Portugaliae
Electrochimica Acta

Abstract Olive mill wastewater (OMW) is the major problem from olive oil extraction, due to its polluting organic and mineral matter and acid pH. This study aims to electrochemically treat OMW in an Al electrode reactor, to oxidize the organic matter, discolor the margins and neutralize the pH, thus reducing the pollutants. Various low cost adsorbents have been studied for the treatment of different types of effluents. In this study, the potential of activated carbon (C) derived from olive stones (OS) was studied for OMW removal. H3PO4 (phosphoric acid) treated OS (AOS), as a low-cost, natural and eco-friendly biosorbent, was investigated for OMW removal from aqueous solutions. This work found that the increase in electrolysis time and current intensity significantly improved the treatment, while energy consumption and electrodes were observed. The results showed thirty-fold diluted margins for effluents with an acid pH of 5.02 and a conductivity of 14.89. The physicochemical parameters evolution during the electrocoagulation (EC) treatment showed that, under the conditions of an electrolysis time of 3 h and a current intensity of 3 A (= 416 A/m-2), the margins discoloration diluted ten times (91%), the mass loss of the electrodes was 0.55 kg.m-3 and the chemical oxygen demand (COD) reduction was 50%. These optimal operational levels allowed a good degradation of the margins. Biosorption kinetic data were properly fitted with the pseudo-second-order kinetic model. The experimental isotherm data were analyzed using Langmuir’s and Freundlich’s isotherms equations. The best fit was obtained by the Langmuir’s model, with maximum OWM monolayer biosorption capacity of 189.83 mg/g. The biosorption was exothermic in nature (entalphy change: H° = -13.11 kJ/mol). The reaction was accompanied by a decrease in entropy (S° = -72.91 kJ/mol). The Gibbs energy (G°) was higher when the temperature was increased from 303 to 318 K, indicating a decrease in the biosorption feasibility at higher temperatures. The results have established good potentiality for EC and ALS to be used for OMW removal. Keywords: OWM, phenol, OS, H3PO4, adsorption, EC, eco-friendly biosorbent, kinetics, equilibrium and thermodynamics.

Abstract The Western Central Valley (WCV) of Costa Rica is an area of interest, due to its high concentration of population and economic activity, presenting itself as a tropical monsoon-type atmospheric basin (AB), with well-defined climatic seasons (dry and rainy). The present study proposes the assessment of low carbon steel (CS) atmospheric corrosion, based on ISO 9223 (2012) and associated standards. A general analysis of the atmospheric basin effect was initially performed on these data, followed by the basic modeling of air pollutants and meteorological parameters. The WCV is an area of low contamination, which corresponds to a C2 or C3 category, according to ISO 9223. It mainly shows significant climatic seasons (dry and rainy) effects on the initial corrosion rates, but obtaining similar annual corrosion results for them. The ISO 9223 annual atmospheric corrosion model overestimated the actual obtained corrosion values, whereas linear or logarithmic models gave better results, especially when time and/or time of wetness (TOW) were considered as variables. Keywords: low CS, mathematical modeling, monsoonal climate, air pollutants, rain, TOW, ISO 9223 and ISO 9225.

Abstract The quality of the Souss-Massa Daraa (S-MD) aquifer is influenced by natural and anthropogenic contaminations. Indeed, geological formations are the main sources of mineralization in the aquifer, which compromises the potential irrigation, and threatens the sustainability of agricultural activities. In this context, hydrochemical and statistical studies were carried out on the major and secondary elements of water, based on different physico-chemical parameters, such as T °C, pH, EC (electric conductivity), NO3- (nitrate), Cl- (chloride), HCO3- (bicarbonate), SO42- (sulfate), Ca2+ (calcium ions), Mg2+ (magnesium ions), K+ (potassium ion), Na+ (sodium), Na%, Mg% and SAR (sodium adsorption ratio). The sampling was carried out in 2018, over two seasons (winter and summer), by analyzing 26 wells distributed over the studied plain. According to the water classification based on EC, it was found that 80% of the samples show very high mineralization, and 96.66% are very hard and unfit for human consumption. Also, Cl- values of most of the samples were within limits inappropriate for irrigation, but some estimated parameters, such as Na% and SAR, were within appropriate levels. In addition, according to the piper diagram, the waters are characterized by a geochemical facies of 86.66% NaCl (sodium chloride), 13.33% CaSO4 (sulphated calcium) and Mg. Thus, the principal component analysis (PCA) shows that the region waters mineralization is of natural origin. Keywords: Souss-Massa Daraa aquifer, hydrogeochemical and statistical studies, Piper and Wilcox’s diagrams, water quality, facies, and agricultural activities.

Abstract Silver (Ag) is considered as an ancient and durable precious metal that is used in different ways, due to its specific properties. The diversity of its uses has been meeting a growing worldwide demand that exceeds the Ag amount extracted from earth crust (primary resource), where a large part of this metal has been exploited. Due to its toxicity, environmental pollution resulting from industrial plants, and high economic value, Ag recovery from industrial plants (second resource) has become increasingly important for scientists. In this study, we focused on Ag recovery from the effluents of mirror industry. This was done by Ag electrodeposition on an aluminum (Al) electrode surface. This work aimed to study the effect of current intensity (CI), electrolysis time (ET), voltage (V) and temperature (T) parameters on Ag electrodeposition, in order to optimize them. According to the obtained results, the optimal parameters were a CI of 4 A, during an ET of 30 min, at 12.5 V, with a maximum T of 30 ºC. Scanning electron microscope (SEM) analyses showed a multilayer rich Ag deposit on the Al surface, followed by a cluster of flowers of different sizes originated from reduced Ag0. Keywords: silver, environmental pollution, Ag recovery, electrolysis and electrodeposition.

Abstract Several engineering mild steel (MS) components have catastrophically failed, due to structural defects, corrosion and wear deformation. These drawbacks have prompted a continuous MS modification, for its higher durability and efficiency. In an attempt to improve the metal performance, Ni–SiO2 (silicon dioxide), Ni–SiO2–C6H5N3 (1H-benzotriazole), Ni–Al2SiO5 (niquel + aluminum silicate) and Ni–Al2SiO5–10C6H5N3 composite films were developed on MS samples, at a constant temperature (T) of 45 ºC, and deposition time of 20 min. The coating performances were investigated by potentiodynamic polarization (PDP) technique, CERT UMT-2 multi-functional tribological testing (MFTT), high resolution optical microscopy (HROM) and high diamond pyramid indentation (HDPI). The samples were further subjected to heat-treatment, and its effects on hardness were examined. PDP study carried out in 0.5 M HCl revealed an improved anti-corrosion resistance. The hardness and wear tests showed better MS mechanical properties. Ni–Al2SiO5–10C6H5N3 coated sample had better hardness and wear resistance features that those from the other samples. HROM unveiled the particles homogeneous distribution throughout MS, with a new surface evolution. MS surface morphology and other properties was optimized by Ni–SiO2, Ni–SiO2–C6H5N3, Ni–Al2SiO5 and Ni–Al2SiO5–10C6H5N3 coatings. Comparatively, NiAl2SiO5–C6H5N3 coated MS exhibited the overall best performance characteristics, and it is thus recommended for advanced applications in petrochemical and marine industries. Keywords: wear, corrosion, MS, hardness and polarization.