- Alkaline/ammonia leach
- Proprietary two stage leaching process
- Ore specific cure/pre-treatment stage
- Heap or tank leaching
- Proprietary solvent extraction step to avoid ammonia carry-over into solvent
- Uses conventional equipment
- Electro-winning is identical to conventional acid circuits
- Replacement acid leach in current operations
- Minimal changes to plant
- Higher organic transfer efficiencies requires smaller plant
- Environmental benefits – ‘green’ process for a ‘green’ metal:
- Reduced transport/shipping impact and costs
- Minimal likelihood of AMD
AmmLeach® – Advantages I
| Parameter | Acid | AmmLeach® |
| Mineralogy | Oxides, carbonates, silicates, some sulphides | Almost any – dependant upon curing stage |
| Curing | Concentrated H 2 SO 4 | Tailored to ore mineralogy |
| Selectivity | Low- iron, manganese, calcium and silica are likely problems | High- no iron, manganese, calcium or silica dissolution |
| Rate of extraction | Limited by acid strength and diffusion | Ammonia concentration in leach solution matched to leaching rate |
| Recovery | 80% of leachable | 70-80% in 130 days typical |
| Heap lifetime | 55-480 days | ~80-130 days typical |
| Sulphate precipitation | Reduced permeability in heap, break down of clays and plant scaling due to precipitation of gypsum and jarosite | Calcium and iron solubilities too low for precipitation, also low sulphate levels in leach solution |
AmmLeach® – Advantages II
| Parameter | Acid | AmmLeach® |
| Leachate consumption | Depends upon carbonate content 3.7-27 kg/t reported | Depends on concentration used, field trials show less than 1kg/t |
| Safety | Concentrated acid required | Gaseous ammonia main hazard, on – demand systems using hydrolysis of urea minimise transport risks |
| Precious metals | Heap to be neutralised before cyanidation | Neutralisation not required, potential for simultaneous recovery using thiosulphate or sequential leaching using cyanide |
| Mine closure | Heap requires washing, neutralisation and long term monitoring to avoid AMD | Heap can be washed and left, residual ammonia acts as fertiliser for vegetation regrowth, minimal likelihood of AMD. |