The Molycorp Tolleson facility, located near Phoenix, Arizona, was originally built in 1966 by Nuclear Corporation of America (NUCOR) and was then known as Research Chemicals. 

It began as a rare earths separation plant, and, from its beginning, was one of the few places in the world that excelled in the production of a wide variety of rare earth products, including bulk metals and alloys, fabricated custom shapes, sheets, and foils, and high purity oxides and salts.

As markets for rare earth metals and alloys expanded in the 1970s and 1980s, additional vacuum induction melting technology was installed to meet this growing demand.

In 1988, Research Chemicals was purchased by Rhône-Poulenc, Inc. (RP) to expand their leadership in separated rare earths into the areas of metals and alloys. It became one of the world leaders in the production of rare earth alloys for the magnet industry, such as neodymium-iron-boron alloy and samarium-cobalt alloy. Other specialty rare earth alloys were also produced for magnetostrictive, magneto-optic, refrigerative, hydrogen storage, and battery uses. 

Additionally, the Tolleson plant's broad analytical experience with rare earth metals, alloys and compounds has made it a world leader in the field of rare earth analysis.  In 1998, RP split the company off into their newly created Rhodia division, where it became part of Rhodia Rare Earths, Inc. 

In October, 1999, Santoku America, Inc. (SAI), the North American Subsidiary of Santoku Corporation, purchased Rhodia Rare Earths' metals and alloys business.  With this purchase, Santoku Corporation's goal of establishing a rare earth metal and alloy manufacturing base outside Japan was realized.

SAI continued to uphold its leadership in the rare earths industry during these transitions, and still do to this day, although the rare earth oxides and salts business that it specialized in for many years remained with Rhodia after the sale of the Phoenix plant in 1999.

In April 2011, Molycorp, Inc., through its subsidiary, Molycorp Minerals, LLC, acquired SAI.  Molycorp changed the name of the company to Molycorp Metals and Alloys, Inc., to better reflect its new U.S.-based ownership and its access to one of the world's richest rare earth ore deposits at Molycorp's Mountain Pass rare earth mine and processing facility.  Today, we refer to the facility as Molycorp Tolleson.