Cyanidation of reef and surface gold ores

The kinetic leaching behaviour of a low-grade surface gold ore and a high-grade reef ore were evaluated to determine the achievable gold recovery from these ores and particularly mixtures of these ores. The reef ore material has a head grade of 13.40 g/t with a relative standard deviation of 3%, and the unprocessed surface ore material a head grade of 0.43 g/t with a relative standard deviation of 15.6%. It is concluded that the kinetic leaching behaviour of these free milling gold ores during cyanidation, is not influenced by mixing of reef and surface ore material. No statistically significant relationship exists between the achievable recovery by direct cyanidation and the head grade of the material fed. No ideal ratio of surface ore to reef ore could be established. It is recommended that these materials should be processed simultaneously to minimize the costs, security risks, and losses incurred in transportation.Paper written on project work carried out in partial fulfilment of B. Eng (Metallurgical Engineering)http://www.saimm.co.za/ai201

Local forage fish abundance influences foraging effort and offspring condition in an endangered marine predator

This is the author accepted manuscript. The final version is available from Wiley via the DOI in this record.All data will be archived in the Dryad Digital Repository and BirdLife Seabird Tracking Database.1. Understanding the functional relationship between marine predators and their prey is vital to inform ecosystem-based management. However, collecting concurrent data on predator behaviour and their prey at relevant scales is challenging. Moreover, opportunities to study these relationships in the absence of industrial fishing are extremely rare. 2. We took advantage of an experimental fisheries closure to study how local prey abundance influences foraging success and chick condition of Endangered African penguins Spheniscus demersus in the Benguela Ecosystem. 3. We tracked 75 chick-provisioning penguins with GPS-time-depth devices, measured body condition of 569 chicks, quantified the diet of 83 breeding penguins and conducted 12 forage fish hydro-acoustic surveys within a 20 km radius of Robben Island, South Africa, over three years (2011–2013). Commercial fishing for the penguins’ main prey, sardine Sardinops sagax and anchovy Engraulis encrasicolus, was prohibited within this 20 km radius during the study period. 4. Local forage fish abundance explained 60% of the variation in time spent diving for 14 penguins at sea within 2 days of a hydro-acoustic survey. Penguin foraging effort (time spent diving, number of wiggles per trip, number of foraging dives and the maximum distance travelled) increased and offspring body condition decreased as forage fish abundance declined. In addition, quantile regression revealed that variation in foraging effort increased as prey abundance around the colony declined. 5. Policy implications. Our results demonstrate that local forage fish abundance influences seabird foraging and offspring fitness. They also highlight the potential for offspring condition and the mean-variance relationship in foraging behaviour to act as leading indicators of poor prey abundance. By rapidly indicating periods where forage resources are scarce, these metrics could help limit seabird-fisheries competition and aid the implementation of dynamic ocean managemen

Leaching characteristics of Ni-Cu matte in the acid-oxygen pressure leach process at Impala Platinum

The mineralogical changes and reaction mechanisms occurring in the Impala Platinum acid-oxygen pressure leaching process of Ni-Cu matte were postulated. The complex interactions of the various minerals with one another were clarified by considering the change in the mineral species during the leaching process. It was found that the key to the selective leaching of the nickel from the Ni-Cu matte is that while leaching Ni3S2, copper ions in solution are continuously precipitated as Cu2S in a substitution reaction liberating nickel ions into solution.Articl

An off-line computer simulation for controlling the repulp section in a plant

An off-line computer simulation program is proposed to control a repulping section of a plant that has previously been controlled solely by an operator. The off-line computer program can be used as a tool by the operator to improve the control of repulping a certain material before leaching commences. Controlling the repulping section is of special importance, especially to processes employing unit operations after the repulping section with fast reaction kinetics. The fast reaction kinetics make it essential to control the conditions of the incoming pulp to the leaching vessel. The simulation uses dynamic mass balance equations to simulate the physical properties of the system. It then solves the set of differential equations with an iteration procedure that uses the fourth order Runge-Kutta(RK) procedure and the Golden Section Search(GSS) optimisation procedure, thus obtaining optimum settings so that the desired conditions in the process could be maintained or reached as quickly as possible. The simulation was tested on a plant and indicated that considerable improvement in the stability of the operation could be achieved. Two calculation methods were also investigated for the mathematical models, i.e. the Runge-Kutta procedure mentioned above and the Laplace transform solution. Comparing the two methods it was evident that the Laplacian solution was not as accurate as the Runge-Kutta solution due to the inherent linearisation step employed. This was especially evident for large deviations from the desired conditions. © 1995.Articl

Men 2A and the role of genetic testing in a Cape Town Xhosa family

Please help us populate SUNScholar with the post print version of this article. It can be e-mailed to: [email protected] Geneeskund

A kinetic model for the acid-oxygen pressure leaching of Ni-Cu matte

A semi-empirical mathematical model for the acid-oxygen pressure leaching of Ni-Cu matte is presented, based on data from batch leaching experiments. The primary controlling factor in the leaching process is found to be galvanic inhibition of the more highly oxidized copper and nickel sulfide species by less oxidized species, particularly Ni alloy and Ni3S2. The leaching rate of many species is greatly reduced by the presence of one or both of these phases, and others will not commence leaching until neither is present. The mathematical model is based on first-order chemical reaction controlled rate expressions, as the reactions occurring are electrochemical in nature. Mass transfer effects are included only empirically. Some possibly diffusion-related phenomena are noted, although the model is not extended to incorporate these effects on a fundamental level. The model is verified and extended by the inclusion of several different factors that were tested experimentally. The effects of variations in O2 flow rate and partial pressure, initial particle size, reaction pulp density and initial acid concentration were all studied, and included in the model. Variations in O2 flow rate and partial pressure are found to affect the reaction rates via the dissolved oxygen concentration in the solution phase. © 2003 Elsevier Science B.V. All rights reserved.Articl

A kinetic model for the acid-oxygen pressure leaching of Ni-Cu matte

A semi-empirical mathematical model for the acid-oxygen pressure leaching of Ni-Cu matte is presented, based on data from batch leaching experiments. The primary controlling factor in the leaching process is found to be galvanic inhibition of the more highly oxidized copper and nickel sulfide species by less oxidized species, particularly Ni alloy and Ni3S2. The leaching rate of many species is greatly reduced by the presence of one or both of these phases, and others will not commence leaching until neither is present. The mathematical model is based on first-order chemical reaction controlled rate expressions, as the reactions occurring are electrochemical in nature. Mass transfer effects are included only empirically. Some possibly diffusion-related phenomena are noted, although the model is not extended to incorporate these effects on a fundamental level. The model is verified and extended by the inclusion of several different factors that were tested experimentally. The effects of variations in O2 flow rate and partial pressure, initial particle size, reaction pulp density and initial acid concentration were all studied, and included in the model. Variations in O2 flow rate and partial pressure are found to affect the reaction rates via the dissolved oxygen concentration in the solution phase. © 2003 Elsevier Science B.V. All rights reserved.Articl