In this work, the effects of alkaline hydroxides (NaOH and LiOH) on the direct mechanochemical carbonation using dry high-energy milling of celestine (SrSO4) under CO2 atmosphere was investigated with X-ray diffraction (XRD), infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and carbon analyses. It was observed that SrSO4 was not directly carbonated by dry high-energy milling under CO2 atmosphere without LiOH or NaOH additives. Direct mechanochemical SrCO3 formation was observed during milling of the SrSO4 and NaOH mixture under CO2 atmosphere, and it was shown that a minimum 50% of the initial SrSO4 was mechanochemically carbonated in the presence of NaOH and CO2 gas. LiOH does not stimulate the direct carbonation. However, it was observed that washing of the milled mixture with water resulted in strontium carbonate (SrCO3) formation because of the enhanced dissolution of Li2CO3 and SrSO4, promoted by the activation effect of high-energy milling. Depending on the alkaline hydroxide used during the milling, strontium carbonates with different space group settings were formed, which have different (split or single) main carbonate absorption bands. (C) 2013 Elsevier Ltd. All rights reserved.