basic slag

GNU Webster's 1913

1. A by-product from the manufacture of steel by the basic process, used as a fertilizer. It is rich in lime and contains 14 to 20 per cent of phosphoric acid. Called also Thomas slag, phosphatic slag, and odorless phosphate.

WordNet 3.0

1. n. slag produced in making steel; low in silica but having large amounts of calcium phosphate; useful as fertilizer