Ion flotation for removal of Ni(II) and Zn(II) ions from ...

International Journal of Mineral Processing 143 (2015) 131–137

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International Journal of Mineral Processing journal homepage: www.elsevier.com/locate/ijminpro

Ion flotation for removal of Ni(II) and Zn(II) ions from wastewaters Fatemeh Sadat Hoseinian a, Mehdi Irannajad a,⁎, Alireza Javadi Nooshabadi b a b

Department of Mining & Metallurgical Eng., Amirkabir University of Technology, Tehran, Iran Mineral Processing Group, Luleå University of Technology, SE 97187 Luleå, Sweden

a r t i c l e

i n f o

Article history: Received 30 September 2014 Received in revised form 17 May 2015 Accepted 31 July 2015 Available online 5 August 2015 Keywords: Ion flotation Experimental design Ni(II) ions Zn(II) ions Wastewaters

a b s t r a c t Ion flotation was applied to Ni(II) and Zn(II) cation removal from low concentration synthetic wastewaters. Ethylhexadecyldimethylammonium bromide (EHDABr) and sodium dodecyl sulfate (SDS) were used as collectors and Dowfroth250 and methyl isobutyl carbonyl (MIBC) as frothers. The effective parameters were investigated by the experimental design performed by DX7 software. In this regard, a two-level factorial method was used, and sixteen experiments including 6-level variables were designed. In the first step, the tests were conducted in a Hallimond tube. It was concluded from test results that the optimum conditions for the removal of Ni(II) and Zn(II) ions by initial concentrations of 10 ppm were: pH = 3, SDS = 300 ppm, Dowfroth250 = 90 ppm and air flow rate = 1.8 ml/min. In the second step, optimal results from the first step were evaluated in a mechanical flotation cell. In optimal conditions, the recovery of Ni(II) and Zn(II) ions were 88% and 92%, respectively at 60 min. This study showed that the use of ion flotation is a very effective method for Ni(II) and Zn(II) ion removal from industrial wastewaters. The flotation time in achieving an optimum recovery of Zn(II) ions is shorter than that for Ni(II) ions. © 2015 Elsevier B.V. All rights reserved.

1. Introduction The removal of heavy metal ions in industrial wastewaters is important due to their harmful effects on the environment. The importance of the problem is related to an increase in industrial production resulting from an increase in the world population, producing a large amount of wastewaters. In this study, the removal of two heavy metal ions of Zn(II) and Ni(II) was investigated. Nickel is a nutritionally essential trace metal for at least several animal species, micro-organisms and plants, and therefore either deficiency or toxicity symptoms can occur when too little or too much Ni is taken up. Nickel exists in various mineral forms that are used for the production of nickel alloys, catalysts and pigments in metallurgical, chemical and food processing industries. It is vital for the functioning of many organisms but it may be toxic for organisms in high concentration. The environment is polluted by Ni through water, air, soil and food containing it. The concentration of Nickel in drinking water is generally less than 10 μg/l (Cempel and Nikel, 2006; Das et al., 2008). Zinc is used in such industries as galvanizing to protect steel from corrosion, zinc based alloys and casting. It has traditionally been regarded as relatively nontoxic, and investigations show that free ionic zinc (Zn2 +) has a harmful effect on neurons, glia and other cell types (Nriagu, 2007). There are a lot of Ni(II) and Zn(II) ions in the effluent of all industry wastewaters mentioned. The ions usually enter the cycles of nature through surface and ground waters. The methods such as ion exchange, ⁎ Corresponding author. E-mail address: [email protected] (M. Irannajad).

http://dx.doi.org/10.1016/j.minpro.2015.07.006 0301-7516/© 2015 Elsevier B.V. All rights reserved.

chemical precipitation, solvent extraction, adsorption and electrodialysis are usually used for removal of these ions from wastewaters (Kongsricharoern and Polprasert, 1995). Flotation is an effective separation method in industrial wastewater treatment. Many types of flotation methods such as ion flotation, precipitation flotation (Stalidis et al., 1989) and sorptive flotation (Zamboulis et al., 2011) were used effectively for environmental applications (Rubio et al., 2002). The ion flotation process has a high potential in the field of wastewater treatment due to its good performance (Rubio et al., 2002). It has benefits in its very easy method, low energy requirements, low costs compared, fast operation, low residual concentration of metals, small space requirements, flexibility in applying the method to a variety of metals at various levels, and production of a small volume of sludge to other separation methods (Salmani et al., 2013). Introduced by Felix Sebba in 1960, ion flotation is a method used for removing heavy metal ions from aqueous solutions. Being a complex physicochemical process, it depends on the type and concentration of the collector and chemical conditions of the solution to optimize the recovery of metal ions (Sebba, 1962; Doyle, 2003). The process involves the attachment of hydrophobic ions on the gas bubbles being introduced in the solution and then removal of ions by bubbles from solutions (Ulewicz and Walkowiak, 2003). The Ni(II) and Zn(II) ions can be removed efficiently from aqueous chloride solutions using the EHDABr collector (McDonald and Ogunkeye, 1981, McDonald and Jaganathan, 1982). More recently, dodecyl diethylenetriamine was used as a chelating surfactant in ion flotation of Co(II), Ni(II) and Cu(II). The effect of triethyleneteraamine as chelating ligand on the ion flotation of Cu(II) and Ni(II) was studied. The results showed that the recovery of

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F.S. Hoseinian et al. / International Journal of Mineral Processing 143 (2015) 131–137

Table 1 Experimental conditions of Ni(II) and Zn(II) ion flotation results. Run

Type of collector

Concentration of collector (ppm)

Type of frother

Concentration of frother (ppm)

pH

Air flow rate (ml/min)

Ni(II) ions recovery (%)

Zn(II) ions recovery (%)

16 6 8 13 15 2 9 3 5 7 14 12 10 4 1 11

EHDABr EHDABr EHDABr SDS SDS EHDABr SDS SDS SDS SDS EHDABr EHDABr EHDABr EHDABr SDS SDS

300 100 300 100 300 100 100 300 100 300 100 300 100 300 100 300

Dowforth250 Dowforth250 Dowforth250 Dowforth250 Dowforth250 MIBC MIBC MIBC Dowforth250 Dowforth250 Dowforth250 MIBC MIBC MIBC MIBC MIBC

90 30 30 90 90 30 90 30 30 30 90 90 90 30 30 90

6 3 6 6 3 6 3 6 6 3 3 3 6 3 3 6

1.8 1.8 0.5 0.5 1.8 0.5 1.8 1.8 1.8 0.5 0.5 0.5 1.8 1.8 0.5 0.5

31 12 25 34 69 25 36 20 47 19 15 20 30 15 15 67

28 9 25 30 33 21 20 26 34 27 9 10 15 8 11 24

ions increased by adding chelating ligand (Doyle and Liu, 2003; Liu and Doyle, 2009). The separation of zinc and cadmium ions from sulfate solutions was investigated by ion flotation, concluding that the rate and removal of floated ions decrease by an anionic surfactant such as sodium dodecylbenzenesulfonate with the increase of sulfate concentration (Ulewicz and Walkowiak, 2003). The removal of heavy metals such as Cu(II), Zn(II), Cr(III) and Ag(I) from wastewaters was studied using sodium dodecyl sulfate (SDS) and hexadecyltrimethyl ammonium bromide as collectors, obtaining a maximum metal removal of 74% (Polat and Erdogan, 2007). Ion flotation has also been used for other ions such as removing halide complexes of aluminum subgroup metals, Ce(III), Y(III), La(III), Ho(III), Cr(VI), Co(II), Cu(II), Ag(I) and Au(II) (Ghazy et al., 2008; Chirkst et al., 2009; Reyes et al., 2009, Strel'tsov and Abryutin, 2010; Chirkst et al., 2012; Mal'tsev and Vershinin, 2012). Removal of cadmium with SDS as collector was studied by ion flotation. It decreased with an increase of ionic strength (Scorzelli et al., 1999). Removal of cadmium, lead and copper by ion flotation with a plant-derived bio-surfactant tea saponin was studied. In this regard, the maximum removal of ions was 81.81% with a ratio of tea saponin to metal of 3:1 (Yuan et al., 2008). In this study the optimal parameters for the removal of Ni(II) and Zn(II) ions from simulated wastewater were investigated using ion flotation with special emphasis on the water recovery along with the ions

removal from wastewater. The DX7 software was used to evaluate the effect of parameters and interaction between them on the ion removal. 2. Experimental 2.1. Materials and reagents In the ion flotation tests, Nickel nitrate ((Ni(NO3)2) and Zinc nitrate ((Zn(NO3)2) from Merck were used to prepare the simulated wastewater solution. SDS from Merck, EHDABr from Fluca and Methyl isobutyl carbinol (MIBC), Dowfroth250 from Merck were used as collectors and frothers, respectively. The pH of the solution was adjusted using NaOH and HCl. 2.2. Method For improving process efficiency, the factorial experimental design is a strong solution. The experimental design is performed to determine the number of experiments and variables in each experiment through the study of their combined effects (Dashti and Eskandari Nasab, 2013). For six parameters each at two levels, the number of experiments by a 2-level factorial design is reduced to the 16 experiments compared

Fig. 1. Half-normal probability plots of the parameter effects for ion flotation Ni(II).


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Fig. 2. Half-normal probability plots of the parameter effects for ion flotation Zn(II).

and frother were added to the solution with a desired concentration being agitated for 8 and 4 min, respectively. At the end of the test, the remaining solution in the cell was analyzed by atomic absorption spectrometry (AAS) to specify the percentage of metal ions remaining in the cell.

to the traditional full factorial design with 64 experiments. The number of required experiments is reduced by combining several variables in an experiment rather than a separate study of each of the variables. In this manner, a better understanding of the process was achieved. Optimal experimental design should be such that required data for analysis and obtaining optimum conditions are provided with the minimum number of experiments (Montgomery, 2008). For this research, the experiments were separately designed for Ni(II) and Zn(II) ions using DX7 software in the 2-level factorial method to obtain the type of materials and their optimal amount. Various parameters such as pH, type and concentration of collector, type and concentration of frother and air flow rate were studied to determine the optimal conditions. Table 1 shows the designed matrix and levels of the ion flotation of Zn(II) and Ni(II) ion variables used in the experiments. Initial experiments were carried out in a small scale by a Hallimond tube with a diameter of 5 cm and a height of 20 cm in order to evaluate different parameters and determine their optimal amounts on the ion flotation. The results of the Hallimond tube tests were evaluated by a mechanical Denver type flotation cell. The initial concentration of Ni(II) and Zn(II) ions in the experiments were 10 mg/L. Each experiment solution was prepared by the addition of the required amount of metal salt, collector and frother in distilled water. Before performing Hallimond tube tests, the flotation solution was conditioned for 16 min: for preparation of the solution with a certain ion concentration, it was agitated for 4 min; then the collector

3.1.1. Effects of parameters Half-normal probability plots of the parameter effects for the ion flotation of Ni(II) and Zn(II) ion experiments are given in Fig. 1 and Fig. 2, respectively. According to Fig. 1, for Ni(II) ion flotation, the important parameter is the type of collector indicated by (A). The order of the effects of other parameters are as follows: concentration of frother (D) N the interaction between concentration of collector and concentration of frother (BD) N the interaction between type of collector and concentration of collector and concentration of frother (ABD) N the interaction between type of collector and concentration of frother (AD). Fig. 2 shows that the most important parameter for Zn(II) ion flotation is the pH (presented by E in the figure). The order of the effects of other parameters are as follows: type of collector (A) N type of frother (C) N concentration of collector (B) N the interaction between type of collector and pH (AE).

Table 2 The results of ANOVA analysis of the Ni(II) ions flotation recovery developed model.

Table 3 The results of ANOVA analysis of the Zn(II) ion flotation recovery developed model.

Source

Sum of squares

Degree of freedom

Mean square

F-value

P-value Prob N F

Model A B D E AB AD BD ABD Residual Total

4158.25 1122.25 169.00 961.00 380.25 72.25 462.25 529.00 462.25 443.75 4602.00

8 1 1 1 1 1 1 1 1 7 15

519.78 1122. 25 169.00 961.00 380. 25 72. 25 462. 25 529.00 462. 25 63.39

8.20 17.70 2.67 15.16 6.00 1.14 7.29 8.34 7.29

0.0059 0.0040 0.1465 0.0059 0.0442 0.3211 0.0306 0.0234 0.0306

Significant

3. Results and discussion 3.1. Hallimond tube tests

Source

Sum of squares

Degree of freedom

Mean square

F-value

P-value Prob N Fs

Model A B C E F AC AE AF Residual Total

1138.50 370.56 52.56 203.06 390.06 10.56 33.06 45.56 33.06 37.44 1175.94

8 1 1 1 1 1 1 1 1 7 15

142.31 370.56 52.56 203.06 390.06 10.56 33.06 45.56 33.06 5.35

26.61 25.53 9.83 37.97 72.93 1.97 6.18 8.52 6.18

0.0001 b0.0004 0.0165 0.0005 b0.0001 0.2027 0.0418 0.0224 0.0418

Significant

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Fig. 3. (a) Interaction between type of collector and concentration of collector, (b) interaction of type of collector and concentration of frother, (c) interaction of concentration of collector and frother.

3.1.2. Process modeling The models for Ni(II) and Zn(II) ions recoveries against the effects of parameters were concluded by DX7 software as follow: Ni(II) ions recovery = + 30.00–8.38 × A + 7.75 × D + 4.88 × E − 5.37 × A × D + 5.75 × B × D (1). Zn(II) ions recovery = + 20.44–4.81 × A + 1.81 × B + 3.56 × C + 4.94 × E − 1.44 × A × C + 1.69 × A × E − 1.44 × A × F (2). In these models, all parameters are in encoded values and A, B, C, D, E and F are the type of collector, concentration of collector, type of frother, concentration of frother, pH and airflow rate, respectively. Table 2 and Table 3 show the results of analysis of variance (ANOVA) using DX7 software for the ion flotation of Ni(II) and Zn(II), respectively. These results indicate that all models are significant in a confidence level of 95% (p-value b 0.05). The results show that the SDS as collector, Dowfroth250 as frother, pH = 3 and airflow rate = 1.8 ml/min were optimal conditions in ion flotation of Zn(II) and Ni(II) ions. At pH = 3, Ni(II) and Zn(II) ions have positive charge and SDS ions have negative charge, therefore they are easily absorbed together in this condition. In a condition of pH N 3, the ions form hydroxyl bonds, changing the ion charges, and recovery is decreased. Simultaneous effects and interactions between flotation parameters were investigated. In Ni(II) removal, these parameters interact with each other and affect ion recovery. Fig. 3 shows the effects of the type and concentration of the collector and frother on the recovery of Ni(II) ions. The recovery of Ni(II) ions increases with increasing the concentration of the collector and frother (Fig. 3.a and Fig. 3.b). Fig. 3.c shows that the maximum recovery of Ni(II) ion archives in the higher concentrations of collector and frother. One of the effective factors in ion flotation is the nature of the collector and frother and interaction between collector and frother and ions. Table 4 shows SDS and EHDABr as collectors and Dowfroth250 and

MIBC as frother structures, respectively (http://www.sigmaaldrich. com, (Finch et al., 2008). The SDS collector has one or several oxygen atoms in its charge group in which oxygen atoms can form dipolar bonds and when the anionic collector is used in the ion flotation, the absorption between the collector and the cation-ligand may be more than the Coulomb absorption (Sebba, 1962). The frother can form hydrogen bonds with collector oxygen atoms. The chemical nature of the specific combination of the frothers and the collectors may have interactions and influence the recovery of ions. Hydrogen in the frother structure of Dowfroth250 and oxygen atom in the SDS collector form hydrogen bonds and provide a convenient stable condition. Fig. 4.a shows interaction of collector and frother effects on the recovery of Zn(II) ions. It is obvious that SDS and Dowfroth250 have proper interaction as collector and frother. Fig. 4.b shows the interaction effect of collector and pH, SDS having a higher recovery in PH = 3. Fig. 4.c shows that SDS has a higher performance in a high air flow rate. Chemical reactions carried out in these interactions and the natures of the products have an important impact on the absorption rate and ion flotation process.

Table 4 Structures of reagents used. Reagent

Formula

Supplier

EHDABr SDS Dowfroth250

[CH3(CH2)15N+(CH3)2CH2CH3]Br− CH3(CH2)11OSO3Na ½ðCH 3 Þ2 −ðCH 2 CH 2 CH 2 −OÞn −OH CH 3 −ðPOÞn −OH (CH3)2 − CH2COHCH3

Fluca Merck Merck

MIBC

Merck


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Fig. 4. (a) Interaction between type of collector and frother, (b) interaction of type of collector and pH, (c) interaction of type of collector and air flow rate.

3.2. Mechanical flotation cell experiments In the industry, mechanical and column flotation cells are mainly used on a large scale. Therefore, experiments were performed on a mechanical cell in order to investigate the effect of agitating speed and time on the recovery. Since one of the important factors in the removal of heavy metals from wastewater is reusing deionized water remaining in the cell, the recovery of lost water in the froth was studied. The experiments in the mechanical cell were carried out on the optimal conditions obtained from Hallimond tube tests. One of the effective factors on the ions recovery is the exposure of metal ions with the collector ions in the solution. As can be seen from Fig. 5, the Zn(II) ions and water recoveries increase with the increase of agitating speed. It seems that the reactions of the metal ions

with the collector ions and air flow rate increase with the increase of agitating speed. The agitation speed of 1000 rpm is selected as the optimal agitation speed for Zn(II) and Ni(II) ion flotation. The result of ion flotation of Zn(II) and Ni(II) is presented in Table 5. According to Fig. 6 and Fig. 7, the recoveries of Zn(II) and Ni(II) ions and water increases by increasing the flotation time. As the bubbles have limited loading capacity, more bubbles are created in the cell by increasing the flotation time, expecting more ion emission from the cell. The recovery of Zn(II) ions is higher than Ni(II) on the optimal conditions. One reason for the different recovery of ions is the different effective metal ionic radius. As shown in Fig. 6 after 10 min of flotation, the Zn(II) ion recovery of more than 92% is obtained but the recovery of Ni(II) ions after 60 min is 88%. The water recovery is directly related to the ion recovery.

Fig. 5. The effect of agitating speed on the Zn(II) ions and water recoveries. (SDS = 300 ppm, Dowfroth250 = 90 ppm, Zn(II) = 10 ppm and pH = 3).

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Table 5 Ni(II) and Zn(II) ion recoveries as a function of flotation time. Time (min)

Recovery of Zn(II) ions (%)

Recovery of Ni(II) ions (%)

10 20 30 40 50 60

89 90 91 92 93 95

52 62 66 75 83 88

Fig. 8. Combination ion flotation of Zn(II) and Ni(II) ions. (Dowfroth250 as frother, pH = 3, Ni(II) = Zn(II) = 10 ppm and agitating speed = 1000 rpm).

Fig. 6. Ni(II) and Zn(II) ion recoveries as a function of flotation time. (SDS = 300 ppm, Dowfroth250 = 90 ppm, Zn(II) = Ni(II) = 10 ppm,pH = 3 and agitating speed = 1000 rpm).

In the combination flotation of Zn(II) and Ni(II) ions, the recovery is reduced due to absence of enough collector ions to remove the ions in the solution (Fig. 8). Recovery of both ions increased with increasing the concentration of the collector. The recoveries of Ni(II) and Zn(II) ions were obtained as 81% and 95% in 600 ppm of concentration of the collector, respectively. The results showed that the removal for Zn(II) is more than that for Ni(II). This can be related to the ionic radius of Zn(II) and Ni(II): Zn(II) ionic radius N Ni(II) ionic radius. On the other hand, the preferential removal of Zn(II) ions can be related to the product stability of the metal-collector compound.

4. Conclusions Ion flotation experiments were carried out to investigate the removal of Ni(II) and Zn(II) ions from wastewaters. In this study, the condition of the real wastewaters was simulated in the laboratory.

Fig. 7. The water recovery variation related to the flotation time. (SDS = 300 ppm, Dowfroth250 = 90 ppm, Zn(II) = Ni(II) = 10 ppm,pH = 3 and agitating speed = 1000 rpm).

Several parameters such as type and concentration of collector, type and concentration of frother, pH and airflow rate were tested in a Hallimond tube to determine the optimum flotation conditions on a small scale. The results were analyzed by DX7software. The results showed that the SDS as collector, Dowfroth250 as frother, pH = 3 and airflow rate = 1.8 ml/min were optimal conditions in the ion flotation of Zn(II) and Ni(II) ions. In these conditions, the recovery of Ni(II) and Zn(II) ions were achieved at 88% and 92%, respectively. The results showed that the recovery of Ni(II) and Zn(II) ions increased by increasing the time of flotation and they have a direct relation with the water recovery. In the combination of ion flotation of Ni(II) and Zn(II) ions, the recovery of ions decrease in comparison with single ion flotation of the ions. The removal of the ions is related to the stability products of the metal ion-collector compounds and to the ionic radius. The study showed that ion flotation has high performance for the removal of heavy metals such as Ni(II) and Zn(II) ions from wastewaters.

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