Recovering Gold from e-Waste

 We use electronic devices every day; computers, drones, home security systems, mobile phones, smart speakers, smart watches, etc. If the device stops working, or we want to upgrade to a newer version, we throw away the old device resulting in electronic waste or e-waste. Each of these devices contains a printed circuit board (PCB) and the metal content of each PCB can be as high as 40% by mass. 

Recycling 1 tonne of mobile phones alone could produce more than 130 kg metal, including about 340 g of gold. The value of just the gold in that tonne of rubbish is over $25,000(AUD). Recovering metal from waste electronics and electrical equipment is becoming big business, but what impact does this have on us and our environment?

 Read this edition of AUS-e-NEWS to find out more ...

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Gold Nuggets in 2019

Between 1850 and 1900, the city of Bendigo in Victoria, Australia, was the centre of a Gold Rush. Central Deborah Gold Mine, the last commercial gold mine to operate in Bendigo, re-opened as a tourist attraction in 1986.
Gold can still be found in the Bendigo area.
On Mothers' Day 2019, a family out walking Lucky their dog on the outskirts of Bendigo walked onto a gold nugget. They took it along to the local IGA supermarket to weigh it. The gold nugget weighed 624 grams (about 20 ounces).
Today, the price of gold in Australia is listed as $65.76 per gram. So, if pure, the gold in this nugget would be worth 624 × $65.76 ≈ $41,000.
How big would this gold nugget be?
We know the mass of the nugget is 624 grams.
We can look up the density of gold in tables, ρ = 19.3 g cm^-3
Since density = mass (g) ÷ volume (cm³)
19.3 = 624 ÷ volume (cm³)
volume (cm³) = 624 g ÷ 19.3 g cm^-3 = 32.3 cm³
Which could be represented by a cube approximately 3.2 cm × 3.2 cm × 3.2 cm
Not very big at all is it!

Ballarat, another Victorian Gold Rush town and site of the historic "Eureka Stockade", was also the place where another spectacular gold nugget was found in June 2019 (and reported nationally in July 2019). This gold nugget weighed about 2 kilograms, or 2,000 grams.
At today's prices, it would have a value of about 2,000 × $65.76 ≈ $130,000
And how big would this nugget be?
density = mass (g) ÷ volume (cm³) volume (cm³)
density = mass (g) ÷ density (g cm^-3) = 2,000 g ÷ 19.3 g cm^-3 = 103.6 cm³
The dimensions of a cube with this volume would be about 4.7 cm × 4.7 cm × 4.7 cm
Which would fit nicely into the palm of your hand as shown in the photograph below

Further Reading:
Density Calculations

Suggested Study Questions:

1.  The density of gold is 19.3 g cm^-3. Calculate the mass of
   • 1 cm³ of gold 
   • 10 cm³ of gold 
   • 1 m³ of gold
2.  The density of gold is 19.3 g cm^-3. Calculate the volume of
   • 1 g of gold
   • 10 g of gold
   • 1 kg of gold 
3.  The density of gold is 19.3 g cm^-3. Calculate the dimensions of a cube of gold which has a mass of
   • 5 g
   • 500 g
   • 5 kg
4. The density of gold is 19.3 g cm^-3. Calculate the diameter of a sphere of gold which has a mass of
   • 2 g
   • 200 g
   • 2 kg
5. A credit card has the approximate dimensions 65 mm × 55 mm × 1 mm. Calculate:
   • volume of the credit card in cm³
   • mass of a gold credit card
   • value of a gold credit card if the cost of gold is $65 per gram
   • Why aren't "gold" credit cards really made out of gold?
6. Gold is one of the few metals that is found in nature as the "native" element (that is, it is found as the element and not in compounds). Explain why gold can be found in nuggets.
7. Name some other metals that can also be found in their native state (that is, found as the element and not as compounds). Explain why these metals can be found in their native state. 
8. Name a metal that is not found on Earth in its native state, and explain why it is not found in nature as the uncombined element.

24 Carat Chemistry

I was trying to buy a present for my mum for Mothers' Day. "A gold chain," I thought, "would be a nice present". But when I got to the jewellery shop I found that there is a huge variety of "gold chains", 24 carat gold, 18 carat gold, 9 carat gold, 995, 750, 375, white gold, rose gold...

So what is a carat?
What do those numbers mean?
How can "gold" be different colours?

Read all about it in the June 2019 issue of AUS-e-NEWS

Subscribe to AUS-e-TUTE's free quarterly newsletter at https://www.ausetute.com.au/ausenews.html

Titanium Gold Alloy

Titanium is the metal used to replace hip and knee joints because it is strong, resistant to wear, and, is nontoxic.

Before titanium was used to replace hips and knees, stainless steel was used.
The density of stainless steel used to make replacement hips and knees is about 7.8 g cm³. The density of titanium metal is 4.506 g cm³, about half the density of stainless steel. This means that a replacement joint made out of titanium will weigh less than the same replacement joint made out of stainless steel.
Titanium is also strong. The strength of the material used to replace hip and knee joints is important because you do not want your new joint to bend or break or under strain.

Titanium has a melting point of 1670°C and a boiling point of 3287°C, which means it remains solid over the range of temperatures humans are exposed to. This is important because you want your new hip or knee replacement to remain a solid!
Naturally occurring titanium is made up of a number of isotopes, all of which are stable so they do not undergo nuclear decay. This is important because it means that there is no loss of titanium mass due to radioactive decay, and there is no fear of damage to cells from the emission of radiation.

isotope	atomic mass	abundance
46Ti	45.953	8.25
47Ti	46.952	7.44
48Ti	47.948	73.72
49Ti	48.948	5.41
50Ti	49.945	5.18

Titanium metal will react with water, halogens and dilute hydrochloric acid, but only if the temperature is elevated well above body temperature. Similarly, titanium metal will react with oxygen in a combustion reaction at elevated temperatures. Titanium metal does not appear to react with bases at all. Therefore, titanium is unlikely to react with substances found in the human body.

Researchers at Rice University have found that alloying titanium with gold can produce an even better material to use for replacement hips and knees. Mixing titanium and gold in the ratio of 3:1 at high temperature produces an alloy that is 3 times harder than steel and 4 times harder than the pure titanium commonly in use for hip and knee replacements. The atoms of titanium and gold in this alloy are packed in a cubic arrangement, an arrangement that is usually associated hardness. The structure of this alloy is shown below:

This titanium gold alloy has been found to be even more biocompatible that pure titanium.
The researchers intend to undertake further studies to investigate whether using chemical dopants might improve the alloy's hardness even further.

Reference:
Rice University. "Titanium and gold equals new gold standard for artificial joints: Titanium-gold alloy that is 4 times harder than most steels." ScienceDaily. ScienceDaily, 20 July 2016. 

Further Reading
Metals and Non-metals 
Density
Isotopes
Relative Atomic Mass
Alloys

Suggested Study Questions

1. Titanium and gold are both metallic metallic elements.
   • What are the physical properties common to most metallic elements?
   • What are the chemical properties common to most metallic elements?
2. Draw up a table of the physical properties of titanium.
3. A typical knee replacement made out of titanium has a mass of 560 g.
   • Calculate the volume of the titanium knee replacement.
   • Calculate the mass of the same knee replacement if it were made out of stainless steel
4. Define the term isotope.
5. Determine the number of protons in the nucleus of an atom of each of the isotopes of titanium listed in the article above.
6. Determine the number of neutrons in the nucleus of an atom of each of the isotopes of titanium lists in the article above.
7. Which is the most abundant isotope of titanium? Explain your answer.
8. Use the data in the article above to calculate the relative atomic mass of naturally occurring titanium.
9. Given the atomic radius of titanium is  176 pm (1.76 x 10^-10 m) and the atomic radius of gold is 174 pm (1.74 x 10^-10 m), do you think the alloy of titanium and gold discussed in the article above is an interstitial alloy or a substitutional alloy? Explain your answer.
10. Consider the structure of the titanium gold alloy shown in the diagram in the article above.
    • The blue balls represent which atoms of which element?
    • The red balls represent which atoms of which element?

Olympic Medal Metals

Metallic medals have been awarded to 1^st, 2^nd and 3^rd place Olympic athletes since the 1900 Paris Olympic Games. The medals awarded at the 2012 London Olympic Games are 7mm thick, 85 mm in diameter, and, weigh 400g.
While we happily refer to these olympic medals as gold, silver and bronze, is this chemically accurate?

"Bronze medals" are often made of bronze, an alloy of copper and tin.
At the 2012 London Olympic Games, the bronze medals are made up of a mixture of 97% copper, 2.5% zinc and 0.5% tin. This composition is actually much closer to the composition of brass which is the term used to refer to an alloy of copper and zinc.

"Silver medals" contain at least 92.5% silver. The silver medals awarded in the 2012 Olympic Games were composed of 92.5% silver and 7.5% copper.

"Gold medals" must also contain at least 92.5% silver, but they are plated with at least 6g of gold so they look like "gold" medals. The 2012 Olympic gold medals are made up of 92.5% silver, 6.16% copper and 1.34% gold.

Reference

www.olympic.org/Assets/OSC%20Section/pdf/QR_1E.pdf

Further Reading
Periodic Table
Percentage Composition
Mass-mole Calculations
Moles-Number of Particle Calculations
Density Calculations

Suggested Study Questions

1. Give the chemical symbol for each of the following elements:
   • gold
   • silver
   • copper
   • tin
   • zinc
2. Explain why chemists refer to bronze and brass as alloys.
3. Calculate the mass of each element present in the bronze olympic medals awarded in 2012.
4. Calculate the mole of each element present.
5. For the 2012 Olympic gold medal, calculate the mass of silver present.
6. Calculate the number of silver atoms present in a 2012 olympic gold medal.
7. Calculate the mass of gold present in a 2012 olympic gold medal.
8. Calculate the volume of an olympic medal and use this to calculate the density of an olympic medal.
9. Calculate the surface area of a 2012 Olympic gold medal.
10. Assuming the 2012 gold medal is coated evenly with gold, what thickness is the layer of gold?

Methane Reactions

By using gold dimer cations as catalysts, Georgia Institute of Technology and the University of Ulm scientists have converted methane into ethene at room temperature, and into methanal at temperatures below 250K (-9^o F). In both the room temperature reaction-producing ethene, and the methanal generation colder reaction, the gold dimer catalyst is freed at the end of the reaction, thus enabling the catalytic cycle to repeat again and again.

The temperature-tuned catalyzed methane partial combustion process involves activating the methane carbon-to-hydrogen bond to react with molecular oxygen.
In the first step of the reaction process, methane and oxygen molecules coadsorb on the gold dimer cation at low temperature.
Subsequently, water is released and the remaining oxygen atom binds with the methane molecule to form methanal.
If done at higher temperatures, the oxygen molecule comes off the gold catalyst, and the adsorbed methane molecules combine to form ethene through the elimination of hydrogen molecules.

Reference
Sandra M. Lang, Thorsten M. Bernhardt, Robert N. Barnett, Uzi Landman. Temperature-Tunable Selective Methane Catalysis on Au2 : From Cryogenic Partial Oxidation Yielding Formaldehyde to Cold Ethylene Production. The Journal of Physical Chemistry C, 2011; 115 (14): 6788 DOI: 10.1021/jp200160r

Further Reading
Balancing Chemical Equations
Nomenclature
Combustion of Hydrocarbons
Oxidation and Reduction
Oxidation States (Numbers)

Study Questions

1. Write the molecular formula for each of the following:
   
   • methane
   • methanal
   • ethene
2. Draw the structural formula for each of the following:
   
   • methane
   • methanal
   • ethene
3. On the structural formula above, identify the functional groups present in methanal and ethene.
   
4. The following molecules are known by other names. Give atleast one other name used for each of the following:
   
   • methane
   • methanal
   • ethene
5. Write a balanced chemical equation for each of the following reactions involving the gold dimer cation catalyst:
   
   • methane and oxygen react to form methanal and water
     
   • methane and oxygen react to form ethene and water
6. Classify each reaction above as an oxidation or a reduction reaction. Justify your answer.
   
7. Write balanced chemical equations to represent the combustion of methane at high temperature, without the aid of a catalyst, under each of the following conditions:
   
   • excess oxygen
   • excess methane
8. Compare the chemical equations in question 7 to those in question 5. In what ways are the reactions similar? In what ways are the reactions different?
   

VMD for Fingerprinting

Forensic experts at the University of Abertay Dundee and the Scottish Police Services Authority (SPSA) are researching vacuum metal deposition (VMD) to recover fingerprint ridge detail and impressions from fabrics.

Vacuum metal deposition, VMD, is a common method of depositing a thin film on a substrate.
The source metal is evaporated in a vacuum which allows the vapor particles to travel directly to the target object, the substrate, where they condense back to the solid state. Evaporated materials deposit non-uniformly if the substrate has a rough surface, and, because the evaporated material attacks the substrate mostly from one direction, protruding features block the evaporated material from some areas which is called "shadowing" or " step coverage".

The Scottish scientists have been using gold and zinc in a VMD process to recover fingerprint marks on fabrics. The fabrics are placed in a vacuum chamber then gold is heated up to evaporate it. The gold particles spread out in a thin film over the fabric. Zinc is then heated up, and the zinc particles attach to the gold particles where there are no fingerprint residues. The fingerprint ridges show up as clear fabric, but where there are no fingerprint ridges the distinctive grey colour of the zinc metal is seen.

While only 20% of the public are classed as "good donors" for leaving fingerprints, the researchers have had great success in revealing the shape of a handprint on a number of fabric types. Handprints could help the police piece together a timeline of events which could be used to provide evidence in cases where someone was pushed, or grabbed, in a particular area of their clothing. For example, an impression of a palm print on the back of someone's shirt might indicate they were pushed off a balcony, rather than jumping.

Reference
Joanna Fraser, Keith Sturrock, Paul Deacon, Stephen Bleay, David H. Bremner. Visualisation of fingermarks and grab impressions on fabrics. Part 1: Gold/zinc vacuum metal deposition. Forensic Science International, 2010; DOI: 10.1016/j.forsciint.2010.11.003

Further Reading
Physical and Chemical Changes

Study Questions

1. What do Chemists mean when they refer to evaporation?
2. What do Chemists mean when they refer to condensation?
3. Are evaporation and condensation examples of chemical or physical changes? Explain your answer.
   
4. Write a chemical equation to represent the evaporation of solid gold as described above in the process of vacuum metal deposition.
5. Do you think the equation you wrote above is an example of an evaporation process? Explain your answer.
6. Write a chemical equation to describe the process of gold vapor condensing on a fabric as described in the process of vacuum metal deposition.
7. Give the name for the change of state being described in each of the following:
   
   • heating solid gold until it forms a liquid
   • heating solid gold in a vacuum so that it forms a vapor
   • cooling gold vapor in a vacuum so that if forms solid gold
   • cooling gold liquid until it forms solid gold
   • heating liquid gold until it forms gold vapor
   • cooling gold vapor until it forms liquid gold
     

Catalysis by Gold Nanoclusters

Since the early 1980s, experiments have indicated that gold nanoparticles exhibit unexpected catalytic activity towards many industrially important chemical reactions that involve activation of atomic bonds inside oxygen or hydrocarbon molecules. Room-temperature formation of carbon dioxide, CO₂, from carbon monoxide, CO, and oxygen molecule, O₂, is one of the most extensively studied processes. A number of different factors have been suggested to contribute to the ability of gold particles to activate the O-O bond, which is considered to be the key reaction step.

Finnish scientists recently exposed monolayer-thick gold clusters to a variable number of oxygen molecules. It was found that even one gold cluster can effectively adsorb multiple oxygen molecules at the boundaries of the cluster, simultaneously weakening, stretching, the O-O bond by transferring electrons to the oxygen molecules. Taking into account the effects of temperature and ambient pressure, the calculations predicted that the oxygen molecules will completely dissociate and the oxygen and gold atoms will form one-dimensional alternating chains at the cluster boundary. The oxygen atoms in these chains are negatively charged and the gold atoms positively charged, creating a system that is reminiscent of a one-dimensional gold-oxide chain. These chains are expected to be the highly catalytically active part towards conversion of carbon monoxide to carbon dioxide at room temperature.

At room temperature and pressure, it appears that gold can catalyse an oxidation reaction by first oxidizing itself to gold oxide, which seems to contradict the known properties of gold in the macroscopic level.

References

1. Pentti Frondelius, Hannu Häkkinen and Karoliina Honkala. Formation of Gold(I) Edge Oxide at Flat Gold Nanoclusters on an Ultrathin MgO Film under Ambient Conditions. Angewandte Chemie International Edition, 2010; DOI: 10.1002/anie.201003851
2. X. Lin, N. Nilius, H.-J. Freund, M. Walter, P. Frondelius, K. Honkala, H. Häkkinen. Quantum Well States in Two-Dimensional Gold Clusters on MgO Thin Films. Physical Review Letters, 2009; 102 (20) DOI: 10.1103/PhysRevLett.102.206801

Further Reading
Naming Compounds
Writing Formula
Balancing Chemical Equations
Oxidation States
Transition Metals
Energy Profiles
Reaction Rate

Study Questions:

1. Write a balanced chemical equation for the formation of carbon dioxide from carbon monoxide and oxygen.
2. For the reaction above, what other possible steps in the reaction mechanism could be rate determining steps?
3. Why do you think that scientists believe that the activation of the O-O bond is the key reaction step in the reaction mechanism for this reaction?
4. What is meant by the term catalysis?
5. Why is gold described as a catalyst for the reaction described in the article?
   
6. What is meant by the term dissociate?
7. Describe how oxygen molecules can dissociate.
8. What is meant by the term oxidize?
9. Given the position of gold in the Periodic Table, what oxidation states are possible?
10. Give the formula for two possible oxides of gold.
11. Name each of the oxides above.
    

Gold Nanoparticle Dispersion

Queensland University of Technology (QUT) scientists have developed a new technique for dispersing metals in nanoparticle form throughout polymers or plastic materials.

The properties of metals change when they are in nano form. When nanoparticles are added to plastics, a new range of composite materials are formed.

When gold nanoparticles are added to paint, essentially a plastic, the intensity of colours and durability are increased.

Mixing gold nanoparticles with titanium dioxide, TiO₂, using a plastic mould makes a very efficient catalyst for water purification as the titania absorbs light, converting it into electricity which is then passed into the conductive gold.

Queensland University of Technology (2010, May 6). Gold nanoparticles promise to enrich everyday products. ScienceDaily. Retrieved May 8, 2010, from http://www.sciencedaily.com­ /releases/2010/05/100505092004.htm