The addition of salt (NaCl) is essential in the chloride leaching process. It can be added to the process as brine or in solid form.
From a chemical point of view salt produces the same effect added as brine or in solid form. From a physical point of view, however, the results may be different. The wetting of the mixture, the quality of the agglomeration and the curing obtained from the treated mineral must be evaluated before deciding on an option.
There are plants that operate with agglomerating equipment and others that mix by means of transfer chutes. The processes that have agglomerators obtain better mixing and agglomeration of the minerals they treat, which are key aspects for the next stages of curing, resting, aeration and irrigation cycles.
How to prepare the brine, where to add the brine, how do we capture the gases generated? These are just some of the initial questions that must be considered before deciding on solid salt or brine.
For large scale mining, the equipment (reactors) required to prepare the volumes of brine that the process will demand will mean major investments in design and construction of facilities and infrastructure. At some sites, dissolution requirements of up to 500 mt/d or more of solid salt can be reached (daily processing based on an addition of 10-15 kg NaCl per mt of ore processed). Solid salt is simpler to handle and can be added in solid form along with the ore feeding the process.
The brine is normally incorporated into the process before or together with the addition of acid and refining to the ore (in some processes the brine is added to the refining prior to being added to the ore).
The mixture of salt and sulfuric acid generates as a parallel reaction gaseous HCl as part of a transient exothermic reaction that enhances the leaching reactions of the treated minerals.
Those processes that have an agglomerator have the advantage of centralizing gas collection in a specific area where it is mainly produced, as opposed to operations that mix in belts, where the generation of HCL occurs in the transfer chutes to the piles where the material is deposited, which makes it difficult to manage.
There is industrial evidence of the application of the two salt inclusion methodologies to the process. So far, brine inclusion has been shown to be less effective than solid salt with respect to the time required to complete the process.
Although what has been described above indicates that the addition of solid salt is simpler than using brine and would have better performance, it is still necessary to evaluate the optimum particle size of the salt to be used (there are sites where a very large particle size of the salt has shown the existence of salt grains in the riprap) and which characteristics will influence the good design of the feeding system (silos, chutes and belts).
The implementation of the alternative of the type of salt to be used (solid or brine) should be discussed with experts whose practice and knowledge of the subject will ensure the best decision on this key factor in the chloride leaching process.
