Electronic Waste- A Journey from Global Menace to Wealth Generation by its Effective Management Strategy

 

Rajni Kumari¹, Prerna Prashant Karthaka², Anand Prem Rajan^3*

¹Department of Biomedical Science, School of Biosciences and Technology, VIT,Vellore- 632014, Tamil Nadu, India

²Department of Biotechnology, School of Biosciences and Technology, VIT Vellore- 632014, Tamil Nadu, India

³Department of Biomedical Science, School of Biosciences and Technology, Research Officer-Renewable Energy in CO₂ and Green Technology Centre, VIT, Vellore, Tamil Nadu, India

 

ABSTRACT:

 

INTRODUCTION:

Electronic waste is one of the most rapidly growing problems in the world. E-waste denotes discarded electrically run devices. About 50-80% of E-waste is presently exported from developing countries particularly Asia and Africa1 as E-waste is a great challenge to tackle². Due to lack of proper E-waste management technologies, issue gets more complicated in the developing countries³.

 

In present Indian scenario recycling relies only on manual operations⁴. Electronic devices contain a mixture of materials, some of which are toxic creating serious health and environmental problems as it is handled improperly⁵. Long term presence of E-waste in dump yards may cause risks to human health and environment⁶. E-waste has become major global concern due to its unregulated entry in environment and persistence.

 

The electronic gadgets have revolutionized our way of living, working and communication, bringing countless profits and prosperity to all its users. The launch of new electronic products has initiated economic globalization making large number of products available at reasonable costs to the public. Purchasing a new electronic product has become an essential part of our daily lives providing more comfort, security, faster attainment and exchange of information⁷. But on the other hand, it has also led to unreserved resource utilization and a huge E-waste generation. Even before an electronic gadget becomes non-functional, microbes start to form biofilm and habitats the gadgets like ATM8 and medical implants⁹.

 

Developed countries and developing countries alike face the menace of E-waste management. The rapid growth of technologies, upgrading of technical innovations and a high rate of obsolescence in the electronics industry have led to one of the greatest growing waste streams in the world which consist of end-of-life electrical and electronic equipment products¹⁰. It comprises of an entire array of electrical and electronic items such as refrigerators, washing machines, computers and printers, televisions, mobiles, i-pods, etc. The presence of toxic materials in the E-waste is credited to complexity in treatment and recycling of these discarded wastes.

 

Extensive literature survey on E-waste management has made known a large scientific void in three areas like optimal management and/or minimization of E-waste, development of cleaner environmentally sustainable recycling and discarding of E-waste. In this review article, we have considered a case study on Indian E-waste generation and problems associated with it and critically analysed to provide an eco-friendly solution for all metal extraction which can be used for E-waste treatment. We formulated solutions for the E-waste management and projected possible green microbial technology to solve this issue in environment friendly manner to solve this global menace ensuring economic growth ensuring good quality of life.

 

 

 

E-waste scenario in developing country, India as case study:

The average Indian uses electronic products and discards it which belong to various categories (Fig 1). It is clearly evident that high income groups produce around 36.93 kg per annum and middle income groups produce 24.13 kg, lower income groups produce 7.6 kg and below poverty line 3.95 kg per annum.

 

 

Figure1. House Hold E-Waste Generated by Different Income Groups in India¹¹.

 

 

Figure 2. A Citizen from a Middle Income Household Generates 21 Kilogram of E-waste Per year Capita in the form of Television i.e. 21.03% (Maximum), Grinder 18.11%, Refrigerator 19.55%, Washing Machine 13.52%, UPS 8.13% as the Major and the Minors are Light, MP3 Player¹².

 

Table: 1 Shows the E- waste produced in twenty major Indian cities and states from 2004 till 2018¹³.

S. No	Cities/ State	Quantity of E –waste (in Metric tons)		Year	Quantity of E-waste produced (2018) in tons
1	New Delhi	30000 tons		2004	98,000
2	Indore	5000 to 6000 tons		2005	58,000
3	Bangalore	70000 tons		2005	92,000
4	Varanasi	7.404 tons		2007	20,000
5	Shillong	446 tons		2016	9,000
6	Mizoram	18 tons		2017	500
7	Mumbai	61,000 tons		2017	1,20,000
8	Chennai		30,700 tons	2017	67,000
9	Kolkata		23,000 tons	2018	55,000
10	Hyderabad		16,000 tons	2018	32,000

 

Figure 3. Weight composition of metals like Iron (Fe), Copper (Cu), Aluminium (Al), Lead (Pb), Nickel (Ni) for different electronic scrap in India¹⁶.

 

 

Figure 4. Showing harmful effects of various metals present in the electronic waste on human health in India²⁹.

 

Composition of E-waste:

The metals in E-waste exists in both pure metal and alloy forms. Recovery of pure forms of metals are obtained by melting in smelters14 as thermo-chemical methods which are relatively very difficult15. Figure 3 shows the composition of different electronic scrap and their E-waste composition.

 

Apart from plastics, wires and glass there are many harmful metals present in E-waste. A few examples of them are Paladium, Gold, Silver, Cadmium, Mercury, Chromium and Arsenic.

 

Health hazards of heavy metals from E-waste:

There are many hazards caused by E-waste to human health. Lead in E-waste is a neurotoxins and affects the male reproductive system^17,18, Cadmium is carcinogenic and structurally modifies the liver¹⁹, Mercury affects the Central Nervous System (CNS) and causes neuro degenerative diseases²⁰, Chromium causes oxidative stress as it exists in several oxidative states such as Cr(0) to Cr(VI)²¹, Arsenic causes cytogenetic damage and apoptotic abnormalities²², Nickel gives Ischemia and causes oral allergy as it is used in braces, Selenium causes Gastrointestinal (GI) disorders but some studies prove that it can also be used as an anti-cancer agent²³, Silver causes asthma and dermatitis²⁴, Lithium also affects the neurological system but can also be used as an anti-convulsant²⁵ and Zinc causes cardiovascular diseases as well as acute respiratory infections in children^26,27. Gastrointestinal disturbances, liver and renal diseases, reproductive health effects, dermal changes and other health disorders are various categories of hazards²⁸.

 

Recent trend in metal recovery methods from E-waste:

The precipitation, solvent extraction, adsorption, ion-exchanger and electro-winning methods used in leaching process are followed in traditional and/or conventional metal recovery processes³⁰. Cyanide, thiourea, thiosulfate and halide solutions have been used as leaching reagents^31,32. Hydrometallurgical methods for processing of E-waste has gained recent attention due to its simplicity and lower capital investments. Hydrometallurgical process, has more advantages like ease to implement and low operational costs when compared to pyrometallurgical methods³³.

 

Hydrometallurgical methods use the dissolution of the metallic fractions of E-wastes in either acidic or alkali solutions and the recovery of precious metals is driven by natural process using microbes. Even though hydrometallurgical processes have proven to be technically feasible but use of toxic reagents such as cyanide and thiourea, continue to be an environmental threat³⁴.

 

 

 

 

Metals Recovery methods from E-waste:

E-waste contains non-metallic compounds along with cocktail of economically important precious metals such as pure metals (Gold, Silver) and base metals. There are mainly five types to metal extraction methods used in metallurgy which has its own advantages and disadvantages while dealing with E-waste.

 

1. Pyrometallurgical methods:

Pyrometallurgical processing is a traditional method to recover non-ferrous metals as well as precious metals from electronic waste for in the past two decades. It includes incineration, smelting in a plasma arc furnace or blast furnace, dossing, sintering, melting finally reactions in a gas phase at high temperatures³⁵. The crushed scraps are burned in a furnace. In this process, plastics have been removed by molten bath and the refractory oxides are removed from a slag phase together with some metal oxides.

 

2. Hydrometallurgical methods:

It consists of a series of acid or caustic leaches of solid material. The isolation and concentration of the metals depends on solutions that are subjected to purification and separation process such as: precipitation of impurities, solvent extraction, and adsorption and ion- exchange. The solutions are treated by electro refining process, chemical reduction or crystallization for metal recovery^36-39. In this method leaching agents like cyanide, halide, thiourea and thiosulfate are used for the recovery of precious metals⁴⁰.

 

(a)  Acid leaching:

Leaching is basically the process in which substances are extracted from solids with the help of liquids. In the chemical processing industry, it has a variety of uses namely extractions of metals from ores, extraction of impurities, separation of metals in alloys, etc.

 

Acid leaching, on the other hand, mainly means dissolving metals by using strong acids. One of the main uses is remediation of contaminated soils. It is mainly used for the extraction of nickel from laterite ores which are traditionally treated by pyrometallurgical methods.

The basic steps in the process are:

 

 

Figure 5. Steps involved in acid leaching⁴¹

 

 

 

(b)  Cyanide leaching:

Cyanide as lixivant for gold is utilized in the mining industries. The mechanism of gold dissolution in cyanide solution is a necessary electrochemical process.

 

4Au + 8CN− → 4Au (CN)₂ − +4e-          (Eq. 1)

O₂+2H₂O + 4e → 4OH−                                            (Eq. 2)

 

pH has immense effect on dissolution rate for the noble metals (Gold, Silver, Palladium, Platinum). Gold, Silver, Palladium, and Platinum gets dissolved at pH 10 to 10.5 in cyanide solution. The environmental concern of cyanide leaching is contamination of rivers & ground water as witnessed in Gold mines^42,43.

 

(c)  Thiourea leaching:

Thiourea (NH2)2CS) is used for the recovery of gold from ores⁴⁴. Thiourea dissolves gold forming a cationic complex in acidic condition. The reaction is rapid and metal extraction efficiency is also very high equivalent to 93% to 99% ⁴⁵.

 

Au + 2CS(NH₂)₂→ Au(CS(NH₂)₂)₂+ +e                 (Eq. 3)

 

Most of the precious metal in E-waste can be easily leached using thiourea leaching. Thiourea leaching is not so favoured in spite of its efficiency as it is costlier compared to cyanide leaching. This technologyis still in its early stages of development⁴⁶. Moreover thiourea gets easily oxidized in solution form⁴⁷.

 

(d)  Thiosulfate leaching:

Thiosulfate (S₂O₃₂−), is used in photography, chemical and pharmaceutical industries. Researchers have proposed this leaching method as a substitute for cyanide leaching^48-50.

 

The ammonical thiosulfate has been leached by electrochemical-catalytic mechanism of gold51. It is directly reduced to Cu (NH₃) ²⁺ because Cu (NH₃)₄²⁺ species present in solution acquires electrons on the cathodic portion of the gold surface. During this time, Au+ (Gold) is made to react with either ammonia or thiosulfate ions on the gold anodic surface and solution change the form to either Au (NH₃) ²⁺ or Au (S₂O₃H₃)₂^3-.It depends on the concentration of S₂O₃^2- and Cu(NH₃)²⁺ ions which are converted to Cu(S₂O₃)₃^5- ions, and the same happens to Au (NH₃)²⁺. Cu (NH₃)₄²⁺ with oxygen gets oxidized by Cu (S²O³) 35- species and Cu (NH3) 2+ species in solution. The relative concentration of the species in solution depends on the predominant cathodic reaction. Metallic gold to aurous Au+ ion is oxidized by the role of copper (II) ions. It can be simplified as:-

 

Au+5S2O32- +Cu (NH3)42+ →Au (S2O3)23-+4NH3 +

Cu(S2O3) 35-                                                               (Eq. 4)

2Cu (S₂O₃)35-+ 8NH₃+ 0.5O₂+H₂O→ 2Cu (NH₃)42+ +2OH-+6S₂O₃₂                                                            (Eq. 5)

 

3. Biometallurgy Process:

Bioleaching and biosorption are two major processes employed for the recovery of metals mainly for metallic sulphides. Majority of base metals and precious metals are economically and precisely recovered by bacterially assisted reactions52. Extraction of Co, Mo, Ni, Pb and Zn metals from their sulfidic ores are effortlessly executed by bioleaching53. Presently metals like copper and gold are produced in significant proportion by industries by bioleaching technology⁵⁴.

 

Passive physico-chemical interaction has been used in the biosorption process between the charged surface groups of microorganisms and ions in solution, in which both living and dead organisms can be used. Algae55, bacteria⁵⁶, yeasts⁵⁷ and fungi⁵⁸ accumulate large quantity of heavy metals and precious metals actively in their protoplasm and also on cellular surface. Few bacteria have advanced various mechanisms of adsorption, methylation, oxidation and reduction of chromium and applying it into less toxic trivalent Cr(III) form⁵⁹. Advantages of biosorption based process includes low operating costs, minimization of the chemical usage and non-toxic biological sludge and detoxifying effluents⁶⁰.

 

4. Bacterial leaching:

The presence of feasible pathogenic or environmental bacteria on non-living things is a matter of importance⁶¹. Bacteria namely chemolithotrophs uptake their energies by redox reaction which are releases metals (M) in the solution form. There are two mechanisms by which microorganisms can increase the leaching rate of metals from mineral ores and/or E-wastes.

 

(a)  Direct action mechanism:

In this mechanism, the microorganisms are directly oxidizing the minerals and solubilize metals

 

MS + H2SO4 + 0.5O2 → MSO4 + S0 + H2O62  (Eq. 6)

S0 + 1.5O2 + H2 O → H2 SO463                            (Eq. 7)

 

(b) Indirect action mechanism:

In this mechanism, ferric ion (Fe3+) is the oxidizing agent for minerals and the organisms act on that, regenerating Fe3+ from Fe2+.

 

2Fe2+ + 0.5O2 + 2H+ → 2Fe3+ H2O65                (Eq. 8)

MS + 2Fe3+ → M2+ + 2Fe2+ +S064                     (Eq. 9)

 

It has been found that, in microbial leaching of metals, physicochemical reactions can contribute in both direct and indirect leaching⁶⁶.

 

Sand and co-workers proposed the mechanism of bacterial metal sulfides by indirect leaching⁶⁷. They proposed two pathways (i) Thiosulphate Pathway and (ii) Polysulfide pathway.

 

Dissolution is achieved by an amalgamation of proton attack and oxidation process. Types of mineral species present in the ore determined the reaction pathway68. Although, the pathway of dissolution is not controlled by structure of crystal (e.g. monosulfide or disulfide structure). Relevant criterion is the result of reactivity of metal sulfides with protons i.e. acid solubility. Electronic configuration is said to determine the latter property⁶⁹.

 

Thiosulfate pathway:

It is exclusively based on oxidative attack of iron (III) ions on the acid-insoluble metal sulfides like FeS2, MoS2, and WS2. Thiosulfate is the main sulphur intermediate.

 

The following are the simplified equations of thiosulfate mechanism.

 

FeS2+6Fe3+ +3H2O→S2O32-+7Fe2++6H+70  (Eq. 10)

S2O32-+8Fe3++5H2O→2SO42-+8Fe2++10H+71 (Eq.11)

 

Polysulfide pathway:

It provide metal dissolution by an attack of iron (III) ions and/or Protons. Polysulfide is the main sulfur intermediate in this case. The two mechanisms can be easily simplified by the equations as follows:72

 

MS + Fe3+ + H+ → M2+ + 0. 5 H2Sn + Fe2+ (n ≥ 2)73 (Eq. 12)

0.5H2Sn +Fe3+ → 0. 125S8 + Fe2+ + H+74      (Eq. 13)

0.125S8 + 1.5O2 + H2O → SO42- + 2H+75      (Eq. 14)

 

Bioleaching of metal sulfides is basically the bacterial function that generates sulfuric acid biologically to supply protons for hydrolysis attack and to keep the iron ions in the oxidized state for an oxidative attack. The main role played by leaching bacteria is regeneration of iron (III) ions in both cases. Iron (III) ions are the most important oxidants in acidic biotopes and the redox potential is controlled by acidophilic iron (II) ions in their environment. The redox potentialis mainly determined by iron (III) /iron (II) ratio in the leaching solutions. The redox potentialis increased by the iron-oxidizing microorganisms, mesophilic or thermophilic organism resulting in metal sulfide biooxidation76. The useful application of bioleaching and benefits of using microorganisms for extraction of metals⁷⁷.

 

5. Fungal leaching:

Leaching is a major challenge in case of non-sulphide ores like silicates and oxides. These hurdles are easily handled by microbes. Fungi is necessary for the leaching of these kinds of ores. Fungi produced organic acid by their metabolic activities, that has dual effect, one is that it provide hydrogen ions for acidolysis of minerals and the other one is complexing metals due to its chelating capacity⁷⁸. Therefore fungi are used for leaching of nickel laterites. Fungi are heterotrophic microorganisms which has very high metal leaching capabilities, especially of oxidic, carbonaceous or siliceous materials⁷⁹. Unlike autotrophs, fungi ingest biomass to obtain their energy and nutrition. These heterotrophs are totally dependent on autotrophs or their biological products. Aspergillus and Penicillium are the two widely studied strains of fungi that can be used in microbial leaching80. Fungi generally use indirect processes with microbial production of organic acid, amino acids, metabolites along with the leaching of metal. Mainly four mechanisms have been identified for the leaching of metals by fungi (i) acidolysis, (ii) complexolysis, (iii) redoxolysis⁸¹(iv) Bioaccumulation⁸²

 

Acidolysis, complexolysis and redoxolysis occur through metabolites excreted by the fungus. Whereas bioaccumulation process is observed when fungus accumulates the metal ions from the solution and by altering the equilibrium between solid and dissolved metal which causes the continuous solubilisation of metals⁸³.

 

The possible reactions that takes place to produce metal (e.g. nickel) ions are as follows84

Proton attack

NiO + 2H+ →Ni2+ + H2O                                      (Eq. 15)

 

MCO3 + 2H+ →M2+ + H2O + CO2                   (Eq. 16)

Where M is Fe, Mg, Mn or Ca etc.

Reduction

MnO2 + 2e‒ + 4H+ →Mn2++2H2O                     (Eq. 17)

Complexation /Chelation

Ni2 + C6H8O7 → Ni(C6H5O7)‒ + 3H+              (Eq. 18)

 

Organic acid produces the proton, that assists in proton promoted mineral dissolution (Eq.15). As per mineralogical aspect, nickel laterite is considered as having a complex mineralogy, i.e. few nickel atoms are stretch in a solid solution of atoms of other elements which materialize in large quantities, such as Fe, Mg, Al, Mn, Ca. Acid attack (Eq.16) of any carbonate material in the ore increases metal/nickel liberation. However, this reaction requires the production of excess acid. In addition, the reduction of soluble manganese (Eq.17) can result in the equilibrium between solid-phase Mn4+ and soluble phase Mn2+ being shifted fairly, enhancing the dissolution of the mineral, thus energizing nickel. Organic acids complex with metal ions in solution (Eq.18), lowering metal activity, and hence increasing the apparent solubility of the mineral.

 

 

 

 

 

First Proposed Postulate for E-waste management – Recycling:

Pre-treatment of E-waste is performed by mechanical process, for enriching and upgrading of commercially important components. The mechanical recycling of electronic waste has been investigated by different researchers. the precious metals cannot be efficiently recovered in mechanical recycling.

 

Figure 6. Recycling of E-waste involves disassembly, upgrading and refining which are major steps.

 

The removal of impurities for recovered metals is carried out using metallurgical techniques such as pyrometallurgical processing and hydrometallurgical processing. A series of chemical reactions are involved in such extractions.

 

The recycling of E-waste is effective processing and management of the discarded waste. It involves three distinct steps i.e. disassembly, upgrading and refining.

 

Disassembly in recycling of E-waste is targeted on singling out hazardous or valuable components for special treatments⁸⁵. Upgrading is a mechanical processing and metallurgical processing to upgrade desirable materials content; i.e. refining process for preparing materials. Refining is last step which involves retreatment of recovered materialsor purification by using chemical (metallurgical) processing Fig 6.

Bioleaching-Second Proposed Postulate for E-waste management:

Bioleaching is a promising technology that utilizes microorganisms, enzymes, smart modified bio-catalysts, plants for the extraction of metals from ores and metals from E-wastes as metabolic by-products. The use of Biohydrometallurgical method is environmentally sound with a huge potential to lower operational cost and energy requirements for reprocessing the wastes. Many aerobic and anaerobic microorganisms are used in the process of bioleaching and biomining⁸⁶. Capability of Acidithiobacillus ferrooxidans to grow under extreme, harsh, and anaerobic conditions makes it a potential microbe for leaching. A. ferrooxidans dissolve metals by direct as well as indirect leaching mechanism making it most useful organism in biohydrometallurgy.

 

Table:2 Electronic waste treated with bacterial leaching90

S. No	Electronic waste	Leached metal	Microorganisms
1.	Lithium batteries	Li, Co	Acidithiobacillus ferrooxidans
2.	Cracking catalysts, hydro-processing catalysts	Al, Ni, Mo, V, Sb	Aspergillus niger, Acidithiobacillus thiooxidans
3.	Jewellery waste, Automobile catalytic converter, Electronic scrap	Ag, Au, Pt	Chromobacterium violaceum, Pseudomonas fluorescens, Pseudomonas plecoglossida
4.	Electronic scrap	Cu, Ni, Al, Zn	Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans

 

Table: 3 The level of various metals leached by means of bioleaching from electronic scrap90

S. No.	Species of microorganisms	Level of leached metal
1	A. ferrooxidans + A. thiooxidans	Cu, Ni, Al, Zn >90%
2	A. ferrooxidans	Cu 99%
3	A. ferrooxidans, A. thiooxidans, A. ferrooxidans + A. thiooxidans	Cu 99%, Cu 74.9%, Cu 99.9%
4	Sulfobacillus thermosulfidooxidans	Ni 81%, Cu 89%, Al 79%, Zn 83%
5	Chromobacterium violaceum,	Au 68.5%
6	Aspergillus niger, Penicillium simplicissimum	Cu, Sn 65%, Al, Ni, Pb, Zn > 95%
7	Thermosulfidooxidans sulfobacilllus + Thermoplasma acidophilum	Cu 86%, Zn 80%, Al 64%, Ni 74%

 

The common mechanisms involved in bioleaching are acidolysis, complexolysis, redxolysis and bioaccumulation. The mineral biooxidation process involved in the microorganisms are believed to be comprised of a consortium of gram negative bacteria at 40˚C or less. It includes iron and sulphur oxidizing A. ferrooxidans.

 

The mechanism of bioleaching, the study of which will announce for developing improved and efficient industrial bioleaching process. The rapidly growing microbial based metal extraction industries utilize a diversity of microbes that can grow at variable temperatures, involves either rapid stirred-tank or slower irrigation technology to recover metals from their ores. The metal recovery from their ores (E-waste) involves either rapid stirred tank or slower irrigation technology. The microbes oxidized ferric ion along with sulfuric acid in the presence of iron and sulfide metals. Microbes convert insoluble sulfides of metals in soluble metals (copper, nickel, zinc). It can be readily recovered from the solution. Extraction of gold from E-waste utilizing Cynogenic bacteria was carried out using A. ferrooxidans87. Microbes like Acidithiobacillus sp, Leptospirillum sp, Ferrromicrobium sp, help in the extraction of Au and Ag using E-waste⁸⁸. Microorganisms are widely used due to their ability to facilitate metal dissolution through a series of biooxidation and bioleaching reactions. The Sulfobacillus thermosulfidooxidans, Bacillus Stearothermophilus, Metallospherasedula organisms and heterotrophic fungi including Aspergillus niger and Penicillum simplicissimum and Cyanobacterium violaceum are used to effectively dissolve various metallic fractions from E-wastes⁸⁹. List of bacteria where are found in mining area can be accessed from https://minemicronet.000webhostapp.com/index.php is hosted by VIT.

 

CONCLUSION:

Recycling of electronic waste is a significant issue not only from the point of waste treatment but also from the recovery of valuable metals. The value allocation for different electronic scrap samples shows that for cell phones, calculators, and printed circuit board scraps, the costly metals build up more than 70% of the value for TV boards and the DVD player they still contribute to about 40%. This indicates that there is a major economic drive for recycling E-waste for the recovery of precious metals. Behind the precious metals come copper and zinc. It has been seen that biotechnology has been one of the most capable technology in metallurgical processing. Bioleaching has been used for revival of precious metals and copper from ores for many years. The conventional methods of electronic waste processing (Pyro and Hydro-metallurgical methods), has been expensive. In bio-hydrometallurgical process, the use of microorganisms may be less expensive and become long term developmental methods for metal recovery. Living or dead biomass which includes bacteria, fungi, yeast and algae are being investigated for precious metal recovery. Immobilization of the biomass may also play a major role in the extraction of metals.

 

ACKNOWLEDGEMENTS:

This work was result of Science and Engineering Research Board by funding the project “Differential membrane lipid profile and fluidity of Acidithiobacillus ferrooxidans during the process of adhesion to minerals” Department of Sciences and Technology, India [grant number DO No. SR/S3/ME/0025/2010], which helped Dr. Anand Prem Rajan to establish Geo-microbiology and Environmental Biotechnology laboratory at VIT, laid foundation to explore industrially important elite chemolithotrophs. All authors would also like to thank management of VIT for all the necessary facilities provided. Dr. Anand Prem Rajan thank Prof. K. A. Natarajan, IISc Bangalore and Dr. Preston Devasia, Singapore for their immense inputs for successful completion of this project. We are indebted to the Almighty God for the wisdom given to complete this work.

 

CONFLICT OF INTEREST:

The authors declare no conflict of interest.

 

Abbreviations:

Short forms

Long forms

Kg E-Waste UPS MP3 Sp. Au CN- H2O OH- H+ (NH2)2CS S2O3 Au(CN)2- Fe Cu Al Pb Ni Li Co Mo V Sb Ag Au Pt Zn Au((NH2)2CS) MS FeS2 Fe3+ SO42- H2S NiO MCO3 MnO2 C6H8O7 Ni(C6H5O7) SERB Scheme DST NH3 Al(S2O3) Cu(S2O3) Cu(NH3) %

Kilogram Electronic-Waste Uninterruptible Power Supplies Media Player 3 Species Silver Cyanide Water Hydroxyl ion Hydronium ion Thiourea Thiosulphate Silver cyanide Ferrum (Iron) Cuprum (Copper) Aluminium Plumbum (Lead) Nickel Lithium Cobalt Molybdenum Vanadium Stibium (Antimony) Argentum (Silver) Aurum (Gold) Platinum Zinc Gold thiourea Gustathion Pyrite Ferric ion Sulphate ion Hydrogen sulphide Nickel (II) oxide Multi copper oxidase Manganese oxide Citric acid Nickel-citrate complex Science and Research Engineering Board Department of Science and Technology Ammonia Aluminium thiosulphate Copper thiosulphate Copper ammonia complex molecule Per cent age

 

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Accepted on 16.07.2018         © RJPT All right reserved

Research J. Pharm. and Tech 2019; 12(2):848-858.