Blackstone Inc. (NYSE:BX) is set to buy out International Gemological Institute (IGI), from China's Fosun International Limited (SEHK:656), Founders Lorie family and other small shareholders at an enterprise value of $500 million-$550 million, two people directly aware of the development said. IGI has $150 million of debt. The world's largest private equity firm is expected to sign a binding agreement with Fosun and IGI's other shareholders in Europe soon, maybe as early as this weekend.