Bis(aminophosphine) diselenides as chemosensors for heavy metal cations: An electrochemical, spectroscopic and theoretical study

Validation of a combined Fe(III)/UV/NaOH process for efficient removal of carboxyl complexed Ni from synthetic and authentic effluents

Nickel, massively used in plating industry but detrimental to ecosystem, tends to form stable complexes with organic additives in industrial effluents. Currently, most of the available processes aim at water decontamination from free toxic metal ions and thus, could not effectively remove nickel-carboxyl complexes from water. Herein, we employed a proprietary combined process Fe(III)/UV/NaOH, namely Fe(III) displacement and UV irradiation followed by alkaline precipitation, to validate its feasibility on the efficient removal of nickel-carboxyl complexes from synthetic and authentic effluents. Fe(III)/UV/NaOH outperformed other commonly used processes including NaOH precipitation, UV/NaOH, Fe(III) coagulation, and Fenton/NaOH. Each unit of the combined process was optimized, and the underlying mechanism was elucidated. Fe(III) displacement favored the stoichiometric release of free nickel ions and formation of Fe(III)-carboxyl complexes, which could be decarboxylated via ligand-metal charge transfer under UV irradiation. The precipitation unit aims at simultaneously removing the released Ni along with Fe species. Attractively, the presence of other organic species (ethylene glycol, ethyl acetate and humic acid) and anions (chloride and sulfate) exerted very slight effect on the final Ni removal, whereas greatly adverse effect occurred on the Fenton process under similar conditions. The feasibility of the combined process was validated by testing on an authentic electroplating effluent, resulting in the residual Ni below 0.1 mg/L, the most stringent discharge standard for Ni in electroplating effluent in China.