The coagulation of a kaolinite suspension with aluminium sulphate

A study has been made of the coagulation of a 50 mg l⁻¹ aqueous suspension of kaolinite for a range of aluminium sulphate and hydrogen ion concentrations. The rate of flocculation was determined from jar tests after stirring for 1 h. The data permitted a stability limit diagram to be drawn from which some indication of the coagulation mechanisms of the system could be ascertained.     

Laboruntersuchungen zur Freisetzung von Unat aus einem Gestein unter oxischen naturnahen Bedingungen

Kurzfassung Im Labor wurden verschiedene Größen (pH-Wert, HCO ₃ —Gehalt, Präsenz von Fe(OH) ₃ ) untersucht, von denen angenommen werden konnte, dass sie die umweltrelevante Freisetzung von Uran aus Gesteinen (z. B. Haufwerken, Halden, Tailings) im neutralen und schwach basischen pH-Bereich (6 bis 9) beeinflussen. Hierzu wurde der Austrag von U _nat aus einem schwach vererzten Urangestein (2,31 %) in Batchversuchen untersucht. Diese Versuche wurden mit 8, 10 oder 40 g/l Gestein und Leitungs- bzw. Mineralwasser durchgeführt. Zum Vergleich wurden parallele Standversuche in deionisiertem Wasser, 0,1 M Na ₂ CO ₃ und 0,1 M H ₂ SO ₄ durchgeführt. Die Ergebnisse zeigen eine Begünstigung der Uranfreisetzung in Anwesenheit von Carbonat (gelöst oder in situ durch Dolomitauflösung entstanden), während die Rolle des Pyrits auf die Freisetzung deutlich komplexer ist. Das Erreichen eines Gleichgewichtszustands kann unter Umständen durch sorptive Einflüsse verzögert werden.

---

Investigations for the release of U_nat from ore bearing rock under natural near oxic conditions

Abstract The effects of carbonate concentration and the presence of iron hydroxide phases on uranium release into the environment were investigated under oxic conditions and in the pH range from 6 to 9. For this purpose not-shaken batch experiments were conducted with a constant amount (8, 10 or 40 g/l) of a uranium bearing rock and different types of water (deionised, tap and mineral water). For comparison parallel experiments were conducted with 0.1 M Na ₂ CO ₃ and 0.1 M H ₂ SO ₄ . The use of dolomite confirmed the favourable role of carbonate bearing minerals for U transport while the presence of pyrite on Uranium mobilisation was shown to be considerably more complex. This study shows that the approach of equilibrium conditions can be strongly delayed by sorption processes.

     

Numerical simulation of concrete encased steel composite columns

This paper investigates the behaviour of pin-ended axially loaded concrete encased steel composite columns. A nonlinear 3-D finite element model was developed to analyse the inelastic behaviour of steel, concrete, longitudinal and transverse reinforcement bars as well as the effect of concrete confinement of the concrete encased steel composite columns. The interface between the steel section and concrete, the longitudinal and transverse reinforcement bars, and the reinforcement bars and concrete were also considered that allowed the bond behaviour to be modeled and the different components to retain their profile during the deformation of the column. Furthermore, the initial overall (out-of-straightness) geometric imperfection was carefully incorporated in the model. The finite element model has been validated against published experimental results. The main objective of the study was to understand the structural response and modes of failure of the columns and to assess the composite column strengths against current design codes. The study covered slender, non-slender, stub and long concrete encased steel composite columns. The concrete strengths varied from normal to high strength (20-110 MPa). The steel section yield stresses also varied from normal to high strength (275-690 MPa). Furthermore, the variables that influence the composite column behaviour and strength comprising different slenderness ratios, concrete strength and steel yield stress were investigated in a parametric study. It is shown that the increase in structural steel strength has a small effect on the composite column strength for the columns having higher relative slenderness ratios due to the flexural buckling failure mode. The composite column strengths obtained from the finite element analysis were compared with the design strengths calculated using the American Institute for Steel Construction AISC and Eurocode 4 for composite columns. Generally, it is shown that the EC 4 accurately predicted the design strength for the concrete encased steel composite columns having a concrete cylinder strength of 30 MPa and structural steel yield stresses of 275 and 460 MPa, which are in the limits of the code, which otherwise, was generally conservative. The AISC predictions were quite conservative for all the concrete encased steel composite columns.     

Reliability of corrosion-damaged steel structures using interval probability theory

Engineering decisions concerning the performance of existing structures must be made in the presence of uncertainties. The remaining capacity of corroded steel structures provides a good example of different aspects of uncertainty. These include: an unknown or partially known extent of damage; a variability in loading and an uncertain reserve of structural capacity depending on the mode of failure. The theory of structural reliability has been developed to provide a method of analysis for structural safety. In this paper, methods are proposed to compute the component reliability of corrosion-damaged steel members. The application of a recently developed theory called interval probability theory for system reliability is illustrated using the data obtained from actual samples of corroded beams.     

Gravity driven counterflow through an open door in a sealed room

Flow measurements using tracer gas techniques were made on the exterior doorway of a test house for indoor-outdoor temperature differences of 0.5–45 K. The time for door opening and closing was constant at 3.75 s, and fully open hold time varied from 0.5 s to 120 s. Predictions of a variable density steady flow model were in good agreement with the measurements when adjustments were made for the time-varying size of the opening and for the effect of cross-stream mixing between the incoming and outgoing air streams. The flow rate is shown to be governed by an effective density very close to the average of inflow and outflow densities, and the control condition at the doorway is fixed by the jet-like behavior of the inflow stream. Dependence of cross-stream mixing on interfacial stability caused the orifice and coefficient to increase from 0.4 to 0.6 as temperature difference increased. This varying orifice coefficient is well represented by the combination of a discharge coefficient for streamline contraction combined with a mixing coefficient which accounts for mixing between the inflow and outflow.     

Lead contamination in tap water of households with children in Lower Saxony, Germany

Lead has numerous acute and chronic adverse effects on human beings. This is especially true for infants and children. The main path of lead ingestion in children can be different according to housing and living situation. The intake of lead through drinking water is commonly due to metal corrosion. The users plumbing can be an important factor. In recent years, many lead pipes in Germany have been replaced by pipes made of an alternative material. The aim of this study is to assess the present state of drinking water contamination and the resulting exposure of infants to lead. For this purpose mothers of new-born babies were offered a free examination of their drinking water. After a written declaration of consent had been obtained and after the infant in question had reached an age of 3 months, a stagnation sample of cold tap-water after overnight stagnation together with a random daytime sample was obtained from the family. The collected samples were analysed by atomic absorption spectrometry for their lead concentration. In total, 1485 samples from households were collected. Of the 1434 stagnation samples, 3.1% had lead concentrations greater than 0.01 mg/l (recommended limit of the WHO) and 0.6% had concentrations above the limit of the German drinking water regulation (0.04 mg/l). The values for the 1474 random daytime samples were 2.1% above 0.01 mg/l and 0.2% greater than 0.04 mg/l, respectively. By region, the areas Bovenden, Friedland, Duderstadt, Northeim and Rosdorf were particularly affected. The highest measured concentrations of lead in the stagnation samples were 0.11 mg/l and 0.15 mg/l in the random daytime samples, respectively.     

Energy and environmental comparison of three variants of a family house during its whole life span

The aim of this study is to analyse and compare three variants of a family house in order to evaluate the total environmental impacts produced during the whole building life cycle. The first variant corresponds to the standard in force in Switzerland, the second alternative to the requirements of a quality control label for houses with low energy consumption and the third case is a very low energy consumption building. The three variants have the same architectural aspect but different insulation thicknesses and types, different energy production systems and the use of different renewable energies. The calculation of the environmental impacts is carried out by means of a life cycle analysis, which includes not only the impact related to the energy consumption during the occupancy stage, but also the materials manufacture, transport, replacement and elimination at the end of the building lifetime. The results are expressed with the Swiss and the UCTE (Union for the Co-ordination of Transmission of Electricity) electricity mix to analyse how they influence the building impact.