An investigation of the failure mechanisms of lead anodes in copper electrowinning cells

Lead alloys are used as permanent anodes for electrowinning of base metals such as copper. The corrosion of anodes is costly because of their relatively short lifetime, material cost, and their impact on cathodic deposit quality. Failure of anodes sometimes occurs before the predicted lifetime, having a negative impact on the efficiency and economics of the electrowinning process.This study investigates some recently failed lead alloy anodes. These failures occurred after a short period of service in a commercially operating electrowinning tank house. The samples were metallographically investigated with the help of an optical, three-dimensional microscope and a scanning electron microscope (SEM) equipped with Energy-Dispersive X-ray Spectroscopy (EDS) analysis. It is suggested that the reasons for failure are improper operational issues in the tank house, especially the level of manganese content in the electrolyte, which leads to unexpected corrosion

Uphill filling system for a bar-like casting

Bar-like sand mould tilted angle reduced free surface fluctuations. The primary and secondary reflected wave heights decreased with the scaling of Re0.8 and Re0.55, respectively. These heights were reduced by 54% and 51% when θ was increased from 0° to 5°. A larger tilted angle was found to generate an air cavity in the cast, the size of which was observed to vary with Reynolds number (Re). An optimised range of tilted angle (2° to 3°) was proposed as a compromise to reduce the free surface fluctuations and maintain a perfect casting shape at the end of the filling stage

Analysis of a centreline failure of a lead alloy anode used in the copper electro-winning process

Thousands of lead anodes are currently used in the electro-winning of copper across the globe. The corrosion and the electrochemical performance of these anodes significantly affect the economy of the process. Premature failure of anodes is often a problem for the commercial operators of tank houses. Recently, the authors were asked to advise on an unusual case where a lead alloy anode split at almost the centreline of the cross section. Different characterization techniques were employed to detect the cause of failure. The fractured samples were metallographically examined with an optical microscope and a Scanning Electron Microscope (SEM) equipped with Energy-Dispersive X-ray Spectroscopy (EDS) analysis. Different phase at the fracture surface were also identified by X-Ray Diffraction technique.The failure mechanism of this anode appears to be manganese contaminated electrolyte attacking the anode perimeter, leading to initial corrosion sites and compounded by subsequent exfoliation corrosion through inter-granular attack and further formation of manganese dioxide. The established practice of producing lead alloy anodes via rolling confers beneficial properties to the finished anodes. However, the resulting elongated grains can in some cases, where the electrolyte is contaminated with elements that are prejudicial to stable oxide layer formation, cause susceptibility to exfoliation corrosion

Particle swarm algorithm with adaptive constraint handling and integrated surrogate model for the management of petroleum fields

This paper deals with the development of effective techniques to automatically obtain the optimum management of petroleum fields aiming to increase the oil production during a given concession period of exploration. The optimization formulations of such a problem turn out to be highly multimodal, and may involve constraints. In this paper, we develop a robust particle swarm algorithm coupled with a novel adaptive constraint-handling technique to search for the global optimum of these formulations. However, this is a population-based method, which therefore requires a high number of evaluations of an objective function. Since the performance evaluation of a given management scheme requires a computationally expensive high-fidelity simulation, it is not practicable to use it directly to guide the search. In order to overcome this drawback, a Kriging surrogate model is used, which is trained offline via evaluations of a High-Fidelity simulator on a number of sample points. The optimizer then seeks the optimum of the surrogate model

Formulation of Generalized Mass Transfer Correlations for Blood Oxygenator Design

This paper numerically investigates non-Newtonian blood flow with oxygen and carbon dioxide transport across and along an array of uniformly square and staggered arranged fibres at various porosity (e) levels, focussing on a low Reynolds number regime (Re < 10). The objective is to establish suitable mass transfer correlations, expressed in the form of Sherwood number (Sh = f (e,Re,Sc)), that identifies the link from local mass transfer investigations to full-device analyses. The development of a concentration field is initially investigated and expressions are established covering the range from a typical deoxygenated condition up to a full oxygenated condition. An important step is identified where a cut-off point in those expressions is required to avoid any under- or over-estimation on the Sherwood number. Geometrical features of a typical commercial blood oxygenator is adopted and results in general show that a balance in pressure drop, shear stress and mass transfer is required to avoid potential blood trauma or clotting formation. Different definitions of mass transfer correlations are found for oxygen/carbon dioxide, parallel/transverse flow and square/staggered configurations, respectively. From this set of correlations, it is found that transverse flow has better gas transfer than parallel flow which is consistent with reported literature. The mass transfer dependency on fibre configuration is observed to be pronounced at low porosity. This approach provides an initial platform when one is looking to improve the mass transfer performance in a blood oxygenator without the need to conduct any numerical simulations or experiments