A process for separating heavy metals from phosphoric starting material comprises the following steps: (i) heating the starting material to a temperature of 600 to 1.200° C. in a first reactor (1) and withdrawing combustion gas; (ii) using the combustion gas of step (i) to preheat an alkaline source; and (iii) transferring the heated starting material of step (i) and the heated alkaline source of step (ii) to a second reactor (20), adding an elemental carbon source, heating to a temperature of 700 to 1.100° C. and withdrawing process gas and a product stream.