In this work, the arsenic (As2O3) amount in colemanite ore was reduced from 4551 to 425 ppm using decrepitation. The crystal and amorphous states of products were determined by XRD measurements and the thermo-dynamic properties of samples were examined by DSC-TGA analysis. Elemental arsenic was analyzed using an ICP-ES/MS analyzer. As a result of the characterizations, a majority of the arsenic mass was found in the waste material for all temperatures. It was concluded that arsenic is carried on the surface of gangue minerals in the calcination process. Moreover, the decrepitated arsenic compounds tend to accumulate back on solid surfaces thus the amount of arsenic was found to be higher than the amount found in literature which is lower than 100 ppm. Therefore the affinity of arsenic compounds to montmorillonite and colemanite surfaces were further studied comparatively using molecular dynamics (MD) and Monte Carlo (MC) simulations. The resulting energy and density profiles show that the arsenic compounds have a higher affinity towards the montmorillonite surface. The simulation results reflect the decrease of accumulation amount on the surfaces with increasing temperature in parallel with the experimental measurements.