Solutions of certain metal cyanides can be treated with a new, four-step process described here. First, the cyanide complexes are concentrated by anion exchange. Second, they are eluted with acid to release small amounts of prussic acid (HCN). Third, the prussic acid is removed with a hollow fiber gas membrane. Fourth, the metal ions released in this way are removed by cation exchange. The prussic acid removal is rapid, so the amount of acid present at any given time can be small while the amount of solution treated per time can be large. Data given here show how the process works and elucidate the mechanisms involved.