Geopolymerization of granulated Cu-Ni slag, mechanically activated in air and in CO2 atmosphere (P = 10(5) Pa) was studied by XRD, SEM-EDXA, FTIR, TEM, and isothermal conduction calorimetry. Mechanical activation of the slag was carried out in a centrifugal-planetary ball mill for 10 min. Geopolymer samples were prepared by mixing of the mechanically activated slag with sodium silicate solution (with molar ratio SiO2/Na2O = 1.5) and curing at 20 +/- 2 degrees C under relative humidity of 95 +/- 5% for up to 360 days. Mechanical activation of the slag in CO2 resulted in higher compressive strength of the geopolymer samples in comparison to mechanical activation in air. Compressive strength for the geopolymer samples prepared using slag mechanically activated in air was 50.5, 74.6, 81.1, 82.8, and 89.5 MPa, after curing for 1, 7, 28, 150, and 360 days, respectively. The same values for the geopolymer samples prepared using slag mechanically activated in CO2 were 53.8, 77.4, 94.4, 106.0, and 119.0 MPa, respectively. Higher compressive strength of the geopolymer samples prepared using slag mechanically activated in CO2 was attributed to higher reactivity of the slag particles during geopolymerization induced by chemisorption of carbon dioxide molecules in the form of distorted carbonate ions in the course of mechanical activation. (C) 2012 Elsevier B.V. All rights reserved.