An Overview of Reclaimed Wastewater Reuse in Gold Heap Leaching

The intensive use of groundwater by the gold mining industry is an important sustainability concern, especially in arid and semiarid regions where groundwater is a scarce resource. Alternatives, such as water reuse, treatment and recycling, have been implemented to overcome this issue. The potential use of reclaimed wastewater in gold heap leaching, without decreasing the process efficiency, has not yet been considered. Hence, this review focuses on the physicochemical, biological, and chemical features (organic matter, microbial loads, metal ions, and anions) of reclaimed wastewater that may limit its use in gold heap leaching.     

Hydrogen production from acid and enzymatic oat straw hydrolysates in an anaerobic sequencing batch reactor: Performance and microbial population analysis

Feasibility of hydrogen production from acid and enzymatic oat straw hydrolysates was evaluated in an anaerobic sequencing batch reactor at 35 °C and constant substrate concentration (5 g chemical oxygen demand/L). In a first experiment, hydrogen production was replaced by methane production. Selective pressures applied in a second experiment successfully prevented methane production. During this experiment, initial feeding with glucose/xylose, as model substrates, promoted biomass granulation. Also, the highest hydrogen molar yield (HMY, 2 mol H₂/mol sugar consumed) and hydrogen production rate (HPR, 278 mL H₂/L-h) were obtained with these model substrates. Gradual substitution of glucose/xylose by acid hydrolysate led to disaggregation of granules and lower HPR and HMY. When the model substrates were completely substituted by enzymatic hydrolysate, the HMY and HPR were 0.81 mol H₂/mol sugar consumed and 29.6 mL H₂/L-h, respectively. Molecular analysis revealed a low bacterial diversity in the stages with high hydrogen production and vice versa. Furthermore, Clostridium pasteurianum was identified as the most abundant species in stages with a high hydrogen production. Despite that feasibility of hydrogen production from hydrolysates was demonstrated, lower performance from hydrolysates than from model substrates was obtained.     

Tribo-corrosion of materials: Interplay between chemical, electrochemical, and mechanical reactivity of surfaces

An attempt is made to link experimental potential variations noticed during tribo-corrosion tests performed at laboratory scale, with a well known mapping tool used in corrosion, namely Pourbaix diagrams also known as E-pH diagrams. Backgrounds of E-pH diagrams and electrochemical kinetics are briefly recalled. Some explanations and/or work hypotheses concerning the effect of test parameters on the potential variation during tribo-corrosion tests are presented. The complex interplay between mechanical, chemical, and electrochemical interactions during tribo-corrosion test is discussed. It demonstrates that further research towards the development of appropriate mapping tools for tribo-corrosion is most indicated.     

Influence of pH and corrosion inhibitors on the tribocorrosion of titanium in artificial saliva

Dental implants are used to replace teeth lost due to decay, trauma, or periodontal diseases. Dental implants are most of the times subjected to micro-movements at the implant/bone interface or implant/porcelain interface (due to the transmitted mastication loads) and chemical solicitations (oral environment). Such implant becomes part of a tribocorrosion system, which may undergo a complex degradation process that can lead to implant failure. In this work, the fretting-corrosion behaviour of titanium grade 2 in contact with artificial saliva was investigated under fretting test conditions. Citric acid was added to artificial saliva to investigate a pH variation on the tribocorrosion behaviour of the material. Additionally, three different inhibitors were added to investigate cathodic and anodic reactions on the electrochemical response. Also, the influence of inhibitors included in the formulation of tooth cleaning agents or medicines was investigated. Degradation mechanisms were investigated by electrochemical noise technique that provided information on the evolution of corrosion potential and corrosion current during fretting tests. Depassivation and repassivation phenomena occurring during the tests were detected and discussed. Considering the influence of corrosion inhibitors, it was observed that the degree of protection varies with the nature of the inhibitors.     

Pasteurisation of Apple Juice by Using Microwaves

Exposure of Escherichia coli to microwave treatments results in a reduction of the microbial population in apple juice. This research determined the effect of pasteurisation at different power levels (270-900 W) on the microbial quality of apple juice, using a home 2450 MHz microwave. Data obtained were compared with conventional pasteurisation (83 °C for 30 s). Apple juice pasteurisation at 720-900 W for 60-90 s resulted in a 2-4 logs population reduction. Using a linear model, the D -values ranged from 0.42±0.03 min at 900 W to 3.88±0.26 min at 270 W. The value forz was 652.5±2.16 W (58.5±0.4 °C). These observations indicate that inactivation of E. coli is due to heat.     

New Insights Leading to Improved Process Control

Composite plating may nowadays be considered as a well-established industrial technology for the synthesis of some types of composite coatings like Ni-SiC in the automotive industry. Potentialities of that composite plating process are numerous but new developments are fastidious and expensive. This paper highlights some recent progresses made in determining the forces bringing and keeping particles in the neighbourhood of electrodes and in detecting the trajectory of particles near electrodes. The last possibility opens the way to the development of an electrochemical sensor suitable for on-line process control in composite plating.     

A Kinetic Study of Furan Formation in Wheat Flour‐Based Model Systems during Frying

Furan is a possible human carcinogen, which is formed in worldwide highly consumed fried starchy foods. In order to elucidate the mechanisms responsible for its occurrence in this food category and propose techniques for its mitigation, the kinetics of furan formation, oil absorption, lipid oxidation, and color change were studied in wheat flour‐based model systems during frying at 160, 170, 180, and 190 °C up to 13 min and data were fitted to mathematical models. Additionally, an Arrhenius‐type dependency with temperature was evaluated for all studied responses. More drastic frying conditions increased significantly (P ≤ 0.05) the furan content of fried samples. Furan formation followed a sigmoid trend with frying time only for frying temperature of 190 °C (RMS_190°C: 7.6%). At lower temperatures, furan generation did not reach the asymptotic concentration level. Color change, lipid oxidation, and oil absorption increased with frying temperature and followed asymptotic relationships with frying time. For all evaluated temperatures, color change (RMS: 4.4% to 12.5%) and polar compound generation (RMS: 2.6% to 7.4%) presented good fit to a first‐order kinetic model. Oil absorption was successfully fit to a mass balance‐based model (RMS: 10.0% to 19.8%). Under the experimental conditions studied, only color change (E_A: 15.47 kJ/mol), lipid oxidation (E_A: 6.67 kJ/mol), and oil absorption (E_A: 76.98 kJ/mol) presented good fit (RMS: 0.7% to 6.3%) to an Arrhenius‐type equation. Based on our results, the keeping of frying temperature below 180 °C and the reduction of the frying time would contribute to reduce not only the final furan occurrence in fried foods but also their oil content.     

In situ modification of activated carbons developed from a native invasive wood on removal of trace toxic metals from wastewater

Activated carbons were developed by phosphoric acid activation of sawdust from Prosopis ruscifolia wood, an indigenous invasive species of degraded lands, at moderate conditions (acid/precursor ratio=2, 450 degrees C, 0.5h). For in situ modification of their characteristics, either a self-generated atmosphere or flowing air was used. The activated carbons developed in the self-generated atmosphere showed higher BET surface area (2281m2/g) and total pore volume (1.7cm3/g) than those obtained under flowing air (1638m2/g and 1.3cm3/g). Conversely, the latter possessed a higher total amount of surface acidic/polar oxygen groups (2.2meq/g) than the former (1.5meq/g). To evaluate their metal sorption capability, adsorption isotherms of Cu(II) ion from model solutions were determined and properly described by the Langmuir model. Maximum sorption capacity (Xm) for the air-derived carbons (Xm=0.44mmol/g) almost duplicated the value for those obtained in the self-generated atmosphere (Xm=0.24mmol/g), pointing to a predominant effect of the surface functionalities on metal sequestering behaviour. The air-derived carbons also demonstrated a superior effectiveness in removing Cd(II) ions as determined from additional assays in equilibrium conditions. Accordingly, effective phosphoric acid-activated carbons from Prosopis wood for toxic metals removal from wastewater may be developed by in situ modification of their characteristics operating under flowing air.     

Electrochemical investigation of the codeposition of SiC and SiO2 particles with nickel

The use of electrochemical impedance spectroscopy (EIS) for the in situ control of the electrolytic codeposition of Ni/SiO₂ and Ni/SiC was investigated. An attempt was made to clarify why silica particles hardly codeposit in comparison to silicon carbide particles. It was found that the presence of SiO₂ and SiC particles influences the metal deposition process in different ways. SiC particles that are being embedded in the growing metal layer cause an apparent decrease in the electrode surface area, probably due to blocking off a part of the surface by partly engulfed particles. In the case of SiO₂ particles, which embed in the metal matrix to a very limited extent, no blocking was observed. It was found that the presence of particles in the solution causes an apparent increase in the electrode surface area, probably due to increased surface roughness.