DOI: 10.3303/CET23107121 Paper Received: 11 July 2023; Revised: 27 September 2023; Accepted: 29 November 2023 Please cite this article as: Quiroz E., Chavez D., Torres Rivera C., Vega-Gonzalez J.A., Valverde Flores J.W., Portilla Rodriguez H.R., 2023, Application of Air Micronanobubbles to Reduce Arsenic Present in an Effluent Generated at the Laboratory Level, Chemical Engineering Transactions, 107, 721-726 DOI:10.3303/CET23107121 CHEMICAL ENGINEERING TRANSACTIONS VOL. 107, 2023 A publication of The Italian Association of Chemical Engineering Online at www.cetjournal.it Guest Editors: Petar S. Varbanov, Bohong Wang, Petro Kapustenko Copyright © 2023, AIDIC Servizi S.r.l. ISBN 979-12-81206-07-6; ISSN 2283-9216 Application of Air Micronanobubbles to Reduce Arsenic Present in an Effluent Generated at the Laboratory Level Erick Quiroza, Daniel Cháveza, Christian Torres Riveraa, Juan A. Vega-Gonzaleza, Jhonny W. Valverde Floresb,*, Hans R. Portilla Rodriguezc aDepartment of Metallurgical Engineering, National University of Trujillo, Trujillo, Peru bFaculty of Sciences, Universidad Nacional Agraria La Molina, Lima, Peru cDepartment of Sciences, Private University of the North, Trujillo, Peru jvalverde@lamolina.edu.pe The objective of this research was applying air Micronanobubbles to reduce Arsenic present in an effluent generated at the laboratory level. In this research, an effluent with arsenic metal was used from a mixture of minerals with the presence of arsenopyrite with 19% As content. This mixture of minerals was stirred in a hot alkaline leaching medium at a temperature of 80 °C, with Na2S (1.5 M) and NaOH (1.0 M), then it was diluted with distilled water to obtain a volume of 100 L with a concentration of 150 ppm As. This effluent was treated with the air micronanobubble (MNB) generator equipment patented by Dr. Jhonny Valverde Flores. The variables of the pressure and the insufflation time of air as MNB in the effluent with content of the arsenic element were analyzed. A 40% decrease of As was obtained in the effluent. The results indicate that the use of MNB is promising in terms of the reduction of arsenic in solutions with concentrations of the same. 1. Introduction Acid mine drainage (AMD) and mining effluents in general result in a very significant negative impact on water bodies and soil. It affects not only these environmental components but all biological activity that is comprised of these components (Hogsden and Harding, 2012; DeNicola and Stapleton, 2002). Although in some cases they are developed due to situations of natural leaching processes (Rodbell et al., 2014). The most worrisome cases are abandoned or inappropriately closed mining works at the national level, but above all Andean areas and those with difficult access, as well as El Faro Mining in Canada or mining companies in Alaska and the United States (Filion et al., 1992). The following elements are found in the water bodies from acid mine drainage (AMD) and mine effluents: mineralized rock, which has been exposed in its internal components usually iron sulfide, water, oxygen, bacteria such as Thiobacillus Ferrooxidans and Thibacillus Thioooxidans (Akcil and Koldas, 2006). As a consequence of the problem analyzed, there are the following factors: sulphide mineral, aqueous medium and bacteria, which influence the concentration of heavy metals, acidity or alkalinity of mine effluents (Kuyukac, 2021). In mining, cyanide leaching is one of the most widespread metallurgical processes and with a high polluting potential, therefore alkaline leaching emerges as an alternative due to its low toxicity and high efficiency (Sun et al., 2020). However, in some alkaline leaching processes, such as gold extraction with high arsenic content, these generate a high content of arsenate ions, which must be removed due to their high damage to the process and especially to the environment (Wang et al., 2019). It has been proven that arsenic can be adequately separated from other metals with optimal conditions of concentration, temperature and solid liquid ratio with NaOH-Na2S in a simple and efficient way (Guo et al., 2016). MNBs are characterized by their prolonged stability in aqueous media as charge, pressure and ionic absorption density (Koshoridze and Levin, 2019; Nirmalkar et al., 2018) as well as the size of their diameter, the nanobubbles being 150-200 nm, 70 µm microbubbles and 1 mm macrobubbles (Abate and Valverde, 2017; Rosa and Rubio, 2018). The insufflation of MNB, specific gases or air, into effluents contaminated with heavy metals is a technique that has been studied more frequently in recent years (Kyzas et al., 2021; Lee et al., 2020; Jin- Hee et al., 2017; Batagoda et al., 2019) and its use in environmental remediation has generated high expectations (Kyzasa et al., 2019) 721 and the precision measurements are measured by scanning electron microscopy SEM, EDX, DLS (Jadhav and Barigou, 2020). Air (Huang et al., 2020), O2 gas has been used to generate MNB, due to its great long-term stability (Wang et al., 2018; Khuntia et al., 2012) and also the use of nanobubbles of CO2 gas bubbled for micro- extraction of heavy metals (Lee et al., 2020) is also an option. This is generated through an adjustment in the physicochemical properties of activated carbon fibers (ACF). In this experiment, the use of CO2 nanobubbles could be a promising method in which case the physicochemical properties of an absorbent affect the overall microextraction performance. However, research using MNB directly as an alternative to reduce heavy metals from mine effluents has not been found. This study aims to find an alternative for environmental remediation by reducing arsenic metal with an effluent generated at the laboratory level in order to obtain a possible water remediation technique. 2. Materials and methods 2.2 Materials One way to obtain samples is to collect directly from the natural source where the discharges or effluents are located (Chen et al., 2020). However, it is possible to carry out sample preparation in a controlled manner under laboratory conditions in order to study some specific characteristics. In this investigation, an alkaline leaching effluent containing various heavy metals was used, taking arsenic into consideration. Given this, the effluent generated in the laboratory was used with an initial concentration of 159.53 ppm of As in solution. 2.3 Preparation of sample To obtain the solution that generates the effluent necessary to carry out this study, a ground sample of 1000 grams of arsenical sulfide mineral - arsenopyrite (19% As) was necessary until obtaining 80% - mesh # 400. With this ground mineral containing arsenic was leached with alkaline solutions of NaOH and Na2S, in concentrations of 1 and 1.5 molar. The leaching reactor had a 3.8 L capacity. The alkaline solutions were then filtered using a 6-inch Denver brand filter press. Subsequently, the As concentration (ppm) was analyzed using ICP-OES Teledyne, Leeman Labs, Prodigy Spec model, N/S 3038. Regardless of the test performed, it is important to highlight that it was necessary to dilute with distilled water to obtain a concentration close to 150 ppm of As and a total of 100 liters of solution, with the purpose of expanding the range of tests. 2.3 Design of applications of MNB in the laboratory The MNB application device used in this study is a gas micro-nano bubble generator equipment patented by Dr. Jhonny Valverde Flores (Patent no. PE20170424, 2017). The purpose of the device is to divide a jet of water under pressure and which goes through multiple holes (Sadatomi et al., 2012;) in a pipe specially designed to mix the gases that are to be insufflated which achieves diffusion of MNB throughout the solution evenly thanks to closed-loop flow (Valenzuela and Valverde, 2018). Figure 1 shows the diagram of the MNB insufflation process for liquid solutions. Figure 1: Diagram of the MNB insufflation process for liquid solutions. Adapted from Garcia and Valverde (2017) 2.4 Treatment description as MNB For this investigation, 3 L of previously prepared solution of the mineral arsenical sulfide (arsenopyrite) was used, described in 2.2. This volume was added to the conditioning tank of the MNB generator equipment. Air was blown at pressures according to established levels: 10, 25, 40 and 55 psi provided by a 2 HP air compressor and volume flow of 0.17 m3/min. The duration intervals of the experiment were 5, 15, 25 and 35 min. Then, the solutions were filtered and the arsenic concentration was analyzed using the ICP-OES equipment. Calculations of the arsenic removal percentage were made using the Minitab software version 19. Figure 2, represents the procedure carried out in the investigation. 722 Figure 2: Experimental Research Procedure 3. Results and discussion 3.1 Aeration time and As reduction Figure 3, shows the average values of the percentage decrease in arsenic as a function of aeration time, expressed in minutes, they were 55.80%, 48.96%, 27.68%, 25.16%, for values of 5 min, 15 min, 25 min and 35 min respectively. In addition, these values were statistically analyzed using a significance level of α = 0.05 and with F_0>F (∝,v1,v2) which determined that the aeration time (min) has a significant effect on the percentage decrease in arsenic, showing the highest value at a time of 5 min, with the percentage of arsenic decrease being 55.80%. Figure 3: Percentage´s variation of arsenic reduction vs. aeration time 3.2 Air pressure and As reduction Figure 4, shows the variation of insufflated air pressures vs. the As reduction of the study sample. It was determined that for the different pressures of insufflated air (psi) 10, 25, 40 and 55; the reduction percentages of As were 47.42%, 37.93%, 40.30% and 31.94% respectively. In addition, these values were statistically analyzed using a significance level of α = 0.05 and with F_0>F_(∝,v1,v2), managing to determine that air pressure (psi) has a significant effect on the percentage of arsenic reduction. It shows a higher value at a pressure of 10 psi, with the arsenic reduction percentage being 47.42%. Figure 4: Percentage´s variation of arsenic reduction vs. air pressure 723 Figure 5: Samples treatment process: Initial solution (left), solution with MNB (center), solution with MNB after 24 h (right) During the treatment of the solution, the formation of whitish precipitates was observed, and as the air pressure increases, it is divided into smaller parts that slow down its settling. It is likely that more precipitates that contain arsenic are being formed. However, their separation becomes more difficult, since they become colloids, and it is likely that for this reason the precipitates formed were taken at the time of obtaining the sample for analysis by ICP-OES. In the ICP-OES analysis procedure, hydrochloric, nitric and perchloric acids are added which, if there is arsenic in the precipitate, will dissolve it and the total arsenic content will increase as the air pressure increases. Table 1: Reduction percentage of arsenic, as a function of air pressure (psi) and aeration time (min) Item N° Air Pressure (Psi) Time (min) Initial As (ppm) Final As (ppm) As Reduction (%) 1 10 5 159.63 71.5 55.21 2 25 5 159.63 63.075 60.49 3 40 5 159.63 70.35 55.93 4 55 5 159.63 78.77 50.65 5 10 15 159.63 71.93 54.94 6 25 15 159.63 89.45 43.96 7 40 15 159.63 75.47 52.72 8 55 15 159.63 95.73 40.03 9 10 25 159.63 96.12 39.79 10 25 25 159.63 127.25 20.28 11 40 25 159.63 114.04 28.56 12 55 25 159.63 135.75 14.96 13 10 35 159.63 100.75 36.89 14 25 35 159.63 119.71 25.01 15 40 35 159.63 127.74 19.98 16 55 35 159.63 129.3 19.00 17 10 5 159.63 69.81 56.27 18 25 5 159.63 65.36 59.06 19 40 5 159.63 68.46 57.11 20 55 5 159.63 77.16 51.66 21 10 15 159.63 70.14 56.06 22 25 15 159.63 86.31 45.93 23 40 15 159.63 72.33 54.69 24 55 15 159.63 90.41 43.36 25 10 25 159.63 93.64 41.34 26 25 25 159.63 117.39 26.46 27 40 25 159.63 108.15 32.25 28 55 25 159.63 131.23 17.79 29 10 35 159.63 97.54 38.90 30 25 35 159.63 124.11 22.25 31 40 35 159.63 125.82 21.18 32 55 35 159.63 130.8 18.06 724 3.3 Time and air pressure in the reduction of As In Figure 6, the interaction of both variables is presented, showing that at 5 min of aeration and 25 psi of air pressure the highest arsenic decrease is obtained, being 59.77% and with a total arsenic concentration in the solution of 64.22 ppm. Figure 6: Reduction percentage variation of arsenic as a function air pressure (psi) and aeration time (min). From the statistical analysis carried out at a significance level of α = 0.05 and with F_0>F_(∝,v1,v2) it was determined that the interaction between aeration time (min) and air pressure (psi) in the treatment of a solution containing arsenic (obtained by alkaline leaching with NaOH and Na2S), by MNB, has a significant effect on the percentage of arsenic decrease, showing a higher value at a time of 5 min and 25 psi of air pressure. Table 1 shows the results of the experimental tests, carried out with the MNB generator equipment at time of aeration of 5, 15, 25 and 35 min, and air pressure of 10, 25, 40 and 55 pounds per square inch (psi). The initial concentration of total As in the solution As was 159.63 ppm. After of the treatment with MNB the reduction was significant in different times. The lowest average concentration of total As was 64.22 ppm [result of [(63.075+65.36)/2]. The average reduction percentage of arsenic concentration was 59.77% [result of (60.49+59.06)/2]. 4. Conclusions The present study demonstrates that the use of MNB can be used as an alternative for the remediation of effluents contaminated with arsenic. In addition, the results suggest that both the application time and the pressure are two important factors to obtain positive and significant results in terms of reducing the arsenic concentration in the effluent with MNB. In this sense, the study shows that the best operating parameters for the application of MNB are the interaction of air pressure and the time of air application have a significant influence at a significance level of 0.05, being the optimal value obtained. an air pressure of 25 psi and 5 min of air blowing, with a decrease of 59.77% and a concentration of 64.22 ppm of arsenic in the effluent. 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