Removal of toxic heavy metals from synthetic wastewater using a novel biocarbon technology

Journal of Environmental Chemical Engineering 1 (2013) 884–890

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Journal of Environmental Chemical Engineering journal homepage: www.elsevier.com/locate/jece

Removal of toxic heavy metals from synthetic wastewater using a novel biocarbon technology Malairajan Singanan a,*, Edward Peters b,1 a b

PG and Research Department of Chemistry, Presidency College (Autonomous), Chennai 600 005, Tamil Nadu, India Water Resources Management Group, Advanced Materials and Processes Research Institute (CSIR), Bhopal, Madhya Pradesh, India

A R T I C L E I N F O

A B S T R A C T

Article history: Received 6 March 2013 Received in revised form 28 July 2013 Accepted 30 July 2013

The toxic heavy metals released into the aquatic environment through various industrial processes are detrimental to all living species. Hence, removal of such contaminants from industrial wastewater is essential before discharge in to the receiving water bodies or in land system. In the present investigation, an attempt was made to develop an ecofriendly technology by using a biocarbon generated from a medicinal plant Marigold (Tagetes spp. – Asteraceae). The influential parameters for the biosorption of heavy metals are its effect on pH, contact time, initial metal ions concentration and biocarbon dose. Biosorption experiments were carried out at the temperature of 28  2 8C. The percent removal of Pb(II) and Cr(III) ions was 94.8 and 95.4 from synthetic wastewater by using BC. These results were observed at the optimum biocarbon dose of 2.5 g and at equilibrium time of 150 min. The removal of heavy metal ions from wastewater is mainly influenced by pH of the synthetic wastewater and the amount of biosorbent dose. The predominant mechanisms are ionic interactions and ion-exchange and weak surface adsorption on the biosorbent material. ß 2013 Elsevier Ltd. All rights reserved.

Keywords: Biocarbon Medicinal plant Marigold Biosorption Toxic heavy metals

Introduction The presence of heavy metals in wastewater and surface water is becoming a severe environmental and public health problem. Heavy metals are often discharged by a number of industries, such as mining, metal plating facilities, tanneries can lead to the contamination of freshwater and marine environment [1,2]. The concentration of these metals in wastewater may therefore rise to a level that can be hazardous to human health, livestock and the aquatic environment. Lead is of particular interest because of its toxicity and its widespread presence in the environment [3,4]. All Pb compounds are considered cumulative poisons. Acute Pb poisoning can affect the gastrointestinal track and nervous system [5]. To eliminate such environmental hazards associated with heavy metals, wastewater streams should be treated using robust techniques. Lead is ubiquitous in the environment and is hazardous at high levels. Long-term drinking water containing high level of lead will cause the nervous system damage, renal kidney disease, mental

* Corresponding author. Tel.: +91 9941317661. E-mail addresses: [email protected], [email protected] (M. Singanan), [email protected] (E. Peters). 1 Tel.: +91 9893683636. 2213-3437/$ – see front matter ß 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jece.2013.07.030

retardation, cancer and anaemia. Lead is non-biodegradable and therefore must be removed from water [6]. Chromium exists in all oxidation states from (III) to (VI) but only the trivalent and hexavalent chromium compounds are of practical importance. Chromium is toxic, corrosive and irritant. The Cr(VI) is a known carcinogen and a designated hazardous pollutant. Cr(III), on the other hand, is less toxic than Cr(VI) and is listed as an essential element, as micronutrient, to maintain good health and helps in maintaining the normal metabolism of glucose, cholesterol, and fat in human bodies. It is poisonous only at high concentration. The maximum allowable limit of total chromium in drinking water as recommended by the World Health Organization is (WHO, 2004) is 0.05 mg/L [7]. The removal of pollutants such as lead from wastewater has conventionally been accomplished through a range of chemical and physical processes [8,9]. In recent years, many naturally occurring biowaste and other industrials materials have been investigated to assess their suitability and ability to be used as an adsorbent. The use of low-cost natural materials includes green coconut shell powder [10], plant biomass [11], rich husk [12], saw dust [13], coir fibre [14], fly ash [15], styrax leaves [16], grape bagasse [17], eucalyptus Bark [18], mangrove Barks [19], pinus sylvestris sawdust [20], fertilizer industry waste [21], There are traditional methods of industrial wastewater treatment, such as precipitation, adsorption and coagulation methods electro kinetics and ion-exchange methods [22]. However, these processes can be

M. Singanan, E. Peters / Journal of Environmental Chemical Engineering 1 (2013) 884–890

expensive and not fully effective and generates the secondary effluent and sludge management problem in the recipient environment. Most methods are not economically feasible for small-scale industries prevalent in developing economies due to huge capital investment. In this context, intensive research and development efforts are being made all over the world to develop low cost adsorbents and to utilize the wastes for remediation of toxic metal ions from aqueous solutions [23]. Biosorption is an attractive technology for treatment of wastewater for removing heavy metals from industrial wastewater. A biosorbent can be considered low cost if it requires little processing, is abundant in nature, or is a by-product or waste material from another industry [24]. Natural plant materials and agricultural wastes are applied in biosorption technology to remove heavy metals from aqueous media. They offer an efficient and cost-effective alternative to traditional chemical and physical remediation and decontamination techniques [25]. In this study an attempt was made to use, the leaves of Marigold (Tagetes spp. – Asteraceae) for the preparation of biocarbon. It is a medicinal and flowering herb found in agricultural fields in Tamil Nadu, India throughout the seasons. The objectives of the present investigation were the potential use of Marigold leaves biocarbon (BC) for removal of Pb(II) and Cr(III) ions from synthetic wastewater as model pollutants. The factors that influence sorption capacity of the biomaterials such as pH, contact time, metal ions concentration and biocarbon dosage were evaluated. Essential biosorption isotherms such as Langmuir and Freundlich models were applied to the experimental data. Materials and methods

condition. Samples were collected at the end of the predetermined time (20 min) intervals and the amount of metal ions content were analyzed using Shimadzu AAS 6200 instrument with air–acetylene flame system. The biosorption experiments were carried out at 28  2 8C. All the experiments were carried out in triplicates and the average values obtained and used for further applications. The pH of the test solution was monitored by using a Hanna pH Instruments (Italy). Data analysis The amount of metal ions adsorbed per unit mass of the biosorbent was evaluated by using the following equation: qmax ¼

  Co  Ce V w

(1)

where Co is the initial metal ions concentration in mg/L, and Ce is the metal ions concentration at equilibrium in mg/L and V is the volume of metal ions solution in millilitres, w is the mass of adsorbent in grams. The percent of metal ions removal was evaluated from the equation: % Removal ¼



Co  Ce Co



 100

Results and discussion

A stock solution (1000 mg/L) of Pb(II) and Cr(III) ions was prepared by dissolving analytical grade substance of Pb(NO3)2 in double distilled water and Cr2O3 dissolved in nitric acid, respectively. The stock solutions was acidified to desired pH using concentrated HCl in order to prevent the formation of metal hydroxide and to return the metal ion to the dissolve state [26]. Further, the desired pH values of the working solutions were adjusted using 0.1 N NaOH and 0.1 N HCl. All the chemicals and reagents are analytical grade purchased from BDH, Bombay, India.

Characterization of biocarbon

Marigold (Tagetes spp. – Asteraceae) plant leaves were collected and air dried for 48 h. The dried leaves were grounded in ball mills and the sieved homogeneous powder was used for the preparation of biocarbon. The activated biocarbon (BC) was prepared by treating the Marigold leaf powder with the concentrated sulphuric acid (Sp. gr.1.84) in a weight ratio of 1:1.8 (biomaterial:acid). The resulting black product was kept in an air-free oven, maintained at 160  5 8C for 6 h followed by washing with distilled water until free of excess acid, and then dried at 120  5 8C [27]. This material was finely crushed and the particle size between 90 and 125 mm was used. The Marigold plant is selected for the adsorption experiments are mainly due to its eco-friendly nature and its rich carbon content. Batch biosorption process Biosorption studies were conducted in 250 mL Erlenmeyer flask containing a 50 mL of Pb(II) and Cr(III) separately. For optimization of the amount of biosorbent; 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 and 3.5 g of biocarbon was treated with 100 mg/L of initial metal ions concentration, respectively. The flasks were agitated at 250 rpm constantly shaking at a rate of 150 min to establish the equilibrium

(2)

All the data were analyzed and standard deviations of the statistical tests were carried out using programme of analysis of variance (ANOVA) by using SPSS 12 package.

Metal solutions

Preparation of biocarbon

885

The biocarbon was characterized for its quality control parameters which are essential to understand the adsorptive behaviour of the biocarbon. The characteristics of the biocarbon are outlined in Table 1. From the analytical results, it was observed that, moisture, ash and total carbon content was high which might be due to its plant origin. Bulk density and particle size of biocarbon are essential parameters which should be known before its application in wastewater treatment systems. Surface area is related to the adsorption capacity of an adsorbent. It is observed that, the surface is relatively high and is responsible for potential removal of metal ions from synthetic wastewater system. As the surface area increases, more binding sites are available for the adsorbate to be adsorbed [19,28]. Further, the values of methylene blue, ion exchange capacity and phenol number are also important to ascertain the adsorption behaviour of the biocarbon. The result indicates the biocarbon with good activity for adsorption. Table 1 Characteristics of the biocarbon (BC). Sl. no.

Parameters

Values for BC

1 2 3 4 5 6 7 8 9 10 11 12

Moisture content Ash content Total carbon Bulk density Matter soluble in water Matter soluble in acid pH Ion exchange capacity Methylene blue value Phenol number Iron Surface area

5.30% 32.50% 65.55% 0.68 g/cc 0.18% 0.23% 3.68 0.56 meq/gm 16.0 78.00 0.07% 178 m2/g

[(Fig._1)TD$IG]

M. Singanan, E. Peters / Journal of Environmental Chemical Engineering 1 (2013) 884–890

886 84.95 84.5 84.0 83.5

3778.35

83.0 82.5

757.50

82.0 81.5

622.34

601.87

925.17

81.0 80.5 %T

80.0 1517.08

79.5

1332.71

1111.08 1050.86

79.0 78.5

1194.19

78.0 77.5 77.0

1717.26

76.5 76.0

2965.64

75.5 74.88 3899.2

3600

3200

2800

2400

2000

1800

1600 cm-1

1400

1200

1000

800

600

324.5

Fig. 1. FT-IR spectrum of biocarbon.

FT-IR analysis The FT-IR technique is an important tool to identify the characteristic functional groups present on the biocarbon surface (Fig. 1). The FT-IR spectrum was recorded on a Spectrum One, Perkin Elmer, USA. The spectrum of biocarbon revealed the presence of a peak at 3778.35 cm1, associated with –O–H group. A peak valley is observed at 2965.65 cm1 is assigned to the –CH– stretching and the –CH2– fractions associated with the biocarbon surface. Peaks at 757.50 cm1 can be assigned to the deformation vibrations at C–H bond in the phenolic rings. Peaks in the vicinity of 1717.26–1517.08 cm1 showed the presence of aromatic rings. The signal at 1332.71 and 1050.86 cm1 in the spectrum are due to –O–H bending belongs to phenol group. Weak bands of the FT-IR spectrum at 1194.19 and 1111.08 cm1 represents the existence of

[(Fig._2)TD$IG]

C–O functionalities on biocarbon surface. The signal at 925.17 cm1 shows the C–C links in the biocarbon. The characteristic peaks at 622.34 cm1 and 601.87 cm1 is associated with C–S stretching and out of plane –O–H bending vibrations. The presence of polar groups on the biocarbon surface is likely to provide the considerable cation exchange capacity to the adsorbent [29]. Surface morphology Scanning electron microscopy (SEM) was used to visualize the surface morphology of the biocarbon (Fig. 2). The sample was scanned by using JSM 6701F JEOL, Japan. The SEM micrograph of biocarbon shows some leaf like structures and large numbers of nanograins thus makes possible for the adsorption of heavy metal ions on different parts of the biocarbon. The SEM image illustrates the surface texture and porosity of biocarbon with holes and small openings on the surface which increased the contact area [30]. Effect of pH

Fig. 2. SEM micrograph of biocarbon.

The pH is one of the important factors that govern the removal of metal ions from aqueous media. It has a significant influence on the amount of metal ions adsorbed. The metal ions are in competition with the protons in the solution at low pH values for the biosorption on active sites biomass surface [31]. The influence of pH on the biosorption capacity for the Pb(II) and Cr(III) ions is shown in Fig. 3. It was observed that, the removal Pb(II) and Cr(III) ions in the aqueous solution is low at low pH values and gradually increased with increasing pH of the solution. In presence of the biocarbon, the optimum pH for the maximum removal of Pb(II) (94.8%) and Cr(III) (95.4%) was 4.2–4.6, respectively. Metal ions uptake increased with pH from 4.0 to 4.6, this is due to more active sites with negative charge being exposed with the subsequent increase in attraction sites to positively charged metal ions [32]. Further, increase of pH beyond 5.0 leads to decrease in metal ions removal efficiency.

[(Fig._3)TD$IG]

[(Fig._5)TD$IG]

M. Singanan, E. Peters / Journal of Environmental Chemical Engineering 1 (2013) 884–890

Pb (II) 25 mg/L Pb (II) 75mg/L Cr (III) 50mg/L

Cr (III)

100

100 80 60

40 20 0 0

1

2

3

4

5

6

7

8

pH values Fig. 3. Effect of pH on the removal of Pb(II) and Cr(III) from synthetic wastewater using BC at 28 8C.

% Removal of Pb (II) and Cr (III)

% Removal of Pb (II) and Cr (III)

Pb (II)

887

Pb (II) 50mg/L Cr (III) 25 mg/L Cr (III) 75mg/L

90 80 70 60 50 0

30

60

90

120

150

180

210

240

Contact Time (min)

The optimization of the equilibrium time is one of the important parameters for the development of an economical wastewater treatment system. The influence of contact time on the biosorption capacity for Pb(II) and Cr(III) metal ions removal is shown in Fig. 4. It is observed that, the maximum removal of Pb(II) and Cr(III) ions from synthetic wastewater on biocarbon was 94.8% and 95.4%, respectively. The optimum equilibrium is reached at this contact time of 150 min for both metal ions. The results clearly revealed that, rate of adsorption is higher at the beginning and this is due to availability of a large number of active sites on the biocarbon. As these sites are exhausted, the uptake rate is controlled by the rate at which the adsorbate is transported from the exterior to the interior sites of the adsorbent particles [33]. It has been observed that, the mechanism of metal ions uptake from the aqueous solutions involved four steps: (i) migration of metal ions from the bulk solution to the surface of the adsorbent; (ii) diffusion through boundary layer to biocarbon surface; (iii) adsorption at a binding site and (iv) intra particle diffusion into the interior of the sorbent surface. The boundary layer resistance will be affected by the rate of sorption and increasing the agitation time will reduce this resistance and increase the mobility of the ions [34]. However, because the process is time dependent, after about 150 min, the biosorption remains constant. The plots of metal ions uptake as a function of time are single, smooth and continuous leading to saturation. This process suggests the possible monolayer coverage of the metal ions on the surface of the biocarbon [35]. Effect of metal ions concentration The effect of initial metal ions concentration on the adsorption efficiency of biocarbon is shown in Fig. 5. The biosorption

[(Fig._4)TD$IG]

% Removal of Pb (II) and Cr (III)

Pb (II) 100 mg/L

Cr (III) 100 mg/L

100 90 80 70 60 50 0

30

60

90 120 150 Contact time (min)

180

210

240

Fig. 4. Effect of contact time on the removal of Pb(II) and Cr(III) from synthetic wastewater using BC at 28 8C.

Fig. 5. Effect of metal ions concentration on the removal of Pb(II) and Cr(III) from synthetic wastewater using BC at 28 8C.

experiments were carried out at different initial Pb(II) and Cr(III) concentrations ranging from 25 to 100 mg/L. It was observed that, at the lower initial metal ions concentration (25, 50 and 75 mg/L), the percent removal of metal ions was significantly increased (92.2% for Pb(II) and 93.5% for Cr(III)) with biocarbon at the lower contact time of 90 min. The transfer of metal ions by biosorption on biocarbon increases with time and attains a maximum value at 90 min and thereafter remains constant for all the metal ions at lower concentration. But in the case of 100 mg/L of the metal ions concentration, the equilibrium time reached at 150 min for the maximum removal. The amount of metal ions adsorbed per unit weight of biocarbon was found to be increased with increase in concentration of the metal ions in synthetic wastewater [36,37]. It is clear from observation that the equilibrium time was independent. Similar results have been reported by other workers for other adsorbate– adsorbent system [38]. The removal of lower concentration metal ions in short equilibrium time has great industrial application as in most of the effluents the lower concentration of metal ions is encountered. Effect of biocarbon dosage The dependence of metal ions on effect dose was studied by varying the amount of biosorbent from 1.0 to 3.5 g/100 mL, while keeping other parameters (pH, contact time, and initial concentration of metal ions) constant. Fig. 6 presents the Pb(II) and Cr(III) ions removal efficiency for BC. Form the results; it can be observed [(Fig._6)TD$IG]that removal efficiency of the adsorbent significantly increased % Removal of Pb (II) and Cr (III)

Effect of contact time

Pb (II)

100

Cr (III)

90 80 70 60 50 0

1

2 Amount of biocarbon (g)

3

4

Fig. 6. Effect of biocarbon dose on the removal of Pb(II) and Cr(III) from synthetic wastewater using BC at 28 8C.

[(Fig._8)TD$IG]

M. Singanan, E. Peters / Journal of Environmental Chemical Engineering 1 (2013) 884–890

with increasing dose. It is due to the fact that the higher dose of adsorbents in the solution, the greater availability of exchangeable sites for the ions. The maximum removal of Pb(II) and Cr(III) is 94.8 and 95.4% for biocarbon at the optimum biosorbent dose of 2.5 g per 100 mL of synthetic wastewater. Further increase in addition of biosorbent shows no effect on removal of metal ions. This suggests that after a certain dose of adsorbent, the maximum adsorption sets in and hence the amount of ions bound to the adsorbent and the amount of free ions remains constant even with further addition of the dose of adsorbent [39]. The predominant biosorption mechanism is the ion-exchange as well as surface adsorption on the biosorbent material.

a

14 Pb (II) removal 12 10

Ce/qe (g/L)

888

8 y = 0.387x - 0.845 r² = 0.991

6 4 2 0 0

5

10

Effect of temperature

Adsorption isotherms The adsorption of a substance from one phase to another leads to a thermodynamically defined distribution of that substance between the phases as the system reaches equilibrium state. The data obtained from biosorption of heavy metals were analyzed using Langmuir isotherms. The linear form of the Langmuir isotherm is given by the following equation. Ce 1 Ce þ ¼ qe qmax b qmax

Pb (II)

Cr (III)

96 95 94 93

91 90

20

25

30

35 40 45 50 Temperature ( 0C )

55

60

65

Fig. 7. Effect of temperature on the removal of Pb(II) and Cr(III) ions from synthetic wastewater on biocarbon.

35

40

Cr (III) removal

10 8

y = 0.390x - 0.847 r² = 0.988

6 4 2 0 0

10

20 Ce (mg/L)

30

40

Fig. 8. (a) Langmuir isotherm model for the removal of Pb(II) from synthetic wastewater by using BC at 28 8C and (b) Langmuir isotherm model for the removal of Cr(III) from synthetic wastewater by using BC at 28 8C.

isotherm for the removal of Pb(II) and Cr(III) ions on biocarbon was illustrated in Fig. 8a and b, respectively. From the plots, qmax and b values of the Pb(II) and Cr(III) ions were obtained. The essential characteristics of Langmuir isotherm can be expressed by a dimensionless constant called equilibrium parameter RL, defined by [40]. 1 1 þ bC 0

(4)

where C0 is the initial concentration of metal ion (mg/L). The characteristics of the RL value indicate the nature of biosorption as unfavourable (RL > 1), linear (RL = 1), favourable (0 < RL < 1) and irreversible (RL = 0). The obtained value of RL is 0.5 for Pb(II) and for Cr(III) ions removal on biocarbon at 28 8C shows that the biosorption of Pb(II) and Cr(III) ions onto the biocarbon is favourable. The equilibrium data for the present adsorbate–adsorbent system were analyzed using Freundlich [41] adsorption isotherm. The linear form of the isotherm can be defined by the following equation: Log qe ¼ Log K f þ

92

30

12

RL ¼

97

20 25 Ce (mg/L)

14

(3)

where qe is the equilibrium metal ion concentration on the biosorbent (mg/g), qmax is the maximum biosorption capacity of biosorbent (mg/g). Ce is the equilibrium concentration of the metal in solution (mg/L). The plot of Ce/qe versus Ce should give a straight line, its slope equals to 1/qmax and the intercept has the value of 1/ [(Fig._7)TD$IG]qmax b, where b is the biosorption coefficient (L/mg). A Langmuir

% Removal of Pb (II) and Cr (III)

b

Ce/qe (g/L)

The effect of temperature on the biosorption of Pb(II) and Cr(III) by the biocarbon was studied at seven different temperatures as 30, 35, 40, 45, 50, 55 and 60 8C, respectively. The initial concentration of Pb(II) and Cr(III) was 100 mg/L and pH was 4.0– 4.6. The results indicate that, the uptake of metal ions was found to increase with the increase in temperature (Fig. 7) and decreases after a 45 8C. The increase in adsorption uptake with increase in temperature might be due to the possibility of large number of total pore volume of the adsorbent, an increase of number of active sites for the adsorption as well as an increase in the mobility of the metal ions. However, the effect temperature could also influences desorption of metal ions and consequently affects the adsorption equilibrium. Hence, rise in temperature beyond certain limits might causes a decrease in adsorption capacity of the biocarbon. This is because of the destruction of active binding sites in the biocarbon matrix [37].

15

1 log C e n

(5)

The constant n is an empirical parameter which reflects the intensity of adsorption that varies with the degree of heterogeneity and Kf is a constant related to adsorption capacity. The constants n and Kf can be calculated by plotting log Ce against log qe (the slope = 1/n and the intercept = log Kf). Freundlich biosorption models for the removal of Pb(II) and Cr(III) on biocarbon (BC) was illustrated in Fig. 9a and b, respectively. The Langmuir and

[(Fig._9)TD$IG]

M. Singanan, E. Peters / Journal of Environmental Chemical Engineering 1 (2013) 884–890

a

Table 3 The biosorption dynamics for the removal of Pb(II) and Cr(III) on BC.

0.6 0.58

Pb (II) removal Metals

0.56 0.54 0.5

First order

Second order 1

Pb(II)

k1 = 0.0276 min r2 = 0.901

Cr(III)

k1 = 0.0207 min1 r2 = 0.979

0.52

Log qe

889

k2 = 2.58  103 g mg1 min1 r2 = 0.904 k2 = .58  103 g mg1 min1 r2 = 0.902

0.48 0.46

The linear form of the pseudo-second-order chemisorption kinetics rate is given in the following equation:

y = -0.172x + 0.709 r² = 0.930

0.44 0.42

      t 1 t ¼ þ t qt qe k2 q2e

0.4 0.5

b

0.7

0.9

1.1 Log Ce

0.6

1.3

1.5

1.7

Cr (III) removal

The constants can be determined by plotting t/qt versus t. The second-order rate constant k2 (g g1 min1) and qe (mg/g) values can be calculated from the intercept and slope of the plot. It was observed that, the correlation coefficient (r2) values for the pseudosecond-order model better for Pb(II) and Cr(III) ions than the first order model. The result indicates that, the removal of metal ions from the synthetic wastewater is well followed the second order kinetics.

0.58

0.56 0.54 Log qe

0.52 0.5 0.48 0.46

y = -0.163x + 0.698 r² = 0.903

0.44

(7)

0.42

Conclusions

0.4 0.5

0.7

0.9

1.1 Log Ce

1.3

1.5

1.7

Fig. 9. (a) Freundlich isotherm model for the removal of Pb(II) from synthetic wastewater by using BC at 28 8C and (b) Freundlich isotherm model for the removal of Cr(III) from synthetic wastewater by using BC at 28 8C.

Freundlich parameters for the removal of Pb(II) and Cr(III) ions on the biocarbon (BC) were presented in Table 2. Biosorption dynamics A study on biosorption dynamics gives an idea about solute uptake rate which controls the residence time of solute at the solid solution interface. Thus, study of adsorption dynamics becomes quite significant in waste water treatment. For this purpose, a kinetic model, developed by using the Lagergren equation, was used. The general pseudo-first-order equation expressed as logðqe  qt Þ ¼ logðqe Þ 



 k1 t 2:303

(6)

where qe and qt are the amounts of metal ions sorbed onto the biocarbon (mg/g) at equilibrium and at time t (min), respectively. By plotting the log(qe  qt) versus t, the first-order rate constant k1 (1/min) and the equilibrium capacity qe can be obtained from the slope and intercept, respectively. The observed rate constant for the removal of Pb(II) and Cr(III) ions on biocarbon was presented in Table 3. Table 2 The Langmuir and Freundlich adsorption parameters for the removal of Pb(II) and Cr(III) on BC. Metals

Langmuir parameters

Freundlich parameters

Pb(II)

qmax = 2.58 mg/g b = 0.1747 l/mg r2 = 0.991

kf = 5.1168 r2 = 0.930

Cr(III)

qmax = 2.56 mg/g b = 0.1897 l/mg r2 = 0.988

kf = 4.9888 r2 = 0.903

The findings in this study revealed that the biocarbon generated from the medicinal herb Marigold (Tagetes spp. – Asteraceae) can be employed as an eco-friendly biosorbent for the removal of Pb(II) and Cr(III) ions from synthetic and industrial wastewater. The data from the batch biosorption studies provided essential information in terms of optimum pH, biocarbon dose and the effective equilibrium time for the removal of Pb(II) and Cr(III) ions from the synthetic wastewater. The biosorption process mainly controlled by pH of solution and its value was in the range of 4.0–4.6. The biosorption of Pb(II) and Cr(III) ions by the biocarbon was reasonably fast, and the equilibrium reached at 150 min for initial concentration of 100 mg/L for both metal ions. The optimum amount of biocarbon dose was 2.5 g for the maximum removal Pb(II) (94.8%) and Cr(III) (95.4%) in presence of BC, respectively. The predominant biosorption mechanism is the ion-exchange as well as surface adsorption. The analytical results are well fitted in both the isotherm models. The investigation clearly indicated that, the biomaterial can be used to develop high capacity biosorbents for the removal potential toxic heavy metals from any aqueous solutions. This system has wide applications for the removal of toxic heavy metals from various industrial wastewaters. References [1] L. Brinza, C.A. Nyga˚rd, M.J. Dring, M. Gavrilescu, L.G. Benning, Cadmium tolerance and adsorption by the marine brown alga Fucus vesiculosus from the Irish sea and the Bothnian sea, Bioresource Technology 100 (2009) 1727–1733. [2] Z. Baysal, E. Cinar, Y. Bulut, H. Alkan, M. Dogru, Equilibrium and thermodynamic studies on biosorption of Pb(II) onto Candida albicans biomass, Journal of Hazardous Materials 161 (2009) 62–67. [3] S.H. Abdel-Halim, A.M.A. Shehata, M.F. El-Shahat, Removal of lead ions from industrial waste water by different types of natural materials, Water Research 37 (2003) 1678–1683. [4] K. Edmond, C. Zandoh, M. Quigley, S. Amenga-Etego, S. Owusu-Agyei, B. Kirkwood, Delayed breastfeeding initiation increases risk of neonatal mortality, Pediatrics 117 (2006) 380–386. [5] K. Zhang, W.H. Cheung, M. Valix, Roles of physical and chemical properties of activated carbon in the adsorption of lead ions, Chemosphere 60 (2005) 1129– 1140. [6] M.M. Rao, A. Ramesh, G.P.C. Rao, K. Seshaiah, Removal of copper and cadmium from the aqueous solutions by activated carbon derived from Ceiba pentandra hulls, Journal of Hazardous Materials 129 (1–3) (2006) 123–129. [7] WHO, Guidelines for Drinking-water Quality, Recommendations, 3rd ed., WHO, Geneva, 2004p. 334.

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