Cr2S3->Cr2(SO4)3->Cr(OH)3->Na3[Cr(OH)6]->NaCrO2->CrCl3
Cr2S3 + 3 H2SO4 = Cr2(SO4)3 + 3 H2S
Cr2(SO4)3 + 6 NaOH = 2 Cr(OH)3 + 3 Na2SO4
Cr(OH)3 + 3 NaOH = Na3[Cr(OH)6]
Na3[Cr(OH)6] = NaCrO2 + 2 NaOH + 2 H2O
NaCrO2 + 4 HCl = NaCl + CrCl3 + 2 H2O
NaCrO2 + 3 NaCl + 2 H2O = CrCl3+4 NaOH