According to the amount of HCl consumed, calculate the mass concentration of each washing solution, the quality of the recoverable NaOH (the sum of 6 times the recovery rate) of each washing and the recovery rate of NaOH and the pH of the washing solution recording solution. Using the influence of washing time and soaking time on the decal effect, at room temperature, when the liquid-solid ratio is 5: 1, after soaking in red mud for 1 day, when washing more than 5 times, it can achieve more than 95% removal of red mud Na + Experiment results are shown in Table 2