Gold mining in the classroom: a lab activity to teach sustainability Teach article

Wondering how to extract gold from mobile phones in a school lab? Explore one of the activities from the project Recycle Your Mobile Phone To Save The Planet.

In the era of so-called ‘digital capitalism’, it is becoming increasingly vital to raise awareness about the responsible use of smartphones and the necessity of recycling the raw materials they contain. 

In this hands-on activity, students will chemically explore the recovery of gold from their smartphones. This resource is part of the multidisciplinary project ‘Recycle Your Mobile Phone To Save The Planet’, which is a joint effort between various schools in Italy and the Jane Goodall Institute Italy.^[1] You can read more about the project in the accompanying Inspire article.

Suggested age range: 14–19 years old

Before you begin: exploring smartphones as an urban mine

Before students dive into the gold extraction experiment, it is a good time to explore certain chemical, environmental and social aspects of the object that almost all students own and love: the smartphone.

There are currently more than 7 billion smartphones in circulation. Yet, when students are asked to estimate how many chemical elements are present inside a smartphone, it turns out that almost all of them are unaware of the number. It is more than 50 elements!^[2]

It is a good practice for students to locate the elements on the periodic table, to classify and learn about the properties of metals and non-metals, as well as to explore their position and function within devices.

It is particularly useful to focus on critical materials, such as rare earth elements and the 3TG (tin, tantalum, tungsten, and gold), which are essential for the construction of all the technological devices we use daily. All of them are finite resources and, behind their extraction, lie stories of exploited young workers, habitat destruction and pollution of local lands.^[3]

It is estimated that, in Europe alone, demand for critical minerals used in green technology and advanced electronics is forecast to quadruple by 2040.^[4] Moreover, WEEE (waste from electrical and electronic equipment) is the fastest-growing waste stream in the world. As you can see in the image below, a record 62 million tonnes of e-waste was produced in 2022, and it is on track to rise another 32%, by 2030.^[5] As a natural consequence of this, we need to shift the focus onto recovering and reusing these raw materials.

However, less than one quarter (22.3%) of the year 2022’s e-waste mass was documented as having been properly collected and recycled. The rest ends up in illegal landfills, where the materials are often burned or informally recycled, which leads to water, air and soil pollution, as well as bearing health risks for local populations and workers.  

We have prepared an information sheet for students (see supplementary materials) covering the most important points of the topic.

Alongside the student information sheet, a teacher guide for optional activities on these points is provided, which helps students to grasps the importance of smartphone recycling. 

Activity 1: Gold recovery from smartphones

In this activity, we use a method for recovering gold from obsolete mobile phones through a process of oxidation followed by reduction, striving to use substances with the lowest possible environmental impact. 

The procedure described here – from the selection of the circuit boards to melting the gold and recovering the final product – takes approximately three days of work given that some reactions last up to 12 hours. It would be best to conduct the experiments over three consecutive days. 

Below, you can find a short description of the procedure. A more detailed procedure is given in the teacher guide in the supplementary materials.  

Materials

For 1 g of recovered circuitry, the following are required:

• 1 ml of a 1:1 mixture of 37% hydrochloric acid (HCl) (or 20% sulfuric acid (H₂SO₄)) and 30% hydrogen peroxide (H₂O₂)
• a few spatula-tips of potassium permanganate (KMnO₄) or alternatively, a 10% solution of sodium hydroxide (NaOH) and a spatula manganese dioxide (MnO₂).
• diluted HCl solution for rinsing: obtained by diluting 37% HCl 1:10 with distilled water 

• distilled water
• 2 g of urea
• 2 g of sodium metabisulfite (Na₂S₂O₅)
• filter papers: Thickness (0.17 mm) Particle retention (5–8 μm) 
• fume hood
• beaker
• flasks
• spatulas
• muffle furnace or alternatively a Bunsen burner
• magnetic stirrer with stir bar
• funnels 
• conical flasks (100 ml and 500 ml, if using 10 g of selected circuits)
• ceramic crucible
• to retrieve the circuits from the smartphone, pliers and screwdrivers are needed
• an ice-water bath, or an ice-water bath with NaCl

Reagents for alternative routes: 

• alternative to HCl: 20% H₂SO₄   
• alternative to KmnO₄: 10% NaOH and MnO₂

Procedure

1. Preparation: Disassemble the discarded cell phones, separate the circuit boards and select the components which are known or suspected to contain gold.^[6]

2. Acid Digestion: Gradually add a 1:1 mixture of 37% hydrochloric acid (HCl) and 30% hydrogen peroxide (H₂O₂) to a beaker containing the selected components.
3. Oxidation reaction: Stir the mixture at room temperature for approximately 12 hours using a magnetic stirrer and stir bar. Subsequently, the reaction mixture is separated from the rest by filtration.
4. Excess Peroxide Elimination: Solid potassium permanganate (KMnO₄) is added to destroy most of the hydrogen peroxide.
5. Precipitation: Add urea, heat gently, add sodium metabisulfite (Na₂S₂O₅), and allow the reaction to proceed until a dark brown or black precipitate forms (this may take several hours, depending on the circuits chosen).
6. Filtration and Collection: Filter the precipitate and wash it with a dilute hydrochloric acid solution.
7. Calcination and Melting: Place the dried filter paper containing the residual precipitate into a suitable crucible and proceed to calcine the paper to eliminate it. Melt the residual gold-bearing powder inside the crucible using a Bunsen burner or a muffle furnace, so as to fuse the powder particles into a single, compact block.

For the detailed procedure, please refer to the Teacher guide.

Results

The final product consists of small gold nuggets or a black/brown powder.^[7] The yield of the two reactions depends on the amount of gold present in the selected printed circuit boards and is therefore highly variable, making it impossible to determine an exact value beforehand. Consequently, careful selection of the printed circuit boards is crucial for effective gold recovery.^[8]

Discussion

To round up the experiment, a discussion can be initiated by dividing the class into groups to address the following topics. Example answers to the questions can be found in the supplementary materials.

• Where should recycling appear in the hierarchy of possible actions? Rank the following actions from most to least preferable and explain your ranking: recycling, repair, reuse, resale, refurbish
• What might prevent people from returning their old phones for reuse or recycling?
• What could encourage more people to return their phones?
• What are possible bottlenecks of recycling smartphones? 
• Gold recovery from circuit boards still requires energy, equipment and chemicals. Why can it nevertheless be environmentally preferable to mining new gold?
• What information would a recycling company need before deciding whether recovering metals from smartphones is economically viable?
• The experiment focuses on gold, but what other components or materials might be reused or recovered from a smartphone?

Conclusion 

Extracting gold from discarded smartphones is an essential educational tool that addresses critical global challenges. 

In a world rapidly approaching the depletion point of raw materials, raising awareness on this topic becomes essential: without a circular management of resources, even the future availability of the smartphones we use every day could be at risk. 

This educational activity fits perfectly into the framework of the UN Sustainable Development Goals (SDGs), particularly SDG 10 (Reduced Inequalities) and SDG 12 (Responsible Consumption and Production), by allowing students to link mining and consumption directly to global ecological and socio-economic impacts. 

Furthermore, holding a physical piece of recovered gold provides students with a vivid and memorable image of the valuable resources in a phone, thereby highlighting the importance of recycling.

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Supporting materials

Student info sheet

Extension activities

Detailed procedure

Discussion answers

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