## 1 Introduction
Until the 1950s, the residues in dried form in quantities of about 3000 t/y were returned to the ironworks as iron containing residues. From the 1950s different approaches tried to make the iron content of the red mud usable for the steel industry. Rotary kiln process for the processing of red mud to obtain sintered iron ore was developed by Krupp. However, the high content of alkali and the low concentration of iron oxide made the process not sustainable. The endeavor to make the iron content of the red mud usable was further pursued by other companies. In example, through a variant of the Halomet process (developed for continuous liquid titanium production [31]), direct reduction was achieved with a threefold carbon excess in the form of lignite dust, whereby a drop-shaped deposition of the metallic iron was achieved. The slag still containing 20% carbon could be separated by sieving from the iron. However, the decisive question was whether or not this procedure can compete economically with conventional ones. Further attempts were conducted by the Lurgi company in 1963, through enrichment experiments using the method of magnetic roasting. The residues were treated at 750 \({}^{\circ}\)C with a CO/CO\({}_{2}\) mixture, then ground and separated by wet magnetism. This resulted in a highly enriched fraction with about 52% iron, but their proportion was so low that the iron output in the concentrate was only 20% to 25%. A variant of this process was implemented by Giulini GmbH [32]: the drying and sintering of the red mud takes place with the addition of waste coal in rotary kilns, with partial reduction of the Fe\({}_{2}\)O\({}_{3}\) to the metallic iron. A subsequent smelting and the residual reduction of the sinter is achieved in the hearth melting furnace; the final products are pig iron and granulated slag. The prerequisite for the application of this method is a 45% Fe\({}_{2}\)O\({}_{3}\) content of the starting material. The process was developed to industrial maturity but stopped for economic reasons. Red mud as such could be actually used in the manufacture of ceramic materials such as tiles, bricks and insulating materials due to its clay-like structure, however the residue must be thoroughly washed and dried prior to use, increasing the cost of the recycling process [2; 8; 33]. Other attempts have been made for the production of Al\({}_{2}\)O\({}_{3}\)-Fe\({}_{2}\)O\({}_{3}\) ceramic fibers [34]. Very recently, a group of designers started the production of ceramics made by red muds that can be used to make design objects like plates, bowls, and vases (the pieces are now undergoing certification for food safety and non-toxicity) [35]. Also, the chemical industry has made attempts to use bauxite residue as a pH modifier in the heap leaching of gold ores, in the removal of sulfur compounds from kerosene oil, and the hydrogenation of anthracene, coals, and aromatic compounds [3; 36; 37; 38; 39; 40; 41]. Finally, in agriculture red mud have been used for wastewater treatment [42; 43; 44; 45; 46; 47]. Unfortunately, despite this ongoing research, economic uses for bauxite residue are virtually non-existent. In this work a novel attempt is presented, employing the red muds from Portovesme (Italy) as a raw material for the production of iron-based secondary raw material (Direct Reduced Iron (DRI) or cast iron). Unlike what has been proposed in the literature [26; 48; 49; 50; 51; 52], red mud reduction will be carried out by exploiting another sub-product of the steel industry, the blast furnace sludge as a reducing agent. Blast furnace sludge has proven to be able to replace carbon coke in the reduction of steelworks dust, zinc, blended iron ore, and jarosite [53; 54; 55; 56; 57], thanks to the residual content of unburnt coke [53]. To determine the correct ratio of red mud/blast furnace sludge; the reducibility of the red mud is evaluated using graphite in different proportions.