Accelerated de-chelation of EDTA-metal complexes: A novel and versatile approach for wastewater and solid waste remediation

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Industrial waste, including wastewater and solid waste, often contains toxic heavy metals that necessitate extraction and separation prior to safe disposal or reusing them. Sewage sludge incineration ash (SSIA), a non-incinerable waste, holds significant amounts of heavy metals such as iron, zinc, copper, nickel, chromium, and lead. Recovery and reuse of heavy metals from SSIA and further application of treated SSIA sludge remain challenging. Ethylenediaminetetraacetic acid (EDTA) is widely used for heavy metals chelation in different applications. While its chelation with heavy metals is rapid and easy to achieve, the de-chelation of the metal complexes is otherwise slow (∼3 days) and challenging due to their high stability constants. In this study, we investigate the recovery of heavy metals from SSIA through chelation using EDTA, and develop, for the first time, a method to rapidly de-chelate the EDTA-metal complexes through the facile chilling process (1 – 3 h) that accelerates the separation of EDTA and metal ions. A sequential precipitation of high-purity heavy metals from the EDTA-metal complexes was demonstrated with and without de-chelation. This novel and versatile method allows the separation of many valuable compounds from the treated SSIA, including regenerated EDTA, potassium hexafluorosilicate, iron phosphate, iron(III) hydroxide, iron silicate, titanium phosphate, calcium phosphate, copper(I) thiocyanate, nickel bis(dimethylglyoximate), lead(II) sulfate, and zinc sulfide. This approach opens doors for more sustainable waste management and the recovery of valuable resources from industrial waste.