Heap Leaching

A case study in mineral processing patents

In early 2022 a decision from the Australian Patent Office in Technological Resources Pty. Limited [2021] APO 52 (the Decision) got me thinking about the technology of heap leaching, and the many components or aspects of the heap leaching process that may properly be the subject of patent protection.

The Decision related to the examination of Australian Patent Application 2016347691 (the Patent Application) directed broadly to the leaching of chalcopyrite ores, in which the ore is agglomerated using a silver containing solution, and subsequently leaching the agglomerates with a suitable leach liquor.  The leach is in a preferred form conducted as a heap leach.

One of the traditional difficulties of heap leaching chalcopyrite ores is the passivation of the ore (ie. the coating of the ore during leaching with an unreactive layer that inhibits extraction of the copper).  The addition of the silver is said to limit this passivation and thereby improve leaching.

Examination of the patent application that is the subject of the Decision had reached an impasse and an ex parte hearing was requested by the Applicant.  Inventive step and support were at issue in the decision, as was novelty in turn.

Application Referred back to Examination

The novelty question arose as a result of the hearing officer reviewing the prosecution history of the Patent Application and noting citations raised but withdrawn during the international phase (the Patent Application is a national phase of a PCT application).  The hearing officer considered that one of the raised but withdrawn citations from the international phase was in fact still relevant and the Patent Application was referred back to examination for further consideration. This was despite submissions made on the Applicant’s behalf by their attorneys during the international phase regarding the content of the citation.  The hearing officer disagreed with those submissions and with the withdrawal of the citation, concluding that the citation was relevant for at least some of the claims of the application.

This is an interesting outcome and not one often seen in the Australian context.  It is worth noting that the prosecution history of an application will be reviewed carefully, even in an ex parte setting, when requesting hearings of this nature.  We are of course more familiar with careful consideration of prosecution history in the context of inter partes patent oppositions before the Patent Office, and patent infringement and revocation matters before the courts.

The patent application was ultimately granted in July 2022, after two further rounds of examination and response with amendments.

Subject Matter of the Application – Heap Leaching

As noted above, whilst the decision itself is of interest, it got me thinking again about heap leaching processes and the many mineral processing unit operations that are required to come together to make a successful heap leach.

The steps include a consideration of at least each of the following:

Ore preparation

Extraction – how, what characteristics does the extracted ore have?

Crushing – what type of crushing equipment is most suitable?

Grinding – what type of grinding equipment is more suitable?

Agglomeration – is it needed (fines, clays), what equipment to use, what should be added during agglomeration (water, agglomeration aids, binders, biological agents, lixiviant etc.), how and where should these items be added, what size agglomerate with what moisture content should be produced?

Curing – is it needed, can it occur in the heap, how long, at what temperature?

Heap Stacking

How many heaps, how high, where are they placed relative to other heaps?


What leaching agent to choose, what concentration of agent is appropriate, how will this be applied, dripper or sprays, surface and/or sub-surface, include a biological agent and if so what one, will the heaps run counter or co-current, over what period is it necessary to add lixiviant?


Does the leach mechanism require oxygen or air to be introduced to the lixiviant and/or the heap, through what means – pipework?

Heap Temperature

Does the leach mechanism require a certain temperature be maintained, does the location of the heap require heating of the lixiviant or anything else added (eg. air/oxygen), does the heap need to be covered?

Iron Handling

Is it ok if iron is deposited in the heap, if so what’s the preferred form, or should iron be handled in a different manner, perhaps precipitated in another heap?

Liquor collection/handling

How is the pregnant leach liquor going to be collected and transferred to downstream processing for recovery of the value metal(s), should the heap(s) be flushed?

Combination with other Leaching Technologies

Can/should the heap leach be combined with other leaching technologies, such as pressure oxidation, to ensure sufficient value metal extraction from the ore?

Everything Old is New Again

In the writer’s 30+ years of practice we’ve seen patent applications directed to combinations of any and all of these features of heap leaching.  It is a technology that moves in and out of favour as commodity prices ebb and flow.  However, as high quality ore reserves become less readily available, technologies such as heap leaching will be considered.

An example of this is the interest shown by many major resource players in the late 1990s and 2000s in the heap leaching of nickel laterite (oxide) ores.  Many patent applications were filed and many patents granted during this time that focused on the use of heap leaching of such ores.  Parties of interest included BHP, Minara Resources Limited, CSIRO and Vale.

In much the same timeframe significant interest was shown by similar companies in heap leaching using biological agents, most commonly carefully cultivated bacterial cultures.

Not only were many patent applications filed and patents granted, but there were many disputes between interested parties as they sought to gain an advantage through their intellectual property rights.

So, heap leaching is a great example of the many aspects of mineral processing routes that may provide a basis for patent protection.  If a combination of steps provides an unexpectedly beneficial result then that combination may well prove patentable and bring significant value to a company wishing to distinguish itself in a crowded marketplace.



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