Activities after the Closure of Diepenlinchen

Ore Processing and Flotation in the Stolberg Region

For many centuries, the so-called density sorting was used to separate valuable ores from worthless rock. This method exploited the differences in specific weight between ore and gangue.

The ore-bearing rock extracted from the mines was first crushed using stamp mills, roller mills, or stone mills. The desired grain size critically depended on how finely the ore was distributed in the host rock. The individual grains had to differ significantly in ore content and worthless rock to make separation by density sorting effective.

The actual separation took place under a weak water flow on tables arranged at an incline, which were mechanically vibrated. In this way, the grains settled according to their specific weight – a process also known as shaking or jiggling tables.

The blende predominantly mined in Stolberg was a polymetallic ore that contained sphalerite, galena, and pyrite (or marcasite). Therefore, it was particularly important to separate the sulfides not only from the gangue but also from each other.

Flotation Process in the 1920s

In the 1920s, ore processing was decisively advanced. The flotation process (also known as floating treatment) utilized the different surface properties of minerals. A fine crushing of the ore heap by stone mills was a prerequisite.

After the closure of the Diepenlinchen mine, the operating company, the Company for Mining and Zinc Production in Stolberg and Westphalia (Stolberger Zink), remained active across Europe. In 1927/28, it established a flotation plant at Weißenberg with a capacity of 5 tons per hour.

Initially, the plant was used for the reprocessing of old pond and dump sludges, as this material was suitable for flotation without further crushing. By 1933, over 4,000 tons of usable ore concentrate could be produced in this way.

With the self-sufficiency efforts of the 1930s, from 1933 to 1942, coarse dump material was increasingly crushed and processed. The resulting sandy residues were deposited on the dump at Weißenberg.