It smells like a dusty dirt road in midsummer. But it’s bitterly cold all around us, we’re in a modern industrial building. Broad conveyor belts rumble as they transport gravel of various grain sizes past us. Watery sand flows from a yellow, vertically mounted metal spiral into the lower level.

Next to it, a structure shakes compact, black soil until it breaks down into small chunks. Across five floors, excavated material, road waste and drilling sludge are processed in the gray Vito Recycling AG building. This joint venture between the cement manufacturer Vigier AG and the construction and demolition company Toggenburger AG in Péry (BE) focuses on gravel and soil that first have to be detoxified due to their contamination with heavy metals or organic pollutants.

Switzerland’s most state-of-the-art soil washing plant

This state-of-the-art soil washing plant in Switzerland went into operation six months ago. “The process is designed for 130 metric tons of material per day, but at the moment we are only at a quarter of the capacity,” says Gérard Tschanz. The facility manager guides the 20 master’s students of the Waste Materials and Circular Economy course at the Institute of Geological Sciences through the noisy and vibrating hall.

It is only possible to ask questions again and have the multi-stage process explained to you once you are back outside: The excavated material is brought here by trucks from all over the region. A complex interplay of sorting and washing processes uses magnets, eddy current separators and other machines to separate out impurities such as metals, wood, plastic and ceramics. What remains is clean recycled gravel and sand that can be recycled back into concrete.

The organic pollutants in the excavated material are enriched in the fines during the washing process. This produces what is known as the filter cake, i.e. filtered and dehydrated sediment, which is used as a raw material substitute at the Vigier AG cement plant located 500 meters away.

Protecting the landscape and climate

The technology used at Vito AG is a sophisticated but extremely complex method of promoting the circular economy in the field of mineral waste. Given the 700,000 tons of lime and 300,000 tons of marl that the Vigier cement factory alone processes into clinker each year, Vito supplies only a fraction of the replacement material. “But it is an example of how the recycling of mineral waste offers the greatest potential for strengthening the circular economy in Switzerland,” explains Mirjam Wolffers from the Office of Secondary Raw Materials at the Institute of Geological Sciences at the University of Bern. “Ninety percent of waste in Switzerland is accounted for by this category, so the leverage is correspondingly high.”

Wolffers points to the multiple ecological effects of building rubble or excavated material being used as a secondary raw material rather than landfill. Firstly, the new use protects the landscape because the quarry does not eat further into the mountain. Secondly, this waste does not have to be sent to landfill – Switzerland will face bottlenecks in landfill in the coming decades. Thirdly, recycling secondary raw materials often saves energy and avoids CO₂ emissions compared to mining new materials.

Cement plants produce a lot of CO₂

The above effect is of key importance in the cement industry, confirms Mathieu Antoni, Environmental Manager at Vigier AG: “We mine one million tons of limestone and marl here every year, but only extract 600,000 tons of clinker, which we then use to produce the cement.” The difference of 400,000 tons is carbon dioxide: When the cement is burned at 1,450 degrees, enormous quantities of CO₂ that were trapped in the limestone escape into the atmosphere. The search for alternative raw materials that reduce the carbon footprint is therefore a top priority. “It’s probably never going to be completely emissions-free. One consideration is to separate the greenhouse gas at the end of the high chimney and bind it over a long period of time so that it does not escape into the atmosphere,” explains Antoni, pointing to the imposing chimney with its red tip. However, the costs are high. Globally, cement plants emit four times as much greenhouse gases as aviation. In Switzerland, the six plants are responsible for 5% of CO₂ emissions.

It would be perfect if not only the marl, but also the limestone could be replaced with secondary raw materials. “The problem is that the market only has a small amount of mineral waste containing a lot of calcium that could be used in cement plants,” says Gisela Weibel, Head of Incineration Residues and Landfills at the Specialist Unit for Secondary Raw Materials at the Institute of Geological Sciences at the University of Bern, indicating an obstacle to integrating cement plants even more strongly into the circular economy. One hurdle that is at least as big is the fact that in some cases considerable reserves of fresh limestone are still available. Vigier, for example, has secured mining rights in Péry for the next 100 years.

When it comes to fuel, the alternatives work

When it comes to fuel, Vigier has almost entirely completed the transformation. “We only use one or two percent coal and light oil here, and we cover the rest with alternative fuels,” explains Antoni proudly. While primarily coal was burned a few decades ago, the Swiss cement industry in general and Vigier in particular relies on waste materials with a high calorific value such as waste oil, solvents, waste plastic, animal meal and waste wood. Even dust from the Swiss tobacco industry once found its way to Péry, as a glass labeled in this way in the visitors’ room shows.

Accepting all these materials is a science in itself. Antoni explains how samples are taken on a daily basis and analyzed in the company’s own laboratory to ensure compliance with limits such as chlorine and organic pollutants.

Visit shows the connections

The current misfortune of the operating company – an accident – is our luck: We have the rare opportunity to take a look inside the rotary kiln, a monster of 4.4 meters in diameter and 68 meters long. Here, too, it smells of dust, but it is fine dust from the cement clinker that forms a thin layer on the floor and covers all the pipes, fittings and sheet metal walls, conveyor systems, lifts and grates in a monotonous anthracite.

Jana von Allmen, who will soon be completing her master’s degree in Earth Sciences at the University of Bern, is also impressed by the possibilities of introducing mineral waste into the material cycle. In her job in a planning and construction support office, where she worked part-time alongside her studies, she repeatedly had to deal with soil analyses. “But I wasn’t aware at the time that the exact chemical and mineralogical composition or moisture had a direct impact on the recycling of excavated material.” Von Allmen will be moving on to the University of Teacher Education in the near future. Nevertheless, she takes something away from Péry: “The operators also offer guided tours for school classes, and I'll remember that. A plant like this clearly shows how even contaminated construction waste can be recycled after treatment.”