CHICAGO — A green technology development company says it will acquire the site of a former 440-acre steel mill on Chicago’s Southeast Side.

Chicago Mayor Rahm Emanuel and Emerald Living on Tuesday announced that the company has agreed to buy the former U.S. Steel South Works property. City officials say preliminary plans for the site are for a mixed-use developments including up to 20,000 housing units built with environmentally friendly technology.

The mammoth South Works complex produced beams and sheets of steel for 112 years until it shut down in 1992. City officials say that under the terms of the purchase and sale agreement announced Tuesday, Emerald Living has five months to close on the sale following a period of environmental review and other required due diligence.