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Assessment of the effectiveness of orange (Citrus reticulata) peel in the recovery of nickel from electroplating wastewater

Hussein, Rim A.

The Journal Of The Egyptian Public Health Association: December 2014 - Volume 89 - Issue 3 - p 154–158
doi: 10.1097/01.EPX.0000457046.78389.33
Original articles
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Background Wastewater discharged from electroplating industry contains different concentrations of heavy metals, which when released into the environment pose a health hazard to human beings.

Objectives The aim of this study was to assess the effectiveness of orange peel as an adsorbent in the recovery of Nickel (Ni) from electroplating wastewater.

Materials and methods The effectiveness of orange peel as an adsorbent was assessed by determining the optimum conditions of adsorption (adsorbent dose, pH, and contact time), calculating the recovery percentage, and characterizing the orange peel sludge resulting from adsorption/desorption process as being hazardous or not.

Results Under optimum conditions for adsorption, orange peel was found to be an effective adsorbent of Ni from electroplating wastewater. It achieved 59.28% removal of the metal from a solution containing 528 mg/l, at a dose of 60 g/l, at pH 7, and for 1-h contact time. The nickel uptake capacity of orange peel was calculated to be 5.2 mg/g. Using HCl for desorption of adsorbed Ni, a recovery of 44.46% of Ni discharged in the wastewater could be reached. Orange peel resulting from the adsorption/desorption process was characterized as being nonhazardous.

Conclusion and recommendation Orange peel was found to be effective in the recovery of nearly half of the amount of Ni discharged in electroplating wastewater. Further studies are required to determine (a) the impact of the recovered NiCl2 solution on the quality of the plated product, (b) the effect of activation of orange peel on the adsorption process, and (c) the number of cycles during which orange peel can be reused as an effective adsorbent.

Environmental Health Department, High Institute of Public Health, Alexandria University, Alexandria, Egypt

Correspondence to Rim A. Hussein, PhD, Environmental Health Department, High Institute of Public Health, Alexandria University, 21561 Alexandria, Egypt Tel: +20 100 251 8599; e-mail: rimahamid@yahoo.com

Received October 21, 2014

Accepted October 26, 2014

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Introduction

Wastewater discharged from electroplating industry contains different concentrations of heavy metals. On the basis of the process applied, it may contain nickel (3–356 mg/l), zinc (4–250 mg/l), chromium (1–40 mg/l), and copper (1–30 mg/l) 1. Once released into the environment, these heavy metals pose a health hazard to human beings. Nickel has been reported to cause lung cancer and inhibit spermatogenesis, insulin formation, and kidney formation. Hexavalent chromium has been known to be carcinogenic and mutagenic. A high concentration of copper has been considered as the leading cause of neurotoxicity – namely, ‘Wilson’s Disease’ 2,3.

To meet the regulatory requirements for the discharge of electroplating wastewater into wastewater treatment plants or receiving streams, several treatment methods have been investigated. They include chemical precipitation 4, ion exchange 5, electrodialysis 6, electrocoagulation 7, use of microfiltration membrane 8, and adsorption.

Adsorption is one of the promising methods for the treatment of electroplating wastewater. The adsorbents used may be of mineral or biological origin, industrial by-products, or agricultural waste 9. Literature review for more than 100 articles (1984–2005) showed that low-cost adsorbents originating from agricultural waste have high capabilities for the removal of heavy metal (Cr6+: 170 mg/g of hazelnut shell activated carbon, Ni2+: 158 mg/g of orange peel, Cu2+: 154.9 mg/g of soybean hull treated with NaOH and citric acid, Cd2+: 52.08 mg/g of jackfruit). In general, technical applicability and cost-effectiveness are the key factors dictating the most suitable adsorbent to remove heavy metal from wastewater 10. Following adsorption, the closed loop system is recommended in which heavy metals adsorbed could be recycled back to the electroplating process without the need of disposing large amounts of heavy metal bearing sludge in secure landfills at high expenses 7.

Generally, the plating process proceeds as follows: alkaline degreasing, acid pickling, and plating. These steps are separated by many rinsing steps during which polluted wastewater is discharged. In addition, frequent dumping of spent rinsing solution, highly charged with the rinsed metal ion, contributes to the volume of wastewater and its heavy metal load 11.

The aim of this study was to assess the effectiveness of orange peel as an adsorbent for the recovery of nickel from electroplating wastewater. This was assessed by determining the optimum conditions of adsorption (adsorbent dose, pH, and contact time), calculating the recovery percentage, and characterizing the orange peel sludge resulting from adsorption/desorption process as being hazardous or not.

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Materials and methods

Sampling

Wastewater was collected from the Ni rinsing step in an electroplating industrial plant. Every 3–4 weeks, the content of two rinsing bathes following each plating step are completely discharged in the wastewater stream to be replaced with clean water. The dumping of the rinsing bathes following nickel plating constituted the wastewater sample of the present study.

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Preparation of adsorbent

Orange peel (adsorbent material under study) was prepared by peeling orange fruits, washing the peel with deionized water three times, drying them in hot air oven at 100°C for 30 min, and cutting the dried peel with scissors to pieces of 0.5×0.5 cm.

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Determination of optimum adsorbent dose

In 13 beakers containing different weights of orange peel, samples of 500-ml Ni-washing wastewater were added. The orange peel weights were as follows: 5, 10, 15, 20, 25, 30, 40, 50, 60, 70, 80, 90, and 100 g. The beakers were shaken in a Memmert shaker at a speed of 8 rpm for 2 h at room temperature (25°C). The mixtures were then filtered and Ni concentration was determined in the filtrates using an atomic absorption spectrophotometer. The percentage of Ni adsorbed was determined as follows:

where C0 is the concentration of Ni in a wastewater sample that has not undergone any treatment, and C is concentration of Ni in different filtrates.

Optimum adsorbent dose was determined as the one resulting in the highest percentage of Ni adsorption.

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Determination of optimum pH

In eight beakers containing the optimum weight of orange peel (determined from the previous step), samples of 500-ml Ni-washing wastewater were added. The pH of different mixtures was adjusted by adding either HCl (35.5%) or NH4OH (25%) to obtain the following pH: pH 3, 4, 5, 6, 7, 8, 9, and 10. The beakers were shaken in a Memmert shaker at a speed of 8 rpm for 1 h at room temperature (25°C). The mixtures were then filtered, and Ni concentration was determined in the filtrates using an atomic absorption spectrophotometer. The percentage of Ni adsorbed was determined as stated previously. Optimum pH was determined as the one resulting in the highest Ni adsorption.

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Determination of optimum contact time

In a beaker containing the optimum weight of orange peel (determined from the step ‘Determination of optimum adsorbent dose’), a sample of 500-ml of Ni-washing wastewater was added. The pH of the sample was adjusted by adding either HCl (35.5%) or NH4OH (25%) to the optimum pH (determined from the step ‘Determination of optimum pH’). The beaker was then shaken in a Memmert shaker at a speed of 8 rpm at room temperature (25°C). Aliquots of 5 ml were taken at every 30-min interval from the shaken solution, starting from 30 min up to 210 min. Ni concentration was determined in these aliquots using an atomic absorption spectrophotometer. The percentage of Ni adsorbed was determined as stated previously. Optimum contact time was determined as the one resulting in the highest Ni adsorption.

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Calculation of orange peel metal uptake capacity 12

Metal uptake capacity (q, mg/g) is used to judge the quality of the adsorbent. Under optimized conditions of adsorption, it is calculated as follows:

where V is the solution volume (l),

Ci is the initial concentration of metal ion in solution (mg/l),

Cf is the final concentration of metal ion in solution (mg/l),

S is the weight of the adsorbent (g).

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Determination of nickel recovery percentage

The orange peel resulting from a nickel adsorption process adjusted to the optimal conditions (adsorbent dose, pH, and contact time determined previously) was subjected to desorption by shaking it with 200 ml of 18% HCl (prepared by mixing 100 ml of 35.5% HCl with 100 ml distilled water) to convert the adsorbed nickel into NiCl2. The only variable tested in the desorption process was contact time. Aliquots of 5 ml were taken at every 20-min interval from the shaken solution, starting from 20 min up to 80 min. Ni concentration was determined in these aliquots using an atomic absorption spectrophotometer. The percentage of Ni desorption was determined as follows:

where Cd is the concentration of desorbed nickel in a 5 ml aliquot, and Ca is the concentration of nickel adsorbed on the orange peel; it equals C0C. Optimum contact time for desorption process was determined as the one resulting in the highest Ni desorption.

Then, Ni recovery percentage was determined as [Cd/C0]×100.

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Characterization of orange peel residue (hazardous/nonhazardous)

Following the desorption process, the orange peel was subjected to the soluble threshold limit concentration (STLC) test for Ni to determine whether it has to be disposed off in a secure landfill for hazardous waste or in a sanitary landfill with household waste. A sample of 5 g of orange peel resulting from the desorption process was tumbled with 50 ml of 0.2 mol/l sodium citrate for 48 h, and the leachate was analyzed for soluble Ni. If the concentration exceeded 20 mg/l, which is the STLC regulatory limit for Ni, the orange peel used for Ni recovery was considered hazardous 13.

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Results and discussion

Determination of optimum adsorbent dose

As shown in Fig. 1, the percentage of adsorbed nickel increased as the dose of the orange peel increased, until a dose of 50 g, at which the adsorption of nickel reached 61.55% of the concentration present in wastewater (528 mg/l) and remained constant thereafter. This could be due to the sticking and overlapping of the orange peel pieces over each other so as not to present more active surface for metal adsorption. It is also clear from Fig. 1 that Ni removal percentages for doses of 30 and 40 g orange peel (59.28 and 59.66%, respectively) were nearly equal to that of the 50 g dose. Therefore, to reduce the amount of sludge produced from the adsorption process, 30 g of orange peel/500 ml wastewater was considered as the optimum adsorbent dose that would be used for further steps of the study.

Figure 1

Figure 1

The percentage of Ni removal reported by similar studies was quite different from the present one. In one study, it was found to reach 33.14% for an orange peel at a dose of 0.2 g/100 ml 14. The variation could be because the study was carried out on synthetic wastewater samples containing only certain amounts of Ni without any interaction from other ions and materials present in the real wastewater used in the current study. In a second study carried out on real wastewater samples, 89% adsorption was achieved using 1 g of orange peel in a wastewater sample of 50 ml 15. Reasons for variation might be due to difference in conditions of the experiment from those in the present study. Examples include the procedure of preparation of orange peel (dried at 100°C for 24 h vs. 30 min drying in the present study), Ni concentration in wastewater (14.5 vs. 528 mg/l in the present study), and the temperature at which adsorption was carried out (50°C vs. room temperature in the present study) 15.

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Determination of optimum pH

As shown in Fig. 2, highest Ni adsorption took place at pH 7 (66.85%), followed by 65.9% adsorption at both pH 5 and 6. Therefore, the optimum pH could be concluded to be in the range of 5–7. This was in accordance with several studies that reported the optimum pH for Ni adsorption to be at pH 5.0–5.5 16, pH 6 15, and pH 6–8 3. At lower pH value, the hydrogen ions compete with Ni for the adsorption sites on the orange peel thereby partially releasing the metal ion. At higher pH, removal of Ni ions from the solution could be contributed to precipitation as hydroxide rather than adsorption.

Figure 2

Figure 2

As pH of electroplating wastewater under study was ranging between 6.8 and 7.3, the usual wastewater pH was considered as optimal condition for adsorption to be used in further steps of the experiment without the need for pH adjustment.

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Determination of optimum contact time

As shown in Fig. 3, the percentage of adsorbed nickel increased as contact time between adsorbent and adsorbate increased until a contact time of 1 h, at which time the adsorption of nickel reached 58.23% of the concentration present in wastewater and started to decrease thereafter. This could be explained by saturation of the surface of the adsorbent with Ni ions. Accordingly, the optimum contact time was found to be 1 h. This was in the range determined by previous studies. It was reported to be 14 min 14, 50 min 17, and up to 2 h 15 according to conditions of the experiments. It is worthy of mention that, following 1-h contact time, the adsorbed metal ion started to be desorbed and the surface of the orange peel returned free to start a new adsorption process. Therefore, it is not recommended to increase contact time in wastewater treatment plants higher than the predetermined contact time as this could lead to a reduced adsorption of the metal ion.

Figure 3

Figure 3

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Calculation of orange peel metal uptake capacity

Under optimized conditions of adsorption (1-h contact time, pH 7, and 30 g of orange peel/500 ml wastewater), the orange peel Ni uptake capacity was calculated to be 5.2 mg/g. It was lower than that determined in earlier studies (16.6 mg/g 14 and 15.45 mg/g 15). The variation could be because these studies were carried out on synthetic wastewater samples, in contrast to the present study in which real wastewater samples were collected from an electroplating industrial plant. This has been confirmed by another study carried out on palm date pits as low-cost adsorbent. It reported that the percentage removal of heavy metals from industrial effluents discharged from electroplating plants is lower than that obtained from experimental samples due to interaction between ions 18.

Other than orange peel, Ni uptake capacity for other adsorbents was studied and was found to be 14.8 mg/g of waste pomace of olive oil industries at 60°C 19, 15.26 mg/g of tea factory waste 20, 4.89 mg/g of activated carbon prepared from almond husk 17, and 17.24 mg/g of acid-treated Parthenium hysterophorus21.

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Determination of nickel recovery percentage

When the orange peel used in the adsorption process was subjected to desorption for different reaction times, the percentage of Ni desorption was found to increase with time, from 53.7% after 20 min until 75.3% after 60 min. After this, the percentage of Ni desorption started to diminish (Fig. 4). This could be attributed to the hydrogen ions of HCl being more preferably adsorbed on the orange peel surface compared with Ni ions.

Figure 4

Figure 4

The nickel recovery percentage following 60 min desorption was calculated to be 44.46%, and the resulting nickel chloride could be recycled to the nickel plating bath as it is composed of a mixture of NiCl2 and NiSO4. Furthermore, there will be a reduction in the amount of chemicals used in the wastewater treatment plant, as well as a reduction in the Ni concentration in the sludge produced from the treatment plant. Table 1 summarizes the findings of the current study as regards Ni recovery.

Table 1

Table 1

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Characterization of orange peel residue (hazardous/nonhazardous)

The results of STLC tests for the orange peel after desorption process revealed that it was not expected to be hazardous as the Ni concentration in the extract was ranging between 10.4 and 16.7 mg/l. Accordingly, the orange peel resulting from the Ni recovery process could be disposed off in a sanitary landfill used for disposal of nonhazardous waste. This was in agreement with the findings of a research carried out on the extraction and recovery of chromium from electroplating sludge; it revealed that commercial HCl could be used for extraction of the metal at room temperature and that, following extraction and leaching tests, the sludge was no longer considered hazardous 22.

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Conclusion and recommendation

Under optimum conditions for adsorption, orange peel was found to be an effective adsorbent of Ni from electroplating wastewater. It achieved 59.28% removal of the metal from a solution containing 528 mg/l, at a dose of 60 g/l, at pH 7, and for 1-h contact time. The orange peel nickel uptake capacity was calculated to be 5.2 mg/g. Using HCl for desorption of adsorbed Ni, a recovery of 44.46% of Ni discharged in the wastewater could be reached. The orange peel resulting from adsorption/desorption process was characterized as being nonhazardous.

It is recommended to carry out further studies to determine (a) the impact of the recovered NiCl2 solution on the quality of the plated product, (b) the effect of activation of orange peel on the adsorption process, and (c) the number of cycles during which orange peel can be reused as an effective adsorbent.

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Acknowledgements

Conflicts of interest

There are no conflicts of interest.

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Keywords:

adsorption; electroplating wastewater; nickel recovery; orange peel; soluble threshold limit concentration

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