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In Northern Chile, large amounts of highly corrosive solutions are currently generated in the process of cathode washing after completing the electrowinning or electrorefining process of copper. This study investigates the electrochemical behavior of ASTM A36 carbon steel in pregnant-leach-solution (PLS) wash water. Measurements of electrochemical impedance spectroscopy and linear sweep voltammetry, complemented with weight loss measurements, were performed. Four ratios of PLS containing reverse osmosis (RO) water are evaluated, considering both quiescent and rotating conditions of the steel specimen. The results indicate that oxygen reduction, hydrogen evolution, and iron oxidation reactions are all involved during the corrosion of carbon steel in pure RO water, with the corrosion rate increasing up to 4 times under rotating conditions. In the case of corrosion in RO wash water containing PLS, a galvanic process occurs whereby copper is reduced at the expense of iron oxidation, superimposed on former partial reactions. The deposited copper induces notable corrosion inhibition of steel, observed as a significant drop in corrosion rate from high initial to constant residual values. Morphological and X-ray analyses support that corrosion is affected by oxide layer formation and galvanic copper deposition, confirming the results obtained from electrochemical analysis and weight loss measurements. [ABSTRACT FROM AUTHOR]

In the present study, the activity of extracts obtained from the stems of two endemic species of the central–northern region of Chile (Eulychnia acida [Copao] and Echinopsis chiloensis [Quisco]), was evaluated as potential corrosion inhibitors for carbon steel in 0.1 M HCl. The total content of phenols and flavonoids in the extracts was determined, and the main components were identified by high‐performance liquid chromatography–mass spectrometry, being similar in both species. The inhibition efficiency of extracts was evaluated by mass loss measures, Tafel polarization curves, and electrochemical impedance spectroscopy. The assay results showed similar values in inhibition percentages, around 88% at extract concentrations of 1,500 ppm. The adsorption on the steel surface followed the Langmuir model adsorption isotherm, whose thermodynamic parameters (ΔG°ads for Copao and Quisco, −17.81 and −17.70 kJ/mol, respectively) suggest a physisorption mechanism. The scanning electron microscopy analyses showed that in the presence of the extracts, the surface of the steel is covered by a thin film that allows the sanding marks to be visualized; while without the extracts the surface is rough due to the HCl corrosion effect. [ABSTRACT FROM AUTHOR]

The implementation of corrosion engineering control methods and techniques is crucial to extend the life of urban and industrial infrastructure assets and industrial equipment affected by natural corrosion. Then, the search of stable and environmentally friendly corrosion inhibitors is an important pending task. Here, we provide experimental evidence on the corrosion inhibitory activity of aqueous extracts of Skytanthus acutus Meyen leaf, a native plant from the Atacama Desert in northern Chile. Skytanthus extracts as a powder should be prepared at 55 °C to avoid thermal decomposition and loss of corrosion inhibitory activity. Corrosion of carbon steel AISI1020 immersed in 0.5 M NaCl was evaluated in the presence of different doses of Skytanthus extract by complementary and simultaneous linear polarization, electrochemical impedance spectroscopy, and weight-loss technique under high hydrodynamic conditions. Mixed Potential Theory was applied to confirm the electrochemical activity of the extract inhibitory capabilities. The Skytanthus extracts reached a 90% corrosion inhibitory efficiency when tested at 100 to 1200 ppm in a time span of 48 h, through an electrochemical interaction between the extract inhibitor component and the carbon steel surface. The corrosion inhibition activity observed in Skytanthus dry extracts involves a protective film formation by a mechanism that includes an iron dissolution at the expense of either oxygen reduction and/or hydrogen evolution, followed by a ferrous-ferric iron cycling, the formation of an iron complex and adsorption to the metal surface, and, finally, desorption or degradation of the protecting film. The water-soluble plant extract was subjected to HPLC-MS analyses that rendered 14 major signals, with quinic acid, protocatechuic acid, chlorogenic acid isomers, vanillic acid hexoside, and patuletin 3-methoxy-7-glucoside as the most abundant components. Then, we propose that a phenolic derivative is responsible for the corrosion inhibitory activity found in Skytanthus extracts. [ABSTRACT FROM AUTHOR]