Roasting waste calcium arsenate with charcoal powder was studied, serving the purpose of minimizing and/or reclaiming the waste by obtaining elemental arsenic of commercial value while regenerating recyclable CaO. Exploratory experiments were carried out to confirm the feasibility of the suggested process, in which elemental arsenic reaching the grade of 94.5% was obtained. Effects including roasting temperature, dosage of charcoal powder and roasting time were then investigated. The results showed that about 99.0% arsenic could be extracted by volatilization after the sample was roasted at 900 degrees C for 150 min with 14% charcoal powder, leaving the roasting residue, mainly consisting of CaO, containing arsenic as low as 0.42%. Thermodynamic calculations with respect to equilibrium compositions of the reaction system are diagramed and discussed. Attempts were made to determine and explain the mechanism by comprehensively analyzing the results of Scanning Electron Microscope-Energy Dispersive Spectrometer (SEM-EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). It was found that As (V) in the waste calcium arsenate was reduced to As (III) before its conversion into the elementary state.