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Preparation of a Novel Coal Gangue–Polyacrylamide Hybrid Flocculant and Its Flocculation Performance
Chinese Journal of Chemical Engineering 22 (2014) 1055–1060
Contents lists available at ScienceDirect
Chinese Journal of Chemical Engineering journal homepage: www.elsevier.com/locate/CJCHE
Materials and Product Engineering
Preparation of a Novel Coal Gangue–Polyacrylamide Hybrid Flocculant and Its Flocculation Performance☆ Xiangao Quan, Huiyun Wang ⁎ School of Pharmaceutical Science, Jining Medical University, Shandong 276826, China
a r t i c l e
i n f o
Article history: Received 21 August 2013 Received in revised form 24 February 2014 Accepted 31 March 2014 Available online 1 July 2014 Keywords: Hybrid flocculant Polyacrylamide Coal gangue Intrinsic viscosity
a b s t r a c t A novel flocculant based on hybrid coal gangue–polyacrylamide (HCGPAM) has been prepared by using modified coal gangue and polyacrylamide. Factors related to the preparation such as reaction time, temperature, concentration of the polymer monomer and ratio of initiators are investigated. The product is characterized by infrared spectra (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), as well as viscometry. The flocculating tests on oilfield drilling wastewater show that the removal efficiency is 85.5% and the light transmittance is 53.6%. The results indicate that the coal gangue could be used for the preparation of inorganic–organic hybrid flocculant and the removal efficiency is much higher than that of commercial polyacrylamide (PAM) or PAM/ coal gangue blend. © 2014 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.
1. Introduction As is known to all, flocculation is an efficient and cost-effective method for natural water and wastewater treatment [1–3]. Various flocculants have been developed for the coagulation and flocculation purposes over the last decades, especially inorganic-based coagulants [4], organic-based flocculants [5] and organic–inorganic hybrid flocculant [6,7]. And the novel hybrid flocculation system has attracted great interest from researchers in recent years [6–16]. The organic–inorganic hybrid flocculants are products composed of two or more different types of components [11], such as inorganic salts/polymer flocculants [6], inorganic flocculants/polymer flocculants [7] and microparticle/polymer flocculants [8,14–16]. It is reported that the microparticle systems give better flocculation and drainage than conventional polymer flocculation systems [17,18]. Up to date, several kinds of microparticle/polymer flocculation systems have been prepared by using inorganic solid particles with high specific area and polymer monomer [8,14–16]. However, to the best of our knowledge, little has been reported on producing organic–inorganic hybrid flocculant with coal gangue particles. Coal gangue (CG), a by-product from the coal mining or coal washing, has become the largest solid waste and has increased every year as the coal industry expands [19,20]. And such a large quantity of this solid waste will invade large area of farmland and cause water or soil pollution without treatment [19]. Therefore, disposal of the coal gangue ☆ Supported by the National Key Technology R&D Program during the “11th Five-Year Plan” period (2008BAC43B02). ⁎ Corresponding author. E-mail address: [email protected] (H. Wang).
becomes an increasing environmental, even economic problem. At present, the beneficial utilization of coal gangue includes power generation [21], construction material [22–27] and other places [28]. However, the utilization efficiency of the coal gangue remains much lower [29, 30]. Coal gangue contains large amount of valuable mineral resources such as SiO2, Al2O3, Fe2O3 and CaO. Some researchers have made attempts to prepare inorganic flocculant by coal gangue [31,32]. In these attempts, it is also observed that the solid waste has extremely high specific surface area after being calcined, and leached by alkali and acid, and shows a potential application as raw material for preparation of organic–inorganic hybrid flocculant. In this work, a new hybrid coal gangue–polyacrylamide (HCGPAM) flocculant is synthesized based on coal gangue through in situ polymerization for inorganic flocculant/AM (acrylamide) mixture. The flocculation effect on oilfield drilling wastewater is investigated and its flocculation efficiency is much higher than that of commercial polyacrylamide (PAM) or PAM/coal gangue blend. It is shown that coal gangue can be used as a material for preparation of inorganic–organic hybrid flocculant, which is beneficial both for environment and economy. 2. Materials and Methods 2.1. Materials The coal gangue used in this study was obtained from a coal mine (Yanzhou Mining Bureau, China) with the mass composition of SiO2 26.58%, Al2O3 5.35%, Fe2O3 14.38%, CaO 3.56% and MgO 1.26%. The waste drilling fluid was supplied by Shengli Oil Field of China. COD of the waste drilling fluid was 2.34 × 104 mg·L−1 with a pH value of 11.6.
http://dx.doi.org/10.1016/j.cjche.2014.06.032 1004-9541/© 2014 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.
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2.2.1.1. Modification of coal gangue. The coal gangue was crushed into powder with an LG 500 crusher and sieved with a 100 mesh screen. Sodium carbonate was added into the coal gangue powder at a mass ratio of 6:5, followed by thorough grinding and blending. Then, the mixture was calcined in the muffle furnace at 750 °C for 2 h. After cooling to room temperature, the coal gangue was subject to alkali leaching with 15% sodium hydroxide and acid leaching with 15% hydrochloric acid under the condition of 100 °C and 5 MPa. The leaching mother liquor and the washing liquor were used to prepare the inorganic polymer flocculant and polysilicate ferro-aluminum sulfate (PSFA) in our previous work [32]. The leached solid was dried at 100 °C after being washed with distilled water, which was used to prepare the coal gangue–polyacrylamide hybrid flocculant.
Fig. 1. FTIR spectra of (a) modified coal gangue, (b) PAM and (c) HCGPAM.
intensity
intensity
Commercial available polyacrylamide (PAM) was purchased from a water treatment agent factory (Henan Gongyi, China). All the chemical reagents were of analytic grade and supplied by Shanghai Chemistry Reagent Co. Ltd. Distilled water was used to prepare all the solutions.
2.2.1.2. Preparation of coal gangue–polyacrylamide hybrid. First, 8 g of acrylamide (AM) and 90 ml of distilled water were added to a 250 ml polymerization bottle. Then, 3 g of modified coal gangue powder was added to above solution under stirring for 30 min. After being vacuumized, the solution was purged with N2 for 3 times to remove the oxygen completely, and different amounts of (NH4)2Ce(NO3)6 as the initiator were injected into the polymerization bottle slowly. After
(b) Calcined coal gangue
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(c) Leached coal gangue
(d) HCGPAM Fig. 2. XRD patterns of the samples.
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that, the bottle was kept in the thermostated water bath at 75 °C (± 0.5 °C) for 6 h. The solution in the polymerization bottle was transferred to a 250 mL beaker and precipitated with acetone, and immersed in acetone for 12 h. It is finally dried in a vacuum oven at 35 °C for 24 h. 2.2.2. Characterization of HCGPAM 2.2.2.1. Intrinsic viscosity [η]. The intrinsic viscosity measurement was conducted by using an Ubbelohde viscometer after the hybrid flocculant was being dispersed in distilled water at (30 ± 0.02) °C. Flux-times were recorded with an accuracy of ± 0.05 s. Intrinsic viscosity [13] was obtained by extrapolation according to the following formula:
(a) Coal gangue 2
ηsp =c¼½η þ kH ½η c
ð1Þ
where c is the concentration of the solution, ηsp is the specific viscosity of the solution, and kH is the Huggins coefficient. 2.2.2.2. FTIR spectroscopy. The samples of HAPAM, PAM, modified coal gangue powder, and HCGPAM were analyzed by an FTIR spectrophotometer (IR Prestige-21, Japan) and potassium bromide pellet method. The spectra were recorded in the range of 4000–400 cm−1. 2.2.2.3. XRD measurement. Powder X-ray diffraction (XRD) patterns were recorded on an X-ray diffractometer (D/MAX-2500, Japan) with Cu K radiation in the 2θ range of 5°–65° at a scan rate of 4° per minute. The structure and layer spacing of samples were calculated by Bragg equation.
(b) Modified coal gangue
2.2.2.4. Scanning electron microscopy measurement. Scanning electron microscopy (TXA-840, Japan) was used to investigate the structure and morphology of modified coal gangue and HCGPAM. 2.2.3. Flocculation experiments for HCGPAM Flocculation experiments were performed on drilling wastewater. All flocculation tests were conducted in 1.0 L beakers using a six-unit stirring system. 500 ml of test sample was placed in a beaker and adjusted to a pH of 3–4 with diluted HCl. It was stirred at 100 r·min−1 for 1 min after adding the flocculant at room temperature, followed by slowly stirring at 50 r·min−1 for 5 min and precipitating for 1 h. After that, supernatant sample was taken 2.0 cm below the surface of test wastewater for transmittance measurement on a T1901 ultraviolet–visible spectrophotometer at 520 nm, and for chemical oxygen demand (COD) measurement by CODcr analysis method (GB/T11914-1989, China).
(c) HCGPAM Fig. 3. SEM micrographs.
3. Results and Discussion 3.1. FTIR, XRD and SEM analyses
vibration of Si\O and Al\O which are belonged to the coal gangue. These results indicate that the HCGPAM is an organic–inorganic hybrid.
3.1.1. FTIR analysis Fig. 1 presents the FTIR spectra of modified coal gangue, PAM and the hybrid flocculant. In Fig. 1(a) and (b), the band at 800–1200 cm−1 is attributed to Si\O stretching vibrations, and the broad band at 3400 cm−1 and 3200 cm−1 is due to the stretching mode of the free \NH2 and the aggregated \NH2 bond in the PAM. The band at 1650 cm−1 is assigned to the first overtone of N\H bending vibration. The bands at 1140 cm−1 and 3000 cm−1 are assigned to C\O stretching and C\H stretching, respectively. The band at 1400 cm−1 is due to C\N stretching vibration and the band at 1700 cm−1 is assigned to the C_O stretching vibrations. Fig. 1(c) shows that the IR spectra of HCGPAM display almost the same characteristic bands as pure PAM except for the nuances of 800, 700 and 560 cm−1. The band at 800–1200 cm−1 is attributed to Si\O stretching vibrations and the band at 700 and 560 cm−1 is assigned to the bending
3.1.2. XRD analysis Fig. 2 shows the XRD spectra of coal gangue, calcined coal gangue, leached coal gangue and HCGPAM. The XRD patterns of coal gangue in Fig. 2(a) show that the major mineralogical composition of raw coal gangue is quartz, kaolinite and muscovite. By comparison, it is found that the diffraction intensities of muscovite and kaolinite reduce and the diffraction intensities of quartz phase increase after being calcined at high temperature. This might be caused by the decomposition of kaolinite and muscovite at 750 °C [33,34] in Fig. 2(b). When the coal gangue is being calcined, the burning of the coal increases the relative content of quartz. The diffraction intensity of quartz further increases evidently and the peak of muscovite and kaolinite vanishes completely in Fig. 2(c). It could be attributed to the reactions of the components (SiO2, Al2O3, Fe2O3, CaO, MgO) in the coal gangue with acid and alkali, which
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Fig. 4. Dependence of intrinsic viscosity of HCGPAM on mass fraction of (a) AM, (b) initiator concentration, (c) reaction time and (d) reaction temperature.
increase the relative content and porosity of quartz remarkably. Fig. 2(d) is the XRD pattern for the hybrid flocculant. It is observed that the characteristic peaks of quartz in the leached coal gangue decrease in intensity or even disappeared, whereas the characteristic peaks of PAM become more evident. This result indicates that the PAM has entered the interlayer spacing of the coal gangue. Compared to pure coal gangue, the diffraction peaks of the hybrids shift to lower diffraction angles slightly. It is also proved that PAM intercalates coal gangue successfully.
increases from 1.0% to 8.0% with an increase of acrylamide mass fraction, but decreases with a further increase. Within the range of AM mass fraction from 1.0% to 8.0%, the increase in intrinsic viscosity may be due to an increase of the crosslinking reaction and molecular mass
3.1.3. SEM analysis The morphologies of the coal gangue, modified coal gangue and HCGPAM are observed by SEM, and the results are presented in Fig. 3. The modified coal gangue has obvious gap, extremely high specific surface area, and shows a potential application as raw material for preparation of organic–inorganic hybrid flocculant. It is obvious that HCGPAM displays a very different surface morphology from modified coal gangue. The surface of HCGPAM consists of certain sorts of cauliflower head with a series of pleated ditches of different widths and depths, which makes it possess much coarser surface and larger specific surface area than modified coal gangue. It can be inferred that HCGPAM is favorable for combining with pollutants. 3.2. Effect of synthesis conditions on intrinsic viscosity of HCGPAM 3.2.1. Effect of acrylamide mass fraction on intrinsic viscosity The effect of the mass fraction of AM on the intrinsic viscosity of HCGPAM is shown in Fig. 4(a). The mass fraction of initiator, reaction of temperature and reaction time are 2.5%, 75 °C and 6 h, respectively. In Fig. 4(a), it can be seen that the intrinsic viscosity of the HCGPAM
Fig. 5. Comparison of the flocculation performances, modified coal gangue (a), PAM (b), HCGPAM (c) and PAM/modified coal gangue blend (d).
X. Quan, H. Wang / Chinese Journal of Chemical Engineering 22 (2014) 1055–1060 Table 1 Light transmittance and COD removal efficiency of the HCGPAM, PAM, modified coal gangue and PAM/modified coal gangue blend
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COD removal efficiency/%
Modified coal gangue PAM HCGPAM Mixture (PAM and modified coal gangue)
Can't be measured Can't be measured 53.6% Can't be measured
4.3 5.2 85.5 4.6
of HCGPAM, which improves the absorbing and bridging capability. However, further increase in acrylamide mass fraction may cause a rapid rise in temperature and the polymerization reaction rate, which would lead to the increase in the extent of chain transfer to the polymer in free radical solution polymerization with the increase of the AM concentration. Thus, the optimized AM mass fraction (8.0%) is suitable for the production of HCGPAM.
COD removal efficiency/%
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Fig. 7. COD removal efficiency of drilling wastewater in coagulation process.
3.2.2. Effect of initiator concentration on intrinsic viscosity Ce(NH4)2(NO3)6 was used as an initiator for the reaction system. The effect of the initiator concentration on the intrinsic viscosity of the HCGPAM was studied with varying concentrations of the initiator (from 1.0% to 7.0%) and reaction time of 6 h with a fixed acrylamide mass fraction 8% at 75 °C [Fig. 4(b)]. In Fig. 4(b), it can be seen that the intrinsic viscosity increases as the Ce(NH4)2(NO3)6 concentration increases from 0.5% to 2.5%, but decreases with further increases in the Ce(NH4)2(NO3)6 concentration. The increasing concentration of the initiator leads to the increase of free radical concentration, thereafter the degree of polymerization. However, when the concentration of the initiator is higher than 2.5%, the intrinsic viscosity will decrease. The possible explanation is that the excessive initiator leads to the rate of termination free radicals and chain transfer, thus resulting in a decrease in the intrinsic viscosity. Therefore, the initiator concentration of 2.5% is optimal in the preparation of HCGPAM according to the experimental results.
3.2.4. Effect of reaction temperature on intrinsic viscosity The effect of reaction temperature on intrinsic viscosity was investigated with varying reaction temperatures from 40 °C to 80 °C, following 6 h reaction time with initiator concentration of 2.5% and acrylamide mass fraction of 8.0%. The results are shown in Fig. 4(d). It can be seen that the intrinsic viscosity increases as the reaction temperature increases from 40 °C to 75 °C, reaching a maximum value at 75 °C, but decreases thereafter. As the reaction temperature increases, the reaction efficiency and the molecule weight of the reaction product increase. Thus, the intrinsic viscosity is improved. The decrease in intrinsic viscosity at temperatures higher than 75 °C can be explained according to the general rules for free radical polymerization: a further increase in temperature may accelerate the decomposition and consumption of the initiators markedly, resulting in the lack of sufficient initiators to sustain the corresponding polymerization reaction [22]. 3.3. Flocculation study
3.2.3. Effect of reaction time on intrinsic viscosity Reaction times from 1 h to 8 h were selected to study the effect of reaction time on the intrinsic viscosity of HCGPAM [Fig. 4(c)]. The mass fraction of AM, mass fraction of initiator and reaction of temperature were 8.0%, 2.5% and 75 °C, respectively. Fig. 4(c) shows that the intrinsic viscosity increases with increasing reaction time between 2 h and 6 h, but decreases with further increase in reaction time. This indicates that the optimum reaction time for preparation of HCGPAM is 6 h.
Fig. 6. Microstructure of floc formed by HCGPAM (magnified 4000 times).
3.3.1. Evaluation of the flocculation performance To evaluate the capability of treating drilling wastewater for HCGPAM, a comparative study of flocculation performance on modified coal gangue, PAM, HCGPAM and PAM/modified coal gangue blend was conducted. The dosage for each of the four samples was 1.0 mg·ml−1. The drilling wastewater was diluted 2 times at pH 4.0. The results are shown in Fig. 5 and Table 1. It can be seen that the COD removal efficiency of the HCGPAM is much higher than that of any other three samples. And the flocculation rate of HCGPAM is found to be very high during the initial 3 min and the rising velocity of the flocs is about 0.21 cm·s−1. However, there is no distinct flocculating performance occurred with the same amount of PAM, modified coal gangue and PAM/modified coal gangue blend within 30 min. Moreover, the flocs formed by HCGPAM have much higher density, which does not re-disperse even at stirring of 100 r·min−1 for 2 min. The microstructure of the floc is shown in Fig. 6. Flocs formed by HCGPAM are very dense, tightly wrapped together and hard to disperse. The structure of floc does not make long chain of polyacrylamide to stretch fully, while to furl particles of sewage. The results indicate that HCGPAM is a strong and effective flocculant for drilling wastewater. 3.3.2. Effect of HCGPAM dosage on flocculating capability The effect of HCGPAM dosage on flocculation capability is studied with varying HCGPAM dosages from 0.2 to 2.5 mg·ml− 1 in drilling wastewater at pH 4.0 (Fig. 7). It can be observed that the COD removal efficiency increases with the increasing dosage of HCGPAM and reaches a maximum at
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2.0 mg·ml− 1, and thereafter, forms a plateau beyond 2.0 mg·ml− 1. This might be attributed to the content of suspended colloids in the drilling wastewater [6] and the increasing viscosity caused by the excessive dosage of the hybrid flocculant. 4. Conclusions A novel coal gangue–polyacrylamide hybrid flocculant (HCGPAM) has been synthesized by free radical aqueous polymerization of acrylamide in coal gangue suspended solution. And the optimal synthesis conditions are obtained: reaction time of 6 h, polymerization temperature at 75 °C, mass fraction of AM with 8%, and mass fraction of initiator with 2.5%. HCGPAM exhibits much higher flocculating capability in drilling wastewater than PAM or PAM/modified coal gangue blend with the same dosage at room temperature. When the dosage of HCGPAM is 2.0 mg·ml−1 with a stirring rate of 100 r·min−1 and a stirring time of 1 min, the COD removal efficiency can reach 85.5%. References [1] M.I. Aguilar, J. Saez, M. Llorens, A. Soler, J.F. Ortuno, Microscopic observation of particle reduction in slaughterhouse wastewater by coagulation–flocculation using ferric sulphate as coagulant and different coagulant aids, Water Res. 37 (2003) 2233–2241. [2] A.L. Ahmad, S. Ismail, S. Bhatia, Optimization of coagulation–flocculation process for palm oil mill effluent using response surface methodology, Environ. Sci. Technol. 39 (2005) 2828–2834. [3] B. Gao, Q. Yue, J. Miao, Evaluation of polyaluminium ferric chloride (PAFC) as a composite coagulant for water and wastewater treatment, Water Sci. Technol. 47 (2003) 127–132. [4] D.S. Wang, W. Sun, Y. Xu, H. Tang, J. Gregory, Speciation stability of inorganic polymer flocculant–PACl, Colloids Surf. A Physicochem. Eng. Asp. 243 (2004) 1–10. [5] Y.C. Ho, I. Norli, F.M. Alkarkhi, N. Morad, Characterization of biopolymeric flocculant (pectin) and organic synthetic flocculant (PAM): A comparative study on treatment and optimization in kaolin suspension, Bioresour. Technol. 101 (2010) 1166–1174. [6] K.E. Lee, T.T. Teng, N. Morad, B.T. Poh, Y.F. Hong, Flocculation of kaolin in water using novel calcium chloride–polyacrylamide (CaCl2–PAM) hybrid polymer, Sep. Purif. Technol. 75 (2010) 346–351. [7] K.E. Lee, T.T. Teng, N. Morad, B.T. Poh, M. Mahalingam, Flocculation activity of novel ferric chloride–polyacrylamide (FeCl3–PAM) hybrid polymer, Desalination 266 (2011) 108–113. [8] J. Zou, H. Zhu, F. Wang, H. Sui, J. Fan, Preparation of a new inorganic–organic composite flocculant used in solid–liquid separation for waste drilling fluid, Chem. Eng. J. 171 (2011) 350–356. [9] N.D. Tzoupanos, A.I. Zouboulis, Preparation, characterisation and application of novel composite coagulants for surface water treatment, Water Res. 45 (2011) 3614–3626. [10] P.A. Moussas, A.I. Zouboulis, A new inorganic–organic composite coagulant, consisting of polyferric sulphate (PFS) and polyacrylamide (PAA), Water Res. 43 (2009) 3511–3524. [11] K.E. Lee, N. Morad, T.T. Teng, B.T. Poh, Development, characterization and the application of hybrid materials in coagulation/flocculation of wastewater: A review, Chem. Eng. J. 203 (2012) 370–386.
[12] K.E. Lee, I. Khan, N. Morad, T.T. Teng, B.T. Poh, Thermal behaviour and morphological properties of novel magnesium salt–polyacrylamide composite polymers, Polym. Compos. 32 (2011) 1515–1522. [13] S.J. Ma, M.L. Fu, F.W. Li, N.F. Wu, J. Yang, H.W. Jia, B. Wang, R. Cheng, Preparation of a new inorganic–organic composite dual-coagulant and application of oily wastewater treatment, Adv. Mater. Res 233–235 (2011) 523–527. [14] S.F. Wang, L. Shen, Y.J. Tong, L. Chen, I.Y. Phang, P.Q. Lim, T.X. Liu, Biopolymer chitosan/montmorillonite nanocomposites: Preparation and characterization, Polym. Degrad. Stab. 90 (2005) 123–131. [15] W.Y. Yang, J.W. Qian, Z.Q. Shen, A novel flocculant of Al(OH)3–polyacrylamide ionic hybrid, J. Colloid Interface Sci. 273 (2004) 400–405. [16] H.L. Wang, J.Y. Cui, W.F. Jiang, Synthesis, characterization and flocculation activity of novel Fe(OH)3–polyacrylamide hybrid polymer, Mater. Chem. Phys. 130 (2011) 993–999. [17] A. Swerin, L. Odberg, L. Wagberg, An extended model for the estimation of flocculation efficiency factors in multicomponent flocculant systems, Colloids Surf. A Physicochem. Eng. Asp. 113 (1996) 25–38. [18] Z.G. Yan, Y.L. Deng, Cationic microparticle based flocculation and retention systems, Chem. Eng. J. 80 (2000) 31–36. [19] D.H. Deng, W.L. Cen, Environmental effect of coal gangue stack area, China Min. Mag. 8 (1999) 87–91. [20] Z.D. Li, Q.L. Zhou, Tailing and gangue: The prosperity resources be recycled, Eng. Sci. 6 (2004) 20–22. [21] Y.P. Chugh, A. Patwardhan, Mine-mouth power and process steam generation using fine coal waste fuel, Resour. Conserv. Recycl. 40 (2004) 225–243. [22] P.F. Zuo, Comprehensive utilization of coal gangue, Coal Technol. 28 (2009) 186–189 (in Chinese). [23] Y.X. Yan, X.F. Wang, X.Q. Wang, Environmental effect and comprehensive utilization of coal-mine waste from Huaibei and Huainan coalfield, J. Anhui Univ. Sci. Technol (Nat. Sci.) 26 (2006) 9–11 (in Chinese with English abstract). [24] J.X. Zhang, H.H. Sun, Y.M. Sun, N. Zhang, Correlation between 29Si polymerization and cementitious activity of coal gangue, J. Zhejiang Univ. Sci. A 10 (2009) 1334–1340. [25] D.X. Li, X.Y. Song, C.C. Gong, Z.H. Pan, Research on cementitious behavior and mechanism of pozzolanic cement with coal gangue, Cem. Concr. Res. 36 (2006) 1752–1759. [26] H.J. Li, H.H. Sun, X.J. Xiao, H.X. Chen, Mechanical properties of gangue-containing aluminosilicate based cementitious materials, J. Univ. Sci. Technol. Beijing 13 (2006) 183–189. [27] X.Y. Song, C.C. Gong, D.X. Li, Study on structural characteristic and mechanical property of coal gangue in activation process, J. Chin. Ceram. Soc. 32 (2004) 358–363. [28] M. Yang, Z.X. Guo, Y.S. Deng, Preparation of CaO–Al2O3–SiO2 glass ceramics from coal gangue, Int. J. Miner. Process. 102–103 (2012) 112–115. [29] US EPA-HQ-RCRA-2008-0329, Materials Characterization Paper in Support of the Advanced Notice of Proposed Rulemaking — Identification of Nonhazardous Materials That Are Solid Waste: Coal Refuse, US EPA, USA, December 16 2008. [30] US EPA-R09-OAR-2012-0398, Materials Characterization Paper in Support of the Final Rulemaking — Identification of Nonhazardous Materials That Are Solid Waste: Coal Refuse, US EPA, USA, February 3 2011. [31] B.Y. Gao, H. Yu, Q.Y. Yue, Study on the preparation of polyaluminum ferric chloride from gangue, Environ. Sci. 17 (1996) 62–63. [32] H.Y. Wang, X.G. Quan, M.J. Shi, Preparation of coal gauge based PSFA and its application to the treatment of drilling wastewater, Ind. Water Treat. 31 (2011) 38–41. [33] H.J. Li, H.H. Sun, Microstructure and cementitious properties of calcined claycontaining gangue, Int. J. Miner. Metall. Mater. 16 (2009) 482–486. [34] C. Li, J. Wan, H. Sun, L. Li, Investigation on the activation of coal gangue by a new compound method, J. Hazard. Mater. 179 (2010) 515–520.
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Chinese Journal of Chemical Engineering journal homepage: www.elsevier.com/locate/CJCHE
Materials and Product Engineering
Preparation of a Novel Coal Gangue–Polyacrylamide Hybrid Flocculant and Its Flocculation Performance☆ Xiangao Quan, Huiyun Wang ⁎ School of Pharmaceutical Science, Jining Medical University, Shandong 276826, China
a r t i c l e
i n f o
Article history: Received 21 August 2013 Received in revised form 24 February 2014 Accepted 31 March 2014 Available online 1 July 2014 Keywords: Hybrid flocculant Polyacrylamide Coal gangue Intrinsic viscosity
a b s t r a c t A novel flocculant based on hybrid coal gangue–polyacrylamide (HCGPAM) has been prepared by using modified coal gangue and polyacrylamide. Factors related to the preparation such as reaction time, temperature, concentration of the polymer monomer and ratio of initiators are investigated. The product is characterized by infrared spectra (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), as well as viscometry. The flocculating tests on oilfield drilling wastewater show that the removal efficiency is 85.5% and the light transmittance is 53.6%. The results indicate that the coal gangue could be used for the preparation of inorganic–organic hybrid flocculant and the removal efficiency is much higher than that of commercial polyacrylamide (PAM) or PAM/ coal gangue blend. © 2014 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.
1. Introduction As is known to all, flocculation is an efficient and cost-effective method for natural water and wastewater treatment [1–3]. Various flocculants have been developed for the coagulation and flocculation purposes over the last decades, especially inorganic-based coagulants [4], organic-based flocculants [5] and organic–inorganic hybrid flocculant [6,7]. And the novel hybrid flocculation system has attracted great interest from researchers in recent years [6–16]. The organic–inorganic hybrid flocculants are products composed of two or more different types of components [11], such as inorganic salts/polymer flocculants [6], inorganic flocculants/polymer flocculants [7] and microparticle/polymer flocculants [8,14–16]. It is reported that the microparticle systems give better flocculation and drainage than conventional polymer flocculation systems [17,18]. Up to date, several kinds of microparticle/polymer flocculation systems have been prepared by using inorganic solid particles with high specific area and polymer monomer [8,14–16]. However, to the best of our knowledge, little has been reported on producing organic–inorganic hybrid flocculant with coal gangue particles. Coal gangue (CG), a by-product from the coal mining or coal washing, has become the largest solid waste and has increased every year as the coal industry expands [19,20]. And such a large quantity of this solid waste will invade large area of farmland and cause water or soil pollution without treatment [19]. Therefore, disposal of the coal gangue ☆ Supported by the National Key Technology R&D Program during the “11th Five-Year Plan” period (2008BAC43B02). ⁎ Corresponding author. E-mail address: [email protected] (H. Wang).
becomes an increasing environmental, even economic problem. At present, the beneficial utilization of coal gangue includes power generation [21], construction material [22–27] and other places [28]. However, the utilization efficiency of the coal gangue remains much lower [29, 30]. Coal gangue contains large amount of valuable mineral resources such as SiO2, Al2O3, Fe2O3 and CaO. Some researchers have made attempts to prepare inorganic flocculant by coal gangue [31,32]. In these attempts, it is also observed that the solid waste has extremely high specific surface area after being calcined, and leached by alkali and acid, and shows a potential application as raw material for preparation of organic–inorganic hybrid flocculant. In this work, a new hybrid coal gangue–polyacrylamide (HCGPAM) flocculant is synthesized based on coal gangue through in situ polymerization for inorganic flocculant/AM (acrylamide) mixture. The flocculation effect on oilfield drilling wastewater is investigated and its flocculation efficiency is much higher than that of commercial polyacrylamide (PAM) or PAM/coal gangue blend. It is shown that coal gangue can be used as a material for preparation of inorganic–organic hybrid flocculant, which is beneficial both for environment and economy. 2. Materials and Methods 2.1. Materials The coal gangue used in this study was obtained from a coal mine (Yanzhou Mining Bureau, China) with the mass composition of SiO2 26.58%, Al2O3 5.35%, Fe2O3 14.38%, CaO 3.56% and MgO 1.26%. The waste drilling fluid was supplied by Shengli Oil Field of China. COD of the waste drilling fluid was 2.34 × 104 mg·L−1 with a pH value of 11.6.
http://dx.doi.org/10.1016/j.cjche.2014.06.032 1004-9541/© 2014 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.
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2.2.1.1. Modification of coal gangue. The coal gangue was crushed into powder with an LG 500 crusher and sieved with a 100 mesh screen. Sodium carbonate was added into the coal gangue powder at a mass ratio of 6:5, followed by thorough grinding and blending. Then, the mixture was calcined in the muffle furnace at 750 °C for 2 h. After cooling to room temperature, the coal gangue was subject to alkali leaching with 15% sodium hydroxide and acid leaching with 15% hydrochloric acid under the condition of 100 °C and 5 MPa. The leaching mother liquor and the washing liquor were used to prepare the inorganic polymer flocculant and polysilicate ferro-aluminum sulfate (PSFA) in our previous work [32]. The leached solid was dried at 100 °C after being washed with distilled water, which was used to prepare the coal gangue–polyacrylamide hybrid flocculant.
Fig. 1. FTIR spectra of (a) modified coal gangue, (b) PAM and (c) HCGPAM.
intensity
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Commercial available polyacrylamide (PAM) was purchased from a water treatment agent factory (Henan Gongyi, China). All the chemical reagents were of analytic grade and supplied by Shanghai Chemistry Reagent Co. Ltd. Distilled water was used to prepare all the solutions.
2.2.1.2. Preparation of coal gangue–polyacrylamide hybrid. First, 8 g of acrylamide (AM) and 90 ml of distilled water were added to a 250 ml polymerization bottle. Then, 3 g of modified coal gangue powder was added to above solution under stirring for 30 min. After being vacuumized, the solution was purged with N2 for 3 times to remove the oxygen completely, and different amounts of (NH4)2Ce(NO3)6 as the initiator were injected into the polymerization bottle slowly. After
(b) Calcined coal gangue
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(d) HCGPAM Fig. 2. XRD patterns of the samples.
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that, the bottle was kept in the thermostated water bath at 75 °C (± 0.5 °C) for 6 h. The solution in the polymerization bottle was transferred to a 250 mL beaker and precipitated with acetone, and immersed in acetone for 12 h. It is finally dried in a vacuum oven at 35 °C for 24 h. 2.2.2. Characterization of HCGPAM 2.2.2.1. Intrinsic viscosity [η]. The intrinsic viscosity measurement was conducted by using an Ubbelohde viscometer after the hybrid flocculant was being dispersed in distilled water at (30 ± 0.02) °C. Flux-times were recorded with an accuracy of ± 0.05 s. Intrinsic viscosity [13] was obtained by extrapolation according to the following formula:
(a) Coal gangue 2
ηsp =c¼½η þ kH ½η c
ð1Þ
where c is the concentration of the solution, ηsp is the specific viscosity of the solution, and kH is the Huggins coefficient. 2.2.2.2. FTIR spectroscopy. The samples of HAPAM, PAM, modified coal gangue powder, and HCGPAM were analyzed by an FTIR spectrophotometer (IR Prestige-21, Japan) and potassium bromide pellet method. The spectra were recorded in the range of 4000–400 cm−1. 2.2.2.3. XRD measurement. Powder X-ray diffraction (XRD) patterns were recorded on an X-ray diffractometer (D/MAX-2500, Japan) with Cu K radiation in the 2θ range of 5°–65° at a scan rate of 4° per minute. The structure and layer spacing of samples were calculated by Bragg equation.
(b) Modified coal gangue
2.2.2.4. Scanning electron microscopy measurement. Scanning electron microscopy (TXA-840, Japan) was used to investigate the structure and morphology of modified coal gangue and HCGPAM. 2.2.3. Flocculation experiments for HCGPAM Flocculation experiments were performed on drilling wastewater. All flocculation tests were conducted in 1.0 L beakers using a six-unit stirring system. 500 ml of test sample was placed in a beaker and adjusted to a pH of 3–4 with diluted HCl. It was stirred at 100 r·min−1 for 1 min after adding the flocculant at room temperature, followed by slowly stirring at 50 r·min−1 for 5 min and precipitating for 1 h. After that, supernatant sample was taken 2.0 cm below the surface of test wastewater for transmittance measurement on a T1901 ultraviolet–visible spectrophotometer at 520 nm, and for chemical oxygen demand (COD) measurement by CODcr analysis method (GB/T11914-1989, China).
(c) HCGPAM Fig. 3. SEM micrographs.
3. Results and Discussion 3.1. FTIR, XRD and SEM analyses
vibration of Si\O and Al\O which are belonged to the coal gangue. These results indicate that the HCGPAM is an organic–inorganic hybrid.
3.1.1. FTIR analysis Fig. 1 presents the FTIR spectra of modified coal gangue, PAM and the hybrid flocculant. In Fig. 1(a) and (b), the band at 800–1200 cm−1 is attributed to Si\O stretching vibrations, and the broad band at 3400 cm−1 and 3200 cm−1 is due to the stretching mode of the free \NH2 and the aggregated \NH2 bond in the PAM. The band at 1650 cm−1 is assigned to the first overtone of N\H bending vibration. The bands at 1140 cm−1 and 3000 cm−1 are assigned to C\O stretching and C\H stretching, respectively. The band at 1400 cm−1 is due to C\N stretching vibration and the band at 1700 cm−1 is assigned to the C_O stretching vibrations. Fig. 1(c) shows that the IR spectra of HCGPAM display almost the same characteristic bands as pure PAM except for the nuances of 800, 700 and 560 cm−1. The band at 800–1200 cm−1 is attributed to Si\O stretching vibrations and the band at 700 and 560 cm−1 is assigned to the bending
3.1.2. XRD analysis Fig. 2 shows the XRD spectra of coal gangue, calcined coal gangue, leached coal gangue and HCGPAM. The XRD patterns of coal gangue in Fig. 2(a) show that the major mineralogical composition of raw coal gangue is quartz, kaolinite and muscovite. By comparison, it is found that the diffraction intensities of muscovite and kaolinite reduce and the diffraction intensities of quartz phase increase after being calcined at high temperature. This might be caused by the decomposition of kaolinite and muscovite at 750 °C [33,34] in Fig. 2(b). When the coal gangue is being calcined, the burning of the coal increases the relative content of quartz. The diffraction intensity of quartz further increases evidently and the peak of muscovite and kaolinite vanishes completely in Fig. 2(c). It could be attributed to the reactions of the components (SiO2, Al2O3, Fe2O3, CaO, MgO) in the coal gangue with acid and alkali, which
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Fig. 4. Dependence of intrinsic viscosity of HCGPAM on mass fraction of (a) AM, (b) initiator concentration, (c) reaction time and (d) reaction temperature.
increase the relative content and porosity of quartz remarkably. Fig. 2(d) is the XRD pattern for the hybrid flocculant. It is observed that the characteristic peaks of quartz in the leached coal gangue decrease in intensity or even disappeared, whereas the characteristic peaks of PAM become more evident. This result indicates that the PAM has entered the interlayer spacing of the coal gangue. Compared to pure coal gangue, the diffraction peaks of the hybrids shift to lower diffraction angles slightly. It is also proved that PAM intercalates coal gangue successfully.
increases from 1.0% to 8.0% with an increase of acrylamide mass fraction, but decreases with a further increase. Within the range of AM mass fraction from 1.0% to 8.0%, the increase in intrinsic viscosity may be due to an increase of the crosslinking reaction and molecular mass
3.1.3. SEM analysis The morphologies of the coal gangue, modified coal gangue and HCGPAM are observed by SEM, and the results are presented in Fig. 3. The modified coal gangue has obvious gap, extremely high specific surface area, and shows a potential application as raw material for preparation of organic–inorganic hybrid flocculant. It is obvious that HCGPAM displays a very different surface morphology from modified coal gangue. The surface of HCGPAM consists of certain sorts of cauliflower head with a series of pleated ditches of different widths and depths, which makes it possess much coarser surface and larger specific surface area than modified coal gangue. It can be inferred that HCGPAM is favorable for combining with pollutants. 3.2. Effect of synthesis conditions on intrinsic viscosity of HCGPAM 3.2.1. Effect of acrylamide mass fraction on intrinsic viscosity The effect of the mass fraction of AM on the intrinsic viscosity of HCGPAM is shown in Fig. 4(a). The mass fraction of initiator, reaction of temperature and reaction time are 2.5%, 75 °C and 6 h, respectively. In Fig. 4(a), it can be seen that the intrinsic viscosity of the HCGPAM
Fig. 5. Comparison of the flocculation performances, modified coal gangue (a), PAM (b), HCGPAM (c) and PAM/modified coal gangue blend (d).
X. Quan, H. Wang / Chinese Journal of Chemical Engineering 22 (2014) 1055–1060 Table 1 Light transmittance and COD removal efficiency of the HCGPAM, PAM, modified coal gangue and PAM/modified coal gangue blend
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Modified coal gangue PAM HCGPAM Mixture (PAM and modified coal gangue)
Can't be measured Can't be measured 53.6% Can't be measured
4.3 5.2 85.5 4.6
of HCGPAM, which improves the absorbing and bridging capability. However, further increase in acrylamide mass fraction may cause a rapid rise in temperature and the polymerization reaction rate, which would lead to the increase in the extent of chain transfer to the polymer in free radical solution polymerization with the increase of the AM concentration. Thus, the optimized AM mass fraction (8.0%) is suitable for the production of HCGPAM.
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Fig. 7. COD removal efficiency of drilling wastewater in coagulation process.
3.2.2. Effect of initiator concentration on intrinsic viscosity Ce(NH4)2(NO3)6 was used as an initiator for the reaction system. The effect of the initiator concentration on the intrinsic viscosity of the HCGPAM was studied with varying concentrations of the initiator (from 1.0% to 7.0%) and reaction time of 6 h with a fixed acrylamide mass fraction 8% at 75 °C [Fig. 4(b)]. In Fig. 4(b), it can be seen that the intrinsic viscosity increases as the Ce(NH4)2(NO3)6 concentration increases from 0.5% to 2.5%, but decreases with further increases in the Ce(NH4)2(NO3)6 concentration. The increasing concentration of the initiator leads to the increase of free radical concentration, thereafter the degree of polymerization. However, when the concentration of the initiator is higher than 2.5%, the intrinsic viscosity will decrease. The possible explanation is that the excessive initiator leads to the rate of termination free radicals and chain transfer, thus resulting in a decrease in the intrinsic viscosity. Therefore, the initiator concentration of 2.5% is optimal in the preparation of HCGPAM according to the experimental results.
3.2.4. Effect of reaction temperature on intrinsic viscosity The effect of reaction temperature on intrinsic viscosity was investigated with varying reaction temperatures from 40 °C to 80 °C, following 6 h reaction time with initiator concentration of 2.5% and acrylamide mass fraction of 8.0%. The results are shown in Fig. 4(d). It can be seen that the intrinsic viscosity increases as the reaction temperature increases from 40 °C to 75 °C, reaching a maximum value at 75 °C, but decreases thereafter. As the reaction temperature increases, the reaction efficiency and the molecule weight of the reaction product increase. Thus, the intrinsic viscosity is improved. The decrease in intrinsic viscosity at temperatures higher than 75 °C can be explained according to the general rules for free radical polymerization: a further increase in temperature may accelerate the decomposition and consumption of the initiators markedly, resulting in the lack of sufficient initiators to sustain the corresponding polymerization reaction [22]. 3.3. Flocculation study
3.2.3. Effect of reaction time on intrinsic viscosity Reaction times from 1 h to 8 h were selected to study the effect of reaction time on the intrinsic viscosity of HCGPAM [Fig. 4(c)]. The mass fraction of AM, mass fraction of initiator and reaction of temperature were 8.0%, 2.5% and 75 °C, respectively. Fig. 4(c) shows that the intrinsic viscosity increases with increasing reaction time between 2 h and 6 h, but decreases with further increase in reaction time. This indicates that the optimum reaction time for preparation of HCGPAM is 6 h.
Fig. 6. Microstructure of floc formed by HCGPAM (magnified 4000 times).
3.3.1. Evaluation of the flocculation performance To evaluate the capability of treating drilling wastewater for HCGPAM, a comparative study of flocculation performance on modified coal gangue, PAM, HCGPAM and PAM/modified coal gangue blend was conducted. The dosage for each of the four samples was 1.0 mg·ml−1. The drilling wastewater was diluted 2 times at pH 4.0. The results are shown in Fig. 5 and Table 1. It can be seen that the COD removal efficiency of the HCGPAM is much higher than that of any other three samples. And the flocculation rate of HCGPAM is found to be very high during the initial 3 min and the rising velocity of the flocs is about 0.21 cm·s−1. However, there is no distinct flocculating performance occurred with the same amount of PAM, modified coal gangue and PAM/modified coal gangue blend within 30 min. Moreover, the flocs formed by HCGPAM have much higher density, which does not re-disperse even at stirring of 100 r·min−1 for 2 min. The microstructure of the floc is shown in Fig. 6. Flocs formed by HCGPAM are very dense, tightly wrapped together and hard to disperse. The structure of floc does not make long chain of polyacrylamide to stretch fully, while to furl particles of sewage. The results indicate that HCGPAM is a strong and effective flocculant for drilling wastewater. 3.3.2. Effect of HCGPAM dosage on flocculating capability The effect of HCGPAM dosage on flocculation capability is studied with varying HCGPAM dosages from 0.2 to 2.5 mg·ml− 1 in drilling wastewater at pH 4.0 (Fig. 7). It can be observed that the COD removal efficiency increases with the increasing dosage of HCGPAM and reaches a maximum at
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2.0 mg·ml− 1, and thereafter, forms a plateau beyond 2.0 mg·ml− 1. This might be attributed to the content of suspended colloids in the drilling wastewater [6] and the increasing viscosity caused by the excessive dosage of the hybrid flocculant. 4. Conclusions A novel coal gangue–polyacrylamide hybrid flocculant (HCGPAM) has been synthesized by free radical aqueous polymerization of acrylamide in coal gangue suspended solution. And the optimal synthesis conditions are obtained: reaction time of 6 h, polymerization temperature at 75 °C, mass fraction of AM with 8%, and mass fraction of initiator with 2.5%. HCGPAM exhibits much higher flocculating capability in drilling wastewater than PAM or PAM/modified coal gangue blend with the same dosage at room temperature. When the dosage of HCGPAM is 2.0 mg·ml−1 with a stirring rate of 100 r·min−1 and a stirring time of 1 min, the COD removal efficiency can reach 85.5%. References [1] M.I. Aguilar, J. Saez, M. Llorens, A. Soler, J.F. Ortuno, Microscopic observation of particle reduction in slaughterhouse wastewater by coagulation–flocculation using ferric sulphate as coagulant and different coagulant aids, Water Res. 37 (2003) 2233–2241. [2] A.L. Ahmad, S. Ismail, S. Bhatia, Optimization of coagulation–flocculation process for palm oil mill effluent using response surface methodology, Environ. Sci. Technol. 39 (2005) 2828–2834. [3] B. Gao, Q. Yue, J. Miao, Evaluation of polyaluminium ferric chloride (PAFC) as a composite coagulant for water and wastewater treatment, Water Sci. Technol. 47 (2003) 127–132. [4] D.S. Wang, W. Sun, Y. Xu, H. Tang, J. Gregory, Speciation stability of inorganic polymer flocculant–PACl, Colloids Surf. A Physicochem. Eng. Asp. 243 (2004) 1–10. [5] Y.C. Ho, I. Norli, F.M. Alkarkhi, N. Morad, Characterization of biopolymeric flocculant (pectin) and organic synthetic flocculant (PAM): A comparative study on treatment and optimization in kaolin suspension, Bioresour. Technol. 101 (2010) 1166–1174. [6] K.E. Lee, T.T. Teng, N. Morad, B.T. Poh, Y.F. Hong, Flocculation of kaolin in water using novel calcium chloride–polyacrylamide (CaCl2–PAM) hybrid polymer, Sep. Purif. Technol. 75 (2010) 346–351. [7] K.E. Lee, T.T. Teng, N. Morad, B.T. Poh, M. Mahalingam, Flocculation activity of novel ferric chloride–polyacrylamide (FeCl3–PAM) hybrid polymer, Desalination 266 (2011) 108–113. [8] J. Zou, H. Zhu, F. Wang, H. Sui, J. Fan, Preparation of a new inorganic–organic composite flocculant used in solid–liquid separation for waste drilling fluid, Chem. Eng. J. 171 (2011) 350–356. [9] N.D. Tzoupanos, A.I. Zouboulis, Preparation, characterisation and application of novel composite coagulants for surface water treatment, Water Res. 45 (2011) 3614–3626. [10] P.A. Moussas, A.I. Zouboulis, A new inorganic–organic composite coagulant, consisting of polyferric sulphate (PFS) and polyacrylamide (PAA), Water Res. 43 (2009) 3511–3524. [11] K.E. Lee, N. Morad, T.T. Teng, B.T. Poh, Development, characterization and the application of hybrid materials in coagulation/flocculation of wastewater: A review, Chem. Eng. J. 203 (2012) 370–386.
[12] K.E. Lee, I. Khan, N. Morad, T.T. Teng, B.T. Poh, Thermal behaviour and morphological properties of novel magnesium salt–polyacrylamide composite polymers, Polym. Compos. 32 (2011) 1515–1522. [13] S.J. Ma, M.L. Fu, F.W. Li, N.F. Wu, J. Yang, H.W. Jia, B. Wang, R. Cheng, Preparation of a new inorganic–organic composite dual-coagulant and application of oily wastewater treatment, Adv. Mater. Res 233–235 (2011) 523–527. [14] S.F. Wang, L. Shen, Y.J. Tong, L. Chen, I.Y. Phang, P.Q. Lim, T.X. Liu, Biopolymer chitosan/montmorillonite nanocomposites: Preparation and characterization, Polym. Degrad. Stab. 90 (2005) 123–131. [15] W.Y. Yang, J.W. Qian, Z.Q. Shen, A novel flocculant of Al(OH)3–polyacrylamide ionic hybrid, J. Colloid Interface Sci. 273 (2004) 400–405. [16] H.L. Wang, J.Y. Cui, W.F. Jiang, Synthesis, characterization and flocculation activity of novel Fe(OH)3–polyacrylamide hybrid polymer, Mater. Chem. Phys. 130 (2011) 993–999. [17] A. Swerin, L. Odberg, L. Wagberg, An extended model for the estimation of flocculation efficiency factors in multicomponent flocculant systems, Colloids Surf. A Physicochem. Eng. Asp. 113 (1996) 25–38. [18] Z.G. Yan, Y.L. Deng, Cationic microparticle based flocculation and retention systems, Chem. Eng. J. 80 (2000) 31–36. [19] D.H. Deng, W.L. Cen, Environmental effect of coal gangue stack area, China Min. Mag. 8 (1999) 87–91. [20] Z.D. Li, Q.L. Zhou, Tailing and gangue: The prosperity resources be recycled, Eng. Sci. 6 (2004) 20–22. [21] Y.P. Chugh, A. Patwardhan, Mine-mouth power and process steam generation using fine coal waste fuel, Resour. Conserv. Recycl. 40 (2004) 225–243. [22] P.F. Zuo, Comprehensive utilization of coal gangue, Coal Technol. 28 (2009) 186–189 (in Chinese). [23] Y.X. Yan, X.F. Wang, X.Q. Wang, Environmental effect and comprehensive utilization of coal-mine waste from Huaibei and Huainan coalfield, J. Anhui Univ. Sci. Technol (Nat. Sci.) 26 (2006) 9–11 (in Chinese with English abstract). [24] J.X. Zhang, H.H. Sun, Y.M. Sun, N. Zhang, Correlation between 29Si polymerization and cementitious activity of coal gangue, J. Zhejiang Univ. Sci. A 10 (2009) 1334–1340. [25] D.X. Li, X.Y. Song, C.C. Gong, Z.H. Pan, Research on cementitious behavior and mechanism of pozzolanic cement with coal gangue, Cem. Concr. Res. 36 (2006) 1752–1759. [26] H.J. Li, H.H. Sun, X.J. Xiao, H.X. Chen, Mechanical properties of gangue-containing aluminosilicate based cementitious materials, J. Univ. Sci. Technol. Beijing 13 (2006) 183–189. [27] X.Y. Song, C.C. Gong, D.X. Li, Study on structural characteristic and mechanical property of coal gangue in activation process, J. Chin. Ceram. Soc. 32 (2004) 358–363. [28] M. Yang, Z.X. Guo, Y.S. Deng, Preparation of CaO–Al2O3–SiO2 glass ceramics from coal gangue, Int. J. Miner. Process. 102–103 (2012) 112–115. [29] US EPA-HQ-RCRA-2008-0329, Materials Characterization Paper in Support of the Advanced Notice of Proposed Rulemaking — Identification of Nonhazardous Materials That Are Solid Waste: Coal Refuse, US EPA, USA, December 16 2008. [30] US EPA-R09-OAR-2012-0398, Materials Characterization Paper in Support of the Final Rulemaking — Identification of Nonhazardous Materials That Are Solid Waste: Coal Refuse, US EPA, USA, February 3 2011. [31] B.Y. Gao, H. Yu, Q.Y. Yue, Study on the preparation of polyaluminum ferric chloride from gangue, Environ. Sci. 17 (1996) 62–63. [32] H.Y. Wang, X.G. Quan, M.J. Shi, Preparation of coal gauge based PSFA and its application to the treatment of drilling wastewater, Ind. Water Treat. 31 (2011) 38–41. [33] H.J. Li, H.H. Sun, Microstructure and cementitious properties of calcined claycontaining gangue, Int. J. Miner. Metall. Mater. 16 (2009) 482–486. [34] C. Li, J. Wan, H. Sun, L. Li, Investigation on the activation of coal gangue by a new compound method, J. Hazard. Mater. 179 (2010) 515–520.