Employee engagement: extension of the job demands resource (JD-R) model with the ubuntu construct

This study contributes to our understanding of the moderation and mediation processes through which job demands, job resources and employee engagement are linked with desired organizational behavioural outcomes [intention to turnover (IT) and affective commitment (AC)]. The study extends the JD-R model with a typical culturally specific African construct, Ubuntu, in order to increase its relevance to the African context. Mediation and moderation analysis were used to test the hypothesised relationships in two cross sectional samples of 175 public sector and 263 private sector employees. Results revealed that organizational based self-esteem (OBSE) and distributive justice (DJ) were positively related to engagement (for public sector employees) and OBSE, DJ and colleague support (CS) were positively related to engagement (for private sector employees). For both sectors combined, OBSE, DJ and job autonomy (JA) were positively related to engagement. The findings supported mediation of employee engagement between DJ and intention to turnover and OBSE and affective commitment for public sector whereas for private sector, mediation of employee engagement between OBSE, DJ, CS and intention to turnover was not supported whereas engagement mediated the relationship between DJ and affective commitment for private sector. For both private and public sector, engagement mediated the relationship between JA, DJ and intention to turnover and the relationship between OBSE, JA and DJ and affective commitment. Moreover, Ubuntu construct was positively related with engagement in both private and public sector employees. Expectedly, Ubuntu mediated the relationship between supervisor support (SS) and employee engagement for all sectors. However surprisingly, mediation of Ubuntu between CS and engagement was not supported. There were no statistically significant interactions for both sectors suggesting that, contrary to the JD-|R model, job demands do not moderate the relationship between resources and employee engagement. Overall, the findings suggest that specific job resources could be provided for each sector to improve engagement and employee engagement could be used as a mechanism to explain the relationship between resources (job and personal) and desired organizational behaviour outcomes (IT and AC) . More importantly Ubuntu construct is positively related to employee engagement and can also be used to explain the relationship between supervisor support, colleague support and employee engagement. Implications for Human Resource Management research and practice are highlighted and directions for future research discussed

Adsorption of Gold and Copper from Alkaline Glycine-based Leach Solutions using Activated Carbon

This study evaluated and optimised the activated carbon adsorption (ACA) process for the recovery of metals from alkaline glycine leachates. The use of activated carbon for metals adsorption remains industry’s preferred choice for the recovery of precious metals, from dilute solutions. The adsorption behaviour of metal glycine complexes on activated carbon, which was studied through the use of isotherms and kinetics, confirmed that ACA can efficiently recover gold over copper from dilute glycine solutions

Activated carbon adsorption of gold from cyanide-starved glycine solutions containing copper. Part 2: Kinetics

The downstream processing of leachates arising from the dissolution of copper bearing gold ores in cyanide-starved alkaline glycine solutions is imperative for the successful implementation of the new leach system at industry level. This study investigates the behaviour of gold adsorption onto activated carbon in the presence of copper from cyanide-starved glycine solutions. The adsorption behaviour was kinetically investigated using the Fleming k,n model. The model had a high consistency with experimental data (up to 6 h) for both gold and copper as evidenced by the regression coefficient (R2) values which were close to 1. The effects of important parameters including glycine concentration, solution pH, cyanide concentration, initial gold concentration, adsorbent concentration and ionic strength of the solution were studied. The results showed that, except for initial gold and carbon concentrations, a variation of these major factors had a pronounced effect on copper adsorption and slightly affected the gold adsorption, both in terms of adsorption rate and overall recovery. It was also seen that the active carbon had a high adsorption tendency towards gold over copper. The gold and copper extraction from a cyanide-glycine solution containing 2 mg/L gold, 300 mg/L copper, pH 11, 5 g/L glycine, Cu:CN of 1:1 (123 mg/L CN) and 8 g/L carbon using lime as a pH modifier reached 99.0% and 52.8% respectively. Most copper and gold was recovered in the first 6 h. The corresponding initial adsorption rates are 1263.8 h-1for gold and 19.0 h-1for copper

Adsorption behaviour of copper and gold glycinates in alkaline media onto activated carbon. Part 1: Isotherms

© 2018 Elsevier B.V. Alkaline glycine/glycinate solutions have been shown to have significant potential in the leaching of gold and copper from ores, concentrates, and wastes bearing these metals. An attempt was made to understand the adsorption behaviour of the gold glycinate complex onto activated carbon in the presence of copper for a pure alkaline glycine/glycinate system, after the gold has been dissolved using hydrogen peroxide as an oxidant and caustic soda as pH modifier. The adsorptive behaviour under various process conditions was evaluated using equilibrium loading isotherms. The linear regression (R2) values for the Freundlich isotherm for all tested parameters are close to unity, suggesting the model to be well suited for gold glycinate adsorption onto activated carbon. The maximum adsorption capacity of the gold complex on the activated carbon was determined as a function of free glycine concentration, solution pH, initial gold and copper concentration and calcium chloride salt concentration using synthetic solutions. The adsorption capacity increased with increasing free glycine, copper and calcium chloride concentrations, but decreased with increasing solution pH and initial gold concentration. This information can be used (with adsorption kinetics) to design and evaluate Carbon-in-Pulp (CIP), Carbon-in-Leach (CIL) and Carbon-in-Column (CIC) circuits for gold when copper may be present

Gold recovery from cyanide-starved glycine solutions in the presence of Cu using a molecularly imprinted resin (IXOS-AuC)

© 2020 Elsevier B.V. The synergistic leaching system using glycine as the main lixiviant with low levels of cyanide as a catalyst has been shown to be an effective approach to leach gold‑copper ores and concentrates, allowing the consumption of cyanide to be remarkably reduced. The recovery of gold from the synthetic cyanide-starved glycine leachate in the presence of copper has been investigated using. It was found that the adsorbed copper was mostly cuprous cyanide. The effects of [CN−]:[CuT] and [Gly]: [CuT] molar ratios were not significant on the adsorption of gold and copper using IXOS-AuC resin. The gold recovery increased, while the copper recovery decreased with the increasing initial gold concentration. The equilibrium and kinetics studies were undertaken, and the experimental adsorption equilibrium and rate data showed an excellent fit using the Freundlich isotherm and pseudo-second-order models respectively. Elution tests showed that the loaded copper can be selectively pre-eluted over gold by 0.4 M NaCN at pH 11.5. Gold can be effectively eluted by either acidic thiourea or alkaline thiocyanate. The multi-cycle adsorption/elution tests showed that the resin can be effectively regenerated by both acidic thiourea and alkaline thiocyanate, with an insignificant decrease in adsorption and elution efficiency over 3 adsorption/elution cycles. From SEM analysis, the change of surface morphology of the resin was not significant after adsorption and the adsorption/elution cycles

Activated carbon adsorption of gold from cyanide-starved glycine solutions containing copper. Part 1: Isotherms

Cyanide-starved alkaline glycine solutions have been shown to have distinct advantages in terms of lower reagent consumption and detoxification needs, or leach rate and recovery, over cyanide- only and glycine-only leach systems respectively for gold ores with nuisance copper. Activated carbon has been shown to be suitable for gold adsorption from alkaline glycine systems, and is well established for cyanide based systems. Activated carbon being an effective substrate for the adsorption of gold thus offers a possible downstream carbon-in-pulp (CIP) recovery route for alkaline glycine leach systems and hybrid systems in the presence of cyanide. Given the frequent occurrence of gold deposits with high levels of nuisance copper, the equilibrium loading of gold and copper onto activated carbon from cyanide-starved alkaline glycine solutions containing copper and gold has been studied. Adsorption efficiency was studied in terms of equilibrium loading isotherms. Results showed that while copper adsorption is more sporadic based on goodness of fit, gold adsorption is more consistent and clearly follows the Freundlich isotherm model (good linear correlation of log Q vs log C values). The adsorption isotherms were obtained using a gold concentration of 2 ppm. In the presence of copper, the equilibrium gold loading increases with increasing glycine and calcium ion concentrations, decreases with increasing cyanide concentration and is not affected by initial gold concentration. The cuprous cyanide and cupric glycinate complexes lowered gold loading through a competitive adsorption with the copper (I) cyanide complexes adsorbing more rapidly on the carbon than their glycinate counterparts. The equilibrium gold loading capacity in cyanide-starved glycine solutions containing 2 ppm Au and 300 ppm Cu, at pH 11 was found to be 9.95 kgAu/toncarbon in 24 h, which is almost four times higher than the gold loading capacity in a pure cyanide system (2.7 kgAu/toncarbon) under similar conditions. The study revealed that activated carbon was an effective adsorbent for removal gold from cyanide-glycine aqueous solutions

Adsorption behaviour of copper and gold Glycinates in alkaline media onto activated carbon. Part 2: Kinetics

The kinetics for the competitive adsorption of gold and copper onto activated carbon from synthetic alkaline glycine solutions was studied. The adsorption rate for both gold and copper at the initial stage was modelled using the Fleming k,n adsorption kinetic model. The coefficient of variation (R 2 ) of the model were close to unity for both gold and copper adsorption data. The effects of pH, free glycine, ionic strength, initial gold and copper concentrations and carbon concentration were assessed on the adsorption kinetics of these two metals. The results showed that > 98% of gold was adsorbed onto activated carbon in 6 h or less under all studied conditions. According to the adsorption tests results, carbon concentration is the only parameter that significantly affected the initial gold adsorption rate. For all other studied parameters, the initial adsorption rate is quite robust, with a few variations in process conditions only affecting it slightly. Activated carbon was found to be very selective for gold glycinate complexes over copper glycinates, with over 99.0% gold adsorbed in 24 h and < 15% copper adsorbed in the same duration under optimum conditions from a solution containing 2 ppm gold and 40 ppm copper

Sulfide precipitation of copper from alkaline glycine-cyanide solutions: Precipitate characterisation

© 2019 Elsevier Ltd A synergistic leaching system using glycine containing starvation levels of cyanide as lixiviants has been shown to be an effective approach to leach gold-copper ores, allowing the consumption of cyanide to be reduced significantly while glycine is recycled. Sulfide precipitation to remove the bulk of the copper was studied. The previous study on the precipitation behaviour of Cu and Au from the alkaline glycine-cyanide solution shows that the cupric (Cu2+) glycinate can be easily precipitated, while the gold and cuprous (Cu+) cyanide species remain stable in the solution. Due to the sparingly soluble nature of metal sulfides, colloidal and poorly settling particles are usually formed without control methods, which create challenges for solid-liquid separation processes such as thickening and filtration. This study investigated the effects of chemical and operational conditions on particle characteristics particularly particle size distributions (PSD). Settling characteristics, particle morphologies and particle structure were also studied. In the presence of divalent cations such as Ca2+ and Mg2+, particularly Ca2+, large and fast settling particle agglomerates were generated. Increasing ionic strength of the solution was also noted to enlarge the particles. The high supersaturation level has insignificant effects on the PSD as long as Ca2+ is present. A relatively large particle size is generated at a medium stirring speed with fast addition rate. There are no significant effects of aging, heating, and seeding on the PSD, but these factors profoundly influenced the morphologies of the individual particles according to the SEM results. SEM and XRD analysis illustrate that a more mature and crystalline copper sulfide precipitates were produced after aging, heating, or seeding

Towards industrial implementation of glycine-based leach and adsorption technologies for gold-copper ores

© 2017 Canadian Institute of Mining, Metallurgy and Petroleum The technology to selectively leach gold, silver and base metals from ores, concentrates, and wastes, using an alkaline glycine solution, has initiated significant interest in using the new technology in various environments such as in situ, in-place, dump, heap, and vat and agitated tank leaching. It has been shown that glycine acts synergistically with a number of other lixiviants to lower the net consumption of the other lixiviants while allowing low-cost glycine solution recovery. Glycine is a non-toxic, stable, environmentally benign reagent that is available in bulk industrial quantities. It has the ability to dissolve most copper oxide and sulphide minerals, as well as native copper, whilst not interacting with acid-consuming gangue nor dissolving iron and various or ubiquitous gangue elements. It acts synergistically with small amounts of cyanide to leach gold-copper ores at leach rates higher than either glycine or cyanide on their own, while significantly reducing cyanide consumption and eliminating detoxification requirements. The leaching behaviour of various glycine-based systems will be reviewed, followed by the evaluation of the adsorption of gold onto activated carbon. Where the economics merit it, copper can be easily recovered using solvent extraction or sulphide precipitation