High temperature leaching process
A method of conducting a bioleaching process including the steps of forming a main heap, culturing at least one microorganism which exhibits bioleaching activity in a predetermined temperature range, monitoring the temperature in the main heap, which is a result, at least, of microbial leaching activity and inoculating the heap with the cultured microorganism at least before the temperature reaches the predetermined range.
1. A method of conducting a bioleaching process to recover metal content from an ore which contains the metal that includes:
(a) forming a main heap from the ore,
(b) inoculating the heap with iron oxidizing mesophilic microorganisms, sulphuroxidising mesophilic microorganisms, and moderate thermophilic microorganisms,
(c) culturing a mixed inoculum of moderate thermophilic and thermophilic microorganisms by using a plurality of reactors, each reactor being used for a respective microorganism that is active in a particular temperature range and wherein the particular temperature range is selected from temperatures which encompass the following temperature values 25° C., 35° C., 50° C., 55° C. and 65° C.,
(d) adding carbon dioxide to the main heap while the main heap temperature is in a mesophilic temperature region, and
(e) inoculating the main heap with the mixed inoculum before the heap temperature reaches a thermophilic temperature range to maintain the cell count in the heap at a value of from 10 6 to 10 12 cells/ton of ore.
2. A method according to claim 1 wherein an inoculum from each reactor is directed to a pond which is aerated and in which the inoculum is stored and maintained and a mixed inoculum from the pond is added to the heap as necessary.
3. A method according to claim 1 wherein inoculum from at least one of the reactors is added to crushed ore together with acid to form an inoculated ore, and the inoculated ore is added to the main heap to introduce the inoculum to the main heap.
4. A method according to claim 1 wherein inoculum from at least one of the reactors is used to irrigate an auxiliary heap which is operated as an inoculum generator and ore from the auxiliary heap, onto which active microorganisms have attached themselves, is added to the main heap to introduce the inoculum to the main heap.
5. A method according to claim 1 wherein an intermediate leach solution and raffinate produced by passing a pregnant leach solution, draining from the main heap, through a metal recovery process, are recirculated to the main heap to increase the active cell count in the main heap.
6. A method of bioleaching ore comprising:
(a) forming a heap from the ore,
(b) inoculating the heap with iron oxidizing microorganisms selected from the group consisting of mesophilic microorganisms, sulphuroxidising mesophilic microorganisms, moderate thermophilic microorganisms and mixtures thereof,
(c) culturing a mixed inoculum of moderate thermophilic and thermophilic microorganisms by using a plurality of reactors, each reactor being used for a respective microorganism that is active in a particular temperature range and wherein the particular temperature range is selected from temperatures which encompass the following temperature values 25° C., 35° C., 50° C., 55° C. and 65° C., and
(d) inoculating the heap with the mixed inoculum before the heap temperature reaches a thermophilic temperature range to maintain the cell count in the heap at a value of from 10 6 to 10 12 cells/ton of ore.