Preparation and characterization of novel nano-mineral for the removal of several heavy metals from aqueous solution: Batch and continuous systems

Kumars Seifpanahi Shabani; Faramarz Doulati Ardejani; Khashyar Badii; Mohammad Ebrahim Olya

doi:10.1016/j.arabjc.2013.12.001

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Original Article

10 (

2_suppl

); S3108-S3127

doi:

10.1016/j.arabjc.2013.12.001

Preparation and characterization of novel nano-mineral for the removal of several heavy metals from aqueous solution: Batch and continuous systems

Kumars Seifpanahi Shabani^{^a,⁎}, Faramarz Doulati Ardejani^{^a}, Khashyar Badii^{^b}, Mohammad Ebrahim Olya^{^b}

a Faculty of Mining, Petroleum and Geophysics, Shahrood University of Technology, Shahrood, Iran

b Department of Environment, Institute for Color Science and Technology, Tehran, Iran

⁎Corresponding author. Tel.: +98 9187807644. q.s11063@yahoo.com (Kumars Seifpanahi Shabani)

Received: 2013-4-1, Accepted: 2013-12-1, Published: 2013-05-01

Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

Results of studies of the sorption activity of diatomite nanoparticles, diatomite–perlite composite nanoparticles and perlite nanoparticles that was provided from internal resource at Iran, with respect to Fe(II), Cu(II), Mn(II) and Cr(III) ions are presented. Thus, diatomite nanoparticles, diatomite–perlite composite nanoparticles and perlite nanoparticles were modified and prepared via particle size decreasing and characterized by XRD, XRF, BET, SEM, TEM and FT-IR. In the batch system the influence of pH, adsorbent dosage, temperature and ions initial concentration was investigated. The results of isotherm and kinetics studies show that the Langmuir isotherm and pseudo-second order kinetic showed better correlation with the experimental data. Calculations of thermodynamic parameters show the negative ΔG° values or spontaneous reaction, the enthalpy (ΔH°) change shows the endothermic process and values of ΔS° indicate low randomness at the solid/solution interface during the uptake of ions. Finally, three adsorbents were packed inside a glass column as a continuous system and the breakthrough curves were obtained. All results show that the ion affinity to adsorption onto adsorbents is as follows: Cu(II) > Fe(II) > Mn(II) > Cr(III). So, these abundant, locally available cheap minerals showed a greater efficiency for the removal of metal ions from the aqueous solution, also can be utilized for other water pollutants.

Keywords

Diatomite

Perlite

Mineral nanoparticles

Heavy metals adsorption

Aqueous solution

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1 Introduction

Contamination of water by heavy metals is a global problem (Danil de Namor et al., 2012) accordingly nowadays everybody knows that heavy metal ions consist of iron, lead, manganese, zinc, copper, chromium, nickel and so on that lead to many problems for human and water environment. In the environment two main sources of heavy metals are natural background derived from parent rocks and anthropogenic contamination, including mineral industrial wastes, Agrochemicals and other output of industrial activities and factories (Li et al., 2012). Several conventional methodologies such as precipitation (Martins et al., 2010), ion exchange (Yuan et al., 2010), filtration membrane technology (Song et al., 2011), electrochemical processes (Karami, 2013) and adsorption process (Chiban et al., 2011) are available for heavy metal removal and other pollutants from wastewaters. Generally, they are expensive or ineffective sometimes, especially when the metal concentration is higher than 100 mg/l (Miretzky et al., 2006; Schiewer and Volesky, 1995). Among all the treatments proposed, adsorption using sorbents is one of the most popular methods. It is now recognized as an effective, efficient and economic method for water decontamination applications and for separation for pilot purpose (Niu et al., 2007). Nowadays, the adsorption of pollutants by natural materials has been widely reported such as diatomite (Caliskan et al., 2011), perlite (Ghassabzadeh et al., 2010), red mud (Lopes et al., 2012), chitosan (Kyzas et al., 2013), orange skin (Lugo-Lugo et al., 2012), soy meal hull (Badii et al., 2008), almond skin (Doulati Ardejani et al., 2008), sawdust (Pehlivan and Altun, 2008), zeolite (Egashira et al., 2012) and clay (Sheikhhosseini et al., 2013). These adsorbents have a natural base and they are environmentally friendly and it is possible to regenerate most of them or be applied in different products, but less researches have focused on metal ions adsorption by natural mineral adsorbents with nano size particles. The comparison of adsorption capacity of different adsorbents for different ion sorption was showed in Table 1. Based on Table 1 we can see that these adsorbents have a suitable adsorption capacity in adsorption process.

Table 1 Comparison of adsorption capacity (mg g⁻¹) of different adsorbents for different ion sorption.

Adsorbent	Ion	Adsorption capacity (mg g⁻¹)	Refs.
Diatomite	Zn(II)	3.2	Caliskan et al. (2011)
Perlite	Ag(I), Cu(II) and Hg(II)	8.46, 1.95 and 0.35	Ghassabzadeh et al. (2010)
Red Mud	As(V)	3.3	Lopes et al. (2012)
Chitosan	Cr(VI) and As(V)	175 and 208	Kyzas et al. (2013)
Orange Skin	Cr(III) and Fe(III)	9.43 and 18.19	Lugo-Lugo et al. (2012)
Soy Meal Hull	Direct dye	15.3	Badii et al. (2008)
Almond Skin (mixture, external and internal shells)	Direct Red 80 dye	20.5, 16.96 and 16.4	Doulati Ardejani et al. (2008)
Sawdust	Cr(VI)	8.01	Pehlivan and Altun (2008)
Zeolite	Cu(II), Zn(II) and Mn(II)	11.3, 3.7 and 6.11	Egashira et al. (2012)
Clay	Ni(II), Cd(II), Zn(II) and Cu(II)	2.7, 2.9, 3.6 and 10.53	Sheikhhosseini et al. (2013)

The results of evaluating the performance of nano-mineral with other materials reported in the literature show that nano-minerals have a higher performance than raw or natural minerals, because of particle size reduction and increase in the surface area of particles and also more adsorption.

So, the objective of the present study is focused on the development of diatomite and perlite nanoparticles separately and as composite for removal of four heavy metal ions Fe(II), Mn(II), Cu(II) and Cr(III) ions that because of their environmental significance were selected. Iron is a vital ion for human but its existence at water resource in higher than the standard concentration (0.3 mg/l (USEPA, 2012)) leads to many problems that were reported by researchers already (Das et al., 2007; Songyan et al., 2009; Tekerlekopoulou and Vayenas, 2007 ). Manganese is another metal found in wastewaters that its concentration in the discharging water must be less than the standard values (0.05 mg/l) to prevent the death of living organisms (USEPA, 2012). Copper is one of the applicable metals in the industry which is considered as a potential source of surface and groundwater contamination (Seifpanahi Shabani et al., 2011). Copper is one of the biologically essential ions but is only required at low concentrations and concentrations higher than 1.3 mg/l (USEPA, 2012) in water lead to environmental and health problems (Danil de Namor et al., 2012). Chromium compounds are extensively used in many industrial processes such as tanning, plating, dyeing, refractory technologies and others. The presence of chromium species in higher than 0.1 mg/l concentration (USEPA, 2012) in water has serious environmental implications and consequently produces a detrimental effect on human health (Guru et al., 2008). The use of diatomite and perlite mineral adsorbents for the removal of heavy metal ions particularly Cu(II) and Cr(III) ions from water have been the subject of numerous publications in recent years (see Table 2).

Table 2 Summary of adsorption of heavy metal ions on natural diatomite and natural perlite.

Adsorbent	Ion	Refs.
Raw diatomite	Cr(III)	De Castro Dantas et al. (2001)
	Cu(II)	Tengjaroenkul et al. (2004)
	Cu(II), Pb(II) and Zn(II)	Murathan and Benli (2005)
	Cr(III)	Guru et al. (2008)
	Cr(III)	Puszkarewicz (2009)
	Cr(III)	Li et al. (2009)
	Cu(II)	Thippraphan et al. (2010)
	Cu(II)	Sljivic et al. (2010)
	U	Sprynskyy et al. (2010)
	Zn(II)	Caliskan et al. (2011)
	Pb(II)	Knoerr et al. (2011)

Raw perlite	Cu(II)	Alkan and Dogan (2001)
	Cd(II)	Mathialagon and Viraraghavan (2002)
	Cu(II) and Pb(II)	Sari et al. (2007)
	Cu(II)	Hasan et al. (2008)
	Cu(II), Co(II) and Ni(II)	Swayampakula et al. (2009)
	Ag(I), Cu(II) and Hg(II)	Ghassabzadeh et al. (2010)
	As(V)	Thanh et al. (2011)

Nanodiatomite	Fe(II), Mn(II), Cu(II) and Cr(III)	This study
Nanoperlite	Fe(II), Mn(II), Cu(II) and Cr(III)	This study

In view of that potentially low cost materials for the sorption of heavy metals have been discussed. The present study is focused on the development, modification and preparation of diatomite and perlite nanoparticles separately and as composite with equal ratio for removal of Fe(II), Mn(II), Cu(II) and Cr(III) ions. So, in the batch system the effects of pH, adsorbent dosage, initial concentration and temperature on the adsorption capacity were investigated. Since optimization of parameters, the characterization of isothermal adsorption and adsorption kinetics was also studied in order to provide a new method and theoretical evidences for wastewater treatment. Also, the column of adsorbent was tested for all ions and obtaining the breakthrough curves. Finally, thermo-dynamic parameters of adsorption process were considered.

2 Materials and methods

2.1

2.1 Materials

In this research the raw diatomite and raw perlite samples were obtained from internal sources, Zanjan mine at North West of Iran (Fig. 1).

Diatomite and perlite reservoirs in the Zanjan mines, North West of Iran.

All other chemicals consist of sodium hydroxide, chloridric acid, iron (II) chloride, manganese (II) sulfate, copper (II) chloride and potassium dichromate were purchased from Merck Company.

2.2

2.2 Adsorbent modification

In assessing the potential applications of diatomite and perlite as nanoparticles for the removal of heavy metal ions from aqueous solution, the modification of the material is an important issue to address. A variety of methodologies can be used to modify the diatomite and perlite surface such as calcination (Ediz et al., 2010; Ghassabzadeh et al., 2010; Jing et al., 2011 ), and functionalization (Fowler et al., 2007; Thanh et al., 2011). So, raw diatomite and raw perlite were washed five times with deionized water and then dried at 100 °C for 8 h. Next the samples were crushed by the laboratory planetary ball mill (Fritsch Pulverisette 6 model) consisting of distilled water in 250 RPM for 5 h. Finally, slurry samples were dehumidifying by spray dryer (B-290 model) in 180 °C and prepared for characterization and investigation of the adsorption processes.

2.3

2.3 Adsorbent characterization

The chemical composition of the modified diatomite nanoparticles (DNPs), diatomite–perlite composite nanoparticles (DPCNPs) and modified perlite nanoparticles (PNPs) which were determined by XRF (XRF-1800 model) is given in Table 3. DNPs, DPCNPs and PNPs are mainly composed of silica as SiO₂.

Table 3 The chemical analysis of modified DNPs, DPCNPs and PNPs.

Constituent	DNPs (wt.%)	DPCNPs (wt.%)	PNPs (wt.%)
SiO₂	65.88	60.98	56.87
K₂O	4.42	12.39	17.70
Al₂O₃	21.36	19.54	18.36
Na₂O	0.30	1.37	2.61
Fe₂O₃	3.03	2.74	2.53
CaO	3.24	1.88	0.96
ZrO₂	0.06	0.09	0.19
MgO	0.34	0.29	0.20
SO₃	0.57	0.37	0.27
TiO₂	0.80	0.28	0.17
MnO₂	0.0	0.07	0.13

The hydroxyl species and acid sites on DNPs, DPCNPs and PNPs surfaces and hydroxyl species on perlite structure were identified as a function of adsorption process. Thus various hydroxyl species including isolated hydroxyl groups, H-bonded hydroxyl groups and water uptake have been identified for diatomite and perlite. In addition, acid sites found on the diatomite surface generally result from clay impurities present in diatomaceous earth (Yuan et al., 2004). Generally, hydroxyl groups are classified according to their coordination with the silicon atom that is shown in Fig. 2.

The various arrays of hydroxyl groups present for SiO2 (Ghassabzadeh et al., 2010; Danil de Namor et al., 2012).

The BET (Quantachrome 2200e model) specific surface area analysis was done for DNPs, DPCNPs, PNPs, raw diatomite and raw perlite. The specific surface areas of DNPs, DPCNPs, PNPs, raw diatomite and raw perlite are shown in Table 4.

Table 4 BET specific surface area of DNPs, DPCNPs and PNPs adsorbents.

Adsorbent	Specific surface area (m²/gr)
DNPs	119.5
DPCNPs	102.1
PNPs	89.7
Raw diatomite	8.3
Raw perlite	3.5

According to Muller (2010) research the increase in surface area by decreasing the particle size of the diatomite and perlite resulted in a higher uptake of heavy metal ions by the smaller particles relative to the larger ones.

X-ray diffraction (XRD) patterns for DNPs, DPCNPs and PNPs were obtained by XMD300-Unisantis X-ray diffractometer that are shown in Fig. 3.

The XRD pattern of DNPs, DPCNPs and PNPs nano minerals.

Scanning electron microscopy (SEM) LEO-1455VP model was used to study the morphology and homogeneity of the DNPs, DPCNPs and PNPs. The SEM images in Fig. 4 show the pristine DNPs and DPCNPs and pure PNPs, respectively. Fig. 4(A) shows that pure DNPs were spherical in shape that are arranged closely with an average diameter of <100 nm and tiny wholly, while DPCNPs samples have a massive structure, as shown in Fig. 4(B). Fig. 4(C) shows the PNPs that have an amorphous-granular morphology with an average diameter of 150–200 nm.

SEM images for DNPs (A), DPCNPs (B) and PNPs (C) nano minerals.

The transmission electron microscope (TEM) PHILIPS CM120 model was used to study the morphology and homogeneity of the DNPs, DPCNPs and PNPs that are shown in Fig. 5A–C, respectively.

TEM images for DNPs (A), DPCNPs (B) and PNPs (C) nano-minerals.

In Fig. 5A the DNPs have a tiny texture, whereas in Fig. 5C the PNPs have the same granular texture and in Fig. 5B the DPCNPs have an intermediate state between DNPs and PNPs.

The FT-IR technique is one of the most important characterization techniques used to elucidate the changes in chemical structures. FT-IR spectra of DNPs, DPCNPs and PNPs for 1 min are shown in Fig. 6, black line consists of 1a, 1b and 1c, respectively. For DNPs, DPCNPs and PNPs five main common absorption bands are observed at 474–482 cm⁻¹ (B₁), 922–936.1 cm⁻¹ (B₂), 1275–1331 cm⁻¹ (B₃), 2095–2106 cm⁻¹ (B₄) and 3595–3615 cm⁻¹ (B₅). One separable band for DNPs, DPCNPs in 3736–3746 cm⁻¹ (B₆) is observed which is not observed in PNPs. B₆ band for DNPs is perspicuous than DPCNPs. Bands B₁ and B₂ are attributed to the Si–O stretching vibrations of Si–O–Si and Si–O–Al, respectively (Sodeyama et al., 1999). Band B₃ is the deformation band of molecular water (Roulia et al., 2006; Varuzhanyan et al., 2006). Band B₄ is attributed to molecular adsorbed water (Sodeyama et al., 1999). Band B₅ is attributed to the combination of the OH stretching arising from hydrogen-bonded and free Si–OH (Hong and Minoru, 1994; Sodeyama et al., 1999). The intensity of B₃, B₄ and B₅ bands is closely related to the water content, similar to other silicate materials and minerals, such as volcanic tuffs and zeolites. B₆ band is the deformation band of molecular water that attributed to the internal water that was absorbed by diatomite. Development of the silicate network has been attributed to de-hydroxylation of mainly Si–OH (Fig. 2) groups during any thermal and chemical treatment, including those treatments that do not lead to modification (Roulia et al., 2006).

FT-IR spectrum of the DNPs∼1a (black line), DPCNPs ∼ 1b (black line) and PNPs ∼ 1c (black line) before and after Fe(II) ∼ 2 (blue line), Mn(II) ∼ 3 (red line), Cu(II) ∼ 4 (green line) and Cr(III) ∼ 5 (orange line) ion adsorption process.

On the other hand in Fig. 6 FT-IR spectra of DNPs, DPCNPs and PNPs before and after Fe(II), Mn(II), Cu(II) and Cr(III) ions adsorption processes were shown. As is obvious the band B₅ has weak OH-band after Fe(II), Mn(II), Cu(II) and Cr(III) ions adsorption processes than before adsorption that is due to OH function saturating by Fe(II), Mn(II), Cu(II) and Cr(III) ions.

2.4

2.4 Environmental application of mineral nanoadsorbents

2.4.1

2.4.1 Batch mode adsorption studies

Stock solutions of 1000 mg/L were prepared by dissolving appropriate quantities of FeCl₂*4 H₂O, MnSO₄*4H₂O, CuCl₂*2H₂O, and K₂Cr₂O₇, respectively in a liter of double distilled water. Working solutions were prepared by diluting each stock solution to give the desired concentration and followed by batch adsorption studies at 25 °C on a multi stirrer hot plate to investigate the sorption processes. Known mass of DNPs, DPCNPs and PNPs was added separately to a 25 mL of the each metal ion solution, thoroughly mixed, and allowing sufficient time for equilibrium. Fast filtration followed and remaining metal ion concentrations were determined directly in the supernatant solution by flame atomic absorption spectrometry (AAS) PG-990 model.

The percentage adsorption of heavy metals from aqueous solution was computed using equation 1.

(1)

Adsorption (%) = ((C_{0} - C_{t}) / C_{0}) * 100

where, C₀ and C_t are the initial concentration and concentration at time t, respectively.

2.4.1.1

2.4.1.1 Effect of pH

The pH of the solution is an important factor that controls the adsorption process. The effect of pH on the Fe(II), Mn(II), Cu(II) and Cr(III) ions adsorption by DNPs, DPCNPs and PNPs was investigated for different pH values. Here it is necessary to note that FeCl₂*4 H₂O, MnSO₄*4H₂O and CuCl₂*2H₂O solutions may undergo precipitation at pH higher than 3.5, 6.2 and 4.5, respectively and is a limitation for pH consideration. In other words, K₂Cr₂O₇ salt is soluble at all pH values. Based on Fig. 7 the Fe(II), Mn(II), Cu(II) and Cr(III) ions adsorption percentage is a function of pH value. As it is shown in Fig. 7 heavy metal adsorption was increased with increasing pH value. For three adsorbents the maximum removal of Fe(II), Mn(II), Cu(II) and Cr(III) ions takes place in 3.2, 6, 4.45 and 7.5 pH values, respectively.

Effect of pH on the adsorption of Fe(II), Mn(II), Cu(II) and Cr(III) ions by DNPs (- - - -), DPCNPs (... .) and PNPs (——) for m = 0.01 gr, C0 = 50 mg/l, V = 25 ml.

2.4.1.2

2.4.1.2 Effect of DNPs, DPCNPs and PNPs dosage

The effect of the DNPs, DPCNPs and PNPs dosage on the removal of Fe(II), Mn(II), Cu(II) and Cr(III) ions which was based on the contact time 120 min was studied by changing the adsorbent dosage. The results are shown in Fig. 8 for Fe(II), Mn(II), Cu(II) and Cr(III) ions, respectively. Based on Fig. 8 the adsorption efficiency increases with increase in the contact time and attained a maximum value at 120 min.

Effect of adsorbent dosage on the adsorption of Fe(II), Mn(II), Cu(II) and Cr(III) ions by DNPs (- - - -), DPCNPs (... .) and PNPs (——) for optimal pH, C0 = 50 mg/l and V = 25 ml.

In Table 5 the optimal parameters consist of pH, adsorbent dosage for three adsorbents and Fe(II), Mn(II), Cu(II) and Cr(III) ions in contact time 120 min were shown.

Table 5 The optimal parameters consist of pH, adsorbent dosage for three adsorbents and Fe(II), Mn(II), Cu(II) and Cr(III) ions in contact time 120 min and solution volume 25 ml.

Adsorbent	Ion	Optimal pH	Optimal adsorbent dosage (gr)	Removal%	Initial concentration (mg/l)
DNPs	Fe(II)	3.2	0.09	85.93	50
	Mn(II)	6	0.09	83.02	50
	Cu(II)	4.45	0.07	69.58	100
	Cr(III)	7.5	0.09	65.55	15

DPCNPs	Fe(II)	3.2	0.13	72.55	50
	Mn(II)	6	0.13	67.51	50
	Cu(II)	4.45	0.11	59.3	100
	Cr(III)	7.5	0.13	54.97	15

PNPs	Fe(II)	3.2	0.15	61.9	50
	Mn(II)	6	0.15	50.51	50
	Cu(II)	4.45	0.13	53.81	50
	Cr(III)	7.5	0.15	50.27	15

2.4.1.3

2.4.1.3 Effect of ions initial concentration

The effect of Fe(II), Mn(II), Cu(II) and Cr(III) ions initial concentration on the adsorption process was investigated by changing the heavy metals’ initial concentration to 5, 15, 25, 50, and 100 mg/l under optimized conditions that are shown in Table 5, contact time 120 min and temperature 25 °C. The adsorption efficiency of Fe(II), Mn(II), Cu(II) and Cr(III) ions was decreased by increasing the initial ion concentration. The consideration of Fe(II), Mn(II), Cu(II) and Cr(III) ion concentration is shown in Fig. 9.

Effect of initial concentration on the adsorption of Fe(II) ∼ A, Mn(II) ∼ B, Cu(II) ∼ C and Cr(III) ∼ D ions by DNPs (- - - -), DPCNPs (....) and PNPs (——) for optimal pH, optimal adsorbent dosage and V = 25 ml, (C0 = 5 mg/l = , C0 = 15 mg/l = , C0 = 25 mg/l = , C0 = 50 mg/l = ●, C0 = 100 mg/l = ).

So, according to Fig. 9 the adsorption process of Fe(II), Mn(II), Cu(II) and Cr(III) ions decreased by increasing the initial concentration.

2.4.1.4

2.4.1.4 Effect of temperature

The effect of temperature on Fe(II), Mn(II), Cu(II) and Cr(III) ions removal from aqueous solution was considered for three temperatures 298.15, 318.15 and 338.15 K. The results of temperature changes are shown in Fig. 10. By observing Fig. 10, it is obvious that by increasing the temperature the removal of Fe(II), Mn(II), Cu(II) and Cr(III) ions increased.

Effect of temperature on the adsorption of Fe(II), Mn(II), Cu(II) and Cr(III) ions by DNPs, DPCNPs and PNPs for optimal pH, optimal adsorbent dose and V = 25 ml.

The amount of adsorption at equilibrium q_e (mg/g) was calculated by Eq. (2).

(2)

q_{e} (mg/gr) = ((C_{0} - C_{e}) \times V) / m

where, C₀ and C_e are the initial and the equilibrium concentrations (mg/L), V the volume of solution (L), m the weight of DNPs, DPCNPs or PNPs (gr) adsorbents. Different adsorbent doses of 25 ml of Fe(II), Mn(II), Cu(II) and Cr(III) metal ion solutions and concentrations that are shown in Table 5 were agitated for equilibrium time. The equilibrium sorbed amount of Fe(II), Mn(II), Cu(II) and Cr(III) ions according to adsorption time for various initial concentrations and different adsorbents are shown in Fig. 11.

The equilibrium sorbed amount of Fe(II), Mn(II), Cu(II) and Cr(III) ions according to adsorption time for various initial concentrations.

The kinetic of adsorption was determined by analyzing adsorption of metal ions from the aqueous solution at different time intervals. For adsorption isotherms, optimal DNPs, DPCNPs or PNPs dosage was added to 25 ml of 5–100 mg/l of Fe(II), Mn(II), Cu(II) and Cr(III) solutions at 298.15 K. And in the thermodynamic studies, adsorption of Fe(II), Mn(II), Cu(II) and Cr(III) metal ion solutions with concentrations that are show in Table 5 was carried out in 298.15, 318.15 and 338.15 K, respectively.

2.4.1.5

2.4.1.5 Isotherms and kinetics of the Fe(II), Mn(II), Cu(II) and Cr(III) adsorption onto DNPs, DPCNPs and PNPs

2.4.1.5.1

2.4.1.5.1 Sorption isotherm

Generally, adsorption isotherms provide vital information on optimizing the use of adsorbents. Descriptions on the affinity between sorbates and sorbents, bond energy and adsorption capacity, to mention a few, can be extracted from isotherm equilibrium models applicable to adsorption processes (Ijagbemi et al., 2009). The equilibrium data were analyzed in accordance with the Langmuir, Freundlich and Temkin isotherm model. All of the models are listed in Table 6.

Table 6 Isotherm models, their linear forms and respective coefficients (Zheng et al., 2009).

Isotherm model	Equation	A linear form	Plot
Langmuir	$q_{e} = \frac{q_{m} K_{L} C_{e}}{1 + K_{L} C_{e}}$	$\frac{C_{e}}{q_{e}} = \frac{1}{K_{L} q_{m}} + \frac{1}{q_{m}} C_{e}$	$\frac{C_{e}}{q_{e}} vs . C_{e}$
Freundlich	$q_{e} = K_{F} C_{e}^{1 / n}$	$\ln (q_{e}) = \ln K_{F} + \frac{1}{n} \ln C_{e}$	$\ln q_{e} vs \ln C_{e}$
Temkin	$q_{e} = \frac{RT}{b} \ln (K_{T} C_{e})$	$q_{e} = \frac{RT}{b} \ln K_{T} + \frac{RT}{b} \ln C_{e}$	$q_{e} vs \ln C_{e}$

where, in Table 6, in Langmuir isotherm q_m is a constant related to the area occupied by a monolayer of the adsorbate, reflecting the maximum adsorption capacity (mg/g), C_e is the equilibrium concentration of solution (mg/l), K_L is a direct measure of the intensity of adsorption (l/mg) and q_e is the amount adsorbed at equilibrium (mg/g). In Freundlich isotherm, K_F ((mg/g)(l/mg)^1/ⁿ) and n (dimensionless) are constants incorporating all factors affecting the adsorption process such as adsorption capacity and intensity, respectively. In Tempkin isotherm R is the gas constant (8.314 J/Mol K), T is the absolute temperature (K) and b is the Temkin constant related to the heat of sorption (J/Mol). The diagrams for isotherm modeling are show in Fig. 12.

The diagrams for isotherm modeling, (A) Langmuir, (B) Freundlich and (C) Tempkin.

Isotherm parameters for the adsorption of Fe(II), Mn(II), Cu(II) and Cr(III) ions onto DNPs, DPCNPs and PNPs adsorbents at 25.0 °C are shown in Table 7. It was found that the Langmuir isotherm showed better correlation with the experimental data than other isotherms.

Table 7 Langmuir, Freundlich and Tempkin isotherm constants for the adsorption of Fe(II), Mn(II), Cu(II) and Cr(III) ions on DNPs, DPCNPs and PNPs adsorbents.

Adsorbent	Isotherm model	Parameters	Metals
			Fe(II)	Mn(II)	Cu(II)	Cr(III)
DNPs	Langmuir	q_m (mg g⁻¹)	111.11	100	142.857	33.2
		K_L	0.023	0.05	0.014	0.096
		R²	0.994	0.992	0.964	0.92
	Freundlich	K_F	45.468	7.569	192.674	2.751
		n	1.323	0.454	0.448	0.463
		R²	0.885	0.988	0.837	0.738
	Tempkin	B₁	13.55	43.15	215.5	6.139
		K_t	3.086	6.674	35.925	3.563
		R²	0.967	0.954	0.874	0.664

DPCNPs	Langmuir	q_m (mg g⁻¹)	21.739	15.625	83.33	1.718
		K_L	0.108	0.044	0.204	1.448
		R²	0.968	0.944	0.941	0.998
	Freundlich	K_F	9.767	5.212	98.692	2.694
		n	1.799	1.23	2.475	11.905
		R²	0.931	0.932	0.745	0.829
	Tempkin	B₁	4.317	6.241	6.022	0.76
		K_t	3.721	5.969	4.751	11.199
		R²	0.959	0.906	0.73	0.831

PNPs	Langmuir	q_m (mg g⁻¹)	16.667	11.111	15.152	1.427
		K_L	0.02	0.021	0.017	0.039
		R²	0.977	0.928	0.952	0.926
	Freundlich	K_F	1.863	1.53	2.904	1.37
		n	1.377	0.918	10.1	1.585
		R²	0.955	0.916	0.263	0.855
	Tempkin	B₁	2.948	5.125	1.312	0.869
		K_t	100.475	76.223	2.894	1.688
		R²	0.97	0.897	0.306	0.866

Adsorption isotherms constants (R²) showed that the uptake of Fe(II), Mn(II), Cu(II) and Cr(III) ions onto DNPs, DPCNPs and PNPs adsorbents could be described by the Langmuir model.

2.4.1.5.2

2.4.1.5.2 Sorption kinetic

The kinetics of the adsorption process was analyzed using the pseudo-first-order and pseudo-second-order equations and intra-particle diffusion model to model the kinetics of Fe(II), Mn(II), Cu(II) and Cr(III) ions adsorption onto DNPs, DPCNPs and PNPs adsorbents. Three kinetics models are listed in Table 8.

Table 8 Kinetic models, their linear forms and respective coefficients (Najafi et al., 2011).

Kinetic model	Equation	A linear form	Plot
Pseudo first-order	$\frac{{dq}_{t}}{dt} = k_{1} (q_{e} - q_{t})$	$\ln (q_{e} - q_{t}) = \ln q_{e} - k_{1} t$	$\ln (q_{e} - q_{t}) vs t$
Pseudo-second-order	$\frac{{dq}_{t}}{dt} = k_{2} {(q_{e} - q_{t})}^{2}$	$\frac{t}{q_{t}} = \frac{1}{k_{2} q_{e}^{2}} + \frac{1}{q_{e}} t$	$\frac{t}{q_{t}} vs t$
Intra-particle diffusion model	$q_{t} = \frac{K_{i}}{m} t^{(0.5)}$	$q_{t} = \frac{K_{i}}{m} t^{(0.5)}$	$q_{t} vs t^{(0.5)}$

Wherein in Table 8 q_e and q_t are the amounts of metal ions adsorbed on the adsorbent (mg g⁻¹) at equilibrium and at time t, respectively, k₁ is the rate constant of the first-order adsorption in min⁻¹ and k₂ is the rate constant of second-order adsorption in (g mg⁻¹ min⁻¹), also for intra-particle diffusion model m is the mass of sorbent (g), q_t the amount of solute adsorbed at time t (mg/g) and K_i is the initial rate of intra-particle diffusion (mg/l s^−1/2). The diagrams for Isotherm and Kinetic modeling are show in Fig. 13.

The diagrams for kinetic modeling, (A): pseudo first-order, (B) pseudo-second order and (C) intra-particle diffusion model.

The values of parameters obtained by different kinetic and intra-particle diffusion model for the adsorption of Fe(II), Mn(II), Cu(II) and Cr(III) ions onto DNPs, DPCNPs and PNPs adsorbents are shown in Table 9. Also, amount of adsorption at equilibrium (q_e Exp) for Fe(II), Mn(II), Cu(II) and Cr(III) ions are shown in Table 9.

Table 9 The values of parameters obtained from different kinetic models for the adsorption of Fe(II), Mn(II), Cu(II) and Cr(III) ions onto DNPs, DPCNPs and PNPs adsorbents.

Adsorbent	Kinetic model	Parameters	Ions
			Fe(II)	Mn(II)	Cu(II)	Cr(III)
DNPs	Pseudo-first order	K₁ (min⁻¹)	0.023	0.03	0.018	0.012
		q_e (mg g⁻¹)	8.254	12.86	799.1	0.017
		R²	0.983	0.983	0.948	0.902
	Pseudo-second order	K₂ (g mg⁻¹ min⁻¹)	0.005	0.011	0.007	0.0001
		q_e (mg g⁻¹)	12.5	12.2	26.316	3.05
		R²	0.993	0.999	0.992	0.997
	Intra-particle diffusion model	K_i	2.361	2.82	9.347	0.446
		R²	0.992	0.985	0.975	0.912
		q_e Exp. (mg/g)	12.48	12.11	26.301	3.01

DPCNPs	Pseudo-first order	K₁ (min⁻¹)	0.039	0.042	0.042	0.01
		q_e (mg g⁻¹)	0.117	0.024	0.484	1.45∗E-7
		R²	0.984	0.916	0.842	0.133
	Pseudo-second order	K₂ (g mg⁻¹ min⁻¹)	0.013	0.023	0.017	0.103
		q_e (mg g⁻¹)	7.63	7.25	13.9	1.6
		R²	0.986	0.966	0.932	0.957
	Intra-particle diffusion model	K_i	0.696	0.853	1.24	0.155
		R²	0.992	0.916	0.842	0.957
		q_e Exp. (mg/g)	7.60	7.21	13.82	1.57

PNPs	Pseudo-first order	K₁ (min⁻¹)	0.023	0.025	0.048	0.007
		q_e (mg g⁻¹)	0.0035	0.011	0.004	4.9∗E-12
		R²	0.931	0.988	0.952	0.174
	Pseudo-second order	K₂ (g mg⁻¹ min⁻¹)	0.024	0.026	0.041	0.483
		q_e (mg g⁻¹)	5.39	4.37	5.40	1.25
		R²	0.985	0.998	0.996	0.997
	Intra-particle diffusion model	K_i	0.419	0.42	0.469	0.134
		R²	0.947	0.99	0.927	0.957
		q_e Exp. (mg/g)	5.34	4.34	5.38	1.23

The correlation coefficients for the pseudo-second-order kinetic model for DNPs, DPCNPs and PNPs were above 0.992, 0.932 and 0.985, respectively. The high correlation coefficients and the agreement of calculating and experimental q_e both demonstrated that the adsorption kinetics of Fe(II), Mn(II), Cu(II) and Cr(III) ions onto DNPs, DPCNPs and PNPs followed the pseudo-second-order kinetic model. Therefore, the rate-limiting step may be a chemical sorption or chemisorptions through sharing or exchange of electrons between sorbent and the adsorbate. Different works have been carried out using pseudo-second-order kinetics for sorption reactions, and some authors have reported the kinetics of the sorption of Cr(III) ion onto raw diatomite such as Guru et al. (2008).

2.4.1.5.3

2.4.1.5.3 Adsorption mechanism

Kinetics data for Fe(II), Mn(II), Cu(II) and Cr(III) ions adsorption onto DNPs, DPCNPs and PNPs adsorbents were further studied according to mass transfer or intra particle diffusion model. The adsorption kinetics can be controlled by different steps (Ijagbemi et al., 2009) that are shown schematically in Fig. 14.

Figure 14

The mass transport of ions and concentration profile of adsorbent (Choy et al., 2004).

Based on Fig. 14 the adsorption kinetics can be controlled by three different steps:

(I): solute transfer to the sorbent particle surface (film diffusion), (II): transfer from the sorbent surface to the intra-particle active sites (particle diffusion), (III): retention on the active sites via sorption, complexation or intra-particle precipitation phenomena.

The third step is assumed to be very rapid and can be considered negligible, the slowest of all the steps, is considered as the rate limiting step for any adsorption process. For design purposes, it is necessary to distinguish between film diffusion and particle diffusion in order to identify the slowest step in the adsorption process. The rate of sorption processes depends on parameters like structural properties of the sorbent (such as porosity, specific area and particle size (see Table 4)), the properties of the metallic ions (such as ionic radius and number of coordination), the concentration of the metal ions and the interactions between metal ions and active sites of the sorbent. If intra-particle diffusion has a significant presence in the adsorption process, it is generally characterized by the relationship between specific sorption (q_t) and the square root of time (Choy et al., 2004; Ko et al., 2003, 2004, 2005 ), as shown in Table 8.

The rate constant of intra-particle diffusion K_i was determined by plotting q_t (mg/g) as a function of the square root of the time which equally presents a nonlinear distribution of points, with two distinct portions. The double nature of the plots (curved and linear) obtained for the four ion sorption processes, indicated the existence of intra-particular diffusion in the processes. According to the intra-particle diffusion model, if a plot of the amount of sorbate adsorbed per unit weight of sorbent, q_t, vs. square root of contact time gives a linear plot, it indicates that intra-particle diffusion is the rate-limiting step in the sorption process (Ijagbemi et al., 2009). The plots obtained in Fig. 15 contrasted the prediction of the intra-particle diffusion model; this indicates that intra-particle diffusion is not the singular rate-limiting step in the adsorption process. The initial curved part is attributed to boundary layer (film) diffusion, the linear, to the intra-particle diffusion and chemical reaction (McKay and Poots, 1980).

Sorption of Fe(II), Mn(II), Cu(II) and Cr(III) ions onto DNPs, DPCNPs and PNPs as a function of square root of time for intra-particle diffusion rate constant determination (metal ion concentration, pH, adsorbent dos base on Table 5 at T: 25 °C).

Owing to the multi step nature of this plot, the linear portions were linearized by the plot of $- log [1 - {(q / q_{e})}^{2}]$ against time (s) as presented in Fig. 16. According to Urano and Tachikawa (1991) model, if the plots are linear and pass through origin, then the slowest (rate-controlling) step in the adsorption process is the internal diffusion, and vice versa (see Fig. 16).

Boyd plot for the adsorption of Fe(II), Mn(II), Cu(II) and Cr(III) ions onto DNPs, DPCNPs and PNPs: (metal ion concentration, pH, adsorbent dos base on Table 5 at T: 25 °C).

From Fig. 16, it was observed that the plots were linear but do not pass through the origin, suggesting that the adsorption process is controlled by film diffusion. It can be assumed that the diffusion of the solute inside the DNPs, DPCNPs and PNPs is more important for the adsorption rate than the external mass transfer that is corresponding with Ijagbemi et al. (2009).

So we can say that the Fe(II), Mn(II), Cu(II) and Cr(III) ions removal process involving DNPs, DPCNPs and PNPs follows the pseudo-second order model, with the intra-particle diffusion as the limiting factor.

2.4.1.6

2.4.1.6 Thermodynamic parameters

The amounts of Fe(II), Mn(II), Cu(II) and Cr(III) uptakes at 298.15, 318.15 and 338.15 K were calculated to obtain the thermodynamic parameters which were evaluated using the Van’t Hoff equation:

(3)

\log K_{d} = \frac{Δ S^{\circ}}{2.303 R} - \frac{Δ H^{\circ}}{2.303 RT}

The values of log K_d were defined as follows:

(4)

K_{d} = \frac{a}{1 - a}

where ΔS° and ΔH° or entropy (kJ/Mol K) and enthalpy (kJ/Mol) change of adsorption, respectively, R is the universal gas constant (8.314 J/Mol K), and T is the absolute temperature (K). The K_d is the equilibrium constant and a is the uptake percentage of adsorbate at equilibrium. The values of ΔH° and ΔS° were calculated from the slope and intercept of linear regression of Ln(K_d) vs. (1/T). Values of ΔG° were estimated by:

(5)

Δ G = - RT ln K_{d}

Calculated thermodynamic parameters consist of ΔH°, ΔS° and ΔG° are given in Table 10.The negative values of ΔG° indicate that the sorption of Fe(II), Mn(II), Cu(II) and Cr(III) ions onto DNPs, DPCNPs and PNPs adsorbents were spontaneous processes. The enthalpy (ΔH°) values’ change is positive, showing that the sorption of Fe(II), Mn(II), Cu(II) and Cr(III) ions are endothermic in nature. All ions uptake increased with the increasing temperature. The sorption of all ions also require a diffusion process, which is an endothermic process; i.e., the rise of temperatures favors Fe(II), Mn(II), Cu(II) and Cr(III) ion transport within the particles of DNPs, DPCNPs and PNPs. In another aspect, the exchanges of the metal ions with H⁺ need first the bond breaking of OH, which is one of the possible existing forms of proton in DNPs, DPCNPs and PNPs. The bond breaking is also an endothermic process. The ΔH° of Fe(II), Mn(II), Cu(II) and Cr(III) uptake by DNPs, DPCNPs and PNPs is as Cr(III) > Mn(II) > Fe(II) > Cu(II), implying that, temperature has a more important influence on Cr(III)-Mn(II)-Fe(II)-Cu(II) uptake, respectively. The positive low values of ΔS° indicate low randomness at the solid/solution interface during the uptake of Fe(II), Mn(II), Cu(II) and Cr(III) onto DNPs, DPCNPs and PNPs adsorbents.

Table 10 Values of thermodynamic parameters for the adsorption of Fe(II), Mn(II), Cu(II) and Cr(III) ions on DNPs, DPCNPs and PNPs adsorbents.

Adsorbent	Ion	ΔH (kJ mol⁻¹)	ΔS (J mol⁻¹ K⁻¹)	ΔG (kJ mol⁻¹)
				298.15 °K	318.15 °K	338.15 °K
DNPs	Fe(II)	0.2079	0.0249	−7.2290	−7.7279	−8.2268
	Mn(II)	0.2744	0.0249	−9.8327	−10.4979	−11.1630
	Cu(II)	0.0831	0.0333	−7.1625	−7.6614	−8.1603
	Cr(III)	0.74	0.0748	−17.0368	−18.2009	−19.3649

DPCNPs	Fe(II)	0.5571	0.0249	−6.9131	−7.4120	−7.9108
	Mn(II)	0.5238	0.0249	−9.7912	−10.4563	−11.1215
	Cu(II)	0.1247	0.0333	−6.8798	−7.3787	−7.8776
	Cr(III)	1.2222	0.1081	−19.4742	−20.8045	−22.1349

PNPs	Fe(II)	2.2615	0.0333	−9.0844	−9.7496	−10.4147
	Mn(II)	0.8315	0.0333	−9.7496	−10.4147	−11.0799
	Cu(II)	0.1663	0.0333	−7.6543	−8.3195	−8.9846
	Cr(III)	2.8602	0.1829	−51.0523	−54.5444	−58.0365

Since, ΔH > 0 and ΔS > 0, thus enthalpy and entropy are unfavorable and favorable agent, respectively, scilicet entropy cause to the adsorption processes was done to more adsorption and enthalpy cause to the adsorption processes was done to less adsorption. So, theses adsorption processes are bilateral and can be done spontaneously. Also, at the reactions that enthalpy and entropy are inversely, the temperature is determinant agent, hence at higher temperatures the entropy is predominant agent and at lower temperatures the enthalpy is effective agent.

2.4.2

2.4.2 Continuous mode adsorption studies

After characterization, preparation and batch mode adsorption studies, the three adsorbents were packed inside a glass column, where it was used for the adsorption/removal of Fe(II), Mn(II), Cu(II) and Cr(III) ions from aqueous solution. A schematic view of glass column is shown in Fig. 17.

DNPs, DPCNPs and PNPs adsorbents packed inside a glass column.

The length and diameter of glass column are 20 and 2 cm, respectively. A known amount of three nanoadsorbents was packed inside a glass column separately and Fe(II), Mn(II), Cu(II) and Cr(III) ion solutions were allowed to flow inside the column with a certain flow rate. The metal ion concentration was determined before and after the treatment using atomic absorption spectroscopy (PG-990 model). So, the column of adsorbent was tested for all ions and obtaining the breakthrough curves. The breakthrough curves that are obtained for Fe(II), Mn(II), Cu(II) and Cr(III) ions adsorption by DNPs, DPCNPs and PNPs adsorbents are shown in Fig. 18.

The breakthrough curves of Fe(II), Mn(II), Cu(II) and Cr(III) ions adsorption by DNPs (- - - -), DPCNPs (...) and PNPs (——) for pH = 3.2 and time 180 min, at three different flow rates (flow rate = 1 mL/min = , flow rate = 3 mL/min = , flow rate = 5 mL/min = ●).

In the breakthrough curve if C_inlet (ion concentration at the inlet) = C_outlet (ion concentration at the outlet), then the saturation of adsorbent at column is occurring. The saturation time for ions adsorption onto DNPs, DPCNPs and PNPs are shown in Table 11.

Table 11 The saturation time of adsorbent at columns for Fe(II), Mn(II), Cu(II) and Cr(III) ions adsorption onto DNPs, DPCNPs and PNPs adsorbent, optimal pH, temperature 25 K and concentration according to Table 5.

Adsorbent	Ion	Flow rate (ml/min)	Saturation time (min)
DNPs	Fe(II)	1	137
	Mn(II)	3	117
	Cu(II)	5	169
	Cr(III)	1	69

DPCNPs	Fe(II)	3	105
	Mn(II)	5	101
	Cu(II)	1	148
	Cr(III)	3	64

PNPs	Fe(II)	5	119
	Mn(II)	0.5	87
	Cu(II)	1	131
	Cr(III)	1.5	53

The following discussion is the results of the illusion of metal ions using three types of adsorbents at temperature 25 °C. Elution of the metal ions did not occur at the same rate (Table 5). The results show that the ease of selection of ions through the adsorption column depends on the metal – OH bond stability. Metal ions weakly retained by the adsorbents eluted first and strongly retained metal ions eluted last, as expected (Fig. 18). The elution profile for Fe(II), Mn(II), Cu(II) and Cr(III) ions and DNPs, DPCNPs and PNPs adsorbents are presented in Fig. 18. The results show that elution values for Cu(II), Fe(II), Mn(II) and Cr(III) ions for DNPs, DPCNPs and PNPs adsorbents are (169, 137, 117 and 69), (148, 105, 101 and 64) and (131, 119, 87 and 53), respectively. So, similar batch state, in continuous stat DNPs > DPCNPs > PNPs and adsorption processes for ions as Cu(II) > Fe(II) > Mn(II) > Cr(III).

Also, in Table 12 we can see that the removal percent of ions after 100 min at the glass column that was adsorbed on nano minerals is as follow:

Table 12 The removal percent of ions after 100 min at the glass column.

Ion	Flow rate mL/min	PNPs	DPCNPs	DNPs
Fe(II)	1	3.9	18.46	51.39
	3	0	0	12.83
	5	0	0	0

Mn(II)	1	0	8.5	27.8
	3	0.2	0	4.45
	5	0	0	0

Cu(II)	1	55.83	55.16	71.84
	3	12.68	18.19	49.84
	5	0	0	7.18

Cr(III)	1	0	0	0
	3	0	0	0
	5	0	0	0

2.4.3

2.4.3 Reusing the adsorbents

Reusing the DNPs, DPCNPs and PNPs is an important factor which aims to utilize the adsorbent in wastewater treatment. So, in this paper we collected the three utilized adsorbents and firstly were washed with NaCl 1 M for 2 h, then the NaCl/adsorbent mixture was filtered. Secondly the adsorbent was washed with NH₄OH 1 M for 2 h. Finally after filtration for expelling the ${NH}_{4}^{+}$ that sits on the OH function, the adsorbent was washed with deionized water and then heated in 300 °C for 2 h. This work has been done four times for three adsorbents after using and the adsorption process was considered for Fe(II), Mn(II), Cu(II) and Cr(III) ions. The results of DNPs, DPCNPs and PNPs reusing Fe(II), Mn(II), Cu(II) and Cr(III) ions for adsorption are shown in Fig. 19.

Reusing the DNPs, DPCNPs and PNPs for Fe(II), Mn(II), Cu(II) and Cr(III) ions adsorption.

According to Fig. 19 the adsorption of Fe(II), Mn(II), Cu(II) and Cr(III) ions by reactivating DNPs, DPCNPs and PNPs for four times kind of decreased that is due to reduction of the adsorbents specific surface area because of coagulation and agglomeration of adsorbent particles and the lack of quite clean absorbent that was collected and reactivated from previous steps.

3 Conclusions

The surface properties and potential use of diatomite nanoparticles (DNPs), diatomite-perlite composite nanoparticles (DPCNPs) and perlite nanoparticles (PNPs) as a sorbent for iron (II), manganese (II), copper (II) and chromium (III) were studied. Thus, DNPs, DPCNPs and PNPs that were prepared from internal resource (Zanjan mine, North West of Iran) firstly were modified and then characterized by XRD, XRF, SEM, TEM, FT-IR and BET analysis. XRD and XRF show that the main component is SiO₂ (Nearly 60%). The FT-IR shows the positive effect of the OH function in SiO₂, also Fig. 6 shows the FT-IR spectra of DNPs, DPCNPs and PNPs before and after Fe(II), Mn(II), Cu(II) and Cr(III) ions adsorption processes it is obvious that the band B₅ has OH weaken after Fe(II), Mn(II), Cu(II) and Cr(III) ions adsorption processes than before adsorption that is due to OH function saturating by Fe(II), Mn(II), Cu(II) and Cr(III) ions. The BET shows specific surface area 119.5 m²/gr for DNPs, 102.1 m²/gr for DPCNPs, 89.7 m²/gr for PNPs, 8.3 m²/gr for raw diatomite, and 3.5 m²/gr for raw perlite. In the batch mode after parameters optimization, the results of isotherm and kinetic studies show that the Langmuir isotherm and pseudo-second order kinetic have a good correlation with adsorption processes. Also, the maximum adsorption values for DNPs, DPCNPs and PNPs for Fe(II), Mn(II), Cu(II) and Cr(III) ions is as: 111.11, 100, 142.857, 33.2, 21.739, 15.625, 83.33, 1.718, 16.667, 11.111, 15.152 and 1.427, respectively. According to Fig. 15 the intra-particle/pore diffusion is not the singular rate-limiting step in the adsorption process. The initial curved part is attributed to boundary layer (film) diffusion, the linear, to the intra-particle diffusion and chemical reaction. From Fig. 16, it was observed that the plots were linear but do not pass through the origin, suggesting that the adsorption process is controlled by film diffusion. It can be assumed that the diffusion of the solute inside the DNPs, DPCNPs and PNPs is more important for the adsorption rate than the external mass transfer. So we can say that the Fe(II), Mn(II), Cu(II) and Cr(III) ions removal process involving DNPs, DPCNPs and PNPs follows the pseudo-second order model, with the intra-particle diffusion as the limiting factor. Calculations of thermodynamic parameters show that the negative ΔG^° values at three different temperatures suggest that the sorption of all metal ions was spontaneous. Change in ΔH^° for all ions show the endothermic process, as ion uptake increased with increase in temperature. Values of ΔS^° indicate low randomness at the solid/solution interface during the uptake of both for all ions by adsorbents. In the long run, the DNPs, DPCNPs and PNPs nanoparticles were packed inside a glass column and used for the removal of four ions from aqueous solution in several flow rates and obtaining the breakthrough curves. After reusing the adsorbents the adsorption of Fe(II), Mn(II), Cu(II) and Cr(III) ions by reactivating DNPs, DPCNPs and PNPs for four times kind of decreased that is due to reduction of the adsorbents specific surface area because of coagulation and agglomeration of adsorbent particles and the lack of quite clean absorption sites of adsorbents that were collected and reactivated from previous steps. All results show that the ion affinity to adsorption onto adsorbents is as follows: Cu (II) > Fe (II) > Mn (II) > Cr (III). Also, the results show that the affinity of adsorption for three adsorbents is DNPs > DPCNPs > PNPs. The high selectivity in the bonding of iron (II), manganese (II), copper (II) and chromium (III) suggests that DNPs, DPCNPs and PNPs may be useful for removal of these toxic heavy metal ions and probably other heavy metal ions from wastewaters. This ability can be explored in treatment technologies since diatomite and perlite are cheap, abundant, and locally available resources.

Acknowledgments

The authors appreciate the support of Shahrood University and Technology and Institute for Color Science and Technology towards the project.

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Kyzas G.Z., Kostoglou M., Lazaridis N.K., Bikiaris D.N., . N-(2-carboxybenzyl) grafted chitosan as adsorptive agent for simultaneous removal of positively and negatively charged toxic metal ions. J. Hazard. Mater.. 2013;244–245:29-38.
[Google Scholar]
Li E., Zeng X., Fan Y., . Removal of chromium ion (III) from aqueous solution by manganese oxide and microemulsion modified diatomite. Desalin. 2009;238:158-165.
[Google Scholar]
Li X., Liu L., Wang Y., Luo G., Chen Xi., Yang X., Hall M.H.P., Guo R., Wang H., Cui J., He X., . Heavy metal contamination of urban soil in an old industrial city (Shenyang) in Northeast China. Geoderma. 2012;192:50-58.
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Muller B.R., . Effect of particle size and surface area on the adsorption of albumin-bonded bilirubin on activated carbon. Carbon. 2010;48:3607-3615.
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Murathan A., Benli S., . Removal of Cu²⁺, Pb²⁺ and Zn²⁺ from aqueous solutions on diatomite via adsorption in fixed bed. Fresenius Environ. Bull.. 2005;14:468-472.
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Najafi M., Yousefi Y., Rafati A.A., . Synthesis, characterization and adsorption studies of several heavy metal ions on amino-functionalized silica nano hollow sphere and silica gel. Sep. Purif. Technol.. 2011;85:193-205.
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Song J., Oh H., Kong H., Jang J., . Polyrhodanine modified anodic aluminum oxide membrane for heavy metal ions removal. J. Hazard. Mater.. 2011;187(1–3):311-317.
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Songyan Q., Fang M., Peng H., Jixian Y., . Fe(II) and Mn (II) removal from drilled well water: a case study from a biological treatment unit in Harbin. Desalin. 2009;245:183-193.
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Sprynskyy M., Kovalchuk I., Buszewski B., . The separation of uranium ions by natural and modified diatomite from aqueous solution. J. Hazard. Mater.. 2010;181:700-707.
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Swayampakula K., Boddu V.M., Nadavala S.K., Abburi K., . Competitive adsorption of Cu (II), Co (II) and Ni (II) from their binary and tertiary aqueous solutions using chitosan-coated perlite beads as biosorbent. J. Hazard. Mater.. 2009;170(2–3):680-689.
[Google Scholar]
Tekerlekopoulou A.G., Vayenas D.V.A., . Iron and manganese removal from potable water using trickling filters. Desalin. 2007;210:225-235.
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Tengjaroenkul, U., Prasertsomboon, C., Jongrak, N., 2004. Adsorption of copper (II) ions on different matrices. 30th Congress on Science & Technology of Thailand, 19–21 October, Bangkok, Thailand.
Thanh D.N., Singh M., Ulbrich P., Strnadova N., Štěpánek F., . Perlite incorporating γ-Fe₂O₃ and α-MnO₂ nanomaterials: preparation and evaluation of a new adsorbent for As(V) removal. Sep. Purif. Technol.. 2011;82:93-101.
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Thippraphan, P., Phanichphant, S., Pookmanee, P., 2010. Adsorption of copper ion (II) by manganese chloride modified diatomite via hydrothermal method. 36th Congress on Science and Technology, 26–28 October, Bangkok, Thailand.
Urano K., Tachikawa H., . Process-development for removal and recovery of phosphorus from waste-water by a new adsorbent 2: adsorption rates and breakthrough curves. Ind. Eng. Chem. Res.. 1991;30:1897-1899.
[Google Scholar]
USEPA or United State Environmental Protection Agency, 2012. Technical Document: Acid Mine Drainage Prediction. EPA 820-R-11-002, Office of Water U.S. Environmental Protection Agency Washington DC. 18 pages.
Varuzhanyan Av. A., Varuzhanyan Ar. A., Varuzhanyan H.A., . A mechanism of perlite expansion. Inorg. Mater.. 2006;42:1039-1045.
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Yuan P., Wu D.Q., He H.P., Lin Z.Y., . The hydroxyl species and acid sites on diatomite surface. a combined IR and Raman study. Appl. Surf. Sci.. 2004;227:30-39.
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Yuan P., Liu D., Fan M., Yang D., Zhu R., Ge F., Zhu J.X., He H., . Removal of hexavalent chromium [Cr(VI)] from aqueous solutions by the diatomite-supported/unsupported magnetite nanoparticles. J. Hazard. Mater.. 2010;173:614-621.
[Google Scholar]
Zheng H., Liu D., Zheng Y., Liang S., Liu Z., . Sorption isotherm and kinetic modeling of aniline on Cr-bentonite. J. Hazard. Mater.. 2009;167:141-147.
[Google Scholar]

Introduction

Materials and methods

Materials
Adsorbent modification
Adsorbent characterization
Environmental application of mineral nanoadsorbents

Conclusions

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[24] Kyzas G.Z., Kostoglou M., Lazaridis N.K., Bikiaris D.N., . N-(2-carboxybenzyl) grafted chitosan as adsorptive agent for simultaneous removal of positively and negatively charged toxic metal ions. J. Hazard. Mater.. 2013;244–245:29-38.
[Google Scholar]

[25] Li E., Zeng X., Fan Y., . Removal of chromium ion (III) from aqueous solution by manganese oxide and microemulsion modified diatomite. Desalin. 2009;238:158-165.
[Google Scholar]

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[28] Lugo-Lugo V., Barrera-Díaz C., Ureña-Núñez F., Bilyeu B., Linares-Hernández I., . Biosorption of Cr(III) and Fe(III) in single and binary systems onto pretreated orange peel. J. Environ. Manag.. 2012;112:120-127.
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[30] Mathialagon T., Viraraghavan T., . Adsorption of cadmium from aqueous solutions by perlite. J. Hazard. Mater.. 2002;94(3):291-303.
[Google Scholar]

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[33] Muller B.R., . Effect of particle size and surface area on the adsorption of albumin-bonded bilirubin on activated carbon. Carbon. 2010;48:3607-3615.
[Google Scholar]

[34] Murathan A., Benli S., . Removal of Cu²⁺, Pb²⁺ and Zn²⁺ from aqueous solutions on diatomite via adsorption in fixed bed. Fresenius Environ. Bull.. 2005;14:468-472.
[Google Scholar]

[35] Najafi M., Yousefi Y., Rafati A.A., . Synthesis, characterization and adsorption studies of several heavy metal ions on amino-functionalized silica nano hollow sphere and silica gel. Sep. Purif. Technol.. 2011;85:193-205.
[Google Scholar]

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[Google Scholar]

[37] Pehlivan E., Altun T., . Biosorption of chromium (VI) ion from aqueous solutions using walnut, hazelnut and almond shell. J. Hazard. Mater.. 2008;155(1–2):378-384.
[Google Scholar]

[38] Puszkarewicz A., . Effectiveness of chromium compounds removal on diatomite beds. Ecol. Chem. Eng. S. 2009;16:185-191.
[Google Scholar]

[39] Roulia M., Chassapis K., Kapoutsis J.A., Kamitsos E.I., Savvidis T., . Influence of thermal treatment on the water release and glassy structure of perlite. J. Mater. Sci.. 2006;41:5870-5881.
[Google Scholar]

[40] Sari A., Tuzen M., Cıtak D., Soylak M., . Adsorption characteristics of Cu (II) and Pb (II) onto expanded perlite from aqueous solution. J. Hazard. Mater.. 2007;148:387-394.
[Google Scholar]

[41] Schiewer S., Volesky B., . Modeling of the proton-metal ion exchange in biosorption. Environ. Sci. Technol.. 1995;29:3029-3058.
[Google Scholar]

[42] Seifpanahi Shabani K., Doulati Aredejani F., Singh R.N., Marandi R., Soleimanyfar H., . Numerical modeling of Cu²⁺and Mn²⁺ ions biosorption by Aspergillus Niger fungal biomass in A continuous reactor. Arch. Min. Sci.. 2011;56(3):461-476.
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[Google Scholar]

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[Google Scholar]

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[Google Scholar]

[46] Song J., Oh H., Kong H., Jang J., . Polyrhodanine modified anodic aluminum oxide membrane for heavy metal ions removal. J. Hazard. Mater.. 2011;187(1–3):311-317.
[Google Scholar]

[47] Songyan Q., Fang M., Peng H., Jixian Y., . Fe(II) and Mn (II) removal from drilled well water: a case study from a biological treatment unit in Harbin. Desalin. 2009;245:183-193.
[Google Scholar]

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[Google Scholar]

[49] Swayampakula K., Boddu V.M., Nadavala S.K., Abburi K., . Competitive adsorption of Cu (II), Co (II) and Ni (II) from their binary and tertiary aqueous solutions using chitosan-coated perlite beads as biosorbent. J. Hazard. Mater.. 2009;170(2–3):680-689.
[Google Scholar]

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[Google Scholar]

[51] Tengjaroenkul, U., Prasertsomboon, C., Jongrak, N., 2004. Adsorption of copper (II) ions on different matrices. 30th Congress on Science & Technology of Thailand, 19–21 October, Bangkok, Thailand.

[52] Thanh D.N., Singh M., Ulbrich P., Strnadova N., Štěpánek F., . Perlite incorporating γ-Fe₂O₃ and α-MnO₂ nanomaterials: preparation and evaluation of a new adsorbent for As(V) removal. Sep. Purif. Technol.. 2011;82:93-101.
[Google Scholar]

[53] Thippraphan, P., Phanichphant, S., Pookmanee, P., 2010. Adsorption of copper ion (II) by manganese chloride modified diatomite via hydrothermal method. 36th Congress on Science and Technology, 26–28 October, Bangkok, Thailand.

[54] Urano K., Tachikawa H., . Process-development for removal and recovery of phosphorus from waste-water by a new adsorbent 2: adsorption rates and breakthrough curves. Ind. Eng. Chem. Res.. 1991;30:1897-1899.
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[55] USEPA or United State Environmental Protection Agency, 2012. Technical Document: Acid Mine Drainage Prediction. EPA 820-R-11-002, Office of Water U.S. Environmental Protection Agency Washington DC. 18 pages.

[56] Varuzhanyan Av. A., Varuzhanyan Ar. A., Varuzhanyan H.A., . A mechanism of perlite expansion. Inorg. Mater.. 2006;42:1039-1045.
[Google Scholar]

[57] Yuan P., Wu D.Q., He H.P., Lin Z.Y., . The hydroxyl species and acid sites on diatomite surface. a combined IR and Raman study. Appl. Surf. Sci.. 2004;227:30-39.
[Google Scholar]

[58] Yuan P., Liu D., Fan M., Yang D., Zhu R., Ge F., Zhu J.X., He H., . Removal of hexavalent chromium [Cr(VI)] from aqueous solutions by the diatomite-supported/unsupported magnetite nanoparticles. J. Hazard. Mater.. 2010;173:614-621.
[Google Scholar]

[59] Zheng H., Liu D., Zheng Y., Liang S., Liu Z., . Sorption isotherm and kinetic modeling of aniline on Cr-bentonite. J. Hazard. Mater.. 2009;167:141-147.
[Google Scholar]

Preparation and characterization of novel nano-mineral for the removal of several heavy metals from aqueous solution: Batch and continuous systems

Abstract

Keywords

Diatomite

Perlite

Mineral nanoparticles

Heavy metals adsorption

Aqueous solution

1 Introduction

2 Materials and methods

2.1 Materials

2.2 Adsorbent modification

2.3 Adsorbent characterization

2.4 Environmental application of mineral nanoadsorbents

2.4.1 Batch mode adsorption studies

2.4.1.1 Effect of pH

2.4.1.2 Effect of DNPs, DPCNPs and PNPs dosage

2.4.1.3 Effect of ions initial concentration

2.4.1.4 Effect of temperature

2.4.1.5 Isotherms and kinetics of the Fe(II), Mn(II), Cu(II) and Cr(III) adsorption onto DNPs, DPCNPs and PNPs

2.4.1.5.1 Sorption isotherm

2.4.1.5.2 Sorption kinetic

2.4.1.5.3 Adsorption mechanism

2.4.1.6 Thermodynamic parameters

2.4.2 Continuous mode adsorption studies

2.4.3 Reusing the adsorbents

3 Conclusions

Acknowledgments

References

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