Flotation is a method of concentrating targeted minerals which uses the physical and chemical properties of the minerals along with process chemicals to separate desired minerals from remaining wastes. Typically, the mineral is entered into an acidic or basic bath of flotation agents. Depending on the type of mineral being concentrated, this bath may consist of such chemicals as sulfuric acid, chromium, phenols, zinc, ammonia, hydrochloric acid, and phosphoric acid. The wastes, including the spent process liquids, are discarded. Heavy media separation utilizes mainly organic chemicals to separate minerals using the minerals' density differences.
Electromagnetic separation uses a magnetic field to remove impurities from the target mineral.
Following is a brief description of processes used in mining crushed and broken stone, including riprap. Nearly all principal types of stone, including granite, diabase, limestone, sandstone, dolomite, and marble may be used as sources of commercial crushed stone. Stone that breaks in chunky, cubical fragments and is free of surface alteration from weathering is preferred for crushed stone. Such stone should also be free of impurities such as opalescent quartz, which may react with lime in cement and cause disintegration of the concrete in which the stone may be used. Surface mining equipment varies with the kind of stone mined, the production capacity needed, the size and shape of the deposit, estimated life of the operation, location of the deposit with respect to urban centers, and other important factors.