Mechanism study on the effect of H2O2 on spray pyrolysis of MgCl2 wastewater in rare earth extraction and separation process

The MgCl2 wastewater generated from rare earth extraction and separation process was treated by spray pyrolysis with H2O2 as an additive for the first time, and achieving full recycling of MgCl2 wastewater. The effect of H2O2 on the spray pyrolysis process, the kinetic of the spray pyrolysis process, and the mechanism of the effect on the activity of MgO powder were investigated. The results showed that H2O2 and the O2 produced by its decomposition had strong oxidizing property, which contributed to the removal of Cl roots. The kinetic results indicated that the rate determining step of MgCl2 spray pyrolysis was transformed from chemical reaction to diffusion process after the temperature exceeded 1023 K. The activity study indicated that the doping of Cl led to severe distortion of the MgO grains, and polycrystalline basic magnesium chloride had more defect sites too. Thus, the powder showed high activity. Moreover, the thermal decomposition rate of MgCl2 reached 99.83 %, the alkalinity of the powder reached 0.044 mol/g, and the iodine absorption value reached 131.81 mg I2/g MgO at temperature of 1073 K and amount of H2O2 addition of 1 %. Meanwhile, the high purity hydrochloric acid with concentration of 6.54 mol/L was obtained.