Use of alumina sludge arising from an electrocoagulation process as functional mesoporous microcapsules for active corrosion protection of aluminum

Abstract

The process of fluoride removal from underground water using the electrocoagulation technique with aluminum electrodes results in the generation of large amounts of drinking-water treatment sludge (DWTS) corresponding to electrocoagulated metal hydroxide sludge (EMHS). EMHS, hazardous for the environment, must be adequately managed from the water treatment plant, causing an additional cost to the process and an environmental impact from its disposal. In this study, the revaluation of the EMHS produced using a laboratory scale electrocoagulation reactor with aluminum electrodes was investigated for the manufacture of mesoporous alumina microcapsules (MAMs). The obtained microcapsules have been characterized using X-ray diffractometry (XRD), scanning electron microscopy (SEM), zeta-potential measurement, thermal gravimetric analysis (TGA), and Brunauer-Emmett-Teller (BET) techniques, allowing them to be classified as mesoporous particles of micro and nanometer dimensions. These particles were used as microcapsules to contain corrosion inhibitors (namely, 8-hydroxyquinoline and benzotriazole), and they were subsequently dispersed in a commercial polymer matrix employed to protect aluminum from the corrosive attack of the environment. The corrosion resistance of the resulting functionalized coatings has been characterized by electrochemical impedance spectroscopy (EIS) in the case of artificially-defective coatings, demonstrating that these MAM's released locally the corrosion inhibitor to effectively heal the damaged area of the metal. The overall study demonstrates that the electrocoagulation sludge can be employed to produce microcapsules for efficient anticorrosion protection of engineering metals.