Capacity of Adsorption of Cadmium (II) Ion by Bio-charcoal from Durian Barks

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Abstract

The study examined the adsorption capacity of definite amount of biocharcoal of Durian barks (Durio zibethinus Murr) to adsorb Cadmium ions at various pH. Biocharcoal was made by using pyrolysis method. The adsorption was monitored by measuring the Atomic Absorption of Cd (II) at 228.8 nm. Result shows that the optimum adsorption of Cadmium ion is 93.46% and the weight is 16.62 mg/g with 80 mg biocharcoal. The optimum pH is 7.0 with the percentage uptake of the cadmium ion 97.94%, and the weight is 17.42 mg/g. The optimum concentration is 20 ppm which can adsorb Cadmium ion 91.97%, or 11.42 mg/g. By using Langmuir isotherm equation, the highest adsorption of biocharcoal of Durian’s barks measured is 33.33 mg/g, which is potential as commercial activated carbon.

Capacity of Adsorption of Cadmium (II) Ion by Bio-charcoal from Durian Barks

Mery Napitupulu

^1*

, Daud K. Walanda

¹

, Yoga Natakusuma

¹

, Muhammad Basir

²

and Mahfudz

²

1Department of Chemistry, Faculty of Science, Tadulako University, Sulawesi Tengah, 94118, Indonesia; [email protected]

2Departement of Agrotechnology, Faculty of Agriculture, Tadulako University, Sulawesi Tengah, 94118, Indonesia

1. Introduction

Durian barks are known to have no economic value and called as organic waste. The existence of the organic and industrial wastes also can lead to contamination of water, soil, and air. The impact of the pollution could be mini- mized by utilizing organic wastes, derived from durian bark as a soil conditioner by making biocharcoal.

Cadmium is a white metal, malleable, soft and bluish.

The existence of cadmium in nature is closely linked to the presence of Lead and Zinc. In Lead and Zinc mining industry, the process of purification always obtains cadmium as side product in the environment [1]. Cadmium is used as a pigment in manufacturing ceramics, electrical plating, alloys and alkaline batteries [2]. Cadmium is toxic, a heavy metal that existed in soil as a result of the process of formation of mineral soil containing heavy metals [3].

Generally, Cadmium content in the soil is not polluted, which is 0.35 mg/kg with a range of 0.001 to 2.0 mg/kg[4].

Anthropogenic activities may increase the content of heavy

metals, and soil contaminated with Cadmium declared if its content has reached 3-8 mg/kg [4].

In farmland, contaminants Cadmium primarily come from phosphate fertilizer made from phosphate rock [5].

It is reported that Cadmium content of phosphate fertil- izers is 30-60 mg/kg [6]. It has been widely described that Cd can enter in soil as a contaminant of animal manure, sludge used as organic materials or industrial waste [3,7].

Charcoal is porous solid with 85-95% carbon, produced from materials containing carbon by heating at high temperature. When heating takes place, efforts are made to prevent leakage of air in the room heating so that the carbon-containing material is simply carbon- ized and oxidized. Charcoal is also used as fuel and adsorbent [8].

Charcoal is the carbon-rich material, derived from biomass such as wood and waste products of process- ing plants that are heated in a container with little or no air [9]. Some biocharcoal making techniques are avail- able from traditional to advanced and the best method is obtained depending on the availability of resources and

*Author for correspondence

J. Surface Sci. Technol. Vol 34(1–2), pp. 30-36, June 2018 ISSN (Print) : 0970-1893

Keywords: Adsorption, Biocharcoal, Cadmium, Durian Barks

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scale. The basic material used will affect the properties of biocharcoal itself and has a different effect on the produc- tivity of soil and plants [10].

Raw material for making charcoal generally is the residual biomass agriculture or forestry, including pieces of wood, coconut shell, bunches of palm oil, corn cobs and rice husk or fruit peels nuts, bark remnants oftimber, and other recyclable organic materials. When these wastes undergo combustion in the absence of oxygen, oxygen-low or even vacuum, they used to generate 3 substances: methane and hydrogen, bio-oil, and biocharcoal [10].

The adsorption is often classified as tertiary treatment [9] and this study aimed to describe the adsorbed cadmium based on biocharcoal weight, pH and concentration.

2. Research Methodology

This research was conducted at the Laboratory of Agrotechnology Faculty of Agriculture, University of Tadulako. The instrument used to measure the adsorption is Atomic Absorption spectrometer (GBC 932 AA, GBC Scientific Equipment Ltd).

2.1 Making Biocharcoal from Durian Barks

The process of making charcoal from durian bark s was adapted by modified procedure of work that has been done previously [11]. Beginning with durian barks, then cleansing of debris with water. Subsequently, the samples were dried in sunlight for 5 days and then put into drum (tool making charcoal). Sample carboniza- tion process is carried out at 500^oC with low oxygen levels until it becomes charcoal. Afterwards, charcoal was allowed to cool and then pulverized using a mor- tar and pestle, then cleaned again using distilled water.

The cleaned charcoal dried in oven at 105^oC to remove water content, then charcoal smoothed again using a 200 mesh sieve size, and stored in a dry place with sealed condition.

2.2 Preparation of Cadmium (II) Ion Standard Solution

A series of standard concentration of Cadmium solu- tions 0, 0.5, 1.0, 1.5, 2.0 and 2.5 ppm were prepared from Cadmium Standard solution of 1000 ppm, obtained from Sigma-Aldrich suitable for atomic absorption.

2.3 Influence of Charcoal weight on Cadmium (II) Ion Adsorption

A series of 20, 40, 60, 80, and 100 mg charcoal mixed with 25 mL of 60 ppm cadmium at pH 6 in a 100 mL bottle, then covered with aluminum foil tied with a rubber band and shake for 10 min then allowed to stand for 24 h. The mixture was filtered and the absorbance was measured by using AAS at wavelength of 228.8 nm with air-acetylene flame. The measurement was repeated twice.

2.4 Influence of pH Solution on Cadmium (II) Ion Adsorbed

The solution of 60 ppm Cadmium (25 mL) placed into 5 different beakers, then the pH set to 6.0; 6.5; 7.0; 7.5 and 8.0 or until turbid by adding HNO₃ or NH₄OH.

Cadmium solution is mixed with optimum weight biocharcoal obtained in the previous step. The Erlenmeyer Flask covered with aluminum foil paper, tied with rubber, then shake for 10 min, allowed to stand for 24 h. The mixture was filtered then absorbance measured by using AAS at a wavelength of 228.8 nm with air-acetylene flame. The measurement repeated twice.

2.5 Influence of Concentration on Cadmium (II) Ion Adsorption

Placed 25 mL of cadmium solution in 4 Erlenmeyer flask with concentration 10, 20, 30 and 40 ppm from 100 ppm standard solution. The initial concentration of the solution is measured by using AAS at a wavelength of 228.8 nm with air-acetylene flame. The procedure repeated twice.The pH was decreased or increased with the addition of HNO₃ or NH₄OH. Each solution is mixed with optimum weight of cadmium on biocharcoal, obtained in the previous step into a 100 mL Erlenmeyer flask.

Erlenmeyer covered on aluminum foil paper, tied with a rubber and then shaken on a shaker for 10 minutes, then allowed to stand for 24 h. Further, the filtrate was sepa- rated from the residue by filtration using Whatman filter paper 41 and absorbance of the solution was measured using AAS at a wavelength of 228.8 nm with air-acetylene flame, and repetition twice.

2.6 Data Analysis Technique

Measurement of adsorbed quantity (q_e), which was obtained from Atomic Absorption Spectrometer (AAS)

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and the absorption OD following analyzed using the following equation:

(

Ci-Ce

)

%adsorbed 100%

= Ci × Where, (Ci - Ce) = qe Description:

qe = concentration of Cd adsorbed (mg / L) Ce= equilibrium concentration (mg / L) Ci = initial concentration (mg / L) [12]

3. Results and Discussion

Adsorption isotherms of cadmium based on weight, pH and concentration of the biocharcoal and are expressed in Tables 1, 2 and 3, respectively.

Data from the measurements of the concentration of cadmium ions adsorbed at various concentrations are shown in Table 3.

3.1 Charcoal-Making

This study is an alternative method of separation of heavy metals in the industry, the utilization of waste durian barks as charcoal. Durian barks was weighed 1 kg and cleaned then dried for 5 days. The dried durian barks were burnt by using drum (tool making charcoal). Burnt barks were then placed into furnace at 500^oC for 60 minutes to form biocharcoal [13]. This was done to make the process of pyrolysis, where the results of the process will only generate carbon as a residue. The resulted biocharcoal pulverized and then cleaned with distilled water to remove remaining impurities. Cleaned biocharcoal then Table 1. Level of cadmium adsorbed (mg/L) and (%) based on weight of biocharcoal

Absorbance FP Adsorbent

weight (mg) Ci (mg/L) Ce (mg/L) Ce(average)

(mg/L) qe (mg/L) % Adsorbed

0.143 100 X 20 56.90 22.30 22.70 34.20 60.11

0.144 100 X 20 56.90 23.10

0.223 100 X 40 56.90 13.40 13.40 43.50 76.45

0.201 100 X 40 56.90 13.40

0.111 20 X 60 56.90 9.66 9.67 47.23 83.01

0.110 20 X 60 56.90 9.68

0.068 20 X 80 56.90 3.76 3.72 53.18 93.46

0.067 20 X 80 56.90 3.68

0.097 20 X 100 56.90 7.74 7.71 49.19 86.45

0.096 20 X 100 56.90 7.68

Description: FP = Dilution Factor

Table 2. Concentration of cadmium adsorbed (mg/L) and (%) at various pH Absorbance FP pH Ci (mg/L) Ce (mg/L) Ce Average

(mg/L) qe (mg/L) % Cd Adsorbed

0.056 25 X 6.0 56.90 2.60 2.74 54.16 95.18

0.057 25 X 6.0 56.90 2.88

0.054 25 X 6.5 56.90 2.33 2.52 54.38 95.57

0.056 25 X 6.5 56.90 2.70

0.047 25 X 7.0 56.90 1.13 1.17 55.73 97.94

0.048 25 X 7.0 56.90 1.20

0.055 25 X 7.5 56.90 2.45 2.67 54.23 95.31

0.057 25 X 7.5 56.90 2.88

0.058 25 X 8.0 56.90 2.95 2.95 53.95 94.82

0.058 25 X 8.0 56.90 2.95

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The increasing of biocharcoal weight from 20 mg to 80 mg caused the increase of cadmium (%) ions are adsorbed, however the adsorbent weight of 100 mg decreased the relative adsorption (Figure 1). This was due to the adsorption of the increasing number of biocharcoal interacting with cadmium ions. The increasing of adsorption of cadmium ions on biocharcoal weight of 20-80 mg due to cell density in solution produced a sufficiently effective interaction between the active center of the biocharcoal cell with cadmium ions, the more adsorbent the more active center of biocharcoal reacting. Therefore, when the number of biocharcoal enlarged, this comparison is no longer met the effect on the activity of ion uptake of cadmium by biocharcoal [11]. However, the relative decline of cadmium ion adsorbed on charcoal weight of 100 mg caused due to the cadmium ions contained in the solution was fully adsorbed by biocharcoal in other words, cadmium ions in solution have been entirely adsorbed by biocharcoal. It can also occur because the surface biocharcoal already in a state saturated with cadmium metal ions so that the increasing in weight would not be affected the adsorption enhancing metal ions by biocharcoal [11]. As can be seen in the Figure 1 above, the optimum adsorption of cadmium ions occurred at 80 mg of biocharcoal with adsorption percentage 93.46.

The degree of acidity is a factor that greatly affects the process of adsorption of metal ions in solution, because of the presence of H⁺ ions in solution will compete with a cation to bind to the active site. In addition, the pH also affects ion species present in the solution so that it will affect the ion interaction with the active site of the adsorbent [15].

placed in oven at 105^oC for 60 minutes for drying process which eliminated moisture that was still present in the biocharcoal. After the drying process, biocharcoal was smoothed using a 200 mesh sieve to obtain an adsorbent particle size finer or having a surface area that is optimal.

This is consistent with the statement [14], which states that the efficiency of adsorption is a function of the surface area of the adsorbent. The larger the surface area of the adsorbent, the greater the capacity of an adsorbent in adsorbing an adsorbate. This process is the last step in the process of biocharcoal making. The amount of 5.9 g of biocharcoal was produced from 1 kg durian barks.

Determining the concentration of cadmium ions in a state of equilibrium is measured using Atomic Absorption Spectrometre (AAS) with air-acetylene flame at 228.8 nm.

The amount of cadmium ions adsorbed (qe) by biocharcoal from durian barks is the difference in concentration of cadmium ions initially with cadmium ion concentration at equilibrium (Ce). To obtain maximum adsorption of cadmium ions will require an optimum condition, as shown in Figure 1.

Figure 1. Influence of charcoal weight (mg) on cadmium ion(%) adsorbed.

Table 3. Cocentration of cadmium adsorbed (mg/L) and (%) based on concentration Concentration

(mg/L) A FP Ci

(mg/L) Ci Average

(mg/L)

A FP Ce

(mg/L) Ce Average

(mg/L)

(mg/L)qe % Cd Adsorbed

10 0.147 25 X 18.35 16.22 0.053 25 X 2.43 2.27 13.95 86.00

10 0.122 25 X 14.08 0.055 25 X 2.10

20 0.271 25 X 39.78 39.74 0.059 25 X 3.15 3.19 36.55 91.97

20 0.270 25 X 39.70 0.059 25 X 3.23

30 0.334 25 X 50.70 50.37 0.135 25 X 16.38 16.73 33.64 66.79

30 0.330 25 X 50.03 0.139 25 X 17.08

40 0.373 25 X 57.38 57.17 0.195 25 X 26.65 26.82 30.35 53.09

40 0.370 25 X 56.95 0.197 25 X 26.98

Remarks: A = Absorbance

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Determination of optimum pH on cadmium ion adsorption using durian barks biocharcoal has been done on the variation of pH 6.0, 6.5, 7.0, 7.5 and 8.0. The determination of the optimum pH aims to determine the optimum of cadmium ion adsorption solution by biocharcoal.

Cadmium ion adsorption is influenced by the pH of the solution, where pH 6.0 to pH 6.5, cadmium ion adsorption is very small, namely with percentage respectively 95.18% and 95.57%, as well as at a pH of 7.5 to pH of 8.0 where the adsorption of the cadmium ions is not too large in the amount of 95.31% and 94.82%, up by adsorption of biocharcoal and steadily at maximum pH 7.0 where the percentage of absorption reached 97.94%

(Figure 2).

Figure 2. Infuence of pH solution on cadmiumion (%) adsorbed.

The low adsorption occurs at pH 6.0-6.5 is due to several possibilities: First, because at low pH there is competition between H⁺ and Cd²⁺to interact with the functional groups on the surface of the biocharcoal;

Second, at low pH functional groups existing on the surface of biocharcoal surrounded by H⁺ ions thus pre- venting the interaction between the ions of cadmium with functional groups on the surface of biocharcoal[16].

Third, the surface of biocharcoal charged positive resulting in rejection of electrostatically to ions Cd²⁺[17]. At pH 7.0, adsorption occurs in large amount of 97.94%.

This is because the number of H⁺ ions decreased so that competition with H⁺ is reduced, and the surface of the biocharcoal tends ionized by releasing H⁺ ions.The surface of the biocharcoal becomes negative [18] resulting in electrostatic interaction between the surface of biocharcoal with Cd²⁺ ions. At pH 7.5 to 8.0 the number of

cadmium ions adsorbed tends to decrease. The decrease was due to a rather high pH cadmium ions undergo hydrolysis to CdOH⁺[19]. The hydrolised of cadmium ion with the positive charge reduced to +1 so that its interaction with the surface of biocharcoal reduced.

Low adsorption of cadmium ion by biocharcoal at lower pH due to protonation of the basic groups (functional) adsorbent material, so that the active sites have a charge of ‘clean’ tend to be positive, as a result of interaction between the cation with the active site is reduced or even disappear. Otherwise, the increase in pH (to below the precipitation pH cations) resulted active sites tend to have a negative charge, causing relatively strong interactions between the cation with the active site, which means increased adsorption capacity [20].

Based on the above findings it can be seen that the optimum adsorption of cadmium ions occurs at pH 7.0 with adsorption percentage 97.94.

The figure below shows the effect of the concentration of cadmium ion on the adsorption process, which is the adsorption of cadmium ion concentration increased from 10 ppm to 20 ppm (Figure 3).

Figure 3. Influence of concentration of cadmium (mg/L) on % of Cd adsorbed.

Cadmium ion adsorption increased at the initial concentration of 16.22 mg/L to 39.74 mg/L, which is 4.36 mg/g to 11.42 mg/g cadmium ion adsorbed per gram biocharcoal, but when adding concentration of 30-40 ppm, the initial concentration of 50.37 mg/L and 57.17 mg/L decreased adsorption of 10.51 mg/g and 9.48 mg/g (Figure 3).

Adsorption is affected by the concentration of the solution, the greater the concentration of the solution, the adsorption of cadmium ions also will be growing to

Concentration of cd (mg/L)

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compounds which were depicted by the adsoption band in long area wave 455.2 - 3402.43 cm^-1.Wide band with strong intensity in the area 3371.57 cm^-1 indicated the presence of an O-H bond and C-H. Band at 1053.13 cm^-1 indicates the presence of aromatic C=C bond, and 466.77- 1400.32 cm^-1 shows the presence of C-C bonds. Based on FTIR spectrum pattern, it can be seen that the intensity of adsorption in the wavelength region, and the presence of C-O and C-H bonds as well as C=C band shows the nature of biocharcoal from durian bark is polar.

4. Conclusion

The optimum weight required of charcoal from durian barks to adsorb cadmium ion is 80 mg. The weight of cadmium ions adsorbed is 16.62 mg/g and the percentage of adsorbed cadmium ions is 93.46. Optimum cadmium ion adsorption occurs at pH 7.0; the weight of cadmium ions adsorbed is 17.42 mg/g and the percentage of adsorbed cadmium ions is 97.94. Optimum cadmium ion adsorption occurs at a concentration of 20 ppm, the weight of cadmium ions adsorbed is 11.42 mg/g and the percentage of absorbed cadmium ions is 91.97. The maximum adsorption capacity of the biocharcoal of durian barks on cadmium ion adsorption using Langmuir isotherm equation is equal to 33.33 mg/g biocharcoal.

5. Acknowledgement

The authors thank to the Laboratory of Agrotechnology Faculty of Agriculture, University of Tadulako and the staf member who have helped the authors in completing this study.

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Figure 4 indicated the metal ions adsorbed on the surface of the biochemical, the metal ion concentration remaining in the solution produces L-type curves like rectanguler hyperbole, showing characteristics of Langmuir isotherm [21]. On the graph, it can be seen that the optimum adsorption of cadmium ions occurs at a concentration of 20 ppm with adsorption percentage 91.97.

Figure 4. Linear Langmuir plot for cadmium ion adsorption.

In this study, the Langmuir adsorption isotherm equation was applied on cadmium ion adsorption kinetics by biocharcoal. Langmuir adsorption isotherm is a good model approach equilibrium and adsorption kinetics.

This model is based on several assumptions, namely: the adsorbent surface is homogeneous, so that the adsorption energy is constant in all parts, each atom adsorbed on a specific location on the surface of the adsorbent, and each part of the surface can only accommodate a single mole- cule or atom [22]. By using the linear regression equation for cadmium ion adsorption correlation coefficient R² = 0.976, affinity adsorption (k) = 1,154 and a maximum cadmium adsorption capacity of 33.33 mg / g (Figure 4).

This means that each 1 gram biocharcoal from durian bark is able to adsorb 33.33 mg cadmium ion.

The previous study of FTIR spectrum of biocharcoal from Durian bark [23] indicated vibration of functional groups of O-H, C-H, C-C and C=C of the aromatic

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