Portugaliae
Electrochimica Acta

Mild steel corrosion behaviour in a 0.5 M hydrochloric acid aqueous medium has been studied using potentiodynamic polarization measurements and Monte Carlo calculations, in the presence and absence of (7-Amino-8-methylphenoxazin-3-ylidene)-diethylazanium dichlorozinc dichloride [known as Brilliant Cresyl Blue (BCB) - dye]. Potentiodynamic measurements indicate that this compound acts as a slightly anodic inhibitor. Monte Carlo simulation was used to understand the studied molecules adsorption ability onto a Fe(1 1 0) surface, at the molecular level. The experimental results and theoretical calculations provided important support for the understanding of the corrosion inhibition mechanism adopted by this molecule.

The technical feasibility of the continuous flow electrocoagulation process for hospital wastewater treatment was evaluated. The wastewater physicochemical characterization was performed according to the chemical oxygen demand (COD), biochemical oxygen demand (BOD), total suspended solids (TSS), naproxen, phenol and phosphates parameters. An experimental Box-Behnken design and statistical response surface methodology (RSM) were used to evaluate the simple and combined effects of the independent parameters (pH, potential, retention time), and to optimize electrocoagulation process conditions, considering the COD response variable. The removal percentage was: COD (75.5%), BOD (59.2%) phenols (80.7%), phosphates (85.3%), TSS (75.6%) and naproxen (55.7%), under optimal electrocoagulation conditions at pH (7.92), potential (40 V) and retention time (15 min). The electrocoagulation process proved to be an efficient and technically viable alternative for hospital wastewater treatment.

Atomic absorption spectroscopy (AAS) of samples taken from the organic phase of a water/1,2-dichloroethane (1,2-DCE) interfacial electrochemical cell, rendered non-polarizable by the tetraphenylarsonium common-ion, revealed significant transfer of heavy metal from the aqueous phase. Heavy metal concentration found within 1,2-DCE cannot be explained via ion pair formation between the metallic species and the common-ion, nor by ion pair formation between the metallic species and the hydrophobic anion of the organic phase. Results suggest that metal may have been anomalously transferred into 1,2-DCE within water-in-oil droplets formed by spontaneous emulsification of the interfacial region.

The presented work was pivoted on iron (II) determination in deep groundwater wells samples by using anodic stripping technique at an iodine-coated platinum electrode. The developed method was based on a preconcentration step for five min., followed by the potential scanning of an iodine-coated platinum electrode between the limit of hydrogen evolution (-0.25 V) and the beginning of iodine desorption from the electrode surface (+0.85 V). The anodic peak of the deposited iron to iron (II) oxidation was clearly centered at ca. 0.74 V. The anodic peak current showed an excellent linear response (R2 = 0.996), within an iron (II) concentration range from 1 to 100 ppm. The obtained limit of detection (LOD) was 0.26 ppm and the limit of quantification (LOQ) was 0.85 ppm. Within the iodine-coated platinum electrode potential window the possible interferences by several ions were evaluated. The developed method was examined by iron (II) concentration determination in deep groundwater wells. The statistical comparisons between the two methods showed the absence of any significant difference between the obtained Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) values and our voltammetric method results, at P = 0.05.

Metallic materials remain an indispensable element in industries. The present study is aimed at the assessment of Parinari polyandra leaves inhibition properties on mild steel in a 1 M HCl solution. This was investigated using gravimetric and electrochemical methods. Physicochemical and spectroscopic analyses of the leaves extract were done using standard methods. A yield of 19.82% was obtained, while the leaves extract FTIR spectra showed bands of 3404 cm-1 and 2926 cm-1, which indicated the presence of a strong band of phenolic O-H and C-H stretch functional groups, respectively. A maximum corrosion inhibition efficiency of 97.22% was obtained. Langmuir adsorption isotherm fitted the inhibitor data well. From electrochemical methods, the corrosion rate value of 17.626 mmpy obtained for the uninhibited mild steel was higher than 0.02044 – 2.2267 mmpy range values recorded for the mild steel surface covered with P. polyandra leaves extract in an acidic medium. SEM images showed the leaves extract inhibition effect against mild steel corrosion in a 1 M HCl solution. Electrochemical analysis using the Tafel plot also showed the leaves extract corrosion inhibition capacity, suggesting a mixed type inhibitor. Thus, P. polyandra leaves extract might act as a green corrosion inhibitor for mild steel utilized in industrial applications.