Search

Acid mine drainage (AMD) presents a challenge to the environment if not well managed, but it also presents an opportunity for the recovery of economically valuable products, including rare earth elements (REEs), which are critical for the development of advanced, and green technologies. REE concentrations in AMD samples from coal and gold mines were determined using inductively coupled plasma optical emission spectroscopy (ICP-OES) and their sorption by different cationic resins (CHT4083, CHP4502 and CHP00712) was evaluated. Optimum conditions for the sorption of the REEs by these resins were determined through batch experiments and desorption of the REEs from the resins using different concentrations of sulphuric acid (H2SO4) solutions. Coal mine drainage (CMD), with a low pH of 2.37, had higher amounts of REEs (ΣREE 226.3732 mg/L) than AMD from the gold mines (ΣREE 4.9705 mg/L), with a pH of 3.21. A REE sorption efficiency of up to 98% was obtained with CHP4502 and CHP00712 resins and further optimisation of CHP00712 revealed that a resin volume of 250 mL and a contact time of 10 min were required to successfully remove REEs from 500 mL AMD. The sorption capacities of the resin for the selected REEs were 3.88 mg/g, 0.88 mg/g, 1.37 mg/g, 3.18 mg/g, 0.67 mg/g, 0.01 mg/g and 0.27mg/g for Pr, Gd, Nd, Ce, Sm, Eu and Y, respectively. Elution of the resin with a 0.5 N solution of sulphuric acid desorbed the REEs. AMD from coal mines could be an alternate source of REEs and cationic resins can be used to recover these REEs from the CMD. Further investigations, including impregnation of resin to improve its sorption capacity, and temperature effects on the sorption process, are recommended. [ABSTRACT FROM AUTHOR]

The control of gastrointestinal parasites in animals has become more challenging every year due to parasite resistance to conventional chemical control, which has been observed worldwide. Ovicidal or opportunistic fungi do not form traps to capture larvae. Their mechanism of action is based on a mechanical/enzymatic process, which enables the penetration of their hyphae into helminth eggs, with subsequent internal colonization of these. The biological control with the Pochonia chlamydosporia fungus has been very promising in the treatment of environments and prevention. When used in intermediate hosts of Schistosoma mansoni, the fungus promoted a high percentage decrease in the population density of aquatic snails. Secondary metabolites were also found in P. chlamydosporia. Many of these compounds can be used by the chemical industry in the direction of a commercial product. This review aims to provide a description of P. chlamydosporia and its possible use as a biological parasitic controller. The ovicidal fungus P. chlamydosporia is effective in the control of parasites and goes far beyond the control of verminosis, intermediate hosts, and coccidia. It can also be used not only as biological controllers in natura but also as their metabolites and molecules can have chemical action against these organisms. Key points: • The use of the fungus P. chlamydosporia is promising in the control of helminths. • Metabolites and molecules of P. chlamydosporia may have chemical action in control. [ABSTRACT FROM AUTHOR]

Oxidative defense or arsenic(As) changes exhibited by Trametes versicolor in response to toxicity under As stress remain unclear. In this study, after internal transcribed spacer identification, a wild T. versicolor HN01 strain was cultivated under 40 and 80 mg/L of As III stress. The antioxidant contents by multifunctional microplate reader and the speciations of As by high performance liquid chromatography in conjunction with inductively coupled plasma mass spectrometry were examined to explore the detoxification mechanisms. The results demonstrated this strain could tolerate As concentration of 80 mg/L with a bio-enrichment coefficients of 11.25. Among the four antioxidants, the activities of catalase, superoxide dismutase, and glutathione in the As-stress group at 80 mg/L improved by 1.10, 1.09, and 20.47 times that of non-stress group, respectively. The speciation results indicated that AsV was the dominant species in the hyphae of T. versicolor regardless of no-stress or As-stress. The detoxification mechanisms of this strain were involved alleviating the toxicity by increasing the activities of antioxidants, especially glutathione, as well as by converting As III into As V and other less toxic As species. T. versicolor could be used as a bio-accumulator to deal with As exposure in contaminated environments based on its extraordinary As tolerance and accumulation capacities. [ABSTRACT FROM AUTHOR]

Several different phenomena are involved in the formation and performance of self-hardening slurry walls, including slurry contamination by soil, penetration of slurry into the ground, confining with the trench, filtration, sedimentation, consolidation, and chemical reactions between the slurry constituents. To evaluate the relative influence of these phenomena, a case study is analyzed-the cutoff wall of Santa Clara-a-Velha Monastery, built in 2001-2002. The performance of this wall is related to the in situ phenomena through data obtained during construction and from a site investigation conducted in 2011. An extensive laboratorial program was performed on samples cored from the wall and on laboratory-made samples. It was found that consolidation was the major contributor to the significant settlement of the wall that occurred after trench excavation, whereas filtration and sedimentation made only a secondary contribution. Contamination by sand only interfered with the physical properties and compressibility of the slurry. The unusual hydromechanical behavior of the wall material, when compared with soils, was attributed to the combined effect of consolidation, cement hydration, and pozzolanic reactions. [ABSTRACT FROM AUTHOR]

In the one-phase construction of cutoff walls, the slurry plays two contradictory roles: it should be fluid while excavating the trench but behave like a solid of low permeability afterward. For hydraulic containment applications, a mixture of water, cement, and bentonite fulfils these requirements, but the range of mix proportions is very limited. In the past, this discouraged systematic research on the subject, and, in consequence, a certain empiricism still prevails in the definition of the slurry composition. This paper presents the results of an extensive experimental program, which is part of a broader investigation regarding the technology of self-hardening slurry walls. Referring to triaxial tests, the stress-strain behavior and permeability of cement-bentonite slurries fabricated and cured in the laboratory is characterized. A conceptual microstructure model is proposed to explain the slurry's behavior in light of the chemical reactions between its constituents. The final objective is to establish a relationship between the behavior of lab-made slurry and that of in situ slurry, and consequently to be able to predict the long-term behavior of the wall. [ABSTRACT FROM AUTHOR]

Durability and recycling are two major concerns in the construction industry. Concrete carbonation may impair reinforced concrete durability as it favors the onset of reinforcement corrosion. The use of recycled aggregates, as a replacement for natural aggregates, in construction applications is a feasible way of recycling given materials from construction and demolition waste. The aim of this study is to quantify the contribution of potential conditioning factors to the carbonation rate of concrete incorporating recycled aggregates. For this purpose, a multiple linear regression technique was used, considering the mix design characteristics, environmental conditions, and recycled aggregates' properties as explanatory variables, capable of predicting the coefficient of carbonation. The investigation was founded on ample experimental data, collated from several studies. This study proposes a general model, in which the carbonation in concrete depends on the 28-day compressive strength, clinker content, environment's CO2 content, and aggregates' equivalent water absorption. The models are statistically significant, with determination coefficients suggesting high correlation between the coefficients of accelerated carbonation of concrete in the experimental data and values predicted by the proposed models. [ABSTRACT FROM AUTHOR]

The use of empirically calibrated moment-rotation models that account for strength and stiffness deterioration of steel frame members is paramount in evaluating the performance of steel structures prone to collapse under seismic loading. These deterioration models are typically used as zero-length springs in a concentrated plasticity formulation; however, a calibration procedure is required when they are used to represent the moment-curvature behavior in distributed plasticity formulations because the resulting moment-rotation response depends on the element integration method. A plastic hinge integration method for using deterioration models in force-based elements is developed and validated using flexural stiffness modifications parameters to recover the exact solution for linear problems while ensuring objective softening response. To guarantee accurate results in both the linear and nonlinear range of response, the flexural stiffness modification parameters are computed at the beginning of the analysis as a function of the user-specified plastic hinge length. With this approach, moment-rotation models that account for strength and stiffness deterioration can be applied in conjunction with force-based plastic hinge beam-column elements to support collapse prediction without increased modeling complexity. [ABSTRACT FROM AUTHOR]

This paper describes a methodology developed to support decision makers in planning work zones for pavement maintenance and rehabilitation interventions, integrating cost, duration, and user effects. The methodology relies on two key stages. First, a computer model generates the set of feasible options for work zone layouts and schedules, and combines them to include all options for the intervention's planning and undertaking. Subsequently, a multiple-criteria decision model is used to compare all the alternatives included in the previously obtained set using agency cost, duration, and traffic delay as criteria, according to the weightings that correspond to the decision-maker's preferences. It constitutes an advance in the current knowledge by avoiding the prior characterization of each alternative and, based on the novel integration of the mentioned criteria, pointing towards the set of alternatives that merit additional analysis. Two case studies with different traffic levels are discussed, showing the capabilities of this methodology while identifying the most adequate alternatives for each context. [ABSTRACT FROM AUTHOR]