Corrosion Science and E-waste Management PDF

Department of Chemistry, Dayananda Sagar College of Engineering MODULE 3 Corrosion Science and E-waste Management Corrosion Chemistry: Introduction When the metal comes in contact with gaseous or liquid environm...

Department of Chemistry, Dayananda Sagar College of Engineering MODULE 3 Corrosion Science and E-waste Management Corrosion Chemistry: Introduction When the metal comes in contact with gaseous or liquid environment they undergo a spontaneous, but gradual destruction which starts at the surface of metals. Corrosion is the chemical or electrochemical reaction of a metal with its surroundings. Corrosion is the destructive attack of a material by reaction with its environment. The serious consequence of the corrosion process has become a problematic issue to the environment. Worldwide overall cost of corrosion is 3-5 % of gross national product which comes out to be 276 billion dollar and 2 lakh crore in India annually. It has been estimated that about 20-25 % of this loss could be saved by the application of corrosion prevention and control. Sudden failure of material due to corrosion like nuclear reactors, high pressure boilers, chemical plants, petroleum refineries, oil pipelines, bridges, aeroplanes can have more catastrophic consequences like loss of human life. It is a fact that about 80-90 % metallic materials produced in the world is disposed off by engineers. Definition: Gradual deterioration or loss of metal at its surface by chemical or electrochemical reaction between the metal and the surrounding environment Electrochemical theory of corrosion According this theory, corrosion is an electrochemical process and the reactions are similar to galvanic cell. Oxidation occurs at anode liberating electrons which flow to cathode where reduction occurs. An aqueous media is required over the surface of metal for the conduction of ions and the completion of electrochemical circuit between anode and cathode. When a metal like iron is exposed to atmosphere (air and aqueous media), the following electrochemical changes takes place leading to the corrosion of iron, a). formation of large number of minute galvanic cells on the surface of metal, b). Large numbers of minute anodic and cathodic areas are formed on the surface. Anodic area: Iron is oxidized liberating electrons and ferrous ion. The electrons released at anodic area move to the cathodic area through the metal. Ferrous ion undergoes corrosion, Fe Fe2+ +2e- Cathodic area: Reduction occurs at the cathodic region and that it does not undergo corrosion and remains unaffected. Depending on the environment, there are three types of possible reduction reaction occur at cathodic area.  Department of Chemistry, Dayananda Sagar College of Engineering 1. if the metal is exposed to moisture (H2O) and air (O2) under neutral condition, then oxygen is reduced to OH- ion, 2. if the metal exposed only to moisture (H2O), water undergoes reduction into H2 and OH- ion 3. if the metal surface is exposed to acidic medium, then H+ ion is reduced to H2 In neutral or alkaline medium and the presence of oxygen, hydroxide ions are formed ½ O2 +2H2O +2e- 4OH- In neutral or alkaline medium and in the absence of oxygen. 2 H2O + 2e- H2 + 2OH- In acidic medium and in the absence of oxygen 2H+ + 2e- H2 The metal ions produced at the anode combines with the OH- ions to form ferrous hydroxide, which undergoes aerial oxidation to form brownish red color ferric oxide (Rust). Fe2+ + 2OH- Fe(OH)2 Ferrous hydroxide 2Fe(OH)2 + O2 + nH2O 2(Fe2O3.3H2O) Ferric oxide (Rust) Types of corrosion According to electrochemical theory, corrosion occurs due to the formation of large number of galvanic cells on the surface of the metal. A galvanic cell is formed, when there is a difference in potential betweenthe cathodic and anodic area across the metal surface. It can be happened in different ways. 1. Differential metal corrosion (Galvanic Corrosion) When two dissimilar metals are in contact with each other, the metal with lower electrode potential becomes anodic and undergoes corrosion whereas the metal with higher potential becomes cathodic and remains unaffected. This kind of corrosion is called as differential metal corrosion. The corrosion depends manly on the difference in potential between two metals. Higher the difference faster is the rate of corrosion. When two metals Fe (-0.44 V) and Cu (0.34 V) are in contact: Since Fe has lower reduction potential compared to Cu, Fe acts as anode and undergoes corrosion whereas Cu acts as cathode and it is protected. Anodic oxidation Cathodic reduction Fe Fe2+ + 2e- ½ O2 +2H2O +2e- 4OH-  Department of Chemistry, Dayananda Sagar College of Engineering When two metals Zn (-0.76 V) and Fe (-0.44 V) are in contact: Since Zinc has lower reduction potential compared to Fe, Znundergoes corrosion and Fe is protected. Anodic oxidation Cathodic reduction Zn Zn2+ + 2e- ½ O2 +2H2O +2e- 4OH- 2. Differential aeration corrosion When a metal is exposed to different concentrations of air (O 2), part of the metal exposed to lower concentration of O2 will have lower potential, and hence becomes anodic and undergoes corrosion. Other part of the metal exposed to higher concentrations of O 2 becomes cathodic and remains unaffected. The difference of oxygen concentration produces a potential difference and causes corrosion current to flow. This kind of corrosion is called as differential aeration corrosion. Example: Fe rod partially immersed in NaCl solution. Part of the metal immersed in solution is exposed to lower concentration of oxygen becomes anodic area and undergoes corrosion. Part of the metal outside water is exposed to more oxygen becomes cathodic and remains unaffected. More Aerated Less Aerated The reactions may be represented as follows: Reactions At anode : Fe → Fe2+ + 2 e- (Oxidation) At cathode : 1/2 O2 + H2 O + 2 e- →2 OH- ( Reduction) 2. (a). Water-line corrosion It is observed in steel or iron water tanks partially filled with water. Part of the tank just below water level (water line in contact with water) is exposed to lower concentration of O 2, becomes anodic and  Department of Chemistry, Dayananda Sagar College of Engineering undergoes corrosion. Part of the tank above the water line which is exposed to higher concentration of O 2 becomes cathodic and remains unaffected. More intense corrosion is observed just below the waterline; hence it is called as water line corrosion. Water line corrosion 2. (b) Pitting corrosion Pitting corrosion is observed when dust particles or oil drops get deposited over the metal surface. The portion of the metal covered by dust which is less aerated becomes anodic and undergoes corrosion. Thus, metal is lost underneath the surface of dust particle forming a deep and narrow pit. The adjacent area of the metal which is exposed to higher concentration of O 2 becomes cathodic and remains unaffected. Pitting corrosion is a more dangerous, localized form of corrosion leads the sudden failure of materials. Pitting Corrosion Factors affecting rate of corrosion The rate of corrosion depends on the following factors. 1. Nature of metal: In general the metals with lower electrode potential values are more reactive than the metal with higher electrode potential values. The rate of corrosion depends upon the difference in potential between anodic and cathodic area. Higher difference in potential, higher is the corrosion current  Department of Chemistry, Dayananda Sagar College of Engineering flowing and higher will be the rate of corrosion of anodic metal. For example, the active metals like k, Na, Mg, Zn etc, with low electrode potential values are highly susceptible for corrosion. The noble metal such as silver, gold, platinum etc, with higher electrode potential values is less susceptible for corrosion. However, there are few exceptions for this general trend as some metal show the property of passivity. Example: the potential difference between Fe and Cu is 0.78 V which is more than that between Fe and Sn (0.3 V). Therefore, Fe corrodes faster in contact with Cu than with Sn. 2. Nature of corrosion product: Most of the metals from their oxides as the corrosion product. This oxide forms a thin film on the surface of the metal and its nature decides the extent of further corrosion. If the corrosion product is stoichiometric in composition, highly soluble, nonporous with low ionic and electronic conductivity, then it forms a protective layer over the surface and effectively prevents further corrosion of metal. Example: Metals which forms protective layer are Al, Cr, Ti, Ta, Mo etc and corrosion product of metals like Fe, Mg and Zn cannot protect metal from further corrosion. 3. Relative areas of anode and cathode: The rate of corrosion depends on the relative surface area of anodic and cathodic part. The smaller surface area of anodic part can be smaller, equal or larger the size of cathodic area. Smaller the size of anodic area and larger the size of cathodic area, then more intense and faster will be the corrosion occurring at anodic area. When cathodic area is large, demand for electrons for reduction reaction will be high. To meet this demand, oxidation reaction occurs more intensely at anodic area. Example: In the coating of Sn on Fe, if some part on Fe is peeled off it results in smaller anodic area (Fe) and larger cathodic area (Sn). In this case more intense corrosion is observed at smaller anodic area (Fe). 4. Nature of the environment: a). pH of the medium: The rate of corrosion increases with decrease in pH. In acidic medium, the rate of corrosion depends upon the rate of evolution of hydrogen at cathode area. When pH 10 corrosion ceases practically due to formation of insoluble metal hydroxides on the surface of metal. Fe2+ + 2OH- Fe(OH)2 b).Temperature: Generally, rate of the corrosion increases with increase in temperature. As the temperature increases conductance of the ions in the aqueous medium increases which reduces the polarization. Therefore, the rate of corrosion increases. Rate of O2 reduction at cathodic area is doubled for every 30 ºC rise in temperature and also rate of H 2 evolution is doubled for every 10 ºC rise in temperature.  Department of Chemistry, Dayananda Sagar College of Engineering c). Conductance of medium: The rate of corrosion increases with increase in the conductance of the medium. As the conductance of the medium increases, ions can move easily through the medium. This decreases the polarization potential and due to this the rate of corrosion increases. For example, metal immersed in sea water (more conducting) corrodes faster than metal immersed in river water (less conducting). Corrosion control According to electrochemical theory, corrosion occurs due to the oxidation and reductions reactions at the anodic and cathodic areas respectively. These reactions occur simultaneously and are interdependent. Therefore by decreasing the rate of any of these reactions or by preventing any one reaction, the rate of corrosion can be decreased. The following methods are commonly used to control corrosion. 1. Protective coating a) Anodic Metal Coating: Galvanization b) Cathodic Metal Coating: Tinning 2. Cathodic protection- Sacrificial Anode Method 3. Anodic protection 4. Corrosion inhibitors 5. Design and selection of materials 1. Protective coating Corrosion of metal occurs mainly due to the interaction of metal surface with the O 2 and moisture in the atmosphere. Therefore, corrosion can be prevented by isolating metal from surrounding environment by coating a protective layer over the surface of the metal. a) Anodic Metal Coating: Galvanization: it is the coating of a layer of metal which are anodic to base metals. Example is Al, Zn etc. in this type of coating, even if base metal is not completely covered, it will not undergo corrosion. This is due to formation oflarge anodic area and small cathodic areas. Example: Coating of Zn or Mg or Cd metal on Fe. It involves the following steps: 1. The iron sheet is passed through solvent to remove grease & oil present on it. 2. The iron sheet is washed with dil. H2SO4 to remove oxide layer (Rust) present on surface (pickling). 3. The sheet is then treated with a mixture of aqueous solution of ZnCl2 and NH4Cl which acts a flux and then dried. 4. The dried sheet is dipped in molten zinc at 450 ºC. 5. Excess Zinc present on iron sheet is removed by passing through rollers.  Department of Chemistry, Dayananda Sagar College of Engineering. Application: Galvanization of iron is carried out to produce roofing sheets, fencing wire, buckets, bolts, nuts, pipes etc. Anodizing is the process of oxidation of outer layer of metal to its metal oxide by electrolysis. Oxide layer formed over the metal itself acts as a protective layer Anodizing of aluminum: In this process Aluminum is cleaned, degreased polished and taken as anode in an electrolytic cell. It is immersed in an electrolyte consisting of 5-10% chromic acid. Steel or copper is taken as cathode. Temperature of the bath is maintained at 35ᵒC. A current density of 100 A /m2 or more is applied which oxidizes outer layer of Al to Al2O3 that gets deposited over the metal. This process is called anodizing of aluminium or anodic oxidation of aluminum. Dc Power Al2O3 H2CrO4 Cathode Anode Anode: 2Al 2Al3+ + 6 e- Cathode: 6H+ + 6e- 3H2 Overall reaction: 2Al3+ + 3/2 O2 Al2O3 Applications: anodized aluminium is used as an attractive highly durable, corrosion resistant material in roof, buildings, home appliances and computer parts. CATHODIC PROTECTION:- In cathodic protection, electrons are supplied from the external source to prevent oxidation of metal at anodic area. Thus anodic area of metal is completely converted to cathodic area. Since cathodes do not undergo corrosion, the metal is protected against corrosion. The process where metal to be protected is made cathode, by supplying electrons from an external source is called as cathodic protection. There are two methods of cathodic protection a) Sacrificial anode method: b) Impressed current method  Department of Chemistry, Dayananda Sagar College of Engineering Sacrificial anode method: Electrical conductor Steel pipe Cathode Mg Block (Anode) In sacrificial anode method, the metal to be protected is connected to a more active metal. For example, when steel pipe is to be protected, it may be connected to a block of Mg or Zn. In such a situation, Mg or Zn act as anode and provide electrons to the steel pipe. Steel pipe acts as cathode and is unaffected. Here Mg or Zn which is anode undergoes sacrificial corrosion. When the sacrificial anode gets exhausted, it is replaced with new ones. Other examples: Mg bars are fixed to the sides of ships to act as sacrificial anode. Mg blocks are connected to buried pipe lines. Corrosion penetration rate (CPR) Corrosion Penetration Rate (CPR) is defined as the speed at which any metal in a specific environment deteriorates due to a chemical reaction in the metal when it is exposed to a corrosive environment. The method used to measure the corrosion rate was weight loss method. This method is used as a measurement of the Corrosion Penetration Rate (CPR) which is expressed in mile per year (mpy) or millimeter per year (mmpy). CPR can be calculated by the following equation, Corrosion penetration rate (CPR) = kW/ ρAt Where, k is a constant, W is the total weight loss, t is the time taken, A is the surface area of the exposed metal, ρ is the metal density in g / cm. k value depends on unit used, when k = 534 the mpy will be used. When k = 87.6 mmpy will be used. The CPR is conveniently expressed in terms of either mils (0.001 inch) per year (mpy) or millimeters per year (mmpy). K=534 for CPR in mpy when surface area of test specimen is in inch2 and K=87.6 for CPR in mmpy when surface area of test specimen is in cm2 Where, 1 mil =0.001 inch Constant CPR in mpy CPR mmpy K 534 87.6 W (wt loss) mg Mg ρ g/ cm3 g/ cm3 A inch2 Cm2 t hrs Hrs  Department of Chemistry, Dayananda Sagar College of Engineering Numerical Problems on CPR 1. To calculate CPR in mm/yr Given CPR mm/yr K 87.6 W 40g 40X1000 mg ρ 7.8 g/cm³ 7.8 g/cm³ A 1mx3m=3m2 3x100x100 cm2 t 6 months 6x30x24 hrs CPR= 𝐾𝑊 𝜌𝑋𝐴𝑋𝑡 CPR = 87.6 X 40 X 1000mg 7.8 g/cm³ x 3x100x100 cm2 x 6x30x24 CPR= 0.003466 mm/yr To calculate CPR in mpy Given CPR in mpy K 534 W 40g 40 x 1000 mg ρ 7.8 g/cm³ 7.8 g/cm³ A 1mx3m=3m2 3 x1550 inch2 t 6 months 6 x 30 x 24 hrs 1 sq m = 1550 sq inch CPR= 𝐾𝑊 𝜌𝑋𝐴𝑋𝑡 CPR = 534 X 40 X 1000mg 7.8 g/cm³ x 3 x1550 inch2 x 6x30x24 CPR= 0.1363 mpy 2. A sheet of carbon steel one meter wide by three meters long has lost 40g to corrosion over the past six months. Convert that mass loss to a penetration rate of the steel in mm units and mpy units. What could be the corrosion rate? (Carbon steel density=7.8g/ cm3) To calculate CPR in mmpy Solution: To calculate CPR in mmpy Given; K = 87.6  Department of Chemistry, Dayananda Sagar College of Engineering W (wt loss) = 40 g = 40 x 1000 mg ρ = 7.8 g/ cm3 = 7.8 g/ cm3 A = 1m x 3m = 3m2 = 3x100 x 100 cm2 T = 6 months = 6 x 30 x 24 hrs We have K.W CPR  . A.t 87.6 x 40 x1000 CPR  7.8 x3 x100 x100 x6 x30 x 24 CPR = 3.466 x10-3 mmpy To calculate CPR in mpy Given; K = 534 W (wt loss) = 40 g = 40 x 1000 mg ρ = 7.8 g/ cm3 = 7.8 g/ cm3 A = 1m x 3m = 3m2 = 3 x 1550 inch2 T = 6 months = 6 x 30 x 24 hrs We have K.W CPR  . A.t 534 x 40 x1000 CPR  7.8 x3 x100 x100 x6 x30 x 24 CPR = 0.0503 mpy 3. Calculate the CPR in both mpy and mmpy for a thick steel sheet of area 100 inch2 which experiences a weight loss of 485g after one year. (Density of steel=7.9g/cm3). Solution: To calculate CPR in mmpy Given; K = 87.6 W (wt loss) = 485 g = 485 x 1000 mg ρ = 7.9 g/ cm3 = 7.9 g/ cm3 A = 100 inch2 = 100 x 6.45 cm2 t = 1 year = 365 x 24 hrs 1 inch2 = 6.45 cm2 1 cm2 = 0.155 inch2 We have K.W CPR  . A.t  Department of Chemistry, Dayananda Sagar College of Engineering 87.6 x 485 x1000 CPR  7.9 x100 x6.45 x365 x 24 CPR = 0.9518 mmpy To calculate CPR in mpy Given; K = 534 W (wt loss) = 485 g = 485 x 1000 mg ρ = 7.9 g/ cm3 = 7.9 g/ cm3 A = 100 inch2 = 100 inch2 t = 1 year = 365 x 24 hrs We have K.W CPR  . A.t 534 x 485 x1000 CPR  7.9 x100 x365 x 24 CPR = 37.424 mpy 4. A piece of corroded steel plate was found in a submerged ocean vessel, it was estimated that the original area was 10inch2 and approximately 2.6 kg had corroded away during the submersion. Assuming a corrosion penetration rate of 200mpy for this alloy in sea water, estimate the time in years, density of steel 7.9g/cc. Given CPR in mpy K 534 W 2.6kg 2.6 x 1000 x1000 mg ρ 7.9 g/cm³ 7.9 g/cm³ 2 A 10 inch 10 inch2 t X X hrs t= 534𝑋2.6𝑋106 7.9𝑔/𝑐m3𝑋10𝑖𝑛2𝑋200𝑚𝑝𝑦 t = 87873.41hrs  Department of Chemistry, Dayananda Sagar College of Engineering 5. A thick steel sheet of area 100 in.2 is exposed to air near the ocean. After a one-year period it was found to experience a weight loss of 485 g due to corrosion. To what rate of corrosion, in both mpy and mm/yr, does this correspond? Therefore the rate of corrosion 37.4 mpy and 0.952 mm/yr. Explanation: The corrosion rate is the rate of material remove. The formula for calculating CPR or corrosion penetration rate is K= constant depends on the system of units used. W= weight =485 g D= density =7.9 g/cm³ A = exposed specimen area =100 in² =6.452 cm² K=534 to give CPR in mpy K=87.6 to give CPR in mm/yr mpy =37.4mpy mm/yr =0.952 mm/yr Therefore the rate of corrosion 37.4 mpy and 0.952 mm/yr. 6. A thick steel sheet of area 400 cm² is exposed to air near the ocean. After a one-year period, it was found to experience a weight loss of 375 g due to corrosion. If the density of the brass is 7.9g/cm², calculate the corrosion penetrating rate in mpy and mm/y (given K= 534 in mpy and 87.6 in mm/y). Find: the corrosion penetrating rate in mp/y and mm/y. Solution: corrosion penetrating rate in mp/y. Corrosion penetrating rate in mm/y. Hence, the corrosion penetrating rate is and  Department of Chemistry, Dayananda Sagar College of Engineering E-waste management Introduction Every year millions of electrical and electronic devices are discarded as products waste and are thrown away to the environment. These discarded devices are considered as E-waste and crates threat to the environment and human health. E-Waste management is intended to reduce the adverse effects of E- waste on human health, the environment, planetary resources, and aesthetics. Sources of E-waste 1. Consumer electronics: The constant desire for newer devices and gadgets has led to a surge in e- waste. This includes televisions, computers, mobile phones, and other home appliances. 2. Medical and laboratory equipment: The healthcare and research sectors use a lot of electronic equipment for diagnostics, treatment, and experimentation. 3. Manufacturing: E-waste can be generated during the manufacturing process. 4. Entertainment and leisure devices: E-waste can come from entertainment and leisure devices. 5. Network infrastructure upgrades: E-waste can be generated during network infrastructure upgrades. 6. Battery disposal: E-waste can come from battery disposal. Types of E-Waste E-Waste has been categorized into following types. 1. Large household appliances: Such as refrigerators and air conditioners 2. Small household appliances: Such as electric toothbrushes, razors, and vaping devices 3. Information technology (IT) and telecommunications equipment: Such as computers, laptops, printers, scanners, and photocopiers 4. Consumer electronics: Such as televisions, stereo equipment, and gaming systems 5. Lighting equipment: Such as LED bulbs 6. Electrical and electronic tools: Such as tools that are not large-scale stationary industrial tools 7. Toys, leisure, and sports equipment: Such as toys with minor electrical components 8. Medical equipment systems: Such as medical equipment systems like MRI machine, insulin pumps etc. 9. Monitoring and control instruments: Such as monitoring and control instruments 10. Automatic dispensers: Such as automatic dispensers (ATM), Vending machines. Effects of e-waste on environment 1. Soil contamination When e-waste is disposed of in landfills, toxic chemicals can leach into the soil and contaminate nearby crops and water supplies. This can lead to illnesses in humans and animals that consume contaminated vegetation. 2. Water pollution When e-waste breaks down, it can release hazardous chemicals into nearby water sources, contaminating the water and impacting crops, livestock, wildlife, and humans.  Department of Chemistry, Dayananda Sagar College of Engineering 3. Air pollution Burning e-waste releases harmful pollutants into the air. 4. Direct harm to wildlife E-waste can have a devastating effect on wildlife, both directly and indirectly. 5. Resource depletion Technology consumes resources faster than they can be replenished, which can lead to aquifer depletion, deforestation, mining for fossil fuels, and soil erosion. Effect on Human health E-waste sources Constituents Health effects Solder in printed circuit boards, Lead Damage to central and peripheral nervous glass panels, and gaskets in systems, blood systems, and kidney damage computer monitors Adverse effects on brain development of children; causes damage to the circulatory system and kidney Chip resistors and semi-conductors Cadmium Toxic irreversible effects on human health Accumulates in kidney and liver Causes neural damage Relays and switches, and printed Mercury Chronic damage to the brain circuit boards Respiratory and skin disorders due to bioaccumulation in fishes Galvanized steel plates and Chromium Causes bronchitis decorator or hardener for steel housing Cabling and computer housing Plastics and Burning produces dioxin that causes PVC reproductive and developmental problem Methods of disposal Non-biodegradable and toxic wastes like radioactive remnants can potentially cause irreparable damage to the environment and human health if not strategically disposed of. Waste disposal has been a matter of concern, the main problem growth in population and industrialization. Here are a few methods of waste disposal. Disposal of E-waste are mainly done in 5 types. 1. Land-filling 2. Incineration 3. Recycling 4. Metal recovery by acid 5. Reuse 1. Landfilling: The most common method for solid and hazardous waste disposal, landfills are economical and don't require much infrastructure. Waste is poured into the soil in a uniform manner 2. Incineration: An inexpensive method that reduces waste volume by about 90%. Incinerators produce heat that can be used to generate energy, and some ash can be used for farming. 3. Recycling: A common method for reducing waste disposal, recycling can reduce waste disposal costs and sometimes generate revenue from the sale of recyclable materials.  Department of Chemistry, Dayananda Sagar College of Engineering 4. Metal recovery by acid: Different types of parts like ferrous and nonferrous metal and printed circuit board are separated by electronic waste. Different types of metals like lead, copper, aluminum, silver, gold, platinum etc. are recovered and reused. 5. Reuse: The metals from the old electronic devices can be extracted and reused. Such as from computers, mobiles, laptops etc. Advantages of Recycling E-Waste 1. Protecting the environment E-waste recycling prevents the release of toxic chemicals and dust into the air, soil, and water. These chemicals can contaminate the environment and harm human health. 2. Conserving resources Recycling e-waste reduces the need to mine for new materials, and instead reuses valuable resources like metals and plastics to make new products. 3. Creating jobs E-waste recycling creates jobs for professional recyclers and a second market for recycled materials. 4. Reducing landfill waste Landfills can't handle the toxic chemicals in e-waste, so recycling helps to keep them out of landfills. Extraction of Gold from e-waste Recovering precious metals from e-waste through hydrometallurgical processes is more attractive economically than other methods. A hydrometallurgical process consists of first a set of operations including acidic or alkaline dissolution (leaching) of solids. The resulting solutions are then exposed to separation and purification methods including deposition, solvent extraction, adsorption, and ion exchange in order to isolate and concentrate the intended metals.  Department of Chemistry, Dayananda Sagar College of Engineering Step 1: Grinding of the CPUs: First, any dust or other particles were removed from the CPUs. The sizeof the grind pieces is 1 mm thickness. Step 2: Leaching in nitric acid: Concentrated nitric acid (65%) is added. Leaching time is 1 h. Step 3: Leaching in aqua regia: The aqua regia solution is obtained using three volumes of HCl and one volume of HNO3 (3:1 V/V ratio). Typically, the gold of composite CPU-containing boards is easily dissolved in 4-to-1 aqua regia. The solution was decanted, and the pieces were subsequently washed with 10 mL of concentrated HCl so that all of the gold content was fed into the solution. Step 4: Removing the excess nitric acid: Sulfuric acid is added to the solution to accelerate the removal of nitric acid and sedimentation of the lead as lead sulfate (if present). The time required for the complete removal of nitric acid from this solution is 45 minutes. Step 5: Precipitation of gold: A certain amount of iron sulfate (per one gram of gold: 4.2 g of iron sulfate) is dissolved in hot water and gradually added to the gold-containing solution. For better dissolution of iron sulfate, some drops of HCl can also be used. Step 6: Washing and Purifying gold deposits: The deposit is dissolved in HCl and boiled. Followed by boiling, the acid is removed and the deposit is re- washed in HCl to ensure the cleanness of the gold powder. Eventually, the deposit was filtered and dried at a temperature of 100°C. Sampling and measuring of precious metals were performed following the first and second stages of leaching, after the stage of gold extraction, and finally following the purification of deposits. ******************