DIFFUSION DIALYSIS FOR RECOVERY OF ACID FROM CONCENTRATED PROCESS SOLUTIONS - THE IMPORTANCE OF CHEMICAL SPECIATION

A diffusion dialysis process for recovery of HF and HNO3 from aluminum and iron process solutions was evaluated. A chemical speciation model was developed to interpret the results and could predict measured F− concentrations with excellent accuracy (r2 = 0.94) over an ionic strength range of 0.5-6 M, a [F−] range of 10−5-10−1 M, and in varied solution species matrices. Transfer rates of acid were related via Fick's law to differences across the membrane in the HNO3 or HF concentrations but were unrelated to the concentration gradients of individual ionic species (e.g., H+, F−, or NO3−). © 1990, American Chemical Society. All rights reserved.