Evaluation of novel synthesis of ordered SBA-15 mesoporous silica from gold mine tailings slurry by experimental design

Journal of the Taiwan Institute of Chemical Engineers xxx (2014) xxx–xxx

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JTICE-1028; No. of Pages 7

Evaluation of novel synthesis of ordered SBA-15 mesoporous silicafrom gold mine tailings slurry by experimental design

Muge Sari Yilmaz, Sabriye Piskin *

Faculty of Chemical and Metallurgical Engineering, Chemical Engineering Department, Yildiz Technical University, Istanbul, Turkey

A R T I C L E I N F O

Article history:

Received 13 February 2014

Received in revised form 2 September 2014

Accepted 14 September 2014

Available online xxx

Keywords:

SBA-15

Tailings slurry

Fractional factorial design

Novel synthesis

Mesoporous silica

A B S T R A C T

This research work demonstrates the use of fractional factorial experimental design technique for the

novel synthesis of ordered mesoporous silica SBA-15 from the tailings slurry of a gold mine treatment

plant. A two-level factorial design was employed to investigate the influence of five factors (weight ratio

of NaOH/slurry, leaching time, stirring time, synthesis temperature, and synthesis time) on specific

surface area (SBET). The experimental design results show that only the weight ratio of NaOH/slurry

influenced SBET significantly and the obtained model predicts the SBET as a function of the weight ratio of

NaOH/slurry. The experimental values were in reasonable agreement with the predicted values. It was

revealed that fractional factorial design is a suitable tool for investigating the effects of large number

factors simultaneously, thus reducing the number of experiments required.

� 2014 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

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jou r nal h o mep age: w ww.els evier . co m/lo c ate / j t i c e

1. Introduction

In 1998, a turning point in the production of mesoporousmaterials was reached with the production of a variety of orderedmesoporous structures denoted as SBA by Zhao et al. [1]. The mostimportant material among these is highly ordered hexagonal SBA-15. SBA-15 has been widely used in various areas such as removalof heavy metals [2,3], catalysis [4,5], drug delivery systems [6,7],immobilization of enzymes [8,9], sensors [10], and photolumines-cence [11] due to their large and uniform pore size distribution andremarkable hydrothermal stability.

Ordered mesoporous silica SBA-15 is synthesized by self-assembly of triblock copolymer template to form micelles andcondensation of silica precursor onto these micelles under acidicmediums. An expensive silica sources such as tetraethyl orthosi-licate (TEOS), fumed silica, silicon tetraethoxide, etc. is generallyused in the synthesis of SBA-15. Development of inexpensive andenvironmentally acceptable ways to prepare mesoporous materi-als is very important [12].

Some authors have recently investigated the conversion of coalfly ash into SBA-15 mesoporous silica [13,14]. On the basis of these

* Corresponding author. Tel.: +90 212 383 4729; fax: +90 212 383 4725.

E-mail address: [email protected] (S. Piskin).

Please cite this article in press as: Sari Yilmaz M, Piskin S. Evaluation

mine tailings slurry by experimental design. J Taiwan Inst Chem En

http://dx.doi.org/10.1016/j.jtice.2014.09.011

1876-1070/� 2014 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V.

studies, it was seen that proper selection of the Si content wasnecessary for the formation of ordered SBA-15 mesoporous silica.

Tailings slurry is the waste from gold mines which is used analternative silica source in the synthesis of mesoporous materialsdue to having high content of SiO2. Tailings slurry is obtained fromthe treatment plant of a gold mine. About 278 tonnes of gold minetreatment tailings slurry are generated every year during therecovery of gold [15]. Large amounts of tailing slurry bring a largedisposal requirement that requires large amounts of area. Therefore,the recycling of this kind of slurry into useful materials is quiteimportant in terms of economical and environmental aspects.

To the best of the authors’ knowledge, optimization of synthesisof SBA-15 from gold mine treatment tailings slurry has notpreviously been reported. In this study, we synthesized andcharacterized of ordered mesoporous silica SBA-15 using unpur-ified tailings slurry as a silica source. In addition, we applied two-level fractional factorial design with five variables that wereconsidered to play a crucial role in the synthesis of SBA-15 in orderto obtain ideal synthesis conditions.

2. Experimental

2.1. Materials

Gold mine tailings slurry was obtained from Bergama OvacıkGold Mine Treatment Plant, Turkey. The slurry sample was dried at

of novel synthesis of ordered SBA-15 mesoporous silica from goldg (2014), http://dx.doi.org/10.1016/j.jtice.2014.09.011

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M. Sari Yilmaz, S. Piskin / Journal of the Taiwan Institute of Chemical Engineers xxx (2014) xxx–xxx2

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105 8C for 2 h and ground to pass through a 90 mm sieve. Thetailings slurry was comprised of SiO2 (77.70%), Al2O3 (12.10%) andsmall amount of other metal oxides [16]. The absence of cyanide inthe slurry was confirmed by application of TS 12271 ‘‘Wastes-standard test methods for the detection of cyanides’’ [17]. Otherchemicals were purchased in analytical purity and used as such,without further purification.

2.2. Apparatus

The small-angle X-ray diffraction (XRD) patterns of the sampleswere recorded on a Philips Panalytical X’Pert-Pro X-ray diffrac-tometer, using Cu Ka radiation (g = 1.540 A). All metal concentra-tions were analyzed using Perkin Elmer Optima 2100 DVinductively coupled plasma optical emission spectrometry (ICP-OES). Infrared spectra of the samples were obtained using a PerkinElmer Spectrum One Fourier-transform infrared (FTIR) spectrom-eter using dry KBr as a standard reference in the range of 4000–450 cm�1. The surface area of the samples (outgassed undervacuum at 300 8C before analysis) were obtained by MicromeriticsASAP 2020 surface area and porosimetry analyzer. Microstructuresproperties of samples were analyzed using a CamScan Apollo 300scanning electron microscope (SEM).

2.3. Preparation of the alkali-fused tailings slurry silica source

The preparation of the silica source from unpurified gold minetreatment plant tailings slurry by alkali fusion method has beenreported previously. Different NaOH/slurry weight ratios (0.8, 1,

Table 1The selected factors, their levels.

Factors Level

�1 0 +1

NaOH/slurry (g/g), X1 1 1.25 1.5

Leaching time (h), X2 16 20 24

Stirring time (h), X3 16 20 24

Synthesis temperature (8C), X4 90 100 110

Synthesis time (h), X5 24 48 72

Y ¼ b0 þ b1X1 þ b2X2 þ b3X3 þ b4X4 þ b5X5 þ b6X1X2 þ b7X1X3 þ b8X1X4 þ b9X1X5 þ b10X2X3

þb11X2X4 þ b12X2X5 þ b13X3X4 þ b14X3X5 þ b15X4X5(2)

and 1.5) were used to explore the effect of this parameter in thefusion process [16]. In this study, the fusion process was performedby mixing slurry and sodium hydroxide at a ratio of 1:1.25 for 20 hleaching time. The amounts of Si, Al, and Na in the extractedsolution were 22,478, 803, and 71,252 mg/l, respectively. Theresults were expressed as the highest Si content was found in theextracted solution from NaOH/slurry ratio of 1.

2.4. Preparation of SBA-15 from tailings slurry

SBA-15 was synthesized using Pluronic 123 (P123) triblockcopolymer as the structure-directing template and tailings slurryas the silica source. The given amount of P123 triblock copolymerwas dissolved in 2 M aqueous solution of HCl at room temperature.Then the extracted solutions which were prepared from differentweight ratios of NaOH/slurry (X1) fusion products for differentleaching times (X2) were added under stirring. After a certain time,concentrated HCl and distilled water was quickly added to thereaction mixture. The stirring was continued for the determinedstirring time (X3). The resulting gel was transferred into a Teflon-lined steel autoclave and heated at synthesis temperature (X4) forthe synthesis time (X5). After cooling to room temperature, thesolid product was filtered, washed and dried overnight at 100 8C.This as-synthesized material was calcined at 550 8C for 6 h.

2.5. Experimental design

In order to determine the most suitable conditions for orderedSBA-15 mesoporous silica synthesis from tailings slurry, fractionalfactorial experimental design was applied to evaluate thepreliminary significance of the factors, as well as the interactions



between them. Fractional factorial design is used to decrease thenumber of experiments to a reasonable amount by eliminating theinsignificant factors. Five factors, weight ratio of NaOH/slurry,leaching time, stirring time, synthesis time, and synthesistemperature were chosen as the control variables, with theresponse variables being the specific surface area (SBET) and unitcell parameter (ao). The X1 factor (weight ratio of NaOH/slurry) andits levels were chosen according to Yang et al. due to the lack ofsimilar studies about synthesis of SBA-15 from waste in theliterature [18]. The other factors levels were chosen according torelated to synthesis of SBA-15 from pure silica source in theliterature [1,19,20].

All factors were evaluated at two levels, low and high. Inaddition, a triple replicate at the center point was included in thedesign. Table 1 shows the coded factors and the levels for eachfactor. According to the fractional factorial design, factors were setat two levels with three replicates at center points, thus a total of19 experiments were carried out in this study.

The reason of selection of ao as response is that the best qualityproduct in the synthesis of mesoporous materials has maximum‘ao’ value [21]. ao value was calculated using the following equationusing XRD data:

ao ¼2 � d1 0 0

ffiffiffi

3p (1)

where d1 0 0 is the (1 0 0) interplanar spacing.The regression model for fractional factorial design relating the

variables to the responses is given by the equation:

where Y is the response, b0 is the constant, bi (i = 1, . . ., 5) areregression coefficients of the coded parameters Xi (i = 1, . . ., 5) andbi (i = 6, . . ., 15) are dual interaction between investigatingparameters. Data analysis was carried out by the use of Minitab16 statistical software.

3. Results and discussion

Fig. 1 gives the XRD patterns of the samples prepared underdifferent experimental treatments. There is a clear differencebetween the samples obtained at the weight ratio of NaOH/slurry1.5 and 1.25 (Run 4, 8, 11, and 18) and those obtained at the weightratio of NaOH/slurry 1 (Run 1, 6, and 10). In Run 1, 6, and 10, XRDpatterns exhibit three diffraction peaks which could be indexed as(1 0 0), (1 1 0), and (2 0 0) reflections, respectively. These arecharacteristics of two-dimensional hexagonal (p6mm) orderedSBA-15 mesoporous phase. In Run 4, 8, 11, and 18, no diffractionpeaks were observed indicating that the ordered mesoporousstructure was collapsed. In these experimental runs, ao values couldnot be calculated due to absence of d100 peaks. Therefore, ao valuewas evaluated in a qualitative rather than quantitative manner.



Fig. 1. Small-angle XRD patterns of the samples: (a) Run 1, (b) Run 4, (c) Run 6, (d)

Run 8, (e) Run 10, (f) Run 11, and (g) Run 18.

M. Sari Yilmaz, S. Piskin / Journal of the Taiwan Institute of Chemical Engineers xxx (2014) xxx–xxx 3

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FTIR spectra of samples prepared under different experimentalruns are shown in Fig. 2. The broad band around 3450 cm�1 wasattributed to vibrations of OH group within the silanol groups. Theband near at 1630 cm�1 is commonly associated to the bending ofH–O–H from adsorbed water, whereas pair of bands at 1080 and800 cm�1 belonged to asymmetrical and symmetrical stretching ofSi–O–Si. The bands around at 960 and 460 cm�1 indicate Si–OHvibrations generated by the presence of defect sites and Si–O–Sibending mode, respectively [22]. The band around at 960 cm�1

was not present in the spectra of the samples obtained at theweight ratio of NaOH/slurry 1.5 and 1.25 (Run 3, 4, and 17).

Fig. 2. FTIR spectra of the samples: (a) Run 6, (b)



The SEM images of samples obtained following syntheses underdifferent operating conditions are shown in Fig. 3. In Run 6,particles consisted of many rope-like domains with average sizesof 1 mm which tend to form wheat-like aggregates in accordancewith the morphology of SBA-15. In Run 15 and 18, the typicalwheat-like structure disappeared and nanosized agglomeratedparticles were observed in the samples.

According to these results, it was seen that the ordered SBA-15mesoporous structure was only obtained from sample prepared atweight ratio of NaOH/slurry 1. The highest Si content was found inthe extracted solution from NaOH/slurry ratio of 1 mentionedabove. This Si content was sufficient for the cooperative self-assembly of silica precursor and triblock copolymer template tothe ordered SBA-15 silica formation. Chandrasekar et al. [13]reported that by increasing the silica content, silica condensationon template assembly enhanced and higher ordered SBA-15mesoporous silica was synthesized. Therefore, proper Si contentwas necessary for the formation of highly ordered mesoporousmaterials.

3.1. Fractional factorial design experiments

The design matrix of coded values of the factors and the values ofthe responses for all experimental runs including replicates, aregiven in Table 2. From the table, low, center and high levels of factors(X1–X5) were denoted as �1, 0 and +1, respectively. The contrastcoefficients of factor X5 is generated from the contrast coefficients offactors X1–X4 through the following equation [23–26]:

X5 ¼ X5 � I ¼ X5 � X1X2X3X4X5 ¼ X1X2X3X4X52 ¼ X1X2X3X4 (3)

As can be seen in Table 2, ao value cannot be calculated becausethe d100 value was not present in some experimental runs.Therefore, ao value was evaluated as a qualitative output (there ornot).

The relationship between response as SBET and ao values wasinvestigated by binary logistic regression (Fig. 4). From the figure,

Run 17, (c) Run 3, (d) Run 4, and (e) Run 10.



Fig. 3. SEM images of the samples: (a) Run 6, (b) Run 15 and (c) Run 18.


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when SBET value was between 14.41 to 229.03 m2/g, probability ofao was 0, while SBET value was between 448.05 to 661.59 m2/gprobability of ao was 100%. Consequently, in order to achieve adetectable ao, SBET must be above 448 m2/g. In other words, theordered mesoporous structure was formed above 448 m2/g of SBET

value. From Table 2, it was seen that all samples having above448 m2/g of SBET were obtained from the highest Si containingextracted solution from NaOH/slurry ratio of 1.

Table 2Fractional factorial design matrix and values of the responses.

Run order X1 X2 X3 X4 X5 SBET (m2/g) ao (A)

1 �1 �1 �1 +1 �1 618.78 110.19

2 �1 +1 �1 �1 �1 448.05 101.07

3 +1 �1 �1 �1 �1 26.65 *

4 +1 +1 �1 +1 �1 37.59 *

5 �1 +1 +1 +1 �1 661.59 102.97

6 �1 �1 +1 �1 �1 564.81 113.61

7 +1 �1 +1 +1 �1 17.69 *

8 +1 +1 +1 �1 �1 19.87 *

9 �1 �1 �1 �1 +1 644.71 110.75

10 �1 +1 �1 +1 +1 575.71 119.09

11 +1 �1 �1 +1 +1 14.41 *

12 +1 +1 �1 �1 +1 19.14 *

13 �1 �1 +1 +1 +1 594.61 113.25

14 �1 +1 +1 �1 +1 544.37 121.78

15 +1 �1 +1 �1 +1 21.28 *

16 +1 +1 +1 +1 +1 20.82 *

17 0 0 0 0 0 229.03 *

18 0 0 0 0 0 187.45 *

19 0 0 0 0 0 193.25 *

* Not determined because of d100 value was absent.



3.2. Regression analysis

The linear and interaction effects of the parameters can beapproximated to a linear regression model using the normal leastsquare technique [23]. The estimated effects and regressioncoefficients (Coef), along with the corresponding standard errorof each estimated coefficient (SE Coef), and t-statistics (T) values inthe model are shown in Table 3. By substituting the coefficients bi

in Eq. (2) with their values from Table 3 we can derive a modelequation relating the level of parameters and SBET:

Fig. 4. The relationship with ao and SBET values.



Table 3Estimated effects and coefficients for SBET.

Term Effect Coef. SE Coef. T

Constant 301.9 5.631 53.61

NaOH/slurry �559.4 �279.7 5.631 �49.67

Leaching time �22.0 �11.0 5.631 �1.95

Stirring time 7.5 3.7 5.631 0.67

Synthesis temperature 31.5 15.8 5.631 2.80

Synthesis time 5.0 2.5 5.631 0.44

Leaching time � NaOH/slurry 26.3 13.2 5.631 2.34

Leaching time � stirring time 34.0 17.0 5.631 3.02

Leaching time � synthesis time �6.8 �3.4 5.631 �0.60

Leaching time � synthesis temperature 34.5 17.3 5.631 3.07

NaOH/slurry � stirring time �12.0 �6.0 5.631 �1.07

NaOH/slurry � synthesis time �11.5 �5.8 5.631 �1.02

NaOH/slurry � synthesis temperature �30.6 �15.3 5.631 �2.72

Stirring time � synthesis time �25.7 �12.9 5.631 �2.28

Stirring time � synthesis temperature 4.6 2.3 5.631 0.40

Synthesis time � synthesis temperature �37.5 �18.8 5.631 �3.33

Ct Pt �98.6 14.170 �6.96

Table 5The result of ANOVA of the reduced regression model (containing only statistically

significant factors).

Source DF Seq SS Adj SS Adj MS F p

Main effects 1 1251,701 1251,701 1251,701 609.81 0.000

NaOH/slurry 1 1251,701 1251,701 1251,701 609.81 0.000

Curvature 1 24,579 24,579 24,579 11.97 0.003

Residual error 16 32,842 32,842 2053

Pure error 16 32,842 32,842 2053

Total 18 1309,122

Y ¼ 301:9 � 279:7X1 � 11:0X2 þ 3:7X3 þ 15:8X4 þ 2:5X5 þ 13:2X1X2 � 6:0X1X3 � 15:3X1X4

� 5:8X1X5þ17:0X2X3þ17:3X2X4 � 3:4X2X5þ2:3X3X4 � 12:9X3X5 � 18:8X4X5 (4)


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3.3. Analysis of variance

Analysis of variance (ANOVA) was used to test how theexperimental factors affect SBET. The degree of freedom (DF),sequential sum of squares (Seq SS), percentage of Seq SS (Seq SS%),adjusted sum of squares (Adj SS) and adjusted mean of squares (AdjMS), of each factor, F test and p value are listed in Table 4. In orderto be able to declare that the effect is significant for a 95%confidence level, the p value, which shows the statistical efficacy ofthe effects in the model, should be less than or equal to 0.05. Theresults revealed that the coefficient of the weight ratio of NaOH/slurry was statistically significant to SBET. Other factors did nothave statistically significant effects.

Table 5 shows the result of ANOVA on the reduced regressionmodel (containing only statistically significant factors). The mainfactor weight ratio of NaOH/slurry was statistically significant.Also, there is a little curvature (difference between the average ofthe center point responses and the average of the factorial points)in the design space. Percentage of Seq SS of curvature in the model

Table 4Analysis of variance (ANOVA).

Source DF Seq SS Se

NaOH/slurry 1 1251,701 9

Leaching time 1 1931

Stirring time 1 225

Synthesis temperature 1 3979

Synthesis time 1 100

Leaching time � NaOH/slurry 1 2772

Leaching time � stirring time 1 4635

Leaching time � synthesis time 1 183

Leaching time � synthesis temperature 1 4769

NaOH/slurry � stirring time 1 579

NaOH/slurry � synthesis time 1 532

NaOH/slurry � synthesis temperature 1 3758

Stirring time � synthesis time 1 2647

Stirring time � synthesis temperature 1 83

Synthesis time � synthesis temperature 1 5633

Curvature 1 24,579

Residual error 2 1015

Pure error 2 1015

Total 18 1309,122 10



was found as 1.88%, which is quite small and very little significantcompared to percentage of NaOH/slurry (95.61%). Moreover, theoptimum result was observed not in the center point but in theaxial point (NaOH/slurry = 1), making the effect of curvature notsignificant enough. Therefore, the curvature effect was neglected inthis study.

A Pareto plot that visually displays the absolute values of theeffects of the individual factors and interaction factors is illustrated

in Fig. 5. In Pareto plot analysis, the reference line indicates theminimal magnitude of statistically significant effects for 95%confidence level. In other words, the factors extending past thisline are potentially important. It can be seen from Fig. 5 that theweight ratio of NaOH/slurry is the only factor extend beyond thereference line.

The main effect plots were generated to visualize the effect ofeach variable on the response (Fig. 6). The mean value in the plotwas obtained by averaging the response SBET for high, low, andcenter levels of each factor. The response decreased when X1 factorchanged from low to high levels. Maximum response values wereobserved in the runs at low of X1 values. On the other hand, theeffects of all other factors on the response SBET varied little acrossall values, indicating that all factors had insignificant effects.

The experimental model for response SBET value which wasproduced after discarding the statistically insignificant terms canbe described by the following equation:

Y ¼ 1700:37 � 1118:79X1 (5)

q SS% Adj SS Adj MS F p

5.61 1251,701 1251,701 2467.60 0.000

0.15 1931 1931 3.81 0.190

0.02 225 225 0.44 0.574

0.30 3979 3979 7.84 0.107

0.01 100 100 0.20 0.700

0.21 2772 2772 5.46 0.144

0.35 4635 4635 9.14 0.094

0.01 183 183 0.36 0.609

0.36 4769 4769 9.40 0.092

0.04 579 579 1.14 0.397

0.04 532 532 1.05 0.413

0.29 3758 3758 7.41 0.113

0.20 2647 2647 5.22 0.150

0.01 83 83 0.16 0.725

0.43 5633 5633 11.11 0.079

1.88 24,579 24,579 48.46 0.020

0.08 1015 507

0.08 1015 507

0



Fig. 5. Pareto plot for standardized effects for synthesis of SBA-15 from tailings

slurry.

Fig. 6. Main effects plot for synthesis of SBA-15 from tailings slurry.

Fig. 7. Small-angle XRD patterns of the samples: (a) Run 22, (b) Run 23, (c) Run 24,

and (d) Run 25.


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3.4. Control analysis

In order to confirm the experimental model, two differentdesign matrices were built. Design analysis matrix and comparisonof experimental and calculated response values are listed inTable 6. The calculated and experimental values of the responseswere in reasonable agreement, indicating that curvature effectplayed a negligible role. Thus, it was proven that only the ratio ofNaOH/slurry has a significant effect on production of SBA-15.

Table 6Control analysis matrix and comparison of experimental and calculated response.

Run order X1 X2 X3 X4 X5 Response

Experimental Calculated Error (%)

20 1 16 16 90 24 603.84 581.58 �3.83

21 1 24 24 110 16 582.13 581.58 �0.10

Table 7Experimental plan for additional analyses.

Run order X1 X2 X3 X4 X5

22 0.8 24 24 110 72

23 0.8 24 16 90 72

24 0.8 16 24 110 24

25 0.8 16 24 90 72



3.5. Additional analyses

When the results of the experimental design analysis wereinspected, it was determined that the only effective parameter onthe synthesis of SBA-15 from slurry is the weight ratio of NaOH/slurry. In the experimental design study, its levels were chosenaccording to the weight ratio of NaOH/bentonite in the synthesis ofmesoporous Al-MCM-41 from bentonite [18]. For this purpose,conducting analysis except for experimental design has been heldby arranging the NaOH/slurry ratio to 0.8 to see the changes of theresults in case of NaOH/slurry ratio less than 1 (Table 7).

The amounts of Si, Al, and Na in the extracted solution ofprepared mixture at weight ratio of NaOH/slurry:0.8 were 24,080,896, and 68,741 ppm for 16 h leaching time and 25,445, 972, and69,670 ppm for 24 h leaching time, respectively.

XRD results for the samples prepared at weight ratio of NaOH/slurry 0.8 are given in Fig. 7. It can be seen from the figure thecharacteristic peaks of SBA-15 mesoporous phase disappear,indicating that the ordered hexagonal structures cannot beobtained under this condition.

The only effective parameter was weight ratio of NaOH/slurryon the synthesis of SBA-15 from tailings slurry according to resultsof experimental design. Ordered mesoporous SBA-15 was observedat weight ratio of NaOH/slurry 1. To reduce cost of synthesis ofSBA-15, most suitable synthesis conditions were selected asfollows: weight ratio of NaOH/slurry 1, leaching time of 16 h,stirring time of 16 h, synthesis temperature at 90 8C, and synthesistime of 24 h.

4. Conclusions

In this study, we report a novel synthesis of SBA-15 using goldmine tailings slurry as a cheap and environmentally friendly silicasource. In order to evaluate the influence of variables on thesynthesis of SBA-15 from tailings slurry, fractional factorial designwas applied.

The response (SBET value) was strongly correlated to a reducedlinear regression model including only one variable. The modelrevealed that the weight ratio of NaOH/slurry was the mostsignificant factor influencing synthesis of SBA-15 from gold minetailings slurry. In control analysis, the predicted SBET value calculatedwith the derived mathematical model showed in a good agreementwith the experimental SBET value. The most suitable condition for the




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synthesis of SBA-15 from tailings slurry included weight ratio ofNaOH/slurry 1, leaching time of 16 h, stirring time of 16 h, synthesistemperature at 90 8C, and synthesis time of 24 h. This developedmethod presents an environmentally friendly and economicalapproach to the synthesis of mesoporous materials.

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Evaluation of novel synthesis of ordered SBA-15 mesoporous silica from gold mine tailings slurry by experimental design