In environmental science, leaching tests play a crucial role in assessing the potential impact of materials on the environment. But what exactly is a leaching test, how does it work and why did we use in project ReSoURCE?

What is a leaching test?

A leaching test is a laboratory procedure used to evaluate how substances, such as metals or chemicals, can be released from a solid material (spent refractories in our case) when it comes into contact with a liquid, typically water. This process mimics natural conditions where rainwater or groundwater might interact with waste materials, soil, or industrial by-products.

How does it work?

The basic principle involves placing a sample of the material in a container and then adding a specific amount of liquid. The mixture is then agitated for a set period to simulate natural leaching conditions. Afterward, the liquid, now called the leachate, is analysed to determine which substances have been released from the solid material and in what concentrations.

Why did we perform leaching tests in project ReSoURCE?

Despite the above-mentioned reason (potential impact on the environment) we also wanted to analyse the behaviour of so-called impurities. When we talk about impurities, we mostly mean alkaline elements like K₂O, Na₂O, Cl^–, and SO₃^– which hinder further recycling by negatively influencing refractory properties. To remove these elements’ further treatment (e.g., washing) is necessary.

Leaching tests are often combined with aqua regia digestions, which provide information about the chemical content. This analysis comes with some limitations as some materials do not dissolve completely in aqua regia (e.g., some silicates). Nevertheless, by comparing the results of these two methods we can see how good a treatment method like washing could perform.

Leaching tests have a lot of variation like for example pH-depending leaching tests, where we analyse the leaching behaviour at different predefined pH.

Applications of Leaching Test Results

The results of leaching tests are vital for several reasons:

• Environmental Safety: They help predict the potential for contaminants to migrate into groundwater or surface water, posing risks to ecosystems and human health.
• Regulatory Compliance: Industries use these tests to ensure that their waste management practices comply with environmental regulations.
• Remediation Planning: Leaching tests guide the development of effective strategies for cleaning up contaminated sites.

By understanding the leaching behaviour of materials, scientists and policymakers can make informed decisions to protect the environment and public health.

The image below shows an overhead shaker loaded with five samples, set to undergo a 24-hour shaking process.

 Sample image. Photo credits: Bettina Ratz.