Carbonation of iron-rich waste streams using chemical additives

Fayalite (Fe2SiO4) is the main component of non-ferrous metallurgical slags such as copper slags and lead slags. It is estimated that such slags are generated at about 80 Mt/y globally. Given that iron is in the ferrous state... [ view full abstract ]

Fayalite (Fe2SiO4) is the main component of non-ferrous metallurgical slags such as copper slags and lead slags. It is estimated that such slags are generated at about 80 Mt/y globally. Given that iron is in the ferrous state in fayalite, carbonation to iron carbonate (FeCO₃, siderite) may be directly achievable with no need for reducing agents. Carbonation of fayalite to siderite and silica is accompanied by an increase in solid volume. This increase in solid volume or space filling capacity can be exploited to fill porosity and as such increase the compressive strength of shaped blocks that can be used as construction material.

Similarly millions of tonnes of fine, albeit not completely pure, iron powder are being produced globally by iron and steel processing industries. Reuse and recycling of this waste is limited mainly by the fine particle size and the presence of impurities. Hence, they have to be landfilled in most of the cases.

This study describes carbonation of fayalite slag and iron-rich waste at increased temperature and CO₂ pressure. To enhance the mobility of ferrous iron and stabilize iron carbonate the effect of a range of chemical additives was evaluated. Several parts of the reaction were targeted. First, enhancement of the dissolution of fayalite and iron by addition of additives was studied. Next, the solubility of the (ferrous) iron was increased by addition of electrolytes and complexants. The reaction was followed by analysis of the pore solution composition using ICP-OES; and analysis of the solid reaction products in terms of carbonation/conversion degree using TC, XRD, TGA and SEM analyses.