a process is provided for the recovery of one or more useful products including fertilizer , animal feed supplements , iron oxide , magnesia , salt , purified brine , and purified water from brines . the source of the brines can be oil and gas field wastes , seawater or effluent from a seawater desalination plant , or other inland brine sources . iron and magnesium are initially precipitated from the brine . then phosphoric acid is added to the brine followed by an alkaline agent to produce precipitates useful as fertilizer and animal feed supplements . the remaining salt in the brine may then be removed and recovered along with purified water .