Pressure, Time, and Type of Gas of Micro-Nanobubbles on the Removal of Heavy Metals - As, Sb, and Cd in Acidic Effluents

Abstract

The objective of this research was to evaluate how pressure, time, and type of gas in micro-nanobubbles affect the removal of heavy metals arsenic, antimony, and cadmium in acidic effluents. A three-factor experimental design was employed, varying the type of gas (air and oxygen), pressure (20, 40, and 60 psi), and treatment time (5, 10, and 15 minutes). To simulate the conditions of an acidic effluent, a solution with an initial pH of 1.77 was prepared in the laboratory, which, in contact with sulfide minerals containing iron, arsenic, antimony, and cadmium, was leached and subsequently adjusted to a pH of 6.5 by adding lime. The results showed significant variation in metal removal by adjusting the pressure and type of gas: with oxygen at 60 psi, arsenic removal reached 48.31%, while with air at 20 psi it reached 83.59%. For antimony, the highest removal with oxygen was 27.34% at 40 psi, compared to 90.78% with air at the same pressure. The exposure time to micro-nanobubbles (MNB) did not produce significant changes in metal removal. In conclusion, it is evident that pressure and type of gas are critical factors in the efficiency of heavy metal removal, more so than the duration of the treatment with micro-nanobubbles.

Keywords:
Air and oxygen MNB; acidic water treatment; metal removal.

HIGHLIGHTS

Critical gas type in metal removal.

Time does not affect treatment efficacy.

INTRODUCTION

Wastewater generated by the mining industry, particularly acid mine drainage (AMD), represents a significant environmental challenge. This effluent, with its load of heavy metals such as As, Sb, and Cd and its low pH, can have long-term detrimental effects on aquatic and terrestrial ecosystems [¹,²]. The focus is on finding treatment methods that are effective and economically viable, minimizing environmental impact according to the maximum permissible discharge limits for liquid effluents in mining [³,⁴].

Conventional wastewater treatment methods, such as chemical precipitation, are well-established and known for their simplicity and effectiveness. However, the production of sludge and the management of resulting waste pose challenges in terms of sustainability and operational costs [⁵-⁷]. Alternatively, adsorption using carbon nanotubes has been identified as a promising approach due to its ability to remove organic and inorganic contaminants in economically efficient ways [⁸-¹⁰].

The application of micro-nanobubbles (MNB) in wastewater treatment is an emerging area of interest, which has shown potential to enhance gas transfer and the activity of microorganisms involved in bioremediation [¹¹-¹³]. Despite the advances, the literature on the effectiveness of MNB under varied conditions is scarce and often contradictory, requiring further research to establish the robustness of this technology [¹⁴-¹⁶].

Among emerging methodologies, electrocoagulation presents itself as a viable alternative, providing a sludge-free treatment method with comparable efficacy to conventional methods [¹⁷,¹⁸]. Electroflocculation, a process that combines partial electrolytic oxidation with precipitation, has proven effective in removing a wide range of contaminants and deserves further exploration as a sustainable solution for heavy metal removal [¹⁹,²⁰].

The progression in research on treatments for acidic effluents has been significant, as evidenced by pioneering studies in the field. Zamora and Trujillo in 2016 compared methodologies for treating acidic waters from the San José Mine, concluding that neutralization-precipitation with lime inside the mine was the most advantageous [²¹]. In a different context, Vicente C. and Valverde J. in 2018 documented significant reductions in lead and zinc levels in mining effluents using air micro-nanobubbles, a procedure replicated by Vicente in his undergraduate thesis with equally promising results [²²]. Similarly, García P. and Valverde J. in 2017 demonstrated the effectiveness of MNB in treating industrial acidic effluents, highlighting the importance of pH in the process [²³]. Azañero G. and Gutierrez E. in 2016 contributed to the methodology of arsenic extraction, emphasizing the influence of particle size [²⁴]. Finally, Chavez D. and Quiroz E. in 2020 optimized the application of MNB for arsenic reduction in alkaline solutions, underscoring the relevance of pressure and treatment time [²⁵]. Valenzuela and Valverde reduced lead and silicon in effluents from washing tower waters using air-ozone nanobubbles [²⁶].

These antecedents collectively underline the versatility and efficacy of micro and nanobubbles in contaminant treatment, establishing a robust foundation for future research in environmental remediation.

The present research focuses on studying MNB under different conditions of pressure, time, and type of gas to evaluate their effectiveness in reducing heavy metal levels in acidic effluents. This methodological approach seeks to contribute significantly to the existing literature by providing a critical evaluation and empirical data that could influence future effluent treatment practices in mining.

The formulation of the problem was, what are the critical factors used in the reduction of heavy metals As, Sb, and Cd present in acid effluents by applying MNB of air and oxygen?

The purpose of this work is to determine the potential of MNB as an environmentally sustainable and technically effective effluent treatment technology, filling a gap in current understanding and offering prospects for future industrial applications. This study aims to provide a comprehensive analysis that not only contributes to the scientific literature but also aligns with sustainability and efficiency goals in the mining industry.

MATERIAL AND METHODS

Materials

The research employed a variety of standard laboratory materials and specialized equipment to ensure the precision and replicability of the results. The list of materials included beakers of various capacities (50, 100, 500, and 1000 mL), bottles for storing 10 liters of water, buckets with a capacity of up to 20 liters, and graduated cylinders (250, 500, and 1000 mL). Test tubes (15 mL), filter paper, and pH measurement strips were also used.

For the study, the population consisted of laboratory-generated acidic effluents, characterized by their specific concentrations of arsenic (As), antimony (Sb), and cadmium (Cd). The selected sample comprised a total volume of 200 liters of acidic water, prepared through the leaching process of sulfide minerals and enriched with effluents from metallurgical operations and acidic digestions. The initial chemical composition of the sample is detailed in Table 1, providing a quantitative basis for evaluating the treatments applied subsequently.

Table 1
Chemical analysis of the laboratory-generated acidic solution.

Element	Concentration (ppm)	Acidic water (pH=1.77)
Cadmium	(ppm)	0.12
Arsenic	(ppm)	50.22
Antimony	(ppm)	9.26

Methods

The study was based on an analytical methodology that integrated inductive and deductive approaches, utilizing experimentally obtained laboratory data and projecting its applicability in industrial settings. Additional variables such as pH and the mineralogical composition of the sample were considered, analyzing different mixtures and proportions of minerals for greater practical relevance.

In terms of the type of research, it is applied, as it is directly oriented towards solving specific problems related to the treatment and proper disposal of acidic effluents in laboratories. The study was structured around a three-factor experimental design, identifying the application time of micro-nanobubbles (MNB), the gas outlet pressure, and the type of gas used as independent variables. The concentrations of arsenic, antimony, and cadmium in the effluent were the dependent variables, whose variations were sought to be explained through manipulations of the independent variables. To ensure data integrity and result validity, parametric conditions such as pH and effluent volume were controlled, keeping them constant throughout the experimentation. The specification of the variables and their respective experimental levels are detailed in Table 2, providing a clear reference for data replication and analysis, which applied only two types of gases (air and oxygen) at three levels for convenience of authors.

Table 2
Independent variables and their levels in natural scale

Factor	Level 1	Level 2	Level 3
A: Pressure (Psi)	20	40	60
B: Application time (min)	5	10	15
C: Type of gas	Air and oxygen

The experimental methodology was meticulously designed to address the interactions between the study variables and their impact on heavy metal concentrations. This methodology included three fundamental stages: standardized preparation of the effluent sample, application of the micro-nanobubble (MNB) treatment in a controlled environment, and precise quantification of metal concentrations.

Regarding machinery and equipment, the study utilized a rotary roller bench for solids sample homogenization and leaching of metals, a magnetic stirrer to facilitate chemical reactions in solutions, and micro-nano bubble generator equipment patented by PhD. Jhonny Valverde Flores (Patent no. PE20170424, 2017), with an air compressor capable of up to 200 psi.

The schematic diagram of the effluent treatment process (Figure 1) breaks down the system setup, identifying key components from the water storage tank (A), pump (B), flow meter (C), air generator (D), pressure valve (E), pressure gauge (F), main valve (G), MNB generator (H), and air MNB treated waters (I).

Figure 1
Schematic diagram of effluent treatment.

Procedure for analysis of metals As, Sb and Cd

250 mL of solution sample is obtained in a beaker, 10 mL of HNO₃ Q.P. is added, placed on a heating plate at 80 °C, and until the solution is reduced to 20 mL, then it is transferred to a 50 mL container, and the reading is carried out using atomic absorption spectrometer equipment.

Additionally, the block diagram of the experimental procedure with MNB (Figure 2) provides a structured representation of the experimental workflow, detailing the sequence of operations and interactions between the different elements of the treatment system.

Figure 2
Block diagram of the testing procedure with micro-nanobubbles.

RESULTS

The results of the tests using micro-nanobubbles with air and oxygen are presented. Table 3 shows the chemical analysis results of acidic water containing As, Sb, and Cd, where the initial concentrations were 50.22 ppm for arsenic, 9.26 ppm for antimony, and 0.12 ppm for cadmium.

Table 3
Chemical analysis results of acidic water containing As, Sb, and Cd

Element	As	Sb	Cd
Concentration	(ppm)	(ppm)	(ppm)
Acidic wáter, pH = 1.77	50.22	9.26	0.12
Acidic water + MNB (O2), pH = 1.85	46.69	7.85	0.07
Acidic water + lime, pH = 6.5	4.08	3.82	0.12

Table 4 shows the chemical analysis results of acidic water treated with micro-nanobubbles for arsenic removal. For example, using air at 40 psi for 5 minutes resulted in an arsenic concentration of 0.99 ppm, with an average removal efficiency of 75.81%. This result allows us to determine, unlike the other results, that the optimal pressure is 40 psi in a fairly short time of 5 minutes.

Table 4
Chemical analysis of acidic water treated with micro-nanobubbles (MNB) for As removal (%).

Gas type	Pressure (psi)	Time (min)	As (ppm)	Average As removal (%)
Air	20	5	0.792	80.59
Air	20	10	0.676	83.42
Air	20	15	0.541	86.75
Air	40	5	0.987	75.81
Air	40	10	1.011	75.23
Air	40	15	1.073	73.69
Air	60	5	2.300	43.63
Air	60	10	2.103	48.46
Air	60	15	1.998	51.02
Oxygen	20	5	3.754	8.00
Oxygen	20	10	3.628	11.07
Oxygen	20	15	3.538	13.28
Oxygen	40	5	2.739	32.86
Oxygen	40	10	2.583	36.69
Oxygen	40	15	2.523	38.16
Oxygen	60	5	2.126	47.89
Oxygen	60	10	2.107	48.36
Oxygen	60	15	2.094	48.68

In

Figure 3, the main effects for As removal (%) are shown, indicating that air generates a higher percentage of As removal compared to oxygen. Additionally, regarding pressure (psi), the highest As removal occurs at 40 psi. Figure 4 shows the effect of time (minutes) on As removal (%) with MNB, where it is observed that longer exposure times result in greater arsenic removal.

Figure 3
Main effects for As removal (%). a) Effect of gas type on As removal (%) with MNB. b) Effect of gas pressure (psi) on As removal (%) with MNB.

Figure 4
Effect of time (minutes) on As removal (%) with MNB.

Figure 5 shows the interaction effect of time (minutes), pressure (psi), and gas type on arsenic removal (%) with MNB.

Figure 5
Interaction effect of time (minutes), pressure (psi), and gas type on As removal (%) with MNB.

In Table 5, the chemical analysis results of acidic water treated with micro-nanobubbles for antimony removal are shown. For example, using air at 40 psi for 5 minutes resulted in an antimony concentration of 0.43 ppm, with an average removal efficiency of 88.69%. This result allows us to determine, unlike the other results, that the optimal pressure is 40 psi in a fairly short time of 5 minutes.

Table 5
Chemical analysis of acidic water treated with micro-nanobubbles (MNB) for Sb removal (%).

Gas Type	Pressure (psi)	Time (min)	Sb (ppm)	Average Sb removal (%)
Air	20	5	0.381	90.03
Air	20	10	0.352	90.78
Air	20	15	0.324	91.53
Air	40	5	0.432	88.69
Air	40	10	0.376	90.16
Air	40	15	0.312	91.83
Air	60	5	0.420	89.02
Air	60	10	0.357	90.65
Air	60	15	0.355	90.7
Oxygen	20	5	3.507	8.2
Oxygen	20	10	3.569	6.57
Oxygen	20	15	3.525	7.71
Oxygen	40	5	2.820	26.17
Oxygen	40	10	2.702	29.27
Oxygen	40	15	2.805	26.58
Oxygen	60	5	3.393	11.19
Oxygen	60	10	3.488	8.68
Oxygen	60	15	3.501	8.36

In

Figure 6, the main effects for Sb removal (%) are shown, indicating that air generates a higher percentage of Sb removal compared to oxygen. Additionally, regarding pressure (psi), the highest Sb removal occurs at 40 psi. Figure 7 shows the effect of time (minutes) on Sb removal (%) with MNB, where it is observed that longer exposure times result in greater antimony removal.

Figure 6
Main effects for Sb removal (%). a) Effect of gas type on Sb removal (%) with MNB. b) Effect of gas pressure (psi) on Sb removal (%) with MNB.

Figure 7
Effect of time (minutes) on Sb removal (%) with MNB.

Figure 8 illustrates the combined effect of time (minutes), pressure (psi), and gas type on the removal of antimony (%) using MNB.

Figure 8
Interaction effect of time (minutes), pressure (psi), and gas type on Sb removal (%) with MNB.

In Table 6, the chemical analysis results of acidic water treated with micro-nanobubbles for cadmium removal are shown. For example, using air at 40 psi for 5 minutes resulted in a cadmium concentration of 0.99 ppm, with an average removal efficiency of 75.81%. This result allows us to determine, unlike the other results, that the optimal pressure is 40 psi in a fairly short time of 5 minutes.

Table 6
Chemical analysis of acidic water treated with micro-nanobubbles (MNB) for Cd removal (%).

Gas Type	Pressure (psi)	Time (min)	Cd (ppm)	Average Cd removal (%)
Air	20	5	0.050	58.33
Air	20	10	0.080	33.33
Air	20	15	0.100	16.67
Air	40	5	0.100	16.67
Air	40	10	0.090	25.00
Air	40	15	0.080	33.33
Air	60	5	0.100	16.67
Air	60	10	0.090	25.00
Air	60	15	0.040	66.67
Oxygen	20	5	0.050	58.33
Oxygen	20	10	0.020	83.33
Oxygen	20	15	0.040	66.67
Oxygen	40	5	0.020	83.33
Oxygen	40	10	0.060	50.00
Oxygen	40	15	0.040	66.67
Oxygen	60	5	0.040	66.67
Oxygen	60	10	0.050	58.33
Oxygen	60	15	0.070	41.67

In

Figure 9, the main effects for Cd removal (%) are shown, indicating that oxygen generates a higher percentage of Cd removal compared to air. Additionally, regarding pressure (psi), the highest Cd removal occurs at 20 psi. Figure 10 shows the effect of time (minutes) on Cd removal (%) with MNB, where it is observed that longer exposure times result in greater cadmium removal, with the optimal time being 5 minutes.

Figure 9
Main effects for Cd removal (%). a) Effect of gas type on Cd removal (%) with MNB. b) Effect of gas pressure (psi) on Cd removal (%) with MNB.

Figure 10
Effect of time (minutes) on Cd removal (%) with MNB.

Figure 11 illustrates the combined effect of time (minutes), pressure (psi), and gas type on the removal of cadmium (%) using MNB.

Figure 11
Interaction effect of time (minutes), pressure (psi), and gas type on Cd removal (%) with MNB.

Figure 12
As-H₂0 Pourbaix diagram [²¹].

DISCUSSION

Until now, no research has been found by authors using MNB in this type of metals. There for, It has been considered to discuss the results with the existing bibliography.

Table 3 presents the chemical analysis results of laboratory-generated acidic water. The acid leaching of minerals produced approximately 20 liters of acidic water, to which destilled water was added to decrease metal concentrations, resulting in a total of 200 liters. The pH was measured at 1.77, and a sample was taken for chemical analysis by atomic absorption, yielding 50.22 ppm As, 9.26 ppm Sb, and 0.12 ppm Cd for the acidic water (pH=1.77). A 3-liter sample of acidic water was treated with micro-nanobubbles (MNB) of oxygen (O₂) at 5 psi pressure for 5 minutes. The results, shown in Tabla 3, line 2, indicate a slight decrease in metal concentrations, with 46.59 ppm As, 7.85 ppm Sb, and 0.07 ppm Cd, and an increase in pH to 1.85.

Since acidic water treatments aim to achieve a pH close to neutral, within a pH range of 5.8 to 8.2 according to the National Water Authority, lime was added until a pH of 6.5 was reached. This significantly reduced metal concentrations, as shown in Table 3, line 3, with 4.08 ppm As, 3.82 ppm Sb, and 0.12 ppm Cd. It is important to note that increasing the pH causes the formation of sludge composed of oxides, hydroxides, and/or carbonates of the metals, reducing the concentration of metals in the supernatant liquid, as indicated by Calderon and Tuiro [²⁷].

For the MNB application tests, the same dose of lime was added as in the test for 1 liter of acidic water to achieve a pH of 6.5, thus determining the influence of air and oxygen MNB. Three liters of acidic water were placed in the MNB equipment, in the right container. The water valve was opened, and the water pump was turned on at 45 Hz. As the water passed to the opposite container, the air compressor was activated or the oxygen valve was opened and regulated to the corresponding pressures (20 psi, 40 psi, and 60 psi). The air or oxygen insufflated time was controlled (5, 10, and 15 minutes). During the treatment, the water was recycled through the return pipes to the initial tank, and then the MNB-treated water was discharged. One liter of treated water was measured, lime was added to adjust the pH to 6.5, and it was mixed for 30 minutes. The solids formed due to the pH variation were allowed to precipitate for 24 hours, and a water sample was then taken for chemical analysis by atomic absorption.

Table 4 shows the results obtained for arsenic, both the concentration of As (ppm) and the removal of arsenic from the treated water (%) after the application of air and oxygen micro-nanobubbles at pressures of 20, 40, and 60 psi, for 5, 10, and 15 minutes.

Figure 3 illustrates the main effects of air and oxygen micro-nanobubbles, the pressure of both gases, and the application time on arsenic removal from acidic water adjusted to pH 6.5. It is observed that increasing the oxygen concentration from air to oxygen decreases the arsenic removal percentage. This could be due to the increase in the oxidation state of arsenic, where arsenic transitions from an oxide form to an ionic form, according to the Pourbaix diagram for As-H₂O.

In the main effect analysis, it is observed that increasing the pressure to 40 psi results in a higher percentage of arsenic removal, after which the removal rate decreases to levels similar to those obtained at 20 psi. Regarding time, it is noted that longer treatment durations yield higher arsenic removal percentages, with an increase of approximately 2% for every 5 minutes.

Figure 3 shows the interaction effect of pressure (psi) and the type of gas (air and oxygen), where a negative slope is observed for air and a positive slope for oxygen as the gas pressure increases. The arsenic removal percentages with oxygen are lower than those with air, but they increase until they match the decreasing removal percentage of arsenic obtained with air at 60 psi, resulting in similar outcomes. This suggests that increasing air pressure results in lower arsenic removal, whereas increasing oxygen pressure increases the removal percentage, though it always remains below that achieved with air MNB. The interaction effect of time (minutes) vs. type of gas (air and oxygen MNB) is also observed, where air consistently yields a higher arsenic removal percentage. This aligns with the Pourbaix diagram (Figure 4), indicating that longer treatment times lead to a higher degree of oxidation and the formation of more arsenic ions, thereby reducing the arsenic removal percentage. Figure 5 demonstrates the interaction effect of time (5, 10, and 15 minutes) with MNB pressure (20, 40, and 60 psi), showing that the highest arsenic removal percentage occurs at 40 psi, while 20 and 60 psi yield similar removal percentages. Longer treatment durations result in higher arsenic removal percentages. Figure 5 illustrates the interaction of the three variables: type of gas (air and oxygen), pressure (20, 40, and 60 psi), and application time (5, 10, and 15 minutes). According to the analysis of variance, the main effects are positively significant with P<0.05, and the variable interactions show a significant effect for type of gas vs. pressure. The other interactions do not present significant effects as their P values are greater than 0.05.

Table 5 presents the chemical analysis results for antimony in treated water using air and oxygen MNB, showing lower concentration values (ppm) than the initial values, resulting in positive antimony removal percentages.

Figure 6 illustrates the main effect of air and oxygen application, with a higher percentage of antimony removal achieved using air MNB compared to oxygen MNB, averaging 90.38% and 14.75% respectively. This is corroborated by the Pourbaix diagram for Sb-H2O (Figure 13), indicating that a higher oxidation state transitions antimony from an aqueous state to an ionic state, thereby drastically reducing the antimony removal percentage.

Figure 13
Pourbaix Sb-H₂0 diagram [¹³].

In

Figure 6, the main effect of pressure application on antimony removal is shown, with a positive slope up to 40 psi, after which the percentage of antimony removal decreases up to 60 psi.

In Figure 7, the main effect of MNB application time on the treatment of acidic water for antimony removal at 5, 10, and 15 minutes is displayed, indicating that the removal percentage increases slightly with time by less than 1%. This suggests that the application time of air and oxygen MNB does not have a significant effect.

In Figure 8, the interaction of the three variables (pressure, gas type, and time) is shown, demonstrating a significant influence. According to the analysis of variance, time does not present a significant effect with P=0.612, similarly, the interaction of gas type vs. time (min) with P=0.063 and pressure vs. time with P=0.294, as well as the interaction of all three variables with P=0.313, are not significant. This indicates that the interaction effect of air and oxygen pressure on antimony removal shows a horizontal linear trend for air and a slight increase for oxygen at 10 minutes, with a significant difference in antimony removal percentage between air (90.38%) and oxygen (14.75%), a difference of 75.63%. Additionally, the interaction effect of MNB application time (min) for air and oxygen on antimony removal shows a higher percentage of removal with air than with oxygen, with time having no significant influence as the trend remains horizontal as time increases.

Table 6 presents the results for cadmium removal using air and oxygen MNB at pressures of 20, 40, and 60 psi for 5, 10, and 15 minutes. In Figure 9, the main effect of gas type on cadmium removal is shown, with a positive slope, achieving 32.41% removal with air MNB and 63.89% with oxygen MNB. As seen in Figure 14, the Pourbaix diagram for Cd-H₂O indicates that at pH above 8, cadmium forms hydroxides, whereas at lower pH, it transitions to an ionic form, reducing the percentage of cadmium removal.

Figure 14
Pourbaix Cd-H₂O diagram [¹⁵].

In

Figure 9, the effect of pressure (psi) on cadmium removal is shown, demonstrating a negative slope, with cadmium removal percentages of 52.78% at 20 psi, 45.83% at 40 psi, and 45.83% at 60 psi. In Figure 10, the main effect of time (minutes) on cadmium removal is displayed, showing a curve that decreases and then ascends, with cadmium removal percentages of 50.00% at 5 minutes, 45.83% at 10 minutes, and 48.61% at 15 minutes.

Figure 11 presents the interaction of the three variables: type of MNB application (air and oxygen), pressure (20, 40, and 60 psi), and time (5, 10, and 15 minutes). According to the analysis of variance, all effects have a significant influence except for the main effect of time, which has a P-value of 0.473. This indicates that the interaction effect of pressure (psi) and gas type on cadmium removal shows a slightly positive slope as air pressure increases and a negative slope as oxygen pressure increases. The interaction effect of time (minutes) and gas type shows that, for air, cadmium removal increases with time, while for oxygen, cadmium removal decreases with time. Additionally, the interaction effect of time (minutes) and pressure (psi) on cadmium removal shows slightly negative curves as MNB pressure increases, with a negative slope at 5 and 10 minutes, which changes to a positive slope at 15 minutes.

The results obtained in this research present an alternative application in the mining industry allowing the use of MNBs to generate cost savings and environmental benefits.

CONCLUSION

This research concluded that the use of air and oxygen micro-nanobubbles (MNB), varying time and pressure, has a significant influence on the removal of arsenic, antimony, and cadmium.

The pressure effect with oxygen micro-nanobubbles at 20, 40, and 60 psi resulted in arsenic removals of 10.78%, 35.90%, and 48.31%, respectively; antimony removals of 7.49%, 27.34%, and 9.41%, respectively; and cadmium removals of 70.50%, 62.12%, and 55.86%, respectively. The pressure effect with air micro-nanobubbles at 20, 40, and 60 psi resulted in arsenic removals of 83.59%, 74.91%, and 47.70%, respectively; antimony removals of 90.78%, 90.23%, and 90.12%, respectively; and cadmium removals of 36.13%, 25.36%, and 36.16%, respectively.

The time effect of oxygen micro-nanobubbles at 5, 10, and 15 minutes resulted in arsenic removals of 29.58%, 32.04%, and 33.37%, respectively; antimony removals of 15.18%, 14.84%, and 14.21%, respectively; and cadmium removals of 64.32%, 64.87%, and 59.29%, respectively. The time effect of air micro-nanobubbles at 5, 10, and 15 minutes resulted in arsenic removals of 66.68%, 69.04%, and 70.49%, respectively; antimony removals of 89.24%, 90.53%, and 91.35%, respectively; and cadmium removals of 30.40%, 28.08%, and 39.18%, respectively.

The interaction effect of pressure and application time of air and oxygen micro-nanobubbles had a significant impact with P < 0.05 for arsenic and antimony in the interaction of gas type with gas pressure. The interactions of gas type vs. time and pressure vs. time had P-values > 0.05. However, for cadmium, all three types of interactions had a significant effect with P-values < 0.05.

• Funding:
  This research received no external funding.

Data Availability Statement:

The research data are available in the body of the manuscript.

Acknowledgments:

We thank the support provided for the preparation of this article to the V Call for Science and Technology Projects at National University of Trujillo, resolution number RCU N° 0262-2021/UNT for the undergraduate thesis research project (modality 2) titled "Pressure and injection time of micro and nano oxygen and air bubbles in the concentration of arsenic, antimony, and cadmium in a mining effluent."

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• Editor-in-Chief:
  Alexandre Rasi Aoki

• Associate Editor:
  Ana Cláudia Barana

Publication Dates

• Publication in this collection
  08 Aug 2025
• Date of issue
  2025

History

• Received
  18 July 2024
• Accepted
  27 June 2025