Removal of Copper(II) from Aqueous Solutionsby Biosorption-Flotation

Ligia Stoica & Ana-Maria Stanescu &

Carolina Constantin & Ovidiu Oprea &

Gabriela Bacioiu

Received: 22 January 2015 /Accepted: 7 July 2015 /Published online: 30 July 2015# Springer International Publishing Switzerland 2015

Abstract This study investigates the removal of Cu(II)from aqueous solutions by biosorption-flotation as afunction of several parameters, such as collector type,pH, molar ratio, air pressure, time, and initial metalconcentration. Dissolved air flotation was applied as apolishing technique for the additional purification of theeffluent resulted after biosorption. The obtained resultswere supported by the physicochemical characteristicsof the surfactants used as flotation reagents and sug-gested that cetylpyridinium bromide (CPB) was theoptimum collector for Cu(II) ion removal. Cu(II) remov-al efficiency exhibited a maximum of 97.09 % in thefollowing operating conditions: biosorption pH 4.5,Cu(II) initial concentration 250 mg/L, biosorbent dos-age 0.5 %w/v, agitation rate 200 rpm, temperature20 °C, biosorption time 30 min, flotation pH 9, airpressure 4.5×105 Pa, dilution ratio 3:1, flotation time10min, collector CPB 0.01M, and molar ratio collector/

Cu(II) 5×10−1:1. The experimental data confirmed thatthe flotation stage contributed to the optimization of theoverall separation process.

Keywords Biosorption . Copper(II) . Dissolved airflotation . Surfactants

1 Introduction

Due to the progressive development of the industry,increasing amounts of toxic heavy metals are beingreleased into the environment in bioavailable form, en-dangering natural ecosystems and human health world-wide. Moreover, because of their high mobility, heavymetal ions are being concentrated and accumulatedthroughout the food chain (Naja et al. 2010; Naja andVolesky 2009; Chojnacka 2009; Kotrba et al. 2011).Consequently, controlling heavy metal discharges andremoving the toxic heavymetals from aqueous solutionshave become a challenge for the field of research anddevelopment (Volesky 2001).

The toxicity of heavy metals is highly associatedwithmetal ion speciation (i.e., dissolved forms are more toxicthan particulate forms, copper is such a case) (Trivunacet al. 2012). Copper is a natural microelement, essentialfor many biochemical pathways, but its excess leads toimportant toxicological concerns (Peng et al. 2010;Hanafiah and Ngah 2009). Copper contamination isgenerally being caused by a variety of industrial pro-cesses, such as the following: electroplating, electronicand electrical industries, paint and pigments

Water Air Soil Pollut (2015) 226: 274DOI 10.1007/s11270-015-2533-0

Electronic supplementary material The online version of thisarticle (doi:10.1007/s11270-015-2533-0) contains supplementarymaterial, which is available to authorized users.

L. Stoica :A.<M. Stanescu (*) :C. Constantin :O. Oprea :G. BacioiuDepartment of Inorganic Chemistry, Physical Chemistry andElectrochemistry, Faculty of Applied Chemistry andMaterialsScience, University Politehnica of Bucharest, Polizu Street 1,Bucharest 011061, Romaniae-mail: anamari.stanescu@gmail.com

A.<M. Stanescu : C. ConstantinNational Research and Development Institute for SoilScience, Agrochemistry and Environment Protection,Bucharest, Romania

manufacturing, fertilizers, refineries, and tannery indus-tries (Hanafiah and Ngah 2009; Jaman et al. 2009).Copper tends to accumulate in the human body whenexposed through air, water, or food sources causingharmful effects to the kidneys, liver, and nervous sys-tem, and it is probably best known for its associationwith Wilson’s disease. In addition, there is some evi-dence to suggest that copper may be carcinogenic (Waseand Forster 2003). United States EnvironmentalProtection Agency (US EPA) recommends a maximumacceptable concentration of copper in industrial efflu-ents and drinking water of 5 and 1.3 mg/L, respectively(http://www.epa.gov/).

Compared to the conventional treatment methodsused for heavy metal decontamination from watersand/or wastewaters (i.e., ion exchange, solvent extrac-tion, reverse osmosis, membrane technologies, chemicalprecipitation, electrochemical technologies, and evapo-ration) that have several drawbacks (i.e., incompletemetal removal, high operating costs, high reagent and/or energy requirements, and generation of toxic sludge),biosorption is regarded as a cost-effective, eco-friendly,and easy to operate alternative technology (Naja et al.2010; Chojnacka 2009; Kotrba et al. 2011; Volesky2001; Peng et al. 2010; Hanafiah and Ngah 2009;Jaman et al. 2009; Wase and Forster 2003; Wang andChen 2006; Zan et al. 2012; Chen and Wang 2008;Wang and Chen 2008; Zhang et al. 2010b; Das2012; El-Sayed and El-Sayed 2014). Biosorption relieson the property of living and/or nonliving biosorbents(i.e., bacteria, fungi, yeast, algae, food industry/agricultural waste, plants, and animal origin by-prod-ucts) to rapidly bind/adsorb/extract and/or concentratetoxic metals, radionuclides, light metals, and rare earthelements even from very diluted aqueous solutions(<100 mg/L) by physicochemical mechanisms (Najaet al. 2010; Naja and Volesky 2009; Chojnacka 2009;Peng et al. 2010; Hanafiah and Ngah 2009; Jaman et al.2009; Wase and Forster 2003; Meneghel et al. 2013;Altun and Pehlivan 2007; Sarkar et al. 2010; Yeddouand Bensmaili 2007; Volesky et al. 1993; Stanescu et al.2014). Since it is not limited to only one mechanism orto a specific type of contaminant, biosorption can findapplications in pollution prevention, pollution control,environment restoration, element and biomass recycle,and/or recovery (El-Sayed and El-Sayed 2014;Chojnacka 2009).

Previous research indicates that biosorption can besuccessfully combined with other separation and/or

decontamination techniques, namely, ultrafiltration,nanofiltration, reverse osmosis, incineration, and flota-tion, in order to develop an optimum technologicalprocess (Tsibranska and Saykova 2013; Won et al.2010; Feris et al. 2004; Matis et al. 2003; Zoubouliset al. 2001). According to the data available in theliterature, it was noticed that the flotation techniquescoupled with biosorption, also known as biosorptiveflotation, were mainly used as solid/liquid separationmethods (Zamboulis et al. 2004; Matis et al. 1996;Matis et al. 2003; Yenial et al. 2014; Ghazy and Ragab2011; Zouboulis et al. 2010; Mohammed et al. 2013;Lazaridis et al. 2001; Lazaridis et al. 2004; Zoubouliset al. 2001). However, in this study, we applied dis-solved air flotation (DAF) as a polishing technique forthe additional purification of the effluent resulted afterbiosorption and not as a solid/liquid separation method.

Flotation had its beginnings in mineral process-ing, and as such, it has been used for a long time,although for a number of years, the process hasfound wide applications to selectively separate dif-ferent microparticles (ions and molecules) (Rubioet al. 2002; Stoica 1997; Shammas and Bennett2010). Furthermore, flotation is also practiced inother fields, such as analytical chemistry; proteinseparation; harvesting and/or removal of algae;separation or harvesting of microorganisms; andclarification of fruit juices (Rubio et al. 2002;Stoica 1997). DAF is by far the most widely usedflotation method for the treatment of industrialeffluents, due to its rapidity, efficiency, selectivity,as well as for its technical and economical advan-tages (Lazaridis et al. 2004; Feris et al. 2004;Rubio et al. 2002; Stoica 1997; Shammas andBennett 2010). The process consists of the follow-ing basic steps: (i) bubble generation into thewastewater; (ii) contact between the gas bubbleand the suspended matter; (iii) attachment of finebubbles to the surface of the suspended matter;(iv) collision between gas-attached suspended par-ticles with the formation of agglomerates; (v) en-trapment of more gas bubbles in the agglomerates;(vi) upward rise of floc structures in a sweepingaction (Stoica 1997; Shammas and Bennett 2010).

The objective of this study was to investigate Cu(II)removal from aqueous systems by combining biosorptiononto inactive dry baker’s yeast Saccharomyces cerevisiaewith flotation. The influence of several factors (collec-tor—characteristics and type, pH, molar ratio, air

274 Page 2 of 11 Water Air Soil Pollut (2015) 226: 274

pressure, flotation time, and initial metal concentration)on Cu(II) removal efficiency was investigated. The im-portance of the physicochemical properties of Cu(II) ions(i.e., speciation), as well as of the collectors in thebiosorption-flotation process, was also discussed.

2 Materials and Methods

2.1 Materials

Commercial instant dry baker’s yeast (S. cerevisiae)purchased from local commercial company was pre-pared as inactive biomass by oven-drying at 105 °Cfor 24 h. Subsequently, the inactive instant dry baker’syeast biomass was stored in desiccators till further use.The average size of the granular biosorbent particles was425 μm (Stanescu et al. 2014).

Copper stock solution of 1000mg/L was prepared bydissolving CuSO4·5H2O (Merck, Germany) of analyti-cal reagent grade into distilled water. Copper test solu-tions of different concentrations (10, 25, 50, 100, 150,200, and 250 mg/L) were obtained by diluting the stocksolution. The pH of the solutions was adjusted byadding 0.1 M H2SO4 or 0.1 M NaOH solutions ifneeded.

Cationic surfactants: dodecylamine (DDA) (C12H27N),cetylpyridinium bromide (CPB) (C21H38BrN), andcetyltrimethylammonium bromide (CTAB) (C19H42BrN)of 0.01 M (Sigma-Aldrich, UK) were used as collectors.The collector solutions were prepared by dissolving theproper amount of surfactant in an ethanol/water mixture(volume ratio 1:1).

2.2 Biosorption-Flotation Experiments

The biosorption-flotation tests were conducted atlaboratory scale. The biosorption experiments wereperformed under batch conditions with continuousstirring (200 rpm), at room temperature (20 °C) andpH 4.5 by adding a constant dose of inactive instantdry baker’s yeast biomass of 0.5 %w/v per 100 mLsample of different initial metal concentrations, for30 min contact time. The biosorption studies werecarried out at the optimal operating parameters pre-viously investigated and reported (Stanescu et al.2014). The metal loaded biomass was separatedfrom the metal solutions by decantation, and the

liquid phase was subsequently subjected to a flota-tion stage for additional purification.

The flotation experiments were conducted byusing a dissolved air flotation unit (Stoica 1997).Prior to the flotation tests, the pH of the samplewas adjusted. The pH values were measured withan ORION 290 A pH meter. The desired quantityof the collector solution was added to the sample,which was maintained under continuous stirring for5 min at 200 rpm (HEILDORPH VIBRAMAX 100shaker); then, the mixture was transferred to theflotation column. The flotation column consists ofa cylindrical glass tube of 4.4 cm inner diameterand 25.5 cm length fitted with a stopcock at thebottom. A water stream presaturated with air keptunder the pressure of 4.5×105 Pa was introduced tothe cell base. Fine air bubbles necessary for anappropriate separation were generated by reducingthe pressure (Stoica 1997). The flotation tests wereperformed for 10 min. The effluents obtained afterflotation were analyzed for Cu(II) final concentra-tion by atomic absorption spectrometry (UNICAMPAY SP9). All biosorption-flotation experimentswere performed in duplicate.

The removal efficiency (Y) was calculated accordingto the following equation (Zhang et al. 2010a):

Y %ð Þ ¼ 1−C f

Ci

� �� 100 ð1Þ

where Ci and Cf are the initial and final metal concen-tration in solution, respectively (mg/L).

In order to obtain a complete description of thesurfactants used as collector reagents in the flotationtests, their main characteristics were evaluated. Themolecular structure simulation was performed with theHyperChem version 8.0 software. The surface tensionof their diluted aqueous solutions held at 20 °C wasdetermined with a Kruss tensiometer by using the ringmethod. A distilled water sample was used as reference.Experiments to evaluate the influence of the surfactantson the surface charge of the system were carried out bymeasuring the electrophoretic mobility of the aqueousdispersions in an electric field with a Zetasizer Nano ZSanalyzer (Malvern Instruments Ltd., U.K.). The specia-tion of Cu(II) ions in solution at 20 °C, pressure1.01325×105 Pa, and metal concentration of 50 mg/Lwas calculated using pH-REdox-Equilibrium(PHREEQC) program (Parkhurst and Appelo 2013).

Water Air Soil Pollut (2015) 226: 274 Page 3 of 11 274

3 Results and Discussion

3.1 Characterization of the Collectors

The collector plays an important role in the flotationprocess, since it affects the hydrophobicity of the sys-tem. The collector or the so-called depressing reagent isa surface-active substance (anionic or cationic) withlong linear carbon chain used in order to change thesurface tension at the gas–solid interface, changing thespecific attachment of bubble and solids (i.e., increasingor decreasing the affinity and/or favoring the foamingprocess) (Ghazy and Ragab 2011; Stoica 1997;Shammas and Bennett 2010).

In order to obtain a complete description of thesurfactants used as collectors (DDA, CPB, and CTAB)in the flotation experiments, their main characteristicswere evaluated. Therefore, the molecular structures ofthe collectors, the surface tension of their diluted aque-ous solutions, as well as their influence on the zetapotential of the biosorbent were disscused. The partialcharges of the constituting atoms, the electrostatic po-tential, the 3D structure, as well as the dipole moment,surface area, and volume for each collector molecule,modeled/simulated with HyperChem Software are pre-sented in Figs. 1, 2, 3 and Table 1, respectively.

As it can be noticed from Fig. 1b, the electrostaticpotential of the DDA molecule consists of a collectionof negative and positive charges. Figures 2b and 3bshow that the charge distribution of CTAB, respectively,CPB is positive. As shown in Table 1, the molecule ofCPB presents the largest surface area and volume of718 Å2 and 1178 Å3, respectively, compared with theother two surfactants. The presence of the collectorreagent in the system decreases the dimension of theair bubbles, increasing thereby the efficiency of theDAF process (Stoica 1997). We estimate that the prop-erties of the collector (i.e., charge distribution, surfacearea, and volume) may influence the removal efficiencyof Cu(II). Therefore, it is possible that the efficiency ofthe biosorption-flotation process may increase with theincrease in the surface area and volume of the collectormolecule.

The surface properties of DDA, CPB, and CTABwere assessed by drawing the surface tension isothermsof their diluted aqueous collector solutions. A distilledwater sample was used as reference (σH2O=71.31×103 N/m). The surface tension isotherms for each col-lector are presented in Fig. 4.

From Fig. 4, it can be seen that the surface tensiondecreases with the increase in the collector concentra-tion. This trend was similar for all the surfactants. Thedescending surface tension isotherms (Fig. 4) suggestthat DDA, CPB, and CTAB present surface-active prop-erties as concerns the surface forces and the coordinat-ing power, and therefore, these surfactants could besuitable for Cu(II) removal by biosorption-flotation(Zouboulis et al. 2010; Stoica 1997).

The zeta potential is a measure of the surface chargeof the biosorbent and was used to study the behavior(Zhang et al. 2010b) of the system after Cu(II) ionbiosorption and cationic collector addition. In our pre-vious study, we investigated and reported the zeta po-tential of the biosorbent (heat pretreated instant drybaker’s yeast) before and after Cu(II) biosorption(Stanescu et al. 2014). The zeta potential of the heatpretreated instant dry baker’s yeast before Cu(II) ionbiosorption as a function of pH (3–6) was negativeand varied from −12.1 to −29.1 mV. The zeta potentialof the biosorbent increased to −9.75 to −22.4 mV, afterCu(II) ion (Ci 50 mg/L) biosorption (Stanescu et al.2014). The zeta potential of the biosorbent as a functionof pH, after Cu(II) ion (Ci 200 mg/L) biosorption andcationic collector addition, is illustrated in Fig. 5.

From Fig. 5, it can be observed that the zeta potentialof the biosorbent after Cu(II), 200 mg/L biosorption wasstill negative, but increased and varied in the range of−7.96 to −10.53mV due to the increase of the amount ofpositive charges of Cu(II) neutralizing the negativecharge of the biosorbent (Zhang et al. 2010b). Thenegative charge of the system after Cu(II) biosorptionjustifies the use of cationic collectors. The influence ofthe flotation reagents on the zeta potential was studied inorder to increase and bring the charge of the biosorbent/system in the range of −5 to 5 mV, given that theflotation process works properly under these conditions.From Fig. 5, it can be seen that the addition of thecollectors increases the zeta potential of the biosorbent/system to −4.77 to −8.36 mV when DDAwas added, to−1.01 to −6.19 mV when CTAB was used and, respec-tively, to 2.3 to −1.09 mV when CPB was added.Therefore, the obtained results suggest that DDA,CPB, and CTAB can be used as collectors in the flota-tion experiments. Similar findings were reported byZouboulis et al. (2001), who also found that the pres-ence of the metal mixture and/or surfactant increased thevalues of the zeta potentials of the yeast suspension usedin the biosorptive flotation experiments.

274 Page 4 of 11 Water Air Soil Pollut (2015) 226: 274

3.2 Biosorption-Flotation Tests

Previous investigations indicated that the heat pretreatedcommercial instant dry baker’s yeast, S. cerevisiae,presents a good adsorption capacity for Cu(II) ions.Consequently, the biosorption experiments wereperformed under batch conditions in accordance to ourprevious study (Stanescu et al. 2014).

3.2.1 Influence of Collector Type

In order to select the appropriate collector necessary forCu(II) removal after biosorption, the three aforemen-tioned flotation reagents were tested: DDA (0.01 M),CPB (0.01 M), and CTAB (0.01 M). The influence ofthe collector type on Cu(II) removal by biosorption-flotation is presented in Table 2.

As shown in Table 2, the removal efficiency of Cu(II)by flotation increased in the order: CTAB (87.85 %)<DDA (91.55 %)<CPB (96.15 %). The maximum re-moval efficiency, 96.15 %, was obtained by using CPBas collector reagent at a molar ratio collector/Cu(II) of5×10−1:1. This result was also supported by the zetapotential data (Fig. 5). Thus, CPB was selected as theoptimum collector necessary for Cu(II) removal bybiosorption-flotation and was used for the followingexperiments.

3.2.2 Influence of pH and Molar Ratio

The pH of the solution represents an important control-ling factor of the process, since it affects both metal (i.e.,speciation) and biosorbent (i.e., surface charge) proper-ties (Peng et al. 2010; Das 2012). Therefore, before we

Fig. 1 Molecular structure of DDA modeled with HyperChem. a Partial charges of the constituting atoms. b The electrostatic potentialmapped as a 3D charge surface; c 3D structure

Water Air Soil Pollut (2015) 226: 274 Page 5 of 11 274

determined the optimum pH for the biosorption-flotation process, we calculated the speciation ofCu(II) ions in solution using PHREEQC program

(Parkhurst and Appelo 2013). It was observed that thespeciation distribution of Cu(II) ions calculated withPHREEQC program was in aggrement with the

Fig. 2 Molecular structure of CPB modeled with HyperChem. a Partial charges of the constituting atoms; b The electrostatic potentialmapped as a 3D charge surface; c 3D structure

274 Page 6 of 11 Water Air Soil Pollut (2015) 226: 274

literature reported data (Zhang et al. 2010b; Doyle andLiu 2003; Aksu and Doyle 2002). Data regarding thespeciation distribution of Cu(II) ions calculated withPHREEQC program can be found in Online Resource 1.

Although precipitation may contribute to the overallremoval of the metal (Naja et al. 2010), it was reportedthat the suitable pH range for Cu(II) biosorption is 1–6,because within this range, the only stable existing spe-cies are represented by hydrated copper ions[Cu(H2O)4]

2+ (Naja et al. 2010; Peng et al. 2010;

Zhang et al. 2010b). At higher pH values, Cu(II) ionsstart to precipitate resulting hydroxides (Cu(OH)+ and

Fig. 3 Molecular structure of CTAB modeled with HyperChem. a Partial charges of the constituting atoms; b The electrostatic potentialmapped as a 3D charge surface; c 3D structure

Table 1 Calculated dipole moment, surface area and volume foreach collector molecule

Collector DDA CPB CTAB

Dipole moment, Debyes 1.325 37.6 38.82

Surface area, Å2 503 718 699

Volume, Å3 791 1178 1152 Fig. 4 Surface tension isotherms of the diluted collector solutions(temperature, 20 °C, σH2O=71.31×10

3 N/m)

Water Air Soil Pollut (2015) 226: 274 Page 7 of 11 274

Cu2(OH)22+ at pH≥6, Cu(OH)2 and Cu(OH)3

− at pH≥10, Cu(OH)4

2− at pH≥12), and the precipitation is com-plete around pH 12.

In order to establish the optimum pH necessary forCu(II) removal by flotation with CPB as collector, thepH was varied from 9 to 11. Within this pH range,copper is almost completely under precipitated form.The influence of pH on Cu(II) removal is summarizedin Table 3. Table 3 also lists the influence of molar ratioon Cu(II) removal by biosorption-flotation.

From Table 3, it can be seen that the maximumremoval efficiency, 96.15 %, was obtained at pH 9 fora molar ratio CPB/Cu(II) of 5×10−1:1. It can be noticedthat at pH values higher then 9, the percentage removalefficiency slightly decreased. These results are

comparable to those obtained by Zouboulis et al.(2001) for zinc, copper, and nickel removal from simu-lated wastewater by biosorptive flotation, usingdodecylamine as collector reagent. Table 3 also showsthat the removal efficiency of Cu(II) increased with theincrease of the molar ratio. Therefore, the pH 9 and themolar ratio CPB/Cu(II) 5×10−1:1 were selected as theoptimum parameters for Cu(II) removal and were usedfor the following experiments.

3.2.3 Influence of Air Pressure

The air pressure necessary for the generation of thebubbles is the major parameter controlling air solubilityin a DAF unit and is an important factor in flotation

Fig. 5 Comparison between the zeta potential of the biosorbentbefore and after collector addition (Ci Cu(II) 200 mg/L, biosorbentdosage 0.5 %w/v, agitation rate 200 rpm, biosorption time 30 min,temperature 20 °C, collector concentration 0.01 M)

Table 2 Influence of collector type on Cu(II) removal efficiency by biosorption-flotation

Ci

Cu(II)Collector Molar ratio

Collector/Cu(II)pH Cf

Cu(II)Y, %±SD

200 DDA 10−1:1 9–9.5 20.3 89.85±0.2

200 DDA 5×10−1:1 9–9.5 16.9 91.55±0.1

200 CPB 10−1:1 9 12.4 93.80±0.1

200 CPB 5×10−1:1 9 7.7 96.15±0.1

200 CTAB 10−1:1 7–7.2 26.5 86.75±0.1

200 CTAB 5×10−1:1 7–7.2 24.3 87.85±0.2

The biosorption-flotation experiments were conducted at Ci Cu(II) 200 mg/L; biosorption pH 4.5; biosorbent dose 0.5 %w/v; agitation rate200 rpm; temperature 20 °C; biosorption time 30 min; pressure 4.5×105 Pa; dilution ratio 3:1; flotation time10 min

Table 3 Influence of pH and molar ratio on Cu(II) removalefficiency by biosorption-flotation

Ci

Cu(II)Molar ratiocollector/Cu(II)

pH Cf

Cu(II)Y, %±SD

200 10−1:1 9 12.4 93.80±0.3

200 10−1:1 9.5 12.9 93.55±0.2

200 10−1:1 10.5 12.6 93.70±0.1

200 10−1:1 11 12.8 93.60±0.2

200 5×10−1:1 9 7.7 96.15±0.1

200 5×10−1:1 9.5 8.9 95.55±0.1

200 5×10−1:1 10.5 8.6 95.70±0.2

200 5×10−1:1 11 9.2 95.40±0.2

The biosorption-flotation experiments were conducted at Ci Cu(II)200 mg/L; biosorption pH 4.5; biosorbent dose 0.5 %w/v; agita-tion rate 200 rpm; temperature 20 °C; biosorption time 30 min;pressure 4.5×105 Pa; dilution ratio 3:1; flotation time 10 min,collector CPB, 0.01 M

274 Page 8 of 11 Water Air Soil Pollut (2015) 226: 274

operation. Thus, the amount of air dissolved in thesolution and consequently the amount of air releasedupon reducing of the pressure are both direct functionsof the initial air pressure (Stoica 1997; Shammas andBennett 2010). The influence of air pressure on Cu(II)removal efficiency is presented in Table 4.

As shown in Table 4, Cu(II) removal efficiency ex-hibited a maximum of 96.15 % at 4.5×105 Pa. Thus,4.5×105 Pa was selected as the optimum pressure nec-essary for Cu(II) removal by biosorption-flotation andwas used for the following experiments.

3.2.4 Influence of Flotation Time

The flotation time is a significant factor to be consideredfor practical applications. Figure 6 shows the influenceof time on Cu(II) removal efficiency by biosorption-flotation.

As seen from Fig. 6, Cu(II) removal efficiency in-creased rapidly and reached maximum after only10 min. It can be noticed that further increase in theflotation time did not caused any significant changes inthe removal efficiency. Thereby, 10 min was selected asoptimum flotation time for Cu(II) removal.

3.2.5 Influence of Initial Metal Concentration

The influence of initial metal concentration on Cu(II)removal by biosorption-flotation is illustrated in Fig. 7.The initial metal concentration was varied in the rangeof 10–250 mg/L.

From Fig. 7, it can be noticed that Cu(II) removalefficiency increased with increasing initial metal con-centration. As the initial concentration of Cu(II) in-creased from 10 to 250 mg/L, the removal efficiencyincreased from 66.7 to 97.09 %, respectively. As wepreviously reported (Stanescu et al. 2014), thebiosorption process was effective (62.30–71.12 %) atlow Cu(II) concentrations (10–50 mg/L). Therefore, the

Table 4 Influence of air pressure on Cu(II) removal efficiency bybiosorption-flotation

Ci

Cu(II)Pressure×105,Pa

Cf

Cu(II)Y, %±SD

200 3 10.83 94.58±0.3

200 2.3 12.11 93.94±0.4

200 4 15.81 92.09±0.3

200 4.5 7.7 96.15±0.1

200 5 12.23 93.88±0.2

The biosorption-flotation experiments were conducted at Ci Cu(II)200 mg/L; biosorption pH 4.5; biosorbent dose 0.5 %w/v; agita-tion rate 200 rpm; temperature 20 °C; biosorption time 30 min;dilution ratio 3:1; flotation time 10 min, collector CPB, 0.01 M;molar ratio CPB/Cu(II) of 5×10−1 :1

Fig. 6 Influence of flotation time on Cu(II) removal efficiency bybiosorption-flotation (Ci Cu(II) 200 mg/L; biosorption pH 4.5;biosorbent dose 0.5 %w/v; agitation rate 200 rpm; temperature20 °C; biosorption time 30 min; pressure 4.5×105 Pa; dilutionratio 3:1; collector CPB, 0.01 M; molar ratio CPB/Cu(II) of 5×10−1:1)

Fig. 7 Influence of initial metal concentration on Cu(II) removalefficiency by biosorption flotation (biosorption pH 4.5; biosorbentdose 0.5 %w/v; agitation rate 200 rpm; temperature 20 °C;biosorption time 30 min; pressure 4.5×105 Pa; dilution ratio 3:1;flotation time 10 min, collector CPB, 0.01 M; molar ratio CPB/Cu(II) of 5×10−1:1)

Water Air Soil Pollut (2015) 226: 274 Page 9 of 11 274

results presented herein (Fig. 7) show that the flotationprocess contributed to the increase of Cu(II) removalefficiency throughout the whole range of concentration.Furthermore, these results demonstrate that DAF can besuccessfully applied after biosorption for the additionalpurification of the resulted effluent and the optimizationof the overall separation process, respectively. Theresults reported byMohammed et al. (2013) for removalof lead ions from wastewater using SDS as surfactantand barley husk as biosorbent also indicated that thesorptive flotation process is more efficient thanthe flotation process.

4 Conclusions

This study was focused on the removal of Cu(II) ionsfrom aqueous solutions by biosorption-flotation. Theinfluence of different operating parameters, such ascollector type, pH, molar ratio, air pressure, time, andinitial metal concentration, was investigated, and it wasnoticed that the separation process is directly related tothese controlling factors. The experimental results weresupported by the physicochemical characteristics of thesurfactants used as collector reagents. The maximumremoval efficiency of Cu(II) by biosorption-flotation,97.09 %, confirmed that the flotation stage contributedto the optimization of the overall separation process.Moreover, these results demonstrate that DAF can besuccessfully applied after biosorption resulting thereby arapid, effective, and relatively low-cost process.

Acknowledgments This work was supported by the SectoralOperational Programme Human Resources Development 2007-2013 of the Romanian Ministry of Labour, Family and SocialProtection through the Financial Agreement POSDRU/107/1.5/S/76903.

References

Aksu, S., & Doyle, F. M. (2002). Electrochemistry of copper inaqueous ethylenediamine solution. Journal of TheElectrochemical Society, 149(7), 340–347.

Altun, T., & Pehlivan, E. (2007). Removal of copper(II) ions fromaqueous solutions by walnut, hazelnut- and almond-shells.Clean Soil Air Water, 35(6), 601–606.

Chen, C., &Wang, J. (2008). Removal of Pb2+, Ag+, Cs+ and Sr2+

from aqueous solution by brewery’s waste biomass. Journalof Hazardous Materials, 151, 65–70.

Chojnacka, K. (2009). Biosorption and bioaccumulation of toxicmetals. New York: Nova Science Publishers Inc.

Das, N. (2012). Remediation of radionuclide pollutants throughbiosorption—an overview.Clean Soil, Air,Water, 40(1), 16–23.

Doyle, F. M., & Liu, Y. (2003). The effect of triethylenetetraamine(trien) on the ion flotation of Cu(II) and Ni(II). Journal ofColloid and Interface Science, 258(2), 396–403.

El-Sayed, H. E. M., & El-Sayed, M. M. H. (2014). Assessment offood processing and pharmaceutical industrial wastes as po-tential biosorbents: a review. BioMed Research International.doi:10.1155/2014/146769.

Feris, L. A., De Leon, A. T., Santander, M., & Rubio, J. (2004).Advances in the adsorptive particulate flotation process.International Journal of Mineral Processing, 74, 101–106.

Ghazy, S. E., & Ragab, A. H. (2011). removal of zinc ions fromaqueous solutions by sorptive-flotation using limestone as alowcost sorbent and oleic acid as a surfactant. LatinAmerican Applied Research, 41, 99–104.

Hanafiah, M. A. K. M., & Ngah, W. S. W. (2009). Preparation,characterization and adsorption mechanism of Cu(II) ontoprotonated rubber leaf powder. Clean Soil Air Water, 37(9),696–703.

http://www.epa.gov/. Accessed 20 June 2014.Jaman, H., Chakraborty, D., & Saha, P. (2009). A study of the

thermodynamics and kinetics of copper adsorption usingchemically modified rice husk. Clean Soil Air Water, 37(9),704–711.

Kotrba, P., Mackova, M., & Macek, T. (2011). Microbialbiosorption of metals. New York: Springer.

Lazaridis, N. K., Matis, K. A., & Webb, M. (2001). Flotation ofmetal-loaded clay anion exchangers. Part I: the case of chro-mates. Chemosphere, 42(4), 373–378.

Lazaridis, N. K., Peleka, E. N., Karapantsios, T. D., &Matis, K. A.(2004). Copper removal from effluents by various separationtechniques. Hydrometallurgy, 74, 149–156.

Matis, K. A., Zouboulis, A. I., Grigoriadou, A. A., Lazaridis, N.K., & Ekateriniadou, L. V. (1996). Metal biosorption – flo-tation. Application to cadmium removal. AppliedMicrobiology and Biotechnology, 45, 569–573.

Matis, K. A., Zouboulis, A. I., & Lazaridis, N. K. (2003). Heavymetals removal by biosorption and flotation. Water, Air, &Soil Pollution, 3, 143–151.

Meneghel, A. P., Goncalves, A. C., Jr., Rubio, F., CardosoDragunski, D., Lindino, C. A., & Strey, L. (2013).Biosorption of cadmium from water using Moringa(Moringa oleifera Lam.) seeds. Water, Air, & Soil Pollution,224, 1383.

Mohammed, A. A., Ebrahim, S. E., & Alwared, A. I. (2013).Flotation and sorptive-flotation methods for removal of leadions from wastewater using SDS as surfactant and barleyhusk as biosorbent. Journal of Chemistry. doi:10.1155/2013/413048.

Naja, G.M., & Volesky, B. (2009). Toxicity and sources of Pb, Cd,Hg, Cr, As, and radionuclides in the environment. In L. K.Wang, J. P. Chen, Y. T. Hung, & N. K. Shammas (Eds.),Handbook on heavy metals in the environment (pp. 13–61).Boca Raton: Taylor & Francis & CRC Press.

Naja, G. M., Murphy, V., & Volesky, B. (2010). Biosorption,metals. In M. Flickinger (Ed.), Encyclopedia of industrialbiotechnology: bioprocess, bioseparation, and cell technol-ogy (pp. 1–47). New York: Wiley Interscience.

Parkhurst, D. L., & Appelo, C. A. J. (2013). Description of inputand examples for PHREEQC version 3—a computer

274 Page 10 of 11 Water Air Soil Pollut (2015) 226: 274

program for speciation, batch-reaction, one-dimensionaltransport, and inverse geochemical calculations, techniquesand methods 6–A43. Denver: U.S. Geological Survey.

Peng, Q., Liu, Y., Zeng, G., Xu, W., Yang, C., & Zhang, J. (2010).Biosorption of copper(II) by immobilizing Saccharomycescerevisiae on the surface of chitosan-coated magnetic nano-particles from aqueous solution. Journal of Hazardous ma-terials, 177, 676–682.

Rubio, J., Souza, M. L., & Smith, R. W. (2002). Overview offlotation as a wastewater treatment technique. MineralsEngineering, 15, 139–155.

Sarkar, D., Das, S. K., Mukherjee, P., & Bandyopadhyay, A.(2010). Proposed adsorption-diffusion model for characteriz-ing chromium(VI) removal using dried water hyacinth roots.Clean - Soil Air Water, 38(8), 764–770.

Shammas, N. K., & Bennett G. F. (2010). In Wang, L. K.,Shammas, N. K., Selke, W. A., Aulenbach, D. B. (Eds.),Flotation Technology (pp.1-41) New York: Humana Press,Springer Science+Business Media.

Stanescu, A.-M., Stoica, L., Constantin, C., Lacatusu, I., Oprea,O., & Miculescu, F. (2014). Physicochemical characteriza-tion and use of heat pretreated commercial instant dry baker’syeast as a potential biosorbent for Cu(II) removal. Clean SoilAir Water, 42(11), 1632–1641.

Stoica, L. (1997). Ionic and Molecular Flotation (In Romanian).Bucharest: Did. and Ped. Ed.

Trivunac, K., Sekulić, Z., & Stevanović, S. (2012). Zinc re-moval from wastewater by a complexation–microfiltrationprocess. Journal of the Serbian Chemical Society, 77(11),1661–1670.

Tsibranska, I., & Saykova, I. (2013). Combining nanofiltration andother separation methods (Review). Journal of ChemicalTechnology and Metallurgy, 48(4), 333–340.

Volesky, B. (2001). Detoxification of metal-bearing effluents:biosorption for the next century. Hydrometallurgy, 59, 203–216.

Volesky, B., May, H., & Holan, Z. R. (1993). Cadmiumbiosorption by Saccharomyces cerevisiae. Biotechnologyand Bioengineering, 41, 826–829.

Wang, J., & Chen, C. (2006). Biosorption of heavy metals bySaccharomyces cerevisiae: a review. BiotechnologyAdvances, 24, 427–451.

Wang, J., & Chen, C. (2008). Biosorbents for heavy metals removaland their future. Biotechnology Advances, 27, 195–226.

Wase, J., & Forster, C. (2003). Biosorbents for metal ions.London: Taylor & Francis e-Library.

Won, S. W., Mao, J., Kwak, I. S., Sathishkumar, M., & Yun, Y. S.(2010). Platinum recovery from ICP wastewater by a com-bined method of biosorption and incineration. BioresourceTechnology, 101, 1135–1140.

Yeddou, N., & Bensmaili, A. (2007). Equilibrium and kineticmodelling of iron adsorption by eggshells in a batch system:effect of temperature. Desalination, 206, 127–134.

Yenial, Ü., Bulut, G., &Ali Sirkeci, A. (2014). Arsenic removal byadsorptive flotation methods. Clean Soil Air Water. doi:10.1002/clen.201300438.

Zamboulis, D., Pataroudi, S. I., Zouboulis, A. I., & Matis, K. A.(2004). The application of sorptive flotation for the removalof metal ions. Desalination, 162, 159–168.

Zan, F., Huo, S., Xi, B., & Zhao, X. (2012). Biosorption of Cd2+

and Cu2+ on immobilized Saccharomyces cerevisiae.Frontiers Environmental Science Engineering, 6, 51–58.

Zhang, Y., Li, Y., Yang, L., Ma, X., Wang, L., & Ye, Z. (2010a).Characterization and adsorption mechanism of Zn2+ removalby PVA/EDTA resin in polluted water. Journal of Hazardousmaterials, 178, 1046–1054.

Zhang, Y., Liu, W., Xu, M., Zheng, F., & Zhao, M. (2010b). Studyof the mechanisms of Cu2+ biosorption by ethanol/caustic-pretreated baker’s yeast biomass. Journal of Hazardous ma-terials, 178, 1085–1093.

Zouboulis, A. I., Matis, K. A., & Lazaridis, N. K. (2001). Removalof metal ions from simulated wastewater by Saccharomycesyeast biomass: Combining biosorption and flotation processes.Separation Science and Technology, 36(3), 349–365.

Zouboulis, A., Lazaridis, K., Karapantsios, T., &Matis, K. (2010).Heavy metals removal from industrial wastewaters bybiosorption. International Journal of EnvironmentalEngineering Science, 1(1), 57–78.

Water Air Soil Pollut (2015) 226: 274 Page 11 of 11 274