Sarai Velazquez-Peña

The goal of this work is to optimize the electrochemical reduction of hexavalent chromium using synthetic solutions employing doped diamond electrodes (BDD) as a cathode material. The rate of Cr(VI) reduction was measured as a function of treatment conditions, the sludge generated in the process was characterized by SEM, EDS and XPS to provide insight into the mechanism of the reduction on the cathode material proposed. Also cyclic voltammetry was used to confirm the cathodic Cr(VI) reduction is taking place.

The goal of this work was to evaluate the effectiveness of iron and boron-doped-diamond (BDD) as cathodic electrodes on the reduction of Cr(VI) in synthetic and wastewater samples. The pH and electrolyte composition were varied, and the effect on the Cr(VI) reduction rate was measured. The optimized conditions from the synthetic water Cr(VI) reduction experimental data, were tasted on electroplating wastewater. The results indicated that both a pH of 2 and the use of NaCl as an electrolyte significantly increase the Cr(VI) reduction rate for all synthetic systems, especially the iron-BDD system. The Cr(VI) reduction rate in Fe-BDD systems was also affected by nitrate and sulfate ions. In the case of electroplating wastewater, Cr(VI) reduction by BDD cathodes was faster than with iron cathodes, achieving a complete reduction of 180 mg Cr(VI)/L in 25 min, with 40% less sludge produced. The elemental composition of sludge was analyzed using SEM/EDS and X-ray spectroscopy to confirm that iron and chromium precipitated out of the solution. The sludge had a chemical composition of (31.9%) Fe2O3, (29.6%) FeOOH, (21%) FeO, and (17.4%) FeSO4. Therefore, BDD as an electrode material effectively reduces Cr(VI) in electroplating wastewater, and can be effectively scaled up to industrial applications.

An electrochemical system was carried out for Cr(VI) reduction from a sample of electroplating wastewater using an iron-boron doped diamond and iron-iron systems and varying current intensity (0.1 and 0.2 A). Also the behavior of nitrates, sulfates and chlorides were monitored in the wastewater. Kinetic results showed a total reduction of Cr(VI) in approximately 25 minutes, however, in both systems (iron-boron doped diamond and iron-iron) the Cr(VI) reduction rate was slower than the theoretical Cr(VI) reduction curve obtained by Faraday's Law. Therefore the presence of nitrate, sulfate and chloride ions in wastewater, significantly affects Cr(VI) reduction. The results showed that iron-boron-doped diamond at 0.2 A is an optimal electrochemical system, with 99.9% efficiency of Cr(VI) reduction, which is attributed to Fe2+ ions generation by anodic electrodisolution and direct reduction of Cr(VI) at BDD surface cathode. Furthermore reduction of nitrate, sulfate and oxidation of chloride ions in the system was registered.

In this study we present the Cr(VI) reduction in synthetic wastewater using an electrochemical cell using boron doped diamond electrodes (BDD). The best conditions were found when Fe-DDB configuration was used. It is observed that when more current is applied into the electrochemical cell faster reduction rates are achieved. To confirm the experimental data, cyclic voltammetry was used and it was found that the cathodic Cr(VI) reduction is taking place.