Conversion of barium sulfate into barium carbonate in rare earth acid insoluble slag using low-temperature roasting with sodium hydroxide

Rare earth acid insoluble slag (REAIS) is a low-level radioactive slag that is stored in most enterprises nowadays. Because of the pressure from negative environmental consequences and stock saturation, it is imperative to reduced dispose of REAIS. In this paper, we propose a sodium hydroxide-assisted low-temperature roasting method for the conversion of barium sulfate in REAIS (approximately 25% of REAIS). And the effects of the mixing method, mass ratio, carbon dioxide flow rate, roasting temperature, and roasting time on the conversion of barium salt were investigated. The results showed that the optimized process, which included a slurry mixing with a REAIS/NaOH mass ratio of 1:1, roasting for 3 h at 425 °C, and a carbon dioxide flow rate of 3 L min⁻¹, produced more than 96% conversion rate of barium salt, 33% efficiency of sodium hydroxide, and 65% reduction rate of REAIS. The efficient conversion of barium salts in the REAIS could lead to the recovery of barium resources. This has made a significant contribution to REAIS reduction, lessening the impact on the environment and public health, and has provided a directional guideline for the reduction of REAIS emissions.