TOMRA Sorting Mining has delivered its first underground sensor-based ore sorting solution to K+S Minerals and Agriculture at its rock salt mine in Grasleben, Germany.

The major salt producer looked to TOMRA, which it has a long-standing research and development relationship with, to replace an existing sorting system at the mine.

At the Grasleben mine, rock salt is extracted from an underground deposit that stretches across two states. It is processed into a wide range of products, from de-icing salt for winter road services, to food-grade table salts and lick stones for livestock and domestic animals.

“For K+S, consistently achieving certified and guaranteed high purity, compliant with the strict standards of the food industry, is a priority,” TOMRA said.

Sven Raabe, Technische Büro Mechanik, K+S Minerals and Agriculture, said: “The sorting of rock salt is complex and demanding due to its crystalline properties. This leads to strong fluctuations in the appearance of the material.”

TOMRA recommended using colour sorting technology for this installation, with Mathilde Robben, Key Account Manager at TOMRA Mining, saying the customised setup of light sources allows the system to “detect the difference in transparency of the different particles, ensuring the high quality of the rock salt”.

The team also advised installing the sorter in the underground mine, so, after the initial underground sorting stage, only the coarsely crushed rock salt undergoes further grinding and sieving above ground.

“Only the valuable product needs to be transported in the shaft, and the final result is high-quality, pure rock salt products in various grain sizes, which are ideal for this application,” TOMRA said. “Furthermore, waste rejects can be backfilled underground, avoiding storage and emissions on the surface.”

TOMRA conducted a demonstration of the proposed solution at its Demonstration and Test Center in Wedel, Germany. Raabe attended the test with colleagues from K+S’s technical team, Florian Lieske, Stephan Meiberg and Sven Lindner.

“The tests were very well prepared,” Raabe said. “The on-site team quickly developed a feel for our product. The uncomplicated adaptation of the program to the different material qualities also convinced us.”

He added: “An important factor in our purchasing decision was the positive test result achieved with the system, using transmitted light to obtain more efficient separation. This has the added benefit of resource conservation. It is possible to react quickly and individually to changing situations during dismantling. We expect this to be more effective, and the ease of use of the system was also convincing.”

Following this experience and the results of the test, K+S placed the order for TOMRA’s solution, with installation planned for September 2020. The negotiations were conducted via video conference due to COVID-19-related travel restrictions and lockdowns.

The order was entered in TOMRA’s production plan and the Factory Acceptance Test was conducted on September 23, with the sorter transported to the Grasleben mine. It was put in position underground at the mine on September 30.

Robben concluded: “This is the first solution we provide for underground sorting, which raises specific challenges due to the dimensions and weight limitations of the mine shaft. In this project we also had to contend with the difficulties created by the COVID-19 pandemic.

“I am very pleased that we have been able to meet K+S’s requirements and deliver on schedule.”