A green process for producing Na2S from waste Na2SO4 through hydrogen agglomerate fluidized bed reduction of BaSO4

A green process is proposed to produce Na 2 S from waste Na 2 SO 4 through hydrogen agglomerate fluidized bed reduction of BaSO 4 . In the new process, BaSO 4 acts as the circulating medium, and the synthesis of Na 2 S from waste Na 2 SO 4 is performed via a two-step approach. First, BaSO 4 is reduced to BaS by hydrogen at high temperatures. Then, the reduction product BaS is put into the Na 2 SO 4 solution to prepare Na 2 S through the metathetical reaction. Simultaneously, insoluble BaSO 4 is regenerated by filtration and drying, and it can be reused in the reduction reaction. Experimental results showed that the looping material BaSO 4 could be reduced to a conversion rate above 80% at 900–950 °C in a conical fluidized bed by agglomerate fluidization. The introduction of Na 2 SO 4 could greatly accelerate the reduction rate of BaSO 4 , and detailed analyses of the reduction kinetics indicated that the addition of Na 2 SO 4 could strongly catalyze the reduction of BaSO 4 by reducing the apparent reaction activation energy, which was realized through the synergistic effect of Na 2 SO 4 and Na 2 S. The consumption of BaSO 4 in the reduction reaction was nearly equal to that regenerated in the metathetical reaction, and the reactivity of BaSO 4 remained almost the same as the original reactivity during multiple cycles, which indicated the strong recyclability of BaSO 4 in the new process. After dehydration treatment of the Na 2 S solution by evaporation concentration, cooling crystallization, and vacuum drying, anhydrous Na 2 S of high purity was obtained eventually. Compared to traditional coal-based reduction approaches, the new process is more environmentally friendly, highly efficient, and low-cost. • No CO 2 or hazardous gases such as H 2 S, SO 2 and NO x are emitted in the new process. • BaSO 4 /BaS acts as the oxygen carrier for the conversion of Na 2 SO 4 to Na 2 S. • In the new process, the looping material BaSO 4 /BaS has a strong recyclability. • Na 2 SO 4 –Na 2 S eutectics could accelerate the high-temperature reduction of BaSO 4 .