bonding to a ligand, which is a large molecule consisting of a number of smaller groups , each possessing a lone electron pair. Because this complex has no charge , it is no longer attracted to polar water molecules and dissolves in the kerosene, which is then easily separated from the solution. Because the initial reaction is reversible , it is determined by pH. Adding concentrated acid reverses the equation, and the copper ions go back into an aqueous solution.

Then the copper is passed through an electro-winning process to increase its purity: An electric current is passed through the resulting solution of copper ions.

Copper is the oxidising agent it accepts electrons , and iron is the reducing agent it loses electrons. Traces of precious metals such as gold may be left in the original solution. Treating the mixture with sodium cyanide in the presence of free oxygen dissolves the gold. The gold is removed from the solution by adsorbing taking it up on the surface to charcoal.

With fungi[ edit ] Several species of fungi can be used for bioleaching. Fungi can be grown on many different substrates, such as electronic scrap , catalytic converters , and fly ash from municipal waste incineration. Aspergillus niger can produce some organic acids such as citric acid. This form of leaching does not rely on microbial oxidation of metal but rather uses microbial metabolism as source of acids that directly dissolve the metal.

Compared with other extraction techniques[ edit ] Extractions involve many expensive steps such as roasting , pressure oxidation, and smelting , which require sufficient concentrations of elements in ores and are environmentally unfriendly.

These microorganisms actually gain energy by breaking down minerals into their constituent elements. The company simply collects the ions out of the solution after the bacteria have finished. There is a limited amount of ores.

Advantages[ edit ] Economical : Bioleaching is in general simpler and, therefore, cheaper to operate and maintain than traditional processes, since fewer specialists are needed to operate complex chemical plants. Environmental : The process is more environmentally friendly than traditional extraction methods.

Less landscape damage occurs, since the bacteria involved grow naturally, and the mine and surrounding area can be left relatively untouched. As the bacteria breed in the conditions of the mine, they are easily cultivated and recycled.

Ore concentration: Bioleaching can be used to extract metals from ores that are too poor for other technologies. It can be used to partially replace the extensive crushing and grinding that translates to prohibitive cost and energy consumption in a conventional process. Disadvantages[ edit ] Economical: The bacterial leaching process is very slow compared to smelting.

This brings in less profit as well as introducing a significant delay in cash flow for new plants. Environmental: Toxic chemicals are sometimes produced in the process. Heavy ions such as iron , zinc, and arsenic leak during acid mine drainage. When the pH of this solution rises, as a result of dilution by fresh water, these ions precipitate , forming "Yellow Boy" pollution. For these reasons, a setup of bioleaching must be carefully planned, since the process can lead to a biosafety failure.

Unlike other methods, once started, bioheap leaching cannot be quickly stopped, because leaching would still continue with rainwater and natural bacteria. At the current time, it is more economical to smelt copper ore rather than to use bioleaching, since the concentration of copper in its ore is in general quite high. The profit obtained from the speed and yield of smelting justifies its cost. Nonetheless, at the largest copper mine of the world, Escondida in Chile the process seems to be favorable.

However, the concentration of gold in its ore is in general very low. In this case, the lower cost of bacterial leaching outweighs the time it takes to extract the metal. Economically it is also very expensive and many companies once started can not keep up with the demand and end up in debt. Projects like Finnish Talvivaara proved to be environmentally and economically disastrous.

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Bioleaching: Making Mining Sustainable

He discovered that the bacteria grew faster and were more motile in high iron concentrations. The byproducts of the bacterial growth caused the media to turn very acidic, in which the microorganisms still thrived. This discovery lead to the development of complex modern biomining systems. Biomining is the use of microorganisms to leach metals from their growth medium. These systems can be used for bioremediation, biohydrometallurgy, or even extracting metals from ores for commercial use. It was later discovered that some fungi also leach metals from their environment. In the microbial leaching process A.

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What is biomining?

No Comments Biomining can be defined as the extraction of minerals from ores by using microorganisms. The microorganisms actually facilitate the extraction of metals from sulfide or iron-containing ores. Metals solubilization process is involved in biomining and it is a combination of microbiology and chemistry. Bioremediation is the use of microorganisms bacteria and fungi to degrade the environmental contaminants into less toxic or nontoxic forms Methods of biomining Bioleaching: A classic method of biomining. In this method, low-grade ore is dumped into a heap called leach pile and then soaked with a weak sulfuric acid wash.

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