Wastewater as a solvent for anticorrosive coatings to protect steel

Purpose Several studies were done to replace toxic and pollutant anticorrosive pigments and solvents with more environmentally friendly compounds. As a result, chromate and lead-based inhibitors were replaced by zinc phosphate and organic solvents were replaced by water. Besides, because of concerns related to zinc phosphate, other anticorrosive pigments were proposed. However, not many studies were done related to the use, as a solvent, of different types of water. The purpose of this study is to study the replacement of distilled water in anticorrosive water-borne paints by wastewater from cleaning paint industry utensils, from air coolers or by rainwater. Design/methodology/approach In a first step, the waters were characterized by physicochemical determinations (total solid dried, pH, conductivity, hardness) and chloride content. Besides, electrochemical tests were done on SAE 1010 steel immersed in the different waters with and without an anticorrosive pigment suspended to study the effect of water composition on substrate corrosion. Tap and distilled water were used as controls. In a second step, anticorrosive paints containing the different waters were prepared, applied and tested by electrochemical tests such as corrosion potential measurements and polarization resistance determinations and by exposure in humidity and salt spray chambers. Findings Results show that the characteristics of the water are not so relevant when they are incorporated in paints, and this fact enhances the use of wastewaters, replacing distilled water in water-borne paints. Originality/value Results of the electrochemical tests on SAE 1010 steel immersed in the different waters with and without an anticorrosive pigment suspended showed that the selected waters have different aggressiveness against steel, enhancing or diminishing the protection afforded by the anticorrosive pigment. However, once incorporated in the paint, the type of water used as a solvent is not so relevant in the coating’s protective behavior. The paints prepared by using wastewaters protected steel (until 888 h in the humidity chamber and 720 h in the salt spray cabinet) as good as distilled water anticorrosive paints; the use of these waters in anticorrosive paints could be an ecological opportunity to save clean water and reuse wastes.