When the crushing process is developed, especially in soft ores or from argillic ores, a large amount of fine material with a P80 of less than 100# is generated. At this particle size, the metal is highly liberated and cannot be discarded. In general, the amount of fines produced represents between 10 to 18% of the total material that enters the comminution process, such amount of fines could be positioned in the interstices of the porous bed thus increasing its apparent density and generating blockages to the leaching solution, which translates into an increase in the water table and the loss of valuable material.
The process of agglomeration and acid curing seeks to generate the adhesion, resistant over time, of the fine particles to the coarse material, through the formation of copper and iron sulfates and their upwelling by inverse capillarity. This chemical attack allows the appearance of microcracks through the action of the salts deposited in the pores of the rocks, which when mixed with the wetting solution increase in volume, thus exerting pressure towards the exterior of the particle until fragmenting it. Then the contact surface increases and along with it the kinetics of cupric ion recovery.
A deficiency in the agglomeration and curing process could generate a glomerate of low geomechanical stability, operational discontinuity of the transport system of the agglomerated material to piles due to clogging, lower production yield, lower copper extraction efficiency due to preferential channeling and compaction of the bed due to size segregation.
To guarantee the quality of the glomer it is necessary to monitor and control certain variables, such as:
Granulometric distribution and mineralogical characteristics of the material. Variables directly associated to the leaching solution consumption, since the higher the presence of fine material, the higher the wetting rate will be.
Dosage of the acid necessary to achieve sulfation, the acid concentration is also what gives the leaching solution its loading capacity, responsible for generating heat through exothermic reactions inherent to the process and acidifying the medium.
Bulk density which should always remain under the control band in order to optimize the permeability of the pile, specifically this variable should be kept between 1.3 to 1.4 g/ml.
Moisture content, which should generally be in the order of 8%, since at a higher moisture content the agglomerated particles could be loosened, allowing the production of a solid-liquid suspension. On the contrary, a deficit in humidity makes the formation of a liquid film between the particles impossible and leads to a segregation of fine material.
Resting time of about two weeks, to ensure the reaction of the acid present to then start the leaching process.
Although today’s technological development allows on-line monitoring of the most important operational variables, the human factor plays a fundamental role in the operation. The correct training of personnel and the implementation of good practices lead to improved decision making and a clear definition of the optimum quality from the technical-economic point of view of the final product.
