Rejeitos da indústria de polpas aplicados como inibidores de corrosão do aço carbono em meio ácido

Abstract

Corrosion is a topic of general interest to humanity, and the need to reduce metal maintenance and prevention costs has prompted studies on environmental and toxicologically safe corrosion inhibitors, notified because most inhibitors used in the industry are toxic. This research aims to investigate the use of aqueous extracts of vegetable tailings of the fruit pulp industry for its inhibition capacities of corrosion processes of carbon steel 1020, using various electrochemical techniques. The aqueous extracts tested as inhibitors of corrosion of carbon steel in HCl 0.1 mol L-1 were obtained from industrial residues of the following fruits: guava, pineapple, orange, mango, lemon, sugar cane, apple, passion fruit, eggplant, tamarind and cucumber. The corrosion inhibition tests were performed by dissolving 1 g L-1 of one of the extracts in the solution. The initial screening was carried out by means of the electrochemical impedance spectroscopy and the results revealed that all extracts inhibited the corrosion of the 1020 carbon steel with the inhibition efficiencies varying from 60% up to 94%. Next, the 4 extracts that had the highest inhibition efficiencies, extracted from tamarind, passion fruit, cucumber and eggplant, were selected for further corrosion studies. Weight loss experiments showed that these extracts had inhibition efficiencies varying from 79.64% up to 88.31% with the following decreasing order: cucumber > tamarind > passion fruit > eggplant. In addition, the corrosion inhibition efficiencies obtained from the potentiodynamic polarization curves were about 93% for the 4 selected extracts. Eggplant and passion fruit extracts were also isolated, obtaining corrosion inhibition efficiencies of 98% for chlorogenic and 88% for tryptophan for both compounds, indicating that these efficiencies are related to these isolated compounds, respectively. It is concluded, since that chlorogenic acid (a polyphenol) and tryptophan do not present any harmful potential to human health and the environment, that these compounds can be used as eco-friendly corrosion inhibitors for 1020 carbon steel electrode in 0.1 mol L-1 HCl acidic médium.