ВЫБОР СХЕМЫ ПОДГОТОВКИ К ПЕРЕЧИСТКЕ ФЛОТАЦИОННЫХ КОНЦЕНТРАТОВ ПНЕВМАТИЧЕСКОЙ ФЛОТАЦИИ ЗОЛОТОСОДЕРЖАЩИХ РУД МЕСТОРОЖДЕНИЙ «КОКПАТАС» И «ДАУГЫЗТАУ»

УДК 66.01

ABSTRACT

The study addresses the challenge of low gold recovery from refractory sulfide ores at the Kokpatas and Daugyztau deposits. The primary goal was to select an optimal pretreatment scheme for rougher flotation concentrates produced by a Jameson Cell L500 pneumatic machine. The methodology involved a comparative analysis of two scenarios: mechanical attrition and regrinding. In Scenario 1, the concentrate underwent surface cleaning (attrition), while Scenario 2 included regrinding in a ball mill. Particle size distribution analysis showed that regrinding reduced the D90 value from 94 μm to 76 μm, ensuring better mineral liberation. Experimental results from 22 observations demonstrated that the regrinding circuit increased gold recovery from 23.3% to 40.7% and improved the Au-concentration ratio from 5.2 to 10.7 times. Statistical analysis confirmed the stability of these results. The findings suggest that for these specific ores, additional grinding is a prerequisite for effective cleaning stages, as surface cleaning alone cannot overcome the limitations of unliberated mineral intergrowths. This research provides a quantitative justification for integrating regrinding units into pneumatic flotation circuits.

АННОТАЦИЯ

В данном исследовании рассматривается проблема низкого выхода золота из тугоплавких сульфидных руд на месторождениях Кокпатас и Даугызтау. Основной целью было определение оптимальной схемы предварительной обработки концентратов грубой флотации, полученных на пневматической машине Jameson Cell L500. Методология включала сравнительный анализ двух сценариев: механического измельчения и повторного измельчения. В сценарии 1 концентрат подвергался очистке поверхности (измельчению), тогда как сценарий 2 включал повторное измельчение в шаровой мельнице. Анализ гранулометрического состава показал, что повторное измельчение снизило значение D90 с 94 мкм до 76 мкм, обеспечив лучшее освобождение минералов. Результаты экспериментов, полученные на основе 22 наблюдений, продемонстрировали, что контур повторного измельчения увеличил извлечение золота с 23,3% до 40,7% и улучшил коэффициент обогащения Au с 5,2 до 10,7 раз. Статистический анализ подтвердил стабильность этих результатов. Полученные данные свидетельствуют о том, что для данных руд дополнительное измельчение является обязательным условием для эффективности очистительных стадий, поскольку одной только поверхностной очистки недостаточно для преодоления ограничений, связанных с неразделенными минеральными проростками. Данное исследование предоставляет количественное обоснование для включения установок повторного измельчения в схемы пневматической флотации.

Keywords: flotation, pneumatic flotation machines, Jameson Cell, dispersed sulfide particles, particle size analysis, regrinding, attrition, gold recovery.

Ключевые слова: флотация, пневматические флотомашины, Jameson Cell, дисперсные сульфидные частицы, гранулометрический анализ, доизмельчение, оттирка, извлечение золота.

Introduction

Today, with the rapid development of the mining and metallurgical industries, traditional flotation equipment for difficult-to-float gold-sulfide ores does not ensure the complete recovery of valuable components. In this regard, significant attention is being paid to alternative methods for the flotation of refractory ores. In particular, there is a trend toward the use of pneumatic flotation machines for the flotation of dispersed sulfide particles. This paper provides a brief overview of research on the selection of a preparation scheme for the re-flotation of primary flotation concentrates from the “Kokpatas” and “Daugyztau” deposits, obtained using pneumatic flotation cells, using the Jameson Cell L500 as an example. As the processing of increasingly low-grade and complex refractory ores becomes more common, the importance of technologies that ensure the efficient recovery of fine-grained and difficult-to-concentrate particles is growing. One such technology is flotation using pneumatic flotation machines—machines with a unique aerator design that allows for the formation of a large number of microbubbles, which increases the frequency of particle-bubble collisions and leads to increased recovery of the valuable component [1]. The Jameson Cell L500 pneumatic flotation machine used in this study is a device in which the primary flotation effect is achieved through intensive aeration of the pulp and the creation of a brief but highly effective zone of initial contact between particles and air bubbles [2]. The machine operates by converting a pressurized pulp jet into a high-velocity flow capable of inducing and dispersing air without the use of mechanical agitators or blowers. The most active interaction between particles and bubbles occurs in the aerator—the zone where the pulp comes into contact with the induced air almost immediately after entering [3]. A key feature of the process is that air is naturally induced by pressure differences and the shear forces of the jet. When the high-velocity flow enters the liquid medium, the induced air is dispersed into fine bubbles. This is precisely what determines the high efficiency of flotation in the Jameson Cell L500: a significant number of small bubbles with a large total interfacial area are formed in the aerator, thereby substantially increasing the probability of particles colliding with the bubbles and subsequently adhering to them [4]. This entire stage takes a few seconds, but the high turbulence intensity and the speed of the hydrodynamic processes ensure the rapid formation of stable “particle–bubble” aggregates. After leaving the aerator, the aerated slurry moves into the main zone of the tank, where the interaction between particles and bubbles continues, but now under the conditions of a calmer, self-sustaining flow [5]. Pulp circulation occurs due to the density difference between the aerated mixture and the surrounding liquid. It is this natural circulation that keeps the mineral particles in suspension without the need for mechanical agitation, making the process not only less energy-intensive but also more selective [6]. The residence time of the material in the pulp zone is several minutes, which allows for the completion of aggregate formation and ensures that particles passing through the aerator have additional opportunity for contact with the bubbles. A foam zone forms at the top of the apparatus, where the final separation of mineralized bubbles from the liquid phase takes place. The foam is maintained in a stable state, which allows for the control of its washing and the removal of the concentrate. The residence time of particles in the foam zone is relatively short—ranging from a few seconds to a minute—but during this interval, effective phase separation and the formation of a concentrate with specified quality parameters are ensured [7].

Thus, the operation of the Jameson Cell L500 pneumatic flotation machine is based on the creation of a high-intensity primary contact zone, self-organizing pulp circulation in the tank, and a stable foam zone, which allows for the effective flotation of finely dispersed particles and ensures high productivity with minimal energy consumption. Despite the advantages of pneumatic flotation machines, the processing of refractory ores continues to face the problem of mineral surface contamination, as well as insufficient liberation of gold-bearing minerals in the primary flotation concentrate. Under-ground or contaminated particles reduce the quality and recovery during re-flotation.

One of the key approaches to improving the efficiency of flotation concentrate re-flotation is the optimization of the product preparation stage, which includes mechanical grinding or re-grinding of the concentrate. Studies show that regrinding concentrates prior to re-flotation increases the degree of intergrowth liberation, which directly affects the quality of the final concentrate and the recovery of valuable components [8]. At the same time, in some cases, the surface quality of the minerals—which is formed during the primary flotation process—plays a key role. On contaminated surfaces of sulfide minerals, films of sulfates, carbonates, and oxidized compounds often form after flotation, which inhibit particle interaction with collectors and reduce the selectivity of the process. To eliminate these adverse effects, mechanical grinding is used, which reduces the content of sulfate and carbonate films on the surface. However, despite the positive effects achieved through grinding, a number of industrial and laboratory studies show that mechanical surface cleaning is effective only when the feed concentrate has sufficient liberation. If the original intergrowths remain intact, grinding does not increase recovery, since the key cause of losses lies not in a contaminated surface but in the insufficient liberation of gold-bearing and other sulfide minerals [9]. Therefore, in processing schemes for finely grained and difficult-to-beneficiate ores, especially gold-sulfide ores, further grinding of the concentrate prior to re-cleaning is considered a priority operation, ensuring the liberation of intergrowths and a reduction in losses of valuable components in the re-cleaning tailings. This paper represents the authors’ attempt to determine the optimal pre-cleaning process (scouring or re-grinding) for flotation concentrates from the “Kokpatas” and “Daugyztau,” obtained using pneumatic flotation machines, using the Jameson Cell L500 flotation machine as an example.

Materials and methods

The study subjects were primary flotation concentrates obtained using a Jameson Cell L500 pneumatic flotation machine from the flotation tailings (control flotation tailings) of ores from the Kokpatas and Daugyztau deposits Hydrometallurgical Plant No. 3 of NMMC JSC. 

The studies were conducted at Hydrometallurgical Plant No. 3 of NMMC JSC: in Scenario No. 1, the primary flotation concentrate was re-flotation using a 100-liter semi-industrial re-flotation machine. In Scenario No. 2, the primary flotation concentrate was reground using a ball mill with a 0.8 x 1.8 grid discharge. In both scenarios, the primary flotation concentrate that had undergone grinding or regrinding was re-flotation on a Jameson Cell L500 pneumatic flotation machine. The tests were conducted in an open circuit.

Results and discussion

When re-processing the re-ground concentrate from the primary flotation stage, the recovery rate was 40.7%, compared to 23.3% in the process involving the re-processing of the scraped-off concentrate, using the same feed material and comparable yields. Furthermore, the quality of the product obtained by re-cleaning the re-ground primary flotation concentrate was more than twice that of the product obtained in the scheme involving re-cleaning of the rejected concentrate (see Table 1—comparison of overall results, and Tables 2 and 3—detailed results for each scenario). Based on the results of the study of the particle size distribution of the screened and re-ground primary flotation concentrates (see Figures 1 and 2), it is evident that re-grinding led to greater mineral liberation: D90 (the particle size at which 90% of the product mass is smaller) is 94 μm in the screening scenario and 76 μm in the regrinding scenario. Based on the above, it can be concluded that in the case of re-processing of primary flotation concentrates from the “Daugyztau” and “Kokpatas” deposits, it is not simply de-flotation that is required to remove surface contaminants from the minerals in order to increase particle hydrophobicity, but rather re-grinding, which is intended to improve mineral liberation.

Table 1

Comparative performance of primary flotation concentrate re-flotation: Process 1 (with attrition) vs. Process 2 (with regrinding)

Table 2

Detailed re-flotation results of the primary concentrate with tailings discharge

Table 3

Detailed re-flotation results of the primary concentrate with regrinding

Figure 1. Particle size distribution of the reground primary flotation concentrate

Figure 2. Particle size distribution of the dewatered primary flotation concentrate

The required samples were collected by extracting pulp directly from the production cycle. A total of 150 samples were obtained (feed, concentrate, and tailings from primary and secondary flotation—25 samples each). All pulp samples were dried in drying ovens at a temperature of 80 degrees Celsius, ground, and analyzed at the Central Plant Laboratory of Hydrometallurgical Plant No. 3 of “NMMC” for chemical composition using the assay method in accordance with the approved procedure and for particle size distribution using a laser particle size analyzer.

Conclusion

The use of the Jameson Cell L500 pneumatic flotation machine demonstrated high efficiency in recovering dispersed particles during the processing of complex refractory gold-sulfide ores from the Kokpatas and Daugyztau deposits. Mechanical treatment of the concentrate prior to the cleaning stage has a decisive impact on the final metallurgical performance. The study revealed that surface cleaning (attrition scrubbing) alone is insufficient for poorly liberated minerals, resulting in a lower recovery rate of 23.3%. Experimental data confirmed that the regrinding circuit significantly improves mineral liberation, reducing the D90 value from 94 μm to 76 μm. This led to a substantial increase in gold recovery to 40.7% and improved the enrichment ratio to 10.7, more than doubling the performance of the attrition scheme. For the refractory sulfide ores of these specific deposits, the inclusion of a regrinding stage before cleaning pneumatic flotation concentrates is highly recommended. This approach minimizes the loss of valuable components in the tailings and ensures high-quality concentrate production with optimized energy consumption.

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