Abstract: A chelation process and apparatus for treating an acid solution, namely nitric acid photoengraving etchant, having a high concentration of magnesium and having a heavy metal contaminant produced by zinc leached during etching. The process requires adjusting pH of a batch quantity of the etch solution to a value permitting chelating to occur and mixing carbamic sodium salt hydrate chelating agent with the solution in quantity sufficient to cause precipitation from the solution of a carbamic salt compound precipitate of the contaminant, and separating the precipitate from the remaining solution by filter press for removal from the solution for safe environmental disposal. The remaining liquor is safely sewered. The apparatus is mobile for use on photoengraving premises.

Abstract: A chelation process and apparatus for treating an acid solution, namely nitric acid photoengraving etchant, having a high concentration of magnesium and having a heavy metal contaminant produced by zinc leached during etching. The process requires adjusting pH of a batch quantity of the etch solution to a value permitting chelating to occur and mixing carbamic sodium salt hydrate chelating agent with the solution in quantity sufficient to cause precipitation from the solution of a carbamic salt compound precipitate of the contaminant, and separating the precipitate from the remaining solution by filter press for removal from the solution for safe environmental disposal. The remaining liquor is safely sewered. The apparatus is mobile for use on photoengraving premises.