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Recovery of iron rich residues from integrated steel making process by hydrated lime/molasses pressurised cold agglomeration

De Gisi, Sabino, Romaniello, Lea, Dalessandro, Michele, Todaro, Francesco, Notarnicola, Michele
Journal of cleaner production 2019 v.233 pp. 830-840
X-radiation, beets, briquettes, calcium hydroxide, circular economy, cold, crushing, dust, furnaces, iron, liquids, molasses, oxygen, phosphorus, recycled materials, scanning electron microscopy, slags, sludge, steel, sulfur
This study aimed at verifying the technical feasibility of recovering and reusing several iron-rich residues from the steel production process through the production of briquettes that could potentially be reintroduced as a ferrous source into the converters during the transformation of hot metal into liquid steel. An experimental investigation was carried out on a pilot-scale briquetting plant that implements a pressurised cold agglomeration; 8 mixtures, with contents varying between 60 and 66% Basic Oxygen Furnace (BOF) slag and a maximum of 27% of stock-house dusts and process sludges were tested. In the context of the circular economy, beet molasses was added in varying amounts as a binder, along with cheaper hydrated lime. Experimental results showed how each mixture of recycled materials was able to make briquettes with a high average crushing resistance (73.3 daN for the best mixture, indicated as 2b mix). The X-ray powder patterns, chemical and scanning electron microscopy (SEM) characterization of 2b mix briquettes revealed clean raw residues as well as the presence of limited amount of unwanted compounds such as phosphorus and sulphur, due to the molasses used. By adopting a replacement ratio of 1 between commercial and 2b mix briquettes, a possible safe use of 2b mix briquettes in BOF converters has been estimated. As a lesson, although other investigations need to be carried out (i.e., the reduction disintegration index assessment), briquetting has proven to be effective. It must be intended as an integration rather than a replacement of the input materials generally used in the BOF converter.