This article presents an overview of the experimental phase equilibria studies of S-containing systems (Ni-Sn-S, Cu-Sb-S, and Cu-Sn-S) and As-containing systems (Fe-Sb-As and Fe-Sn-As). These systems improve the prediction capabilities of FactSage in a 20-component ‘Cu2O’-PbO-ZnOFeO- Fe2O3-CaO-SiO2-S-(Al2O3-MgO-CrO-Cr2O3-Na2O)-(As, Sn, Sb, Bi, Ag, Au, Ni, Co) system for complex pyrometallurgical operations during both refining and recycling. Experiments involved equilibration at predetermined temperatures (300–1200°C) with or without preheating, followed by rapid quenching in a brine. Quenched samples were then directly measured using an electron probe microanalyser. For the Ni-Sn-S system, liquid phases (NiS- and SnS-rich mattes and liquid metal) and solid phases (Ni1+xSn, SnS, Ni3Sn, FCC-Ni, Ni1-xS, NiS2, Ni3Sn4, SnS2, Sn2S3 and β-Ni3S2) were observed. A new Ni3Sn2S2 phase was found to melt incongruently. For the Cu-Sb-S system, liquid metal, matte, FCC-Cu, digenite, Sb, CuSbS2, Cu3SbS3 and Cu3SbS4 phases were observed. For the Cu-Sn-S system, liquid metal, matte, digenite, SnS and Cu3Sn phases were found at liquidus. Also, the immiscibility gaps spread from: 1. The Sn-S binary toward the Ni-rich side in the Ni-Sn-S system. 2. The Cu-S binary toward the Sb-S binary in the Cu-Sb-S system. 3. The Cu-S binary toward the Sn-S binary in the Cu-Sn-S system. The immiscibility gap in the Cu-Sn-S system is wider than in the Cu-Sb-S system. For the Fe-Sb-As system, liquid metal, FeAs2, Fe1-xSb, Fe2As, FeAs, FeSb2 and BCC-Fe phases were found. For the Fe-Sn-As system, an immiscibility gap near the Fe-Sn system was observed with liquid metal (Ferich and Sn-rich) and Fe5(Sn, As)3, Fe2As, FeAs and FeAs2 phases.