Carbonation/granulation of mine tailings using a MgO/ground-granule blast-furnace-slag binder

[Display omitted] •Mine tailings were carbonated/granulated with MgO/ground-granule blast-furnace slag.•The granules were strong and had good acid neutralizing capacities.•The carbonation conditions strongly affected the granule strength.•Curing the granules in 20% CO2 gave the strongest granules.•The robust granule structure was most likely attributed to hydromagnesite. A carbonation/granulation process for treating mine tailings using a MgO/ground-granule blast-furnace-slag (GGBS) binder was developed. The materials were mixed and granules produced using a granulator, then the granules were cured in a CO2 atmosphere. The optimum granulator rotation speed and retention time were 60 rpm and 7 min, respectively. The binder composition MgO0.5GGBS0.5 and binder: mine tailings ratio 3:10 gave the strongest granules. Carbonation generally increased the granule strength, but different CO2 concentrations, between 0.04% and 100%, changed the granule strength to different degrees. Granules cured in 20% CO2 for 28 d had a strength of 4.71 MPa, which was higher than the strengths of granules cured in other CO2 concentrations and of granules produced using Portland cement. The granules had relatively high CO2 storage capacities of 0.157–0.167 kg CO2/kg binder and good acid-neutralizing capacities (higher than the acid-neutralizing capacity of granules produced using Portland cement). The strength of the granules cured in 20% CO2 for 28 d was probably mainly attributed to the formation of hydromagnesite during carbonation. The hydromagnesite contributed dense and connected structures within the granules. The granules produced show great potential for use as aggregates for reclamation work and backfilling in mining areas.