Recovery of EDTA from Power Plant Boiler Chemical Cleaning Wastewater

The deposition of iron oxides, metallic copper, and other impurities on boiler tube surfaces causes loss of heat transfer efficiency at electrical power plants. Hence, the tubes are cleaned every 3-5 years in order to restore the heat transfer efficiency. Chelating agents, mainly ethylenediaminetetraacetate (EDTA) and its salts, have been extensively used for the removal of metal deposits from the boiler tube surfaces. Consequently, the boiler chemical cleaning wastewater (BCCW) contains large amounts of iron, copper, and chelating agents. An electrochemical reduction process that reduces metal ions to their elemental state is tested and evaluated in order to provide the potential option to recover EDTA for reuse from power plant BCCW. Results from controlled direct current electrolysis experiments show that the electroreduction process can successfully remove metal ions from the synthetic solution and field BCCW samples and can deposit elemental metals on the cathodic plate. At a current density of 15.5 mA/cm2 and a temperature of 40°C, the percentage metal removal and current efficiency were 94.16 and 8.27%, respectively, with a cadmium cathodic plate. Moreover, results also indicate that the percentage of metal removal and overall current efficiency increase with increasing current density and temperature under the optimal condition (15.5 mA/cm2 and 40°C). The electroreduction process is able to separate metal ions from their EDTA complexes. The free EDTA can be recovered from field power plant BCCW and be reused again as cleaning agent.