Method for the recovery of minerals and production of by-products from coal ash

A method for the recovery of mineral values from ash derived from coal gasification and combustion which ash contains carbon, magnetite, cenospheres and mineral values including aluminum and iron, said method comprising the steps of:

• (a) screening said ash to provide a first carbon and cenosphere-containing ash fraction which contains the major portion of the cenospheres and carbon present in the ash as well as mineral values and a second ash fraction;
• (b) separating and recovering cenospheres from said first ash fraction to yield a mineral value and carbon-containing ash fraction;
• (c) removing and recovering said carbon from said carbon-containing ash fraction by froth flotation to separate said carbon from mineral values contained in said fraction;
• (d) subjecting the mineral value-containing ash fraction produced in step (c) to wet magnetic separation to yield a non-magnetic ash fraction and a magnetite-rich fraction;
• (e) subjecting said second ash fraction to dry magnetic separation to produce a non-magnetic ash fraction and a magnetite-rich fraction;
• (f) subjecting the magnetite-rich fraction resulting from step (e) to wet magnetic separation to yield a non-magnetic ash fraction;
• (g) combining the non-magnetic ash fractions resulting from steps (d), (e) and (f) to provide a combined non-magnetic ash fraction;
• (h) leaching mineral values from said combined non-magnetic ash fraction by countercurrent contact of said fraction with a hydrochloric acid solution, said leaching occurring at a temperature in the range of about 70.degree. to 110.degree. C. and at a pressure in the range of about 10 to 20 psia;
• (i) contacting the leach solution resulting from step (h) with an ion exchange resin for removal of iron salts from said solution to provide an iron-lean leach solution and recovering said iron from said ion exchange resin in the form of an iron oxide;
• (j) concentrating said iron-lean leach solution by removal of water contained therein;
• (k) sparging anhydrous hydrochloric acid gas at a temperature in the range of about 60.degree. to 80.degree. C. and a pressure in the range of about 10 to 20 psia through said concentrated iron-lean leach solution to precipitate aluminum chloride therefrom in the form of aluminum chloride hexahydrate and recovering said aluminum chloride hexahydrate;
• (l) washing, drying and calcining said recovered aluminum chloride hexahydrate to yield alumina;
• (m) washing leached ash produced in said countercurrent leaching step by countercurrent contact with water and recovering said washed ash;
• (n) drying said washed ash to provide an acid-leached pozzolan;
• (o) leaching mineral values from the cenospheres recovered in step (b) with an aqueous leach solution of hydrochloric acid;
• and
• (p) recovering said leached cenospheres from said leach solution, washing said recovered cenospheres and drying said recovered cenospheres.