Ind. Eng. Chem. Res. 2007, 46, 6801-6805
6801
Recycling of Industrial Wastewater by Its Immobilization in Geopolymer Cement Dorith Tavor,* Adi Wolfson, and Anat Shamaev Green Processes Center, Chemical Engineering Department, Sami Shamoon College of Engineering, Bialik/ Basel Sts. Beer-SheVa, 84100 Israel
Asia Shvarzman R&D Center for Building Materials and Processes, Sami Shamoon College of Engineering, Bialik/Basel Sts. Beer-SheVa, 84100 Israel
In this work, we report, for the first time, on the recycling of industrial wastewater with a residual organic compound via its solidification in a geopolymer matrix. It was determined that, in most geopolymer compositions, the compressive strength of the binder increased with time, up to 4 weeks. The addition of phenol to the polymerization mixture of fly-ash-based geopolymers yielded high compressive strengths of 70-85 MPa, as for phenol-free geopolymers. The analysis of phenol leaching from the fly-ash-based geopolymer showed some leakage only where the concentration of phenol in the water was similar to the phenol saturation concentration, whereas the metakaolin-based geopolymer also showed leakage, in lower concentrations. 1. Introduction As part of the growing awareness to environmental issues, industrial wastewater became one of the main concerns of the chemical, petrochemical, and process industry. This waste has high potential of environmental damage, because it contains various types of contaminants, including organic compounds that can pollute the soil, the underground water, and, in parallel, also produce toxic gases.1 Currently, various biological and chemical methods are used to treat industrial wastewater.1-7 The most commonly used process is aerobic biological degradation of the organic compounds.8 Yet, this method has several disadvantages, which limits its ability to decrease the high concentration of organic compounds to the required level: (i) the existence of nondegradable organic compounds, (ii) unpleasant smell, and (iii) the high quantities of sludge that must be treated and removed.1,2,6,7 Another commonly used method is combustion of the waste under high pressure and temperature; however, it requires special and expensive reactors to support these extreme conditions.1,4 Alternatively, catalytic oxidation that convert the organic compounds to substances that are biodegradable or can be fully incinerated is also applied. Yet, this method is limited as each catalyst is compound-specific, whereas a typical waste stream contains a wide range of organic substances.1 Recently, it was reported that geopolymers are high-performance materials for construction and waste immobilization.9-12 Geopolymers are amorphous, three-dimensional aluminosilicate binder materials, which were first discovered by Professor V. D. Glukhovsky in the former Soviet Union in the 1950s. In the later 1970s, Davidovits, in France, started similar work and named those materials “geopolymers”.13 Geopolymer binder materials can be synthesized by mixing aluminosilicate-reactive materials and strong alkaline solutions, followed by curing at room temperature. Under such a strong alkaline solution, the aluminosilicates form free SiO4 and AlO4 tetrahedral clusters, which are linked together to yield polymeric precursors {-SiO4AlO4-}.13-15 Any pozzolanic materials that contains mostly * To whom correspondence should be addressed. Tel: 972-86475635. Fax: 972-8-6475636. E-mail address:
[email protected].
Figure 1. Influence of the water/solid molar ratio on the compressive strength of fly-ash-based geopolymers drying in air.
silicon and aluminum in amorphous form (such as fly ash, metakaolin, and silica fumes) is a possible source material for the manufacture of geopolymers.14-17 The unique properties of geopolymers resulted in their fast development as alternative environmentally friendly materials. First, geopolymers are produced at relatively low temperature (requiring less energy) and emit less CO2. At the end of the synthesis, they reach very high compressive strengths (70-100 MPa). In addition, these materials have unique high-temperature resistance (up to 1200 °C), low permeability, long-term durability, and good fire and acid resistance. Moreover, they have good affinity to heavy-metal ions and, thus, they can be used to solidify radioactive elements.18,19 These properties make geopolymer cement an excellent substitution candidate for portland cement, which is used in the fields of civil, bridge, pavement, hydraulic, and underground engineering.15,17,18,20 In terms of waste stabilization or encapsulation, the most significant physical property imparted by geopolymers is their ability to transform soft, disaggregated, or sludgelike wastes into hard and cohesive solids in remarkably short time frames.17-19,21-23 In this work, we report, for the first time, on the recycling of industrial wastewater with residual organic compounds by its solidification in a geopolymer matrix. Because geopolymers are polymerized in the presence of an aqueous solution that remains
10.1021/ie0616996 CCC: $37.00 © 2007 American Chemical Society Published on Web 04/27/2007
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Ind. Eng. Chem. Res., Vol. 46, No. 21, 2007
Table 1. Compressive Strength of Different Samples with Verity Composition Value parameter molar ratio Al2O3/NaOH SiO2/NaOH water/solid aluminosilicate source admixturea quartz sand compressive strength [MPa] 7 days 21 days 28 days a
sample 1
sample 2
sample 3
sample 4
sample5
sample 6
sample 7
sample 8
4 13.1 0.37 fly ash none yes
4 13.1 0.38 fly ash none yes
4 13.1 0.38 fly ash SL yes
4 13.1 0.38 fly ash SA yes
4 13.1 0.37 fly ash none no
1.5 4.8 0.35 fly ash SA no
1.8 5.6 0.31 fly ash none no
0.9 2.4 0.72 metakaolin Galinum 51 no
26.19 34.40 38.01
25.44 37.03 42.28
15.79 21.23 14.72
15.79 29.08 22.99
34.02 36.06 44.16
46.26 49.60 59.68
81.84
47.94 48.29 58.04
88.07
1 wt %; dry in air at room temperature.
in the polymer matrix, it was suggested that this method can be used as a generic treatment to many industrial waste streams, with various organic and inorganic materials. 2. Experimental Section 2.1. Materials. Two different geopolymer sources were used: metakaolin and fly ash. The metakaolin (Engelhard USA, Ltd.) contained 52.18% SiO2, 43.36% Al2O3, 0.25% Fe2O3, and 4.21% TiO2. The fly ash, produced by the power station of Ashkelon, had a composition of 47.04% SiO2, 29.37% Al2O3, 3.56% Fe2O3, and 1.97% TiO2. Both a solution of 47% NaOH and sodium silicate with a composition of 10.9%-12% Na2O, 25.6%-29.3% SiO2, and 58.2%-63.5% H2O were purchased from Romicol, Ltd. Other materials were purchased from the following companies: quartz sand, from Ashdod; admixture (polynaphthalene sulfanate sodium salt, 50% in water) [SA], and superplasticizer FEYZAL ASTM C-494 Type F, from Advanced Chemicals & Technology S.A.E. [SL]; Borresperse NA sodium lignosulfonate (50% water), from Lignotech; Gileneum 51 (70% water), from Degusa; and phenol (99% pure), from Fluka. 2.2. Synthesis. Inorganic geopolymers were synthesized via the reaction of metakaolin or fly ash, sodium silicate, NaOH solution, and quartz sand at room temperature. The dry materials were weighed, added to a mixer, and mixed for 2 min. The liquid materials then were weighed and added to the mixture slowly in the following order: sodium silicate, water, and admixture. A water solution of phenol was added at the end, to avoid reaction with NaOH. The phenol concentration was up to 3.84 wt % in the solution, which is ∼0.3 wt % of the mold. The viscous mixture was mixed for 6 min and then placed into a mold of 12 cubes (with dimensions of 25 cm × 25 cm × 25 cm) that were placed on vibrating table. The molds were covered and cured at 50 °C for 24 h and then dried in the oven or in the air. 2.3. Analysis. The compressive strength of the geopolymer was measured using a press (ADR300, Ele). The leaching of the organic component was determined after the addition of 1 g of ground geopolymer (70 MPa). It was suggested that the decrease of the compressive strength with increases in the phenol concentration at the beginning of the reaction is attributed to the reaction of phenols and NaOH to form phenolates that inhibited the polymerization. To verify this hypothesis, the corresponding amount of NaOH (on a molar ratio basis) was added in excess to the parent mixture (see Figure 3). The results in Figure 3 compare the change in the compressive strength with time, for fly-ash- and metakaolin-based geopolymers with and without the addition of phenol (3.84 wt %) and with the addition of extra NaOH. Generally, Figure 3 shows that metakaolin-based geopolymers have lower compressive strength than fly-ash-based geopolymers; this can be explained by the difference of their compositions, which leads to different structures. Metakaolin-based geopolymers are known to be more amorphous than fly-ash-based geopolymers.12,23-26 As previously mentioned, for fly-ash-based geopolymers, the addition of phenol affected the compressive strength only at the beginning of the curing, whereas, after 28 days, the compressive strength of molds with and without phenol were equal. On the other hand, the addition of phenol to metakaolinbased geopolymers did not change the compressive strength during the 14 first days; yet, the addition of phenol decreased the compressive strength after 28 days (44 MPa with phenol and 58 MPa without phenol). Adding excess NaOH to the mixture did not significantly change the compressive strength of both materials, reviling that phenolate formation is not the reason for the compressive strength differences with the addition of phenol. Finally, because the addition of phenol did not influence the compressive strength of the final geopolymer, leaching of the phenol from the mold was tested. The leakage of phenol from the geopolymer matrix was measured as a result of temperature, time, and extraction conditions (see Table 2). It was observed that, for fly-ash-based geopolymers, a small amount of phenol leaching occurred, only when phenol values close to the saturation concentration in the water were added to the parent mixtures (with and without the addition of excess NaOH). On the other hand, metakaolin-based geopolymers also showed leaching in lower concentrations. In both materials, the leaching of phenol decreased as the polymerization process progressed from 1 day to 28 days as the polymerization reaction was completed. In addition, there is also a correlation between the compressive strength value and geopolymer stability and phenol leaching, and increasing of compressive strength decreased the leaching, because of the high degree of crosslinking. 4. Conclusions To conclude, for most geopolymer compositions, the compressive strength of the binder was increased with time, up to 4 weeks. Increasing the phenol concentration in the parent alkaline solution up to saturation and using these solutions for the polymerization of fly-ash-based geopolymers yielded lower compressive strength then phenol-free geopolymer at the beginning of the process; however, as the process proceeded, the difference became negligible and the compressive strength values reached 85 MPa. Phenol leaching from fly-ash-based geopolymers was measurable only when solutions that contained values similar to its saturation concentration were used. In contrast, metakaolin-based geopolymers also showed leakage in lower phenol concentrations.
These preliminary promising results support the feasibility of the new concept of recycling of industrial wastewater by their immobilization in geopolymers. The effects of various other parameters, such as the influence of salts and other organic mixtures in wastewater on the immobilization process, are under investigation. Furthermore, because the loading of water also is a critical point, it is desirous to immobilize as much waste as possible, and the addition of different water adsorbents to the polymerization mixture should also be tested. Finally, the effect of phenol and other waste on the mechanism of the polymerization, as well as their state in the final mold, should be studied. Literature Cited (1) Tchobanolous, G.; Burton, F. L.; Stensel, H. D. Wastewater Engineering Treatment and Reuse, 4th Edition; McGraw-Hill: New York, 2003. (2) Sonune, A.; Ghate, R. Developments in Wastewater Treatment Methods. Desalination 2004, 167, 55. (3) Van der Bruggen, B.; Braeken, L. The Challenge of Zero Discharge: From Water Balance to Regeneration. Desalination 2006, 188, 177. (4) Bermejo, M. D.; Cocero, M. J. Destruction of an industrial wastewater by supercritical water oxidation in a transpiring wall reactor. J. Hazard. Mater. 2006, 137, 965. (5) Bozzi, A.; Yuranova, T.; Lais, P.; Kiwi, J. Degradation of industrial waste waters on Fe/C-fabrics. Optimization of the solution parameters during reactor operation. Water Res. 2005, 39, 1441. (6) Bhatnagar, A. Removal of bromophenols from water using industrial wastes as low cost adsorbents. J. Hazard. Mater. 2007, 139, 93. (7) Tziotzios, G.; Teliou, M.; Kaltsouni, V.; Lyberatos, G.; Vayenas, D. V. Biological phenol removal using suspended growth and packed bed reactors. Biochem. Eng. J. 2005, 26, 65. (8) Laursen, K.; Benefield, L. D.; Randall, C. W. In Biological Process Design for Wastewater Treatment; Benefield, L. D., Randall, C. W., Eds.; Prentice-Hall: Englewood Cliffs, NJ, 1980. (9) Palomo, A.; Grutzeck, M.; Blanco, M. Alkali Activated Fly Ashes: A Cement for the Future. Cem. Concr. Res. 1999, 29, 1323. (10) Roy, D. Alkali Activated Cements, Opportunities and Challenges. Cem. Concr. Res. 1999, 29, 249. (11) Xu, H.; van Deventer, J. The Geopolymerisation of Alumino-Silicate Minerals. Int. J. Miner. Process. 2000, 59, 247. (12) Xu, H.; van Deventer, J. Geopolymerisation of Multiple Minerals. Miner. Eng. 2002, 15, 1131. (13) Davidovits, J. Geopolymers: Inorganic Polymeric New Materials. J. Therm. Anal. 1991, 37, 1633. (14) Davidovits, J. Geopolymers: Man-Made Rocks Geosynthesis and the Resulting Development of Very Early High Strength Cement. J. Mater. Educ. 1994, 16, 91. (15) Sun, W.; Zhang, Y.; Lin, W.; Liu Z. In situ monitoring of the hydration process of K-PS geopolymer cement with ESEM. Cem. Concr. Res. 2004, 34, 935. (16) Shvarzman, A.; Kovler, K.; Grader, G.; Shter, G. Using Cement and Cement Free Building Materials Made with Metakaolin. Presented at the International Symposium on Non-Traditional Cement & Concrete, Brno, Czech Republic, 2002. (17) Swanepoel, J.; Strydom, S. Utilisation of fly ash in Geopolymeric Material. Appl. Geochem. 2002, 17, 1143. (18) Cheng, T.; Chiu, J. Fire-Resistant Geopolymer Produced by Granulated Blast Furnace Slag. Miner. Eng. 2003, 16, 205. (19) Palomo, A.; Fernandez-Jimenez, A.; Lopez, C. Precast Elements Made of Alkali-Activated Fly Ash Concrete. Presented at the CANMET/ ACI International Conference on Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, Las Vegas, NV, 2004. (20) Zhang, S.; Gong, K.; Lu, J. Novel modification method for inorganic geopolymer by using water soluble organic polymers. Mater. Lett. 2004, 58, 1292. (21) Wang, S.; Li, L.; Zhu, Z. H. Solid-state conversion of fly ash to effective adsorbents for Cu removal from wastewater. J. Hazard. Mater. 2007, 139, 254. (22) Li, L.; Wang, S.; Zhu, Z. H. Geopolymeric Adsorbents from Fly Ash for Dye Removal from Aqueous Solution. J. Colloid Interface Sci. 2006, 300, 52.
Ind. Eng. Chem. Res., Vol. 46, No. 21, 2007 6805 (23) van Deventer, J. S. J.; Provis, J. L.; Duxson, P.; Lukey, G. C. Reaction Mechanisms in the Geopolymeric Conversion of Inorganic Waste to Useful Products. J. Hazard. Mater. 2007, 139 (3), 506-513. (24) Bakharev, T. Geopolymeric Materials Prepared Using Class F Fly Ash and Elevated Temperature Curing. Cem. Concr. Res. 2005, 35, 1224. (25) Duxson, P.; Mallicoat, S. W.; Lukey, G. C.; Kriven, W. M.; van Deventer, J. S. J. The Effect of Alkali and Si/Al Ratio on the Development of Mechanical Properties of Metakaolin-Based Geopolymer. Colloids Surf., A 2007, 292, 8.
(26) Lee, W. K. W.; van Deventer, J. S. J. Use of Infrared Spectroscopy to Study Geopolymerization of Heterogeneous Amorphous Aluminosilicates. Langmuir 2003, 19, 8726.
ReceiVed for reView December 31, 2006 ReVised manuscript receiVed March 14, 2007 Accepted March 16, 2007 IE0616996
