Richard Browner

The use of bauxite waste mud in the treatment of gold ores

Abstract The relative effectiveness of bauxite waste mud as a pH modifier in the cyanidation of gold has been studied. The red mud was effective in modifying the pH of gold ore slurries. Any gold contained in the red mud is easily concentrated by gravity separation and is recovered along with gold from the gold ore. Carbon activity tests were conducted on cyanide leach solutions to determine the amount of deactivation caused by organics in the bauxite waste mud.

Effect of pyrrhotite reactivity on cyanidation of pyrrhotite produced by pyrolysis of a sulphide ore

Abstract The effect of the metal to sulphur ratio in the nonstoichiometic compound, pyrrhotite, is related to the consumption of cyanide in gold leaching. Reactive pyrrhotite (Fe (I-X) S) is produced during the pyrolysis of refractory pyrite (FeS 2 ). Iron vacancies give pyrrhotite its non stoichiometric nature and determine its fugacity and hence reactivity. Separate trends for cyanide consumption were found when pyrite was partially converted to pyrrhotite compared to where all the pyrite was converted to pyrrhotite. Samples that were partially converted to pyrrhotite, and hence remained in equilibrium with the unconverted pyrite, showed an increase in cyanide consumption with increasing metal to sulphur ratio. Samples in which all the pyrite was converted to pyrrhotite showed a decrease in cyanide consumption with an increasing metal to sulphur ratio. For all samples the higher the pyrolysis temperature the lower the cyanide consumption.

A method for measuring HCN(g) emission from CIP/CIL tanks

Abstract Hydrogen cyanide gas (HCN( g )) is released from CIP/CIL slurries through either entrainment in the air/oxygen injected into the tanks, or through direct evolution from the pulp surface. The HCN(g) released by entrainment has been measured by placing capped pipes over aerated/oxygenated tanks to collect the evolved gas. The collected gas was passed through a scrubber to remove the HCN(g). The scrubber solution was then titrated for cyanide, giving a measure of the HCN(g) released by aeration/oxygenation. HCN (g) evolved directly from the pulp surface was measured using capped pipes that were modified to have nitrogen injected into the pipe close to the slurry surface. The injected nitrogen then carried the HCN(g) from the pulp surface to the scrubber. The nitrogen was injected at a rate sufficient to ensure that HCN( g ) loss from the surface was under diffusion control. HCN (g) emission from the tanks of the CIP circuit surveyed accounted for approximately 1 % of the total cyanide added with the majority of that being evolved directly from the pulp surface. The rate of HCN(g) evolution from the tanks was found to be directly proportional to the HCN (aq) concentration in the pulp liquor.

Low pH cyanidation of gold

Abstract Lime is used in CIP/CIL slurries to increase the pH, which partially stops the formation of aqueous hydrogen cyanide. Hydrogen cyanide gas can be evolved directly from the pulp surface or purged from the leach tank in oxygen or air that is sparged into the tanks to provide oxygen for the dissolution of gold. Savings in lime consumption can be achieved by leaching at a reduced pH, especially in aqueous solutions high in magnesium such as to be found in the Kalgoorlie Goldfields in Western Australia, but a greater percentage of cyanide is then present as aqueous hydrogen cyanide. Another proposed procedure to reduce lime consumption is closed tank leaching where a reduced pH or the natural pH of the ore is used and hydrogen cyanide loss is prevented by the closed vessel. The dissolution rate of pure gold as a function of pH for constant total cyanide concentration has been determined. Dissolution was directly proportional to the concentration of the cyanide ion present, with the contribution to dissolution from aqueous hydrogen cyanide too low to be measured. Ore leached in high magnesium, hyper-saline, process water showed increased gold dissolution at low pH compared to the pure gold. Reducing pH caused more cyanide to be consumed by the pulp but did not significantly increase the amount lost to the atmosphere.

Effect of Silver in Thiosulfate Leaching of Gold–Silver Alloys in the Presence of Copper and Ammonia Relative to Pure Gold and Silver

One promising alternative to cyanide for the leaching of gold is thiosulfate due to its low toxicity and efficiency in leaching gold from low-grade and carbonaceous ores and concentrates. Much of the published research focuses to optimizing the reagent concentrations to develop a suitable process for industrial applications. However, there are few studies on the effect of silver content on gold dissolution rate in the thiosulfate leaching system. In this paper, the dissolution rate of pure gold, pure silver, and gold–silver alloys of silver compositions, 4, 8, 20, and 50 wt% are reported. The effects of various parameters on the rate of gold and silver dissolution have been determined. The results show that the pure silver dissolution rate is around 6.89 times greater than pure gold. The results show that silver enhances gold dissolution in thiosulfate solutions. The dissolution rate of gold from pure gold is higher than that obtained from 4% and 8% silver alloys, but less than that obtained from 20% and 50% silver alloys.

The effect of oxidant addition on ferrous iron removal from multi-element acidic sulphate solutions

This study was an investigation on the hydrolytic precipitation of iron from simulated pregnant leach solution (PLS) of nickel laterite atmospheric leaching. The effect of equilibrium pH, temperature and the addition of oxidant on total iron (ferrous (Fe (II)) and ferric (Fe (III)), aluminium and chromium removal was investigated together with the associated nickel and cobalt losses to the precipitate. Systematic variations of the experimental variables revealed ≥99% of the ferric iron can be removed from solution at conditions similar to those used in standard partial neutralisation in zinc and nickel production, pH of 2.5 and temperature less than 100 °C with minimal losses (<0.5%) of both nickel and cobalt. Temperature variation from 55 to 90 °C had no significant effect on the magnitude of Fe (III) precipitation but led to a significant increase in aluminium removal from 67% to 95% and improved the filterability of the precipitates. There was no ferrous iron precipitation even at a pH of 3.75 in the a...

Nickel Loss during Iron Precipitation and Product Characterization

In this study, the iron precipitation and associated nickel loss from synthetic ferric and nickel sulphate solutions were investigated. Two types of common neutralizing agents, magnesium oxide and calcium carbonate were applied in the investigation. The results indicated that pH and temperature had significant impacts on nickel loss during the iron precipitation process, whereas the type of neutralizing agents had little effect. It was found that increasing in pH and temperature resulted in more nickel loss in the pH range of 2 to 4 and temperature range of 25 to 85 °C. Mineralogical examination by XRD indicated that the iron precipitates were combinations of schwertmannite, ferrihydrite and goethite. In addition, more crystalline goethite was formed from the ferric solutions when no nickel was present, indicating that nickel might play a role in inhabiting the crystallization of goethite.