30 Research rare earths from the mined ore and separate them from each other, enormous amounts of rock are moved, ground, and treated with toxic chemicals and highly concentrated acids, which leaves the mining areas permanently polluted. Enormous losses from mining to production The coveted europium — like all rare earth elements — comes primarily from China and Brazil, although there are also deposits in the U.S., Australia, and some European countries. "At every stage, from mining to processing, production of components to recycling of rare earths, we have enormous losses that we really cannot afford anymore. Mining, in particular, often destroys landscapes and the environment extensively," knows Vinzenz Brendler, head of the Department of Thermodynamics of Actinides at HZDR's Institute of Resource Ecology. The processes involved in ore beneficiation, further processing, and reprocessing can only be made more efficient and compatible based on sound and reliable data regarding the chemical behavior of these elements. Data expert Brendler and his colleague Norbert Jordan have therefore designed a major study on europium and enlisted the support of partners: experts from the Paul Scherrer Institute (PSI) in Switzerland and from repository safety research in Sweden. Their results are now available in a structured database and accessible to everyone. Europium: known for its luminescence Discovered in 1901, europium is, along with americium, the only element named after a continent. With a density of 5.24 grams per cubic centimeter, it is a lightweight among the heavy metals. It has a silvery sheen but tarnishes immediately upon contact with air and is highly reactive. In aqueous solutions or with acids, it can react to form complex compounds. At temperatures above 150 degrees Celsius, it spontaneously ignites. Its physical properties make europium particularly valuable, in fact, for some applications, even indispensable: It glows intensely red when exposed to light of a particular wavelength. In the past, europium was used in the red pixels of cathode screens for color televisions; today, it makes light-emitting diodes glow, is needed for medical imaging processes, and its fluorescence makes banknotes counterfeit-proof. For this purpose, it is incorporated into host lattices made of metallic or semiconducting elements and, depending on the environment, can also glow in colors other than red. Europium is also used as an additive in catalysts, magnets, alloys, and glass — or as a strong neutron absorber in the control rods for nuclear reactors. The annual global production volume is around 400 metric tons of europium oxide. This seems small compared to production quantities of other raw materials, but since bastnasite is composed of only 0.1 percent of the element, large amounts of overburden containing environmentally harmful components are produced. "Many believe that the chemical and thermodynamic properties of europium are very well known, but this is not the case, even though more publications on europium exist than on any other rare earth element," explains Norbert Jordan. For example, more than 50 publications on the behavior of europium with sulfate in aqueous solution can be found. After a thorough review, however, only the data from eight of these papers proved to be reliable. 120 years of publications evaluated More than ten years ago, Jordan had already begun to question results from older publications on europium critically. Since then, he has continued to work on this topic in a small team, but more or less on the side. Only when he succeeded in acquiring funding did the europium project gain momentum. Now Jordan and Brendler, together with their cooperation partners, have reviewed all major publications — no less than 350 references with 1,430 values — from scientifically recognized journals published between 1901 and 2021. "Publication culture has changed a lot during this large timespan; moreover, we also included publications in Russian and Chinese and evaluated them with the help of native-speaking colleagues," Jordan explains. About half of all the data come from 1960 to 1980. "For the more recent publications, we often contacted the research groups if something was unclear to us," the chemist continues. At the same time, he emphasizes the quality of some of the publications, which illustrate in detail how the results were obtained. But that was not always the case: "Sometimes it took us days to understand a paper because important information was missing. Other times, the results presented were unlikely or contradictory." In some cases, Jordan repeated the experiments in his own lab. "For example, the results on the complexation of europium with phosphate that we found in the literature were incorrect. We therefore obtained accurate data in the lab that can now be used to improve processes," Jordan reports. In the presence of chloride in aqueous solutions, europium also behaves quite differently — it does not react as strongly as claimed, but on the contrary, rather weakly. Computer simulation instead of trial and error The new findings on the chemical and physical behavior of europium in different environments are much needed. Until now, many technological processes for extracting and processing europium have been based on estimates and experience. With reliable data, chemical reactions could be simulated in advance on a computer. This would help developing more environmentally friendly methods or improve e-waste recycling processes — for less mining and a viable circular economy. "We started with europium because we had extensive research data on it. However, such a database would also be necessary for the other elements in the rare earth group," emphasizes Brendler. His colleague Jordan hopes the new findings will also motivate other research groups to generate