A report commissioned by Alexander Mining examining the construction and running of a typical 50,000 t/y and 100,000 t/y copper/cobalt mine in the Democratic Republic of the Congo (DRC) using its AmmLeach® process, compared with conventional sulphuric acid, has shown “substantial capital and operating cost savings” according to CEO Martin Rosser. AmmLeach uses ammonia-based chemistry under ambient conditions to selectively extract base metals.
Rosser: “The savings range from $94-177 million for capital and $29-51 million/y for operating costs. Moreover, these figures are for one medium sized copper mine only, and amply illustrate the major potential commercial value of our AmmLeach technology for the copper industry alone.”
The capital and operating cost savings are shown in the table below as percentages:
| Case | Ore head grade | Production rate copper t/y | Capital cost savings | Annual operating cost savings | ||
| Copper (%) | Cobalt (%) | |||||
| Heap leaching | 2 | 0.2 | 50,000 | 30% | 42% | |
| Agitated leaching | 3 | 0.4 | 100,000 | 29% | 43% | |
50,000 t/y DRC copper mine
The comparison assumes the treatment of a typical DRC carbonate hosted oxide orebody with 100 kg/t of ore acid consumption and with a head grade of 2% Cu and 0.2% Co. Certain aspects of the project were assumed to be common to both leach systems, i.e. recoveries (as test work recently undertaken by AmmLeach has shown the recoveries from the two leach regimes to be similar, i.e. 85% and 80% for copper and cobalt respectively), mining, mine infrastructure, mine waste disposal, process plant residue disposal, project buildings, site access roads, the power transmission line and the water supply line.
In the context of this comparison, the reagent consumptions drive the capital and operating cost differential, along with the much simpler and lower cost cobalt process circuit.
The capital cost differential is $94 million in favour of AmmLeach. The main reasons are that the AmmLeach option does not require an acid plant and the cost of the ammonia plant to generate the reagent from urea is significantly lower. Also the costs of the cobalt circuit associated with the AmmLeach process are lower than those of the acid route.
The major differential in terms of operating cost is associated with reagents and, in particular, the differential costs of ammonia and sulphuric acid. The saving in favour of AmmLeach is $29 million/y or, over a 15 year mine life, a saving of about $435 million at a production rate of 50,000 t/y of copper (plus cobalt).
100,000 t/y DRC copper mine
The comparison was undertaken to compare the costs of the AmmLeach process to those of conventional acid agitated leaching for a DRC copper/cobalt oxide ore with a head grade of 3% Cu and 0.4% Co. The base case is the production of 100,000 t/y copper and assumes overall copper and cobalt recoveries of 95% and 90% respectively (again as test work recently undertaken by AmmLeach has shown the recoveries from the two leach regimes to be similar).
The capital cost differential is $177 million in favour of AmmLeach. The main determinants of this are similar to that for the heap leaching option, i.e. the AmmLeach option does not require an acid plant, the cost of the ammonia plant to generate the reagent from urea is significantly lower, and the costs of the cobalt circuit associated with the AmmLeach process are lower than those of the acid route.
The operating cost saving in favour of AmmLeach is $51 million/y or, over a 15 year mine life, a saving of about $765 million. Again, it can be seen that the major differential is associated with reagents and, in particular, the differential costs of ammonia and sulphuric acid. Aside from the very substantial capital and cost savings, AmmLeach has several major advantages over conventional acid leaching technology, specifically:
- Much simpler process circuits because of the low level of impurities in the leach solutions, and hence lower capital to clean up
- Much less complex cobalt winning circuits.
The substantial potential cost savings should, in turn, lead to much lower cutoff grades, particularly for heap leach projects. Current cutoff grades in the DRC using AmmLeach and heap leaching should drop to less than 1% Cu (agitated leaches are currently around 2% copper cutoff) resulting in a substantial increase in reserves.
