Iron precipitation from zinc-rich solutions: defining the Zincor Process

The para-goethite (PG) iron removal process is one of the several precipitation processes that is utilised today to remove iron from zinc-rich processing solutions. In this paper, the para-goethite process is reviewed and compared with results obtained from a study of similar Zincor Process. The distribution of iron in the Zincor iron residue was found to be as follows: approximately 50% as a combination of schwertmannite and fenihydrite, 20% as jarosites, 25% as franklinite and trace amounts of pyrite as well as 5% of an unknown phase. This study confirmed that goethite is not present in Zincor's iron residue and that iron is mainly removed in the form of poorly crystalline, intermediate iron phases such as schwertmannite and ferrihydrite. The presence of these intermediate phases in zinc plant iron residues is proposed to be mainly a function of the specific pH profile employed during iron removal and the coprecipitation of silica. Based on these findings, it can be concluded that the Zincor Process in its current form is distinctly different to that historically considered to be the similar patented para-goethite iron removal process, as practiced at the Porto Vesme and the Pasminco Hobart hydrometallurgical zinc plants. (C) 2002 Elsevier Science B.V. All rights reserved.