Capturing carbon dioxide (CO2) emissions is necessary for a multi-faceted approach to combating climate change. It is only one of several essential strategies, including reducing emissions at the source, enhancing natural carbon sinks such as minerals and rocks, and transitioning to renewable energy sources. This pioneering study used abundant and cheap K-feldspar mechanochemically modified with CaO for in situ CO2 sequestration during planetary ball milling. These innovative novel in situ CO2 capture experiments consisted of two simple steps. The first step involved the mechanochemical modification of K-feldspar using CaO and the subsequent second step, direct in situ CO2 sequestration in the same milling chamber during milling. X-ray diffraction patterns demonstrated the formation of the calcite phase, and elemental analysis confirmed the binding of approximately 1.69% carbon, representing a CO2 mineralization ratio of 6.05% after 60 min of milling with CO2 gas. Infrared spectroscopy, and thermogravimetric analysis equipped with mass spectroscopy verified CO2 mineralization of CaO-modified K-feldspar. The morphology of the product after CO2 capture containing calcite and unreacted K-feldspar was monitored by scanning electron microscopy.