Removal of iron–cyanide complexes from wastewaters by combined UV–ozone and modified zeolite treatment

Abstract

A treatment system was developed to remove iron-complexed cyanide from wastewaters discharged by small surface finishing workshops. Alkaline chlorination, a widely used treatment method, does not remove iron–cyanide complexes and produces chlorine secondary pollution effects. In this work, the effectiveness of a bench scale system with a UV–ozone step, followed by a fixed bed made of manganese-modified natural zeolite was studied to remove potassium hexacyanoferrate(II) K4[Fe(CN)6]. The system was operated on a semi-continuous basis processing up to 7.2l batches of synthetic wastewater. The optimal residence time was established by feeding the system with a free iron solution and using a residence time distribution (RTD) model.With the employed experimental conditions, a 66% cyanide removal was observed at the UV–ozone stage. The fixed bed retained 55% of the total iron fed and an additional 5% of iron was precipitated. Cyanide removal was slightly increased by fixed bed up to 68%. This method achieved a significant removal of iron–cyanide complexes. The results were analysed by using an RTD model and a mechanism for the processes occurred was proposed. Technical and economical scaling up conditions must be studied in future works to assess the feasibility of treating wastewaters from small electroplating workshops.