New data regarding the identification of critical raw materials recoverable from raw, processed and the waste mining industry materials from Romania

Several EU initiatives focused on renewable energy, sustainable infrastructure and green transport require a sustainable supply of a wide range of raw materials. The increase in the population and, implicitly, the increasing demand for necessary resources led to accelerated degradation of the environment, a pressing issue which the contemporary world faces. The mining activities produced huge amounts of waste, which may now become a potential secondary raw materials source that offer the potential to extract critical mineral elements of current interest. This study is intended as a historical literature data processing combined with recent analyses according to modern test methods to confirm the presence of selected critical raw materials (CRMs). The aim of the work was an integrated approach to identify the presence of Ga, In, Ge, Bi, Co and Te in ore, ore concentrates, tailing ponds and ore dumps from some Romanian historical mining regions: Apuseni Mountains (5 deposits) and the northern part of the Eastern Carpathians (Baia Mare area 2 deposits and Fundu Moldovei area 1 deposit). The consulted literature data highlighted that the tailing ponds and dumps from Romania contain a noticeable quantity of secondary resources of critical elements, respectively, an average of 2172 mg/kg Bi, 1737 mg/kg Co, 691 mg/kg Ga, 667 mg/kg In, 74 mg/kg Ge and 108 mg/kg Te in ore and 1331 mg/kg Ga, 1093 mg/kg Co, 180 mg/kg Bi, 72 mg/kg In and 35 mg/kg Ge in tailings. The overall statistics for the 2008-2018 period show a decrease in the amount of hazardous waste produced by the extractive industry in Romania. The older literature data (from about 50 years ago) for the investigated deposits was confirmed by the laboratory analysis of selected CRMs from several samples collected from known former and current mining activities. Furthermore, the optical microscopy investigations coupled with modern electronic microscopy and quantitative and semi-quantitative techniques have provided further details regarding the sample nature and constituents. High levels of Bi (35,490 mg/kg) and Sb (15,930 mg/kg) were determined in samples from Baita Bihor and Coranda-Hondol ore deposits (Apuseni Mountains), and the presence of some rare elements such as Te was also detected. The recovery of critical elements present in the mining waste significantly contributes to the transition to a circular economy that is essential for the development of a sustainable and resource-efficient economy. This study enables future research focused on the recovery of critical elements present in the mining waste, with benefits for the environment, economy and society.