Electric arc furnace dust as coating material for iron ore pellets for use in direct reduction processes

Abstract

Disclosed are coating compositions and methods for their use, comprising 90 wt. % electric arc furnace dust based on the total dry weight of the coating composition. The electric arc furnace dust includes at least 40 wt. % of Fe 2 O 3 and at least 30 wt. % of CaO and CaCO 3 combined, based on the total dry weight of the electric arc furnace dust.

1 . A coating composition comprising:
 (a) at least 90 wt. % of electric arc furnace (EAF) dust based on the total dry weight of the coating composition, wherein the electric arc furnace dust comprises greater than 40 wt. % of iron (III) oxide (Fe 2 O 3 ) and greater than 30 wt. % of calcium oxide (CaO) and calcium carbonate (CaCO 3 ) combined, based on the total dry weight of the electric arc furnace dust; and   (b) at least one binder material selected from a clay material or a cement material or both.   
     
     
         2 . The coating composition of  claim 1 , wherein the electric arc furnace dust comprises at least 20 wt. % CaCO 3  and at least 10 wt. % CaO. 
     
     
         3 . The coating composition of  claim 2 , wherein the electric arc furnace dust comprises 45 wt. % to 60 wt. %, preferably 50 wt. % to 55 wt. % Fe 2 O 3 , 20 wt. % to 30 wt. %, preferably 23 wt. % to 27 wt. % CaCO 3 , and 10 wt. % to 20 wt. %, preferably 12 wt. % to 17 wt. % CaO. 
     
     
         4 . The coating composition of  claim 3 , wherein the electric arc furnace dust comprises 50 wt. % to 55 wt. % Fe 2 O 3 , 23 wt. % to 27 wt. % CaCO 3 , and 12 wt. % to 17 wt. % CaO. 
     
     
         5 . The coating composition of any one of  claims 1  to  4 , further comprising 0.5-5 wt. % of MgO and 0.5-5 wt. % of SiO 2  relative to the total dry weight of the coating composition. 
     
     
         6 . The coating composition of any one of  claims 1  to  4 , which is substantially free of zinc, chromium, manganese, lead, nickel, sodium and potassium. 
     
     
         7 . The coating composition of any one of  claims 1  to  4 , which is substantially free of reducing agents comprising ferrous chloride and/or ferrous sulfate. 
     
     
         8 . The coating composition of any one of  claims 1  to  4 , wherein the coating composition is a granular powder having an average particle size of 1-20 μm. 
     
     
         9 . Iron ore pellets comprising:
 an iron ore core;   a first coating comprising at least one selected from the group consisting of bauxite, bentonite, and dolomite; and   a second coating comprising the coating composition of any one of  claims 1  to  9  in an amount of at least 90% based on the total dry weight of the second coating,   wherein the first coating is disposed between a surface of the iron ore core and the second coating.   
     
     
         10 . The iron ore pellets of  claim 9 , wherein the average diameter or average longest length of the pellets ranges from 5-20 mm. 
     
     
         11 . The iron ore pellets of  claim 9 , wherein the iron ore pellets comprise from 0.05-2 wt. % of the first coating relative to the total weight of the iron ore pellets and from 0.05-2 wt. % of the second coating relative to the total weight of the iron ore pellets. 
     
     
         12 . The iron ore pellets of  claim 9 , wherein the first coating covers greater than 75% of the surface of the iron ore core and the second coating covers greater than 75% of the surface of the first coating. 
     
     
         13 . The iron ore pellets of  claim 9 , wherein the average thickness of the first coating is 50-150 μm and the average thickness of the second coating is 50-150 μm. 
     
     
         14 . The iron ore pellets of  claim 9 , wherein the first and second coating reduce the formation of agglomerated iron ore pellets at temperatures in the range of 20° C. to 1100° C. compared to a substantially similar iron ore pellet without the first coating, the second coating, or both coatings. 
     
     
         15 . A process for manufacturing iron ore pellets, the process comprising:
 applying a first coating as a slurry comprising at least one selected from the group consisting of bauxite, bentonite, and dolomite in an amount of 10-30 wt. % based on the total weight of the slurry to an iron ore core to form a coated iron ore core coated with a first coating; and   applying a second coating as a slurry comprising the coating composition of any one of  claims 1  to  8  in an amount of 10-30 wt. % based on the total weight of the slurry to the coated iron ore core to form the iron ore pellets coated with the first coating and the second coating,   wherein the second coating is applied as a slurry comprising a solid concentration of 0.25-5 kg of the coating composition per ton of coated iron ore cores.   
     
     
         16 . The process of  claim 15 , further comprising determining a clustering index of the iron ore pellets in accordance with ISO 11256 to evaluate the quality of the iron ore pellets as a feedstock for a direct reduction process. 
     
     
         17 . The process of  claim 15 , wherein the iron ore pellets have a Midrex standard requirement of 0% agglomerated pellets with a longest length of greater than 25 mm relative to the total weight of iron ore pellets after 10 or fewer tumbling revolutions. 
     
     
         18 . A process for manufacturing reduced iron pellets, the process comprising:
 applying a first coating comprising at least one selected from the group consisting of bauxite, bentonite, or dolomite to an iron ore core to form a coated iron ore core;   applying a second coating comprising the coating composition of any one of  claims 1  to  8  to the coated iron ore core to form iron ore pellets;   feeding the iron ore pellets into a reduction furnace; and   reducing the iron ore pellets with a reducing gas at temperatures up to 1100° C. to form reduced iron pellets.   
     
     
         19 . The process of  claim 18 , wherein the first coating is applied to the iron ore core as a slurry comprising 10-30 wt. % of bauxite, bentonite, or dolomite based on the total weight of the slurry, the second coating is applied to the coated iron ore core as a slurry comprising 10-30 wt. % of the coating composition based on the total weight of the slurry, and wherein the second coating is applied as a slurry comprising a solid concentration of 0.25-5 kg of the coating composition per ton of iron ore pellets to be coated.