Arcadium Lithium (NYSE:ALTM) shares are trading higher Wednesday after the company inked a deal to be acquired by Rio Tinto. What Happened: Rio Tinto and Arcadium Lithium entered into a definitive agreement under which Rio Tinto will acquire Arcadium in an all-cash transaction for $5.85 per share, valuing the company at approximately $6.7 billion. The transaction price represents a 90% premium to Arcadium’s closing price on Oct. 4. Shares raced higher on Tuesday on reports the companies were in talks about a potential acquisition. Arcadium Lithium shares were up more than 30% Wednesday morning…