RE:Serbia and RTSerbia would not have issued a mining permit without an evironmental impact assessment approval. I suspect the EU will also be reluctant to offer Serbia membership without some sort of compensation to RT for their massive investment in this project.
Granted, there will not be a problem with environmental impact at Piskanja. But, who is going to buy out EV once they are awarded a mining licence? Mining companies may be reluctant to invest in Serbia in the future.