Barium compounds are important chemical materials obtained from barite. Barium slag (BS) is an insoluble alkali residue derived from the product of barium compounds following the process of carbothermal reduction and water/acid leaching. In this study, two BS-derived samples named BS-YP and BS-ZN were characterized using analytical methods of XRF, ICP-MS and XRD. The environmental impacts of both BS residues were assessed. From the data of corrosivity and extraction toxicity test, the extraction solutions of BS-YP and BS-ZN residues had barium concentrations as high as 1285 and 1325 mg/L, respectively, much higher than the limit value (100 mg/L for barium) for hazardous materials, and both were identified as hazardous materials. To address this issue, acid industrial waste phosphogypsum (PG) was proposed to neutralize BS residues and to immobilize barium ion due to the slightly soluble sulfate included. It is demonstrated that with the ratios of 10:1–20 (BS:PG), the barium concentration can be lowered to <2 mg/L in both BS residues.