Mining waste

Mining is one of humanity's oldest economic activities, and also one of the largest generators of waste. These materials, known as mining waste (or extractive waste), are produced during every phase of mineral exploitation: exploration, extraction, concentration, processing and mine closure.

Spain, with a mining tradition dating back to Roman times and significant operations in Andalusia, Asturias, Galicia and Castile and León, has faced for decades the challenge of managing millions of tonnes of waste from extractive activity.

What is mining waste?

Under the EU Extractive Waste Directive 2006/21/EC and Spain's Royal Decree 975/2009, mining waste is the solid, liquid or semi-solid waste generated during the prospecting, extraction, treatment and storage of mineral resources and the working of quarries. It includes:

• Overburden and waste rock: rock with no economic value that is separated from the useful ore.
• Tailings: fine sludge generated in mineral concentration plants.
• Slags and metallurgical dust: from smelting and refining processes.
• Contaminated water: acid drainage and leachate loaded with heavy metals.

Types of mining waste

Overburden and waste rock

Inert rock and material extracted alongside the target mineral. Although often not hazardous, it can contain traces of sulphides that, when oxidised, generate acid drainage.

Tailings

The most problematic stream: sludge resulting from washing and concentrating the ore. It is stored in large settling ponds and contains water, fine sands and chemical reagents.

Acid mine drainage (AMD)

Generated when sulphide minerals react with water and oxygen, producing sulphuric acid that dissolves toxic metals (arsenic, lead, cadmium). This process can persist for centuries and is a major source of leachate.

Metallurgical waste

Includes slags, dust and ash from smelters. It can qualify as hazardous waste because of its heavy-metal and toxic-compound content.

Environmental risks

Poor management of mining waste carries multiple risks:

• Water pollution: leaching of heavy metals and acidity.
• Soil contamination: accumulation of toxic substances.
• Accident risk: failure of tailings dams.
• Landscape impact: large spoil heaps and ponds visible for decades.
• Biodiversity effects: habitat loss and toxicity for flora and fauna.

Applicable rules

European Union

• Directive 2006/21/EC on the management of waste from extractive industries.
• Directive 2010/75/EU on industrial emissions.

Spain

• Royal Decree 975/2009, which transposes Directive 2006/21/EC.
• Law 7/2022 on waste and contaminated soil for a circular economy.
• Regional legislation in autonomous communities with mining operations.

These rules require operators to draw up a mining-waste management plan, design storage facilities with safety guarantees, provide financial guarantees to cover potential environmental damage, and restore the site after closure.

How mining waste is managed

• Prevention and reduction: optimising concentration processes to reduce tailings.
• Safe storage: lined ponds and stabilised spoil heaps.
• Treatment of acid water: neutralisation with lime and constructed wetlands.
• Recovery: extracting residual metals and reusing inert material in construction.
• Environmental restoration: revegetation, sealing of abandoned mines and post-closure monitoring.

Mining waste and the circular economy

The circular economy opens new possibilities for this stream:

• Re-mining: reworking old spoil heaps to recover metals with new technologies.
• Recovery in construction: using waste rock and ash in recycled aggregates and cements.
• Recovery of critical raw materials (rare earths, cobalt, lithium) essential for the energy transition.

Turning mining waste into useful resources is one of the great challenges of 21st-century mining and a condition for reconciling resource extraction with environmental protection and social wellbeing. The main pending tasks are managing historic environmental liabilities, increasing control and transparency in current operations, and innovating in recovery technologies.

At Manglai we help companies measure their environmental footprint and prepare their sustainability reporting, including waste indicators. Discover how Manglai can help you.