Sofia-based Harmonee 2012 won a public auction for 50% of indebted lead and zinc smelter OTZK.
The firm offered to pay 8.6 million levs ($5.7 million/4.4 million euro) in the auction on Friday in which the starting price was set at 8.3 million levs, the state-run Bulgarian National Radio (BNR) reported.
The assets put up for sale last month cover an area of 162,000 square metres.
In addition to Harmonee 2012, bids in the tender were placed by First Investment Bank (FIBank) and Finance&Consulting.
The sale aims to repay part of OTZK debt to creditors estimated at more than 300 million levs.
Visiting the plant on Saturday, prime minister Boiko Borissov told workers that it will start operations shortly, BTA reported.