RESUMEN
With the continuous worsening of water pollution, the use of various collectors to remove heavy metal ions from aqueous solutions has attracted widespread attention. In this work, an acid-resistant collector, sodium acetyldithiocarbamate (ADTC) that combines acetamide with carbon disulfide was proposed for heavy metal removal. The structure of ADTC was characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance spectrometer (NMR). Flame atomic absorption spectrophotometry (FAAS) was used to detect the concentration of metal ions in the solution before and after the treatment of the chelating agents. The chelation removal efficiency are compared for different chelating agents for Cu2+ and Ni2+ in acidic aqueous solution with pH = 1-7, and compared to the chelation removal efficiency of sodium diethyldithiocarbamate (DDTC) and sodium ethyl xanthate (SEX) chelating agents. The experimental results suggest the order of the chelating ability is ADTC > DDTC > SEX for Cu2+ and Ni2+. The chelating ability of ADTC to Ni2+ is stronger than that of Cu2+. The chelating ability of the collector is greatly affected by the pH value. The ADTC has a good chelating ability in the pH range of 3-7. The molecular orbital distribution, charge and electrostatic potential surfaces in quantum chemistry are used to explore the main active sites of the chelating agent are the S atom. The results of high resolution mass spectrometry showed that the ADTC is coordinated with the positive divalent metal ion in the ratio of 2:1. According to the results, the dithioamino (-NHCSS-) groups are coordinated with the positive divalent metal ion in a 2:1 ratio. Molecular dynamics simulation is used to explore the adsorption energy and binding strength of the chelating agent on the metal surface.
RESUMEN
The deposition of CaCO3 scale in circulating cooling water on metal surface is a major concern in industry. This paper focuses on the feasibility of electrochemical methods to study the scale inhibition performance of 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) and 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA), Polyacrylic Acid (PAA), including linear sweep voltammetry, chronoamperometry, and electrochemical impedance spectroscopy (EIS). In addition, the coverage, morphology and structure of deposited CaCO3 crystal on titanium alloy surface in the absence and presence of inhibitors were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). A new method for calculating the efficiency of scale inhibitors was proposed so that it can be calculated by using the change in residual current density (ir). In order to prove the feasibility and accuracy of such method, the efficiencies of inhibitors were evaluated using ir and charge transfer resistance (Rct), respectively. In addition, molecular dynamics (MD) simulations were performed to evaluate the interaction between the scale inhibitor molecule and the CaCO3 crystal. The experimental results show that both the residual current density obtained by chronoamperometry and the charge transfer resistance obtained by electrochemical impedance spectroscopy can be used to evaluate the efficiency of scale inhibitors, and there is high consistency from the calculation results. It is also confirmed by X-ray diffraction and scanning electron microscopy studies that the presence of inhibitor reduces the surface coverage of CaCO3 at metal electrode and that the crystal structure of CaCO3 is transformed from the original aragonite into the most unstable vaterite. The best inhibition efficiency of PBTCA for CaCO3 deposit is confirmed by the results of MD simulations.
