Electrowinning of Copper in the Presence of Anodic Depolarisers - A Review

Abstract

Alternative anodic reactions have been investigated to reduce the cell voltage and hence energy consumption in the electrowinning of copper. It is necessary to avoid oxygen evolution reaction at the anode, which requires a high potential of 2 V in order to reduce the cell voltage. An extensive literature review reveals that the cell voltage can be reduced by using various ionic couples, such as Fe²⁺/Fe³⁺, Cu²⁺/Cu¹⁺. Addition of cobalt, soluble sulfites and sulfur dioxide to the electrolyte modifies the anodic reaction. Examination of several electrode materials for anodic oxidation confirms that graphite is the most suitable material. Some fundamental studies on the anodic oxidation of sulfur dioxide have also been reviewed.     

TEM mode analysis of parallel cylinders of unequal radii using conformal transformation

A method of analysing iransmission lines represented by parallel cylinders of unequal radii supporting the TEM mode is to transform them to parallel plale and coaxial configurations. The cotangent-hyperbolic transformation transforms the line to a parallel plate structure. A bilinear transformation expressed in terms of mutually inveise points transforms the same line to a coaxial configuration. The general formula for the capacitance per unit length of parallel cylinders with unequal radii leads to an exact expression for the particular case of the line consisting of parallel cylinders of equal radii. Numerical data on capacitance and charge distribution are presented.     

Quantitative microscopy approach for shape‐based erythrocytes characterization in anaemia

Anaemia is one of the most common diseases in the world population. Primarily anaemia is identified based on haemoglobin level; and then microscopically examination of peripheral blood smear is required for characterizing and confirmation of anaemic stages. In conventional approach, experts visually characterize abnormality present in the erythrocytes under light microscope, and this evaluation process is subjective in nature and error prone. In this study, we have proposed a methodology using machine learning techniques for characterizing erythrocytes in anaemia associated with anaemia using microscopic images of peripheral blood smears. First, peripheral blood smear images are preprocessed based on grey world assumption technique and geometric mean filter for reducing unevenness of background illumination and noise reduction. Then erythrocyte cells are segmented using marker‐controlled watershed segmentation technique. The erythrocytes in anaemia, such as, tear drop, echinocyte, acanthocyte, elliptocyte, sickle cells and normal erythrocytes cells have been characterized and classified based on their morphological changes. Optimal subset of features, ranked by information gain measure provides highest classification performance using logistic regression classifier in comparison with other standard classifiers.     

Operator training in a repetitive production task— a comprehensive approach

For a repetitive production task, a comprehensive operator training method was developed through the use of MTM analysis, operator instruction sheet, demonstration, practice session, feedback and guidance. At the end of 72 minutes demonstration and practice session, all the operators were able to perform the assigned drilling task by employing the prescribed motions and came close to reaching the measured production standard. The average quantity and quality output increased from the draft to the fourth quarter (15-minute) by 25 and 37%, respectively. Statistically the improvement was highly significant.     

Use of gain and other estimates to obtain sub-optimal solution of a class of Markov decision processes†

Studies in the past decade have indicated considerable interest in the problems of optimizing processes having Markovian property. Certain properties of the transition matrix, associated with such processes, regarding the estimates of the steady-state probability distribution, gain estimate, their order of approximation, error in estimate- etc., has been considered in some depth in this paper. The computational ease of these estimates have led to the development of a direct search type sub-optimal algorithm. The algorithm has been employed to Howard's Taxi-Cab problem and Hamza's problem of coupled Markov processes. Often, this sub-optimal solution is itself the optimal solution, which interestingly is the case for the problems solved in this paper. In case whore a strictly optimal solution is necessary, the Howard's algorithm may be persued with the sub-optimal decision as the starting policy. This will still be advantageous from the point of view of computation time for small-scale systems.     

Spatial reuse efficiency calculation for multihop wireless networks

A multihop network provides an increase in the spatial and frequency resource reuse as compared to a single-hop network. However, a precise quantification of the benefit obtained in terms of spatial reuse is still an open issue. In this paper, a mathematical analysis is carried out in order to derive the spatial reuse efficiency of a multihop wireless network. It is demonstrated through both approximate and exact analysis, that for an unbounded network, the reuse efficiency of the wireless system increases with the number of multiple hops, M  , and the spatial protection margin, Δ$\Delta$, defined around the receiver. Significantly, it has been found that even in case of an infinitely large spatial protection margin, the obtained reuse efficiency is a finite value and is limited by the number of multiple hops in the communicating link.     

Influence of energy induced from processing parameters on the mechanical properties of friction stir welded lap joint of aluminum to coated steel sheet

Friction stir welding has been attempted to evaluate joint strength of lap joint between aluminum sheet (AA6063) and zinc-coated steel (HIF-GA) sheet under different combination of rotational speed and traverse speed. The shear strength decreases significantly when rotational speed increases from 700 to 1,500 rpm at a traverse speed of 30 mm/min. At traverse speed of 50 mm/min, increasing rotational speed from 700 to 1,500 rpm, shear strength remains more or less the same. However, at a traverse speed of 100 mm/min, the shear strength increases significantly with increasing rotational speed from 700 to 1,500 rpm. Essentially, higher fracture load of the lap joint is obtained within a certain range of energy. The results have been correlated with the microstructural characteristics at the bond interface using energy dispersive X-ray spectroscopy, electron probe micro analyzer, and X-ray diffraction. The results show that characteristics of intermetallic compound formed at the interface derived from energy input takes predominating role towards lap joint of Al and coated steel. Furthermore, force and torque responses influenced by the processing parameters can be utilized as weld quality check.     

CASHeW: Cluster-based Adaptive Scheme for Multimedia Delivery in Heterogeneous Wireless Networks

Multimedia streaming over heterogeneous wireless networks has attracted significant interest in recent years from both telecom network operators and end users. However, the heterogeneity of the wireless network makes it very difficult to synchronize real-time multimedia streaming to different types of end-user devices across different wireless networks. In addition, with different delay and packet loss across different networks, multimedia delivery over the heterogeneous wireless networks cannot provide good quality streaming video. This paper proposes CASHeW—a novel cluster-based design with an in-built feedback-based adaptive mechanism that results in a higher video perceived quality in two-hop heterogeneous wireless network environments. CASHeW employs a proxy-client-server mechanism between the base station (BS) and the end-user; and importantly uses a quality-oriented adaptive scheme for efficient multimedia delivery. Simulation-based tests indicate that the performance of CASHeW not only outperforms transport layer adaptive delivery protocols like the TCP-Friendly Rate Control Protocol (TFRCP) and Loss Delay Adaptation (LDA+), but also is better than that of medium access control (MAC) layer protocols such as the Receiver Based Auto Rate (RBAR) and Enhanced Distributed Channel Access (EDCA) in terms of average perceived quality, average bit rate and loss rate.     

Total Coliform Survival Characteristics in Frozen Soils

Survival characteristics of total coliform bacteria in soil samples, with different moisture contents (24–49%) and at different temperatures (from ?28 to 20°C), were studied. The study showed that a significant fraction of coliform bacteria survive for more than six months in soil at subfreezing temperatures. Survival of total coliform bacteria at subfreezing temperatures decreased with an increase in moisture content and an increase in temperature. For 24% moisture, approximately 66% of the coliforms survived at ?28°C after 170 days, whereas less than 0.1% survived at room temperature. First-order die-off rate constants varied between 0.041/day at room temperature and 0.002/day from ?15 to ?28°C (for 24% moisture). The impact of temperature on the die-off rate constant was described by the Arrhenius equation. The high survival at subfreezing temperatures indicates that fecal bacteria at honeybucket dumpsites may survive throughout the Alaskan winter which may lead to the contamination of water sources during spring thaw.