The application of activated carbon for the adsorption and elution of platinum group metals from dilute cyanide leach solutions

The research presented in this paper investigated the practical aspects of the recovery of platinum group metals (PGMs) from a dilute cyanide leach solution containing base metals, in a manner similar to that used for gold extraction in a typical CIP process, and focuses on both the adsorption and elution stages. The carrier phase extraction of precious metals using activated carbon offers significant advantages over other processes in terms of simplicity, the high pre-concentration factor, rapid phase separation, and relatively low capital and operating costs. As a sorbent, activated carbon is still by far the most important material because of its large surface area, high adsorption capacity, porous structure, negligible environmental toxicity, low cost, and high purity standards. Adsorption tests were conducted on a pregnant alkaline leach solution (0.15 ppm Pt, 0.38 ppm Pd, 0.1 ppm Au) resulting from cyanide extraction performed in column leach tests. The initial adsorption rates of Pt, Pd, and Au were very fast and recoveries of these three metals were approximately 90 per cent after 2 hours, and 100 per cent for Pt, 97.4 per cent for Pd, and 99.9 per cent for Au after 72 hours. The parameters that influence the extraction of PGMs and Au were examined to assess their relative importance during the adsorption process in order to provide the basis for process optimization. The concentration of thiocyanate was not identified as significant factor for PGMs adsorption, while Ni concentration was the most significant extraction process parameter. Base metal cyanide complexes adsorb and compete with the PGM complexes for sites on activated carbon, and while copper adsorption can be minimized by adjusting the residence time, Ni adsorbs at approximately the same rate as the PGMs, influencing the loading capacity and adsorption kinetics of the PGMs.The feasibility of eluting platinum and palladium cyanide complexes from activated carbon using an analogue of the AARL process was investigated. Platinum and palladium elute from activated carbon almost to completion in 4 to 5 bed volumes at 80°C, while the elution of gold at this temperature is slow, with a significant amount of gold still to be eluted after 16 bed volumes. The equilibrium loading of gold is exothermic in nature (Fleming and Nicol, 1984) which will result in an increase in gold elution kinetics with an increase in temperature at similar pre-treatment conditions. A similar result was found for the elution of Pt and Pd. Cyanide pre-treatment was found to have a significant influence on PGM elution. Higher cyanide concentration in the pre-treatment step results in more efficient elution up to a point, and results suggest the possibility of an optimum cyanide concentration, beyond which elution efficiency starts decreasing due to increased ionic strength

The Adsorption and Elution of Platinum Group Metals (Pt, Pd, and Au) from Cyanide Leach Solutions using Activated Carbon

This paper investigates the recovery of platinum group metals (PGMs) from a dilute cyanide leach solution containing base metals, in a manner similar to that used for gold extraction in a typical CIP process, and focuses on both the adsorption and elution stages. The carrier-phase extraction of precious metals using activated carbon offers significant advantages over other processes in terms of simplicity, the high pre-concentration factor, rapid phase separation, and relatively low capital and operating costs. As a sorbent, activated carbon is still by far the most important material because of its large surface area, high adsorption capacity, porous structure, negligible environmental toxicity, low cost, and high purity standards. Adsorption tests were performed on a pregnant alkaline leach solution (0.15 ppm Pt, 0.38 ppm Pd, 0.1 ppm Au) resulting from cyanide extraction performed in column leach tests. The initial adsorption rates of platinum, palladium, and gold were very fast and recoveries of these three metals were approximately 90 per cent after 2 hours and 100 per cent, 97.4 per cent, and 99.9 per cent respectively after 72 hours. The parameters that influence the extraction of PGMs and Au were examined to assess their relative importance during the adsorption process in order to provide the basis for process optimization. The concentration of thiocyanate was not identified as significant factor for PGMs adsorption, while nickel concentration was the most significant extraction process parameter. Base metal cyanide complexes adsorb and compete with the PGM complexes for sites on activated carbon, and while copper adsorption can be minimized by adjusting the residence time, nickel adsorbs at approximately the same rate as that of the PGMs, influencing the loading capacity and adsorption kinetics of the PGMs.The feasibility of eluting platinum and palladium cyanide complexes from activated carbon using an analogue of the AARL process was investigated. Platinum and palladium elute from activated carbon almost to completion in 4 to 5 bed volumes at 80°C, while the elution of gold at this temperature is slow, with a significant amount of gold still to be eluted after 16 bed volumes. Cyanide pre-treatment was found to have a significant influence on PGM elution. Higher cyanide concentration in the pre-treatment step results in more efficient elution up to a point, and experiments suggest the possibility of an optimum cyanide concentration, beyond which elution efficiency starts decreasing

Investigation of flow regime transition in a column flotation cell using CFD

Flotation columns are normally operated at optimal superficial gas velocities to maintain bubbly flow conditions. However, with increasing superficial gas velocity, loss of bubbly flow may occur with adverse effects on column performance. It is therefore important to identify the maximum superficial gas velocity above which loss of bubbly flow occurs. The maximum superficial gas velocity is usually obtained from a gas holdup versus superficial gas velocity plot in which the linear portion of the graph represents bubbly flow while deviation from the linear relationship indicates a change from the bubbly flow to the churn-turbulent regime. However, this method is difficult to use when the transition from bubbly flow to churn-turbulent flow is gradual, as happens in the presence of frothers. We present two alternative methods in which the flow regime in the column is distinguished by means of radial gas holdup profiles and gas holdup versus time graphs obtained from CFD simulations. Bubbly flow was characterized by saddle-shaped profiles with three distinct peaks, or saddle-shaped profiles with two near-wall peaks and a central minimum, or flat profiles with intermediate features between saddle and parabolic gas holdup profiles. The transition regime was gradual and characterized by flat to parabolic gas holdup profiles that become steeper with increasing superficial gas velocity. The churn-turbulent flow was distinguished by steep parabolic radial gas holdup profiles. Gas holdup versus time graphs were also used to define flow regimes with a constant gas holdup indicating bubbly flow, while wide gas holdup variations indicate churn-turbulent flow

Review of power line communications standards in Africa

The standards in power line communications (PLC) calibrate parameters such as frequencies allocation, signal level, security, topology of the network and many others parameters. The leap forward of power line communications technology is motivated by the willingness of the standardization organizations (SDO)s such as ITU, IEC, ISO, IEEE, CENELEC to define how the technologies are going to be deployed. This paper presents the different SDOs, Alliances and groups regulating the PLC sector. The interoperability and coexistence for some technologies are underlined. The process of developing PLC standards by ITU, IEEE 1901, CENELEC is described. The advantages and disadvantages of using PLC technology in Africa are discussed

The anticonvulsant retigabine suppresses neuronal Kv2-mediated currents

Enhancement of neuronal M-currents, generated through K(V)7.2-K(V)7.5 channels, has gained much interest for its potential in developing treatments for hyperexcitability-related disorders such as epilepsy. Retigabine, a K(V)7 channel opener, has proven to be an effective anticonvulsant and has recently also gained attention due to its neuroprotective properties. In the present study, we found that the auxiliary KCNE2 subunit reduced the K(V)7.2-K(V)7.3 retigabine sensitivity approximately 5-fold. In addition, using both mammalian expression systems and cultured hippocampal neurons we determined that low μM retigabine concentrations had ‘off-target’ effects on K(V)2.1 channels which have recently been implicated in apoptosis. Clinical retigabine concentrations (0.3–3 μM) inhibited K(V)2.1 channel function upon prolonged exposure. The suppression of the K(V)2.1 conductance was only partially reversible. Our results identified K(V)2.1 as a new molecular target for retigabine, thus giving a potential explanation for retigabine’s neuroprotective properties

Effect of nitrogen incorporation on N-doped DLC thin film electrodes fabricated by dielectric barrier discharge plasma: Structural evolution and electrochemical performances

peer reviewe

Investigating the behaviour of PGEs during first-stage leaching of a Ni-Fe-Cu-S converter matte

CITATION: Snyders, C. A., et al. 2018. Investigating the behaviour of PGEs during first-stage leaching of a Ni-Fe-Cu-S converter matte. Journal of the Southern African Institute of Mining and Metallurgy, 118(4):353-360, doi:10.17159/2411-9717/2018/v118n4a4.The original publication is available at http://www.scielo.org.zaENGLISH ABSTRACT: In a first-stage atmospheric leach in a Sherritt Ni-Cu matte leach process, a Ni-Cu-Fe-S Peirce-Smith converter matte is contacted with recycled aqueous copper sulphate/sulphuric acid solution (spent solution) with the purpose of dissolving nickel, while simultaneously removing copper (via metathesis and cementation reactions) from solution. While the iron content has been found to have a significant impact on the first-stage leach, a previously expected relationship between copper and PGM behaviour has not been established clearly. For this study, a converter matte consisting mainly of heazlewoodite (Ni3S2), chalcocite (Cu2S), and awaruite (Ni3Fe) was leached in a laboratory-scale batch reactor. The temperature, acid, and copper concentration under both oxidative and non-oxidative conditions were varied, while the copper, iron, and PGEs were tracked and the pH and Eh measured. Palladium was generally found to be closely related to the behaviour of copper, while platinum did not leach. The other platinum group metals such as iridium and rhodium were found to precipitate only with accelerated precipitation being observed during Fe precipitation reactions.http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S2225-62532018000400007Publisher's versio

Au nanoparticle-functionalised WO3 nanoneedles and their application in high sensitivity gas sensor devices

A new method of synthesising nanoparticle-functionalised nanostructured materials via Aerosol Assisted Chemical Vapour Deposition (AACVD) has been developed. Co-deposition of Au nanoparticles with WO3 nanoneedles has been used to deposit a sensing layer directly onto gas sensor substrates providing devices with a six-fold increase in response to low concentrations of a test analyte (ethanol)

Identification of IKr Kinetics and Drug Binding in Native Myocytes

Determining the effect of a compound on IKr is a standard screen for drug safety. Often the effect is described using a single IC50 value, which is unable to capture complex effects of a drug. Using verapamil as an example, we present a method for using recordings from native myocytes at several drug doses along with qualitative features of IKr from published studies of HERG current to estimate parameters in a mathematical model of the drug effect on IKr. IKr was recorded from canine left ventricular myocytes using ruptured patch techniques. A voltage command protocol was used to record tail currents at voltages from −70 to −20 mV, following activating pulses over a wide range of voltages and pulse durations. Model equations were taken from a published IKr Markov model and the drug was modeled as binding to the open state. Parameters were estimated using a combined global and local optimization algorithm based on collected data with two additional constraints on IKrI–V relation and IKr inactivation. The method produced models that quantitatively reproduce both the control IKr kinetics and dose dependent changes in the current. In addition, the model exhibited use and rate dependence. The results suggest that: (1) the technique proposed here has the practical potential to develop data-driven models that quantitatively reproduce channel behavior in native myocytes; (2) the method can capture important drug effects that cannot be reproduced by the IC50 method. Although the method was developed for IKr, the same strategy can be applied to other ion channels, once appropriate channel-specific voltage protocols and qualitative features are identified