Effects of Some Multivalent Ions on Coagulation and Electrokinetic Behaviours of Colemanite Particles

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1 CSIRO PUBLISHING Aust. J. Chem. 13, 66, Review Effects of Some Multivalent Ions on and Electrokinetic Behaviours of Colemanite Particles Havvanur Ucbeyiay A,C and Alper Ozkan B A Department of Mining Engineering, Seydisehir Ahmet Cengiz Engineering Faculty, Selcuk University, Seydisehir, 4237 Konya, Turkey. B Department of Mining Engineering, Engineering and Architecture Faculty, Selcuk University, 475 Konya, Turkey. C Corresponding author. hucbeyi@selcuk.edu.tr The effects of magnesium, barium, aluminium, and ferric cations as multivalent ions on the coagulation and electrokinetic behaviours of colemanite have been investigated in relation to and cation concentration. The zero point of charge for colemanite was determined to be at.2. The positive surface charge of colemanite increased in the presence of multivalent ions at values below the zero point of charge. Also, these ions changed the zeta potential of colemanite from negative to positive within the range.2 to 12. In the experiments, the coagulation of colemanite with ferric ions was more efficient than with the other ions and the effect of ferric ions varied considerably depending on the concentration and. The coagulation recovery values of colemanite suspension increased quickly up to M concentration of ferric ions and the maximum value (,93 %) was obtained at a of It was also found that the coagulation behaviour of the colemanite suspension in the presence of multivalent cations was in good agreement with the electrokinetic characteristics. Manuscript received: 18 July 12. Manuscript accepted: 22 September 12. Published online: 31 October 12. Introduction Colemanite (Ca 2 B 6 O 11 5H 2 O) is a popular natural source of insoluble boron minerals and Turkey has a large proportion of the world boron reserves. Boron compounds have many uses, such as in soaps, washing powders, glasses, ceramics, specialty alloys, fillers, and advanced technological materials. [1 3] Also, colemanite has a friable nature and therefore, a large amount of colemanite fines are formed in mineral processing operations. Aggregation of fine particles can be achieved by neutralizing the electrical charge of the interacting particles by coagulation, or flocculation can be carried out by bridging the particles with polymolecules. [4] Generally, repulsive electrostatic forces are found between particles. When these repulsive forces are minimized, coagulation is obtained. The magnitude of the zeta potential of most inorganic salt ions and their ability to compress the thickness of the electrical double layer are related to the ionic charge of the ion itself. Also, these inorganic salts form hydroxyl complexes as a function of and they are very surface-active. Therefore, they adsorb strongly onto solid surfaces and reverse the sign of the zeta potential. [5 8] The zeta potential is the electrokinetic potential on the shear plane of the mineral surface (within the electrical double layer). [9] The coagulation process is achieved by adjusting or electrolyte concentration to reduce the absolute values of zeta potentials of particles. For this purpose, multivalent electrolytes are usually added to the suspension according to the surface charge of the mineral. Assistant Professor Dr. Havvanur Ucbeyiay was born in Konya, Turkey, in She graduated from the Mining Engineering Department of Selcuk University in 3. She received her Master of Science (M.Sc.) degree and her Doctor of Philosophy (Ph.D.) degree in Mineral Processing at Selcuk University in 5 and, respectively. She has been at the Department of Mining Engineering at Selcuk University Seydisehir Ahmet Cengiz Engineering Faculty as Assistant Professor since 11. Her major research interests involve flotation and flocculation. Professor Dr. Alper Ozkan was born in Sivas, Turkey, in He graduated from the Mining Engineering Department of Cumhuriyet University in He received his Master of Science (M.Sc.) degree and his Doctor of Philosophy (Ph.D.) degree in Mineral Processing at Cumhuriyet University in 1996 and 1, respectively. He has been in the Department of Mining Engineering at Selcuk University since 3. His major research interests involve flotation, flocculation, and grinding. Journal compilation Ó CSIRO 13

2 4 H. Ucbeyiay and A. Ozkan Many studies have been reported on the flotation characteristics of colemanite mineral in the literature. However, there have been no studies on the coagulation properties of this mineral. Therefore, the purpose of this paper is to define those characteristics experimentally. The definition of such properties of colemanite will also help dewatering and enrichment of boron ore and tailings containing colemanite. Experimental Materials A high-purity colemanite sample from Bigadic, Turkey, was used for the coagulation experiments. The studied colemanite sample contained % B 2 O 3, 3.6 % CaO, 4.76 % SiO 2,. % MgO, and.12 % Fe 2 O 3. The sample was dry-ground to pass a 38-mm sieve with a steel ball mill and 7 % of the ground sample was found to pass 17 mm in an Andreasen pipette. Magnesium chloride (MgCl 2 6H 2 O), barium chloride (BaCl 2 2H 2 O), aluminium chloride (AlCl 3 6H 2 O), and ferric chloride (FeCl 3 ) were used as coagulants with colemanite and were obtained from Merck. Sodium hydroxide and hydrochloric acid (Merck) were used for adjustments and was monitored with a digital meter. All of these reagents were analytical grade and all experiments were carried out using once-distilled water. Experiments A 4-cm 3 cylindrical cell with four baffles was used for the coagulation experiments. A schematic diagram of the stirred cell system is shown in Fig. 1. The diameter of the cell (T) and the diameter of the impeller (D) are 78 and 42 mm respectively. H and H b are the height of the cell and baffle respectively. A centrally located turbine impeller with four blades is used to stir the suspension. The shaft of the impeller is driven through a variable-speed gearbox and the shaft speed is measured with a digital tachometer. A total of 1 g solid and 3 cm 3 water were used in the experiments. The mineral water suspension was stirred for 1 min in order to disperse the particles in the suspension. The dispersed suspension was first stirred at 5 rpm for 5 min before the coagulant addition. During this time, the of the suspension was adjusted. Then, the coagulant was added and the suspension was stirred for 3 min. After 3 min, the stirring speed was reduced to 16 rpm for 2 min to allow floc growth; thereafter, a settlement time of 2 min was allowed. After that, the top 4.5cm of supernatant was siphoned off with a syringe system. The sediment remaining in the cylindrical cell was filtered, dried, and weighed to determine the percentage coagulation recovery (% coagulation recovery ¼ (settled weight/weight of feed) ). The of the suspension was controlled continuously in the experiments. Also, it was determined that the accuracy of the coagulation recoveries was within an experimental error of 5%. Zeta Potential Measurements The zeta potential of the colemanite particles was measured with a ZetaPlus apparatus (Brookhaven). The mineral sample (1 g) was added to water ( cm 3 ) of different and the suspension was stirred for 5 min. Thereafter, the suspension was conditioned for 5 min with the addition of appropriate reagents. Then the suspension was kept still for 5 min to let larger particles settle. An average of runs was recorded for the measurement of zeta potential of each sample. Each experiment was repeated three times and the average of these values is reported. All recovery [%] H b T Fig D/8.4 D/7 D T Suspension level T/19 D/2.8 Schematic diagram of stirred cell and impeller. 4 M Mg 2 2 M Mg 2 8 H 1.3 T measurements were made at 228C and an experimental error of 4 % was obtained in the experiments. Results and Discussion Fig. 2 shows the coagulation of colemanite suspension as a function of in the presence of 4 and 2 M magnesium ion. In addition, the variation of zeta potential of colemanite with is shown in Fig. 2. As can be seen in Fig. 2, the zero point of charge (ZPC) of the colemanite sample occurs at.2 in the absence of the cations. This value is very close to that 12 Fig. 2. of colemanite as a function of in the presence of magnesium ions. [mv]

3 Behaviours of Colemanite Particles 5 (a) 4 Mg 2 Mg(OH) 2 (s) (b) Ba(OH) 2 log concentration [M] 5 6 Mg(OH) log concentration [M] Ba 2 OH Ba(OH) (c) 4 Al 3 Al(OH) 3 (s) Al(OH) 4 (d) 4 Fe 3 Fe(OH) 3 (s) log concentration [M] 5 Al(OH) 2 Al(OH) 2 6 Al(OH) 3 (aq) Concentration [M] 5 FeOH 2 6 Fe(OH) 2 Fe(OH) 2 FeOH 2 Fe 2 (OH) Fig. 3. Species distribution diagrams for (a) 4 MMg 2þ ; (b) 1 MBa 2þ ; (c) 4 MAl 3þ ; and (d) 4 MFe 3þ. [11 13] in previous studies. [,11] The positive surface charge of colemanite increased in the presence of magnesium ions at values below the ZPC of the colemanite mineral. Also, the zeta potential of colemanite changed from negative to positive within the range.2 to 12. of the colemanite suspension with 2 M magnesium ion was not achieved in the range studied. Moreover, the dispersion degree of the suspension increased, that is, stabilization took place. However, coagulation of the colemanite suspension occurred in the presence of 4 M magnesium ion above 9. The magnitude of the negative potential of the colemanite surfaces at values above the ZPC decreased with the adsorption of magnesium ions, and therefore coagulation was enhanced owing to a decrease in the repulsive forces. In addition, the positive zeta potential value of the colemanite decreased with increasing in the range 9.2, and therefore coagulation also took place. Free Mg 2þ ions have a strong influence in the suspension at near-neutral levels and the colemanite mineral has a positive surface charge, but as the increases, the concentration of Mg 2þ ions begins to decrease and hydrolysis species of the cation predominate. As a result, the less hydrated Mg(OH) þ and Mg(OH) 2 forms precipitated at high values adsorb onto the positively or in particular, on the negatively charged colemanite surfaces. [11] The species distribution diagrams [12 14] of magnesium, barium, aluminium, and ferric ions at different values are given in Fig. 3. As seen from Fig. 3, the results of the coagulation experiments obtained for these ions may be explained by the species distribution diagrams. The effects of the concentration of magnesium ion on the coagulation of colemanite suspension at 7 and 11.5 are shown in Fig. 4. As seen in Fig. 4, a slight increase in the stabilization of the suspension was observed at 7. However, the coagulation recovery values did not change significantly above 5 MMg 2þ. This result showed that the hydrated Mg þ2 ions adsorbed little onto the colemanite surfaces at 7. The increase in the zeta potential values of colemanite with magnesium ion at 7 also supports this observation (see Fig. 2). Maximum coagulation recovery was obtained with, 4 M Mg 2þ at As shown in Fig. 4, the surface charge of colemanite was very low with, 4 M Mg 2þ and

4 6 H. Ucbeyiay and A. Ozkan 8 8 recovery [%] [mv] recovery [%] [mv] Mg 2 concentration [M] Fig. 4. Effect of the concentration of magnesium ions on the coagulation of colemanite Ba 2 concentration [M] Fig. 6. Effect of the concentration of barium ions on the coagulation of colemanite. recovery [%] ( 5 M Ba 2 ) ( 4 M Ba 2 ) ( 3 M Ba 2 ) 6 8 consequently, the coagulation and zeta potential results for colemanite were consistent with each other. The coagulation degree of colemanite suspension began to decrease owing to the increased precipitation of Mg(OH) 2 at concentrations higher than 5 4 M, and simultaneously the colemanite surfaces had more positive charge values. The coagulation of colemanite as a function of in the presence of 5 and 3 M barium ions is shown in Fig. 5. As seen in Fig. 5, the coagulation recovery values of colemanite with 3 MBa 2þ were higher than those obtained with 5 M Ba 2þ. In addition, it can be said that the colemanite particles could coagulate owing to the decrease in the positive charge of the colemanite above 9. Fig. 6 shows the effect of the concentration of barium ion on the coagulation of colemanite suspension at 7 and Fig. 5. of colemanite as a function of in the presence of barium ions. [mv] Similarly to the findings obtained with magnesium ions, a slight increase in the stabilization of the suspension was observed with barium ions at 7. However, coagulation of the colemanite suspension showed a clear increase above 5 4 MBa þ2 concentration at In general, the effects of barium ions in terms of their hydrolysis and precipitation properties on the coagulation behaviour of colemanite were similar to those obtained with magnesium ions. However, a decrease in degree of coagulation with increasing barium concentration was not observed owing to relatively low amounts of barium hydroxide precipitation and low values of zeta potential compared with the magnesium ion. The hydrolysis species of both magnesium and barium cations formed at high specifically adsorbed onto the negatively charged surfaces of colemanite particles above.2. Thus, the negative surface charge of colemanite decreased and coagulation occurred. The effect of magnesium and barium ions on the shear flocculation of colemanite with sodium oleate and sodium dodecyl sulfate was investigated by Ucbeyiay and Ozkan. [11] They stated that these ions showed a similar effect to that obtained in the current study on the shear flocculation of colemanite. The effect of on the coagulation of colemanite in the presence of 4 and 2 M aluminium ions is given in Fig. 7. As shown in Fig. 7, at 2 M concentration of aluminium ions, coagulation of the colemanite suspension was obtained in the range Apart from this range, the dispersion degree of stabilization of the suspension increased and a large degree of stabilization of the suspension took place. However, the coagulation of colemanite in the presence of 4 MAl 3þ occurred between and Also, as shown in Fig. 7, the positive zeta potential of colemanite with Al 3þ ion decreased with increasing. Aluminium ion hydrolyzes above 2.4 and Al(OH) 3 starts to precipitate at 4.4 (see Fig. 3). In addition, the ZPC value of Al(OH) 3 is approximately 9.3. [13] Therefore, coagulation of the colemanite particles usually takes place owing to low values of positive potential at, 9.3. In fact, the surface charge of colemanite mineral is expected to be negative at values higher than 9.3, all the more so because of the lack of positively charged hydrolysis products of aluminium ion in

5 Behaviours of Colemanite Particles 7 recovery [%] M Al 3 2 M Al [mv] recovery [%] ( 5 M Fe 3 ) ( 4 M Fe 3 ) ( 3 M Fe 3 ) 12 [mv] Fig. 7. of colemanite as a function of in the presence of aluminium ions. Fig. 9. of colemanite as a function of in the presence of ferric ions. 8 recovery [%] [mv] recovery [%] [mv] Al 3 concentration [M] Fe 3 concentration [M] Fig. 8. Effect of the concentration of aluminium ions on the coagulation of colemanite. Fig.. Effect of the concentration of ferric ions on the coagulation of colemanite. the suspension above neutral. However, the results of the zeta potential measurements indicated that the colemanite particles had a positive surface charge in the range Moreover, the findings obtained for the coagulation behaviour were consistent with the zeta potential measurements. Fig. 8 shows the effect of the concentration of aluminium ion on the coagulation of colemanite. of the colemanite suspension increased slightly with increasing aluminium concentration. However, stabilization of the suspension took place at concentrations higher than 3 M. This was due to the increase in the zeta potential of colemanite. The effect of on the coagulation of colemanite induced by ferric ion is shown in Fig. 9. As seen from Fig. 9, the coagulation recoveries with ferric ion were high in the range and these findings were also consistent with the zeta potential curve. It can also be noted that Fe(OH) 3 precipitates at,2.8 in the presence of 4 M ferric ion (see Fig. 3). In addition, the ZPC value of Fe(OH) 3 is reported as 8. [15] Similarly to the results obtained with aluminium ions, the colemanite is also expected to have a negative surface charge in the presence of ferric ion above 8. However, the zeta potential measurements indicated that the particles had a positive surface charge in the range A similar result to this finding was reported by Yukselen and Kaya, [16] who found that kaolin mineral had a positive surface charge in the presence of Cu 2þ ions at, although the ZPC value of Cu(OH) 2 was 9.4. [17] A somewhat similar result was also reported by Fornasiero and Ralston, [18], who found that quartz mineral had a positive charge with Cu 2þ ions in the range 9. The effect of ferric ion concentration on coagulation of the colemanite suspension is shown in Fig.. As seen in Fig., the coagulation of colemanite increased up to 3 MFe 3þ ; however, a significant change did not occur at higher concentrations. It can also be noted that the maximum coagulation

6 8 H. Ucbeyiay and A. Ozkan recovery value (,93 %) for the colemanite suspension was obtained in the presence of M ferric ion at Conclusions The ZPC value of the colemanite mineral was determined as a of.2. At values below this value, the adsorption of magnesium, barium, aluminium, and ferric ions increased the positive zeta potential of the mineral. Also, these cations reversed the zeta potential of colemanite at values higher than the ZPC. In general, the coagulation behaviour of the colemanite suspension with these multivalent cations was in good agreement with the electrokinetic properties. Magnesium and barium ions affected colemanite coagulation in a similar manner. Although these cations were not effective on the coagulation process of colemanite at neutral where magnesium and barium ions exist as free ions, an increase in led to the coagulation of the particles in the suspension. In the case of aluminium and ferric ions, the coagulation of the suspension was more affected by both the concentration and. The maximum coagulation recovery (,93 %) for the colemanite suspension was obtained with ferric ions at a of As a general result, it can be said that the control of the zeta potential of colemanite was observed to be a key factor for coagulation with these multivalent ions and the coagulation of the colemanite suspension could be usually achieved when the zeta potential was less than, mv in magnitude. Acknowledgement The authors acknowledge the financial support of Selcuk University Scientific Research Project Fund (project no. 89). References [1] D. E. Garret, Borates 1998 (Academic Press Ltd: New York, NY). [2] M. S. Celik, M. Hancer, J. D. Miller, J. Colloid Interface Sci. 2, 256, 121. doi:.6/jcis [3] S. Koca, M. Savas, Appl. Surf. Sci. 4, 225, 347. doi:.16/ J.APSUSC [4] J. S. Laskowski, in Colloid Chemistry in Mineral Processing (Eds J. S. Laskowski, J. Ralston) 1992, Ch. 7, pp (Elsevier: New York, NY). [5] M. C. Fuerstenau, Advances in Interfacial Phenomena of Particulate/ solution/gas Systems. Applications to Flotation Research AICHE Symposium Series No. 15, (Eds P. Somasundaran and R. B. Grieves) 1975, 71, pp (American Institute of Chemical Engineers: New York, NY). [6] P. Somasundaran, in Fine Particle Processing (Ed. P. Somasundaran) 198, pp (AIME: New York, NY). [7] R. R. Klimpel, Introduction to Chemicals Used in Particle Systems 1997, pp. 13 (ERC Particle Science & Technology: Gainesville, FL). [8] R. Hogg, Int. J. Miner. Process., 58, 223. doi:.16/s (99)23-x [9] J. R. Hunter, in Zeta Potential in Colloid Science: Principles and Applications, 3rd edn 1988, pp (Academic Press: San Diego, CA). [] M. S. Celik, E. Yasar, J. Colloid Interface Sci. 1995, 173, 181. doi:.6/jcis [11] H. Ucbeyiay Sahinkaya, A. Ozkan, Separ. Purif. Tech. 11, 8, 131. doi:.16/j.seppur [12] J. N. Butler, Ionic Equilibrium 1964, pp (Addison Wesley: Boston, MA). [13] J. Kragten, Atlas of Metal Ligand Equilibria in Aqueous Solution 1978, pp (Ellis Horwood: Chichester). [14] L. Dusoulier, R. Cloots, B. Vertruyena, J. L. Garcia-Fierro, R. Moreno, B. Ferrari, Mater. Chem. Phys. 9, 116, 368. doi:.16/j.match EMPHYS [15] M. Kosmulski, Adv. Colloid Interface Sci. 9, 152, 14. doi:.16/ J.CIS [16] Y. Yükselen, A. Kaya, Water Air Soil Pollut. 3, 145, 155. doi:.23/a: [17] G. A. Parks, Chem. Rev. 1965, 65, 177. doi:.21/cr6234a2 [18] D. Fornasiero, J. Ralston, Int. J. Miner. Process. 5, 76, 75. doi:.16/j.minpro

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