DIVALENT CATION CU-PB-ZN SOLUTIONS AND THEIR MIXTURES TREATED BY METALLIC ELECTRODEPOSITION ON PENCIL GRAPHITE ELECTRODES.

Buenos Aires

Congreso; 11th World Congress of Chemical Engineering.; 2023

The presence of heavy metal ions in the water streams is a relevant issue to considerer by public and governmental policies and is a crucial factor for the development of industrial processes [1]. Lead and zinc are toxic substances for human beings when they rise their bioavailability in water and can build up in the food chain. Even though, copper and zinc ions are essential for metabolic activities. Copper ions are also antiseptic and can affect water and soil biodiversity [2]. The aim of this work is to study the decrease in the initial concentration of divalent cation solutions and their mixtures to innocuous levels by means of metal electrodeposition on pencil graphite electrodes. An open 1 L reactor at room temperature and with magnetic stirring was used for electrodeposition in a 2-electrode cell from synthetic solutions of the individual cations and their mixtures. Cu(II), Pb(II) and Zn(II) synthetic solutions containing 1; 5 and 10 mg/L were prepared by dissolving the corresponding nitric salts (Merck) in deionized water (Mili Q). Potassium nitrate 0.1 M was used as electrolyte. Working electrodes were 3B and 3H pencil graphite leads (KOH-I-NOOR, Austria), diameter 0.22 cm; counter electrode was a coiled Platinum Wire Electrode (BASi) of 0.18 cm2. Distance between electrodes in a parallel arrangement was 1.5 cm. The applied voltage was constant at 30 V for 40 minutes, with a current density between 0.20-0.25 A/cm2. Samples of the supernatant solution were taken at regular times, during the metal electrodeposition, in order to quantify the decrease in the concentration of the cations under analysis. The remaining concentration of the cations was determined by atomic absorption spectroscopy, reporting the results as a percentage decrease for each metal. The surface of the working electrodes used in the different tests was analyzed by scanning electron microscopy with an energy dispersive spectrometer (SEM-EDS) to determine the morphology and chemical composition of the deposits. Therefore, it was concluded that a 100% cation removal is reached within a few minutes, obtaining meta electrodeposits with a high purity degree. A greater fragility of the working electrodes was observed at the end of the process when using 3B graphite, compared to those of 3H graphite.