Process for treating a gas contaminated by at least one element selected from the group consisting of heavy metals, organic compounds, and combinations thereof, wherein a calcium-phosphate reactant (reagent) particle comprising apatite is brought into contact with the contaminated gas at a temperature of at least 30 DEG C and preferably at most 1100 DEG C. The metal(s) and/or organic compound(s) to be removed from the contaminated gas may be selected among the list of : Al, Ag, As, Ba, Be, Bi, Ce, Co, Cd, Cu, Cr, Fe, Hf, Hg, La, Li, Mg, Mn, Mo, Ni, Pb, Pd, Rb, Sb, Se, Sn, Sr, Th, Ti, U, V, Y,Zn, Zr, VOC, aromatic compounds, PAHs, dioxins, furans, or any mixture thereof. In such process, an alkaline compound particle comprising sodium bicarbonate, sodium carbonate, sodium sesquicarbonate (trona), quick lime, hydrated lime, lime stone or combinations thereof, may be further brought into contact with the contaminated gas.