The paper treats investigation of the desulphurization process of damped Pb-paste by Na2CO3 or NaOH. There is determined the effect of Na2CO3 (NaOH) concentration and the liquid–solid phase ratio on the process parameters (degree of desulphurization and degree of Na2CO3 (NaOH) utilization in function of the temperature and process duration). The optimum conditions for carrying out desulphurization of Pb-pastes by Na2CO3 or NaOH are determined in dependence of the used reactors (common reactor with laboratory agitator and rotary reactor of drum type). The content of inclusions in the solutions is examined with the purpose of producing sufficiently pure crystalline Na2SO4 for the industry.