The potential of Artocarpus heterophyllus (Jackfruit) seed powder in adsorption of chromium(VI) from aqueous solution was studied using batch technique. The performance of the adsorption process was evaluated against contact time, pH, adsorbent dose, temperature and initial chromium(VI) ion concentration. The influence of the presence of interfering anionic species including chlorides, nitrates and sulphates on the adsorption process was also evaluated. The adsorption of chromium(VI) by Jackfruit seed powder reached equilibrium after 60 minutes. Higher chromium(VI) adsorption was observed at lower pH values with maximum removal (96.05%) occurring at pH 2. A great deal of adsorption (92.53%) was observed at the adsorbent dosage level of 1.0 g/100 ml solution. There was an improvement in the adsorption process when the temperature was increased from 25 °C (95.35%) to 60 °C (99.56%) followed by a decrease to 98.76% at 70 °C. Adsorption decreased with increasing initial chromium(VI) ion concentration. The adsorption followed both Freundlich and Langmuir adsorption models with correlation coefficients of 0.998 and 0.994 respectively, and Q m of 0.57 mg/g. The presence of nitrate and chloride ions significantly lowered the adsorption, with all the p values < 0.05 at 95% significant level. Meanwhile, the presence of sulphate ions enhanced chromium(VI) adsorption as most of the p values were >0.05. From the obtained Q m, Jackfruit Seed Powder is a good adsorbent for the aqueous solutions of Cr(VI). The adsorption process is slowed by the presence of the interfering anionic species.
Chromium(VI) is one of the major heavy metals of great concern in wastewater management. Most of the chromium contamination in Uganda arises from industrial activities which include leather tanning, cement mining, electroplating, photography, dye manufacturing, and fertilizer industries. Majority of these industries are small scale and cannot afford the conventional methods of treating wastewater containing chromium. These industries therefore, channel untreated or partially treated effluents into the neighbouring water bodies, especially Lake Victoriaor deposit precipitated chromium into landfills from where it leaches into the underground water [
Some studies show that heavy metals can be removed from aqueous solution using plant materials such as papaya seeds [
In this study, the effectiveness of Artocarpus heterophyllus (jackfruit) seed powder in removing the chromium(VI) from aqueous solution by adsorption was investigated. The Artocarpus heterophyllus believed to originate from the rain forests of the Western Ghats of India is the largest tree-born fruit in the world. It is widely distributed in Uganda, both cultivated and wild, and a popular food item. The juicy pulp is commonly eaten as dissert but the seeds are often regarded as a waste and therefore, discarded. Since the seeds can be readily obtained from the consumers in large quantities, it might provide material for the remediation of chromium contamination from the contaminated water system as well.
Fresh jackfruit seeds were collected from Bugema village, Luwero district, Ugandain February, 2013 and the seed coat removed. The seeds were dried completely under the sun for 30 days, pulverised and sieved using a sieve of particle size 710 µm.
A stock solution containing 100 mg・l−1 of Cr(VI) was prepared by dissolving 0.2828 g of AR grade potassium dichromate, K2Cr2O7 (Merck) in distilled water to make 1000 mL of solution. The stock solution was appropriately diluted to give Cr(IV) standard solutions of the required concentrations. The pH of the standard solutions was adjusted with either 0.1 M sulphuric acid or 0.1 M sodium hydroxide solution.
Batch adsorption studies were conducted at different conditions to assess the potential of jackfruit seed powder in the adsorption of Cr(VI) from aqueous solution. Experimental procedures followed were as outlined in [
where; V is the initial solution volume (L), Co and Ce are theinitial and equilibrium Cr(VI) concentration of the solution (mg・l−1), and W is the amount of JSP (g).
The effect of initial pH, contact time, temperature, adsorbent dosage level and initial chromium(VI) ion concentration were determined as per the procedures described by [
While maintaining all other factors constant, the initial pH of the standard Cr(VI) solution was varied from 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10 using 0.1 M H2SO4 or 0.1 M NaOH solution. Jackfruit seed powder (2.0 g) was added to 250 ml Pyrex glass beaker containing 5 mg・l−1 Cr(VI) solution (100 ml). The mixture was agitated using a glass rod every after 10 minutes. After 1 hour, 10 ml of the solution was obtained, to which was added 0.2 ml of 0.1 M H2SO4 followed by 1 ml of 1,5-diphenyl carbazide. The solution was left to stand for 5 to 10 minutes and residual concentration of Chromium(VI) determined.
Jackfruit seed powder (2.0 g) was added to 100 ml of 5 mg・l−1 chromium(VI) solution at pH 2 for 1, 3, 5, 10, 20, 30, 40, 50, 60, 90 and 120 minutes at 25˚C. The mixture was filtered and the amount of residual chromium(VI) in solution determined.
Jackfruit seed powder (2.0 g) was added to 100 ml of 5 mg・l−1 chromium(VI) solution at pH 2 while maintaining the temperature at 25, 30, 40, 50, 60 and 70˚C using a water bath for 1 hour.
Different masses of jackfruit seed powder (0.2, 0.5, 0.8, 1.0, 1.5, 2.0 and 3.0 g) were added to 100 ml of 5 mg・l−1 chromium(VI) at pH 2, and temperature of 25˚C and the mixture stirred after every 10 minutes for 1 hour.
Jackfruit seed powder (2.0 g) was added to 100 ml of 5.0, 7.5, 10.0, 12.5, 15.0, 17.5 and 20.0 mg・l−1 of chromium(VI) at the pH 2 for 1hour while maintaining the temperature at 25˚C.
Effect of interfering ions was determined as per the procedure listed in [
A solution of chromium(VI) (100 ml, 5.0 mg・l−1) was added different sodium chloride, potassium nitrate or sodium sulphate of concentration of 0, 5, 10 and 20 g/l at pH 2. To the resulting solutions, 2.0 g of jackfruit seed powder was added. While maintaining the temperature at 25˚C, the mixture was stirred after every 10 minutes for 1 hour. The procedure was repeated for 7.5 mg・l−1 chromium(VI).
Cr(VI) removal by JSP was found to be highly dependent on the initial pH of the solution as illustrated by
perecentage adsorption. The pH best suitable for the adsorption of Cr(VI) species by plant seeds is 2 [
There was a slight change in the pH of the solution after the whole adsorption process as illustrated by
The general increase in adsorption as per
for the chromium(VI) ions to interact with the JSP active sites. The initial rapid rate of adsorption leading up to 85.91% adsorption after 10 minutes may be due to the availability of the free active sites on JSP for the Cr(VI) ions. The next gradual adsorption rate to 98.73% at 90 minutes was either due to the electrostatic hindrance caused by the already adsorbed chromium(VI) anionic species and the incoming ions, or reduced probability of the chromium(VI) in finding a free adsorption site, since most active sites are already occupied [
The general increase in adsorption in
On the contrary adsorption capacity diminished with increasing adsorbent dose because adsorption capacity is inversely proportional to the adsorbent
dosage level.
Percentage adsorption decreased with initial ion concentration as illustrated by
The adsorption thermodynamic parameters were determined from the relations as described in [
The standard change in the Gibbs free energy was calculated from
where R is gas constant (8.314 kJ・mol−1) and T is temperature in kelvin (K), Kc is the equilibrium constant obtained by the equation below
Cad is the concentration of Cr(VI) adsorbed onto the JSP at a given temperature, Co is initial Cr(VI) concentration.
Finally, the standard enthalpy change ∆Ho of +61789.648 J・mol−1 and entropy changes ∆So of +232.38 JK−1・mol−1 were obtained using the slope and intercept of
The positive value of ∆Ho indicated that the adsorption process between jackfruit seed powder and chromium(VI) was endothermic [
The negative values of ∆Go indicated the feasibility and spontaneity of the adsorption process. Furthermore, the amount of ∆Go (>41.858 kJ or 10 kcal) suggests
that adsorption is chemical. The increasing magnitude of ∆Go with temperature as shown in
Presence of a salt in the solution introduced interfering anionic species that competed with chromium(VI) for the same jackfruit seed powder adsorption sites. Interference significantly occurred in presence of the nitrate and chloride ions as per
Temp. (K) | 1/T (K−1) | Kc | lnKc | ∆Go (J・mol−1) | ∆Ho (J・mol−1) | ∆So (JK−1・mol−1) |
---|---|---|---|---|---|---|
298 | 0.0034 | 20.4961 | 3.02 | −7459.592 | +61789.648 | +232.38 |
303 | 0.0033 | 27.3768 | 3.31 | −8621.492 | ||
313 | 0.0032 | 69.9220 | 4.25 | −10945.292 | ||
323 | 0.0031 | 176.3050 | 5.17 | −13269.092 | ||
333 | 0.0030 | 235.9668 | 5.46 | −15592.892 |
Interference by the chloride or nitrate ions was because of their relative small size as compared to
On the contrary, increasing sodium sulphate concentration and hence sulphate (
In this case, the jackfruit seed powder may have acted as a reducing agent owing to the presence of electron-donor groups under acidic conditions. In turn, Cr(VI) probably received electron which then reduced it to Cr(III) [
From
Two adsorption isotherm models were selected to fit the data, namely the Langmuir and Freundlich models [
where Qm is the maximum adsorption capacity, while Ka is a coefficient related to the affinity between the adsorbent and metal ions also related to the energy of adsorption, used to determine a dimensionless constant separation factor or
Salt | [Cr(VI)] (mg/l) | [Salt] (g/l) | Ce (mg/l) | Qe (mg/g) | Aeq (%) |
---|---|---|---|---|---|
NaCl | 5.0 | 0 | 0.2185 | 0.2391 | 95.63 |
5 | 0.2819* | 0.2359 | 94.36 | ||
10 | 0.4087*** | 0.2296 | 91.83 | ||
20 | 0.5708**** | 0.2215 | 88.58 | ||
7.5 | 0 | 0.8598 | 0.3320 | 88.54 | |
5 | 1.1276* | 0.3186 | 84.97 | ||
10 | 1.4376** | 0.3031 | 80.83 | ||
20 | 1.8745**** | 0.2813 | 75.01 | ||
Na2SO4 | 5.0 | 0 | 0.2185 | 0.2391 | 95.63 |
5 | 0.4972** | 0.2251 | 90.42 | ||
10 | 0.2960* | 0.2352 | 94.08 | ||
20 | 0.0987 | 0.2451 | 98.03 | ||
7.5 | 0 | 0.8598 | 0.3320 | 88.54 | |
5 | 0.2678 | 0.3616 | 96.43 | ||
10 | 0.1382 | 0.3681 | 98.16 | ||
20 | 0.1263 | 0.3687 | 98.32 | ||
KNO3 | 5.0 | 0 | 0.2185 | 0.2391 | 95.63 |
5 | 0.5567*** | 0.2222 | 88.87 | ||
10 | 0.7259**** | 0.2137 | 85.48 | ||
20 | 1.1783**** | 0.1911 | 76.43 | ||
7.5 | 0 | 0.8598 | 0.332 | 88.54 | |
5 | 1.4235** | 0.3038 | 81.02 | ||
10 | 1.9168*** | 0.2792 | 74.44 | ||
20 | 2.5652**** | 0.2467 | 65.80 |
*(p ≤ 0.05), **(p ≤ 0.005), ***(p ≤ 0.0005) and ****(p ≤ 0.00005).
equilibrium parameter RL, which is defined by the following relationship:
The parameter RL indicates the shape of the isotherm accordingly; if RL > 1, adsorption is unfavourable; RL = 1, Linear adsorption; RL = 0, irreversible adsorption; therefore, RL has a shape of 0 < RL < 1 for the sorption process to be favourable [
Rearranging the equation, a linear equation is obtained
A linear plot of Ce/Qe vs. Ce, in
Additionally, the empirical data was fitted to the Freundlich adsorption isotherm, which can be expressed as below:
The Freundlich isotherm being empirical, it is used for non-ideal adsorption and when the surface is heterogeneous. This isotherm describes nonlinear adsorption where Kf is the Freundlich constant, indicating the relative adsorption capacity related to the binding energy. The factor n, known as heterogeneity factor, represents the deviation from linearity of the adsorption. The linearised form of the Freundlich model is as shown below:
A linear plot of logQe vs. logCe yielded Freundlich isotherm at 25˚C.
The experimental results were fitted into the Langmuir as per
Maximum adsorption capacity (Qm) of Cr(VI) using JSP was 0.57 mg/g, which compared well with those reported in literature for other bioadsorbents (
Activated rice husk carbon, activated alumina and modified oak sawdust exhibited higher Qm owing to the high initial carbon content, activation process as well as the pore development due to the basic morphology of the raw material [
JSP successfully demonstrated the ability to remove Cr(VI) from aqueous acidic solution and its Qm compared well with those of other bio adsorbents reported in literature. Cr(VI) removal percentage by JSP was dependent on pH, temperature, contact time, adsorbent doses, and initial Cr(VI) concentration. Furthermore, it
Isotherm | R2 | Estimated isotherm parameters |
---|---|---|
Freundlich | 0.998 | Kf = 134.896, n = 0.2213 |
Langmuir | 0.994 | Qm = 0.57 mg/g, Ka = 1.44 L/mg and RL = 0.0336 - 0.1220 |
Adsorbents | Qm (mg/g) | pH | Co (mg/l) | Reference |
---|---|---|---|---|
Activated rice husk carbon | 0.8 | 2 | 10 | [ |
Activated alumina | 1.6 | 4 | 10 | [ |
Sawdust | 0.229 | 2 | 5 | [ |
Pine leaves | 0.277 | 2 | 5 | [ |
Raw rice bran | 0.07 | 2 | 5 | [ |
Modified oak sawdust | 1.7 | 3 | - | [ |
CETYL-amended zeolite | 0.65 | - | - | [ |
EHDDMA-amended zeolite | 0.42 | - | - | [ |
Jackfruit seed Powder (JSP) | 0.57 | 2 | 5 | Present study |
was found out that Cr(VI) adsorption strongly depended on initial pH of the solution. Thus, the removal of Cr(VI) is highly applicable at very low pH values owing to the need for protonation of the surface active sites of JSP. Thermodynamic investigation showed that the process is spontaneous even at room temperature. The affinity of JSP for the Cr(VI) increases with temperature as well as the process being majorly chemisorption, as portrayed by positive standard entropy changes. The positive value of enthalpy change indicates that the reaction is endothermic.
Both Freundlich and Langmuir adsorption models well described the equilibrium data of Cr(VI) adsorption by JSP as the data best fitted both with high regression coefficients. According to Langmuir model, the monolayer adsorption capacity (Qm) was found to be 0.57 mg of Cr(VI) per gram of JSP. The obtained Qm implies that JSP is a better adsorbent as compared to saw dust, pine leaves, raw rice bran among others. Therefore, JSP is a potential adsorbent for chromium(VI) contaminated water. Finally, it was observed that the adsorption efficiency of Cr(VI) by JSP was highly influenced by interfering ionic species present in the matrix. Therefore, it is important to have an idea of the ionic species present in the effluent before the use of JSP to remediate it or the effectiveness of JSP to remove Cr(VI) from aqueous environments will greatly depend on the chemical components present. Similarly, because percentage adsorption decreases with increasing Cr(VI) concentration, it would be better to increase the amount of the JSP used as well as contact time in the case of highly polluted water systems.
Lubanga, C., Ntambi, E. and Adaku, C. (2017) Potential of Artocarpus heterophyllus Seed Powder in the Adsorption of Chromium(VI) from Aqueous Solution. Journal of Water Resource and Protection, 9, 614-628. https://doi.org/10.4236/jwarp.2017.96041