The sedimentation characteristics of two clays, namely kaolinite and bentonite, were determinated at high clay (5 % wt/vol) and electrolyte (1 N) concentrations using various inorganic-organic compounds. It was observed that the settling behaviour of kaolinite (1:1 clay) and montmorillonite (2:1 clay) is quite different due to the structural differences between these minerals. Although, similar initial settling rates and final sediment volumes were obtained after 24 hours of settling time for kaolin suspensions, the corresponding rates and volumes for bentonite suspensions varied greatly with the used chemical compound. According to the experimental results, a further intensive theoretical and experimental investigation is needed to reveal the mechanism underlying the sedimentation characteristics of clay minerals at high clay and electrolyte concentrations

Abdulah Obut

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 Acta  Montanistica  Slovaca     Ročník 10 (2005), mimoriadne číslo 1, 145-150  Sedimentation Characteristics of Kaolin and Bentonite in Concentrated Solutions   Abdulah Obut1  Charakteristika sedimentácie kaolínu a bentonitu v koncentrovaných roztokoch  The sedimentation characteristics of two clays, namely kaolinite and bentonite, were determinated at high clay (5 % wt/vol) and electrolyte (1 N) concentrations using various inorganic-organic compounds. It was observed that the settling behaviour of kaolinite (1:1 clay) and montmorillonite (2:1 clay) is quite different due to the structural differences between these minerals. Although, similar initial settling rates and final sediment volumes were obtained after 24 hours of settling time for kaolin suspensions, the corresponding rates and volumes for bentonite suspensions varied greatly with the used chemical compound. According to the experimental results,     a further intensive theoretical and experimental investigation is needed to reveal the mechanism underlying the sedimentation characteristics of clay minerals at high clay and electrolyte concentrations.  Key words: Industrial minerals; Fine particle processing; Dewatering   Introduction  The coagulation-flocculation characteristics of clay mineral suspensions, especially montmorillonite and kaolinite, were extensively investigated by several workers in the presence of various inorganic and organic compounds (Swartzen-Allen and Matijević, 1976; Melton and Rand, 1977; Oster et al., 1980; Goldberg and Glaubig, 1987; Keren et al., 1988; Pierre and Ma, 1999; Duan and Gregory, 2003; Petzold et al., 2003; Proskurina et al., 2003). In these studies, generally, the critical coagulation concentration (c.c.c.) values         of clay suspensions, which are low with respect to the concentrations used in this study, have been determined at different pH values. The NaOH and HCl used in these studies for the pH adjustments also affect the corresponding c.c.c. values. Although the coagulation behaviours of clay suspensions for low electrolyte concentrations have been determined, there is no study found in the literature that compares the effects of various inorganic-organic substances at high concentrations on the settling behaviours of the same clay suspensions under same physical conditions. Such kind of information is useful in some type of mineral processing operations that includes clays and in the preparation of new types of inorganically or organically modified clay minerals.    So, this study has been performed to find out the effects of inorganic-organic compounds at high concentrations on the sedimentation characteristics of kaolin and bentonite suspensions.  Experimental  Materials 5 1 52 53 54The original high grade kaolin and bentonite samples (Turkish Republic) were sieved through 38 µm sieve and the sieve undersizes (<38 µm fractions) were used in the sedimentation experiments. The clay samples were identified using XRD patterns of randomly oriented <38 µm fractions (Fig. 1.) and specially prepared (normal, glycolated, heated and Li-250 treated) clay fractions (Lim and Jackson, 1986; Wilson, 1987). XRD studies showed that the kaolin sample is nearly pure kaolinite and the bentonite sample contains mainly montmorillonite (>90 % Na-montmorillonite, d001=12.3 Å) with little amounts of zeolite, feldspar, calcite and opal-CT.    5                                                                         Fig. 1.  Randomly oriented XRD patterns of <38 µm kaolin and bentonite samples (k: kaolinite, m: montmorillonite, z: zeolite, f: feldspar,             c: calcite). 2 theta [°]    1 Abdulah Obut, Visiting Researcher, Institute of Geotechnics, Slovak Academy of Sciences, Watsonova 45, 043 53, Košice, Slovak Republic.,Permanent Address: Hacettepe University, Mining Eng. Dept., 06532, Beytepe, Ankara, Turkish Republic. abdullah.obut@lycos.com Abdulah Obut, Visiting Researcher, Institute of Geotechnics, Slovak Academy of Sciences, Watsonova 45, 043 53, Košice, Slovak Republic.,Permanent Address: Hacettepe University, Mining Eng. Dept., 06532, Beytepe, Ankara, Turkish Republic. abdullah.obut@lycos.com    (Recenzovaná a revidovaná verzia dodaná 16. 8. 2005)      145  A. Obut: Sedimentation Characteristics of Kaolin and Bentonite in Concentrated Solutions  Methods Test tubes were used in the settling experiments. After filling each test tube with concentrated solutions of different inorganic or organic compounds, the clay was added to each tube providing a solids concentration of 5 % by wt/vol. After mixing each tube for the same period of time, the settled volumes       for the tubes which has a sharp solid-liquid  interface  and  clear  supernatant  were  recorded  against  time           to determine the sedimentation curves of the used clays. There were no pH adjustments done on the test tubes, because the acids and bases themselves also affect the sedimentation behaviors of the clays due to their dissolving and/or ion exchange properties.  All the chemicals used in the sedimentation experiments were chemically pure. All the used solutions, except boric, oxalic and citric acids, had concentrations of 1,0 N. Due to the low dissolution values in water, only boric, oxalic and citric acid solutions were prepared at 0,5 N concentration. The clay was directly added to the liquids when organic liquids such as carbon tetrachloride, nitrobenzene or alcohols vere used.                     The initial volume (settling time is zero) of clay suspensions was constantly 10 cm3.  Results and discussion  At first, the chemical susbstances were grouped as “acids”, “salts” and “organic liquids”. Acids and salts were chosen due to their dissolving or ion exchange effects on the used clays. Pure organic substances like carbon tetrachloride, ethanol etc. were used to collect data about the dispersion and settling behaviours of the used clays in pure organic substances. The settling curves of kaolin and bentonite samples in the presence     of “acids” are given in Fig. 2. and 3., respectively. 0123456789101 10 100 1000 10000HClHFHNO3HClO4 (C4H6O ik asit) 6 (L(+) tartarC6H8O ) 7.H2O (sitrik) (0.5 NC4H6O6C6H8O7⋅H2O C2H2O  N) 4.2H2O (okzalik) (0.5 C2H2O4⋅2H2O H2SO4H3PO4CH2O2 (formik)CH3COOHH2SO4H3PO4CH2O2CH3COOH 100,46 g/mol)H2O2H3BO3HCl HF HNO3HClO4 (0.5 N)H2O2H3BO3Sedimentation volume [cm3] Settling time [mins]   Fig. 2.  Sedimentation volume vs. time curves of kaolin suspensions in “acids”.  For the kaolin suspensions (Fig. 2.), except with HF, the settling curves follow a similar pattern in each case. The HF (which can dissolve the silicate  structure)  containing  kaolin  suspension  settles  in  first               10 minutes at a faster rate and then the rate diminishes greatly. Considering the bentonite suspensions (Fig. 3), only suspensions containing HClO4, HCl and HNO3 show settling with a clear solid-liquid interface up to 10th minute and no settling was observed, interestingly, for the suspensions including HF, H2O2, H3BO3 and C2H2O4·2H2O  (oxalic  acid)  for  a  1440  minutes               of sedimentation time. In “salt” solutions, all the kaolin suspensions settle following a very similar pattern (Fig. 4). In CCl4 (carbon tetrachloride) and C6H5NO2 (nitrobenzene). On the other hand, according to the Fig. 5, the bentonite suspensions that show similar settling patterns can be grouped as; ‘Li+’ – ‘K+, Cs+, NH4+’ – ‘Na+, Mg2+, Ca2+, Ba2+, Zn2+, Al3+, Fe3+’ – ‘CCl4, C6H5NO2’.  146  Acta  Montanistica  Slovaca     Ročník 10 (2005), mimoriadne číslo 1, 145-150   0123456789101 10 100 1000 10000HClHFHNO3HClO4 mol)HNO3 HNO3HF  HF HCl  HCl C6H8ON)7.H2O (sitrik) (0.5 C6H8O7⋅H2O  C6H8O7⋅H2O C2H2O(0.5 N)4.2H2O (okzalik)C4H6O arik asit) 6 (L(+) tart C4H6O6 C4H6O6C2H2O4⋅2H2O  C2H2O4⋅2H2O CH3COOH CH3COOH  CH3COOH H2SO4H3PO4CH2OH3PO4 H3PO4H2SO4 H2SO42 (formik) CH2O2 CH2O2H2O2H3BOH2O2 H2O23 (0.5 N) H3BO3 H3BO3 (100,46 g/ HClO4 HClO4Sedimentation volume [cm3] Settling time [mins]  Fig. 3.  Sedimentation volume vs. time curves of bentonite suspensions in “acids”.  Fig. 4.  Sedimentation volume vs. time curves of kaolin suspensions in “salts” and “organic liquids”. 0123456789101 10 100 1000 10000LiClNaClKClCsClNH4ClMgCl2.NH4Cl CsCl KCl NaCl LiCl Nitrobenzen C6H5NO2FeCl3.6H2OKarbon ür  tetraklor CCl4FeCl3⋅6H2O ZnCl2AlCl3.6ZnCl2H2O AlCl3⋅6H2O BaCl2.2H2O BaCl2⋅2H2O CaCl2.2H2O CaCl2⋅2H2O 6H2O MgCl2⋅6H2OSedimentation volume [cm3] Settling time [mins]  Tab. 1. shows the initial sedimentation rates of clay suspensions in the first 10 minutes and the final sediment volumes of suspensions. For kaolin suspensions, the fastest settling rates were observed for HF, C6H5NO2, ZnCl2, CCl4 and H2O2 and the slowest rates were observed for C6H8O7·H2O (citric acid),      147  A. Obut: Sedimentation Characteristics of Kaolin and Bentonite in Concentrated Solutions C2H2O4·.2H2O, H3PO4 and HNO3 containing suspensios. The settling rates of bentonite suspensions are generally higher than the kaolin suspensions.   0123456789101 10 100 1000 10000LiClNaClKClCsClNH4ClMgCl2.NH4Cl  NH4Cl CsCl  CsCl KCl  KCl NaCl  NaCl LiCl  LiCl Nitrobenzen C6H5NO2 C6H5NO2FeCl3.6H2OKarbon rür  tetrakloFeCl3⋅6H2O CCl4 CCl4FeCl3⋅6H2O ZnCl2AlCl3.6ZnCl2 ZnCl2H2O AlCl3⋅6H2O  AlCl3⋅6H2O BaCl2.2H2O BaCl2⋅2H2O  BaCl2⋅2H2O CaCl2.2H2O CaCl2⋅2H2O  CaCl2⋅2H2O 6H2O MgCl2⋅6H2O  MgCl2⋅6H2O Sedimentation volume [cm3] Settling time [mins] Fig. 5.  Sedimentation volume vs. time curves of bentonite suspensions in “salts” and “organic liquids”.  For bentonite suspensions, the nitrobenzene and CsCl containing suspensions were settled at a fastest rate while the acetic acid and LiCl suspensions settle at a slowest rate. No settling was observed in the first 10 minutes for the suspensions containing HF, H2O2, H3BO3, H2SO4, H3PO4, C2H2O4·2H2O and C6H8O7·H2O. When salt solutions are considered, although the final sediment volumes for +2 and +3 valence cations (Mg, Ca, Ba, Zn, Al, Fe) were nearly same, the final sediment volumes of +1 valence cations (Li, Na, K, Cs) differ greatly. The pictures showing final sediment volumes of kaolin and bentonite suspensions for some of the +1 valence cations are given in Fig. 6. and 7., respectively.  Fig. 6.  The final sediments of kaolin suspensions in the presence of a.HCl, b.LiCl, c.NaCl, d.KCl and e.NH4Cl.    Fig. 7.  The final sediments of bentonite suspensions in the presence of a.HCl, b.LiCl, c.NaCl, d.KCl and e.NH4Cl.   Since no sharp solid-liquid interfaces and clear supernatants were observed, the settling curves in some organic liquids (alcohols, acetone etc.) were not included in Fig. 4. and 5. Only final settled volumes of these suspensions are given in Tab. 1. When comparing the experimental results,       it should be remembered that there were no pH adjustments done in the test tubes due to the effects of acid    or bases on the sedimentation behaviors of the used clays. Whereas the pH values of the kaolin suspensions were nearly the same after the sedimentation experiments, the pH values of corresponding bentonite suspensions generally increased by 2. Maximum pH increase after sedimentation was observed for the boric acid containing bentonite suspension, from pH 4 to 7. 148  Acta  Montanistica  Slovaca     Ročník 10 (2005), mimoriadne číslo 1, 145-150                   Tab. 1.  Initial settling rates and final sediment volumes of kaolin and bentonite suspensions. Settling rate (for the first 10 mins, mm/min)  Sediment vol. (at 1440th minute, cm3) Group Compound Kaolin Bentonite Kaolin Bentonite HCl 0.72 2.58 2.30 3.80 HF 3.98 0.00  2.10  10.00 HNO3 0.31 2.27 2.30 4.15 HClO4 0.50 3.52 2.65 3.10 H2O2 1.74 0.00 2.00  10.00 H3BO3 0.93 0.00 2.30  10.00 H2SO4 0.61 0.00 2.10 7.80 H3PO4 0.12 0.00 2.60 8.40 CH2O2 0.90 0.19 3.20 5.30 CH3COOH  0.93 0.44 3.10 5.50 C2H2O4·2H2O 0.00  0.00  2.50  10.00 C4H6O6 0.31 0.84 2.50 9.50 Acids C6H8O7·H2O  0.00 0.00 2.90 7.70 LiCl 1.18 0.19 2.15 7.60 NaCl  0.97 3.36 2.20 2.45 KCl 1.06 4.92 2.75 1.70 CsCl 1.11 5.07 2.60 1.55 NH4Cl  0.68 4.64 2.60 1.80 MgCl2·6H2O  0.81 3.44 2.20 2.30 CaCl2·2H2O  0.88 3.80 2.40 2.30 BaCl2·2H2O  0.97 3.70 2.70 2.30 ZnCl2 2.02 3.18 2.20 2.30 AlCl3·6H2O  0.68 3.98 2.10 2.05 Salts FeCl3·6H2O  0.65 3.42 2.30 2.20 CCl4 1.87 4.00 5.90 3.45 C6H5NO2 2.37 5.35 4.10 1.20 CH3OH n.a.  n.a.  2.50  1.20 C2H5OH n.a.  n.a.  2.35  1.20 C3H8O n.a.  n.a.  1.20  1.00 CH3COCH3 n.a. n.a. 3.10  1.35 Organic liquids (CH3)2NOCH n.a.  n.a.  1.90  3.65 n.a.: not applicable  Conclusion  In this study, it was showed that sedimentation behaviour of clay in a concentrated suspension, both high electrolyte and high clay concentrations, is very different from the corresponding behaviour in dilute suspensions reported in the literature. Although similar sedimentation volumes after 24 hours of settling time (2-3 cm3) and initial settling rates for the first 10 minutes (from 0 to ~4 mm/min, average 1.0 mm/min) were observed for the kaolin suspensions, the correspoding volumes (1 cm3  to  no  settling)  and  rates  (from              0 to ~5 mm/min, average 2,3 mm/min) of bentonite suspensions are varying greatly with the used reagent. It was shown that at high bentonite content of, one can hold the clay in suspension without settling for 24 hours using hydrofluoric acid, hydrogen peroxide, boric acid and oxalic acid. On the other hand, one can easily separate bentonite at a fastest rate from its concentrated suspension with KCl, CsCl and NH4Cl because of the high sedimentation velocities reached.   References  Duan, J., Gregory, J.: Coagulation by hydrolysing metal salts. Advances in Colloid and Interface Science, 2003, 100 -102, 475–502. Goldberg, S., Glaubig, R., A.: Effect of saturating cation. pH. and aluminum  and  iron  oxide                          on the flocculation of kaolinite and montmorillonite. Clays and Clay Minerals, 1987, 35(3), 220–227.      149  A. Obut: Sedimentation Characteristics of Kaolin and Bentonite in Concentrated Solutions Keren, R., Shainberg, I., Klein, E.: Settling and flocculation value of sodium montmorillonite particles                 in aqueous media. Soil Science Society of America Journal, 1988, 52, 76–80. Lim, C., H., Jackson, M., L.: Expandable phyllosilicate reactions with lithium on heating. Clays and Clay Minerals, 1986, 34(3), 346–352. Melton, I., E., Rand, B.: Particle interactions in aqueous kaolinite suspensions. III. Sedimentation volumes. Journal of Colloid and Interface Science, 1977, 60(2), 331–336. Oster, J., D., Shainberg, I., Wood, J., D.: Flocculation value and gel structure of sodium/calcium montmorillonite and illite suspensions. Soil Science Society of America Journal, 1980, 44, 955–959. Petzold, G., Mende, M., Lunkwitz, K., Schwarz, S., Buchhammer, H., M.:  Higher  efficiency                          in the floccuation of clay suspensions by using combintions of oppositely charged polyelectrolytes. Colloids and Surfaces A: Physicochem. Eng. Aspects, 2003, 218, 47–57. Pierre, A., C., Ma, K.: DLVO theory and clay aggregate architectures formed with AlCl3.  Journal                   of the European Ceramic Society, 1999, 19, 1615–1622. Proskurina, V., E., Akhmetova, L., A., Myagchenkov, V., A.: Sedimentation kinetics of bentonitic clay suspension as influenced by pH of the medium, chemical nature and concentration of surfactants, and molecular properties of cationic acrylamide copolymer flocculants. Russian Journal of Applied Chemistry, 2003, 76(4), 610–615. Swartzen-Allen, S., L., Matijević, E.: Colloid and surface properties of clay suspensions. III.Stability            of montmorillonite and kaolinite. Journal of Colloid and Interface Science, 1976, 56(1), 159–167. Wilson, M., J.: X-ray powder diffraction methods. In: A Handbook of Determinative Methods in Clay Mineralogy, M.J.Wilson (ed.), 1987, Blackie & Son Ltd., London, 26–98. 150 

Sedimentation Characteristics of Kaolin and Bentonite in Concentrated Solutions

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