Gold
The Australian gold industry produces in excess of 300 tonnes of the precious metal each year in an industry worth nearly 5 billion dollars AUD. AMMTEC provides a full and comprehensive testing facility to the Australian and overseas gold mining industries.
Sample Preparation and Analysis
AMMTEC has extensive crushing, screening and splitting equipment for the production of accurate, representative samples. Test samples from a few kilograms to many tonnes can be prepared and treated.
Cyanidation - Batch
AMMTEC has a modern, dedicated, fully equipped laboratory for the testing of gold recovery by cyanidation. Bottle roll leaching or mechanical agitation in perspex vats can be carried out to determine the effect of grind size, pH, cyanide level, oxygen level and leach time on gold recovery. Leach tests may be carried out using leach vessels from 1 litre to 1500 litres.
Cyanidation - Pilot
Pilot scale facilities are available where ore can be milled at the rate of up to 250 kg/hr and subsequently passed through the pilot leaching plant. A range of pilot plant sizes and configurations are available to suit the testwork programme.
Carbon-In-Pulp (CIP) - Batch and Pilot
The loading of gold onto activated carbon can be described by the Fleming equation. AMMTEC can carry out sequential batch carbon loading tests to determine the Fleming constants k and n. Activated carbon is contacted with several batches of pre-leached slurry simulating carbon contact in practice. The Fleming constants can be used by design engineers to size CIP contactors. Pilot scale CIP facilities are available to confirm laboratory test results.
Carbon-In-Leach (CIL) - Batch and Pilot
Some gold bearing ores also contain active constituents which adsorb the leached gold and so reduce gold recovery. The use of CIL can reduce or eliminate the loss of gold by the process of competitive adsorption. AMMTEC can perform laboratory scale CIL tests thus allowing comparisons with conventional cyanidation to be made. Pilot scale CIL facilities are available to confirm laboratory test results.
Heap Leaching
Column leach tests are used to investigate the feasibility of heap leaching. Crushed ore samples can be studied to ascertain the reagent consumption, percolation rate and leaching time. Testing samples over a range of crush sizes can be trialed to determine optimum size. Ores which have high fines or clay content can be agglomerated with additives such as cement to improve the percolation rate and reduce fines transport. A wide range of column sizes is available from 100 mm diameter up to 1000 mm diameter to carry out long term leaching tests. Pregnant leach solutions may be passed through activated carbon columns and the regenerated cyanide recycled.
Gravity Separation
Free gold can be recovered prior to cyanidation thus enhancing the economics of gold recovery. Amalgamation, spirals, tables and hydrocyclones are available to study the recovery of gravity gold. Centrifugal concentrators eg Knelson and Falcon test units are also available for the recovery of fine free gold.
Roasting
Refractory sulphide ores may be roasted to produce a calcine amenable to cyanidation. A Dorr-Oliver 100mm continuous fluid bed pilot roasting unit is available at AMMTEC to study the roasting of sulphide concentrates. Bench scale tests using batch fluid bed, muffle or tube furnaces are carried out prior to pilot testing to establish the influence of gas composition, temperature and the roasting scheme to be used. The calcine products from the roasting oxidation are cyanide leached using conventional methods. Feed material for roasting studies are usually produced by laboratory or pilot scale flotation tests.
Ultra Fine Grinding (UFG)
Some refractory ores, such as those containing pyritic gold, can benefit from very fine grinding prior to cyanidation. A Metprotech mill is available at AMMTEC for ultra fine grinding of ore or concentrate. Grind sizes down to 2-3 µm have been achieved. Various sensors on the UFG mill are used to determine grinding energy requirements. This data can be used for scale-up calculations. AMMTEC also has available a Svedala Stirred Media Detritor mill which has been specifically developed to effectively apply high specific work inputs.
Pressure Oxidation Leaches
Refractory ores where gold is contained within sulphides, such as pyrite or arsenopyrite, can be chemically oxidised to enhance gold recovery. Oxidation is carried out in an autoclave typically at temperatures of 180-240 C and at oxygen pressures in excess of 3000 kPa. The autoclave in use at AMMTEC is a PARR 3.8 litre unit which is certified to 300°C. The pressure leach residue is neutralised by washing with lime and then leached using conventional cyanidation methods.
Oxygen Enhanced Leaching
The rate of gold leaching can be greatly enhanced by the injection of pure oxygen into a cyanide leach slurry. AMMTEC has available oxygen injection technology, such as the Filblast shear reactor for the enhanced leaching of gold ores.
Carbon Elution
In conjunction with beaker scale testwork, carbon elution studies can be performed under atmospheric conditions to simulate the AARL and Zadra processes. A pilot plant pressure unit capable of operating up to 500 kPa and 140 C is also available. This unit is used for continuous elution of plant carbons and has the capacity to process 1 litre of carbon (500 grams) at a time. The unit also has attachments which enable elution studies to be performed in conjunction with the AARL process. (Anglo American)
Carbon Characterisation
- ASTM ball pan hardness
- Attrition in rotary tumbler over 24 hours
- Adsortion testing with calculation of kinetic rate constants
Copper Gold Ores
Ores containing soluble copper can have very high cyanide consumption and so increasing operating costs. Ammoniacal cyanidation can dramatically reduce the overall level of cyanide consumption. AMMTEC can carry out leach tests to optimise reagent conditions.
Diagnostic leaching of gold residues
Feed and residue size analysis
Cyclosizer analysis of fine materials
Slurry viscosity measurements
Flocculant screening and settling testing
Oxygen uptake testing Bacterial leaching - batch and pilot