Here is an oft-repeated definition of the word agglomeration, the topic of this posting:

  1. The act or process of collecting in a mass; a heaping together.
  2. A jumbled cluster or mass of usually varied elements.

A better definition for our purposes is from outotec: “The formation of a lump by the coalescence of smaller globules; refers to briquetting, nodulizing, sintering, etc.

A persistent cause of failure of heap leach operations is the presence of excess fines in the materials placed on the pad. Excess fines results in a low permeability material and thus the seepage rate of the lixiviant is too slow for economic pad operations.

A similar situation occurs if you intend to leach tailings. Generally tailings are primarily clay and silt—the seepage rate of most lixiviants through these fine-grained, low permeability materials is generally too slow for cost-effective heap leaching.

It may be possible to agglomerate the fines in the ore or the tailings to be leached. This normally involves adding a binder to the fines so that the resulting material consists of individual particles that are larger than the original material and hence of higher permeability.

Additives for effective agglomeration vary greatly and depend on the ore type and gradation, the chemistry of the ore and the lixiviant, and the physical characteristics of the heap leach pad, including the height and the stresses imposed on the agglomerated fine grained materials.

Typical agglomerating materials include Portland cement, lime, or ash for gold ores. Polymers have been used for coppers ores. In some cases, after crushing, sulfide ores may be treated by roasting, autoclaving, bio-oxidations, or chlorination prior to heap leaching. The web notes these recent patent applications for agglomeration additives:

No 6428597: Methods and compositions for increasing the recovery of precious metals from ore during heap leaching operations are disclosed. The methods add polypropylene glycol and alkylphenol ethoxylate in a paraffin oil solvent with the cyanide lixivant to the ore heap.

No 5186915: Agglomerating agent and method for use in heap leaching of mineral bearing ores. A moderate to high molecular weight anionic polymer in combination with lime provides a highly effective agglomerating agent. The anionic polymer is preferably a copolymer of acrylamide and acrylic acid. The polymer preferably has a molecular weight of about 1 to 8 million or higher.

From Metallic Ventures Gold comes this description of testing they plan to characterize the leachability of agglomerated materials:

A testing program for evaluation of pulp agglomeration heap leach processing, based on results from the testing described above. As discussed earlier, practicality of selectively mining and processing high grade ore should be closely considered before proceeding with such a testing program. The relative tonnages of high grade and low grade ore from the Converse Project will also be an important consideration for potential pulp agglomeration processing. Pulp agglomeration heap leaching is simply a combined process whereby tailings generated from processing the milled, high grade ore are agglomerated onto the crushed lower grade ore before heap leaching. This processing presents a number of potential advantages over conventional milling and/or heap leaching. Pulp agglomeration allows for the tailings from a conventional milling process (cyanidation, gravity or flotation) to be leached on a heap over a long period of time, thereby incrementally increasing metal recovery from the higher grade ore. Because the tailings are placed onto the heap, a conventional tailings impoundment may not be required. In the case of the higher copper ores present in the Converse deposit, pulp agglomeration allows for the potential removal/recovery of copper from the high grade ore before placement on the heap, potentially decreasing cyanide consumption in the heap. A detailed testing program to evaluate pulp agglomeration processing cannot be made until some of the testing described above has been completed.

Here is another from Bear Creek Mining Corporation

Preliminary metallurgical test-work has shown that heap-leaching processing methods will likely be the best option for lower grade portions of the Santa Ana deposit, whereas milling and vat-leaching may be used for the "high-grade" silver mineralization encountered in the Phase III drilling program. Both the mill products and crushed heap-leach material will ultimately be combined on the heap-leach pad in a processing method known as pulp agglomeration. The positive results of the first-phase metallurgical program were recently confirmed by two separate laboratories based on 10 representative samples from five drill holes spaced throughout the Santa Ana deposit. Bottle-roll tests from the two labs showed average silver recoveries of 71% and 85%, respectively. At this stage, Bear Creek anticipates that the potential combined leach recovery of both the mill products and crushed heap-leach material will be about 70%, with up to 85% recovery after grinding of the higher grade silver mineralization. Large-scale column-leach tests are under way in order to evaluate expected recoveries under actual heap-leach conditions and define optimal crush size, as well as cyanide and lime consumption.

The bad news is summarized by this extract from a 2004 research proposal, the results of which are, I think, at this link:

Currently, heap leaching operations are plagued by poor permeability of the heap which leads to uneven distribution of the leaching solution, unleached zones in the heap, and poor metal recovery. This poor permeability is caused by excessive amounts of fine particles clogging the spaces between the larger ore particles. By agglomerating ores, individual ore particles wil be held together in coarse, porous masses with the use of a binder. ….Unfortunately there are no know agglomeration binders that work satisfactorily in the acidic environment encountered in many heap leach operations, and few binders that produce high strength without sintering. Alkaline binders, for instance, are destroyed by acid attack. Other binders are synthetic polymer compounds, but many of these binders also perform poorly in acidic environments. Because of problems with effectiveness or cost, all binders that have been evaluated for use in acidic leaching conditions have either performed poorly, or proven to be be too expensive for commercial use.

I suspect there really is only one person who can sort all this out: W. Joseph Schlitt.

For what it is worth, here are the suppliers in Infomine who come up under the key word agglomeration: