hydrous metal oxide composites from coal fly ash as efficient adsorbents for removal of methylene blue from water

    Synthesis of zeolite/hydrous metal oxide composites from coal fly ash as efficient adsorbents for removal of methylene blue from water Lidan Lin, Yan Lin, Chunjie Li, Deyi Wu, Hainan Kong PII: DOI: Reference:

S0301-7516(16)30009-6 doi: 10.1016/j.minpro.2016.01.010 MINPRO 2846

To appear in:

International Journal of Mineral Processing

Received date: Revised date: Accepted date:

1 August 2015 25 December 2015 15 January 2016

Please cite this article as: Lin, Lidan, Lin, Yan, Li, Chunjie, Wu, Deyi, Kong, Hainan, Synthesis of zeolite/hydrous metal oxide composites from coal fly ash as efficient adsorbents for removal of methylene blue from water, International Journal of Mineral Processing (2016), doi: 10.1016/j.minpro.2016.01.010

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

Synthesis of zeolite/hydrous metal oxide composites from coal fly ash as

IP

T

efficient adsorbents for removal of methylene blue from water

SC R

Lidan Lin, Yan Lin, Chunjie Li, Deyi Wu*, Hainan Kong1 School of Environmental Science and Engineering, Shanghai Jiao Tong University, No. 800

AC

CE P

TE

D

MA

NU

Dongchuan Rd., Shanghai, 200240, China

*

1

ACCEPTED MANUSCRIPT

T

Abstract. Zeolites are useful crystalline aluminosilicate minerals, and zeolite synthesis from

IP

coal fly ash (ZFA) has been investigated widely to recycle solid waste. This synthesis process

SC R

produces waste alkaline solution as a by-product. To date, research has focused mainly on ZFA synthesis and use; the problematic waste alkaline solution has rarely been addressed. In this

NU

study, we developed two composites of zeolite/hydrous iron oxide (ZFA/HIO) and

MA

zeolite/hydrous zirconia (ZFA/HZ) by adding, after zeolite synthesis, a step in which waste alkaline solutions are neutralized with an iron or zirconium salt. The composites were

D

characterized by X-ray fluorescence, X-ray diffractometry, scanning electron microscopy,

TE

acid–base neutralizing ability, specific surface area and pore size distribution, and their

CE P

performance as adsorbents for the removal of methylene blue (MB) from water was investigated. MB adsorption by ZFA/HIO and ZFA/HZ was much higher than that by ZFA, and

AC

increased with increasing pH. This behavior was explained by the increased variable charge on the metal oxides. The adsorption was rapid, and nearly complete removal could be achieved at a sufficiently high dose. Material heating resulted in a decrease in pH and adsorption, but heating with pH adjustment could regenerate adsorbents for repeated use in MB removal. Zeolite/hydrous metal oxide synthesis from coal fly ash was environmentally friendly and products exhibit a high potential as reusable adsorbents for MB removal from water.

Keywords: adsorption; hydrous metal oxide; methylene blue; variable charge; zeolite

2

ACCEPTED MANUSCRIPT 1. Introduction

T

Product coloring with dye is an important manufacturing process in, amongst others, textile,

IP

paper, plastics, tannery, and paint industries. Large amounts of dye wastewater are generated

SC R

annually worldwide. Dye release into the environment can reduce water quality by reducing water clarity and aesthetic value and influencing photosynthetic activity, and may even pose a

NU

health risk for aquatic organisms and human beings because many dyes are toxic and

MA

carcinogenic (1–3). Therefore, decontamination of dyes from wastewater is critical before discharge.

D

Biological treatment is used widely, but it does not yield satisfactory color elimination

TE

because of its complex structure, artificial origin, and xenobiotic nature of dyes (4, 5). Thus,

CE P

further treatment is often needed to remove dyes efficiently. Adsorption can produce a high-quality treated effluent without sludge and secondary harmful substance production (3, 4).

AC

Most commercial systems currently use activated carbon as adsorbent to remove dyes from wastewater because of its excellent adsorption ability. However, the drawback of activated carbon is its high cost. In recent years, numerous materials have been studied as inexpensive and effective alternative adsorbents; these include mineral materials, biosorbents, waste materials from industry and agriculture, and artificially synthesized materials (1–4). Basic dye is one of the main classes of dyes and is used widely. This water-soluble product exists as a cation in water. Methylene blue (MB) is a representative basic dye that has been investigated extensively for its adsorptive removal from water/waste water (5–22). Zeolite has received much attention amongst the numerous adsorbent materials investigated for MB 3

ACCEPTED MANUSCRIPT removal (12–22). Zeolites are aluminosilicate minerals with permanent negative charges in their porous crystal structures, which makes them suitable to adsorb cationic dyes.

IP

T

A method to produce zeolite from coal fly ash (ZFA) has been developed to recycle global

SC R

coal fly ash (CFA), which is a solid waste generated in large amounts worldwide (23–30). Zeolite manufacture of this nature is appealing because of its low- or zero raw material cost and

NU

the possibility of reusing solid waste. Our previous study has shown that the capacity of ZFA to adsorb MB is comparable to or higher than other natural, commercial or chemically synthesized

MA

pure zeolites (29).

Although ZFA preparation and application has been investigated widely to recycle solid

TE

D

waste, large amounts of problematic waste alkaline solution remain after the synthesis process. We have recently initiated a novel method to synthesize ZFA/hydrous metal oxide hybrid

CE P

material by introducing a reaction step into the traditional ZFA synthesis route that involves neutralizing waste alkaline solution with soluble metal salts (31, 32). We also found that the

AC

newly developed material had a higher cation exchange capacity and specific surface area than the corresponding ZFA (31, 32). Our new composite material may be an alternative to remove cationic dyes from wastewater. The aim of this study was to synthesize two hybrid materials, i.e., ZFA/hydrous iron oxide (ZFA/HIO) and ZFA/hydrous zirconia (ZFA/HZ), from CFA using our new method and to investigate their performance for the first time as efficient materials in MB removal. Hydrous oxides of iron and zirconium were selected to represent the trivalent and tetravalent metal oxides. Iron and zirconium are affordable, non-toxic and environmentally friendly (33–35). The obtained materials were characterized and MB 4

ACCEPTED MANUSCRIPT adsorption was tested under different solution conditions. Finally, material regeneration was

IP

T

tested to establish its behavior in repeated usage.

SC R

2. Materials and methods

NU

2.1 Materials

A CFA sample with chemical composition as given in Table 1 was collected from Minhang

MA

thermal power plant, Shanghai, China and was used as raw material to synthesize ZFA/HIO and

D

ZFA/HZ. Approximately 150 g of fly ash sample and 900 mL of 2 mol/L NaOH solution were

TE

placed in a continuously stirred reactor. The mixture was heated with stirring for 24 h at 98ºC.

CE P

After being cooled to room temperature, the mixture was titrated, with stirring, using 1 mol/L FeCl3 or ZrOCl2·7H2O solution until the pH reached ~10.0. The mixture was aged for 24 h in

AC

an oven at 20°C, without stirring. The solid phase was recovered by centrifugation and washed with ethanol three times and acetone once. Finally, the ZFA/HIO or ZFA/HZ product was dried in an oven at 24ºC (a higher temperature such as 120oC was not used to facilitate metal oxide preparation in order to obtain a poorly crystallized material of higher specific surface area, which has a greater adsorptive performance) for 24 h, ground to pass through an 80-mesh sieve and stored in a sealed polyethylene sample bottle. For comparison, ZFA was also synthesized by the same method but without titration whereas hydrous oxides of iron and zirconium were prepared separately by titration of waste alkaline solution with corresponding metal salts.

5

ACCEPTED MANUSCRIPT 2.2 Material characterization

T

The material chemical composition was determined by X-ray fluorescence (PW2404,

IP

Philips Company). Crystalline material phases were identified by powder X-ray diffraction

SC R

(XRD) analysis (D/max 2550VL/PC) with Cu-Kα filtered radiation (30 kV, 15 mA). Particle morphology was observed by scanning electron microscopy (SEM, OVA NanoSEM 230, FEI,

NU

USA). The Brunauer–Emmett–Teller (BET) specific surface area and pore size distribution

MA

were measured using the nitrogen adsorption method (ASAP 2010 M+C, Micromeritics Inc., USA). The pore size distribution curve was obtained by the Barett–Joyner–Halenda (BJH)

TE

D

method.

CE P

2.3 Acid and base neutralizing capacity

AC

A batch titration procedure was used to examine the neutralizing capacity of the materials. Approximately 0.2 g of each material and 40 mL of deionized water were placed into 50 mL centrifuge tubes. Appropriate volumes of 0.1 mol/L HCl or NaOH were added to the tubes to achieve amounts of H+ or OH- ranging from 0 to 6 mmol H+/g. The tubes were sealed and placed in an orbital shaker. After being shaken continuously for 24 h at 25°C and 200 rpm, the suspension pH was determined using a HACH sension+ pH meter. The amount of H+ or OHrequired to achieve a certain pH, i.e., the acid neutralizing capacity (ANC) and base neutralizing capacity (BNC), respectively, can be estimated by subtracting the amount of H + or OH- required to achieve the same pH using deionized water in the blank experiment. The pH as 6

ACCEPTED MANUSCRIPT

T

a function of the amount of H+ or OH- added was drawn as the neutralizing curve.

SC R

IP

2.4 Batch adsorption experiments

To determine the adsorption isotherms, approximately 0.2 g of adsorbent was placed into 50

NU

mL centrifuge tubes to which was added 40 mL aqueous solution with MB concentrations of ~0–2000 mg/L. The pH was adjusted to 5.0, 8.0, and 11.0, according to the material

MA

neutralizing capacity. Tubes were sealed and agitated continuously in an orbital shaker (25°C， 200 rpm) for 4 h. This reaction time was sufficient to achieve MB equilibrium in the kinetic

TE

D

studies. Tubes were centrifuged at 4000 rpm for 10 min. The concentrations of MB in the supernatants were determined using a visible Unico spectrophotometer at 668 nm. The

CE P

supernatant was diluted with deionized water before determining when the absorbance was out of the range of the calibration curve. The amount of MB adsorbed per unit mass of adsorbent

Qe 

AC

was calculated from: ( CO Ce )V m

(1)

where Qe is the amount of MB adsorbed per unit mass of adsorbent (mg/g), Co is the initial MB concentration (mg/L), Ce is the MB concentration (mg/L) at equilibrium, m is the mass of adsorbent on a dry basis (g), and V is the solution volume (L). The effect of pH on MB adsorption was studied from pH 4.0 to 12.0. Approximately 0.2 g of adsorbent was placed into a 50 mL centrifuge tube to which was added 40 mL of MB 7

ACCEPTED MANUSCRIPT aqueous solution with an initial MB concentration of 250 mg/L. Appropriate amounts of 0.1 or 1 mol/L HCl or 0.1 mol/L NaOH were added to the mixture to achieve a specified final pH

IP

T

according to the neutralizing capacity measurements. After 4 h, MB concentrations in the

SC R

supernatants were measured and the amount of MB adsorbed was calculated. The final suspension pH was detected using a Hach Sension+ pH meter.

NU

The effect of adsorbent dosage was studied by mixing 250 mg/L MB aqueous solution and 0.25 to 12.5 g/L adsorbents at pH 11.0 and 25°C.

MA

To study the regeneration of ZFA/HIO and ZFA/HZ, adsorbents were initially reacted to remove MB with an initial concentration of 250 mg/L at 5 g/L. After separation of the

TE

D

supernatant and solid phase, MB concentrations in the supernatants were measured to calculate the amount of MB adsorbed. The solid was heated at 450°C for 2 h to decompose MB and to

CE P

regenerate the adsorbents. These treatment conditions were based on a previous study that showed that they were satisfactory for ZFA regeneration with adsorbed MB (29). The

AC

regenerated materials

were

used as

adsorbents

adsorption–regeneration was repeated several times.

3. Results and discussion

3.1 Material characterization

8

to

remove

MB again

and the

~

CE P

TE

D

MA

NU

SC R

θ

IP

T

ACCEPTED MANUSCRIPT

SEM images of the investigated materials are given in Fig. 2. The original ash particles

AC

typically had spherical shapes, with a smooth surface made of an aluminosilicate glass phase. Upon formation of the zeolite, the surface became rough, which indicates the deposition of clusters of zeolite crystals. Hydrous metal oxide formation changed the material surface further, i.e., the surface became more coarse, porous and uneven. A comparison of images of ZFA/hydrous metal oxides with those of separately prepared hydrous metal oxides illustrated that the zeolite surface was covered with agglomerates of hydrous metal oxide. The specific surface areas of CFA, ZFA, ZFA/HIO, and ZFA/HZ were 1.1, 28.7, 173.0, and 196.7 m2/g, respectively. The greater specific area of ZFA than CFA occurred because of the 9

ACCEPTED MANUSCRIPT formation of zeolite, which is a porous material. The ZFA/hydrous metal oxide composite synthesis improved the BET surface area significantly. Compared with ZFA, the BET surface

IP

T

area of ZFA/hydrous metal oxides increased more than six times because of the formation of

SC R

amorphous metal oxide. The nitrogen adsorption–desorption isotherm (Fig. 3) for ZFA/HIO and ZFA/HZ was rather similar and exhibited a type II nature (36). Materials possessed a total

NU

pore volume of 0.41 mL /g for ZFA/HIO and 0.34 mL /g for ZFA/HZ, respectively, as determined at P/P0 = 0.99. The slight adsorption–desorption hysteresis for 0.45 < P/P0 < 0.9,

MA

indicates a mesopore size distribution of 1–5 nm (37, 38). The pore structure for the hydrous oxides of iron and zirconium has also been observed previously (37–39). The corresponding

TE

D

pore size distribution data, calculated by the BJH method from the adsorption branch of the nitrogen isotherm, shows a narrow pore size distribution (Fig. 4) with a peak pore diameter of

AC

CE P

4.0 nm for ZFA/HIO and ZFA/HZ.

3.2 Acid and base neutralizing capacity

Figure 5 gives the material ANC and BNC curves. ZFA had the highest ANC. Possible origins of the ZFA ANC include (i) permanent negative charges that can bind H+ through cation exchange, (ii) carbonate and alkali or alkali earth metal oxides and (iii) sesquioxides of aluminum and iron. Origins of (ii) and (iii) should come from CFA. Because CFA had a low ANC, the high ANC of ZFA is presumed to occur mainly because of its permanent negative charge. However, the ANC of hydrous metal oxides of iron and zirconium would originate 10

ACCEPTED MANUSCRIPT solely from the surface hydroxyls. Hydrous zirconia exhibited higher ANC than hydrous iron oxide possibly because of the higher specific surface area of the former than the latter. The

IP

T

difference between these two oxides could explain the higher ANC of the ZFA/HZ than the

SC R

ZFA/HIO. The BNC, on the other hand, may be attributed mainly to the surface hydroxyls of metal oxides because only hydroxyl groups on the oxide surface were presumed to accept OH

NU

ions in solution (M─OH + OH─ → M─O̶ + H2O, where M is a metal atom of Zr or Fe). It is therefore not surprising that hydrous oxides of zirconium and iron had a high BNC whereas the

MA

BNC of ZFA and CFA was low. As a result, ZFA/HZ and ZFA/HIO had a BNC that was higher than ZFA or CFA but lower than hydrous metal oxides. Similar to ANC, the BNC of hydrous

TE

D

zirconia was also greater than hydrous iron oxide most probably because of the difference in specific surface area of the two oxides. The resultant ANC and BNC curves also serve as a

AC

CE P

basis for pH adjustment in our studies.

3.2 Effect of contact time

Figure 6 shows results of the percentage removal of MB versus reaction time for ZFA/HIO, ZFA/HZ, and ZFA. The adsorption was rapid and the percentage of removed MB increased sharply in a short time initially. Compared with ZFA, MB adsorption by ZFA/HIO and ZFA/HZ was faster and the adsorption capacity was much higher. To better characterize the adsorption kinetics, pseudo-first- and pseudo-second-order models were applied to fit the experimental data. The pseudo-first-order kinetic model equation 11

ACCEPTED MANUSCRIPT

(2)

SC R

IP

The pseudo-second-order kinetic model equation is given by:

T

is given by:

(3)

NU

where qt and qe are the amounts of MB adsorbed per unit mass of adsorbent at time t (min) and

MA

at equilibrium, respectively (mg/g); k1 (min–1) and k2 (g mg–1 min–1) are the rate constants of the pseudo-first- and pseudo-second-order models, respectively. The fitting results are given in

D

Table 2. From the correlation coefficients, it is clear that the pseudo-second-order model fitted

TE

the experimental data quite well whereas the pseudo-first order model presented poor fitting

CE P

results. The calculated qe values from the pseudo-second-order model agreed well with the experimental values. Therefore, adsorption by the materials in our study followed a

AC

pseudo-second-order adsorption rate expression, which suggests that the rate-limiting step may be chemical adsorption (40). Values of the pseudo-second-order model rate constant k2 for the three materials decreased as ZFA/HZ > ZFA/HIO >> ZFA, which agrees with the adsorption capacity. Thus, ZFA/hydrous metal oxides had a higher adsorption capacity and faster adsorption kinetics than ZFA. The experimental results suggest that the composites of zeolite/hydrous metal oxides developed in our study are environmentally friendly during the synthesis process, i.e., do not discharge waste alkaline solution, and also act as a better adsorbent for MB than ZFA obtained by traditional synthesis.

12

ACCEPTED MANUSCRIPT

3.3 Adsorption isotherm

IP

T

Adsorption isotherms of MB by ZFA/HIO, ZFA/HZ and ZFA are presented in Fig. 7. At low

SC R

concentrations, large amounts of MB were adsorbed, and the initial part of the curve was nearly vertical, which implies a high affinity of the adsorbents for MB. The MB adsorption isotherms

NU

eventually leveled off at high equilibrium concentrations, which suggests that the adsorption sites approached saturation. Data from the adsorption isotherms of ZFA/HIO, ZFA/HZ, and

MA

ZFA were fitted to the Langmuir and Freundlich models. The Langmuir model equation is

TE

D

given by:

(4)

CE P

The Freundlich model equation is given by:

AC

(5)

where Qmax is the calculated adsorption maximum (mg/g) and KL is a constant related to the binding strength of MB. KF (mg/g) and 1/n are constants related to the adsorption of MB and its intensity. The parameters and regression coefficients of the two models are listed in Table 3, from which it is evident that the data were better fitted to the Langmuir model. In this model, Qmax is the most important parameter because it is indicative of maximum adsorption capacity, namely, the potential of a material toward MB removal. A vast number of relevant publications exist on

13

ACCEPTED MANUSCRIPT the removal of MB by different adsorbents, including zeolites. We have been interested in ZFAs, to develop new materials for environmental applications because the preparation of this

IP

T

type of zeolite could reuse solid waste CFA as raw material with low- or zero-cost. To compare

SC R

the MB removal of our materials developed from CFA with other zeolites, maximum adsorption capacities obtained by previous workers for other zeolites, including natural,

NU

commercial or chemically synthesized pure zeolites, are listed in Table 4. Tables 3 and 4 show that (i) ZFA and other zeolites had a comparable adsorptive capacity for MB; (ii) a great

MA

enhancement in adsorption performance of MB was observed for ZFA, especially ZFA/hydrous metal oxides at higher pH levels; and (iii) ZFA/hydrous metal oxides showed a much higher

TE

D

adsorptive capacity than ZFA under alkaline conditions. Without artificial pH adjustment, the three materials used in this study had pH values close to 10.0. Therefore, ZFA/HIO and

CE P

ZFA/HZ are potentially excellent adsorbents for MB.

AC

3.4. Influence of pH

Figure 7 and Table 3 have shown that MB adsorption depends significantly on pH, and increases with increasing pH. This behavior could be explained by the fact that the materials contain components that could generate pH-dependent variable charges. In ZFA/HZ and ZFA/HIO, metal oxides of iron and zirconium are the main source of variable charges, whereas in ZFA, although the content was much lower, metal oxide components that originate from CFA account for the generation of variable charges. The change in variable charge with pH could be described as follows: 14

ACCEPTED MANUSCRIPT M—OH + OH– → M—O– + H2O

(6)

M—OH + H+ → M—OH2+

(7)

IP

T

where M represents a metal atom on the solid surface. Thus, the metal oxide surface is

SC R

negatively charged at high pH, positively charged at low pH, and equal to zero at the point of zero charge (PZC) pH. The PZC for hydrous zirconia is 4.0–5.0 (41, 42) and is close to 9.0 for

NU

hydrous iron oxide (43). Therefore, the greater adsorption capacity of ZFA/HZ than ZFA/HIO could be ascribed to the lower PZC and higher BET surface area of the former than the latter.

MA

However, because both metal oxides in the adsorbents were nearly not negatively charged at pH 5.0, their adsorption capacities for MB were similar under acidic conditions. At acidic pH,

TE

D

the adsorption capacity was presumed to result from zeolite. Covering the zeolite surface with metal oxides could reduce the MB adsorption, and ZFA exhibited a higher adsorption capacity

CE P

for MB than ZFA/hydrous metal oxides. The influence of pH on MB adsorption was examined in more detail over the pH range

AC

from 4.0 to 12.0. Results in Fig. 8 shows that at acidic pH, the percentage of MB removed was low for all three tested materials. A significant increase in adsorption with increasing pH was observed for ZFA/HIO and ZFA/HZ, and it reached ~100% when the pH was greater than ~7.0. The adsorption of MB on ZFA kept increasing with increasing pH and the removal efficiency did not achieve ~100% even when the pH reached ~11.5. As mentioned above, the increase in adsorption at higher pH resulted mainly from variable charges rather than permanent charges on the zeolite surface. The metal oxide content in ZFA/HIO and ZFA/HZ was much higher compared with that of ZFA (Table 1). Thus, at high pH, ZFA/HIO and ZFA/HZ had a much 15

ACCEPTED MANUSCRIPT higher adsorption capability than ZFA. A higher MB adsorption at higher pH values was also reported in previous zeolite studies

IP

T

(14, 16, 18, 21, 25). Because MB is a cationic dye, the lower adsorption at acidic pH was

SC R

explained by the presence of excess H+ ions competing with cation groups on the dye for adsorption sites. On the other hand, however, the number of positively charged sites decreases

NU

and the number of negatively charged sites increases as the pH increases. Therefore, the higher adsorption capacity of MB onto zeolite at higher pH can be explained by the fact that the

MA

electrostatic attraction force of MB with the zeolite surface is likely to be raised when the pH

TE

higher than for other zeolites.

D

value increases. It is clear that, at high pH, MB adsorption by ZFA/HIO and ZFA/HZ was much

CE P

3.5 Influence of adsorbent dosage

Figure 9 shows results for the influence of adsorbent dosage on MB adsorption. At a higher

AC

adsorbent dose, a greater surface area and a greater number of binding sites should be available for the constant amount of MB, and it is not surprising that the percentage removal of MB increased with increasing adsorbent dose whereas the amount of MB adsorbed per unit mass of adsorbent decreased at higher dosages. At a sufficiently high dosage, MB could be almost completely removed. For ZFA/HIO and ZFA/HZ, a dose of 5 g/L was sufficient to achieve ~100% removal efficiency, whereas for ZFA, a dose of 10 g/L was required. In a practical application, a high amount of adsorbed MB and high percentage of MB removed would be desirable. Therefore, the above doses could be presumed to be suitable. The higher adsorption 16

ACCEPTED MANUSCRIPT

SC R

IP

3.6 Desorption of adsorbed MB and regeneration of adsorbents

T

performance of ZFA/HZ than ZFA/HIO was noticeable at low dosage.

To understand the possibility of adsorbent regeneration for repeated use in MB removal, the

NU

desorption of adsorbed MB on ZFA/HIO and ZFA/HZ was achieved by heating at 450°C for 2 h because this method was found to be successful for ZFA (29). Unfortunately, a gradual

MA

decrease in adsorption performance occurred for ZFA/HIO and ZFA/HZ (Table 5). A gradual decrease in pH also resulted from the heating. Because pH was a key parameter that governs

TE

D

the adsorption performance of MB, we tried to examine the adsorption of MB on the heated materials after artificially adjusting the pH to a high level. This technique was very effective.

CE P

Even after five heating cycles, the adsorption capability of MB by the ZFA/HIO could be restored by raising the pH. This suggests that pH regulation was a viable method to regenerate

AC

the adsorbents before their reuse to remove MB. The decrease in pH by heating may result from surface dehydroxylation, and NaOH addition appeared to be capable of restoring the surface hydroxyls. These experimental results show that regenerated ZFA/HIO and ZFA/HZ can be used repeatedly as efficient adsorbents for MB. High-temperature calcination has been used previously for regenerating MB adsorbents because it can decompose organic dyes on surfaces or in pores of solid to carbon and then oxidize the carbon to carbon oxides in air (15, 44, 45). Heat treatment reduced adsorption because of changes in surface functional groups. MB adsorption by calcined kaolinite (44) and 17

ACCEPTED MANUSCRIPT diatomite (45) increased with increasing pH. In studies of MB adsorption by diatomite, Khraisheh et al. (45) pointed out that, when heated at high temperature, surface –OH groups of

IP

T

Si–OH on diatomite are removed according to: 2Si–OH → Si–O–Si + H2O. The removal of

SC R

hydroxyl groups from the diatomite surface and the formation of Si–O–Si bridges lead to a decrease in adsorption. However, Si–O–Si formed in calcined diatomite is cleaved by

NU

nucleophilic reagents such as sodium hydroxide according to: Si–O–Si + OH– → Si–O– + Si–OH. The enhancement in MB adsorption by calcined diatomite at high pH was interpreted

MA

in terms of the appearance of negative charge and the formation of hydroxyl groups (45). Therefore, in our study, the decrease in adsorption by heating for MB decomposition could be

TE

D

attributed to a reduction in pH and the removal of hydroxyl groups. Therefore, the successful regeneration of calcined ZFA/HIO and ZFA/HZ through pH elevation and the restoration of

AC

4. Conclusions

CE P

surface hydroxyl groups could be achieved by NaOH treatment.

Using CFA as raw material, hybrid materials of zeolite/hydrous metal (iron and zirconium) oxide were developed successfully by a new method that combines a neutralization reaction step of ‘waste alkaline solution’ with an iron or zirconium salt together with the traditional ZFA synthesis process. Composite materials were studied in terms of their removal of MB, a cationic dye pollutant. The materials had a great adsorption capacity for MB. pH was a key influencing factor in dye adsorption and a high adsorption ability resulted at high pH, because of the induced negative charges from metal oxides. The zeolite/hydrous metal oxide had a high 18

ACCEPTED MANUSCRIPT suspension pH without artificial adjustment. Heating could decompose the adsorbed MB but resulted in a decrease in pH and adsorption capacity. Results revealed that regeneration of used

IP

T

zeolite/hydrous metal oxides could be achieved by heat treatment plus pH adjustment. It is

SC R

concluded that zeolite/hydrous metal oxides are highly efficient adsorbents to remove basic

NU

cationic dyes from water.

Acknowledgement: This research was supported by the National Key Project for Water

D

MA

Pollution Control (grant No. 2012ZX07105002-03).

CE P

TE

References:

[1] G. Crini, Non-conventional low-cost adsorbents for dye removal: a review. Bioresour. Technol. 97 (2006)1061–1085.

AC

[2] V.K. Gupta, Suhas, Application of low-cost adsorbents for dye removal – a review. J Environ. Manag. 90 (2009)2313–2342. [3] T. Y. Mustafa, K.S. Tushar, A. H.M.A. Sharmeen, Dye and its removal from aqueous solution by adsorption: A review. Adv. Colloid and Interface Sci. 209(2014)172-184. [4] T. Robinson, G. McMullan, R. Marchant, P. Nigam, Remediation of dyes in textile effluent: a critical review on current treatment technologies with a proposed alternative. Bioresour. Technol. 77(2001)247–255. [5] M.A.M. Khraisheh, M.A. Al-Ghouti, S.J. Allen, M.N. Ahmad, Effect of OH and silanol 19

ACCEPTED MANUSCRIPT groups in the removal of dyes from aqueous solution using diatomite. Water Res. 39(2005)922–932.

IP

T

[6] D. Ghosh, K.G. Bhattacharyya, Adsorption of methylene blue on kaolinite. Applied Clay

SC R

Sci. 20(2002)295– 300.

[7] M. Dogan, Y. Ozdemir, M. Alkan, Adsorption kinetics and mechanism of cationic methyl

NU

violet and methylene blue dyes onto sepiolite. Dyes and Pigments 75(2007)701-713. [8] C.A.P. Almeida, N.A. Debacher, A.J. Downs, L. Cottet, C.A.D. Mello, Removal of

Interface Sci. 332(2009)46–53.

MA

methylene blue from colored effluents by adsorption on montmorillonite clay. J. Colloid

TE

D

[9] T. Yao, S. Guo, C.F. Zeng, C.Q. Wang, L.X. Zhang, Investigation on efficient adsorption of cationic dyes on porous magnetic polyacrylamide microspheres. J. Hazard. Mater.

CE P

292(2015)90-97.

[10] Z.H. Chen, J.N. Zhang, J.W. Fu, M.H. Wang, X.Z. Wang, R.P. Han, Q. Xu, Adsorption of

AC

methylene blue onto poly (cyclotriphosphazene-co-4,4′-sulfonyldiphenol)nanotubes: Kinetics, isotherm and thermodynamics analysis. J. Hazard. Mater. 273(2014)263-271. [11] C. Kannan, K. Muthuraja, M.R. Devi, Hazardous dyes removal from aqueous solution over mesoporous aluminophosphate with textural porosity by adsorption. J. Hazard. Mater. 244–245(2013)10-20. [12] R.P. Han, Y. Wang, W.H. Zou, Y.F. Wang, J. Shi, Comparison of linear and nonlinear analysis in estimating the Thomas model parameters for methylene blue adsorption onto natural zeolite in fixed-bed column. J. Hazard. Mater. 145(2007)331–335. 20

ACCEPTED MANUSCRIPT [13] S.B. Wang, H.T. Li, L.Y. Xu, Application of zeolite MCM-22 for basic dye removal from wastewater. J. Colloid Interface Sci. 295(2006)71–78.

IP

T

[14] R.P. Han, J.J. Zhang, H. Pan, Y.F. Wang, Z.H. Zhao, M.S. Tang, Study of equilibrium,

zeolite. Chem. Engin. J. 145(2009)496–504.

SC R

kinetic and thermodynamic parameters about methylene blue adsorption onto natural

NU

[15] Wang SB, Zhu ZH, Characterisation and environmental application of an Australian natural zeolite for basic dye removal from aqueous solution. J. Hazard. Mater. 136:946–952(2006).

MA

[16] S.B. Wang, H.T. Li, S.J. Xie, S.L. Liu, L.Y. Xu, Physical and chemical regeneration of zeolitic adsorbents for dye removal in wastewater treatment. Chemosphere 65(2006)82–87.

TE

D

[17] W.T. Tsai, K.J. Hsien, H.C. Hsu, Adsorption of organic compounds from aqueous solution onto the synthesized zeolite. J. Hazard. Mater. 166(2009)635-641.

CE P

[18] X.Y. Jin, M.Q. Jiang, X.Q. Shan, Z.G. Pei, Z.L. Chen, Adsorption of methylene blue and orange II onto unmodified and surfactant-modified zeolite. J. Colloid Interface Sci.

AC

32(2008)243-247.

[19] K. Rida, S. Bouraoui, S. Hadnine, Adsorption of methylene blue from aqueous solution by kaolin and zeolite. Applied Clay Sci. 83–84 (2013) 99–105. [20] N. Sapawe, A.A. Jalil, S. Triwahyono, M.I.A. Shah, R. Jusoh, N.F.M. Salleh, B.H. Hameed, A.H. Karim, Cost-effective microwave rapid synthesis of zeolite NaA for removal of methylene blue. Chem. Engin. J. 229 (2013) 388–398. [21] M. Shirani, A. Semnani, H. Haddadi, S. Habibollahi, Optimization of Simultaneous Removal of Methylene Blue, Crystal Violet, and Fuchsine from Aqueous Solutions by 21

ACCEPTED MANUSCRIPT Magnetic NaY Zeolite Composite. Water Air Soil Pollut. 225(2014)2054-2069. [22]

C.X. Li, H. Zhong, S. Wang, J.R. Xue, Z.Y. Zhang, Removal of basic dye (methylene blue)

IP

T

from aqueous solution using zeolite synthesized from electrolytic manganese residue. J.

SC R

Ind. Engin. Chem. 23 (2015) 344–352.

[23] X. Querol, N. Moreno, J.C. Uma˜na, A. Alastuey, E. Hern´andez, A. L´opez-Soler, F. Plana,

NU

Synthesis of zeolites from coal fly ash: an overview, Int. J. Coal Geol. 50 (2002) 413–423. [24] N. Murayama, T. Takahashi, K. Shuku, H. Lee, J. Shibata. Effect of reaction temperature

MA

on hydrothermal syntheses of potassium type zeolites from coal fly ash. Int. J. Miner. Proc. 87(2008)129-133.

TE

D

[25] I. Majchrzak-Kucęba, W. Nowak, Characterization of MCM-41 mesoporous materials derived from polish fly ashes. Int. J. Miner. Proc. 101(2011)100-111.

CE P

[26] R. Sommerville, R. Blissett, N. Rowson, S. Blackburn, Producing a synthetic zeolite from improved fly ash residue. Int. J. Miner. Proc. 124(2013)20-25.

AC

[27] G. Itskos, A. Koutsianos, N. Koukouzas, C. Vasilatos, Zeolite development from fly ash and utilization in lignite mine-water treatment. Int. J. Miner. Proc. 139(2015)43-50. [28] S.S. Bukhari, J. Behin, H. Kazemian, S. Rohani, Conversion of coal fly ash to zeolite utilizing microwave and ultrasound energies: A review. Fuel, 140(2015)250-266. [29] Z. Sun, C.J. Li, D.Y. Wu, Removal ofmethylene blue from aqueous solution by adsorption onto zeolite synthesized from coal fly ash and its thermal regeneration. J. Chem. Technol. Biotechnol. 85(2010)845–850. [30] N．Koukouzas, C. Vasilatos, G. Itskos, I. Mitsis, A. Moutsatsou. Removal of heavy metals 22

ACCEPTED MANUSCRIPT from wastewater using CFB-coal fly ash zeolitic materials. J. Hazard. Mater. 2010(173) 581–588.

IP

T

[31] J. Xie, Z. Wang, D.Y. Wu, Z.J. Zhang, H.N. Kong, Synthesis of Zeolite/aluminum oxide

SC R

hydrate from coal fly ash: a new type of adsorbent for simultaneous removal of cationic and anionic pollutants. Ind. Eng. Chem. Res. 52(2013)14890−14897.

NU

[32] J. Xie, Z. Wang, D. Fang, C.J. Li, D.Y. Wu, Green synthesis of a novel hybrid sorbent of zeolite/lanthanum hydroxide and its application in the removal and recovery of phosphate

MA

from water. J. Colloid Interface Sci. 423 (2014) 13–19. [33] U.S. Department of the Interior, US Geological Survey. Zirconium and Hafnium. In

D

Mineral Commodity Summaries. Washington, DC, 2008, pp192–193.

TE

[34] R.H. Nielsen, G. Wilfing, Zirconium and Zirconium Compounds. In Ullmann's

CE P

Encyclopedia of Industrial Chemistry; Wiley-VCH: Weinheim 2005; pp753-776. [35] H.A. Schroeder, J.J. Balassa, Abnormal trace materials in man: Zirconium. J. Chronic Dis.

AC

19(1966)573–586.

[36] K.S.W. Sing, D.H. Everett, R.A.W. Haul, L. Moscow, R.A. Pierotti, J. Rouquerol, T. Siemieniewska, Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity. Pure Appl. Chem. 57(1985)603-619. [37] M. Jang, S.H. Min, T.H. Kim, J.K. Park, Removal of arsenite and arsenate using hydrous ferric oxide incorporated into naturally occurring porous diatomite. Environ. Sci. Technol. 40(2006)1636-1643. [38] A. Hofmann, M. Pelletier, L. Michot, A. Stradner, P. Schurtenberger, R. Kretzschmar, 23

ACCEPTED MANUSCRIPT Characterization of the pores in hydrous ferric oxide aggregates formed by freezing and thawing. J. Colloid Interface Sci. 271(2004)163-173.

IP

T

[39] W.J. Wang, J. Zhou, D. Wei, H.Q. Wan, S.R. Zheng, Z.Y. Xu, D.Q. Zhu,

Colloid Interface Sci. 407 (2013) 442–449.

SC R

ZrO2-functionalized magnetic mesoporous SiO2 as effective phosphate adsorbent. J.

NU

[40] Y.S. Ho, G. Mckay, Kinetic of sorption of basic dyes from aqueous solution by sphagnum moss peat. Can. J. Chem. Eng. 76(1998)822–827.

MA

[41] Y. Su, H. Cui, Q. Li, S.A. Gao, J.K. Shang, Strong adsorption of phosphate by amorphous zirconium oxide nanoparticles. Water Res. 47(2013)5018–5026.

TE

D

[42] G.A. Parks, P.L. de Bruyn, The zero point of charge of oxides. J. Phys. Chem. 66(1962) 967–972.

CE P

[43] L. Lijklema, Interaction of Orthophosphate with Iron( 111) and Aluminum Hydroxides, Environ. Sci. Technol. 14(1980)537–541.

AC

[44] D. Ghosh, K.G. Bhattacharyya. Adsorption of methylene blue on kaolinite. Applied Clay Sci. 20 (2002) 295– 300. [45] M.A.M. Khraisheh, M.A. Al-Ghouti, S.J. Allen, M.N. Ahmad. Effect of OH and silanol groups in the removal of dyes from aqueous solution using diatomite. Water Res. 39 (2005) 922–932.

24

SC R

IP

T

ACCEPTED MANUSCRIPT

CFA

ZFA

SiO2

48.00

38.67

Al2O3

38.05

34.19

16.18

20.89

Fe2O3

2.90

2.77

17.60

1.58

CaO

2.32

2.42

1.12

1.32

MgO

0.67

0.75

0.38

0.47

Na2O

0.47

D

8.41

8.80

7.02

TE

Table 1. Chemical composition of materials (%).

1.55

0.66

0.42

0.34

1.64

1.34

0.73

0.86

ZrO2

N.D.a)

N.D.

0.08

25.54

HfO

N.D.

N.D.

0.00

0.49

SO3

0.58

0.04

0.13

0.09

Cl

0.08

N.D.

4.70

2.72

LOIb)

3.18

10.49

25.53

12.26

Others

0.56

0.29

0.09

0.08

K2O

AC

CE P

TiO2

a) not determined b)

ZFA/HIO ZFA/HZ 24.24

NU

MA

Item

Loss on ignition at 1000oC

25

26.34

ACCEPTED MANUSCRIPT

T

Table 2. Parameters of kinetic models of MB adsorption on materials studied. Pseudo-first order

Pseudo-second order

Material

K1

qe

-1

IP

True qe

K2

r2

(mg/g)

(min )

(mg/g)

ZFA/HZ

238

80.02

0.012

10.88

ZFA/HIO

238

77.57

0.011

33.00

ZFA

238

37.69

0.010

43.00

-1

qe

r2

(g mg min )

(mg/g)

0.9832

0.0063

80.12

0.9999

0.8979

0.0022

77.88

0.9998

0.0006

38.66

0.9944

NU

(mg/l)

-1

SC R

Co

MA

0.8998

TE

D

Table 3. The constants of the Langmuir and Freundlich models, the calculated maximum adsorption capacity.

pH

Qmax

KL

18.94

0.157

71.43

11.0

ZFA/HZ

ZFA

Freundlich r2

r2

KF

1/n

0.9902

5.622

0.251

0.9417

0.181

0.9997

23.529

0.196

0.8126

156.25

0.126

0.9993

28.589

0.342

0.9154

5.0

17.82

0.017

0.9862

1.581

0.386

0.9692

8.0

80.64

0.288

0.9996

22.782

0.241

0.8228

11.0

222.76

0.033

0.9938

24.121

0.349

0.9361

5.0

38.61

0.036

0.9697

10.544

0.208

0.9463

8.0

42.19

0.190

0.9969

20.720

0.133

0.8877

11.0

79.36

0.082

0.9961

18.651

0.267

0.9835

5.0 8.0

AC

ZFA/HIO

CE P

Langmuir

Material

26

SC R

IP

T

ACCEPTED MANUSCRIPT

Table 4. Lists of the MB adsorption maxima of various zeolites in literatures Temperature

Adsorptive capacity*

Kind of zeolite material o

(mg/g)

NU

( C)

16.37

Han et al. (2009)14

19.36

Wang and Zhu (2006)15

30

51.19

Wang et al. (2006)16

25

16.86

Tsai et al. (2009)17

25

8.67

Jin et al. (2009)18

room

22.00

Rida et al. (2013)19

30

64.80

Sapawe et al. (2013)20

50

2.05

Shilani et al. (2014)21

30–40

34.97–39.12

Li et al. (2015)22

20

37.04–50.51

Sun et al. (2010)25

25

Natural zeolite (Australia)

30

MA

Natural zeolite (China)

MCM–22 (purely synthesized)

D

Zeolite–P2 (purely synthesized)

Zeolite 4A (commercial)

TE

ZMS–5 (commercial)

CE P

Zeolite NaA (purely synthesized) Zeolite NaY (commercial)

Reference

Zeolite synthesized from electrolytic

AC

manganese residue

Zeolite synthesized from coal fly ash *

Calculated from Langmuir model (for the two natural zeolites and MCM–22) or based on the adsorption

data at the highest initial MB concentration used (for ZMS–5, zeolite 4A and zeolite–P2).

27

SC R

IP

T

ACCEPTED MANUSCRIPT

Table 5. The adsorption of MB of the fresh and regenerated ZFA/HIO and ZFA/HZ.

Amount pH

NU

ZFA/HIO

Removal

MA

adsorbed

(mg/g)

Heated once

9.39

Heated twice

7.19

Heated four times

pH

Removal adsorbed

(mg/g)

(%)

45.27

96.77

10.02

44.83

97.54

45.88

98.08

8.97

41.72

81.39

40.02

87.06

6.28

31.42

61.28

33.08

64.53

8.63 a)

38.51

78.69

4.05

29.41

57.73

8.85 a)

38.16

77.97

7.71 a)

39.69

81.09

12.07 a)

47.70

97.50

11.20 a)

46.35

94.71

11.20 a)

45.09

91.17

6.67

CE P

Heated three times

Amount

(%)

D

9.85

TE

Unheated

ZFA/HZ

Heated five times for ZFA/HIO

AC

and four times for ZFA/HZ

Five times heated for ZFA/HIO and four times for ZFA/HZ a)

pH artificially adjusted;

28

CE P

TE

D

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

AC

Fig 1. XRD patterns of materials. ◆:quartz; ♥: mullite; ♣: NaP1 zeolite.

29

SC R

IP

T

ACCEPTED MANUSCRIPT

(b)

(d)

AC

CE P

c)

TE

D

MA

NU

(a)

(e)

(f)

Fig. 2. SEM images of CFA (a), ZFA (b), ZFA/HIO(c), hydrous iron oxide (d), ZFA/ HZ (e) and hydrous zirconia (f).

30

T

ACCEPTED MANUSCRIPT

IP

250

SC R

ZFA/HIO adsorption ZFA/HIO desorption ZFA/HZ adsorption ZFA/HZ desorption

200 150

NU

100 50 0 0.0

MA

3

Volume adsorbed (cm /g STP)

300

0.2

0.4

0.6

0.8

1.0

p/p0

CE P

TE

D

Fig 3. N2 adsorption/desorption isotherm of ZFA/HIO and ZFA/HZ.

0.030

AC

Pore volume (cm /(gnm))

0.035

0.025

3

ZFA/HIO ZFA/HZ

0.020 0.015 0.010 0.005 0

2

4

6

8 10 12 14 Pore Radius(nm)

16

18

20

Fig. 4. Pore size distribution of ZFA/HIO and ZFA/HZ.

31

AC

CE P

TE

D

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

Fig. 5. Acid (upper) and base (lower) neutralizing capacity curves of the investigated materials.

32

SC R

IP

T

ACCEPTED MANUSCRIPT

NU

90 80

MA

70 60 50

D

40 30 0

200

400

CE P

20

ZFA/HIO ZFA/HZ ZFA

TE

percentage removal of MB (%)

100

600 800 1000 1200 1400 Time (min)

Fig. 6. Removal efficiency of MB by ZFA/HIO, ZFA/HZ and ZFA as a function of time. Initial MB

AC

concentration 250 mg/L; adsorbent dosage 5 g/L; pH not adjusted (~8.0).

33

AC

CE P

TE

D

MA

NU

SC R

IP

T

ACCEPTED MANUSCRIPT

Fig. 7. Adsorption isothermal curve of ZFA/HIO, ZFA/HZ and ZFA. Adsorption time 4 h; adsorbent dosage 5 g/L.

34

SC R

IP

T

ACCEPTED MANUSCRIPT

NU MA

80 60

20

4

5

CE P

0

ZFA/HIO ZFA/HZ ZFA

D

40

TE

Percentage removal of MB (%)

100

6

7

8

9

10

11

12

pH

AC

Fig. 8. Removal of MB by ZFA/HIO, ZFA/HZ and ZFA as a function of pH value. Initial MB concentration 250 mg/L; adsorbent dosage 5 g/L; adsorption time 4 h.

35

IP

T

ACCEPTED MANUSCRIPT

140

NU

120 100 80

40 20 0

2

4 6 8 10 Dosage of adsorbent (g/L)

80 60

20

12

0 14

TE

0

100

40

MA

60

D

Amount of MB adsorbed (mg/g)

160

pecentage of MB removed (%)

SC R

180

CE P

Fig. 9. Influence of adsorbent dosage on the adsorption of MB. Solid symbols: removal efficiency; open symbols: amount adsorbed. Circle: ZFA/HZ; square: ZFA/HIO; triangle: ZFA. Initial MB concentration 250

AC

mg/L; adsorption time 4 h; pH 11.0.

36

ACCEPTED MANUSCRIPT

Highlights

Hybrid materials of zeolite/hydrous metal oxides were prepared from coal fly ash.



The materials showed high adsorption ability for the removal of methylene blue.



Adsorption of methylene blue increased with increasing pH.



Adsorption was very fast and removal efficiency reached ~100% at suitable doses.



Heating plus pH adjustment was viable to regenerate the materials for further use.

AC

CE P

TE

D

MA

NU

SC R

IP

T



37