ALUMINA MARKET:

Working Out How Bauxite Residue Turns to Dust
Bauxite residue is a by-product of the Bayer process for alumina production. An understanding of the mechanism of the formation of dust from bauxite residue as it dries in bauxite residue disposal areas was developed, based on the alkali chemistry of the residue. This understanding could assist with finding ways to decrease dust formation in bauxite residue disposal areas.

Modelling the Gibbsite Secondary Nucleation Rate
The ability to manage the seed balance in gibbsite (alumina trihydrate) precipitation circuits is crucial for alumina refineries. Gibbsite secondary nucleation, a source of new gibbsite crystals (fines), is one of the precipitation mechanisms that can significantly affect the seed balance. Within the AMIRA P521B project, a novel model of the gibbsite secondary nucleation rate was developed based on an extensive experimental database. This model will provide the alumina industry with a quantitative tool to predict the rate of gibbsite fines generation as a function of main process variables. The developed model can be integrated into gibbsite precipitation process simulators to facilitate further improvements in process design, optimisation and control.

Tackling the Problem of Scale
Knowledge of the surface chemistry of mild steel in caustic solutions was improved. At least three distinct iron oxidation phases were found to form on the surface of mild steel, and one of these appears to act as a “seed” for the formation of crystalline gibbsite scale deposits. An understanding of the nucleation of scale on metal surfaces is needed to develop strategies to prevent or reduce the rate of unwanted scale formation on alumina refinery processing equipment.

Understanding the Nature of Bauxite Deposits Assists Alumina Companies
Work characterising the composition and mineralogy of a number of bauxite deposits, and also determining the bauxite “processability” under planned alumina refinery conditions, was undertaken for clients. This included work on the Aurukun deposit in far-north Queensland for the Queensland State Government and companies tendering to develop this deposit; on the Wenlock deposit for Cape Alumina, an Australian small-to-medium enterprise (SME); on a deposit located in Vietnam and on a deposit in Guinea in West Africa. Such characterisation is needed by companies wanting to develop bauxite deposits.

BASE METALS MARKET:

Applying Synergistic SX to Recover Metals from a Client’s Heap Leach Solution
Synergistic solvent extraction (SSX) systems use a combination of two commercially available extractants to improve metal selectivity and thus metal separation and recovery in solvent extraction. A patented SSX technology developed by Parker Centre researchers is being applied to the separation of nickel and cobalt from manganese, magnesium and calcium in a client’s heap leach solution from which iron and aluminium have been removed by precipitation.

Evaluating Pressure Oxidation Leaching Processes for Chalcopyrite
A number of different hydrometallurgical processes for treating chalcopyrite (copper iron sulfide) that utilise pressure oxidation have been developed and patented by various commercial companies. The Parker Centre’s “Pressure Hydrometallurgy” project team has examined and compared the kinetics (rates) and products from the pressure oxidation of a chalcopyrite concentrate using a range of process conditions involved in five of these patented processes. The research results were published in the international journal Hydrometallurgy.

Understanding Properties Affecting the Flow of Ore Slurries
An important limitation in increasing nickel production from pressure leaching autoclaves is the rheology or flow behaviour of the feed slurry which limits the pulp density (the % of solids in the pulped ore slurry) that can be pumped into an autoclave. Rheological studies on the flow characteristics of laterite ores were undertaken to understand the key properties which affect the viscosity of laterite leach slurries, with a view to increasing the pulp density of ore slurries pumped into continuous autoclaves and thus enhancing nickel extraction.

GOLD MARKET:

Effectiveness of New Elution Method for Gold-Thiosulfate Demonstrated
The new technology for elution of gold thiosulfate from resins was further developed. The chloride-based elution in the presence of an additive was successfully tested over a number of repeated resin loading and elution cycles. Electrowinning of the gold and recycle of the eluent was also successfully undertaken. This is another step taken by the Parker Centre to make the thiosulfate process for gold recovery viable. A full patent application has been lodged for the new elution process.

Quantifying Cyanide & Sulfur Chemical Species Leads to Better Understanding of Sulfide Oxidation
The high performance liquid chromatography method developed to determine the chemical species in cyanide leach solutions was used in surveys of two operating sites. Cyanide and sulfide reaction products can also be quantified with the new method, which has allowed the study of sulfide ore and concentrate leaching processes. This has led to an understanding of the sulfide oxidation mechanism in cyanide solutions, including the detection of polysulfides as reaction intermediates, and thiosulfate, sulfite and thiocyanate as the reaction products. The mechanism of the effect of lead addition on sulfide oxidation was also established.

Studying Gold Adsorption Through 3D Imaging and Computer Modelling
3-dimensional maps of the adsorption of gold onto activated carbon were produced using X-ray microtomography. Under typical cyanidation conditions, gold adsorption is limited to the surface pores in the carbon, with little adsorption in macro-pores. The modelling of the competitive adsorption between copper and gold on carbon was advanced through incorporation of the effect of ionic strength on the chemical activity, and hence on the solution chemical speciation. This is particularly important for gold operations with high saline process water. A framework for performing these calculations during simulation of processing plants was established by interfacing a flowsheeting software package with a thermochemical software package.

New Process for Refractory Ores Couples Pressure Oxidation with Thiosulfate Leaching
Refractory (“difficult to leach with cyanide”) gold ores are problematic, as standard cyanide leaching only yields low gold recoveries. A new process based on pressure oxidation (POX) followed by thiosulfate leaching has been developed in the Parker Centre for recovering gold from such ores, and a provisional patent lodged for this process. There are a number of synergies between the POX step and the thiosulfate leach, and conditions for the POX were established whereby a high gold recovery can be achieved using very mild thiosulfate leaching conditions. This decreases the rate of thiosulfate oxidation, and reduces the generation of polythionates, which are known to impair the adsorption of gold thiosulfate onto resins.