Use of industrial sub-products - Coal shales

Coal shale is derived from coal mining residues.

Coal mining came to a gradual halt in France, until virtually all mining sites were closed in the late 1990s. A large number of large slag heaps, created during mining operations, have remained standing for several decades. Slag heaps are characteristic of the landscape of mining regions and form part of their heritage.

In this article, we focus on the exploitation and valorization of the material resources represented by coal shale contained in slag heaps. The national and regional public services concerned are encouraging the use of these stocks, as it contributes to the simultaneous resolution of several major issues:

• a regional or local economic issue: the appropriate use of these by-products in the construction industry;

• an environmental issue: the development of slag heaps, which requires significant measures – for safety, erosion protection, landscaping... – are facilitated during and at the end of the operation;

• a significant contribution to sustainable development, in particular by reducing the need for distant quarries and the associated transport.

Around a quarter of the 1 billion tonnes of coal shale in the slag heaps have been mined.

Coal shale utilization techniques are still used today, but are in decline, notably due to the decline in higher-quality by-products.

Depending on their characteristics, the materials are used in the following ways:

• backfill, including water-insensitive backfill;

• for road subgrades, usually in the road and motorway sectors;

• logistics platforms and roads, networks and miscellaneous facilities;

• sometimes in the rail sector, including high-speed lines (LGV).

The coalfields essentially concern three regions:

• Nord-Pas-de-Calais ;

• Lorraine ;

• Center and Midi.

The BHNPDC (Nord-Pas-de-Calais coalfield) is the largest. This region is poor in rock material resources. Coal shale has been used extensively for the construction of embankments and sub-bases for the motorway and road network in the Nord-Pas-de-Calais region. Several tens of millions of tonnes have been used for these purposes.

The expected development in the Nord-Pas-de-Calais region lies mainly in the recovery of unprocessed black shale, by screening, crushing or treatment...