Solvent extraction of nickel ions from electroless nickel plating wastewater using synergistic green binary mixture of D2EHPA-octanol system

Accepted Manuscript Title: Solvent Extraction of Nickel Ions from Electroless Nickel Plating Wastewater using Synergistic Green Binary Mixture of D2EHPA-Octanol System Authors: Raja Norimie Raja Sulaimana, Norasikin Othman PII: DOI: Reference:

S2213-3437(18)30108-8 https://doi.org/10.1016/j.jece.2018.02.035 JECE 2227

To appear in: Received date: Revised date: Accepted date:

11-9-2017 14-2-2018 21-2-2018

Please cite this article as: Raja Norimie Raja Sulaimana, Norasikin Othman, Solvent Extraction of Nickel Ions from Electroless Nickel Plating Wastewater using Synergistic Green Binary Mixture of D2EHPA-Octanol System, Journal of Environmental Chemical Engineering https://doi.org/10.1016/j.jece.2018.02.035 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Solvent Extraction of Nickel Ions from Electroless Nickel Plating Wastewater using Synergistic Green Binary Mixture of D2EHPA-Octanol System Raja Norimie Raja Sulaiman a, Norasikin Othman a, b,* a Department of Chemical Engineering, Faculty of Chemical and Energy Engineering, Universiti

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Teknologi Malaysia, 81310, UTM, Johor Bahru, Johor, Malaysia. bCentre of Lipids Engineering and Applied Research (CLEAR), Ibnu Sina Institute for Scientific and Industrial Research, Universiti Teknologi Malaysia, 81310, UTM, Johor Bahru, Johor, Malaysia.

Abstract

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A study on the synergistic green solvent extraction of nickel ions from real electroless nickel plating wastewater using an organic phase containing a binary mixtures of Di (2-ethylhexyl)

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phosphoric acid (D2EHPA) and octanol in palm oil was conducted. The effects of diluent

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composition, synergist, carrier and stripping agent types and its concentrations were

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experimentally investigated and the optimum conditions were determined. Results revealed that both D2EHPA and octanol acted as a carrier and synergist, respectively. A significant synergistic

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effect occurred when the octanol helped destroy the dimer structure of D2EHPA for cation exchange mechanism with nickel ions, hence improving the nickel ions extraction up to 90%

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with the maximum distribution ratio of 8.8 under optimum condition of 0.7M D2EHPA and 15% (v/v) octanol in palm oil. Afterwards, the stripping experiment showed that nickel ions could be

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recovered from the loaded mixture of carrier using 1.0M nitric acid solutions. Besides, the slope analysis method showed that the nickel ions were extracted from weak acidic electroplating feed

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solution as nickel-D2EHPA-octanol complex and recovered as nickel nitrate complex in the stripping phase. Thus, it can be concluded that the green synergistic formulation containing binary mixtures of D2EHPA-octanol system is one of the promising approaches as well as a

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green and efficient separation method for nickel ions extraction from the real electroless nickel plating wastewater. Keywords: Solvent extraction of ions; nickel extraction; carrier synergies in extraction

*Corresponding author. Tel.: +607 5535561; Fax: +607 5581463. E-mail address: [email protected] 1

1.

Introduction Nickel is the 24th most abundant element in the earth’s crust having a concentration of 0.008%

by weight. This metal is commercially applied in various types of industrial applications such as stainless steels, electroplating, ceramics, magnets, batteries, and catalyst [1]. In the electroplating

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field, nickel is normally alloyed with other metals to enhance the strength and corrosion resistance over a wide range of temperature. Usually, electroplating wastewater containing high nickel concentration which comes from the major processes such as rinsing and spent plating bath solutions where the effluent compositions are equivalent to the compositions in relevant plating operation [2]. Unfortunately, the extensive utilization of nickel in the electroplating industry has led to a very serious environmental pollution. This problem has gained the attention among the

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researchers who reported the removal of nickel via numerous methods. Popular amongst these are chemical precipitation, membrane technology and adsorption. Chemical precipitation of nickel is

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accomplished by increasing the pH to basic conditions around pH 9 to 10, where the nickel appears

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as an insoluble complex, nickel hydroxide. Nevertheless, the sludge formed mostly needs the

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second treatment for disposal [3]. On the other hand, membrane technology usually suffers an instability problem whilst adsorption process needs the adsorbents, which are sometimes high cost materials [4-6].

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Solvent extraction is one of the most versatile methods used for the extraction of diverse range

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of metal ions from an aqueous medium. This process is based on the principle that the solute can distribute itself in a certain ratio between two immiscible solvents. Besides, this method employs

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a carrier which depends on the type of the targeted metal ions to be extracted [7-9]. Mostly the acidic carrier is used in this process for the extraction of various metal cations through cation

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exchange mechanism [10-12]. Due to the low extraction efficiency of using a single carrier in solvent extraction system, carrier synergism is gaining extensive attention among the researchers in recent years. Basically, synergism is established when the extractive capability of the carrier

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mixture is greater as compared to the sum of their individual or single extractive capability. Meanwhile, a synergistic solvent extraction system could improve the extraction efficiency as well as selectivity among the metal ions. The other advantages of synergism are the enhancement of the solubility degree of the extracted complexes in the organic phase and inhibition of the formation of the third phases [13]. Commonly the binary mixtures for the synergistic solvent extraction involved various combinations of carriers such as acidic-neutral, two acidic, two neutral carriers, and anionic2

neutral carriers [14-16]. A diluent is also another important constituent in solvent extraction process. In order to reduce the chemical consumptions as well as promoting the greener process, several studies have found that the vegetable oils provided high potential to be greener substitutes over the conventional petroleum-based organic solvents extraction [17-18]. To the best of our knowledge, the synergistic solvent extraction of nickel ions from the

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aqueous solution using a green synergic binary mixture of D2EHPA–octanol system has not been reported yet. The aim of this work is to investigate the synergistic solvent extraction of nickel ions via binary mixtures of D2EHPA-octanol system from real electroplating wastewater. Several parameters such as carrier and synergist type, composition of palm oil to kerosene, carrier and synergist concentration, and stripping agent type and concentration were evaluated to find the optimum condition as well as formulation for nickel ions extraction from real electroplating waste

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On the other hand, the effect of the nickel extraction using the regeneration of the organic phase

2.

Experimental

2.1.

Reagents and apparatus

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A

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was investigated as well.

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Electroless nickel plating wastewater was obtained from Senai, Johor Malaysia. The

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extractants or carriers namely Di-2-ethylhexyl phosphoric acid (D2EHPA, purity 95%), Diisooctylthiophosphinic acid (Cyanex 302, purity 85%), Tridodecylamine (TDA, purity 98%), and octanol (purity 99%) were purchased from Sigma Aldrich. Besides kerosene and commercial

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cooking palm oil as diluents were obtained from Sigma Aldrich and local markets in Malaysia, respectively. In addition, the stripping chemicals such as nitric acid (purity 65%), sulfuric acid

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(purity 97%) and hydrochloric acid (purity 37%) were procured from Sigma Aldrich. All these materials were used directly as received from the manufacturer without further purification.

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Subsequently, the apparatus used in this study includes a Mettler Toledo pH Meter for pH measurement of the aqueous waste solutions, a mechanical shaker for the equilibrium experiments and Atomic Absorption Spectrophotometer (AAS) for the analysis of the nickel ions concentration.

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2.2.

Solvent extraction process Solvent extraction process was carried out by shaking an organic solution (10 mL) containing

a mixture of D2EHPA and octanol in palm oil with 10 mL of aqueous feed phase containing 500 ppm of nickel electroplating waste solution. The reaction of this mixture was performed in the stoppered

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conical flasks using a mechanical shaker at a speed of 320 rpm for 18 hours to achieve the equilibrium. Henceforth, the phase separation was done using a separation funnel for about 30 minutes. As a consequence, two phases were formed which were aqueous and organic phases. The aqueous phase might contain the untreated nickel ions, whilst the organic phase was loaded with nickel ions extracted from the aqueous feed phase. Subsequently, in order to determine the extraction efficiency, the nickel ions concentrations in the aqueous phase were analysed using the

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AAS.

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For the stripping part, an equal volume of 10 mL of the organic phase loaded with nickel ions

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extracted from the feed phase and stripping agent solutions (hydrochloric, sulfuric and nitric acid) were shaken in the stoppered conical flasks using a mechanical shaker at a speed of 320 rpm for 18

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hours. Then, the phase separation was carried out using a separation funnel and two phases were

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formed which were aqueous and organic phase. Afterwards, in order to determine the stripping efficiency, the nickel ions concentrations in aqueous stripping phase were measured using the AAS.

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All experiments were performed at room temperature (25±1ºC). For regeneration study, after completing one cycle for the extraction and stripping, the organic phase was mixed with the distilled water

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before continuing with subsequent cycles [19].

2.3.

Data analysis

In solvent extraction, the analysis was carried out in triplicate for each run with standard

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error was found to be less than 1%. The percentage of extraction and stripping of nickel ions were calculated using Eqs. (1) and (2) whereas the distribution ratio was determined using Eq. (3). Extraction (%)

=

𝐶𝑖 − 𝐶𝑎𝑞 𝑥 100 𝐶𝑖

(1)

Stripping (%)

=

𝐶𝑠 𝑥 100 𝐶𝑜𝑟𝑔

(2)

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Distribution ratio, D

=

𝐶𝑜𝑟𝑔 𝐶𝑎𝑞

(3)

Where, 𝐶𝑖 is the initial nickel concentration in aqueous feed phase (ppm), 𝐶𝑎𝑞 is the nickel

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concentration in aqueous feed phase after extraction (ppm), 𝐶𝑠 is the nickel concentration in aqueous stripping phase after extraction (ppm), and 𝐶𝑜𝑟𝑔 is the nickel concentration in organic phase after extraction (ppm).

Results and discussion

3.1.

Electroless nickel plating wastewater characterization

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3.

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Essentially, the electroless nickel plating wastewater was obtained from the electroplating bath solution through an electroless nickel plating process. Physically, the effluent appeared as a

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dark green solution at pH 4.8. During a plating process, the main constituents involved in the plating

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bath solution include nickel sulfate, ammonium sulfate and sodium hypophosphate. Sodium hypophosphate plays the role as a reducing agent during the plating operation. Consequently, the

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high concentrations of several ions were discovered in the electroplating wastewater such as

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sodium (3.406 %w/w), nickel (0.4156 %w/w), sulfate (3.041 %w/w), ammonium (1.722 %w/w) and phosphate (5.6144 %w/w). Similar observation was reported by Bulasara et al. [20] who indicated the presence of nickel sulfate, sodium hypophosphite and ammonium sulfate as the main

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compositions of the electroless nickel plating bath solutions.

3.2.

Effect of single carrier type on the extraction of nickel

The effects of several types of single carrier towards nickel extraction were studied and

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tabulated in Table 1. Based on the result obtained, the acidic carriers were capable in extracting the nickel ions from the acidic electroless plating wastewater whereas the basic and solvating carriers showed a negligible effect for the nickel extraction. In this study, LIX63, D2EHPA and Cyanex 302 which are chelating, phosphinic and phosphoric acids, respectively were investigated for the nickel extraction. As can be observed, D2EHPA provided the highest magnitude of nickel extraction (60%) followed by LIX63 (45%) and Cyanex 302(4%). According to Narita et al. [21], 5

D2EHPA became the most ideal carrier for the nickel extraction owing to its chemical stability, low aqueous solubility and high loading characteristics. Besides, since the nickel extraction is highly pH dependent, the higher acidic carrier like D2EHPA is more preferable. This is in accordance with Zhang et al. [22] who indicated that D2EHPA provided the highest acidity constant with high solubility and protonation degree, thus the proton in the D2EHPA bond is easily

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substituted by the nickel ion. Meanwhile, LIX63 which is a hydroxyoxime carrier also was able to extract the nickel at lower pH values efficiently but exhibited slower nickel extraction kinetics [9]. Subsequently, the main problem associated with Cyanex 302 is it can extract nickel at very low pH but is not stable and easily decomposed [23]. Additionally, it is more suitable for nickel extraction from neutral aqueous solutions [12].

However, the basic and solvating carrier showed an insignificant effect towards nickel

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extraction. Commonly, the basic carrier which is mostly the amine group performed the extraction

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via ion-pair formation. They are more suitable for the anion complexes extraction through anion exchange reaction [24]. Henceforth, the extraction by solvation is done by a solvating carrier. The

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solvating carrier is weakly basic in nature, hence extracting either neutral metal complexes or acids

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by forming a solvate. In order to increase the extraction performance, the mixed carrier was used to overcome the problems arising from utilizing a single carrier. Based on the maximum extraction

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efficiency of nickel, D2EHPA is used as a main carrier for further investigation.

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Table 1. Effect several types of single carrier towards nickel extraction (Experimental conditions: [Nickel]: 500 ppm; pH: 4.8; carrier concentration: 1.0M; diluent: kerosene; aqueous waste volume:

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320 rpm.

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10 mL; organic volume: 10 mL; temperature: 25±1ºC; duration time: 18 hours; agitation speed:

Carrier

Type

Extraction (%)

D2EHPA

Phosphoric acidic

60

LIX63

Chelating acidic

45

Cyanex 302

Phosphinic acidic

4

TDA

Basic

0

Octanol

Solvating

0

TBP

Solvating

0

6

3.3.

Effect of synergist type on the synergistic extraction of nickel Apparently, amongst the single carrier types studied in section 3.2, it can be concluded that

the acidic carrier was preferable for the nickel ions extraction. However, out of the three acidic carriers investigated, D2EHPA provided the highest extraction of nickel ions (60%) in comparison

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with LIX63 (45%) and Cyanex 302 (4%). Particularly, the nickel extraction is a pH dependent wherein Cyanex 302, D2EHPA and LIX63 is suitable for the neutral, slightly acidic and strongly acidic wastewater containing nickel, respectively. Hence, D2EHPA dominates the nickel ions extraction since the electroless nickel plating wastewater provided slightly acidic pH of 4.8. Therefore, it was chosen as a main carrier for further experiments. Meanwhile, synergistic extraction is defined as a cooperation of two carrier molecules to transfer metal ions from an

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aqueous medium to an organic phase, as well as improving the extraction efficiency. The

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synergistic extraction can be performed with any type of carrier combinations. Hence, in order to synergistically improve the nickel ions extraction, several synergists namely Cyanex 302, TDA,

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and octanol which are acidic, basic and neutral carriers, respectively are investigated as depicted

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in Fig. 1. Both D2EHPA and synergist concentrations were fixed at 1.0M and 10% (v/v), respectively. It is based on the preliminary study which indicated that upon increasing the D2EHPA

D

concentration beyond 1.0M there is not much difference in the extraction efficiency owing to the

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competitive reaction with the high concentration of sulfate ions in the electroplating waste [25]. Subsequently, the 10% (v/v) octanol concentration employed was based on the literature studied [22]. Meanwhile, the distribution ratio of the mixture system, 𝐷𝑚𝑖𝑥 is presented as well.

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Distribution ratio, 𝐷 is defined as a ratio concentration of the nickel ions in the organic and feed phases. The higher distribution ratio is proportional to the higher nickel ions concentration in the

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organic phase, hence enhancing nickel ions extraction from feed to the organic phase. Basically, the carrier synergism is established when the distribution ratio of the carrier mixture system, 𝐷𝑚𝑖𝑥

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is greater than the single carrier system whereas the antagonistic effect occurs vice versa [14]. It can be seen that the D2EHPA-octanol system yielded the highest nickel extraction (80%) followed by single D2EHPA (60%), D2EHPA-Cyanex 302(49%) and D2EHPA-TDA (48%). Furthermore, the distribution ratios for single D2EHPA, D2EHPA-octanol, D2EHPA-Cyanex 302 and D2EHPA-TDA were 1.5, 0.9, 0.9 and 3.9, respectively. Surprisingly, the combination of D2EHPA and octanol indicated the significant synergistic effect in the mixed carrier systems as compared 7

with the single D2EHPA that was solely employed to extract nickel with the maximum extraction percentage and distribution ratio,𝐷 of 80% and 3.9, respectively. Hence in this present work, it can be inferred that the carrier synergism was found to occur in the mixed carrier system consisting of D2EHPA and octanol. This can be attributed to the polar group in the alcohol which forms a weak hydrogen bonding with the dimer structures of D2EHPA, thereby promoting the extraction sites

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for the nickel ion through the cation exchange mechanism. This is in conformity with Zhang et al. [22] who revealed that isooctanol (alcohol group) alone was unable to extract metal ions but capable of interacting as well as modifying D2EHPA molecules via hydrogen bonding for enhancing metal ion extraction.

Nevertheless, the effect of the nickel extraction by D2EHPA-cyanex 302 and D2EHPATDA mixture system provided an antagonistic effect when they showed the relatively small

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magnitude of nickel extraction percentage. Essentially, the nickel electroplating wastewater is a

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slightly acidic effluent with pH of 4.8. The higher acidic carrier type seems suitable for the metal cation extraction in the acidic aqueous solution to create the chemical potential between the

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aqueous and organic phases [26]. However the mixture of the D2EHPA-cyanex 302 reduced the

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acidity constant due to the low acidity of Cyanex 302 compared to D2EHPA, hence suggesting the nickel extraction inefficiency. Furthermore, other observation was reported by Dimitrov et al. [12]

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who reported that Cyanex 302 was found to be the most suitable carrier for the nickel extraction

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from neutral aqueous solutions. Chauhan and Patel. [23] also found that D2EHPA requires a strict control of pH which is within 3 to 5 only for nickel ions separation. On the other hand, the nickel ions extraction was negatively affected upon employing the

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D2EHPA-TDA mixture system. The antagonistic effect is due to the utilization of the basic carrier of TDA which is highly suitable for the extraction of an anionic metal complexes through an

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anionic exchange reaction. This is strongly supported by Parhi. [27] who stated that due to the basic features of carrier containing amine group, the metal ion can be extracted via ion pair formation

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wherein these basic carriers need to be protonated first before performing anionic exchange reaction. In addition, the combination of the acidic (D2EHPA) and basic carriers (TDA) seemed to reduce the acidity of carrier concentration, hence causing nickel inefficiency. Thus, the optimal synergistic effect is selected based on the maximum magnitude of nickel extraction percentage and distribution ratio. In this part, D2EHPA-octanol mixture system with the highest nickel extraction as well as distribution ratio was employed for further investigations. 8

Fig. 1. Effect several types of synergist towards nickel extraction (Experimental conditions: [Nickel]: 500 ppm; pH: 4.8; [D2EHPA]: 1.0M; [octanol]: 10% (v/v); diluent: kerosene; aqueous waste volume: 10 mL; organic volume: 10 mL; temperature: 25±1ºC; duration time: 18 hours;

3.4.

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agitation speed: 320 rpm.

Effect of composition palm oil to kerosene on the synergistic extraction of nickel

The feasibility of using palm oil as a diluent in nickel ions extraction is another main focus of this present work. Thus, the effect of the composition palm oil to kerosene towards synergistic extraction of nickel ions is examined as illustrated in Fig. 2. The results indicated that all the composition studied showed around 80 to 85% of nickel ions was extracted. This means the palm

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oil can replace the conventional volatile organic solvents for nickel ions extraction. In addition, palm oil is known as a non-polar solvent which promotes a weak interaction with the polar

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compounds like nickel, thus inhibiting the reaction among them. This is strongly supported by

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Chang et al. [28] who claimed that due to the low extractability of palm oil for polar compound

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(metal ions), palm oil functions more as a diluent than as an additional extractant or a carrier in the extraction of metal ions from aqueous solutions. Previously several researchers also reported the

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metal ions extraction such as copper and mercury using vegetable oils as a green diluent [18, 28]. Moreover, besides being readily available, palm oil possesses many advantages such as

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biodegradable, renewable, nontoxic, high flash and low melting points [28]. Then, the 100% palm

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oil was utilized as a green diluent for further experiments.

Fig. 2. Effect of composition palm oil to kerosene towards nickel extraction (Experimental

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conditions: [Nickel]: 500 ppm; pH: 4.8; [D2EHPA]: 1.0M; [octanol]: 10% (v/v); diluent: mixture of palm oil and kerosene; aqueous waste volume: 10 mL; organic volume: 10 mL; temperature:

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25±1ºC; duration time: 18 hours; agitation speed: 320 rpm.

3.5.

Effect of D2EHPA concentration on the synergistic extraction of nickel D2EHPA as a main carrier plays a vital role during the extraction process owing to the

complexation with the nickel ions at the interphase of aqueous feed and organic phase. The effect of D2EHPA concentration was studied by varying D2EHPA concentrations from 0.05 to 1.0M as 9

presented in Fig. 3. The result demonstrates that upon increasing D2EHPA concentration from 0.05 to 0.7M, the nickel extraction have increased from 40 to 84%, respectively. Beyond 0.7M, the nickel percentage seemed slightly decreased to 82%. It can be deduced that the slight difference in the extraction efficiency after enhancing higher concentration of 1.0M were showing that they were reaching the plateau stage. It is believed that the carriers in the organic phase need to compete with

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the higher number of sulfate ions available in the electroplating waste for nickel ions extraction into the organic phase. This finding is in agreement with Zhang et al. [22] who found that the negative effect of increasing concentration of sulfate ion in the aqueous phase caused in the decrease in chromium (III) extraction due to the formation of chromium sulfate. Then 0.7M of D2EHPA is obviously enough for the nickel complexation.

Subsequently, the reaction mechanism involved during nickel extraction can be represented

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in Eqs. (4) to (5). From on the equation, the relationship of the equilibrium constant, 𝐾𝑒𝑞 and

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distribution ratio, 𝐷 of the stoichiometric reaction were described as shown in Eqs. (6) to (10).

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Consequently, a plot of log D vs. log [𝐻𝑅 − 𝐻𝑂𝑅 ′ ] yields a straight line with slope, n which gives number of extractant or carrier molecules involved in the nickel extraction. Fig. 4 portrays the

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stoichiometry study performed for the nickel extraction with respect to the D2EHPA-octanol complex concentration. As a result, the straight line plotted provided a slope, n of 0.8 which

D

indicates that one mole of D2EHPA-octanol complex was involved in the nickel-carriers reaction

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as represented in the Eqs. (4) and (5):

The reaction in the organic phase (octanol destroy the dimerization of D2EHPA):

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(𝑅𝐻)2 + (𝑅 ′ − 𝑂𝐻)2 → 𝐻𝑅 − 𝐻𝑂𝑅′ + 𝐻𝑅 − 𝐻𝑂𝑅′

(4)

The reaction in the organic-aqueous interface:

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𝑁𝑖 2+ (aq) + 𝑛(𝐻𝑅 − 𝐻𝑂𝑅 ′ ) (org) → 𝑁𝑖(𝑅 − 𝐻𝑂𝑅′)𝑛 (org) + 𝑛(𝐻 + )(aq)

(5)

Where (𝑅𝐻)2 is a dimer of D2EHPA; (𝑅 ′ − 𝑂𝐻) is an octanol; 𝐻𝑅 − 𝐻𝑂𝑅′ is a form of

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D2EHPA- octanol system where 𝑅 and R’= C8H17; 𝑁𝑖 (𝑅 − 𝐻𝑂𝑅′) represents Ni-D2EHPAoctanol complex in the organic phase and n is a number of mole involved. From Eq. (5), the equilibrium constant, 𝐾𝑒𝑞 can be defined as,

𝐾𝑒𝑞 =

[𝑁𝑖 (𝑅−𝐻𝑂𝑅)]𝑛 [𝐻 + ]𝑛

(6)

[𝑁𝑖 2+ ][𝐻𝑅−𝐻𝑂𝑅 ′ ]𝑛

Additionally, the distribution ratio, 𝐷 can be given as, 10

𝐷=

[𝑁𝑖 (𝑅−𝐻𝑂𝑅)]𝑛

(7)

[𝑁𝑖 2+ ]

Hence, the relationship between the distribution ratio, 𝐷 and the equilibrium constant, 𝐾𝑒𝑞 can be described in Eq. (8) 𝐷[𝐻 + ]𝑛

(8)

[𝐻𝑅−𝐻𝑂𝑅 ′ ]𝑛

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𝐾𝑒𝑞 =

Rearranging Eq. (8), 𝑛

𝐷=

𝐾𝑒𝑞 [𝐻𝑅−𝐻𝑂𝑅′ ]

(9)

𝑛

[𝐻+ ]

In logarithmic form, Eq. (9), can be expressed as, log 𝐷= 𝑛 log [𝐻𝑅 − 𝐻𝑂𝑅′ ] + log [𝐾𝑒𝑞 / [H+] n]

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(10)

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Fig. 3. Effect of D2EHPA concentration towards nickel extraction (Experimental conditions:

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[Nickel]: 500 ppm; pH: 4.8; [octanol]: 10% (v/v); diluent: palm oil; aqueous waste volume: 10 mL;

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organic volume: 10 mL; temperature: 25±1ºC; duration time: 18 hours; agitation speed: 320 rpm.

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Fig. 4. Stoichiometric plot for the equilibrium extraction of nickel using synergistic D2EHPA-

3.6.

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octanol system.

Effect of octanol concentration on the synergistic extraction of nickel

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Being a synergist, the octanol concentration is a crucial factor which significantly influences the synergistic extraction of nickel from electroplating wastewater. Fig. 5 illustrates the

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effect of octanol concentrations towards nickel extraction ranging from 5 to 20% (v/v). As can be observed, the nickel extraction percentage increased from 76 to 90% as the octanol concentration

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increased from 5 to 15% (v/v), respectively and reached a plateau up to 20% (v/v). This indicates that there is an excess of octanol in the mixture system. Meanwhile, the distribution ratio also seemed gradually increased from 3.1 to 8.8 with octanol concentrations. Basically, during the extraction process, octanol itself cannot extract the nickel ions but it helps to destroy the dimer structure of D2EHPA for cation exchange mechanism with nickel, thus improving the nickel extraction efficiency as depicted in Fig. 6. Nevertheless, according to Zhang et al. [22], the excess octanol concentration tend to encapsulate the D2EHPA molecules, hence preventing the extraction 11

of nickel. Thus, the synergist concentration of 15% (v/v) is clearly enough to be maintained throughout the subsequent investigations and is chosen as an optimum synergist concentration.

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Fig. 5. Effect of synergist concentration towards nickel extraction (Experimental conditions: [Nickel]: 500 ppm; pH: 4.8; [D2EHPA]: 0.7M; diluent: palm oil; aqueous waste volume: 10 mL; organic volume: 10 mL; temperature: 25±1ºC; duration time: 18 hours; agitation speed: 320 rpm. Fig. 6. Synergistic nickel extraction mechanism by D2EHPA-octanol system; where R= C8H17 and

Effect of stripping agent type on the synergistic extraction of nickel

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3.7.

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R’=C8H17.

Stripping agent type is another important variable for the back extraction of nickel from

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loaded organic phase in a solvent extraction process. Commonly, the inorganic acid is usually

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employed as the stripping agent for the metal ions from the loaded acidic carrier. Table 2 tabulates the effect of the several inorganic acids which include hydrochloric, sulfuric and nitric acid towards

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the stripping performance of nickel. The results revealed that all the stripping agents provided

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excellent performance of nickel stripping (almost 100%) from the nickel loaded organic phase. As reported by Alagiri et al. [29], nickel is more soluble in dilute nitric acid and sparingly soluble in dilute hydrochloric and sulphuric acids. Besides, the organic solution tends to decompose when

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using a stronger acid such as hydrochloric and sulfuric acid [12]. Hence, among them, nitric acid is preferable due to the lowest ranking of strong acids as compared to the sulfuric and hydrochloric

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acid because they provide low hazardous effect.

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Table 2. Effect several types of stripping agent towards nickel extraction (Experimental conditions: [Nickel]: 500 ppm; pH: 4.8; [D2EHPA]: 1M; [octanol]: 10% (v/v); aqueous nickel: 10 mL; organic volume: 10 mL; temperature: 25±1ºC; duration time: 18 hours; agitation speed: 320 rpm; diluent: kerosene. Stripping agent type

Extraction (%) 12

100

sulfuric acid

99

nitric acid

100

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Hydrochloric acid

3.8.

Effect of stripping agent concentration on the synergistic extraction of nickel

The effect of nitric acid concentration towards synergistic nickel extraction using palm oil as a diluent was studied within the ranges of 0.1 to 1.0M as exhibited in Fig. 7. It is observed that the nickel stripping percentage increased linearly up to 88% with the maximum stripping agent concentration (1.0M). The stripping reaction mechanism which occurs at the organic-aqueous

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interface can be represented in Eq. (11). In order to determine the number of moles stripping agent

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involved, the equilibrium constant, 𝐾𝑒𝑞 and distribution ratio, 𝐷 are related as given in Eqs. (12) to (16). As a result, a plot of log 𝐷 vs. log [𝐻𝑁𝑂3] was obtained. Fig. 8 shows that the plot of log 𝐷

A

vs. log [𝐻𝑁𝑂3] was a straight line with a slope of 0.9 which is nearly one, indicating that one mole

At the organic-stripping interface,

M

of Ni-carrier complex requires one mole of nitric acid for stripping reaction to occur.

D

(𝑁𝑖 − 𝑅 − 𝐻𝑂𝑅′)(org) + 𝑛𝐻𝑁𝑂3 (aq) → 𝑁𝑖(𝑁𝑂3 )2n (aq) + (𝐻𝑅 − 𝐻𝑂𝑅′)(org)

(11)

TE

Where (𝑁𝑖 − 𝑅 − 𝐻𝑂𝑅′)represents nickel-D2EHPA-octanol complex in organic phase whereas 𝑁𝑖(𝑁𝑂3 )2n denotes nickel nitrate complex in aqueous stripping phase.

[𝑁𝑖(𝑁𝑂3 )2𝑛 ][𝐻𝑅−𝐻𝑂𝑅′]

(12)

[𝑁𝑖−𝑅−𝐻𝑂𝑅′][𝐻𝑁𝑂3 ]𝑛

CC

𝐾𝑒𝑞 =

EP

From Eq. (11), the equilibrium constant, 𝐾𝑒𝑞 can be defined as,

Meanwhile the distribution ratio, 𝐷 can be given as, [𝑁𝑖(𝑁𝑂3 )2𝑛 ]

A

𝐷=

(13)

[𝑁𝑖−𝑅−𝐻𝑂𝑅′]

Hence, the relationship between the distribution ratio, 𝐷 and the equilibrium constant, 𝐾𝑒𝑞 can be described in Eq. (14)

𝐾𝑒𝑞 =

𝐷[𝐻𝑅−𝐻𝑂𝑅′]

(14)

[𝐻𝑁𝑂3 ]𝑛

Rearranging Eq. (14), 13

𝑛

𝐾𝑒𝑞 [𝐻𝑁𝑂 ]

3 𝐷= [𝐻𝑅−𝐻𝑂𝑅′]

(15)

In logarithmic form, Eq. (15), can be expressed as, log 𝐷= 𝑛 log [𝐻𝑁𝑂3 ] + log [𝐾𝑒𝑞 / [𝐻𝑅 − 𝐻𝑂𝑅′]]

SC RI PT

(16)

Fig. 7. Effect of stripping agent concentration towards nickel extraction (Experimental conditions: [Nickel]: 500 ppm; pH: 4.8; [D2EHPA]: 0.7M; [octanol]: 15% (v/v); diluent: palm oil; aqueous waste volume: 10 mL; organic volume: 10 mL; temperature: 25±1ºC; duration time: 18 hours; agitation

U

speed: 320 rpm.

3.9.

M

A

N

Fig. 8. Stoichiometric plot for the equilibrium stripping of nickel using nitric acid as a stripping agent.

Regeneration of green organic phase towards nickel extraction

D

The regeneration of the organic phase is one of the main advantages in minimizing the

TE

consumption of an expensive carrier in the solvent extraction process. In the regeneration part, after completing one cycle of the extraction and stripping process, the organic phase was mixed with the

EP

distilled water before continuing to the subsequent cycles. This can be explained by the fact that the water molecules are enable to adsorb the D2EHPA molecules via hydrogen bonding, hence destroying the dimerization between the D2EHPA and palm oil complexes which thereby

CC

providing an extraction site for nickel [19]. Table 3 exhibits the results for the regeneration study of the green organic phase towards nickel extraction and stripping using the best condition obtained

A

from the solvent extraction process. The result demonstrates that upon increasing up to four consecutive recycles, around 60 to 70% of nickel ions have been successfully extracted. Meanwhile, each cycle also provided 100% of stripping which means nearly 100% of free carrier was recycled back for the next nickel extraction. Nevertheless, in terms of the nickel extraction, the efficiency performance seemed to decrease gradually from 70 to 60%. This is probably due to the loss of the octanol which act as a synergist into the aqueous phase and therefore decreases the 14

synergistic effect to the extraction process. Basically, octanol tends to escape to the aqueous phase owing to the hydrophilic part in their structure. Thus, the recycling of the organic phase is needed especially for the industrial process since the cost of the operation can be cut as well as minimizing

SC RI PT

the utilization of an expensive carrier.

Table 3. Effect regeneration of organic phase towards synergistic nickel extraction. Palm oil

2 (1st recycle)

70

3 (2nd recycle)

69

4 (3rd recycle)

100 100 100 100

59

100

TE

EP

4. Conclusion

Stripping (%)

64

D

5 (4th recycle)

A

69

M

1

N

Extraction (%)

U

Run/Diluent type

In conclusion, the green binary mixtures of D2EHPA-octanol system is capable of extracting the

CC

nickel from real electroless nickel plating wastewater up to 90% with the maximum distribution ratio of 8.8 at the best condition of 0.7M D2EHPA and 15% (v/v) octanol in palm oil. Subsequently,

A

1.0M nitric acid is employed as a stripping agent for the back extraction of nickel from the nickel loaded organic phase. The stoichiometry study for nickel extraction showed only one mole of D2EHPA and nitric acid was involved in the extraction and stripping reaction of nickel. The regeneration study proved that the green organic phase can be recycled back for the nickel extraction as well as minimizing the use of an expensive carrier in the solvent extraction process.

15

Acknowledgements The authors would like to express their sincere gratitude to Ministry of Higher Education (MOHE) and Universiti Teknologi Malaysia (UTM) for the financial support under Research Universiti Grant (RUG), Vote Q.J130000.2546.14H21 and FRGS Grant, Vote R.J130000.7846.4F949.

SC RI PT

Besides, one of the authors (Raja Norimie Raja Sulaiman) also would like to express her sincere gratitude to the Universiti Teknologi Malaysia for the sponsorship of UTM Zamalah.

U

References

[1] V. Coman, B. Robotin, P. Ilea, Nickel recovery/removal from industrial wastes: a review, Resour.

N

Conserv. Recycl. 73(2013)229-238.

A

[2] B.R. Babu, S.U. Bhanu, K.S. Meera, Waste minimization in electroplating industries: a review, J.

M

Environ. Sci. Health. Part C 27(2009)155-177.

D

[3] M.Z. Mubarok, J. Lieberto, Precipitation of nickel hydroxide from simulated and atmospheric

TE

leach solution of nickel laterite ore, Procedia Earth Planet. Sci. 6(2013) 457- 464. [4] R.N.R. Sulaiman, N. Othman, N.A.S. Amin, Recovery of ionized nanosilver from wash water using

EP

emulsion liquid membrane process, Jurnal Teknologi 65(4)(2013) 33-36. [5] R.N.R. Sulaiman, N. Othman, Removal and recovery of chromium (VI) ion via tri-n-octyl

CC

methylammonium chloride-kerosene polypropylene supported liquid membrane, Malays. J. Anal. Sci. 21(2) (2017)416-425.

A

[6] D. Zamboulis, E.N. Peleka, N.K. Lazaridis, K.A. Matis, Metal ion separation and recovery from environmental sources using various flotation and sorption techniques, J. Chem. Technol. Biotechnol. 86(2011)335-344. [7] Y. Zhang, B. Jin, B. Ma, X. Feng, Separation of indium from lead smelting hazardous dust via leaching and solvent extraction, J. Environ. Chem. Eng. 5(3) (2017)2182-2188. 16

[8] N. Othman, N.F.M. Noah, R.N.R. Sulaiman, N.A. Abdullah, S.K. Bachok, Liquid-liquid extraction of palladium from simulated liquid waste using phosphinic acid as a carrier, Jurnal Teknologi 68(5) (2014)41–45. [9] R.N.R. Sulaiman, N. Othman, Synergistic green extraction of nickel ions from electroplating

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waste via mixtures of chelating and organophosphorus carrier, J. Hazard. Mater. 340 (2017)7784.

[10] X. Yang, Y. Zhang, S. Bao, Separation and recovery of sulfuric acid from acidic vanadium leaching solution of stone coal via solvent extraction, J. Environ. Chem. Eng. 4(1) (2016) 1399-1405.

[11] M. Tanaka, S. Alam, Solvent extraction equilibria of nickel from ammonium nitrate solution with

U

LIX84I, Hydrometallurgy 105(2010)134-139.

N

[12] K. Dimitrov, V. Rollet, A. Saboni, S. Alexandrova, Recovery of nickel from sulphate media by

A

batch pertraction in a rotating film contactor using Cyanex 302 as a carrier, Chem. Eng. Process.

M

47(2008)1562-1566.

[13] V. Eyupoglu, R.A. Kumbasar, Extraction of Ni (II) from spent Cr–Ni electroplating bath solutions

D

using LIX 63 and 2BDA as carriers by emulsion liquid membrane technique, J. Ind. Eng. Chem.

TE

21(2015) 303-310.

[14] R. Sarkar, S. Ray, S. Basu, Synergism in solvent extraction and solvent extraction kinetics, J. Chem.

EP

Biol. Phys. Sci. 4(2014)3156-3181. [15] C. Homsirikamol, N. Sunsandee, U. Pancharoen, K. Nootong, Synergistic extraction of amoxicillin

CC

from aqueous solution by using binary mixtures of Aliquat 336, D2EHPA and TBP, Sep. Purif. Technol. 162 (2016)30-36.

A

[16] N.K. Batchu, H.S. Jeon, M.S. Lee, Solvent extraction of praseodymium (III) from chloride solutions by a mixture of Cyanex 301 and LIX 63, J. Ind. Eng. Chem. 26(2015) 286-290.

[17] P. Kazemi, M. Peydayesh, A. Bandegi, T. Mohammadi, O. Bakhtiari, Stability and extraction study of phenolic wastewater treatment by supported liquid membrane using

17

Tributylphosphate and sesame oil as liquid membrane, Chem. Eng. Res. Design. 92(2014)375383. [18] K. Chakrabarty, P. Saha, A. K. Ghoshal, Separation of mercury from its aqueous solution through supported liquid membrane using environmentally benign diluent, J. Membr. Sci. 350 (2010)

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395–401. [19] D. Darvishi, H.F. Haghshenas, S. Etemadi, E.K. Alamdari, S.K. Sadrnezhaad, Water adsorption in the organic phase for the D2EHPA–kerosene/water and aqueous Zn2+, Co2+, Ni2+ sulphate systems, Hydrometallurgy 88( 2007) 92-97.

[20] V. K. Bulasara, M. S. Abhimanyu, T. Pranav, R. Uppaluri, M. K. Purkait, Performance

U

characteristics of hydrothermal and sonication assisted electroless plating baths for nickel–

N

ceramic composite membrane fabrication, Desalination 284 (2012) 77–85.

A

[21] H. Narita, M. Tanaka, Y. Sato, Structure of the Extracted Complex in the Ni (II)-LIX84I System

M

and the Effect of D2EHPA Addition, Solvent. Extr. Ion. Exch. 24(2006)693–702. [22] G. Zhang, D. Chen, W. Zhao, H. Zhao, L. Wang, W. Wang, T. Qi, A novel D2EHPA-based synergistic

D

extraction system for the recovery of chromium (III), Chem. Eng. J. 302(2016) 233-238.

2014) 1315-1322.

TE

[23] S. Chauhan, T. Patel T, A review on solvent extraction of nickel, Int. J. Eng. Res. Technol. 3(9)

EP

[24] A.A. Nayl, H.F. Aly, Solvent extraction of V (V) and Cr (III) from acidic leach liquors of ilmenite

CC

using Aliquat 336, Trans. Nonferrous. Met. Soc. China. 25 (2015) 4183−4191. [25] N. Othman, R.N.R. Sulaiman, M. H. A. Daud, D2EHPA-Sulfuric Acid System for Simultaneous Extraction and Recovery of Nickel Ions via Supported Liquid Membrane Process, Regional

A

Postgraduate Conference on Sustainable Environmental Technology 2017 (RCET 2017). In Press.

[26] R.N.R. Sulaiman, N. Othman, N.A.S. Amin, Recovery of ionized nanosilver by emulsion liquid membrane process and parameters optimization using response surface methodology, Desalin. Water Treat. 57(2016)3339-3349. 18

[27] P. K. Parhi, Supported liquid membrane principle and its practices: a short review, J. Chem. 2013 (2013)1-11. [28] S.H. Chang, T.T. Teng, N. Ismail, Extraction of Cu(II) from aqueous solutions by vegetable oilbased organic solvents, J. Hazard. Mater.181 (2010) 868-872.

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[29] M. Alagiri, C. Muthamizhchelvan, S. Ponnusamy, Structural and magnetic properties of iron,

A

CC

EP

TE

D

M

A

N

U

cobalt and nickel nanoparticles, Synthetic Metals 161(2011)1776-1780.

19

LIST OF FIGURES

4

80

% Extraction 3

Distribution ratio, D

60

SC RI PT

Extraction (%)

70

Distribution ratio , D

90

50

2

40 30

1

20 10

0

A

N

U

0

M

Type of synergist

Fig. 1. Effect several types of synergist towards nickel extraction (Experimental conditions:

D

[Nickel]: 500 ppm; pH: 4.8; [D2EHPA]: 1.0M; [octanol]: 10% (v/v); diluent: kerosene; aqueous

TE

waste volume: 10 mL; organic volume: 10 mL; temperature: 25±1ºC; duration time: 18 hours;

A

CC

EP

agitation speed: 320 rpm.

20

0

10

SC RI PT

Extraction (%)

90 80 70 60 50 40 30 20 10 0

30 50 70 Palm oil fraction (%)

90

100

U

Fig. 2. Effect of composition palm oil to kerosene towards nickel extraction (Experimental

N

conditions: [Nickel]: 500 ppm; pH: 4.8; [D2EHPA]: 1.0M; [octanol]: 10% (v/v); diluent: mixture

A

of palm oil and kerosene; aqueous waste volume: 10 mL; organic volume: 10 mL; temperature:

D

M

25±1ºC; duration time: 18 hours; agitation speed: 320 rpm.

90

A

CC

EP

Extraction (%)

TE

80 70 60 50 40 30 20 10 0

0.05

0.3

0.5

0.7

1.0

[D2EHPA] (M)

Fig. 3. Effect of D2EHPA concentration towards nickel extraction (Experimental conditions: [Nickel]: 500 ppm; pH: 4.8; [octanol]: 10% (v/v); diluent: palm oil; aqueous waste volume: 10 mL; organic volume: 10 mL; temperature: 25±1ºC; duration time: 18 hours; agitation speed: 320 rpm.

21

SC RI PT

Fig. 4. Stoichiometric plot for the equilibrium extraction of nickel using synergistic D2EHPA-

M

60

TE

20

D

Extraction (%)

80

40

10 9 8 7 6 5 4 3 2 1 0

A

100

0

EP

5

10 15 [Octanol] (% v/v)

Distribution ratio, D

N

% Extraction Distribution ratio

U

octanol system.

20

CC

Fig. 5. Effect of synergist concentration towards nickel extraction (Experimental conditions: [Nickel]: 500 ppm; pH: 4.8; [D2EHPA]: 0.7M; diluent: palm oil; aqueous waste volume: 10 mL;

A

organic volume: 10 mL; temperature: 25±1ºC; duration time: 18 hours; agitation speed: 320 rpm.

22

SC RI PT

Fig. 6. Synergistic nickel extraction mechanism by D2EHPA-octanol system; where R= C8H17 and

U N A M

D

90 80 70 60 50 40 30 20 10 0

0.1

0.5

1.0

[Nitric acid] (M)

EP

TE

Extraction (%)

R’=C8H17.

Fig. 7. Effect of stripping agent concentration towards nickel extraction (Experimental conditions:

CC

[Nickel]: 500 ppm; pH: 4.8; [D2EHPA]: 0.7M; [octanol]: 15% (v/v); diluent: palm oil; aqueous waste volume: 10 mL; organic volume: 10 mL; temperature: 25±1ºC; duration time: 18 hours; agitation

A

speed: 320 rpm.

23

0.5 0 -2

-1.5

-1

-0.5

0 -0.5 -1

SC RI PT

y = 0.9132x + 0.2134 R² = 0.8

Log D

-2.5

-1.5

-2

Log [HNO3]

-2.5

A

CC

EP

TE

D

M

A

N

U

Fig. 8. Stoichiometric plot for the equilibrium stripping of nickel using nitric acid as a stripping agent.

24