Review

Oil palm biomass-based activated carbons for the removal of cadmium—a review

  • Received: 24 March 2021 Accepted: 08 June 2021 Published: 11 June 2021
  • Serious water pollution due to climate change as the consequences of non-ecological wastewater treatment and unsustainable agricultural activities had emerged water scarcity problem. The utilization of oil palm biomass into cadmium adsorbent could play a role in killing two birds with one stone, which is to solve the oil palm biomass disposal issue and cadmium pollution issue. The adsorbent modifications discussed in this review focused on furnace heating and microwave heating as well as the combined methods with chemical activating agents. Among the modification methods, the output of chemical activation followed by microwave-induced irradiation of palm kernel shells (PKS) produced activated carbon with high specific surface area (854.42 m2/g) and high adsorption capacity, qmax (227.27 mg/g). This review is to provide a comprehensive understanding of cadmium adsorption mechanisms and up-to-date progress of modification technologies for different types of oil palm biomass.

    Citation: Hafizah Naihi, Rubiyah Baini, Ibrahim Yakub. Oil palm biomass-based activated carbons for the removal of cadmium—a review[J]. AIMS Materials Science, 2021, 8(3): 453-468. doi: 10.3934/matersci.2021028

    Related Papers:

    [1] Kah Hon Leong, Azrina Abd Aziz, Yee Li Kang, Sheau Wei Goh, Kulhar Vijay Singh, Lan Ching Sim, Pichiah Saravanan . Synergized mechanistic and solar photocatalysis features of N-TiO2 functionalised activated carbon. AIMS Materials Science, 2017, 4(3): 800-813. doi: 10.3934/matersci.2017.3.800
    [2] Nagesh K. Tripathi . Porous carbon spheres: Recent developments and applications. AIMS Materials Science, 2018, 5(5): 1016-1052. doi: 10.3934/matersci.2018.5.1016
    [3] Aman Santoso, Novita Agustin, Sumari Sumari, Siti Marfuah, Rini Retnosari, Ihsan Budi Rachman, Anugrah Ricky Wijaya, Muhammad Roy Asrori . Synthesis of methyl esters from palm oil, candlenut oil, and sunflower seed oil and their corrosion phenomena on iron nail. AIMS Materials Science, 2022, 9(5): 719-732. doi: 10.3934/matersci.2022044
    [4] Noha Ahmed Mahmoud, Ehssan Nassef, Mohamed Husain . Use of spent oil shale to remove methyl red dye from aqueous solutions. AIMS Materials Science, 2020, 7(3): 338-353. doi: 10.3934/matersci.2020.3.338
    [5] Rasaq Kazeem, Tien-Chien Jen, Godwin Akande, Stephen Akinlabi, Esther Akinlabi . Performance evaluation of hybrid biodegradable oils as a lubricant during cylindrical turning of AISI 304 austenitic stainless steel. AIMS Materials Science, 2024, 11(2): 256-294. doi: 10.3934/matersci.2024015
    [6] Ayu Azera Izad, Rosimah Nulit, Che Azurahanim Che Abdullah, A'fifah Abdul Razak, Teh Huey Fang, Mohd Hafiz Ibrahim . Growth, leaf gas exchange and biochemical changes of oil palm (Elaeis guineensis Jacq.) seedlings as affected by iron oxide nanoparticles. AIMS Materials Science, 2019, 6(6): 960-984. doi: 10.3934/matersci.2019.6.960
    [7] Mahmoud A. Rabah, Mohamed B. El Anadolly, Rabab A. El Shereif, Mohamed Sh. Atrees, Hayat M. El Agamy . Preparation of valuable products from cleaned carbon of fuel ash. AIMS Materials Science, 2017, 4(5): 1186-1201. doi: 10.3934/matersci.2017.5.1186
    [8] Sekhar Chandra Ray . Possible magnetic performances of graphene-oxide and it's composites: A brief review. AIMS Materials Science, 2023, 10(5): 767-818. doi: 10.3934/matersci.2023043
    [9] Amany Mahmoud, Ehssan Nassef, Hesham Salah, Yehia El-taweel . Use of hydrazide derivative of poly methylacrylate for the removal of cupric ions from solutions. AIMS Materials Science, 2020, 7(4): 420-430. doi: 10.3934/matersci.2020.4.420
    [10] Hashem Al-Mattarneh, Musab Abuaddous, Rabah Ismail, Ahmad B. Malkawi, Yaser Jaradat, Hamsa Nimer, Mohanad Khodier . Performance of concrete paving materials incorporating biomass olive oil waste ash and nano-silica. AIMS Materials Science, 2024, 11(5): 1035-1055. doi: 10.3934/matersci.2024049
  • Serious water pollution due to climate change as the consequences of non-ecological wastewater treatment and unsustainable agricultural activities had emerged water scarcity problem. The utilization of oil palm biomass into cadmium adsorbent could play a role in killing two birds with one stone, which is to solve the oil palm biomass disposal issue and cadmium pollution issue. The adsorbent modifications discussed in this review focused on furnace heating and microwave heating as well as the combined methods with chemical activating agents. Among the modification methods, the output of chemical activation followed by microwave-induced irradiation of palm kernel shells (PKS) produced activated carbon with high specific surface area (854.42 m2/g) and high adsorption capacity, qmax (227.27 mg/g). This review is to provide a comprehensive understanding of cadmium adsorption mechanisms and up-to-date progress of modification technologies for different types of oil palm biomass.



    Water quality worldwide is degrading gradually due to industrial wastewater and unsustainable agricultural activities which affected around one-tenth of all river stretches in Latin America, Africa, and Asia with severe and moderate salinity pollution (fertilizer runoffs, stormwater runoffs, and urban wastewater discharge). As in a report published by The United Nations Educational, Scientific and Cultural Organization (UNESCO) in 2020 entitled "Water and climate change", the quality of freshwater system is one of the consequences of climate change and this problem can be solved using some mitigation measures. These included pollutant discharge reduction through ecological wastewater treatment and source pollution reduction actions from the economic and domestic sectors which are the main wastewater generators [1]. Another organization that works towards climate policies since 1990 is European Union (EU) that had introduced the latest 2050 European Green Deal plan which not only focusing on 'water goal' itself but also reinforcing energy efficiency and renewable energy through the sustainable industry. According to the plan, EU has introduced some strategies to achieve their 2050 climate-neutrality target such as the 2030 Climate Target Plan as presented in 17 September 2020 as a prudent pathway to climate neutrality by 2050 which requires greenhouse gas emissions reduction target of at least 55% by 2030. As in Malaysia, the country continued its commitment to achieving the 2030 Agenda and the Sustainable Development Goals (SDG) implementation programs are monitored by the National SDG Council. Currently, Malaysia is in the execution process of the SDG Roadmap Phase 2 (2021–2025) for the 2030 Agenda achievement.

    One of the pollutants that is still becoming a hot topic in the scientific review is cadmium; about 54735 scientific articles had been published and listed on the PubMed.gov website during 2021. Cadmium ranks seventh on the top of 20 toxic chemicals priority list and top 10 chemicals of major public health concern. For short-term effects, cadmium can cause nausea, vomiting, diarrhea, muscle cramp, sensory disturbances, liver injury, convulsions, shock, and renal failure. Meanwhile, cadmium can cause kidney, liver, bone, and blood damage for long-term effects [2]. Due to the regulatory restrictions on the amount of cadmium in effluents, effluent treatment must be addressed to reduce the cadmium concentration before discharging. "Ecological" wastewater treatment is desired as the conventional techniques for the heavy metal's removal such as electrocoagulation, ion-exchange, chemical precipitation, and photocatalysis are known to have disadvantages like high operation cost, high energy requirement, and generation of toxic sludge. Researchers have recently shown an increasing interest in adsorption technology because the system reduces energy consumption, improves yield, selectivity, and non-toxic sludge production. Adsorption is the physical adhesion or bonding of molecules (or ions) to another substance's surface, that is, to a two-dimensional surface [3].

    A lot of agricultural waste is produced annually such as oil palm waste which is generated in millions of tons every year from Malaysia, Indonesia, Cameron, Africa, China, and Nigeria. Malaysia contributes 34% of palm oil world exports and produces approximately 168 Mt of biomass annually. Of this, over 80 Mt of solid biomass is generated by the palm oil industry whereby only 10% of oil palm biomass was utilized in 2015 for wood and bioenergy industries [4]. The rest of the biomass is left lying in the palm oil estate and vicinity of the mill, thus sacrificed its future economic value and usefulness. Therefore, there is a huge urgency to tackle this problem by finding alternate applications for biomass, such as utilization as adsorbent. Meanwhile, sustainable agriculture consumption and production are required as ways to reduce the source of water pollution.

    Some main criteria need to be thoroughly studied before selecting waste as an adsorbent which are capacity, selectivity, regenerability, kinetics, compatibility, and cost. Adsorption capacity is the most critical characteristic of an adsorbent and it is defined as the amount of adsorbate taken up by the adsorbent, per unit mass or volume of the adsorbent. The capacity of adsorption is very importance to the cost of capital since it determines the amount of adsorbent required. The low adsorption capacity of raw agriculture waste can be significantly improved upon modifications.

    In this literature review, the adsorption process by different types of palm oil biomass will be discussed with an evaluation of different types of adsorbent modification methods used.

    In Malaysia, the Langat River cadmium concentration of 1.22 ± 0.88 μg/L surpassed the limit of the continuous concentration criterion of 0.72 μg/L as set down in the United States Environmental Protection Agency (USEPA) and the annual average concentration of 0.2 μg/L as set down in the European Commission Standard. Electroplating, paint pigment, battery, smelting, mining, fertilizer, and alloy industries are among the industries that are responsible for the discharge of huge quantities of cadmium into the environment.

    In Sarawak, a Malaysian state on Borneo, the majority of edible aquatic organisms such as mollusc and cockles have also surpassed both limits as shown in Table 1. This is quite alarming for the community to beware of the cadmium pollution that surrounds them as cadmium has detrimental impact on human health through build-up of Cd in human body through human food chain.

    Table 1.  Cadmium concentrations in the edible aquatic species from various rivers in Sarawak.
    Location Aquatic species Cadmium (mg/kg) Malaysia Food Act 1983/FAO/WHO (mg/kg) Remark
    Estuary area of Sarawak River [5] Mollusc (Polymesoda expansa, Meretrix meretrix, and Solen regularis) 1.15–2.35 1.00/0.05 Exceeded the limit standard
    Moyan [6] Razor clam (Solen regularis) 0.7 Exceeded the FAO/WHO limit standard
    Serpan [6] Razor clam (Solen regularis) 0.6 Exceeded the FAO/WHO limit standard
    Miri Coast [7] Shrimp (Harpiosquilla harpax, Acetes indicus, Parapenaeopsis sculptilis, Litopenaeus vannamei, Penaeus merguiensis) 0.12–2.10 Exceeded the limit standard
    Village of Sambir, Village of Tambirat, Beliong Temple, and Village of Tanjung Apong [8] Cockles (Anadara granosa) 1.35–2.22 Exceeded the limit standard

     | Show Table
    DownLoad: CSV

    Six main types of oil palm biomass are generated as by-products of the palm oil industry which are oil palm mill effluent (POME), empty fruit bunches (EFB), oil palm fronds (OPF), palm kernel shells (PKS), oil palm trunks (OPT), and mesocarp fiber (MF). Other types of oil palm biomass including palm oil fuel ash (POFA), oil palm decanter cake (OPDC), and palm kernel cake (PKC). Currently, this biomass is used to produce wood products (plywood, flooring, and medium-density fiberboards (MDF)), bioenergy (co-firing at mills), fertilizer, animal feed, and palm pellet biomass as an ideal fuel to substitute other types of fossil fuel such as coal, firewood, and lignite. Other incoming technologies planning that is still in the development stage were set for biofuels, bioethanol, and bio-based chemicals. However, the real business was only utilized about 10% of total oil palm biomass in Malaysia, and a majority of the 90% balance is left unattended in the plantations and thus creates a disposal problem [4].

    Oil palm biomass generated as shown in Table 2 is calculated based on the ratio of total wet basis of EFB, PKS, POME, and PKC to FFB extraction rate as in a study by Hamzah et al. [9]. These biomasses are produced daily and more consistent in term of supply compared to oil palm trunks which are mostly available during replanting while fronds can be obtained from the pruning activity. Therefore, the total amount of biomass generated worldwide is estimated at 379.5 Mt based on 317.57 Mt of FFB processed in 2017. Meanwhile, Malaysia and Sarawak generated about 120.7 and 29.37 Mt of oil palm biomass in 2019, respectively. POME contributes the largest number which is about 56% of total oil palm biomass in Malaysia. Malaysia is struggling to manage the biomass waste recycling and recovery biomass disposal issues due to this huge number of agricultural residues generated annually.

    Table 2.  Estimation of total oil palm biomass generated in worldwide, Malaysia, and Sarawak.
    Aspect Standard biomass to FFB extraction rate (wet basis) Worldwide Malaysia Sarawak References
    Area (Mha) - 21.09 5.9 1.59 [10]
    Total palm oil mills - 800 452 81 [11]
    FFB yield (Mt/yr) - 317.57 101 24.7 [10]
    Crude palm oil (CPO) (Mt/yr) 1 t of CPO: 5 t of FFB 63.51 19.86 4.24 -
    EFB production (Mt/yr) 22% of FFB 69.87 22.22 5.28 -
    OPF production (Mt/yr) 36.7 t/(ha yr) 774 216.53 58.35 -
    PKS production (Mt/yr) 5.5% of FFB 17.47 5.56 1.36 -
    POME production (Mt/yr) 67% of FFB 212.77 67.67 16.55 -
    OPT production (Mt/yr) 9.2 t/(ha yr) 194.03 54.28 14.63 -
    MF production (Mt/yr) 13.5% of FFB 42.87 13.64 3.33 -
    PKC production (Mt/yr) 1 t of PKC: 4 t of FFB 79.39 25.25 6.18 -
    Estimates of total biomass generated (total wet basis of EFB, PKS, POME, and PKC) (Mt/yr) - 379.5 120.7 29.37 -

     | Show Table
    DownLoad: CSV

    Oil palm biomass residues are lignocellulosic materials that largely comprised of cellulose, hemicellulose, and lignin. Table 3 shows the lignocellulosic content of different types of oil palm biomass compared to the percentage content in cellulose standard.

    Table 3.  Chemical composition of different types of oil palm biomass and cellulose standard.
    Type of biomass Cellulose (%) Hemicellulose (%) Lignin (%) References
    EFB 23.70–38.30 21.60–35.30 22.10–29.20 [12], [13], [14]
    OPF 39.50–40.01 29.80–30.78 23.30–29.50 [12], [13]
    PKS 20.50–27.70 21.60–22.70 44.00–51.50 [12], [13], [14]
    OPT 30.60–34.44 23.94–33.20 28.50–35.89 [12], [13]
    Cellulose standard 80.8 16.6 2.6 [15]

     | Show Table
    DownLoad: CSV

    OPF contained the highest cellulose, 40.01% and higher percentage of these components provide higher number of chemical functional groups that could act as metal-binding sites. Cellulose is by far the most abundant resources of biopolymer that not only can be found in plant resources such as cotton and wood. These polymers of carbohydrate consist of tens to hundreds to several thousands of monosaccharide units (glucose). Depending on the source, age, growth stage, climatic conditions, and others, the composition of different lignocellulose materials varies significantly [15].

    The raw oil palm biomass adsorbents and the cadmium adsorption studies are summarized in Table 4. All studies were using single system, which means only one component adsorbate in an adsorption process, and this solution was prepared from metal ion stock solution. According to the Table 4, PKS showed the highest removal percentage of cadmium, 84.23% with qmax = 42.12 mg/g compared to other types of oil palm biomass listed. The high fixed carbon (18.09%) and very low ash contents of PKS (5.64%) signify that this biomass is suitable for the usage in the production of adsorbents. The optimum operating conditions of the study were at pH 6, adsorbent dosage of 1.5 g per 100 mL cadmium solution, initial concentration of 5 ppm, and contact time of 90 min [16]. The adsorption studies showed that the PKS was following the Freundlich model that assumes multilayer adsorption occurred on the surface of the adsorbent and also followed the pseudo-second-order model that assumes chemisorption is the main adsorption mechanism.

    Table 4.  The raw palm oil biomass adsorbents and the cadmium adsorption studies.
    Biomass type Specific surface area (m2/g) Adsorption studies References
    Isotherm Kinetics Removal percentage (%)
    PKS - Freundlich Pseudo-second-order 84.23 [16]
    EFB - - - 56.85 [17]
    PKS - - - 55.49 [17]
    OPDC 2.74 - - 43.95 [18]
    POME - Freundlich - - [19]
    MF 248.42 - Pseudo-second-order - [20]

     | Show Table
    DownLoad: CSV

    There was a finding by Amaludin [17] that showed the cadmium removal percentage of raw EFB, raw PKS and commercial adsorbent (Amberlite XAD-16, Rohm and Haas Company) were 56.85%, 55.49%, 55.03%, respectively, and thus indicated that oil palm biomass is comparable to Amberlite XAD's in terms of cadmium removal percentage. The cadmium removal percentage from the study conducted by Baby et al. [16] was higher (84.23%) than the finding from Amaludin [17] (55.49%) that is due to some different environmental factors that had not been optimized during the adsorption process. For example, for particle size, Baby et al. [16] used PKS powdered type whereas Amaludin [17] used 0.5–1.0 mm of particle size. As particle size decreases, specific surface area increases, resulting in the increment of the saturation adsorption per unit mass of the adsorbent and thus increase the removal percentage of cadmium.

    Nevertheless, overall, the adsorption capacity of raw biomass is comparatively low and this natural material needs to undergo chemical as well as physical activation to develop a highly porous surface to increase the adsorption capacity so that it can compete with other conventional adsorbents in the market. Said et al. [21] had converted male oil palm flowers (MOPF) into hydrochar through physical activation (hydrothermal carbonization) and investigated its BET surface area. It was found that a higher surface area (5.30 m2/g) was observed for the hydrochar than for the raw MOPF (1.28 m2/g) because the carbonization process strongly affected the porosity of hydrochar-based porous carbon by removing some organic compounds and thus opened the material's pores, increasing the binding sites for appropriate interaction with adsorbate substances. In conclusion, the low adsorption capacity of raw palm oil biomass can be improved upon modifications. Section 5 below shows a review of the physical modification of palm oil biomass methods which were furnace heating and microwave heating as well as the combination of these methods with chemical modification methods in term of adsorption capacity.

    The adsorbent modifications discussed in this section focused on furnace heating and microwave heating as well as the combined methods with chemical activating agents. Figure 1 schematizes the synthesis routes to activated carbons from oil palm biomass. Physical and chemical activation are the most common methods for producing activated carbon.

    Figure 1.  The synthesis routes to activated carbons from oil palm biomass.

    Furnace heating processing is a process in which the source of heat comes from outside and is transferred by convection, conduction, or radiation into the particles in the absence of oxygen. The sample is heated starting from the surface, then only the heat is transferred to the inner part [22]. The furnace heating modified biomass adsorbents and the adsorption studies are summarized in Table 5. In this method, the pyrolysis was done at fixed values of temperature, heating rate, and holding time. All of the adsorption studies listed in Table 5 used batch mode and synthetic cadmium solution as the single system except for Aziz et al. [23] who used both batch and continuous mode for adsorption studies. According to the table, POS shows the highest adsorption capacity, 38.61 mg/g with 98% of cadmium removal compared to other types of oil palm biomass listed. According to Goh et al. [24], it is acknowledged that the chemical properties of POS biochar prepared at a low temperature significantly affect cadmium adsorption. Surface functional groups were the dominating factor at low temperature while the surface area is the dominating factor at a higher temperature. Moreover, the product quality of charcoal resulting from pyrolysis by flowing nitrogen gas continuously is relatively higher than without flowing nitrogen gas into the reactor. This is what had been done by Goh et al. [24], purging the nitrogen gas continuously (500 mL/min) to minimize the amount of oxygen present and enters the reactor during pyrolysis.

    Table 5.  The furnace heating modified biomass adsorbents and the adsorption studies.
    Biomass Modification condition BET surface area (m2/g) Adsorption studies References
    Heating rate (℃/min) Temperature (℃) Time (h) Isotherm Kinetics qmax (mg/g)
    OPDC 10 500 1 27.27 Langmuir Pseudo-second-order 24.30 [25]
    EFB - 300–350 - 46.32 Langmuir - 15.1515 [26]
    POFA - 250 24 206.577 Langmuir Pseudo-second-order 15.823 [27]
    POFA - 250 24 206.58 - Bed depth service time (BDST) 34.9 [23]
    POS 15 400 1.5 16.3 Langmuir Pseudo-second-order 38.61 [24]

     | Show Table
    DownLoad: CSV

    Given the fact that the adsorption processes for wastewater purification can be carried out either discontinuously, in batch reactors, or continuously, in fixed-bed columns, the performance of the adsorbent should be evaluated in both batch and column studies. Aziz et al. [23] had conducted cadmium removal by POFA using batch and column system and the findings showed that the adsorption capacity in continuous mode (34.9 mg/g) was higher than the batch mode (15.823 mg/g). This showed that column study is more preferred than batch study. A similar finding had also been found in the experiment of cadmium removal by activated charcoal from neem leaf powder [28]. However, checking the practicality of the adsorbent in continuous mode is important due to the lack of column study data that is usually attributed to the fact that adsorption in fixed-bed columns does not necessarily operate under equilibrium conditions since the contact time is not sufficiently long for the attainment of equilibrium.

    Overall, the adsorption studies showed that most of the biomass was following the Langmuir model that assumes monolayer adsorption occurred on the surface of the adsorbent. The biomass also followed the pseudo-second-order model that assumes chemisorption is the main adsorption mechanism.

    Activated carbon can also be made through two steps, namely pyrolysis and activation or also known as impregnation. As the pyrolysis process is conducted in the absence of oxygen and other chemicals, impregnation is the treatment of physically activated carbon using chemical activators such as acids, bases, or salts and heated in an inert space. The impregnation treatment aims to enlarge the pore by breaking the hydrocarbon bond or oxidizing the surface molecule so that the activated carbon is changing in either its physics or chemistry as a larger surface area will increase the adsorption capacity [29].

    The combined furnace heating followed by chemical activation modified biomass adsorbents and the adsorption studies are summarized in Table 6. In this method, the pyrolysis was done at fixed values of temperature, heating rate, and holding time and chemically activated afterwards using chemicals such as sodium hydroxide and hydrochloric acid. All of the adsorption studies listed in Table 6 used batch mode and synthetic cadmium solution as the single system except for Fuadi et al. [30] who used continuous mode and simulated wastewater containing heavy metals such as cadmium, zinc, nickel, chromium, vanadium, and lead for adsorption studies. According to the Table 6, PKS treated with NaOH showed higher adsorption capacity compared to PKS treated with liquid smoke at the same range of physical activation temperature. There are various content of organic acids in liquid smoke and acetic acid is the organic acid that has an important role in liquid smoke [31]. Indeed, alkali modified adsorbent has a larger surface area, a higher ratio of surface aromaticity (H/C), higher N/C ratio with a lower value of O/C as compared to acid-modified adsorbent. Both studies had a good agreement with Langmuir isotherm and Pseudo-first-order that assumes physisorption is the main adsorption. In contrast, adsorption studies from the adsorbent that was subjected to pyrolysis and chemically activated using hydrochloric acid (HCl) conducted by Ujile and Okwakwam [32] in the petrochemical plant effluent treatment showed that the second-order kinetic constants cadmium contaminant was 49.6 g/(min mg) and chemisorption is the main adsorption mechanism. This technique was also found to remove 90% cadmium.

    Table 6.  The combined furnace heating followed by chemical activation modified biomass adsorbents and the adsorption studies.
    Biomass Physical activation condition Chemical activation condition Surface area (m2/g) Adsorption studies References
    Temp. (℃) Time (h) Agents Immersion time (h) Isotherm Kinetics qmax (mg/g)
    PKS 380 - 0.1 M NaOH 24 - Langmuir Pseudo-first-order 22.37 [33]
    PKS 300–400 3 Liquid smoke (acetic acid) 24 - Langmuir Pseudo-first-order 14.81 [31]
    PKS 500 5 Acetone and benzene 24 - - - - [30]
    EFB 600–800 - HCl - 691.85 BET Pseudo-second-order - [32]

     | Show Table
    DownLoad: CSV

    Fuadi et al. [30] had conducted a comparison experiment between physically modified and combined physical and chemical modified palm shell activated carbon on cadmium removal in simulated wastewater using a continuous system. The results showed that the combined physical and chemical treatment using acetone and benzene exhibited a good adsorption capacity with a lower area under graph which represented a lower amount of cadmium left after adsorption compared to physical treatment only. Organic solvents are used over the years as surface modifiers in the adsorption process. Acetone and benzene are the examples of an organic solvent which are carbon-based solvents that have a C–H bond in their structure. The organic agents are capable to introduce several species that are needed for metal ions and dye molecules to be adsorbed. However, because of their high cost, safety, and lack of stability, the practical application of organic agents may get limited.

    Activated carbon from the palm kernel shells (PKS) was prepared by Rosmi et al. [34] and Kwasi Opoku et al. [35] using chemical activation followed by the furnace heating method as shown in Table 7. In this method, the biomass was chemically activated at first using chemicals such as phosphoric acid, potassium carbonate, and sodium bicarbonate and later, pyrolysis was done at fixed values of temperature and holding time. Rosmi et al. [34] used batch mode and synthetic cadmium solution as the single system whereas Kwasi Opoku et al. [35] used filter beds system and lubricating oil containing heavy metals such as Cu, Fe, Zn, Cd, Pb, Cr, and Mg for adsorption studies. It was found that both adsorbents had the BET surface area in the range of the most common values of chemical activated carbons (600 to 1000 m2/g) [35]. The adsorption studies showed that both PKS adsorbents were following the Langmuir model that assumes monolayer adsorption occurred on the surface of the adsorbent. Kinetics study by Rosmi et al. [34] showed that the adsorption system followed the pseudo-second-order model that assumes chemisorption is the main adsorption mechanism and the adsorption study showed that only 30% of cadmium can be removed with a low adsorption capacity (0.1576 mg/g). The acid modification is mainly affected by the impregnation ratio, activation temperature, and time. The prolonged activation time might have damaged the pores developed earlier and therefore the cadmium adsorption capacity decreased. An optimum impregnation ratio is important to facilitate pore development, however, a higher impregnation ratio led to the rupture of the linkages between the lignin and cellulose followed by the formation of larger structural units and strong cross-linked solids [29].

    Table 7.  Combined chemical activation followed by furnace heating modified adsorbent and the adsorption studies.
    Biomass Chemical activation condition Physical activation condition BET surface area (m2/g) Adsorption studies References
    Activating agent Time (h) Temp. (℃) Time (min) Isotherm Kinetics qmax (mg/g)
    PKS Phosphoric acid (H3PO4) - 500 120 900.81 Langmuir Pseudo-second-order 0.1576 [34]
    PKS 1 M K2CO3 and NaHCO3 3 800 40 717.142 Langmuir - - [35]

     | Show Table
    DownLoad: CSV

    Alkali treatment using alkali activating agents such as K2CO3 and NaHCO3 is a well-known method to improve the development of microporosity for porous materials. During the alkali treatment, the alkali dissolvable extractive and chemical constituents of the fiber are removed. According to Kwasi Opoku et al. [35], analysis of cadmium removal revealed that palm kernel shells activated carbons are very effective in the adsorption processes. The concentrations of cadmium metal in the 6 months old used lubricating oils before and after the filtration process with palm kernel activated carbons in the filter beds was 0.030 ± 0.008 ppm and 0.000 ± 0.000 ppm, respectively.

    The method of microwave irradiation is to create a hot spot in the sample and generate heat from the inside, so the inner temperature is higher compared to the sample surface. In microwave processing, the electric energy is converted into heat energy through the interacting process of dielectric materials. The microwave irradiation method is effective as a source of thermal energy in terms of time-saving [22]. The microwave activation eliminated the volatile matter in the sample, resulting in the increment of fixed carbon content in the activated carbon [29]. The combined chemical activation followed by microwave-induced irradiation adsorbents and the adsorption studies are summarized in Table 8. In this method, the palm oil biomass was soaked with chemical activation agents such as phosphoric acid and polyacrylamide and later, the carbonization was done using microwave irradiation process at fixed values of microwave power level and microwave radiation time. All of the adsorption studies listed in Table 8 used batch mode and synthetic cadmium solution as the single system except for Ling et al. [36] who used continuous packed-bed column system for adsorption studies. According to the Table 8, oil palm shell PKS showed the highest removal percentage, 99% with an adsorption capacity of 227.27 mg/g compared to other types of oil palm biomass listed. The modification method that had been used by Tan et al. [29] was chemical activation using phosphoric acid followed by microwave-induced irradiation 700 W for 5 min. Adsorption studies showed that the adsorption process was following the Langmuir model that assumes monolayer adsorption occurred on the surface of the adsorbent. The adsorption system also followed the pseudo-second-order model that assumes chemisorption is the main adsorption mechanism.

    Table 8.  Combined chemical activation followed by microwave-induced irradiation modified adsorbent and the adsorption studies.
    Biomass Chemical activating agent Physical activation condition BET surface area (m2/g) Adsorption studies References
    Power (W) Time (min) Isotherm Kinetics Removal percentage (%)
    PKS Phosphoric acid (H3PO4) 700 5 - - Thomas - [36]
    OPF Polyacrylamide (C3H5NO)n 100 2 - - - 56.84 [37]
    PKS Phosphoric acid (H3PO4) 700 5 854.42 Langmuir Pseudo-second-order 99 (qmax = 227.27 mg/g) [29]
    PKS Phosphoric acid (H3PO4) 700 8 - - - 97.38 [29]

     | Show Table
    DownLoad: CSV

    From the Table 8, it shows that the cadmium removal percentage was lower at lower microwave power and this was due to low porosity. Surface area increases with an increase in microwave power until the optimum range is achieved. However, at a certain limit, even the highest surface area adsorbent produced the same pattern of adsorption, and thus chemical activating agents are needed to maximize adsorption. In a study conducted by Ukanwa et al. [38] which is using trona ore (Na2CO3·NaHCO3·2H2O) also known as crude soda ash as an activating agent, the optimum microwave power range for PKS, MF, EFB, and combine palm waste was 600 W. There was no corresponding increase in porosity beyond this range and thus, wasting the energy and also increase the energy consumption cost. At 20 minutes of microwave heating time, the BET surface area of PKS, MF, EFB, and combine palm waste (CPW) (3:2:1 proportion by weight of EFB, MF and PKS) was 1030, 1220, 735, and 980 m2/g, respectively. This showed that the type of feedstock did affected the carbonization process occured. A study by Tan et al. [29] revealed that the 5-minute microwave irradiation time showed marginally higher cadmium removal than the 8-minute heated sample, suggesting that prolonged exposure to the microwave may have damaged the earlier formed pores and thus decreased the capacity of cadmium adsorption.

    Another study by Yacob [39] had discovered the effect of phosphoric acid (H3PO4) on the BET surface area of PKS activated carbon at constant immersion time (48 h), microwave power (350 W), and heating time (10 min). The increment of the H3PO4 concentration resulting in a more potential site that to be penetrated and occupied by the activating agent who causes the pore opening and widening while removing the heavier volatile organic compound (VOC) in the palm shells. For example, the BET surface area of 30% and 60% H3PO4 modified AC were 158 and 630 m2/g, respectively. The effect of impregnation ratio on cadmium removal had been also conducted by Tan et al. [29] whereby H3PO4 impregnation ratio of 1:2 with microwave irradiation power of 700 W for 5 min showed the highest removal percentage for cadmium, that was 99%. Meanwhile, the removal percentage for the H3PO4 impregnation ratio of 1:1 and 1:3 adsorbents were 45% and 95.91%, respectively. An optimum impregnation ratio showed that the amount of acid was sufficient enough to react with the amount of precursor effectively to facilitate the pore development.

    By comparing the maximum cadmium adsorption capacities from the findings in Section 5, the output of chemical activation followed by microwave-induced irradiation of palm kernel shells (PKS) produced activated carbon with highest adsorption capacity (227.27 mg/g). The comparison of adsorption capacity of the best adsorbent presented in Section 5 with other adsorbents was listed in Table 9. It was found that PKS treated with chemicals and microwave heating still outperformed as compared to other adsorbents.

    Table 9.  Comparison of adsorption capacity of different adsorbents for cadmium adsorption.
    Adsorbents Treatment Method Maximum adsorption capacity, qmax (mg/g) References
    PKS (Best adsorbent in Section 5) Phosphoric acid (H3PO4) activation followed by microwave-induced irradiation (700 W, 5 min) 227.27 [29]
    Sunflower Head Carbon (SHC) H2SO4 activation followed by oven heating (150 ℃, 24 h) 15.95 [40]
    Sunflower Stem Carbon (SSC) H2SO4 activation followed by oven heating (150 ℃, 24 h) 17.61 [40]
    Sunflower head waste activated carbon combined with iron oxide nanoparticles H2SO4 activation + furnace heating (500 ℃, 1 h) + FeCl3·6H2O and FeSO4·7H2O 2.15 [41]
    Sewage sludge and waste tires Furnace heating (700 ℃, 2h) 50.25 [42]
    Peanut shell Furnace heating (565 ℃, 45 min) 1.038 [43]

     | Show Table
    DownLoad: CSV

    The other modification methods produced very low adsorption capacities in the range of 1–50 mg/g. The similarity of the above-mentioned methods as they were all using furnace heating method which contributed to lower adsorption capacity as compared with microwave heating method. Microwave irradiation provided a greater BET surface area compared to conventional heating systems as proven by research conducted by Koo et al. [22]. The BET surface area of microwave processing and furnace heating processing of EFB were 807.54 and 255.77 m2/g, respectively. The study also revealed that the microwave radiation method also performed a higher carbon yield and adsorption capacity due to micropore structure, the existence of carboxylic groups, and higher charge density on the surface of the absorbent. This is in line with a study by Ukanwa et al. [38] which concluded that a single-step activation with microwave has more unbroken pores while the two-step and conventional techniques produce activated carbons with broken and uneven pore linkages. Hence, this comparison helps the researchers to identify appropriate methods and conditions for application in cadmium adsorption as there is limited literature on single pollutant adsorption review using oil palm activated carbon with one recent review found for oil palm-derived activated carbon for CO2 capture [44].

    The utilization of oil palm biomass into cadmium adsorbent could play a role in killing two birds with one stone, which is to solve the oil palm biomass disposal issue and cadmium pollution issue. Worry less, the spent activated carbon can be recycled and sold as new by reactivation method. As the biggest biomass contributor in Malaysia, the oil palm biomass has been chosen to adsorb cadmium by more and more researchers in recent years. The modification of oil palm biomass has become the key point to improve the adsorption capacity. In fact, the modification process has been the emerging key challenge in the field of adsorption technology to industrial applications for a long time, and a wide variety of methods have been studied including physical modification such as heat pyrolysis and microwave irradiation, as well as dual modification of physical and chemical activation. The output of chemical activation followed by microwave-induced irradiation of palm kernel shells (PKS) produced activated carbon with high BET surface area (854.42 m2/g) and high adsorption capacity (227.27 m2/g). Further studies are needed to look at the adsorption capacity of oil palm biomass adsorbent in terms of the selectivity adsorption of pollutants, cost comparison with other conventional adsorbents, and its performance at a larger scale (pilot-plant studies). Hence, sustainable palm oil industry and safe water quality are possible, if the authority and stakeholders in the supply chain are committed to implementing the recommended modified adsorbent through policy changes and management practices that will bring benefits to the supply chain in the long run. Indeed, oil palm biomass is a promising adsorbent candidate for the removal of cadmium from wastewater.

    The authors gratefully acknowledge the financial support from Hadiah Latihan Persekutuan (HLP), and the technical support from Universiti Malaysia Sarawak.

    All authors declare no conflicts of interest in this paper.



    [1] The United Nations World Water Development Report 2020: Water and Climate Change. UNESCO, 2020. Available from: https://unesdoc.unesco.org/ark:/48223/pf0000372985. locale=en.
    [2] Jacobo-Estrada T, Santoyo-Sánchez M, Thévenod F, et al. (2017) Cadmium handling, toxicity and molecular targets involved during pregnancy: Lessons from experimental models. Int J Mol Sci 18: 1590. doi: 10.3390/ijms18071590
    [3] Tizo MS, Blanco LAV, Cagas ACQ, et al. (2018) Efficiency of calcium carbonate from eggshells as an adsorbent for cadmium removal in aqueous solution. Sustainable Environ Res 28: 326-332. doi: 10.1016/j.serj.2018.09.002
    [4] Malaysia Biomass Industries Review 2015/2016. MBIC, 2019. Available from: https: //www.biomass.org.my/.
    [5] Yusoff NAM, Long SM (2011) Comparative bioaccumulation of heavy metals (Fe, Zn, Cu, Cd, Cr, Pb) in different edible mollusk collected from the estuary area of Sarawak River. Empowering Sci Tec Innovat Towards Better Tomorrow 2011: 806-811.
    [6] Kanakaraju D, Ibrahim F, Berseli MN (2008) Comparative study of heavy metal concentrations in razor clam (Solen regularis) in Moyan and Serpan, Sarawak. GJER 2: 87-91.
    [7] Anandkumar A, Nagarajan R, Prabakaran K, et al. (2017) Trace metal dynamics and risk assessment in the commercially important marine shrimp species collected from the Miri coast, Sarawak, East Malaysia. Reg Stud Mar Sci 16: 79-88. doi: 10.1016/j.rsma.2017.08.007
    [8] Hossen M, Hamdan S, Rahman M (2014). Cadmium and lead in blood cockle (Anadara granosa) from Asajaya, Sarawak, Malaysia. Sci World J 14: 924360.
    [9] Hamzah N, Tokimatsu K, Yoshikawa K (2019) Solid fuel from oil palm biomass residues and municipal solid waste by hydrothermal treatment for electrical power generation in Malaysia: A review. Sustainability 11: 1060. doi: 10.3390/su11041060
    [10] Overview of the Malaysian Oil Palm Industry 2019. MPOB, 2020. Available from: http://palmoilis.mpob.gov.my/V4/overview-of-industry-2019/.
    [11] Parveez GKA, Elina H, Loh SK, et al. (2020) Oil palm economic performance in Malaysia and R & D progress in 2019. J Oil Palm Res 32: 159-190.
    [12] Onoja E, Chandren S, Abdul Razak FI, et al. (2019) Oil palm (Elaeis guineensis) biomass in Malaysia: The present and future prospects. Waste Biomass Valorization 10: 2099-2117. doi: 10.1007/s12649-018-0258-1
    [13] Saka S, Munusamy MV, Shibata M, et al. (2008) Chemical constituents of the different anatomical parts of the oil palm (Elaeis guineensis) for their sustainable utilization, JSPS-VCC Group Seminar 2008—Natural Resources and Energy Environment, 19-34.
    [14] Aziz MA, Uemura Y, Sabil KM (2011) Characterization of oil palm biomass as feed for torrefaction process, National Postgraduate Conference, 1-6.
    [15] Burhani D, Septevani AA (2018) Isolation of nanocellulose from oil palm empty fruit bunches using strong acid hydrolysis, AIP Conference Proceedings, 2024: 020005.
    [16] Baby R, Saifullah B, Hussein MZ (2019) Palm kernel shell as an effective adsorbent for the treatment of heavy metal contaminated water. Sci Rep 9: 1-11. doi: 10.1038/s41598-019-55099-6
    [17] Amaludin S (2009) Adsorption of lead and cadmium in aqueous solution onto oil-palm solid wastes, bentonite and amberlite polymeric adsorbents[Bachelor's thesis]. Universiti Teknologi Petronas, Perak.
    [18] Yusoff M, Mohamed E, Idris J, et al. (2019) Adsorption of heavy metal ions by oil palm decanter cake activated carbon. Makara J Technol 23: 59-66. doi: 10.7454/mst.v23i2.3760
    [19] Lee XJ, Hiew BYZ, Lee LY, et al. (2017) Evaluation of the effectiveness of low cost adsorbents from oil palm wastes for wastewater treatment. Chem Eng Trans 56: 937-942.
    [20] Abia AA, Asuquo ED (2008) Sorption of Pb(Ⅱ) and Cd(Ⅱ) ions onto chemically unmodified and modified oil palm fruit fibre adsorbent: Analysis of pseudo second order kinetic models. Indian J Chem Techn 15: 341-348.
    [21] Said A, Tekasakul S, Phoungthong K (2020) Investigation of hydrochar derived from male oil palm flower: Characteristics and application for dye removal. Pol J Environ Stud 29: 807-816. doi: 10.15244/pjoes/103355
    [22] Koo WK, Gani NA, Shamsuddin MS, et al. (2015) Comparison of wastewater treatment using activated carbon from bamboo and oil palm: An overview. JTRSS 3: 54-60.
    [23] Aziz ASA, Manaf LA, Man HC, et al. (2014) Column dynamic studies and breakthrough curve analysis for Cd(Ⅱ) and Cu(Ⅱ) ions adsorption onto palm oil boiler mill fly ash (POFA). Environ Sci Pollut R 21: 7996-8005. doi: 10.1007/s11356-014-2739-5
    [24] Goh CL, Sethupathi S, Bashir MJ, et al. (2019) Adsorptive behaviour of palm oil mill sludge biochar pyrolyzed at low temperature for copper and cadmium removal. J Environ Manage 237: 281-288. doi: 10.1016/j.jenvman.2018.12.103
    [25] Dewayanto N, Husin MH, Yong LK, et al. (2010) Waste to valuable by-product : Kinetic and thermodynamic studies of Cd, Cu and Pb ion removal by decanter cake. J Eng Technol 1: 85-98.
    [26] Sari NA, Ishak CF, Bakar RA (2014) Characterization of oil palm empty fruit bunch and rice husk biochars and their potential to adsorb arsenic and cadmium. Am J Agric Biol Sci 9: 450-456. doi: 10.3844/ajabssp.2014.450.456
    [27] Aziz ASA, Manaf LA, Man HC, et al. (2015) Equilibrium studies and dynamic behavior of cadmium adsorption by palm oil boiler mill fly ash (POFA) as a natural low-cost adsorbent. Desalination Water Treat 54: 1956-1968. doi: 10.1080/19443994.2014.891466
    [28] Patel H (2020) Batch and continuous fixed bed adsorption of heavy metals removal using activated charcoal from neem (Azadirachta indica) leaf powder. Sci Rep 10: 16895. doi: 10.1038/s41598-020-72583-6
    [29] Tan IAW, Chan JC, Hameed BH, et al. (2016) Adsorption behavior of cadmium ions onto phosphoric acid-impregnated microwave-induced mesoporous activated carbon. J Water Process Eng 14: 60-70. doi: 10.1016/j.jwpe.2016.10.007
    [30] Fuadi NA, Ibrahem, AS, Ismail KN (2014) Removal of heavy metals from simulated wastewater using physically and chemically modified palm shell activated carbon. J Appl Sci 14: 1294-1298. doi: 10.3923/jas.2014.1294.1298
    [31] Gani A, Faisal M (2020) Evaluation of liquid smoke-activated palm kernel shells biochar for cadmium adsorption. Rasayan J Chem 13: 1451-1457. doi: 10.31788/RJC.2020.1335872
    [32] Ujile AA, Okwakwam C (2018) Adsorption process of iron, cadmium, copper, lead from aqueous solution using palm bunch adsorbent. Chem Process Eng Res 55: 11-21.
    [33] Faisal M, Gani A, Muslim A (2019) Cadmium adsorption onto NaOH activated palm kernel shell charcoal. Int J GEOMATE 17: 252-260.
    [34] Rosmi MS, Azhari S, Ahmad R (2014) Adsorption of cadmium from aqueous solution by biomass: Comparison of solid pineapple waste, sugarcane bagasse and activated carbon. Adv Mater Res 832: 810-815. doi: 10.4028/www.scientific.net/AMR.832.810
    [35] Opoku BK, Friday JO, Kofi ED, et al. (2020) Adsorption of heavy metals contaminants in used lubricating oil using palm kernel and coconut shells activated carbons. Am J Chem Eng 8: 11-18. doi: 10.11648/j.ajche.20200801.13
    [36] Ling CP, Ai I, Tan W, et al. (2016). Fixed-bed column study for adsorption of cadmium on oil palm shell-derived activated carbon. J Appl Sci Process Eng 3: 60-71. doi: 10.33736/jaspe.308.2016
    [37] Selvakumaran N, Lazim, A (2019) Superabsorbent hydrogel from extracted oil palm frond waste cellulose using microwave irradiation for cadmium ion removal from aqueous solution. Chem Chem Technol 13: 518-525. doi: 10.23939/chcht13.04.518
    [38] Ukanwa KS, Patchigolla K, Sakrabani R, et al. (2020). Preparation and characterisation of activated carbon from palm mixed waste treated with trona ore. Molecules 25: 5028. doi: 10.3390/molecules25215028
    [39] Yacob AR (2013) Microwave induced carbon from waste palm kernel shell activated by phosphoric acid. Int J Eng Technol 5: 214-217.
    [40] Jain M, Garg VK, Garg UK, et al. (2015) Cadmium removal from wastewater using carbonaceous adsorbents prepared from sunflower waste. Int J Environ Res 9: 1079-1088.
    [41] Jain M, Yadav M, Kohout T, et al. (2018) Development of iron oxide/activated carbon nanoparticle composite for the removal of Cr(VI), Cu(Ⅱ) and Cd(Ⅱ) ions from aqueous solution. Water Resour Ind 20: 54-74. doi: 10.1016/j.wri.2018.10.001
    [42] Fan X, Zhang J, Xie Y, et al. (2021) Biochar produced from the co-pyrolysis of sewage sludge and waste tires for cadmium and tetracycline adsorption from water. Water Sci Technol 83: 1429-1445. doi: 10.2166/wst.2021.058
    [43] Pineda EP, Guaya D, Tituana C, et al. (2020) Biochar from agricultural by-products for the removal of lead and cadmium from drinking water. Water 12: 2933. doi: 10.3390/w12102933
    [44] Lai JY, Ngu LH, Hashim SS, et al. (2021) Review of oil palm-derived activated carbon for CO2 capture. Carbon Lett 31: 201-252. doi: 10.1007/s42823-020-00206-1
  • This article has been cited by:

    1. Kayode Adesina Adegoke, Solomon Oluwaseun Akinnawo, Oluwaseyi Aderemi Ajala, Tosin Adewumi Adebusuyi, Nobanathi Wendy Maxakato, Olugbenga Solomon Bello, Progress and challenges in batch and optimization studies on the adsorptive removal of heavy metals using modified biomass-based adsorbents, 2022, 19, 2589014X, 101115, 10.1016/j.biteb.2022.101115
    2. Nur Syazwani Athirah Sazuan, Saiful Irwan Zubairi, Nurul Hanisah Mohd, Rusli Daik, Synthesising injectable molecular self-curing polymer from monomer derived from lignocellulosic oil palm empty fruit bunch biomass: A review on treating Osteoarthritis, 2023, 16, 18785352, 104500, 10.1016/j.arabjc.2022.104500
    3. Rudi DUNGANI, Sasa Sofyan MUNAWAR, Tati KARLIATI, Jamaludin MALIK, Pingkan ADITIAWATI, , Study of Characterization of Activated Carbon from Coconut Shells on Various Particle Scales as Filler Agent in Composite Materials, 2022, 50, 1017-0715, 256, 10.5658/WOOD.2022.50.4.256
    4. Thi Kim Ngan Tran, Thi Cam Quyen Ngo, Quang Vinh Nguyen, Trung Sy Do, Ngoc Bich Hoang, Chemistry potential and application of activated carbon manufactured from coffee grounds in the treatment of wastewater: A review, 2022, 60, 22147853, 1914, 10.1016/j.matpr.2022.01.020
    5. Yu Wang, Chunrong Wang, Rongfei Feng, Yang Li, Zhiqiang Zhang, Saisai Guo, A review of passive acid mine drainage treatment by PRB and LPB: From design, testing, to construction, 2024, 251, 00139351, 118545, 10.1016/j.envres.2024.118545
    6. N. Rashmi, S.A. Salmataj, P. Senthil Kumar, Pushpanjali Bhat, Exploring chemically and physically modified plant-based fiber biomass for biosorption in wastewater treatment: A concise review, 2024, 67, 22147144, 106245, 10.1016/j.jwpe.2024.106245
    7. Mohamed M. El-Fahaam, Mohamed N. Sanad, Mohamed Farouz, Achievements and Difficulties with Batch and Optimization Investigations of Heavy Metal Adsorptive Removal Utilizing Enhanced Biomass-based Adsorption Materials, 2025, 21, 15734137, 24, 10.2174/0115734137282899240102085324
  • Reader Comments
  • © 2021 the Author(s), licensee AIMS Press. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0)
通讯作者: 陈斌, bchen63@163.com
  • 1. 

    沈阳化工大学材料科学与工程学院 沈阳 110142

  1. 本站搜索
  2. 百度学术搜索
  3. 万方数据库搜索
  4. CNKI搜索

Metrics

Article views(3616) PDF downloads(263) Cited by(7)

Other Articles By Authors

/

DownLoad:  Full-Size Img  PowerPoint
Return
Return

Catalog