MIXTURE COMPRISING A SULFIDIZING AGENT AND AN ALKALINIZING AGENT AND ITS USE

Description

FIELD OF THE INVENTION

The present invention relates to a process and mixture for the safe dosing of a sulfidizing agent in a mineral flotation process.

BACKGROUND OF THE INVENTION

Traditionally, two methods have been employed for processing minerals in order to recover metals from their ores. In the case of ores composed of metal oxides, the recovery process has involved a sequence of steps that include leaching, followed by solvent extraction and finally electroextraction, generating pure metal cathodes as the final product.

In this methodology, the ore is initially subjected to a crushing stage to achieve an optimal size that allows for efficient processing operation. Subsequently, this crushed ore is placed in a specially designed heap, the base of which has been previously prepared to facilitate the collection and drainage of the resulting leaching solutions.

The heap composed of the previously crushed ore is then subjected to an irrigation process using a leaching solution, generally based on sulfuric acid. This leaching agent has the ability to dissolve the copper present in the ore, allowing for its separation and recovery.

In the case of ores composed of metal sulfides, the conventional approach for their recovery involves a process that includes initial crushing, followed by a froth flotation stage aimed at obtaining a sulfide concentrate. Subsequently, this concentrate undergoes a pyrometallurgical purification process.

In recent years, there have been significant advances in the development of hydrometallurgical processes that have allowed for the exploration of new pathways for processing sulfide minerals. In particular, there has been a focus on leaching and electroextraction of these minerals, highlighting bacterial leaching of copper sulfides and alkaline leaching of sulfide minerals.

In the case of bacterial leaching, the interaction with bacteria and the iron content present in the minerals plays a crucial role. These bacteria facilitate the oxidation of certain species of copper sulfides into soluble copper sulfate. Subsequently, this soluble copper sulfate can be recovered through solvent extraction and electroextraction, thus obtaining high-purity copper.

One of the complexities that certain mining operations must face throughout their activity cycle lies in the dual composition of the minerals, presenting as a combination of sulfides and oxides. This raises the dilemma of choosing between processing the mixture through flotation, which entails a potential loss of the oxides, or employing the hydrometallurgical leaching route, which may imply a decrease in the yield of the sulfides.

There are several mineral flotation processing plants that are fed with sulfide minerals mixed with oxides, or sulfides that have been oxidized on their surface and therefore cannot be recovered in normal flotation processes.

Altered or superficially oxidized sulfides behave in the flotation process like oxides, preventing the adsorption of collectors and, therefore, cannot be recovered in the flotation process.

In some cases, “sulfidization” is an important tool to improve the recovery of some oxides during the froth flotation of sulfides. In this case, a sulfidizing agent, such as sodium hydrosulfide, sodium sulfide, or polysulfides of different metals, is added. This incorporation is carried out during froth flotation or just before feeding the ground mineral pulp to the flotation cells. The purpose is to modify the surface of the oxides or sulfide minerals with superficial oxidation, allowing the sulfide collectors to adhere to the mineral surface and convert the mineral particles into hydrophobic ones, so that they can be recovered through normal sulfide flotation.

This methodology presents a notable advantage by enabling the recovery of significant amounts of metal that would otherwise be lost. Most notably, this improvement can be achieved without requiring investments in the acquisition of new infrastructure or equipment. In fact, the only distinction from the conventional flotation technique lies in the incorporation of the sulfidation agent into the process.

The implementation of sulfidization basically requires developing a product distribution system in the flotation circuit, in addition to adding safety controls, such as flow control and monitoring of hydrogen sulfide gas concentration in the environment, to ensure safe operation of the process.

Generally, in the specific case of sodium hydrosulfide, it is required to reach doses of approximately 80 grams per ton of ore. For example, copper flotation plants that use the addition of sodium hydrosulfide prior to or during flotation, where improvements in copper recovery can range from 2% to 8%.

In most copper ores, there are usually pyrite minerals. To obtain a clean concentrate free of iron contamination, lime is added to the flotation process. This raises the pH value to a level at which pyrite is depressed, meaning it does not float and is separated along with the tailings. Generally, this pH value is around 8 or 9.

To achieve the depression of pyrite, lime is normally incorporated during the grinding stage of the flotation process. In some cases, a new dosing is performed during the flotation stages.

Consequently, most plants carry out the flotation of their minerals in a pH range of approximately 8 to 9. Likewise, during the grinding stage, pH values range from 7 to 9.

Traditional sulfidization during the flotation process, where, for example, sodium hydrosulfide or another sulfidizing agent is added, manages to recover some minerals that oxidize on the surface and cannot be recovered with traditional collector reagents.

The Chilean patent application No. 201800471 discloses that it is possible to recover minerals that are easily soluble, even without the addition of an acid, by adding an ionizing agent in the grinding process.

It has been observed that minerals such as chalcanthite (CuSO₄·5H₂O) or brochantite (Cu₄(SO₄)(OH)₆) are normally lost in traditional flotation circuits.

It has also been observed that atacamite minerals Cu₂Cl(OH)₃ dissolve easily during grinding. For example, in an ore from the Atacama Region in Chile, which contains 0.41% atacamite mineral prior to grinding, when analyzed after grinding, it was found that the atacamite content had decreased to only 0.18%.

Some other plant feedings, such as minerals coming from old tailings, which still have a high copper content, sufficient to be processed, have a natural pH value of approximately 5, a condition in which part of the metal is present as soluble metal sulfate.

In most copper processing plants, lime is added during the crushing stage to depress pyrite. If this occurs, the dissolved copper precipitates as metal hydroxide, and as metal hydroxide, this metal is not recovered later in the flotation process, even if a sulfidizing agent is added to the flotation after this precipitation occurs.

The patent application JP2010229542 describes a method for separating pyrite from a copper-containing ore. In this method, the flotation of the ore is carried out, adding a flotation agent to the pulp and adjusting the pH to an alkaline value, specifically to pH 10 or higher.

The U.S. Pat. No. 1,483,270 describes the sulfidation process to increase copper recovery by floating non-sulfide ores.

The Chilean patent CL201800471 describes a process to improve copper recovery in flotation operations of minerals containing sulfides and/or easily soluble copper oxides by adding an ionizing sulfide.

The U.S. Pat. No. 4,008,072 A describes a process in which an alkaline sulfide is added in a specially designed reactor to an acidic leaching pulp to precipitate sulfides and recover them by flotation. This patent also indicates that sulfidization is “highly successful in processing some ores, such as lead ores,” but that “sulfidation has been of limited utility concerning copper ores.”

The German patent DE3690783 describes a process for concentrating copper oxide ore by flotation that involves pre-sulfidation with molten sulfur.

Some sulfidizing agents, such as alkaline sulfides like sodium hydrosulfide, can under certain pH dosing conditions release hydrogen sulfide gas, especially if dosed in acidic environments. While the mining industry uses sodium hydrosulfide on a large scale to depress copper in selective copper-molybdenum flotation processes in doses much higher than those used in sulfidization, plants generally have safety concerns regarding the incorporation of a sulfidizing agent in their processes, since if for any reason the pH of the pulp were to become acidic, for example, due to changes in lime dosing or changes in the mineralogical composition of the ore fed to the plant, there could be a risk of hydrogen sulfide gas emission, which would affect the safety of the operation. To mitigate these risks, gas measurement systems are generally installed that stop the dosing of the sulfidizing agent in the presence of hydrogen sulfide gas.

Some mining operations have their processing plants located very close to populated centers, so they try to avoid any odor problems in their processes to not disturb the coexistence with nearby communities.

Other mining operations have their flotation processes installed underground in caverns or in closed buildings with little ventilation. In these cases, ensuring air quality inside the flotation cavern or building becomes very important, so finding a way to safely dose a sulfidizing agent, without the risk of hydrogen sulfide gas emission, represents a significant advancement in safety.

In some operations, it has been demonstrated that sulfidization would generate significant improvements in process efficiency, but given the characteristics of the plant, for example, its location near a populated center or its location within an underground cavern with few ventilation possibilities, these operations prefer to simply forgo copper recovery by not applying a sulfidizing agent to avoid exposing themselves to the risks that such a process could entail, either to their collaborators working in the flotation plant or by affecting nearby communities due to gas and odor emissions.

On the other hand, sulfidizing agents are generally sulfurated products in aqueous solution that have a relatively high crystallization point, such as sodium hydrosulfide at 42%, which has a crystallization point in its pure form of around 15° C. and therefore must be handled with great care to avoid crystallization in the dosing or storage process, especially in operations located at high altitudes, as is the case with the Chilean mining industry.

The problem of product crystallization is particularly exacerbated when there are other salts present or when the product is mixed with alkaline products such as sodium hydroxide, lime, etc., either generating a solid directly or a highly viscous pulp, depending on the mixing proportions.

Considering the above, there is a need to have a process that allows for the incorporation of sulfidizing agents to improve copper production, but that at the same time can be used in mining operations close to populated areas or underground operations, safely and without problems of crystallization and/or increased viscosity of the sulfidizing agent before being incorporated into the mineral mixture.

SUMMARY OF THE INVENTION

The present invention provides a process and a mixture for the safe dosing of a sulfidizing agent such as sodium hydrosulfide, sodium sulfide, potassium hydrosulfide, potassium sulfide, or calcium sulfide, polysulfides of the same in the flotation process, especially in operations where this type of reagents is normally not used due to safety restrictions to avoid the emission of hydrogen sulfide gas during the process.

The inventors developed a process where, instead of dosing the sulfidizing agent directly into the flotation process after grinding, as is traditionally done in the industry, this sulfidizing agent is mixed in a prior stage with lime slurry. In this way, lime is added, which allows for the depression of the present pyrite while maintaining the medium at an alkaline pH that prevents the formation of hydrogen sulfide.

DETAILED DESCRIPTION OF THE INVENTION

Surprisingly, it was found that in the proportions that sulfidizing agents are usually dosed into the flotation process to recover altered or oxidized copper and the lime used to depress pyrite, and under the conditions of lime and water proportions of the lime slurry that are typically used in flotation plants, it is possible to mix the sulfidizing agent with the lime slurry without generating a crystallization problem or significant rheological change in the obtained lime slurry. Therefore, if an ionizing sulfide or a sulfidizing agent, such as sodium hydrosulfide, sodium sulfide, potassium hydrosulfide, potassium sulfide, ammonium hydrosulfide, or ammonium sulfide, hydrogen sulfide (H2S), potassium, sodium, calcium, magnesium, or ammonium polysulfides are added to the lime slurry dosed to the flotation plant, instead of dosing the sulfidizing agent to the flotation process or to the mill as described in the literature, the risk of hydrogen sulfide gas emission in the process is completely eliminated, since the lime slurry, fed in a proportion much higher than that of the sulfidizing agent, ensures that the pulp and the sulfidizing agent are always at an appropriate pH to not release hydrogen sulfide gas. Thus, if the addition of lime to the process were to be accidentally stopped, the addition of the sulfidizing agent would also immediately stop, eliminating any possibility of dosing in an acidic environment.

In this way, by mixing the sulfidizing agent beforehand with lime slurry in proportions that avoid a rheological change in the lime slurry, a sulfidizing agent can be safely dosed into the flotation process without the risk of hydrogen sulfide gas emission and without the need to modify the existing plant.

Furthermore, the dosing of the sulfidizing agent over the lime slurry ensures that at all times, this dosing occurs over an alkaline pulp or solution, thus avoiding the formation of hydrogen sulfide gas in the process.

By sulfidizing in this manner, several advantages are visualized, some of which are listed below:

The described process eliminates the risk of hydrogen sulfide gas emission in the flotation process.

By dosing the sulfidizing agent in this way, there is no need to install reagent distribution pipes in the plant, as the existing lime dosing system is used.

It allows the sulfidization process to be applied in operations where, due to location characteristics, either near a populated center or within a poorly ventilated cavern, under normal conditions, a sulfidizing agent could not be directly applied to the process as is traditionally done.

There are no problems of increased viscosity or crystallization of the sulfidizing agent in plant operations where lime doses are approximately 10 times higher than the doses of the sulfidizing agent.

The studies conducted showed that a mixture of a sulfidizing agent, in this case sodium hydrosulfide, with calcium oxide in lime slurry at concentrations of between 5 and 25% CaO in proportions of 0.1 to 10 up to 1 is to 10 can be used without significantly affecting the viscosity of the slaked lime slurry, thus allowing for a joint dosing.

EXAMPLES

An 8% lime slurry in water was prepared, and sodium hydrosulfide was added in a proportion of one to ten in relation to the lime dose.

A flotation test was conducted in a 2-liter laboratory flotation cell with a mineral composed of 92% copper sulfide mineral and 8% oxidized mineral, with an overall grade of 0.7% copper.

Table 1 shows the results obtained.

Additionally, tests were conducted to evaluate the fluidity of the mixtures of [slaked lime slurry/NaSH] and [slaked lime slurry/sulfide mixture].

Slurries of lime were prepared at 5%, 10%, 15%, 20%, and 25% using lime with 80% purity, which is commonly used in the plants.

Furthermore, two solutions of sulfiding agent were prepared, NaSH at 42% and a solution of a sulfide mixture at 38%.

Tables 2 and 3 show the results.

In both cases, for concentrations and proportions greater than those indicated, the formed mixture begins to increase its viscosity until total solidification, which prevents its use and handling.

The pH of the slaked lime slurry is approximately 12.5 and that of the sulfidizing agent is around 13. Therefore, the formed mixture has a pH of at least 12. This value prevents the production of hydrogen sulfide, so the developed mixture allows for its safe use in mining operations located in enclosed places such as caves or in operations close to populated areas.

The preceding specification is considered solely illustrative of the principles of the invention. The scope of the claims should not be limited by the embodiments provided as examples in the previous section, but should be given the broadest interpretation consistent with the descriptive memory as a whole.