Acid balance in a chloride heap leach
A method of controlling the acid balance in a high chloride heap leach process tomaximise the copper dissolution in a cure step and to increase overall copper recovery which include an agglomeration stage in which acid and process solutions are combined with the ore prior to stacking to form a heap followed by a cure phase to leach a portion of the copper in the ore in the heap followed by an irrigated leach phase in which the remaining copper minerals are leached and copper is recovered from a pregnant leach solution by a solvent extraction step followed by an electrowinning step wherein the acid concentration in the pregnant leach solution which reports to the solvent extraction step is less than 10 g/L to allow effective copper recovery from the pregnant leach solution in the solvent extraction step.
1. A method of controlling acid balance in a high chloride heap leach process carried out at ambient temperature, wherein a chloride concentration is between 100 g/L and 180 g/L to ensure that copper dissolution in an agglomeration stage is not limited by acid to maximize the copper dissolution in a cure phase and thereby increase an overall copper recovery, wherein the method comprises:
an agglomeration stage in which acid and process solutions are combined with an ore prior to stacking to form a heap;
an aerated, but non-irrigated, cure phase to leach a portion of copper in the ore in the heap, wherein the copper dissolution in the aerated, but non-irrigated, cure phase is at least 30% by mass; and
an irrigated leach phase during which remaining copper minerals are leached and copper is recovered from a pregnant leach solution by a solvent extraction process followed by an electrowinning process, and
wherein the heap comprises a plurality of heap sections in which excess acid in the irrigated leach phase is reduced by circulating leach-liquor to the plurality of heap sections counter-current to the ore loading onto the plurality of heap sections and removal of ore from the plurality of heap sections, thereby increasing acid consumption by gangue mineral dissolution in proportion to a number of the plurality of heap sections irrigated during the irrigated leach phase and acid concentration in the pregnant leach solution, which reports to the solvent extraction process, is less than 10 g/L, to allow effective copper recovery from the pregnant leach solution in the solvent extraction process.
2. The method according to claim 1 , where overall copper dissolution in the aerated, but non-irrigated, cure phase and in the irrigated leach phase is greater than 40% by mass.
3. The method according to claim 1 , wherein an acid concentration in the pregnant leach solution is lower than 7 g/L.
4. The method according to claim 3 , wherein the acid concentration in the pregnant leach solution is lower than 2 g/L.
5. The method according to claim 1 , where a raffinate generated during the solvent extraction process comprises a copper content that is less than 1 g/L.
6. The method according to claim 5 wherein the copper content is less than 0.5 g/L.
7. The method according to claim 1 , wherein, after completion of the irrigated leach phase, the heap is washed.
8. The method according to claim 1 , wherein a quantity of acid added during the method is calculated from acid consumed by gangue minerals and acid required to leach the copper minerals.
9. The method according to claim 8 , wherein acid required for copper leaching is added to the ore during the agglomeration stage.
10. The method according to claim 8 , wherein acid addition to a raffinate solution which is used to irrigate the heap is done to meet increased acid demand by mineral leaching in the irrigated leach phase.
11. The method according to claim 8 , which further comprises a preceding process of conducting tests to determine the acid consumed by the gangue minerals for a specific type of ore as a function of at least one of the following: solution pH, acid concentration, temperature, and ore particle size.
12. The method according to claim 1 , wherein an optimal addition of acid added during the method is determined by content of acid-soluble gangue minerals and the copper minerals in the ore.
13. The method according to claim 12 , wherein the pregnant leach solution collected from initial irrigation of the heap following the aerated, but non-irrigated, cure phase is added to the ore during the agglomeration stage so as to utilize acid content in the pregnant leach solution during a subsequent cure phase.
14. The method according to claim 12 , wherein acid added to the ore during the agglomeration stage is determined by demand for copper mineral and gangue mineral dissolution in the aerated, but non-irrigated, cure phase.