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Potential use of FCC spent catalyst as partial replacement of cement or sand in cement mortars
Construction and Building Materials 39 (2013) 77–81
Contents lists available at SciVerse ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Potential use of FCC spent catalyst as partial replacement of cement or sand in cement mortars Khalifa Al-Jabri a,⇑, Mahad Baawain a, Ramzi Taha b, Zahran Saif Al-Kamyani a, Khalid Al-Shamsi a, Aysser Ishtieh a a b
Department of Civil and Architectural Engineering, College of Engineering, Sultan Qaboos University, Oman Department of Civil and Architectural Engineering, College of Engineering, Qatar University, Qatar
h i g h l i g h t s " Effect of using spent catalyst on the compressive strength of mortars. " Encouraging results were achieved when spent catalyst was used as sand replacement. " Strength decreases by increasing water/binder ratio at cement replacement. " Spent catalysts contained small traces of heavy metals below the international limits.
a r t i c l e
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Article history: Available online 4 July 2012 Keywords: Spent catalyst FCC Cement mortar Sand Waste recycling Strength
a b s t r a c t This paper studies the effect of using FCC spent catalyst, produced from local refineries on the compressive strength of mortars. The main constituents of mortar; sand and cement were partially replaced by different percentages of spent catalyst. Five levels of sand replacement were used ranging from 5% to 25% by weight of sand. The same was done for cement but with different proportions from 2% to 10% by weight of cement. Three water-to-binder ratios were used; 0.50, 0.55 and 0.60 whereas the binderto-sand ratio was kept constant at 1:3. The specimens were tested at 7, 14, 28, 56 and 91 days of curing. Encouraging results were achieved when Sohar Refinery’s spent catalyst was used as sand replacement. The substitution reached up to 20% without affecting the mortars’ compressive strength. Spent catalysts from both refineries showed negligible effect on the strength of cement mortars when used as partial substitute of cement. Leachate tests showed that mixtures prepared using both spent catalysts contained small traces of heavy metals that are far below the international limits. Hence, no environmental harm should be anticipated from the use of these spent catalysts in construction. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction The original catalysts used in fluidized catalytic cracking units (FCCUs) at refineries consist basically of zeolite with other additives [1–4]. The zeolite catalyst constitutes around 1/5 of the world production of catalyst [5]. Fluid catalytic cracking (FCC) catalyst is used in refineries to improve the yield of higher octane gasoline from crude oil during oil refining and cracking. When the catalytic properties of the FCC catalyst are degraded, the deactivated catalyst must be replaced with active (regenerated) or fresh catalyst [6,7]. Spent FCC catalyst which consists primarily of active silica ⇑ Corresponding author. Address: Department of Civil and Architectural Engineering, College of Engineering, Sultan Qaboos University, P.O. Box 33, Al-Khoud, PC 123, Oman. Tel.: +968 24141331/24141332. E-mail addresses: [email protected], [email protected] (K. Al-Jabri), [email protected] (M. Baawain), [email protected] (R. Taha), zahrank@squ. edu.om (Z.S. Al-Kamyani), [email protected] (K. Al-Shamsi). 0950-0618/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conbuildmat.2012.05.035
(SiO2) and alumina (Al2O3), is considered as a waste material [2–4,6,7]. Spent FCC catalyst constitutes a major fraction of the solid waste generated in the petrochemical industry [8]. In every catalytic operation, the activity of the catalyst gradually decreases. This decrease can be offset by changing some operational parameters. However, at a certain point, catalyst replacement is unavoidable. The spent catalysts can be regenerated and returned to the operation [6]. The regeneration of spent hydro-processing, fluid catalytic cracking (FCC) and reforming catalysts has been performed commercially for several decades. After several cycles, recovery of the catalyst activity is not sufficient to warrant regeneration [6]. Cumulative amounts of spent catalyst are dumped in landfills and thus generating an environmental problem. According to Oman Oil Refineries and Petroleum Industries Company (Orpic), around 20 tons of RFCC and around 200–500 kg of spent alumina catalyst are produced daily, as waste products from Sohar and Mina Al-Fahl Refineries, respectively. Most of the spent
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catalysts are disposed on-site or at nearby disposal sites, without any further reuse or treatment. More than twenty thousand tons of spent catalysts have been accumulated close to Sohar Refinery, thereby, posing major disposal and environmental concerns. Different studies on reusing spent catalyst were conducted to solve this problem and to save energy and natural resources [2–6]. The use of FCC spent catalyst as cement or sand partial replacement present interesting potentials in the conservation of natural resources and reducing cement cost production. Many previous research works evaluated the effect of replacing cement and sand with spent catalyst on mortars’ compressive strength. Conclusions were varied depending on the spent catalyst source, replacement percentage, water-to-binder ratio and particles size distribution. The catalytic cracking catalyst can be used to replace 15–20% of cement content [9] or 10% of sand without adverse effect [10,11]. Curing results showed initial decrease in compressive strength at early age (2 days) [9]. Then, the compressive strength enhanced more than the control mixture after 7 and 28 days of the curing [9]. It was noted that grinding the material to finer size enhanced the reaction with calcium hydroxide to contribute more hydrated calcium silicate gel and hence improving the compressive strength [10,11]. Also, the cementitious properties and consequently the mortar compressive strength were enhanced since the powder catalyst work as pozzolanic material and as filler for the pores [10,12]. The leachate study of heavy metals of spent catalyst was found in low concentration [11]. This indicated that the material can be categorised as non-hazardous. Also, it gives higher confidence in its potential use as a construction material [11]. The main objective of this research was to study the effect of using spent catalyst produced from two refineries in Oman as a partial substitute of sand and cement on the strength of mortars.
2. Experimental program 2.1. Materials The cement used in this study was ordinary Portland cement (OPC) purchased from Oman Cement Company. Sand was brought from Wadi Al-Khoudh. The sand was sieved to meet the specified requirements for mortars’ sand as in BS45506:1978 in which it passed 850 lm and retained on 600 lm. The spent catalysts used in this study were brought from Sohar (SR) and Mina Al-Fahl (MAF) Refineries. The spent catalyst from SR was used ‘‘as-received’’ due to its powder nature for both cement and sand replacement. The spent catalyst from MAF was crushed then sieved to meet the sand specifications to replace the sand and the material that passed 600 lm was used for cement replacement. Table 1 shows the physical properties of the spent catalysts that were determined according to ASTM standards. There are some visible differences between the catalysts in term of odor, color and the shape of the particles. The water demand of SR spent catalyst is about 72.8% to reach its liquid limit, while the spent catalyst from MAF requires less water by about 20%. The spent catalysts from MAF and SR
Table 1 Physical properties of spent catalysts. Property
MAF refinery
SR refinery
Physical state Color Shape Odor
Solid White to off-white Spheres or granules Acidic smell and reacts very vigorously in water Insoluble in water, oil and solvents 51.9 2.79 92.6 72.4 31.2 3235
Solid Gray Crystalline powder Odorless
Solubility Liquid limit (%) Bulk specific gravity Sand equivalent (%) L.A. abrasion (%) Absorption (%) Surface area (cm2/g) NA: not available.
Insoluble in water, oil and solvents 72.8 2.60 NA NA NA 900
Table 2 Chemical composition of spent catalysts. Composition (%)
MAF refinery
SR refinery
SiO2 Al2O3 Fe2O3 CaO MgO Na2O K2O LOI
1.71 66.66 0.07 0.08 0.02 8.29 0.26 26.13
39.21 37.68 0.66 0.05 0.26 0.43 0.06 2.43
have bulk specific gravity of 2.79 and 2.60, respectively. The surface area of SR spent catalyst was 900 cm2/g and for MAF spent catalyst (particles passing 0.075 mm) it was 3235 cm2/g. The dominant components of the spent catalysts are SiO2 and Al2O3 as shown in Table 2. These two compounds constitute more than 68% and 77% of the chemical composition of spent catalyst from the MAF and SR Refineries, respectively. Spent catalyst from MAF had more organics compounds as confirmed by the loss-on-ignition (LOI) value. Alkali content in MAF spent catalyst is relatively high which might react with the silica and adversely affect the properties of mortars. Also, the silica to alumina ratio in SR is about 1:1, whereas the alumina is much higher in MAF spent catalyst. The lime content is considerably low in both spent catalysts. Also Table 2 shows that SR spent catalyst has high concentrations of SiO2 and Fe2O3 compared with MAF spent catalyst whereas MAF has high concentration of Al2O3. In comparison with the chemical composition of natural pozzolans of ASTM C618-99, the summation of the three oxides (SiO2 + Fe2O3 + Al2O3) in SR spent catalyst is nearly 77.6%, which exceeds the 70% requirement for Class N for both raw and calcined natural pozzolans. Therefore, SR spent catalyst might be more beneficial as cement replacement in cement mortars than MAF spent catalyst. 2.2. Mix proportion Mix proportions, by weight, for mortars were 1 (cement or binder): 3 (sand): n (water), where the values of ‘‘n’’ were 0.50, 0.55 and 0.60. The binder content which consists of cement and spent catalyst was kept constant for all mixtures. Mortar specimens were placed in 70 mm 70 mm 70 mm cubes. Two sets of mixtures were prepared. The first set includes the use of spent catalyst as cement replacement (i.e. 0%, 2%, 4%, 6%, 8% and 10%) whereas the second set includes the use of spent catalyst as sand replacement (i.e. 0%, 5%, 10%, 15%, 20% and 25%). Mortars were designed in accordance with OS26-1981. Samples were compacted in three layers using a vibrating table. After 24 h, specimens were removed from the molds and submerged in a water tank for testing at 7, 14, 28, 56 and 91 days. 2.3. Testing procedure Compressive strength test was conducted on the cubes to study the strength development of mortars containing various amounts of spent catalyst as sand or cement replacement at different curing ages. Three samples were tested at 7, 14, 28, 56 and 91 days of curing for each mixture under loading rate of 0.2 kN/s using automatic compression machine.
3. Results and discussion 3.1. Use of spent catalyst as cement replacement Table 3 and Figs. 1 and 2 show the effect of SR and MAF Refinery’s spent catalyst substitution as cement replacement on the compressive strength of cement mortars at w/b ratios of 0.5, 0.55 and 0.6, respectively. Results indicated that the compressive strength of mortars decreases with the increase of w/b ratio due to the increase in the free water content in the mix. The average 28-day compressive strength for the control mixtures with no spent catalyst substitution was 36.6 MPa, 34.3 MPa and 29.9 MPa for w/b ratios of 0.5, 0.55 and 0.6, respectively. Results also indicate that the compressive strength of the mortars increases as the curing period increases. Fig. 1 shows that the substitution of cement up to 2% with SR spent catalyst produces mortars with comparable strength to the control mixture at w/b of 0.5. Further increase in the spent catalyst content however, causes significant reduction in the mortar’s strength. At w/b ratio of 0.55 and 0.6, the compressive strength of mortars with spent catalyst up to 8% content was comparable with the control mixture. The results therefore,
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K. Al-Jabri et al. / Construction and Building Materials 39 (2013) 77–81 Table 3 Compressive strength of cement replacement (MPa). Cement replacement – SR (days)
Cement replacement – MAF (days)
7
14
28
56
91
7
14
28
56
91
0.50
0 2 4 6 8 10
28.4 27.9 19.7 23.2 23.8 20.1
32.7 29.9 25 27.8 32 20.8
36.6 35.3 32.5 30.1 23.8 29.9
42.5 35.9 28.4 34 39.7 25.9
47 35.1 38.7 37.3 36.1 30.5
28.4 26.6 30.5 27 29.1 27.8
32.7 25.6 30.5 27.2 27.4 23.8
36.6 33.7 34.4 30.2 26.3 27.8
42.5 31.8 34.3 30.9 31.3 25.9
47 32.7 36.6 31.9 32.9 25.4
0.55
0 2 4 6 8 10
24.8 17.1 24.7 24.3 20.4 19.5
30.1 26.3 25.7 26.1 26.9 22.6
34.3 34.9 32.6 31 34.9 32.3
39.9 34.9 36.9 33.8 38.6 36.1
42.2 35.4 38.8 38.4 35.6 34.3
24.8 21.3 23.5 22.6 20.6 20.1
30.1 24.2 26.7 26.2 23.4 22.8
34.3 28.3 27.4 27.7 26.1 25.2
39.9 32.8 32.9 34.2 29.1 27.4
42.2 40 36.8 35.7 29.2 28.5
0.60
0 2 4 6 8 10
20.9 18.4 20.9 19.3 18.2 17.2
25.7 22.2 23.9 23.7 22.3 20.1
29.9 26.8 29.2 29.1 27 24.6
31.1 31.6 37.1 34.4 27.1 29
35.2 31.5 34.5 34.4 33.5 30.7
20.9 20 22.2 20.4 20 19.5
25.7 23 24.4 23.8 23.2 23.2
29.9 27.1 27.9 25.4 25.6 26.1
31.1 31.9 30.7 28.2 27.8 27.6
35.2 31.9 30.9 32.1 30.7 31.5
40 35 30 25
0%
20
2% 4%
15
6%
10
8%
5 0
10% 0.50
0.55
Compressive Strength (MPa)
Rep.%
Compressive Strength (MPa)
w/b
0.60
50 45 40 35 30 25 20 15 10 5 0
0% 5% 10% 15% 20% 25% 0.50
0.55
0.60
Fig. 1. Effect of using spent catalyst from SR as cement replacement at 28 days.
Fig. 3. Effect of using spent catalyst from SR as sand replacement at 28 days.
40 35 30 25
0%
20
2% 4%
15
6%
10
8%
5 0
10% 0.50
0.55
0.60
Water/Binder
Compressive Strength (MPa)
Water/Binder
Compressive Strength (MPa)
Water/Binder
40 35 30 25
0%
20
5% 10%
15
15%
10
20%
5 0
25% 0.50
0.55
0.60
Water/Binder
Fig. 2. Effect of using spent catalyst from MAF as cement replacement at 28 days.
Fig. 4. Effect of using spent catalyst from MAF as sand replacement at 28 days.
indicates that although increasing w/b ratio reduces the strength of the control mixtures, it may have the benefit of increasing the spent catalyst content in the mixture without having an adverse effect on mortar strength. Those findings suggest that the optimum spent catalyst content that can be used in cement mortars made with SR spent catalyst is 2%, 8% and 6% at w/b ratios of 0.5, 0.55 and 0.6, respectively. Table 3 and Fig. 2 show the effect of MAF spent catalyst substitution as a cement replacement on the compressive strength of cement mortars at w/b ratios of 0.5, 0.55 and 0.6. Fig. 2 shows that substitution of cement up to 4% with spent catalyst produced
mortars which have comparable strength to the control mixture at w/b of 0.5. However, further increase in the spent catalyst content caused significant reduction in the mortar’s strength. At w/b ratio of 0.6, the compressive strength of mortars with spent catalyst up to 10% content was found comparable with the control mixture. Fig. 2 indicates that although increasing w/b ratio reduces the strength of the control mixtures, it may have the benefit of increasing the spent catalyst content in the mixture without negative effect on mortar strength. Therefore, it may be concluded that the optimum spent catalyst content that can be used in mortars is 4% and 10% at w/b ratios of 0.5 and 0.6, respectively.
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Table 4 Compressive strength of sand replacement (MPa). w/b
Rep.%
Sand replacement –SR (days)
Sand replacement –MAF (days)
7
14
28
56
91
7
14
28
56
91
0.50
0 5 10 15 20 25
28.4 35.6 29.2 18.4 9.3 5.2
32.7 40.3 37.4 27.2 11.6 7.2
36.6 45.6 42.9 28 14.9 8.4
42.5 51.9 43.5 33 17.7 12.1
47 55.3 45.9 38.2 20.3 13.9
28.4 14.3 23 16.1 7.1 13.5
32.7 15.8 20.4 15.8 7.1 13.3
36.6 16.1 23.1 16.5 6.8 14.1
42.5 18 24.3 17.1 7.2 13
47 20.6 23 18.2 7.2 15.7
0.55
0 5 10 15 20 25
24.8 27.1 31.4 24.9 25.6 14.1
30.1 36.7 38.5 31.1 27.9 16.5
34.3 39.4 41.6 36 32.9 19.7
39.9 38.1 52.8 43.4 40.2 26.8
42.2 50.6 51.9 41.6 42.2 30.5
24.8 24.7 18 13.7 9.4 9
30.1 29.9 18.5 16.1 9.3 10.8
34.3 32.8 18.3 17.3 10.7 9.9
39.9 33.7 22.7 18 8.5 11.5
42.2 39 24.3 21.5 9.4 12.5
0.60
0 5 10 15 20 25
20.9 26.5 28 24.3 23.9 20
25.7 30.2 32.1 27.9 22 21.7
29.9 34.5 36.7 36.3 30 24.2
31.1 42 45.5 40.9 36.3 29
35.2 45.3 53 49.9 36.1 36.2
20.9 27.1 21.3 20.4 16.1 14.8
25.7 30.4 26 23.8 16.2 17.7
29.9 35.2 28.2 28.2 17.7 18.1
31.1 34.9 29.9 28.3 19.5 20.2
35.2 37.1 30.6 30 20.3 20.1
Table 5 TCLP results of mortar application (ppm). Source
w/b
Replacement%
Cd
Co
Cu
Cr
Fe
Pb
Mn
Mo
Ni
V
Zn
Ca
K
Mg
Na
Control SR –sand replacement
0.50 0.50 0.55 0.60 0.50 0.55 0.60 0.50 0.55 0.60 0.50
0 25 25 25 10 10 10 25 25 25 10
N.D 1.35 1.29 0.67 N.D N.D N.D N.D N.D N.D N.D
0.01 1.59 1.14 2.47 N.D N.D N.D N.D N.D N.D N.D
0.02 N.D N.D 0.03 N.D 0.03 N.D 0.04 N.D N.D N.D
2.63 0.00 1.98 3.24 1.41 2.05 2.13 2.05 1.87 1.91 N.D
0.31 N.D 0.06 0.10 0.05 0.18 0.16 0.26 0.05 0.17 N.D
N.D N.D 0.01 N.D N.D N.D 0.01 N.D 0.01 N.D N.D
0.03 N.D 0.02 0.01 0.01 0.02 0.02 0.02 0.01 0.02 N.D
0.01 N.D 0.31 0.32 0.03 0.05 0.05 0.01 0.02 0.04 N.D
0.54 N.D N.D 0.01 0.02 0.01 0.03 0.01 N.D 0.01 N.D
0.01 N.D 0.72 0.52 N.D 0.02 0.02 N.D N.D 0.01 N.D
0.03 N.D 0.02 N.D 0.01 0.01 0.01 N.D N.D N.D N.D
378.21 389.59 369.27 410.31 373.44 386.51 380.91 396.89 396.75 421.00 378.78
39.83 32.19 23.97 22.34 26.6 24.58 28.64 15.72 14.48 20.81 24.31
114.22 22.73 16.82 9.40 0.75 2.06 2.14 6.95 38.04 9.17 1.84
16.93 21.16 17.88 21.31 7.68 7.48 8.24 66.64 30.9 112.44 28.24
0.55 0.60
10 10
N.D N.D
N.D N.D
0.03 N.D
1.82 2.14
0.13 0.14
N.D N.D
0.01 0.01
0.01 N.D
0.03 0.01
N.D 0.01
0.01 0.01
386.08 386.45
24.52 23.61
1.76 2.09
30.21 29.33
SR – cement replacement
MAF – sand replacement
MAF – cement replacement
3.2. Use of spent catalyst as sand replacement Table 4 shows the effect of using spent catalyst as sand replacement on the compressive strength results. At w/b of 0.50, using 5% spent catalyst from SR yielded 24.6% increase in the strength. Replacing up to 15% of the sand with SR spent catalyst at w/b of 0.55 resulted in strength comparable to the control mixture. Furthermore, sand replacement up to 20% with SR spent catalyst at w/b 0.60 did not cause any reduction in the strength. Comparing the compressive strength of 15% sand replacement (Fig. 3) at different w/b ratios; w/b 0.60 yielded in similar strength to w/b 0.55 and higher strength than at w/b 0.50 by about 28%. It is clear from Fig. 4 that the crushed grains of the spent catalyst from MAF have lower strength resistance than the sand grains. Moreover, it is clear that MAF spent catalyst has very low pozzolanic activity [12]. Hence, all of the strength results at w/b 0.50 were less by 37% than the control mixture. However, the strength was enhanced by increasing the w/b ratio to 0.60. At w/b 0.60, replacing 5% of sand by spent catalyst from MAF increased the strength by about 18%. Then, it decreased gradually by increasing the replacement percentages. Consequently, the strength increment was balanced mostly by two variables; water absorption which is more related to the spent catalyst and the particles interlock that is affected by adding a new material to the mixture. Hence, it may be concluded, that the optimum spent catalyst to be used in mortars made with SR spent catalyst is 10% at w/b ratio of 0.5, 20% at w/b ratio of 0.55 and 20% at
w/b ratio of 0.6. In the case of MAF spent catalyst, the optimum spent catalyst to be used is 5% and 15% at w/b ratios of 0.55 and 0.6, respectively. 4. Environmental assessment Toxicity Characteristics Leachate Procedure (TCLP) test was conducted for only some selected samples as shown in Table 5. The selected samples were the control mixture and the highest replacement percentages, 10% in case of cement replacement and 25% in case of sand replacement. It is clear from the table that the leachate of toxic metals concentrations was not detected or did not exceed the allowable limits by US-EPA. The concentrations of Mo, Ni, V and Zn were less than 1 ppm; whereas, Pb was not detected or less than 0.01 ppm (limited for 5 ppm). Cadmium was detected in three samples only, it was just higher than the allowable limit (1.0 ppm) and its concentration decreases by increasing w/b ratio. Chromium was detected in all samples in low concentrations and it is limited to be less than 5 ppm. Thus, the material can be classified as non-hazardous material. 5. Conclusions Spent catalysts generated by Mina Al-Fahl and Sohar Refineries have beneficial applications in cement and sand replacement due
K. Al-Jabri et al. / Construction and Building Materials 39 (2013) 77–81
to their chemical compositions. For cement replacement at w/b ratio of 0.60, the use of spent catalyst from both Refineries results in no significant drop in the compressive strength. Substitution of 10% of SR spent catalyst as sand resulted in a higher compressive strength than the control mixture. Encouraging results were obtained using SR spent catalyst as sand replacement with w/b ratios of 0.55 and 0.60 where the substitution reach up to 20% without affecting the compressive strength. Spent catalyst from SR yielded better results than the spent catalyst from MAF. Mixtures prepared from both spent catalysts can be used without any detrimental environmental impact which is evidenced by the low level leachate analysis of heavy metals. Acknowledgments The research team gratefully acknowledges the financial support provided by Oman Refineries and Petrochemical Company under Sultan Qaboos University Grant No. CR/ENG/CIVL/09/01. We are also grateful to the undergraduate and postgraduate students and engineering technicians who diligently worked on this project. References [1] Sadeghbeigi R. Fluid catalytic cracking handbook. Houston, TX: Gulf publishing company; 2000.
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[2] Bukowska M, Pacewska B, Wilinska I. Corrosion resistance of cement mortars containing spent catalyst of fluidized bed cracking (FBCC) as an additive. J Therm Anal Calorim 2003;74:931–42. [3] Pinto CA, Büchler PM, Dweck J. Pozzolanic properties of a residual FCC catalyst during the early stages of cement hydration. J Therm Anal Calorim 2007;87(3):715–20. [4] Dweck J, Pinto CA, Büchler PM. Study of a Brazilian spent catalyst as cement aggregate by thermal and mechanical analysis. J Therm Anal Calorim 2008;92(1):121–7. [5] Su N, Chen ZH, Fang HY. Reuse of spent catalyst as fine aggregate in cement mortar. Cem Concr Compos 2001;23:111–8. [6] Furimsky Edward. Spent refinery catalysts: environment, safety and utilization. Catal Today 1996;30:223–86. [7] Zornoza E, Paya J, Garces P. Chloride-induced corrosion of steel embedded in mortars containing fly ash and spent cracking catalyst. Corros Sci 2008;50:1567–75. [8] Bayraktar O. Bioleaching of nickel from equilibrium fluid catalytic cracking catalysts. World J Microbiol Biotechnol 2005;21:661–5. [9] Paya J, Monzo J, Borrachero MV. Physical, chemical and mechanical properties of fluid catalytic cracking catalyst residue (FC3R) blended cements. Cem Concr Res 2001;31:57–61. [10] Chen Hsiu-Liang, Tseng Yun-Sheng, Hsu Kung-Chung. Spent FCC catalyst as a pozzolanic material for high-performance mortars. Cem Concr Compos 2004;26:657–64. [11] Nan Su, Chen Zong-Huei, Fang Hung-Yuan. Reuse of spent catalyst as fine aggregate in cement mortar. Cem Concr Compos 2001;23:111–8. [12] Hilal Al-Dhamri, Khaled Melghit. Use of alumina spent catalyst and RFCC wastes from petroleum refinery to substitute bauxite in the preparation of Portland clinker. J Hazard Mater 2010;179:852–9.
Contents lists available at SciVerse ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Potential use of FCC spent catalyst as partial replacement of cement or sand in cement mortars Khalifa Al-Jabri a,⇑, Mahad Baawain a, Ramzi Taha b, Zahran Saif Al-Kamyani a, Khalid Al-Shamsi a, Aysser Ishtieh a a b
Department of Civil and Architectural Engineering, College of Engineering, Sultan Qaboos University, Oman Department of Civil and Architectural Engineering, College of Engineering, Qatar University, Qatar
h i g h l i g h t s " Effect of using spent catalyst on the compressive strength of mortars. " Encouraging results were achieved when spent catalyst was used as sand replacement. " Strength decreases by increasing water/binder ratio at cement replacement. " Spent catalysts contained small traces of heavy metals below the international limits.
a r t i c l e
i n f o
Article history: Available online 4 July 2012 Keywords: Spent catalyst FCC Cement mortar Sand Waste recycling Strength
a b s t r a c t This paper studies the effect of using FCC spent catalyst, produced from local refineries on the compressive strength of mortars. The main constituents of mortar; sand and cement were partially replaced by different percentages of spent catalyst. Five levels of sand replacement were used ranging from 5% to 25% by weight of sand. The same was done for cement but with different proportions from 2% to 10% by weight of cement. Three water-to-binder ratios were used; 0.50, 0.55 and 0.60 whereas the binderto-sand ratio was kept constant at 1:3. The specimens were tested at 7, 14, 28, 56 and 91 days of curing. Encouraging results were achieved when Sohar Refinery’s spent catalyst was used as sand replacement. The substitution reached up to 20% without affecting the mortars’ compressive strength. Spent catalysts from both refineries showed negligible effect on the strength of cement mortars when used as partial substitute of cement. Leachate tests showed that mixtures prepared using both spent catalysts contained small traces of heavy metals that are far below the international limits. Hence, no environmental harm should be anticipated from the use of these spent catalysts in construction. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction The original catalysts used in fluidized catalytic cracking units (FCCUs) at refineries consist basically of zeolite with other additives [1–4]. The zeolite catalyst constitutes around 1/5 of the world production of catalyst [5]. Fluid catalytic cracking (FCC) catalyst is used in refineries to improve the yield of higher octane gasoline from crude oil during oil refining and cracking. When the catalytic properties of the FCC catalyst are degraded, the deactivated catalyst must be replaced with active (regenerated) or fresh catalyst [6,7]. Spent FCC catalyst which consists primarily of active silica ⇑ Corresponding author. Address: Department of Civil and Architectural Engineering, College of Engineering, Sultan Qaboos University, P.O. Box 33, Al-Khoud, PC 123, Oman. Tel.: +968 24141331/24141332. E-mail addresses: [email protected], [email protected] (K. Al-Jabri), [email protected] (M. Baawain), [email protected] (R. Taha), zahrank@squ. edu.om (Z.S. Al-Kamyani), [email protected] (K. Al-Shamsi). 0950-0618/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conbuildmat.2012.05.035
(SiO2) and alumina (Al2O3), is considered as a waste material [2–4,6,7]. Spent FCC catalyst constitutes a major fraction of the solid waste generated in the petrochemical industry [8]. In every catalytic operation, the activity of the catalyst gradually decreases. This decrease can be offset by changing some operational parameters. However, at a certain point, catalyst replacement is unavoidable. The spent catalysts can be regenerated and returned to the operation [6]. The regeneration of spent hydro-processing, fluid catalytic cracking (FCC) and reforming catalysts has been performed commercially for several decades. After several cycles, recovery of the catalyst activity is not sufficient to warrant regeneration [6]. Cumulative amounts of spent catalyst are dumped in landfills and thus generating an environmental problem. According to Oman Oil Refineries and Petroleum Industries Company (Orpic), around 20 tons of RFCC and around 200–500 kg of spent alumina catalyst are produced daily, as waste products from Sohar and Mina Al-Fahl Refineries, respectively. Most of the spent
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catalysts are disposed on-site or at nearby disposal sites, without any further reuse or treatment. More than twenty thousand tons of spent catalysts have been accumulated close to Sohar Refinery, thereby, posing major disposal and environmental concerns. Different studies on reusing spent catalyst were conducted to solve this problem and to save energy and natural resources [2–6]. The use of FCC spent catalyst as cement or sand partial replacement present interesting potentials in the conservation of natural resources and reducing cement cost production. Many previous research works evaluated the effect of replacing cement and sand with spent catalyst on mortars’ compressive strength. Conclusions were varied depending on the spent catalyst source, replacement percentage, water-to-binder ratio and particles size distribution. The catalytic cracking catalyst can be used to replace 15–20% of cement content [9] or 10% of sand without adverse effect [10,11]. Curing results showed initial decrease in compressive strength at early age (2 days) [9]. Then, the compressive strength enhanced more than the control mixture after 7 and 28 days of the curing [9]. It was noted that grinding the material to finer size enhanced the reaction with calcium hydroxide to contribute more hydrated calcium silicate gel and hence improving the compressive strength [10,11]. Also, the cementitious properties and consequently the mortar compressive strength were enhanced since the powder catalyst work as pozzolanic material and as filler for the pores [10,12]. The leachate study of heavy metals of spent catalyst was found in low concentration [11]. This indicated that the material can be categorised as non-hazardous. Also, it gives higher confidence in its potential use as a construction material [11]. The main objective of this research was to study the effect of using spent catalyst produced from two refineries in Oman as a partial substitute of sand and cement on the strength of mortars.
2. Experimental program 2.1. Materials The cement used in this study was ordinary Portland cement (OPC) purchased from Oman Cement Company. Sand was brought from Wadi Al-Khoudh. The sand was sieved to meet the specified requirements for mortars’ sand as in BS45506:1978 in which it passed 850 lm and retained on 600 lm. The spent catalysts used in this study were brought from Sohar (SR) and Mina Al-Fahl (MAF) Refineries. The spent catalyst from SR was used ‘‘as-received’’ due to its powder nature for both cement and sand replacement. The spent catalyst from MAF was crushed then sieved to meet the sand specifications to replace the sand and the material that passed 600 lm was used for cement replacement. Table 1 shows the physical properties of the spent catalysts that were determined according to ASTM standards. There are some visible differences between the catalysts in term of odor, color and the shape of the particles. The water demand of SR spent catalyst is about 72.8% to reach its liquid limit, while the spent catalyst from MAF requires less water by about 20%. The spent catalysts from MAF and SR
Table 1 Physical properties of spent catalysts. Property
MAF refinery
SR refinery
Physical state Color Shape Odor
Solid White to off-white Spheres or granules Acidic smell and reacts very vigorously in water Insoluble in water, oil and solvents 51.9 2.79 92.6 72.4 31.2 3235
Solid Gray Crystalline powder Odorless
Solubility Liquid limit (%) Bulk specific gravity Sand equivalent (%) L.A. abrasion (%) Absorption (%) Surface area (cm2/g) NA: not available.
Insoluble in water, oil and solvents 72.8 2.60 NA NA NA 900
Table 2 Chemical composition of spent catalysts. Composition (%)
MAF refinery
SR refinery
SiO2 Al2O3 Fe2O3 CaO MgO Na2O K2O LOI
1.71 66.66 0.07 0.08 0.02 8.29 0.26 26.13
39.21 37.68 0.66 0.05 0.26 0.43 0.06 2.43
have bulk specific gravity of 2.79 and 2.60, respectively. The surface area of SR spent catalyst was 900 cm2/g and for MAF spent catalyst (particles passing 0.075 mm) it was 3235 cm2/g. The dominant components of the spent catalysts are SiO2 and Al2O3 as shown in Table 2. These two compounds constitute more than 68% and 77% of the chemical composition of spent catalyst from the MAF and SR Refineries, respectively. Spent catalyst from MAF had more organics compounds as confirmed by the loss-on-ignition (LOI) value. Alkali content in MAF spent catalyst is relatively high which might react with the silica and adversely affect the properties of mortars. Also, the silica to alumina ratio in SR is about 1:1, whereas the alumina is much higher in MAF spent catalyst. The lime content is considerably low in both spent catalysts. Also Table 2 shows that SR spent catalyst has high concentrations of SiO2 and Fe2O3 compared with MAF spent catalyst whereas MAF has high concentration of Al2O3. In comparison with the chemical composition of natural pozzolans of ASTM C618-99, the summation of the three oxides (SiO2 + Fe2O3 + Al2O3) in SR spent catalyst is nearly 77.6%, which exceeds the 70% requirement for Class N for both raw and calcined natural pozzolans. Therefore, SR spent catalyst might be more beneficial as cement replacement in cement mortars than MAF spent catalyst. 2.2. Mix proportion Mix proportions, by weight, for mortars were 1 (cement or binder): 3 (sand): n (water), where the values of ‘‘n’’ were 0.50, 0.55 and 0.60. The binder content which consists of cement and spent catalyst was kept constant for all mixtures. Mortar specimens were placed in 70 mm 70 mm 70 mm cubes. Two sets of mixtures were prepared. The first set includes the use of spent catalyst as cement replacement (i.e. 0%, 2%, 4%, 6%, 8% and 10%) whereas the second set includes the use of spent catalyst as sand replacement (i.e. 0%, 5%, 10%, 15%, 20% and 25%). Mortars were designed in accordance with OS26-1981. Samples were compacted in three layers using a vibrating table. After 24 h, specimens were removed from the molds and submerged in a water tank for testing at 7, 14, 28, 56 and 91 days. 2.3. Testing procedure Compressive strength test was conducted on the cubes to study the strength development of mortars containing various amounts of spent catalyst as sand or cement replacement at different curing ages. Three samples were tested at 7, 14, 28, 56 and 91 days of curing for each mixture under loading rate of 0.2 kN/s using automatic compression machine.
3. Results and discussion 3.1. Use of spent catalyst as cement replacement Table 3 and Figs. 1 and 2 show the effect of SR and MAF Refinery’s spent catalyst substitution as cement replacement on the compressive strength of cement mortars at w/b ratios of 0.5, 0.55 and 0.6, respectively. Results indicated that the compressive strength of mortars decreases with the increase of w/b ratio due to the increase in the free water content in the mix. The average 28-day compressive strength for the control mixtures with no spent catalyst substitution was 36.6 MPa, 34.3 MPa and 29.9 MPa for w/b ratios of 0.5, 0.55 and 0.6, respectively. Results also indicate that the compressive strength of the mortars increases as the curing period increases. Fig. 1 shows that the substitution of cement up to 2% with SR spent catalyst produces mortars with comparable strength to the control mixture at w/b of 0.5. Further increase in the spent catalyst content however, causes significant reduction in the mortar’s strength. At w/b ratio of 0.55 and 0.6, the compressive strength of mortars with spent catalyst up to 8% content was comparable with the control mixture. The results therefore,
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K. Al-Jabri et al. / Construction and Building Materials 39 (2013) 77–81 Table 3 Compressive strength of cement replacement (MPa). Cement replacement – SR (days)
Cement replacement – MAF (days)
7
14
28
56
91
7
14
28
56
91
0.50
0 2 4 6 8 10
28.4 27.9 19.7 23.2 23.8 20.1
32.7 29.9 25 27.8 32 20.8
36.6 35.3 32.5 30.1 23.8 29.9
42.5 35.9 28.4 34 39.7 25.9
47 35.1 38.7 37.3 36.1 30.5
28.4 26.6 30.5 27 29.1 27.8
32.7 25.6 30.5 27.2 27.4 23.8
36.6 33.7 34.4 30.2 26.3 27.8
42.5 31.8 34.3 30.9 31.3 25.9
47 32.7 36.6 31.9 32.9 25.4
0.55
0 2 4 6 8 10
24.8 17.1 24.7 24.3 20.4 19.5
30.1 26.3 25.7 26.1 26.9 22.6
34.3 34.9 32.6 31 34.9 32.3
39.9 34.9 36.9 33.8 38.6 36.1
42.2 35.4 38.8 38.4 35.6 34.3
24.8 21.3 23.5 22.6 20.6 20.1
30.1 24.2 26.7 26.2 23.4 22.8
34.3 28.3 27.4 27.7 26.1 25.2
39.9 32.8 32.9 34.2 29.1 27.4
42.2 40 36.8 35.7 29.2 28.5
0.60
0 2 4 6 8 10
20.9 18.4 20.9 19.3 18.2 17.2
25.7 22.2 23.9 23.7 22.3 20.1
29.9 26.8 29.2 29.1 27 24.6
31.1 31.6 37.1 34.4 27.1 29
35.2 31.5 34.5 34.4 33.5 30.7
20.9 20 22.2 20.4 20 19.5
25.7 23 24.4 23.8 23.2 23.2
29.9 27.1 27.9 25.4 25.6 26.1
31.1 31.9 30.7 28.2 27.8 27.6
35.2 31.9 30.9 32.1 30.7 31.5
40 35 30 25
0%
20
2% 4%
15
6%
10
8%
5 0
10% 0.50
0.55
Compressive Strength (MPa)
Rep.%
Compressive Strength (MPa)
w/b
0.60
50 45 40 35 30 25 20 15 10 5 0
0% 5% 10% 15% 20% 25% 0.50
0.55
0.60
Fig. 1. Effect of using spent catalyst from SR as cement replacement at 28 days.
Fig. 3. Effect of using spent catalyst from SR as sand replacement at 28 days.
40 35 30 25
0%
20
2% 4%
15
6%
10
8%
5 0
10% 0.50
0.55
0.60
Water/Binder
Compressive Strength (MPa)
Water/Binder
Compressive Strength (MPa)
Water/Binder
40 35 30 25
0%
20
5% 10%
15
15%
10
20%
5 0
25% 0.50
0.55
0.60
Water/Binder
Fig. 2. Effect of using spent catalyst from MAF as cement replacement at 28 days.
Fig. 4. Effect of using spent catalyst from MAF as sand replacement at 28 days.
indicates that although increasing w/b ratio reduces the strength of the control mixtures, it may have the benefit of increasing the spent catalyst content in the mixture without having an adverse effect on mortar strength. Those findings suggest that the optimum spent catalyst content that can be used in cement mortars made with SR spent catalyst is 2%, 8% and 6% at w/b ratios of 0.5, 0.55 and 0.6, respectively. Table 3 and Fig. 2 show the effect of MAF spent catalyst substitution as a cement replacement on the compressive strength of cement mortars at w/b ratios of 0.5, 0.55 and 0.6. Fig. 2 shows that substitution of cement up to 4% with spent catalyst produced
mortars which have comparable strength to the control mixture at w/b of 0.5. However, further increase in the spent catalyst content caused significant reduction in the mortar’s strength. At w/b ratio of 0.6, the compressive strength of mortars with spent catalyst up to 10% content was found comparable with the control mixture. Fig. 2 indicates that although increasing w/b ratio reduces the strength of the control mixtures, it may have the benefit of increasing the spent catalyst content in the mixture without negative effect on mortar strength. Therefore, it may be concluded that the optimum spent catalyst content that can be used in mortars is 4% and 10% at w/b ratios of 0.5 and 0.6, respectively.
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Table 4 Compressive strength of sand replacement (MPa). w/b
Rep.%
Sand replacement –SR (days)
Sand replacement –MAF (days)
7
14
28
56
91
7
14
28
56
91
0.50
0 5 10 15 20 25
28.4 35.6 29.2 18.4 9.3 5.2
32.7 40.3 37.4 27.2 11.6 7.2
36.6 45.6 42.9 28 14.9 8.4
42.5 51.9 43.5 33 17.7 12.1
47 55.3 45.9 38.2 20.3 13.9
28.4 14.3 23 16.1 7.1 13.5
32.7 15.8 20.4 15.8 7.1 13.3
36.6 16.1 23.1 16.5 6.8 14.1
42.5 18 24.3 17.1 7.2 13
47 20.6 23 18.2 7.2 15.7
0.55
0 5 10 15 20 25
24.8 27.1 31.4 24.9 25.6 14.1
30.1 36.7 38.5 31.1 27.9 16.5
34.3 39.4 41.6 36 32.9 19.7
39.9 38.1 52.8 43.4 40.2 26.8
42.2 50.6 51.9 41.6 42.2 30.5
24.8 24.7 18 13.7 9.4 9
30.1 29.9 18.5 16.1 9.3 10.8
34.3 32.8 18.3 17.3 10.7 9.9
39.9 33.7 22.7 18 8.5 11.5
42.2 39 24.3 21.5 9.4 12.5
0.60
0 5 10 15 20 25
20.9 26.5 28 24.3 23.9 20
25.7 30.2 32.1 27.9 22 21.7
29.9 34.5 36.7 36.3 30 24.2
31.1 42 45.5 40.9 36.3 29
35.2 45.3 53 49.9 36.1 36.2
20.9 27.1 21.3 20.4 16.1 14.8
25.7 30.4 26 23.8 16.2 17.7
29.9 35.2 28.2 28.2 17.7 18.1
31.1 34.9 29.9 28.3 19.5 20.2
35.2 37.1 30.6 30 20.3 20.1
Table 5 TCLP results of mortar application (ppm). Source
w/b
Replacement%
Cd
Co
Cu
Cr
Fe
Pb
Mn
Mo
Ni
V
Zn
Ca
K
Mg
Na
Control SR –sand replacement
0.50 0.50 0.55 0.60 0.50 0.55 0.60 0.50 0.55 0.60 0.50
0 25 25 25 10 10 10 25 25 25 10
N.D 1.35 1.29 0.67 N.D N.D N.D N.D N.D N.D N.D
0.01 1.59 1.14 2.47 N.D N.D N.D N.D N.D N.D N.D
0.02 N.D N.D 0.03 N.D 0.03 N.D 0.04 N.D N.D N.D
2.63 0.00 1.98 3.24 1.41 2.05 2.13 2.05 1.87 1.91 N.D
0.31 N.D 0.06 0.10 0.05 0.18 0.16 0.26 0.05 0.17 N.D
N.D N.D 0.01 N.D N.D N.D 0.01 N.D 0.01 N.D N.D
0.03 N.D 0.02 0.01 0.01 0.02 0.02 0.02 0.01 0.02 N.D
0.01 N.D 0.31 0.32 0.03 0.05 0.05 0.01 0.02 0.04 N.D
0.54 N.D N.D 0.01 0.02 0.01 0.03 0.01 N.D 0.01 N.D
0.01 N.D 0.72 0.52 N.D 0.02 0.02 N.D N.D 0.01 N.D
0.03 N.D 0.02 N.D 0.01 0.01 0.01 N.D N.D N.D N.D
378.21 389.59 369.27 410.31 373.44 386.51 380.91 396.89 396.75 421.00 378.78
39.83 32.19 23.97 22.34 26.6 24.58 28.64 15.72 14.48 20.81 24.31
114.22 22.73 16.82 9.40 0.75 2.06 2.14 6.95 38.04 9.17 1.84
16.93 21.16 17.88 21.31 7.68 7.48 8.24 66.64 30.9 112.44 28.24
0.55 0.60
10 10
N.D N.D
N.D N.D
0.03 N.D
1.82 2.14
0.13 0.14
N.D N.D
0.01 0.01
0.01 N.D
0.03 0.01
N.D 0.01
0.01 0.01
386.08 386.45
24.52 23.61
1.76 2.09
30.21 29.33
SR – cement replacement
MAF – sand replacement
MAF – cement replacement
3.2. Use of spent catalyst as sand replacement Table 4 shows the effect of using spent catalyst as sand replacement on the compressive strength results. At w/b of 0.50, using 5% spent catalyst from SR yielded 24.6% increase in the strength. Replacing up to 15% of the sand with SR spent catalyst at w/b of 0.55 resulted in strength comparable to the control mixture. Furthermore, sand replacement up to 20% with SR spent catalyst at w/b 0.60 did not cause any reduction in the strength. Comparing the compressive strength of 15% sand replacement (Fig. 3) at different w/b ratios; w/b 0.60 yielded in similar strength to w/b 0.55 and higher strength than at w/b 0.50 by about 28%. It is clear from Fig. 4 that the crushed grains of the spent catalyst from MAF have lower strength resistance than the sand grains. Moreover, it is clear that MAF spent catalyst has very low pozzolanic activity [12]. Hence, all of the strength results at w/b 0.50 were less by 37% than the control mixture. However, the strength was enhanced by increasing the w/b ratio to 0.60. At w/b 0.60, replacing 5% of sand by spent catalyst from MAF increased the strength by about 18%. Then, it decreased gradually by increasing the replacement percentages. Consequently, the strength increment was balanced mostly by two variables; water absorption which is more related to the spent catalyst and the particles interlock that is affected by adding a new material to the mixture. Hence, it may be concluded, that the optimum spent catalyst to be used in mortars made with SR spent catalyst is 10% at w/b ratio of 0.5, 20% at w/b ratio of 0.55 and 20% at
w/b ratio of 0.6. In the case of MAF spent catalyst, the optimum spent catalyst to be used is 5% and 15% at w/b ratios of 0.55 and 0.6, respectively. 4. Environmental assessment Toxicity Characteristics Leachate Procedure (TCLP) test was conducted for only some selected samples as shown in Table 5. The selected samples were the control mixture and the highest replacement percentages, 10% in case of cement replacement and 25% in case of sand replacement. It is clear from the table that the leachate of toxic metals concentrations was not detected or did not exceed the allowable limits by US-EPA. The concentrations of Mo, Ni, V and Zn were less than 1 ppm; whereas, Pb was not detected or less than 0.01 ppm (limited for 5 ppm). Cadmium was detected in three samples only, it was just higher than the allowable limit (1.0 ppm) and its concentration decreases by increasing w/b ratio. Chromium was detected in all samples in low concentrations and it is limited to be less than 5 ppm. Thus, the material can be classified as non-hazardous material. 5. Conclusions Spent catalysts generated by Mina Al-Fahl and Sohar Refineries have beneficial applications in cement and sand replacement due
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to their chemical compositions. For cement replacement at w/b ratio of 0.60, the use of spent catalyst from both Refineries results in no significant drop in the compressive strength. Substitution of 10% of SR spent catalyst as sand resulted in a higher compressive strength than the control mixture. Encouraging results were obtained using SR spent catalyst as sand replacement with w/b ratios of 0.55 and 0.60 where the substitution reach up to 20% without affecting the compressive strength. Spent catalyst from SR yielded better results than the spent catalyst from MAF. Mixtures prepared from both spent catalysts can be used without any detrimental environmental impact which is evidenced by the low level leachate analysis of heavy metals. Acknowledgments The research team gratefully acknowledges the financial support provided by Oman Refineries and Petrochemical Company under Sultan Qaboos University Grant No. CR/ENG/CIVL/09/01. We are also grateful to the undergraduate and postgraduate students and engineering technicians who diligently worked on this project. References [1] Sadeghbeigi R. Fluid catalytic cracking handbook. Houston, TX: Gulf publishing company; 2000.
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