Establishment of technologically feasible modes of electrocoagulation purification of wastewater from nickel ions

Abstract

The object of research is the technology of electrochemical purification of wastewater from heavy metal ions. The work, in particular, is devoted to the purification of effluents with a low concentration of the Nickel ion. The main task of the experimental research was to select the material of the electrodes and the mode of electrochemical dissolution of the anodes, under which the efficiency of wastewater purification will be maximum, as well as to confirm the practical possibility of deep purification of the specified wastewater to the standards that correspond to the maximum permissible concentrations (MPCNi=0.5 mg/dm3). It was established that in the process of electrocoagulation wastewater purification there is an induction period (10 min), during which the coagulant accumulates in the electrolyzer and the degree of purification increases sharply. As a result of an increase in the current density from 10 A/m2 to 20 A/m2, the degree of purification on iron electrodes increased from 60 to 84% for a process duration of 20 minutes. This is explained by the intensification of the anodic dissolution of the metal and the increase in the concentration of Fe(OH)3. Increasing the current density to 30 A/m2 practically does not affect the degree of purification, which is explained by the phenomenon of polarization of the anodes and is confirmed by the increase in the process voltage from 2.40 V (10 A/m2) to 12.59 V (30 A/m2). Therefore, it is impractical to increase the current density in the future. For iron anodes, it was not possible to achieve the required degree of purification (≥98.3 %), the maximum degree of purification did not exceed 85 %, and the content of Ni2+ ions in purified water exceeds the MPC by an order of magnitude. It was experimentally established that it is advisable to use aluminum electrodes for the process of electrocoagulation purification of wastewater from Nickel ions. At a current density of 20 A/m 2 and process duration of 40 minutes, the concentration of Ni2+ ions did not exceed the MPC of Ni. When using aluminum electrodes, an increase in the current density from 15 A/m2 to 20 A/m2 does not lead to polarization of the electrodes, and the process in both cases takes place at a steady state at a voltage of ~6.7 V. The technologically appropriate operating mode of the electrolyzer is chosen: aluminum electrodes at an anodic current density 20 A/m2 and the duration of the purification process – ≥40 min. The obtained results can find practical use in the design of waste water purification systems of galvanic industries.