SUMMARY
      The residues of hexavalent chromium and their compounds are originated in industries such as car manufacturing, petroleum refining, surface treatment, chromat preparation, fertilizer industries and those industries which use compounds of Cr(VI) as a corrosion inhibitor. The compounds derived from Cr(VI) are very pollutant, they have an highly oxidizing effect and they are easy to penetrate biological membranes, in addition to being carcinogenic to humans and animals. 
      
      This doctoral thesis which is entlited “Treatment of solutions containing hexavalent chromium through electrocoagulation with iron anodes” is focused on the possibility of removing the hexavalent chromium from wastewaters by electrocoagulation process.

      Electrocoagulation (EC) is an electrochemical method that is simple and effective to the treatment of contaminated wastewaters from several origins presents different advantages, including environmental compatibility, versatility, performance, safety and low cost. In this process, the coagulations agents are generated because of the electro-oxidation of the Sacrificial anode, which gets dissolved due to the application of a difference of pottencial, producing active coagulations precursors. The treatment is carried out without adding any chemical coagulant or chemical flocculant. 

      The essencial purpose of this doctoral thesis is studying in detail the parameters which have an influence on the process of hexavalent chromium (Cr(VI)) removal by means of the electrocoagulation technique (EC) with iron anodes.
      
      Specifically, it is studied the effect of pH, the NaCI concentration, the reactors agitation, the applied current density, the initial Cr(VI) concentration, the electrode configuration and the number of electrodes that were used in order to remove the hexavalent chromium from wastewaters of surface treatment industries through electrocoagulation using two reactors of 1 L and    7 L capacity.
      
      On the basis of the obtained results, it can be concluded that the presence of CI- ions is necessary to carry on the removal of Cr(VI) through electrocoagulation, since apart from increasing the conductivity of the solution and, therefore, decreasing the energy, it prevents the anode passivation by hexavalent chromium and facilitates their dissolution due to pitting corrosion. Once Cl- ions are added to the solution, its concentration does not significantly influence the process of electrocoagulation of Cr(VI). Another variable that has great influence in the electrocoagulation process of Cr(VI) is pH, since the reduction of Cr(VI) to Cr(III) is favored at low pH, while the co-precipitation of iron and chromium mixed hydroxides occurs at high pH. The concentration of iron ions in solution, obtained by oxidizing the anode, increases until it reaches the pH of precipitation (approximately 3), from which the pH value continues to increase, while the concentration of iron and chromium decreases due the co-precipitation of mixed hydroxides of iron and chromium. As for the other variables, the agitation and the configuration of the electrodes do not significantly influence the electrocoagulation process, while the increase of the current density increases the specific productivity, but with more energy and lower current efficiency associated to the anodo disolution. The initial concentration of Cr(VI) only has a notable influence: the higher the concentration of the solution to be treated is, the lower the energy consumption is. Finally, the increase of the number of electrodes causes an increase in productivity; it also reduces energy consumption and increases current efficiency related to the anode disolutions.