Effect of elaboration parameters of a membrane ceramic on the filtration process efficacy

Author’s Accepted Manuscript Effect of elaboration parameters of a membrane ceramic on the filtration process efficacy Malek Sayehi, Rym Dhouib Sahnoun, Salma Fakhfakh, Semia Baklouti www.elsevier.com/locate/ceri

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S0272-8842(17)32835-3 https://doi.org/10.1016/j.ceramint.2017.12.127 CERI17007

To appear in: Ceramics International Received date: 10 October 2017 Revised date: 15 December 2017 Accepted date: 18 December 2017 Cite this article as: Malek Sayehi, Rym Dhouib Sahnoun, Salma Fakhfakh and Semia Baklouti, Effect of elaboration parameters of a membrane ceramic on the filtration process efficacy, Ceramics International, https://doi.org/10.1016/j.ceramint.2017.12.127 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Effect of elaboration parameters of a membrane ceramic on the filtration process efficacy Malek Sayehia, Rym Dhouib Sahnoun*a Salma Fakhfakha, Semia Bakloutib. a: Laboratory of Industrial Chemistry, BP 1173, 3038 Sfax, Tunisia b: Laboratory of Materials Engineering and Environment, National School of Engineering, University of Sfax.BP 1173, 3038 Sfax, Tunisia

*

Corresponding author: Tel.: +216 98 2512 55; fax: +216 74 67 69 08. E.mail address: [email protected] (R. Dhouib Sahnoun).

Abstract: The formation of the flat membrane from kaolin and potassium phosphate was investigated with a particular focus on the appropriate elaboration parameters and the effect of their separation performance. The first step consisted in the fabrication of flat ceramic membrane supports from mechanochemicaly-treated kaolin (K) and starch (S). The mechanical properties, permeability and porosity of these supports were studied as a function of the milling time of kaolin, the starch content, the sintering temperature and time. The optimization of the elaboration parameters led to the fabrication of supports from kaolin milled for 30 min and 5% starch at sintering temperature of 1100 °C and sintering time of 1 hour. In the second step, the potassium phosphate was added as a binder in the kaolin- 5% starch mixture. In this case, we noted the improvement of the permeability without reduction of the mechanical strength and porosity. Also, the separation performances and the fouling of 1

membranes elaborated with different potassium phosphates were evaluated using Bovine Serum Albumin (BSA) solution. Keywords: Mechanochemical treatment; Ceramic membrane supports; Kaolin; Mechanical properties; Permeability and fouling.

1. Introduction Membrane technology covers different technology disciplines, such as material sciences and technology, mass transport and process design. By manipulating material properties, the membrane can be fitted for particular separation tasks to perform under specific separation conditions.

Porous ceramic membranes exhibit more remarkable advantages than there organic counterparts such as high mechanical strength, good chemical corrosion resistance, high separation efficiency, superior high-temperature resistance, good structural stability, low energy consumption and easy clean-regeneration [1-4]. As a result, they are increasingly applied in many industrial separation fields. Recently, they have been attracting much attention in the scientific community due to their high separation selectivity, low permeation resistance and good mechanical performance [5].

The kaolin’s applicability, widely used as a material for membrane supports, is determined by its physical, chemical, structural, and surface properties, which can be significantly modified by mechanochemical activation through dry grinding [6-8]. Dry grinding significantly changes the morphology (surface area, pore volume) [9], the thermal

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behavior [10] and the molecular structure of the surface (active sites of the tetrahedral and octahedral sheets) of the clay [11]. The aim of this work is to manufacture ceramic membrane supports from mechanochemically-treated kaolin (K), starch (S) (as porosity agent) and potassium phosphates (as binder agent). We undertake, in the first part, a very detailed study on the effect of grinding time, starch content, sintering temperature and sintering time on the rupture strength, the porosity and permeability of the ceramic supports. The impact of adding KH2PO4, K2HPO4 and K3PO4 in the kaolin structure on the mechanical, morphological and hydraulic characterizations is determined in the second part. Therewith, the membrane process performance (permeate flux) and the fouling resistance were studied for bovine serum albumin (BSA) filtration. 2. Experimental procedure 2.1. Preparation of membrane supports After being dried at 120 °C, the raw kaolin (provided by BWW Minerals [12]) was ground using a planetary ball mill (Retsh PM 100). Each milling was carried out with a 100 g air-dried sample in an 500 cm3-capacity pot using eight stainless-steel balls (10 mm in diameter), with an applied rotation speed of 400 rpm. The main stages of the preparation process required for the flat membrane supports used in this work are described in Fig. 1. 2.2. Characterisation The particle size distribution (PSD) of the natural and milled kaolin was determined on MASTERSIZER 2000 instrument. The test was conducted in suspension. In order to avoid flocculation, samples were supplied with sodium polyphosphate (1%) as dispersant and ultrasonicated for 10 min.

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The linear shrinkage was determined by dilatometry (Setearam TMA 92 dilatometer). The heating and cooling rates were 10 ˚C min-1 and 20 ˚C min-1, respectively. The rupture strength σr was evaluated through the following equation: σr = 2P/πDe where D and e are the diameter and the thickness of the sample, respectively, and P is the maximum applied load. The rupture modulus was measured using LLOYD EZ50 equipment. At least six specimens were tested for each test condition and an average of the values was then calculated. The porosity of the as-sintered kaolin ceramics was determined by mercury porosimetry (Micrometric). Four specimens were selected to determine porosity with an error of less than 1% of the measured porosity value. The microstructure of the sintered compacts was investigated by scanning electron microscopy (SEM Phillips XL 30) on sample-fractured surfaces. For liquid permeation experiments, a laboratory-made permeation setup of capacity of 40 ml was used. The setup (as shown in Fig. 2) used for these experiments is composed of a tubular cell stainless steel (type AMICON). The protein solutions consisting of 0.1 gL−1 bovine serum albumin (BSA) dissolved in distilled water. BSA has an isoelectric point (IEP) of 4.9, a molecular weight of 67.000 Da. All experiments were carried out under the condition of constant pH which is the IEP of BSA. The membrane was cleaned after each run according to the sequence basic/acid until the original water flux was restored 3. Results and discussion 3.1. Particle size distribution

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The particle-size-distribution analysis of the unground and ground kaolin samples are shown in Fig. 3. The increase of the particle diameters of the kaolin grounded for 60 and 120 min may be associated with a release of the water molecules [8,13], during the mechanochemical treatment, which favors the formation of the agglomerates. Indeed, the larger kaolin agglomerates behave as individual large particles, thus reducing the surface area of the samples. The effectiveness of the mechano-chemical treatment of kaolinite depends on different settings as studied by Frost et al. [8] who demonstrated in their research that the optimum grinding time depends on its initial water and the quantity of impurities such as quartz. He has shown that there is an optimum time for grinding kaolin, beyond which any additional crushing will be of no use, but rather harmfultt. 3.2. The sintering shrinkage behaviors of the studied samples

The sintering shrinkage behaviors of the starting clay and samples milled for various milling times are given in Fig. 4. For the kaolin, whatever the temperature, the linear shrinkage is the lowest (Fig. 4). The mechanically treated samples exhibit some differences in sintering shrinkage behaviors, which are described as follows: - The shrinkage increases with the grinding time; - The shrinkage of the treated kaolin powders (particularly K60 and K120) shows a gradual variation, without inflexion points, when the sintering temperature increases; - For the all mechanically treated kaolin the most shrinkage is obtained at the low temperature (T < 900 ˚C). Thus, the shrinkage of 9% was obtained at about 1255 °C, 1190 °C, 1140 °C, 990 °C and 990 °C for the raw kaolin, K15, K30, K60 and K120, respectively. The destruction of the kaolinite structure by the distortion and breakage of the crystalline network caused by milling, as mentioned elsewhere [14], is confirmed by the dilatometric analyses (Fig. 4). It has been proposed that dry grinding removes the hydroxyl 5

groups from the kaolinite and results in the formation of new kaolinite surfaces [14-15]. The dry grinding process causes the breaking of the hydrogen bonds between the adjacent kaolinite layers and the decrease of bonding energy of hydroxyl groups. However, the loss of the hydroxyl groups at low temperature and the spherical shape of particles after mechanical treatment promote the reunification of the grains and therefore their coalescence. This fact explains the gradual shrinkage made recorded in the case of milled kaolin samples especially K60 and K120. 3.3. Mechanical, morphological and hydraulic characterizations of membrane supports To optimize the different processing parameters for making membrane supports, we studied the effect of the grinding time, the content of starch, the sintering temperature and time on the rupture strength, the porosity and the permeability. It is noted that the permeability is determined according to the Darcy equation:

(1) Where, Jw is pure water flux, Lp is the hydraulic permeability and P is the transmembrane pressure. 3.3.1. Effect of grinding time Table 1 presents the effect of grinding time on the characteristics of the membrane supports, made from the powders compacted at 58.5 MPa and sintered at 1100 °C for 1 h. The reduction of the particle size improves the sintering behavior of kaolin, and hence the resulting product is denser and more compact, which is the case of the K30 supports. On the other hand, extending the grinding beyond 30 min improves the porosity and permeability and reduces the rupture strength of the kaolin supports sintered at the same temperature. This may be due to the formation of the aggregates, which modifies the sintering behavior of the obtained supports. 6

In the case of the porous materials, the microstructure can dramatically change their physical properties [16,17]. For these reasons, it seemed interesting to study the morphology of the prepared membrane supports by SEM (Fig. 5). The observation of the micrographs collected in Fig.5 shows that after sintering, the grain size decreases when the kaolin is ground for 30 min. While the extension of the grinding of kaolin favors the formation of larger grains specifically for the supports from K60 and K120. Indeed these micrographs show that the growth of the grains is greater than the supports prepared from kaolin, K15 and K30. In addition, the micrographs have confirmed that the increase in the grinding time until 30 min decreases the porosity and increases the pore size of the sintered supports. This increase could be explained by the merger of small pores causing the formation of larger pores during calcinations. 3.3.2. Effect of starch content The starch is the most widely used agent of porosity. In purpose to verify the evolution of porosity and pore size we performed SEM observations on a supports fabricated from K30 and K30-5 mass% S powders (Fig. 6). It appears, from the micrographs of Fig. 6, that the porosity and the pore size increase considerably in the presence of starch. As clearly indicated in table 2, the addition of 5 mass% of starch to the K30 satisfies the compromise between permeability and mechanical properties of the support. 3.3.3. Effect of sintering temperature and time As clearly indicated in Table 3, although the increase in temperature improves mechanical properties, the permeability and pore radius, it decreases the porosity of the sintered supports. This result has been proven by the SEM micrographs of flat support, elaborated with K30- 5 mass% S and sintered at three temperatures (900, 1000 and 1100 °C) as reported in Fig. 7. The membrane sintered at 1100°C shows the presence of almost 7

spherical pores, which indicates that the sintering is controlled by a viscous flow mechanism. Table 4 exhibits that permeability increases with the rise of sintering time, raising from 37.57 to 60.89 L h−1 m−2 bar−1 when the sintering time increases from 1 to 3 hours. This is probably due to the increase in pore size as the sintering time increases, which is confirmed by the relation between permeability and pore size [17]. Therefore, it is concluded that the flat kaolin supports, K30-5 mass% S sintered at 1100 °C for 1 h have the optimum properties as sufficient porosity, sufficient mechanical strength and high permeation flux. In the remainder of the present study, the effect of binding agents, KH2PO4, K2HPO4 and K3PO4, on the kaolin structure are performed only on the supports K30-5 mass% S. In this case, the membrane process performances (permeate flux) and the fouling resistances were studied for the standard solution filtration (BSA). 3.4. Effect of binding agents KH2PO4, K2HPO4 and K3PO4 on the hydraulic, morphological and mechanical characterizations of membrane supports The results of the permeability of the different tablets are presented in Table 5 and Fig. 8 and 9. The tablets made with potassium phosphate as binding agents appear to have better permeability than those prepared only with clay-starch. This is probably due to the increase in mean pore size and the increase in the filter hydrophilicity [18]. These results are not in good agreement with those of Palacio et al. [19], reporting that phosphate binding have negligible influence on water permeability. From Table 5, the rupture strength and porosity show minor changes, which is contrary to expectation. 3.5. Permeate flux and fouling rate of bovine serum albumin BSA In order to evaluate the separation performance of membranes with different potassium phosphate, a filtration applied to BSA solution was carried out. The permeate flux

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of BSA solution decreases gradually with time due to the membrane fouling as illustrated in Fig. 10. With all three membranes (K1-5, K2-5 and K3-5), the flux of BSA solution is generally smaller than that observed with pure water. However, with K30-5%S membrane, the permeate flux of BSA solution appeared similar than that of water flux (Figs. 8 and 10). The amount of protein deposited on and/or within the membrane is significantly lower for K30-5 mass% S, compared to the other supports, probably due to its structure. There are three parameters of membrane resistance-in-series model based on Darcy’s law, which were used to quantify their influences on flux decline.

where J is solution flux through the membrane, P is the transmembrane pressure, µ is the dynamic viscosity of permeate, Rm is the clean membrane hydraulic resistance, Rcp is the concentration polarization layer resistance, could be removed by water, Rf is the fouling can be removed by chemical cleaning. The distilled water and solution were filtered using the procedure describe by Fakhfak et al. [20] to quantify all hydraulic resistances. As presented in Table 6, the resistances of the fouling layers (Rf) and the polarised layer (Rcp) for the four supports were different because its structure were changed. The fouling of the kaolin-starch-potassium phosphate membranes is probably due to a greater interaction membrane-species deposited on or within the pores. This interaction is slightly lower for the kaolin-starch membrane, which indicates no significant changes of permeate flux BSA against the water flux. Most particles are adsorbed on, or plugged into the kaolinstarch-potassium phosphate membrane (Rcp
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deposited on the surface of membrane kaolin-starch, contributing to a polarised layer formation ( Rp> Rf) [21]. 3.6 Chemical corrosion resistance of porous kaolin- starch- potassium phosphate support The chemical resistance of the Kaolin-starch-potassium phosphate supports sintered at 1100 °C for 1 h was characterized in terms of mass loss, after boiling in the acidic and alkali solutions. The specimens were cut and then placed in HNO3 (0.3 M) at 60 °C and NaOH (0.5 M) at 80 °C solutions, with time. All the samples were rinsed in distilled water and dried at 105 °C. The degree of corrosion was characterized by the percentage of the mass loss. An approximately linear relationship exists between mass loss and boiling time for three supports (Fig. 11). Three membrane supports exhibit a better acid corrosion resistance than alkali. This is due to the fact that the hydroxide ions reacted better with the samples in alkali solution than in acid at the same corrosion time. The poor acid and alkali resistance of the K3-5 supports is mainly due to the nature of potassium phosphate, as well as the existence of K3PO4 in the starting materials. The corrosion mechanisms begin after sixty six hours. Therefore, the observed results in mass loss during corrosion tests suggest that the prepared supports possess a good chemical corrosion resistance and are suitable for applications involving acidic and basic media. 4. Conclusion The optimization of processing parameters for making membrane supports has given the following results: The reduction of the particle size improves the sintering behavior of kaolin, and consequently the mechanical properties, which is the case of the K30 supports. The sintering temperature of 1100 °C and sintering for 1 hour were considered optimum and seems appropriate to provide the K30-5 mass% S support with suitable mechanical properties and permeability for an eventual filtration.The prepared membrane K30-5 mass% S type 10

could offer a satisfactory separation, but the problem of membrane fouling should not be overlooked. The supports made with potassium phosphate as binding agents have better permeability than those prepared only with clay-starch but their rupture strength and porosity are almost invariable. Compared to the other supports, the amount of protein deposited on and/or within the membrane is significantly lower for K30-5 mass% S, this is probably due to its structure.

Acknowledgments This study was supported financially by the Ministry of Higher Education and Scientific Research of Tunisia. Moreover, the authors gratefully acknowledge Mrs Leila MAHFOUDHI, for proofreading and polishing the language of this manuscript. References [1] T. Tsuru, Inorganic porous membrane for liquid phase separation. Separ. Purif. Method. 30 (2001) 191–220. [2] A. Larbot, J.P. Fabre, C. Guizard, L. Cot, J. Gillot, New inorganic ultrafiltration membranes: titania and zirconia membranes. J. Am. Ceram. Soc. 72 (1989) 257–261. [3] T. Van Gestel, B. Van der Bruggen, A. Buekenhoudt, C. Dotremont, J. Luyten, R. Leysen, C. Vandecasteele, G. Maes, Surface modification of γ-Al2O3/TiO2 multilayer membranes for applications in non-polar organic solvents, J. Membrane Sci 224 (2003) 3–10.

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[4] J. Caro, M. Noack, P. Kolsch, Chemically modified ceramic membranes 1. Micro. Meso. Mater. 22 (1998) 321–332. [5] N.P. Xu, W.H. Xing, Y.J. Zhao, Separation technology and application of inorganic membrane, Chem. Ind. press, Beijing, 2003. [6] R.L. Frost, É. Makó, J. Kristóf, E. Horváth, J.Th. Kloprogge, mechanochemical treatment of kaolinite. J. Colloid Interface Sci. 239 (2001) 458-466. [7] R.C. Reynolds Jr, D.L. Bish, The effects of grinding on the structure of a low-defect kaolinite. Am. Mineral. 87 (2002) 1630. [8] R.L. Frost, E. Horváth, É. Makó, J. Kristóf, Modification of low- and high-defect kaolinite surfaces: implications for kaolinite mineral processing. J. Colloid Interface Sci. 270 (2004) 337-46. [9] A.Z. Juhász, L. Opoczky, Mechanical Activation of Minerals by Grinding: Pulverizing and Morphology of Particles, Academia Press, Budapest, 1990. [10]E. Horváth, R.L. Frost, É. Makó, J. Kristóf, T. Cseh, thermal treatment of mechanochemically activated kaolinite.Themochim. Acta 404 (2003) 227-234. [11] R.L. Frost, E. Horváth, É. Makó, J. Kristóf, Modification of low- and high-defect kaolinite surfaces: implications for kaolinite mineral processing. J. Colloid Interface Sci. 270 (2004) 337-46. [12] R Dhouib Sahnoun, J. Bouaziz, Sintering characteristics of kaolin in the presence of phosphoric acid binder, Ceram. Inter. 38 (2012) 1–7. [13] É. Makó, , Z. Senkár, J. Kristóf, , V. Vágvölgyi, Surface modification of mechanochemically activated kaolinites by selective leaching , J. of Coll. and Inter. Sci., 294 (2006) 362–370.14] R.Dhouib Sahnoun, K. Chaari and J. Bouaziz,

mechanochemical

synthesis of kaolin-potassium phosphates complexes for application as slow-release fertilizer, Mediterr. J. of Chem. 4(3) (2015) 156-162. [15] F. Dellisanti, G. Valdrè, The role of microstrain on the thermostructural behaviour of industrial kaolin deformed by ball milling at low mechanical load, Inter. J. Mine. Process. 102–103 (2012) 69–77. [16] R. Dhouib Sahnoun, S. Baklouti, Characterization of flat ceramic membrane supports prepared with kaolin-phosphoric acid-starch, App. Clay. Sci. 83–84 (2013) 399–404 .

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[17] B.K. Nandi, R. Uppaluri, M.K. Purkait, preparation and characterization of low cost ceramic membranes for micro-filtration applications, App. Clay Sci. 42 (2008)102-110. [18] K. Riedl , B. Girard , R. W. Lencki, Influence of membrane structure on fouling layer morphology during apple juice clarification J. Membrane. Sci. 139 (1998) 155-166. [19] L. L.Palacio, Y. Bouzerdi, M. Ouammou, A. Albizane, J. Bennazha, A. Hernández, J.I. Calvo, Ceramic membranes from Moroccan natural clay and phosphate for industrial water treatment, Desalination 245 (2009) 501–507. [20] S.Fakhfakh, S. Baklouti, S. Baklouti, J. Bouaziz Preparation, characterization and application in BSA solution of silicaceramic membranes, Desalination 262 (2010) 188–195. [21] I.H. Huisman, P. Prádanos, A. Hernández, The effect of protein–protein and protein– membrane interactions on membrane fouling in ultrafiltration, J. of Membr. Sci. 179, (2000) 79-90

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Mechanochemical Figure captions treatment of kaolin (kaolin+starch)

Dry mixing of grinded kaolin and starch

Pressing of the powder (58.5MPa)

Cylindrical compacts (=30mm, thickness = 7mm)

D=20 mm; e= 6 mm. Characterization of the membrane supports

Fig. 1. The main stages of the preparation process required for the flat membrane supports.

Valve Feed Compressed air Pressure gauge

Membrane

Permeate

Fig. 2. Experimental setup for the permeation experiments.

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Fig. 3. The particle-size-distribution analysis for the original and ground kaolin samples for different times. Ungrounded kaolin: Knb Ground kaolin 15 min: K15 Ground kaolin 30 min: K30 Ground kaolin 60 min: K60 Ground kaolin 120 min: K120

15

Fig. 4. The sintering shrinkage behaviors of the starting clay and samples milled for various milling times.

16

Fig. 5. The micrographs of the membrane supports prepared with kaolin and ground kaolin and sintered at 1100°C for 1 hour.

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Fig. 6. The micrographs of the supports made from K30 and K30-5 mass% S powders and sintered at 1100°C for 1 hour

Fig. 7. The micrographs of the surface of flat supports (K30-5 mass% S ) sintered at three temperatures (900, 1000 and 1100°C).

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Fig.8. Variation of pure water flux with time at 3 bars trans-membrane with different potassium phosphates: K30-5mass%S: grinding kaolin during 30 min- starch 5% K1-5 grinding: kaolin 30 min - starch 5%-KH2PO4 K2-5: grinding kaolin 30 min – starch5% -K2HPO4 K3-5 grinding: kaolin 30 min – starch 5% -K3PO4

Fig.9. Variation of pure water flux with trans-membrane pressure

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Fig.10. Variation of BSA solution flux with time at 3 bars trans-membrane pressure

18

Mass loss (%)

16 14

K1-5

12

K2-5

10

K3-5

8

K1-5'

6

K2-5'

4

K3-5'

2 0 66

116

166

216 Time (h)

20

266

316

Fig. 11 Mass loss of the flat the Kaolin-starch-potassium phosphate supports boiled in the 0.3 M HNO3 solutions at 60°C (K1-5;K2-5;K3-5) and 0.5 M NaOH solution (K1-5’;K2-5’;K35’) as a function of time

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Table1. The rupture strength, the permeability and the porosity of the membrane supports prepared at different grinding times

Knb K15 K30 K60 K120

Rupture strength (MPa) 4.25 5.24 11.34 3.84 1.54

Permeability (L/hm2bar) 3.48 5.98 9.02 9.12 11.3

Porosity (%) 35.55 42.62 23.52 44.24 54.88

K15: grinding kaolin during 15 min K30: grinding kaolin during 30 min K60: grinding kaolin during 60 min K120: grinding kaolin during 120 min

Table 2: The effect of the starch content on the rupture strength, the permeability and the porosity of the membrane supports, made from the K30-S system and sintered at 1100 °C for 1 h. Permeability (L/hm2bar) 9.02

Rupture strength (MPa) 11.34

Porosity (%)

K30-5 mass% S

37.57

8.92

32.36

K30-10mass% S

43.91

2.30

39.47

Supports K30

22

23.52

Table 3: The rupture strength, the permeability and the porosity of the membrane supports, made from the K30-S system and sintered at different temperatures. Temperature (oC) 800 900 1000 1100

Permeability (L/h.m2.bar) 10.85 23.03 37.57

Rupture strength (MPa) 2.41 3.50 3.47 8.92

Porosity (%) 48.71 51.63 44.80 32.36

Table 4: The rupture strength and the permeability of the supports made from K30-5 mass% S powders and sintered at 1100°C for various times.

Sintering time (h) 1 1.5 2 3

Rupture strength (MPa) 8.92 6.63 6.04 17.46

Permeability (L/h.m2.bar) 37.57 34.70 45.79 60.89

Table 5: the effect of binding agents ; KH2PO4, K2HPO4 and K3PO4 content on the rupture strength, the permeability and the porosity of the membrane supports, made from the K30-S system and sintered at 1100 °C for 1 h. Supports

Permeability (L/h.m2.bar)

Rupture strength (MPa) 8.92

Porosity (%) 32.36

K30-5 mass% S

37.57

K1-5

89.25

8.50

35.71

K2-5

72.49

7.66

35.68

K3-5

52.00

7.26

33.22

K30-5mass%S: grinding kaolin during 30 min- starch 5% K1-5 grinding: kaolin 30 min - starch 5%-KH2PO4 23

K2-5: grinding kaolin 30 min – starch5% -K2HPO4 K3-5 grinding: kaolin 30 min – starch 5% -K3PO4

Table 6: Resistance values of for membranes Rm10-11 (m-1) 95.82

Rf10-11 (m-1) 11.23

Rt10-11 (m-1) 135

Rcp10-11 (m-1) 27.96

Rm/Rt (%)

Rf/Rt (%)

Rcp/Rt (%)

70.97

8.32

20.71

40,33

13.82

60

5.85

67.21

23.03

9.75

K2-5

49,35

15.39

72

7.26

68.54

21.37

10.08

K3-5

69.23

41.88

120

8.88

57.69

34.90

7.40

K30-5 mass% S K1-5

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Table7: Retention rate of BSA

R%

K1-5

K2-5

K3-5

37.77

65.55

85.55

25