The Development of Sustainable Hydrometallurgical Processes for the Recovery of Precious Metal

The study investigates the utilization of cedar wood bark as bioadsorbent for the adsorption and simultaneous precipitation of gold as flakes. This is with a view to establishing the electrochemical study of the adsorption and evaluate pre-treated cedar wood bark as possible adsorbent for gold in various solutions. The research plan for this project is divided into two parts. Part one focuses on understanding the adsorption of gold using the cedar wood bark as adsorbent. The second part focuses on the electrochemical study of the redox reaction during adsorption process using cyclic voltammetry technique. Synthetic solution of gold is prepared with dissolution of gold (III) chloride in hydrochloric acid, sodium thiosulfate and sodium thiourea lixiviants. Cedar wood bark is pre-treated with dilute and concentrated sulfuric acid under various experimental conditions to obtain three bioadsorbents, dilute-air dried (D-AD), concentrated washed-air dried (CW-AD) and concentrated not washed-oven dried (CNW-OD). The gold solutions are electrochemically tested for redox reaction using cyclic voltammetry (CV) techniques. One-point adsorption test is carried out on the various gold solutions to determine the suitable samples for the research. The outcome of the CV experiment indicates that redox reaction of gold in hydrochloric acid medium is easily measured through the anodic and cathodic peak formation. The one-point adsorption test favors the use of D-AD as adsorbent in acidic gold solution with percentage adsorption of 99.999%. Hence, the research is narrowed down to the use of D-AD adsorbent and acidic gold solution. Solid/liquid ratio and hydrochloric acid concentration tests indicate that 1.5 and 0.5 M, respectively, are the best suitable for the research. For the kinetic study of the adsorption process at temperatures of 298, 303 and 313 K in 96 hours, pseudo-second order model has determination coefficients of 0.988, 0.996 and 0.998, respectively, while the pseudo-first order model has determination coefficients of 0.91, 0.77 and 0.62 at those three different temperatures. Hence, the adsorption process follows the pseudo-second order model. The activation energy from the pseudo-second order rate constant indicates that the process is chemisorption with a value of 59.86 kJ/mol. The adsorption isotherm is found to follow Freundlich isotherm model, which might have favored the formation of gold flakes on the adsorbent. The CV experiment shows the disappearance of anodic peaks as the adsorption of gold progresses, which is an indication of reduction reaction synonymous to adsorption process. X-ray diffractometer (XRD) and Fourier transform infrared (FTIR) instruments were used to determine the presence of gold precipitates and the spectra obtained from the two experiments confirm the presence of gold. In conclusion, the study established cedar wood bark as a potential source of biomass for adsorption of gold (III) ions from acidic chloride solution, and that cyclic voltammetry (CV) technique was successfully used to examine the adsorption process

2k Factorial Experiments on Factors that Influence the Recovery of Gold during the Upgrade of Ilesha-Itagunmodi Gold Ore through Froth Flotation

A low-grade gold ore from Ilesha-Itagunmodi, south western Nigeria was panned, dried and ball-milled before sieving into fractions. The morphological, mineralogical and chemical composition was studied by optical micro-scopy (Reflected and Transmission), X-ray diffraction (XRD) and Energy Dispersive X-ray fluorescence (XRF), respectively. The sieved fractions were subjected to chemical analysis (AAS). The +106 μm sieve had the highest concentration of the mineral and was then selected for the upgrade through froth flotation using standard rea-gents. In this paper a report on a 2k factorial experiment that provides an understanding of the impact of opera-tional variables on the quantity of gold mineral obtained from the ore during froth flotation is presented. Analy-sis results showed that Ilesha-Itagunmodi gold ore is non-refractory with fine grain particles, amenable to froth flotation and contained about 20 other associated minerals, gold had a concentration of about 0.0024%. A com-bination of P-Xanthate and amine glycol collectors at a pH of 9.2 only produced a considerable increase in gold yield. This translated to about 87.13% increase in recovery of gold from the ore. Analysis of variance (ANOVA) was carried out and the model equation obtained was subsequently optimised to obtain a model equation that could be used in predicting the recoverable quantity of gold, indicating that F11,1-values for Collector concentra-tion, Frother concentration, pH and Conditioning time were 156.86, 6.96, 43.81, and 56.77 respectively. A model with an F value of 88.41 was obtained which indicated that the model was significant. The model equation obtained was subsequently optimised to be able to predict the recoverable quantity of gold. A “Pred R-Squared” value of 0.9365 (93.65%) was also obtained and is in reasonable agreement with the “Adj R-Squared” value of 0.9534 (95.34%). It was established that Ilesha placer gold ore is amenable to froth flotation using standard reagents

Investigation of Sida acuta (Wire Weed) Plant Extract as Corrosion Inhibitor for Aluminium-Copper-Magnessium Alloy in Acidic Medium

Abstract This work is an investigation of the aqueous corrosion inhibition of Al-Cu-Mg Alloy in acidic medium using extract of Sida acuta (wire weed) plant as corrosion inhibitor at 10%, 20%, 30% and 40% v/v of the extract. After exposing the alloy to the medium, the results showed that the plant extract inhibited the acid induced corrosion. The presence of Sida acuta plant extract reduces corrosion rate from 0.0012 to 0.0001 MPY and percentage protection increases from 37.42% to 93.63% within a ten-day period with increase in percentage volume of the extract. The result has clearly shown that Sida acuta plant extract can be used as a corrosion inhibitor in the part of chemical plant that is made of Al-Cu-Mg Alloy where acid is used for descaling and cleaning