Flotationsverfahren 1927

Activities after the closure of Diepenlinchen

Ore processing and flotation in the Stolberg mining district

For many centuries, so-called density sorting was used to separate usable ore from waste rock. This exploited the differences in specific gravity between ore and waste rock.

The ore-bearing rock extracted from the mines was first crushed using pug mills, pan mills or rock mills. The desired grain size depended crucially on how finely the ore was distributed in the parent rock. The individual grains had to be clearly differentiated in terms of the ore content and the waste rock in order to make separation by density sorting effective.

The actual separation took place under a weak stream of water on inclined tables that were mechanically vibrated. In this way, the grains settled according to their specific weight - a process also known as shaking or impact hearths.

The shell blende predominantly mined in Stolberg was a polymetallic ore containing zinc blende, galena and sulphur pyrite (pyrite or marcasite). It was therefore particularly important to separate the sulphides not only from the surrounding rock, but also from each other.

Flotation process in the 1920s

In the 1920s, ore processing underwent significant further development. The flotation process (also known as floatation processing) utilized the different surface properties of the minerals. This required the ore to be finely crushed using rock mills.

Following the closure of the Diepenlinchen mine, the operating company, the Gesellschaft für Bergbau und Zinkfabrikation zu Stolberg und in Westfalen (Stolberger Zink), remained active throughout Europe. In 1927/28, it built a flotation plant at Weißenberg with a capacity of 5 tons per hour.

Initially, the plant was used for the post-treatment of old pond and tailings sludge, as this material was suitable for flotation without further crushing. By 1933, over 4,000 tons of usable ore concentrate had been obtained in this way.

With the self-sufficiency efforts of the 1930s, coarse dump materialwas also increasingly crushedand processed from 1933 to 1942. The resulting sandy residues were deposited on the Weißenberg slag heap.