Ability of Palm Kernel Shell Adsorbent in Reducing Mercury (Hg)

One method to reduce the content of heavy metal mercury in wastewater is adsorption. Several media materials have been investigated for use as adsorbents. In this study the characteristics of the palm kernel shell were analysed so that it could be used as an adsorbent. In addition, it also analysed its ability to reduce levels of mercury in wastewater. Palm kernel shells were activated using two types of activators, namely H3PO4 and NaOH and variations in adsorbent sizes of 50 mesh and 100 mesh, as well as variations in contact time for 30 and 60 minutes. Based on the results of this study, it was obtained that the characteristics of the adsorbent of palm kernel shells with the use of H3PO4 and NaOH activators met the quality based on SNI 06-330-95. The adsorption efficiency of mercury (Hg) removal can reach 99.7% with a contact time of 60 minutes and an adsorbent size of 100 mesh activated by NaOH.


Introduction
Pollution of the heavy metal mercury comes from various industrial activities that have a very dangerous impact on the environment and ecosystems.Mercury has a negative impact on health because it can combine with enzymes that eliminate the ability of the catalyst in the human body.The amount of mercury accumulated is quite significant causing adverse health effects [1].Acute poisoning by Hg can cause digestive tract damage, acute kidney failure or shock, cause nervous system disorders, hearing loss, and decreased intelligence [2].Mercury is usually found in industrial wastewater from electrochemical, electroplating, washing of electronic components, mining activities, electroplating, laboratories and leachate from landfills.
the standard for mercury content in class II water (Regulation of the Government of the Republic of Indonesia Number 82 of 2001) is 0.002 mg/L.Several treatment alternatives to reduce mercury content are adsorption processes, membrane filtration, ion exchange, reverse osmosis, solvent extraction, chemical precipitation, and coagulation [3].The adsorption process is a process that has several advantages, namely relatively simple, relatively high efficiency, effective and does not have a negative impact on the environment [4].Palm kernel shell is a material that has the potential to be used as an adsorbent.one ton of oil palm fresh fruit bunches produces 5% -9% or 50 kg -90 kg of palm kernel shell waste [5].Meanwhile the average production capacity of the oil palm plantation industry in 1250 (2023) 012023 IOP Publishing doi:10.1088/1755-1315/1250/1/012023 2 Indonesia reached 30 tons of fresh fruit bunches/hour [6].Based on its abundant availability, palm kernel shell can be used as an adsorbent in the adsorption process of heavy metal mercury.
The content of the palm kernel shell is 45% cellulose and 26% hemicellulose [7].Currently, palm kernel shells have been used as an additive in the manufacture of concrete [8], an additional ingredient in cement production [9], as activated charcoal [10], an additive for road hardeners, an additional fuel for boilers in the palm oil industry, an ingredient in raw charcoal, and sold in the form of shells.
Activated charcoal or activated carbon is a material resulting from the pyrolysis process of charcoal at a temperature of 600 -900 o C [11].Activated carbon has a surface area of 300 -2000 m2/g [12].The particle size of activated carbon in powder form (Powdered Activated Carbon) is <0.188 mm and the particle size of granular activated carbon (Granular Activated Carbon) is 0.2 -5 mm [13].The three stages of the activated carbon manufacturing process are as follows [14]: the dehydration stage is to remove the water content and is carried out by heating the raw material to a temperature of 100°C; carbonization is carried out using a furnace and produces three main components, namely carbon, tar, and CO2, CO, CH4, H2, and others; the activation process to enlarge the pores by breaking the hydrocarbon bonds or oxidizing the surface molecules.Enlarged pores and larger surface area affect the adsorption power [15].Activation is carried out by adding certain chemical compounds to the charcoal.H3PO4, NaOH, ZnCl2, H2SO4, K2CO3, Na2CO3, NH4Cl and KOH are chemical compounds used as activating agents in the kernel shell of palm oil.The type and concentration of activator is important because it affects the characteristics of activated carbon [16].The quality of activated carbon according to SNI Number 06-3730-1995 can be seen in Table 1.
Adsorption is the absorption of a substance on the surface of a solid substance which is called the adsorbent and the adsorbed phase is called the adsorbate.Physical adsorption is an interaction process between the adsorbent and the adsorbate.This process involves intermolecular forces such as Van der Waals forces.Chemical adsorption occurs due to the interaction of the adsorbent and adsorbate resulting in the formation of chemical bonds [17].The factors that will affect the adsorption process in general are surface area, type of adsorbate, adsorbate concentration, pH, stirring speed, contact time, and other compounds in the adsorbate [18].Adsorption can be carried out using a batch system and a column system [19].

Methods
The activator materials used to make activated charcoal from palm kernel shells were 0.1 N H3PO4 and 0.1 N NaOH.The particle sizes of the adsorbents used were 50 and 100 mesh and the contact times were 30 and 60 minutes.The concentration of artificial mercury waste contains 10 mg Hg/L, with the added adsorbent mass of 1 gram.
The oil palm shells are washed thoroughly with distilled water and dried in the sun until dry (empty weight).Authoring uses a furnace at 650 o C for 2 hours [20].Charcoal is crushed and sieved with passing size of 50 and 100 mesh to get particle size < 0.150 -0.300 mm.
Charcoal activation was carried out by immersing it in 0.1 N NaOH solution and stirring thoroughly with a magnetic stirrer and allowing it to stand for 24 hours.The charcoal was filtered, drained and washed with distilled water before being dried in an oven at 105°C for 1 hour.Drying is intended to remove excess water and achieve a constant weight.Activation using 0.1 N H3PO4 was carried out in the same way and under the same conditions as activation using NaOH.
Characteristic tests of activated charcoal from palm shells included tests for water content, ash content, volatile matter content and fixed carbon content in accordance with SNI 06-3730-1995.Scanning Electron Microscope (SEM) tests were carried out to determine the morphological differences of activated charcoal which had not been activated and which had not been activated.Mercury solution is prepared from HgCl2 dissolved in distilled water and 65% HNO3, to obtain a solution concentration of 1000 ppm or 1000 mg Hg/L [21].based on the standard solution, then a Hg solution with a concentration of 10 mg Hg/L was prepared.
In determining the adsorption capacity, 1 gram of activated carbon was added to 250 ml of mercury solution with a concentration of 10 mg/L.The mixture was stirred at 100 rpm [20].It was allowed to stand for 30 and 60 minutes with variations in contact time.After being filtered using filter paper, measurements of Hg concentration were carried out using atomic absorption spectrophotometry.The adsorption capacity can be determined by the following formula [22].

Characteristic of Activated Carbon
The characteristics of the activated carbon of the palm kernel shell can be seen in Table 2 and Table 3.
Previous research obtained a water content value of activated carbon of palm kernel shell activated with H3PO4 concentration of 5% at 650 o C of 10.51% [20].Another study was also conducted on activated carbon <500 m obtained from carbonization at 750 o C was 2.62% [23].The water content value of the activated carbon of activated palm kernel shell NaOH 0.125 M -0.25 M with a carbonization temperature of 500 o C with a size of 500 m is 6.07%-17% [24].Differences in water content values are caused by differences in the size of the adsorbent.The size of the adsorbent < 0.300 mm (50 mesh) has a greater water content value than the adsorbent size < 0.150 mm (100 mesh).This is due to the influence of the resulting pore size on the 50 mesh activated carbon so that the water molecules are trapped in the lattice.Large particle sizes have fewer pores compared to small particle sizes so that the water content contained in the activated carbon particles is less because it has evaporated [25].
The value of ash content shows a decrease in percentage after activation.The ash content value of activated carbon of chemically activated palm kernel shells is lower than the threshold for the quality of activated carbon, which is a maximum of 10% (SNI 06-3730-95).Meanwhile for activated carbon without chemical activation has a large ash content and exceeds the standard, this is due to the influence and function of using chemical activators.The carbon of the palm kernel shell before activation still contains tar and other substances, so that the ashing process produces a higher ash content.The resulting volatile matter content (14.31%) is in accordance with the results of previous studies using activated carbon of 100 mesh palm kernel shells and 5% H3PO4 activated [20].Measurement of volatile matter content on activated carbon of palm kernel shells activated by NaOH with a carbonization temperature of 400 -600 o C obtained volatile matter levels of 10 -15% [26].Palm kernel shell activated carbon without chemical activation treatment with a carbonization temperature of 800-1000 o C obtains a volatile matter content of 24% [27].
The fixed carbon value in H3PO4 and NaOH activated carbon has a fairly high value.The fixed carbon value is affected by the amount of carbon released from the palm kernel shell along with the water content, ash content, and volatile matter content during the carbonization and activation processes.In addition, another cause is the incomplete carbonization process so that the activator binds more mineral salts and is able to push out the main content [28].
The morphology of activated carbon based on size differences and differences in activation treatment was observed using Scanning Electron Microscopy (SEM) with 5000x magnification.Activated carbon measuring 100 and 50 mesh and activated with H3PO4 respectively can be seen in Figures 2 and 3.The morphology of activated carbon activated with NaOH is shown in Figures 4 and 5 for sizes 100 and 50 mesh, respectively.Whereas the morphology of activated carbon without chemical activation is shown in Figures 6 and 7 for sizes 100 and 50 mesh respectively.

Mercury Adsorption by Palm Kernel Shell Activated Carbon
The adsorption process of mercury by the activated carbon of the palm kernel shell is a chemical adsorption process, due to the interaction between the adsorbate and the adsorbent to form chemical bonds.The adsorption process which forms chemical bonds, is categorized as chemical adsorption [17].
The adsorption ability of activated carbon of palm kernel shells is supported by the cellulose content it has.In activated carbon there is a -OH group which interacts with the adsorbate component [29].The hydroxyl group can form a series of adsorption with cationic or anionic compounds [30].The mechanism that occurs between the -OH bond and the positively charged metal ion on the surface can be seen in Figure 7 [31].Y is a matrix where -OH groups are bound and M 2+ is a metal ion, where the interaction between -OH groups and metal ions is also possible through the mechanism of the formation of coordination complexes [31].One of the factors that can affect the adsorption process is the pH of the adsorbate.In this study, the pH of the solution was 5.12.Research conducted on adsorbing mercury using activated carbon fiber polymers with a solution concentration of 20 mg/l and variations in pH used were 3, 4, 5, 6, and 7 resulted in an optimum pH of 5 and removal efficiency of 99.5% [32].Adsorption of mercury using activated carbon from banana peel waste with a solution concentration of 40 ppm, variations in adsorbate pH of 1, 2, 3, 4, 5, and 6 obtained an optimum pH of 5 and an average absorption of 98% [33].pH value is one of the determining factors in the adsorption process.when the pH of the adsorbate is too acidic, competition occurs between H + ions and Hg 2+ ions in occupying the surface of activated carbon [36].if the adsorbate is in high or alkaline pH conditions, precipitation will occur due to the reaction between Hg 2+ and OH and form HgO [33].

Contact Time Effect.
The contact time affects the efficiency of the mercury adsorption process.The adsorption ability showed different results between 30 and 60 minutes contact time.longer contact time provides a decrease in the concentration of mercury and an increase in adsorption capacity.NaOH activated carbon with a size of 100 mesh is able to absorb up to 9.97 mg/l of mercury in 60 minutes.Figure 8 shows the absorption ability of activated carbon of palm kernel shells based on contact time.

Adsorbent and Activator Size
Effect.The smaller the particle size, the greater the surface area of the adsorbent, the greater the adsorbent ability of the material [34].Figures 9 and 10 show graphs of the absorption efficiency of activated carbon in palm kernel shells at 30 and 60 minutes, respectively.The best absorption of mercury can be achieved by activated carbon with a size of 100 mesh and activated by NaOH with a contact time of 60 minutes, which is 99.7%.

Conclusions
The activator materials used to make activated charcoal from palm kernel shells were 0.1 N H3PO4 and 0.1 N Na 1) Characteristics of activated carbon of palm kernel shells activated by H3PO4 and NaOH can meet the quality standards of activated carbon according to SNI 06-3730-95.
2) The ability of mercury adsorption by activated carbon of palm kernel shells which has been activated with NaOH shows that the longer the contact time (60 minutes) and the smaller the adsorbent particle size (100 mesh) can achieve an adsorption capacity of 2.49 mg/g and removal efficiency.up to 99.7 %

6 Figure 8 .
Figure 8.The Absorption Ability of Mercury Based on Contact Time

Figure 9 .
Figure 9.The Absorption Ability of Mercury Based on Adsorbent Size at 30 minutes

Table 1 .
Quality of Activated Carbon

Table 2 .
Carbon Active Characteristic with Size of 50 Mesh

Table 3 .
Carbon Active Characteristic with Size of 100 Mesh