Recovery of sulfuric acid from a stone coal acid leaching solution by diffusion dialysis

- The acid recovery reached 71.12% under optimum conditions.
- Controlling water osmosis was more important than obtaining a higher acid recovery.
- Vanadium and other impurities were well blocked.

Diffusion dialysis was employed to recover sulfuric acid from a stone coal acid leaching solution. The dialysis coefficients of H+, V, Al, Fe, Mg, K, F, P, and S ions in a stone coal acid leaching solution for an anion exchange membrane were determined. The effects of the flow rate, flow rate ratio, and water osmosis rate as well as ion rejection on sulfuric acid recovery were investigated. The results demonstrated that the DF120-III anion exchange membrane showed a good separation performance for separating sulfuric acid from the stone coal acid leaching solution. In the diffusion dialysis process, the water osmosis rate, sulfuric acid recovery, ion rejection, water equilibrium and processing ability were taken into consideration. Controlling water osmosis was more important than obtaining a higher acid recovery. Under the optimum operating conditions of a feed flow rate of 12 mL/min and flow rate ratio of water to feed of 1-1.1, sulfuric acid recovery reached 71.12%, the water osmosis rate was controlled at approximately 14.95%, and vanadium rejection was approximately 95.50%. The rejection of impurity ions, such as Al, Fe, Mg, K, F, P, and S was approximately 99.04%, 97.37%, 98.01%, 85.12%, 98.33%, 91.16%, and 69.96%, respectively. The high rejections of F in the form of complexes and P in the form of incompletely dissociated acid were disadvantageous to the recovery of sulfuric acid. The recovered acid was able to be reused in the acid leaching process by the addition of fresh acid.