• Canada
• 020501 mining & metallurgy close

Air bubble – bitumen attachment is a critical step in the flotation of bitumen from mined oil sand. In this study, single bubble – bitumen drop attachment was observed directly using a novel experimental technique. Induction time is determined and used as an indication of bubble-bitumen attachment potency for both hydrogen and oxygen bubbles. The attachment tests were conducted in deaerated municipal water (City of Edmonton tap water) at temperatures ranging from 22–50°C. Induction times measured for hydrogen bubble attachment were shorter than those for oxygen bubbles. Coalescence tests were also conducted in the absence of bitumen, and showed that hydrogen bubbles coalesced more rapidly than oxygen bubbles in both deaerated municipal water and clear (solids-free) process water. La liaison bulle d'air-bitume est une etape critique dans la flottation du bitume issu d'un minerai de sables bitumineux. Dans cette etude, la liaison bulle unique-goutte de bitume a ete observee directement par une nouvelle technique experimentale. Le temps d'induction est determine et utilise comme indicateur du potentiel de liaison bulle-bitume pour des bulles d'hydrogene et d'oxygene. Les tests de liaison ont ete menes dans une eau municipale desaeree (eau du robinet de la ville d'Edmonton) a des temperatures comprises entre 22 et 50 °C. Les temps d'induction mesures pour la liaison des bulles d'hydrogene sont plus courts que ceux des bulles d'oxygene. Des tests de coalescence ont egalement ete menes en l'absence de bitume et ont montre que les bulles d'hydrogene se combinent plus rapidement que les bulles d'oxygene a la fois dans l'eau municipale desaeree que dans l'eau de procede claire (sans solides).

The final properties of an industrial product depend on the processing route of the material. Hence there is an impetus to study different processing routes to obtain the most desirable final properties. In the present study, low carbon steels have been subjected to the novel deformation induced ferrite transformation (DIFT) technique to produce dual-phase microstructures that are composed of ultra-fine ferrite with martensite and/or bainite as a second transformation product. In this thermomechanical processing technique, the steels have been rapidly cooled from the austenitization temperature to the deformation temperature (which is at least 25°C above the Ar3 temperature) to produce highly undercooled austenite, followed by heavy deformation, and subsequently rapidly cooled thereby facilitating transformation to fine grained ferrite. Comparing the final microstructures obtained by this route with those attained by conventional thermo-mechanical processing, it can be concluded that significant ferrite g...

Abstract The control of rougher flotation circuits represents a challenging control problem due to the non linearities, multiple inputs-multiple outputs and the wide variety of disturbances acting on the system. Many concentrators rely on regulatory control loops to maintain a stable operation and on the plant operators to find the best operational results. As a mean of using the operator's knowledge in a consistent manner Expert Systems have been proposed to emulate the current practices in flotation plants. In this work, an algorithmic supervisory system, as opposed to rule-based systems, is proposed and analyzed using simulations of an industrial rougher flotation circuit.

Abstract In this paper we study approximations to the infinite-horizon quadratic optimal control problem for linear systems that may be only asymptotically stabilizable. For linear systems, this issue only arises with infinite-dimensional systems. We provide sufficient conditions which guarantee when approximations to the optimal feedback result in the cost converging to the optimal cost. One technique for approximate solution of the optimal control problem is to use Newton–Kleinman iterations for the associated Riccati equation. Some new results in this direction are provided. Several important classes of systems, lightly damped second-order systems and a platoon-type system, are shown to be optimizable. Also, finding an initial stabilizing control for the Newton–Kleinman iteration can be non-trivial. The initial iterate for these classes is described.

Abstract In this study, a conductivity sensor was designed that allows the vertical water content profile of a two-phase flotation froth to be measured with a minimum vertical measurement resolution of 15 mm. The conductivity sensor consists of 32 ring electrodes, three of which measuring the collection zone gas holdup and 29 measuring the water content in the froth zone at various heights. The sensor was applied to study the water content profile for three increasing average molecular weight polypropylene glycols (PPG 425, PPG 725 and PPG 1000), under various operating conditions (1.0–3.0 cm s−1 input gas velocity and 5–45 ppm frother concentrations). For all conditions, a large increase in a defined degradation function occurred at 70–80% of the froth equilibrium height, indicating a point where small increases in froth height will have large effects on the froth stability.

A mining complex may be comprised of multiple components, including open-pit and underground operations. Traditional approaches in mine planning do not account for the various components simultaneously leading to under-value solutions. Over the last decade, some methods have been developed to incorporate multiple components of the mining value chain during optimisation. Even though these new methods incorporate more decisions and flexibility to the optimisation of a mining complex, they may either ignore uncertainties associated with the mining project or consider decisions taken before optimisation. This paper presents a method that optimises mining complexes comprised of multiple open-pits, underground operations and processing destinations. Mining, blending, processing and transportation decision variables are simultaneously optimised while accounting for geological uncertainty. The method uses a simulated annealing algorithm at different decision levels in order to generate a stochastic-based extracti...

Resource recovery from two metallurgical residues by flotation was investigated applying an electrostatic model to select initial conditions. The first, a sulphation roast/water leach residue, was processed to float lead sulphate, comparing dodecylamine and xanthate collectors. From the second, a neutralization residue, gypsum, was recovered by reverse flotation of ferric hydroxide, comparing oleate and sulphonate collectors. In both cases, further upgrading by acid leaching was considered.

Abstract Active and passive behaviors of pure gold (Au) and roasted gold ore (RGO) electrodes were investigated at 25 °C in de-aerated agitated cyanide media. Cyclic voltammetry and potentiodynamic polarization with agitation at 100 r/min in 0.04 mol/L NaCN solution showed different peak positions and current densities. Potentiodynamic tests illustrate that the peak current densities increase greatly with increasing the cyanide concentration. Increasing the pH value from 10 to 11 resultes in a great decrease of current density, while it increases noticeably by decreasing the agitation from 100 to 60 r/min. In the presence of oxygen, Au and RGO electrodes show different characteristics of peak positions and corrosion rates. The potentiostatic studies show that increasing the potential from 1 to 1.4 V at pH value of 11 results in an 80% decrease of current density while decreasing the pH value from 11 to 10 at 1 V gives a 1.7 fold increase of current density, possibly due to more effective passive layer. Following polarization, electrochemical noise measurements (ENM) during decay periods show that Au results in more passive states at high potentials, showing pitting corrosion. The ENM results show that this technique can be a promising tool for a better understanding of gold leaching. The XPS studies prove the presence of passive oxides.