Student viewpoints on the importance and consequences of toxic object management and end of life disposal

1 Introduction

Batteries are sources of electric power that work through a spontaneous oxidation-reduction reaction, or redox reaction, responsible for generating the electric current.

They are composed of two electrodes, positive and negative, and by an electrolyte, an ionic conductor that surrounds the electrodes. Batteries are also composed of cells connected in series and can be rechargeable or not (Bocchi et al., 2000). It is possible to see the different parts that compose a battery, as shown in Figure 1.

Figure 1:

Parts of a battery. Note. https://monomole.com/2019/09/25/basic-electrochemistry-8/.

There are several substances that form the composition of batteries, and among them are potentially toxic metals such as zinc, manganese, lead, mercury, cadmium, nickel, copper, and chromium, which can be present either as impurities or as additives to improve battery efficiency. In addition, according to Bartolozzi (Vatistas et al., 2001), even after depletion, a battery can still contain 30 % zinc (Zn) in its composition, showing that the total oxidation-reduction reaction, or redox reaction, does not occur completely. In many cases, the theory and underlying electrochemical principles of batteries is all that students learn about in their curriculum. The waste produced through non-rechargeable battery use and the potential environmental impact is rarely covered.

In 1999, the Resolution 257 was approved by the Brazilian National Environment Council (CONAMA), being the only act of law that issues the collection of electronic material in Brazil. According to the Article 13 of the resolution, batteries and electronic components for domestic use, after being depleted, can be disposed of in regular garbage along with household waste, provided that they are deposited in licensed landfills and contain less than a specific amount of mercury, cadmium and lead in their formulation. However, due to the potential toxicity of zinc and manganese in high concentrations, on November 4, 2008, CONAMA created Resolution 401, which revoked Resolution 257. This new resolution establishes that depleted batteries, even if they do not exceed the allowable amount of potentially toxic metals, should no longer be disposed of in household waste, but rather sent to an adequate environmentally monitored dumping ground (Brazilian National Environment Council (CONAMA), 2008). But, even with the current new legislation, electronic waste is still discarded inappropriately, ending up in places such as common garbage, landfill soil, streams, rivers and seas. The legislation and whether students have seen incorrectly disposed batteries in their day-to-day lives can serve as a discussion point in class either before or after experiments are performed.

In Brazil, only 1 % of the 400 million batteries and more than 1 billion cells sold per month, are recycled (ReciclaSampa, 2018). That because the process demands a high energy consumption and the treatments to recycle the rest of the components require high economic investment. Recycling 1 ton of cells and batteries, for example, costs an average of one thousand Reais (approximately 200 USD) (Mossali et al., 2020). Besides that, it is worth mentioning that the recycling process is complex and goes through several stages, with two main methods: hydrometallurgy and pyrometallurgy.

Hydrometallurgy is a recycling process that involves the selective dissolution of Li-ion battery components in acid or alkaline solutions. It allows the recovery of valuable materials such as lithium, cobalt, nickel, and manganese. The general process includes disassembling the batteries, followed by grinding the components to increase the surface area for exposure. Subsequently, the crushed materials are subjected to controlled chemical reactions in acid or alkaline solutions to separate and recover the metals. Pyrometallurgy is an alternative method that involves the use of high temperatures to separate and recover the materials of Li-ion batteries. In this process, the batteries are subjected to high temperatures in controlled furnaces. During combustion, organic materials are eliminated, while metals are melted and separated based on their melting temperatures. It results in recovering metals such as lithium, cobalt, nickel, and aluminum. Some of these metals have been highlighted by EUCHEMS and other organizations as scarce elements with rising threats due to increased use (EuChemS Periodic Table, 2023).

Both processes have advantages and disadvantages. Hydrometallurgy is more selective and effective in recovering materials but requires proper chemical waste management. Pyrometallurgy is a robust thermal approach, but it can bring about the loss of valuable materials during the melting process. Recycling processes, scarcity and sustainability of element supplies and other points related to battery use can be discussed in classes.

Even with challenges, over the past few years, there has been a noticeable increase in interest from the scientific community in addressing the challenges of recycling batteries. This phenomenon can be attributed to several factors, including, for instance, technological advances that have made recycling more efficient. Their interest is remarkably important as it has been contributing to public awareness and education of the seriousness in recycling batteries, which is crucial for mitigating environmental degradation.

2 Objectives

This project was designed by students in their 2nd year of High School (aged 16–17 years old), with the goal of participating at the Olimpíada Estadual de Química de São Paulo [State Chemistry Olympiad of São Paulo] – in which the group was among the 150 winners and moved on to the second phase of the Olympiad. Thus, to verify the harm that cells and batteries cause to the environment when they are discarded improperly, knowing that they contain toxic substances that can be leached, research and experiments were made that led to draft the following hypotheses: if batteries are discarded improperly, and mixed with common waste, it is likely that they will end up in landfills, where they will be subject to physical impacts and, especially, to the influence of external factors, such as rain. Rain can trigger the oxidation process on the batteries, rupturing their casing. In addition, studies were conducted on how the improper disposal of batteries can contribute to marine pollution, as batteries can somehow reach the seas and affect these sensitive ecosystems.

3 Materials and methods

The materials used in the experiment consisted of two alkaline cell batteries in series; four lithium batteries; 100 ml of natural water; 100 ml of rainwater; 10 g of sodium chloride; four beakers.

In two of the beakers, the tests were conducted by using the two alkaline cell batteries; one beaker with 55 ml of rainwater, collected in the city of Sorocaba, and the other with 55 ml of natural water and 1 teaspoon of sodium chloride, simulating sea water, salt mixtures can be purchased at pet supply or aquarium stores to make artificial seawater with ion levels similar to those seen in the ocean. Each alkaline cell was submerged in each of the beakers, allowing the observation of the reactions that occurred over time.

For the other two remaining beakers, the tests were conducted using lithium batteries; one beaker with 45 ml of the same rainwater collected previously, and the other with 45 ml of natural water and 1 teaspoon of sodium chloride. In the same way, the lithium batteries were also submerged in each of these two beakers to observe the reactions.

The entire experiment was regularly monitored over the time of 3 weeks.

4 Results and discussion

In the first days of the experiment with the cell batteries, it was not possible to identify any visible changes in the water. However, after the course of 2 weeks, an orange-colored substance leaked from the battery inside the beaker with “sea water”, as shown in Figure 2.

Figure 2:

Cell batteries connected in series submerged in a seawater simulation. Note. Photo taken by students themselves.

On the other hand, the same cell batteries connected in series added in rainwater, after a few weeks, did not release any type of substance of different color, as shown in Figure 3. Since the experiments were purely qualitative, this test was the only one that did not show any visible changes during the period of the tests, but this material could probably show changes over the years, considering its improper disposal.

Figure 3:

Cell batteries connected in series submerged in a rainwater sample. Note. Photo taken by students themselves.

From the obtained results, it is plausible that a reaction occurred, releasing potentially toxic metals, more quickly in the seawater simulation, which leaked an orange-colored component and may be the result of the oxidation reaction of the batteries.

In contrast, the lithium batteries immersed in the beaker with rainwater released grayish/blackish substances, as shown in Figures 4 and 5.

Figure 4:

Lithium batteries submerged in a seawater simulation. Note. Photo taken by students themselves.

Figure 5:

Lithium batteries submerged in a rainwater sample. Note. Photo taken by students themselves.

Although rainwater does not tend to be an aggressive leaching agent to the batteries used, it is clear that new substances enter the water, which can be, among others, potentially toxic metals from the batteries and this increases through test time.

What is more, according to textbooks, it was expected to find a greater release of Iron (Fe), zinc (Zn) and manganese (Mn) in these tests, however, since the experiment was merely qualitative, it was not possible to determine which or if any of them was released, or if it was some other metal (Camara et al., 2012). It is possible, though, within a different project or experimentation, to identify which metal ions are responsible for originating colored or colorless solutions, for example, Zn²⁺ and the Fe^2+/3+. Such an experiment might be possible within an undergraduate analytical chemistry teaching laboratory setting (Kendüzler and Türker, 2002).

It is noteworthy that, in certain cases, highly toxic substances can manifest themselves as colorless solutions, highlighting the limitation of visual information as a reliable indicator for determining the presence or absence of toxic agents. This phenomenon highlights the need for sensitive and specific analytical evaluation methods of potentially hazardous compounds in environmental or chemical situations.

After those testings, a second batch of tests were conducted, with a larger amount of rainwater, 150 ml, and 2 teaspoons of sodium chloride for simulated seawater. Notably, about 10 min after immersion in the beaker with seawater simulation, it was observed the leaking of an “unidentified substance” from both the alkaline and lithium batteries along with some bubbles, as shown in Figure 6.

Figure 6:

Alkaline battery submerged in a new seawater simulation. Note. Photo taken by students themselves.

On the other hand, the lithium battery submerged in rainwater began to show signs of oxidation about 15 min after the start of the experiment, as shown in Figure 7.

Figure 7:

Lithium battery submerged in a new rainwater sample. Note. Photo taken by students themselves.

After 24 h, significant changes were observed in both simulations. In the beakers with rainwater, the changes remained more subtle compared to the beakers with “seawater”. Regarding the alkaline battery, it was detected emission of brownish residues, possibly manganese oxide, while the lithium battery continued oxidizing and releasing hydrogen bubbles. Surprisingly, in the seawater simulation, the results were greater in comparison to the first experiment: the amount of manganese oxide released was larger, indicating a direct influence from seawater salinity over the reactivity of the cell battery. In addition, the oxidation of the lithium battery generated reddish byproducts, which altered the coloration of the water, as shown in Figure 8.

Figure 8:

Oxidation of cell and lithium batteries in the seawater simulation. Note. Photo taken by students themselves.

It is worth mentioning that one of the challenges of this project was that none of the students involved live in a coastal city, rendering them unable to collect a real sample of seawater, thus the need of a simulation using water and sodium chloride, which can slightly affect the results since the concentration of sodium can be different, in addition to it not being the only factor present in real environment.

What is more, although the experiments provide valuable information about the reactions of cell and lithium batteries in different simulated environments, they do not represent real scales. Several details differ in a simulated environment from the real ones. For instance, landfills are designed with the purpose of preventing contamination of water, soil, and air. They are usually located far from urban centers and occupy an extensive area of land. However, for this research, it was opted for an approach involving a reduced area, without implementing or considering the necessary treatments present in a conventional landfill, thus based only on the effects of rainwater in these places. This project was carried out solely to study the consequences of improper disposal of cells and batteries, providing a scenario that differs substantially from proper waste management practices in landfills (BRK Ambiental, 2020a, 2020b). Besides that, landfills are predominantly under dry conditions most of the time, although during periods of rain the soil can become moist. Then, due to rain, the batteries get wet with the moist soil, initiating its oxidation and degradation process, and releasing substances into the environment. These substances have the potential to affect both human and animal health. Experiments undertaken and led by students as described in this current article can help introduce students to the concepts of environmental, sustainable and green chemistry (Celestino, 2023).

It is worth mentioning that the deterioration of batteries in landfills occurs more slowly compared to the simulated environment in the beakers. The main reason for this difference is the greater amount of water present in the beakers compared to the daily basis of landfills. The presence of a larger amount of water in the beakers can accelerate the degradation process of the batteries, since water plays a key role in this process. Therefore, the speed and extent of degradation of batteries are influenced by the humidity conditions of the environment in which they are disposed of (BRK Ambiental, 2020a, 2020b).

In the sea, the dynamics of the battery’s deterioration presents some notable variations compared to the studied scenarios. Due to the presence of additional substances in real seawater, such as magnesium and sulfate, which were not present in the samples of this project, batteries go through an accelerated degradation process, thus also leaking substances faster. In addition to that, it is noteworthy that the concentration of salts present in seawater is proportionally greater than in the one used in the experiments. This greater concentration of salts in seawater has an additional impact on how quickly the batteries deteriorate.

That said, the students came to the conclusion that the amount of water itself is not responsible for affecting degradation time, since both batteries were submerged in water, but it is due to the existence of different substances and their concentration in said water. Therefore, the rate of degradation of the batteries in the marine environment is mainly influenced by the chemical composition of seawater, particularly the concentration of salts and other components (Canaltech, 2021).

The reason why many of these batteries end up reaching the seas is simple, often involving shortcuts taken to avoid declaration of the containers’ total weight, along with inadequate packaging of the products within these containers. Weather factors, such as strong winds and storms, and the incorrect stacking or grouping of those containers can also expose them to risks of loss or damage.

The understanding of these incidents, mainly by countries that produce this type of material the most, is fundamental for the research of adequate solutions and, consequently, protecting the marine environment (Cargostore).

5 Conclusions

In conclusion, the results of this project were able to explain that batteries deteriorate more rapidly when immersed in water, due to oxidation. This further reinforces the importance of the correct disposal of these objects. The cobalt oxide found in lithium batteries can cause an allergic skin reaction, cancer, and is also very toxic to aquatic organisms, causing harm to entire ecological chains and biodiversity (CETESB, 2020). The sodium hydroxide present in alkaline batteries can cause damage to the tissues of mouth, throat, esophagus, and stomach, severe skin burns, and is also harmful to aquatic life (ICSC & ÓXIDO, 2004). Therefore, it is utterly important that people are aware of how to correctly discard these materials and their proper extraction points, instead of just disposing of them with common garbage without proper care. Only by the proper disposal of these materials will the risks to the ecosystem and public health be mitigated. As shown by others (Transforming Education for Sustainability pp 227–245), teaching chemistry in context can help introduce students to examples of environmental injustice and highlight the importance of chemistry in their day-to-day lives.