A cost-effective scalable chemical route to produce pH-responsive active colloids (ACs) is developed here. For the first time, calcium carbonate particles are half-coated with a silica layer via Pickering emulsion methodology. This methodology allows to create anisotropy on the particles' surfaces and benefit from the decomposition of the calcium carbonate in acidic media to generate self-propulsion. The coupling between the self-diffusiophoretic motion of these ACs and acid concentrations is experimentally investigated in Newtonian media via optical microscopy. With increasing hydrogen-ion concentrations, the pH-responsive colloids experience higher mean-square displacements because of self-propulsion velocities and enhanced long-time diffusivities. Because they are biocompatible and environmentally friendly, these ACs constitute a platform for advanced diagnostics, targeted drug delivery, and water/soil remediation.