Chemical Feasibility of Chlorine Dioxide as an Extractant of Transition Metals from Chelated Complexes in Wastewaters for Recycling and Reuse

In this article experimentation to establish the feasibility of a chemical reaction between free radical chlorine dioxide ClO2 and chelated complexes of Co2+, Ni2+ and Cu2+ with citric acid (C6H8O7) and ethylenediaminetetraacetic acid (EDTA, C10H16N2O8) as ligands, leading to the stoichiometric recovery of the metallic ions, is described. The procedure is one of empirical observation and discovery in the laboratory. This novel concept of the chemical-induced separation process predicated upon its ability to extract and precipitate metallic ions as insoluble metal oxides and oxyhydroxides, but not as hydroxides which are epitomized by the green hydrophilic gel Ni(OH)2 and extremely difficult to dewater. Chelation technology has many applications in industry and the wastewaters from these operations also contain a myriad of noncomplexing agents such as brighteners used in electroplating. This work explores the option of in-house recovery of valuable resources such as transition metals, recognizing that the most formidable challenge is the separation of metallic ions from the organic ligands that protect them from precipitation in alkaline environments. Simulated wastewaters are used to study this reaction, free from the interference of proprietary additives and imposed operational conditions of the commercial sectors. The near 99% recovery of cobalt, nickel and copper ions is successful. This creates the possibility of scaling up from laboratory glassware to larger reactor vessels such as a semi-batch reactor in a small pilot-plant facility. This present work is not about the production of potable water, but much expertise has been accumulated pertaining to the efficacy of chlorine dioxide as a disinfectant and some of the relevant literature deserves attention here. The "future work" section discusses process development by way of a pilot plant investigation. It must be emphasized that this technology is not developed to be applied in public sewage treatment and no such inference should be made.