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Iron Metal Ion Adsorption Capacity on Palm Oil Mill Effluent (POME) Using Montmorillonite Adsorbent
Maria Dayanti Mellanie,1 Tisna Harmawan,1* and Puji Wahyuningsih1
1 Department of Chemistry, Faculty of Engineering, Universitas Samudra
*Corresponding email : [email protected]
Received 31 December 2021; Accepted 03 October 2022
ABSTRACT
Palm oil mill effluent (POME) is the most produced waste among other types of waste, which is around 60% in every 100% processing of fresh fruit bunches containing heavy metals, namely ferrous metal (Fe). Montmorillonite (MMT) is one of the best adsorbents used to reduce the concentration of Fe in POME. In addition, this mineral (MMT) also has a high cation fertilization capacity so that the space between layers of MMT is able to accommodate large amounts of cations and make MMT a unique material. In this review, the assurance of the mass variety of the MMT as adsorbent and the variety of the contact time on the adsorption capacity of Fe metal in POME was resolved utilizing a Atomic Absorption Spectrophotometer (AAS) and surface morphology analysis of MMT before and after adsorption using Scanning Electron Microscope (SEM). Based on the results of AAS analysis, the greater the mass of the adsorbent, the higher the amount of Fe adsorbed from the POME. Moreover, the longer the contact time between MMT and Fe, the higher the amount of Fe in the palm oil mill effluent adsorbed on the adsorbent surface. The best adsorption conditions occurred at an adsorbent mass of 8.5 g MMT in 50 mL adsorbate and a contact time of 5 hours with an adsorption capacity of 0.0383 mg/g. The results of the SEM showed the presence of empty spaces in the MMT before adsorption, in which after adsorption white granules occupies the empty spaces evenly on the surface of the MMT.
The granules indicate the presence of Fe metals in the POME samples which are adsorbed on the MMT surface.
Keywords: Palm Oil Mill Effluent (POME), Montmorillonite (MMT), Adsorption, Fe Metal.
INTRODUCTION
Oil palm plantations are currently experiencing very rapid growth because they have a positive impact on the economic growth sector of the Indonesian people, especially in the District of Aceh Tamiang, Aceh. The area of oil palm plantations in Aceh to date has reached 1,073,220 hectares (ha) with a production of 1,006,534 tons, which consists of smallholder plantations with an area of 840,068 ha (78.3%) and a production of 693,080 tons and large plantations with an area of 233,152 ha (22.7%) and production of 313,454 tons. The palm oil industry not only contributes to national economic growth, but also has a negative impact, namely the production of large amounts of liquid waste [1].
Waste is material that disposed from a human activity or natural process that has no economic value and pollutes the environment [2].Waste from several industries has great potential to pollute the environment. Industrial waste is divided into three types, namely liquid waste, solid waste, and gas waste [3]. Industrial waste in the form of liquid waste is
very dangerous for society. Liquid waste can contaminate rivers or water sources commonly used by the surrounding community, such as contamination of surface water and water used by the community, intervention of life in water, reduction of aquatic animals and plants, and production of unpleasant odors [4]. Currently, the estimated amount of liquid waste produced by palm oil mills in Indonesia is 28.7 million tons [5].
Palm oil mill effluent (POME) is the most produced waste among other types of waste, which is around 60% for every 100% of the fresh fruit bunch processing process. Generally, palm oil mill wastewater contains metals such as manganese (Mn), boron (B), cobalt (Co), molybdenum (Mo) [6], iron (Fe), copper (Cu), and zinc (Zn) [7]. The appears in the palm oil processing process due to contact of the oil with the metal-based equipment during the high temperature process.
Fe is one type of pollutant that is widely found in waters [8]. One way of handling of Fe pollution in palm oil mill effluent which is also the most commonly used by Palm Oil Mill (POM) is by using an open pond. The drawbacks of this system are it requires a large area of land and long retention times. To overcome the drawbacks of treating wastewater with this conventional systems [9], it is necessary to develop another method to reduce the Fe levels in the POME, one of which is by adsorption method.
The adsorption method has some advantages compared to other methods, namely the concept is simpler and more economical [10]. Some known adsorbents that oftenly used are chitosan [11], activated carbon [12], zeolite [13], cobalt ferrite [14], and bentonite [15]. One type of adsorbent that can possibly be used to adsorb heavy metals is bentonite. Bentonite is a type of clay which contains 85-95% montmorillonite (MMT) with a chemical composition of 66% silicon oxide (SiO2), 28.3% aluminum oxide (Al2O3) and 5% dihydrogen monoxide (H2O). MMT is a group of smectite clay minerals with a layered structure, crystalline in shape, has swelling properties when dispersed in water [16] and has a large surface area [17], thus it is a promising adsorbent candidate [16].
Various studies have reported the use of MMT as heavy metal adsorbent using bentonite clay used for the adsorption of Fe(II) from aqueous solutions in various concentration of 80-200 ppm, stirring time of 1-60 minutes, and adsorbent masses of 0.02 to 2 g of bentonite. Based Tahir’s study, it was reported that more than 90% of Fe(II) effectively removed from wastewater using a 2 g of bentonite and at pH 3 [15]. The same research, activation HCl activated bentonite. HCl activators are used to improve efficiency Adsorption of Metal Fe where the optimum concentration of HCl is used for the adsorption of metal Fe is 2 M. Based on the results of the study it is known that optimum adsorbent mass in the absorption of Fe metal in used lubricant waste is 20 g [17].
Based on this background, researchers are interested in conducting research on the effectiveness of the adsorption of Fe metal in POME using MMT as an adsorbent.
EXPERIMENT
Chemicals and instrumentation
The materials used in this study were MMT, ICP multi-element standard solution IV, HNO3 (63%), distilled water and POME located in Karang Baru, Aceh Tamiang, Aceh, Province of NAD Indonesia.
The tools used in this study were shaker Orbital SK-O3300 pro, oven (Memmert), hot plate, analytical balance (Mettler Toledo AB 204-S), a set of glassware, AAS-240 FS, SEM merk FEI type Inspect-S50.
Procedures Sampling
The process of POME sampling was carried out by dividing the sample location into three sampling locations with a 10-step distance difference, which is taken from upstream to downstream lines of the waste pond [18].
Preparation of the MMT
A total of 50 g of Aceh Tamiang Bentonite Powder with a size of 250 mesh was added in a beaker glass, then 2 litres aquades was added and given the ultrasonic waves for 15 min with a power of 750 watt. Prepared bentonite then dispersed at ambient temperature for equilibrium (ca. 3 days) to swell all the clay minerals. The bentonite solution was poured into a filtration tank and gently stirred at a rate of 60 rpm. Particles left on the filtration tank were discarded and all the filtered solution was controlled. The filtered solution was then centrifuged twice. The supernatant solution was collected and dried by freeze-drying at -40 for 3 days[19].
Sample preparation
Sample preparation using the wet destruction method was carried out after the Fe adsorption process using MMT. The filtrate was measured as much as 50 mL and then added with 5 mL of concentrated HNO3, then heated until the volume was reduced by half using a hot plate. The solution was allowed to cool down, then the solution was placed into a 50 mL volumetric flask and added with distilled water up to the volumetric flask mark. The solution was then homogenized, filtered off using Whatman 42 filter paper and placed it into a 50 mL volumetric flask.
Preparation of Fe Standard Solution
A 10 mL ICP multi-element standard solution IV 1000 ppm was placed into a 100 mL volumetric flask, then added with distilled water as off the limit mark resulting in 100 ppm solution. The solution of 100 ppm was diluted to 0.5 ppm; 1 ppm; 2 ppm; 4 ppm; and 8 ppm in a separate 100 mL volumetric flask. The absorbance of each standard solution was measured with AAS (λ=248,3 nm) and the results are plotted for a calibration curve[20].
Calibration Curve
The tool was operated and optimized in accordance with the instructions for using the tool for Fe metal measurement. The blank solution in AAS was then set to zero. Fe standard solution with a concentration of 0.5 ppm; 1 ppm; 2 ppm; 4 ppm; and 8 ppm were then analyzed by AAS. From the measurement of each absorbance of the standard solution, a calibration curve was made for each metal[20].
Determination of Concentration Using AAS analysis on Variations in Mass
A total of 50 mL of the POME was put into an Erlenmeyer 150 mL, MMT was added then the solution was stirred using a shaker for 1 hour and wet digestion was carried out [17].
The concentration of Fe before and after adsorption was determined by AAS through the calibration curve. The determination of the mass variation of the MMT adsorbent on the adsorption ability of Fe from POME can be seen in Table 1.
Table 1. Mass Variation of MMT on the Adsorption of Fe from POME
POME (mL) MMT (g) Contact Time (hour)
50 1.5 1
50 2.5 1
50 3.5 1
50 4.5 1
50 5.5 1
50 6.5 1
50 7.5 1
50 8.5 1
Determination of Concentration Using AAS on Variations in Contact Time
The determination of the contact time was carried out using the maximum mass obtained in the previous treatment, which was 8.5 g with variations in contact time, namely 1 hour, 2 hours, 3 hours, 4 hours, and 5 hours and wet digestion was carried out [17]. The concentration of Fe before and after adsorption was determined by AAS through the calibration curve. Determination of contact time variation on the adsorption ability of Fe from POME using MMT can be seen in Table 2.
Table 2. Contact Timing Variation of MMT on the Adsorption of Fe from POME
POME Sample (mL) MMT (g) Contact Time
(hours)
50 8.5 1
50 8.5 2
50 8.5 3
50 8.5 4
50 8.5 5
Determination of Fe Adsorption Capacity
The determination of the adsorption capacity of Fe was determined based on the data obtained from the AAS analysis. The data obtained is then calculated adsorption capacity using the formula below [21].
Description:
Qe = Adsorption capacity (mg/g) Co = Initial metal concentration (mg/L) Ce = Final metal concentration (mg/L) W = Adsorbent mass (g)
V = Volume of metal solution (L)
Surface Morphological Analysis Using SEM on Adsorbent.
The SEM analysis begins with cleaning the specimen holder until it is clean and then
is then placed in a specimen holder and inserted into the specimen chamber. The sample is directly placed into the Bruker SEM device to determine the surface morphology on the adsorbent [22].
RESULT AND DISCUSSION Sample Preparation
Sample preparation using the destruction method was carried out after the Fe adsorption process using MMT. Destruction method aims to break the bonds between organic compounds and metals to be analyzed. In this research, the method used is the wet destruction method. Wet digestion is a process of overhauling organic metals using strong acids, either singly or in a mixture, then oxidizing using an oxidizing agent to produce free inorganic metals [23].
Wet destruction is very suitable for determining the concentration of Fe that the compounds contained in the sample do not interfere with each other in the analysis, then compounds such as cellulose, protein and fat contained in POME must be removed. The wet digestion method is better than dry digestion because it does not damage the sample with a very high ashing temperature and does not require a long time [24].
Concentrated nitric acid (HNO3) solution is used as a destructor for Fe. The addition of HNO3 serves to break the bonds of organometallic complex compounds. Nitric acid is heated at 100°C in destruction process to accelerate the breaking of organometallic bonds to become inorganic. In the destruction process, thin brown gas bubbles appear, this gas is NO2 (a by- product of the destruction process using nitric acid). The presence of this gas indicates that the organic matter has been completely oxidized by nitric acid. After the destruction process ended, the obtained filtrate was measured the absorbance of Fe using AAS.
Standard Solution Preparation
Standard solutions are made with various concentrations and then the absorbance value is measured using AAS. The calibration curve of the standard solution of Fe is obtained can be seen in Figure 1.
Figure 1. Fe Standard Solution Calibration Curve
Based on Figure 1, the Fe calibration curve equation is y = 0.0840x + 0.0505. This equation is used to determine the concentration of Fe in mass variations and variations in contact time of MMT adsorption on POME.
Effect of MMT Mass on Adsorption of Fe in POME
Mass has an important role in determining the adsorption process in which different masses will produce different concentrations of adsorbed Fe. The mass variation used in this study was 1.5 g; 2.5 g; 3.5 g; 4.5 g; 5.5 g; 6.5 g; 7.5 g; and 8.5 g, with a contact time of 1 hour and wet destruction. Furthermore, the concentration of Fe metal before and after adsorption was determined by AAS analysis through the calibration curve. The effect of adsorbent mass variation on the concentration of Fe in POME adsorbed using MMT is shown in Figure 2.
Figure 2. MMT Mass Influence Curve on Fe Adsorption
Based on Figure 2 shows that there was an increase in the concentration of adsorbed Fe with the best MMT mass of 8.5 g at 6.331 ppm. This is because the concentration of Fe is directly proportional to the amount of MMT particles, the more mass of MMT used then greater the concentration of adsorbed Fe. Amount of adsorbents increases that the active site and surface area of the adsorbent increase, causing the adsorbed Fe to increase [23].
Effect of Contact Timing on Adsorption of Fe in POME
Contact time is an important parameter in the adsorption process. The contact time affects the diffusion process and the attachment of the adsorbate molecule that goes well.
Variations of contact time used were 1 hour, 2 hours, 3 hours, 4 hours, and 5 hours and wet destruction was done. Furthermore, the metal concentration of Fe before and after adsorption was determined by AAS analysis through the calibration curve. The results of the effect of time on the concentration of Fe in POME adsorbed using MMT can be seen in Table 4 and Figure 3.
Based on Figure 3 shows that the concentration of Fe adsorbed at a contact time of 1 hour was 6.331 ppm, but at a contact time of 2 hours there was a decrease of 6.224 ppm. This is because the Fe that binds to the active site of MMT is released again. Metal Fe is adsorbed on the MMT structure physically through Van der Walls bonds. This adsorption is relatively fast and reversible [24]. Weakly bound Fe occurs in the interlayer of MMT where the cation exchange process from the solution occurs in it. The MMT interlayer has balancing cations that are easily exchanged, because there is a competitive nature for the struggle for the active side of MMT between Fe metal and other metal ions found in POME, causing metal ions to separate and dissolve back into solution [25].
In the variation of contact time from 3 hours to 5 hours there was an increase in the amount of Fe which was adsorbed the most compared to other times. The adsorbed concentration of Fe metal showed that the adsorption equilibrium was reached at the contact time of 5 hours with the adsorbed Fe metal concentration of 6.504 ppm. The longer the contact time, the higher the ability of the adsorbent to absorb the adsorbate. This is because the long contact time between the adsorbent and the adsorbate allows more bonds to form between the adsorbent and adsorbate particles until an equilibrium point is reached [26].
Adsorption Capacity of Fe
Determination of the adsorption capacity of Fe was carried out. This adsorption capacity is influenced by the active site on the adsorbent surface. The more active sites there are in the adsorbent, the more adsorbate will be adsorbed [27]. Adsorption capacity measures the amount of Fe ions absorbed in each adsorbent mass unit 28]. Variation of contact time is 1 hour, 2 hours, 3 hours, 4 hours and 5 hours. The adsorption capacity value with the variation of the adsorbent contact time can be seen in Figure 4.
Figure 4. Curve of Contact Time Variation on Adsorption Capacity
Based on Figure 4, it shows that the variation in contact time from 1 hour to 2 hours decreased, then the contact time from 3 hours to 5 hours increased again. At the contact time of 1 hour, 2 hours, 3 hours, 4 hours, and 5 hours, the adsorption capacity was obtained, respectively 0.0372 mg/g; 0.0366 mg/g; 0.0381 mg/g; 0.0382 mg/g, and 0.0383 mg/g. At the contact time of 2 hours the adsorption capacity decreased by 0.0381 mg/g. This is because the Fe that binds to the MMT active site is released again. Fe will be adsorbed on the MMT structure physically through Van der Walls bonds. This adsorption is relatively fast and reversible [26]. At 3 hours, 4 hours, and 5 hours there was no significant increase in Fe adsorption capacity, because at that time there was an adsorption equilibrium between the
adsorbed Fe concentration and the remaining Fe concentration in solution. The biggest adsorption capacity was at 5 hours at 0.0383 mg/g. Based on the results of variations in contact time, the adsorption capacity showed the same results, where the adsorption capacity value increased with increasing time.
Surface Morphological Analysis Using SEM
The physico-chemical characterization using SEM aims to describe the surface (morphology) of the solid. Scanning Electron Microscope is a type of electron microscope that depicts the surface of a sample through a scanning process using a high energy beam of electrons in a raster scan pattern. Electrons interact with atoms that will make the sample produce signals and provide information about the sample's topography, composition and other properties such as electrical conductivity. The results of the MMT analysis before and after adsorption using SEM can be seen in Figure 5.
(a) (b)
Figure 5. MMT Morphological Analysis (a) Before Adsorption and (b) After Adsorption
Based on Figure 5, it can be seen that there are differences in the surface of the MMT before and after adsorption. In Figure 5(a) the shape of the MMT surface before adsorption is infrequent, this can be seen from the presence of black parts which are empty spaces around the MMT surface. Meanwhile, in Figure 5 (b), which is a picture of the MMT after adsorption, a denser surface is seen when compared to the image of the MMT surface before adsorption. Presence of white granules that occupy empty spaces evenly on the surface of the MMT after adsorption which indicates the presence of metals in the POME sample being adsorbed on the MMT surface.
CONCLUSION
Based on the research that has been done, it can be concluded that the greater the mass of the adsorbent used then greater the amount of Fe in POME that is adsorbed on the surface of the adsorbent. The longer the contact time between MMT and Fe then the greater the amount of Fe in POME that is adsorbed on the surface of the adsorbent. The best adsorption conditions occurred at an adsorbent mass of 8.5 g MMT, a contact time of 5 hours with an adsorption capacity value of 0.0383 mg/g.
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