bioleaching

Extraction of metals from electronic waste by Bacterial leaching

Dr.M.Meyyappan,Professor of Physics,URCW.Karaikudi-630003

Introduction
Microbiological processes (bacterial leaching)  are successfully used in mining  and biohydrometallurigal recovery of metals  from low-percentage ores(copper bioleaching from chalcopyrites),mines with low yield after long use. It is now extended in the process of recovery of metals particularly copper from electronic scarp and gold from jewellery waste. For example printed circuit boards (PCBs) which are part of almost all electronic devices among which copper is the dominant component.The uses of electronics devices in industries, research and academic institutions,  government and private offices, transport and communication systems are increasing day-by-day enormously  which  ultimately results with dumping of electronic waste every where.It is estimated that about 50 million tones of e-waste is produced annually world over.of which only 10 % is recycled and the remaining are dumped as waste, which slowly pollute our environment. Recycling of such e-waste will help for our economical and industrial growth. Recycling of these wastes with economically viable process at all places is now possible with bacterial leaching.Microbiological leaching uses the natural ability of microorganisms to transform metals present in the wastein a solid form to a dissolved form.The bacterial leaching can be formed either in alkaline or acidic medium depending upon the specific nature of the bacteria employed and metals to be extracted from the waste. Among major groups of bacteria, the most commonly used are acidophilus (acidithiobacillus ferrooxidans and acidithiobacillus thiooxidans) and sulfolobus sp. Fungi such as Penicillium sp  and Aspergillus niger are also used in bioleaching technique.The bioleaching process is cheaper and simpler to perform at all places in comparison to conventional techniques.,since microorganisms easily adapt to changing and even extreme living conditions. It requires less energy, less space and well suitable even   for smaller resource of metals to be extracted. As it is eco-friendly in comparison to chemical methods, it is now becoming as green technology.
Bioleaching of Electronic waste
The metal content in the elements of mobile phones is about 28% including 10-20 % of copper1-5 % of lead and 1-3 % nickel with very small amount of some precious metals The traditional methods used for processing electronic scrap are pyro and hydrometallurgical methods Bacterical leaching for the extraction of copper ,zinc, nickel, tin, aluminum from electronic waste has been discovered and used successfully. Bioleaching from electronic waste is a complex process determined  by many factors-types of microporganisms,pH value of the medium,concentration of ferrous ion (Fe²⁺) in the system ,toxicity of ingredients,fineness of the material particles(smaller the size of the particles of the crushed samples of waste greater will be the efficiency) and temperature. Bioleaching is analogous to metal sulfide leaching..Material heterogeneity of waste, in particular of alkaline particulate components of the solid phase may hinder the bioleaching process and slow down its dynamics.High aluminum concentrations and alkaline character of the non-metallic components in the invironment inhibits the growth of bacteria like acidithiobacillus ferrooxidans and acidithiobacillus thiooxidans.The addition of acidifying agent improves the efficiency of the process.In such conditions nickel,aluminum,zinc and copper are converted into soluble components in solution with effectiveness close to 90 %.The concentration Fe³⁺ ions,pH and the number of used microorganisms play a crucial role in the leaching process of metals from solid state to solution.Adding higher dose of A.ferrooxidans,iron ion Fe²⁺ to the system, one can achieve the pH value of the solution for the most convenient environment required for bacterial leaching.For example pH in the range 1.5 to 2.0 adjusted with H₂SO₄  improves the efficiency of copper extraction from the waste.
Suggestions
 After analyzing the bioleaching techniques used for extraction of copper and other metals, we found some bio-physical parameters to improve this method
1.Bacteria can grow under very diverse conditions, which is why they are found nearly everywhere on earth. Although bacteria are good at adapting to their environments, certain conditions promote bacterial growth . These conditions include temperature,moisture,oxygen and pH.
The bacterial growth can be improved by improving the adaptability of the bacteria in any changing environment. This can be performed by changing the temperature of the system periodically within certain convenient range particularly from 25-40^oC(The optimum temperature for Acidithiobacillus is 28 -35^oC)  and the pH value of the solution  may also be changed periodically around 7, the neutral pH within tolerable range, before the process of extraction is performed. However the process of extracting the metals from the waste must be done at the optimum temperature and optimum pH.
2.A mixture of A.ferrooxidans and A.thiooxidans may be used. For their survival one will try to dominate the other by growing fast, utilizing the environment to the maximum extent.
3.Water content in food materials provides an excellent environment for bacteria to grow. The essence of waste vegetables will provide the best environment to the growth of bacteria.
4.Although some bacteria (anaerobe) can survive without oxygen ,in general the presence of oxygen greatly affect the growth of bacteria (aerobes) b.Almost all bacteria require CO₂ for their growth. The optimum abundance of CO₂ varies from bacteria to bacteria.
5.The bacteria used for bioleaching thrive on the sulphuric compounds of some metals.Since in nature copper is usually combined with sulphur, these bacteria like copper ore. By oxidizing copper sulphides insoluble in water, the microbes turn them into readily soluble compounds and the process is very fast.To activate this process without any lagging  vegetable waste of onion and garlic may be added in the system, since both onion and garlic are rich with sulphur.A small amount of copper sulphate may be added to the system before leaching which will improve the efficiency of the process considerably.
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A simple and direct method for Desalination of salty water by solar energy with innovative design

Popular methods for purifying water are  Filtration in stages, Boiling, Distillation (De-salination of seawater), Reverse osmosis, In Situ Chemical Oxidation(ISCO) . Boiling is the oldest and most effective method  since it eliminates most microbes causing intestine related diseases, but it cannot remove chemical toxins or impurities. However for human health, complete sterilization of water is not required, since the heat resistant microbes are not intestine affecting. In general distillation involves boiling the water to produce water vapour. The vapour contacts a cool surface where it condenses as a liquid. Because the solutes are not normally vapourized, they remain in the boiling solution. Even distillation does not completely purify water, because of contaminants with similar boiling points and droplets of unvapourised liquid carried with the steam. However, 99.9% pure water can be obtained by distillation.
Solar disinfection  is a low-cost method of disinfecting water that can often be implemented with locally available materials .No complicated technical knowledge is required so that it can be well used by all kind of people even uneducated. One of the main advantages of this method is it has low impact on the environment .It does not require any fire-wood, or electricity ,and it is well suitable to country like India where solar flux is available almost throughout the year. By adopting this method by all the nationals for their requirements of water, the nation can solve both the energy crisis (by reducing the energy used for water purifications) and drinking water problem.

Distillation by solar energy at NTP will remove from water almost anything, even heavy metals, poisons, bacteria and viruses. But if it done under reduced pressure, as the process is carried out at lower temperature, the removal of such unwanted things will not be complete. A simple and very ingenious method of achieving desalination under reduced pressure is given below:

  Requirements: one cylindrical aluminium vessel (little broad) and a similar vessel made of plastic or glass, a broad twice bend glass tube( like  inverted      ) 

Initially the bend tube is fully filled with pure water and kept  such that one end is kept immersed in the salty water taken in the aluminium vessel placed on the flat plate collector  and the other end is kept immersed in the pure water taken in the glass vessel placed outside the system.The connecting bend tube is fixed so that it is slightly inclined towards the glass tube .It helps the condensed water to flow towards the glass container.When the water filled bend tube is erected like this the pressure inside the connecting tube will be less than the NTP which will help promoting the process of vapouraization.

 

creative thoughts

இந்தியா முன்னேறுமா முன்னேறாதா  ?
1.அரசு அலுவலகங்கள் எல்லாம் பொருளின்றி வியாபாரம் செய்யும் வளாகங்களாக இருக்கும் வரை
2.அரசுப் பணியில் சேருவதற்கும், அரசு சார்ந்த திட்டப் பணிகளை நிறைவேற்ற வாய்ப்புப் பெறுவதற்கும் கமுக்கத் தேர்வு மூலம் வேண்டியவர்களைத் தேர்வு செய்வது நீடிக்கும் வரை
3. ஆளுமையற்ற அரசியல்வாதிகளும் அதிகாரிகளும் உழைப்பின்றி பொருள் குவிக்கும் வழிமுறை நிலைத்திருக்கும் வரை
4. நெடுநாள் வேலையின்றி மனம் நொந்து தவறான வழிமுறைகளைப் பின்பற்றத் துணியும் இளைஞர்களை ஆக்கப்பூர்வமாகப் பயன்படுத்த திட்ட மிடாத வரை

5. எல்லாவற்றையும் தனியார் வசம் ஒப்படைத்துவிட்டு , காசைமட்டும்

தானே எண்ணும் மனப்போக்கை அரசியல்வாதிகள் கைவிடாத வரை  

6. எதையும் கண்காணிக்காமல் விட்டுவிட்டதால் பெருகிப் போன ஊழலைத் தடுத்து நிறுத்த உருப்படியான வழிமுறையைப் பின்பற்றத் துணிவில்லாத வரை

7.நாட்டு நலத் திட்டங்களும் பணிகளும் மக்களைச் சென்றடைகின்றதா   என்பதைப் பற்றி ஏதும் கவலைப்படாமல் தன்நலத்தை மட்டும் சுவைக்கும் கொடுஞ் செயலை விடாத வரை

8.மதுவால் மக்களை  மனத்தால் முரடர்களாகவும் செயலால் திறமையற்றவர்களாகவும் உருவாக்கி வரும் சூழலைத் தடுக்க முயலாத  வரை

இந்தியாவில்
வேலியே பயிரை மேயும் நிலை ஒருபோதும் நின்று போய்விடுவதில்லை