The main sources of rock  phosphate are  located in Rajasthan, Mussoorie (U.P.), Singhbhum  (Bihar), Purulia (W.B.) etc. Phosphate  rocks generally occur as calcitic, siliceous and ferruginous in nature. Rajasthan and Muss-oorie rocks are calcareous (CaO 40-50%). Hence to enrich the phosphate in the rock from average 16-20% to above 30% P205 two possible alternatives to beneficiate this ore

Das, B K L

Rastogi, M C

English

eprints@NML

Simulated model studies on the beneficiation of calcareous phosphate ore * M. C. Rastogi and * B. K. L. Das INTRODUCTION The main sources of rock phosphate are located in Rajasthan, Mussoorie (U.P.), Singh-bhum (Bihar), Purulia (W.B.) etc. Phosphate rocks generally occur as calcitic, siliceous and ferruginous in nature. 	 Rajasthan and Musso- orie rocks are calcareous (CaO 40-50%). Hence to enrich the phosphate in the rock from average 16-20% to above 30% P205  two po- ssible alternatives to beneficiate this ore are : 1. Calcining the ore at 900° to 1000°C followed by hot quenching, attrition, scrubbing and repeated desliming. This method could increase the P205 content around 28%. 2. Separation of calcite or phosphorite by flotation method. Both these have been utilised in different laboratories namely Cerphos, Paris; Serrans, Jacupirange, Brazil; Sala International, Sweden; National Metallurgical Laboratory, India and Indian Bureau of Mines, India. Except Sala International, other organisations have followed basically the same method for separating cal-cite from phosphorite. The results reported from different laboratories are quite divergent. It seems that the basic characteristics at solid-liquid-gas interfaces of the minerals in a flotation cell have not been thoroughly investi-gated. Before attempting to separate calcite from phosphorite, an attempt was made to study the surface properties of calcite and phosphorite in presence of conditioner and collectors by measuring the electrokinetic potential of the suspension. So far, a detailed study has been made on calcite and attempt is being made to extend the study to phosphorite. However,  laboratory tests have indicated that calcite can be separated even without the use of phosphoric acid as phosphorite depressant used all over the world. EXPERIMENTALS : Material Distilled water used throughout the experiment was deionised and then redistilled in a pyrex glass still and had a conductivity of 1x10-6 ( Q cm ) — 1. Standard samples of HCI and Na2CO3 were from B. D. H. Glaxo, India. 	 Hexadecyl Pyridinium Bromide ( C. P. B. ) and Dodecyl Pyridinium Bromide (D. P. B.) were prepared in laboratory. Sodium dodecyl sulphate (S.D.S.) was from Fluka AG, Switzerland. Other chemicals viz. copper sul-phate, thorium nitrate, lanthanum carbonate were either certified or Analar grade reagents. Certified 'A' grade of measuring glass apparatus were used in the study .  Preparation and characterisation of sot and suspension of CaCO3  A suspension of calcium carbonate bearing negative charge was prepared in the laboratory. The ionic strength in suspension medium was 2mM in terms of sodium carbonate and sodium chloride. The sol was allowed to age for one and half hour and was stable subsequently for three hours. The concentration of the sol was —.063 gm/litre. The particle size of the sof was found to be-2x10-6  cm using electron micrography technique and the crystalline para-meters were a = 1.135A°, C -= 8.524 A° C/a= 1.1947, Z=6 where Z equal to no. of formula unit per unit cell. It was identified as /4—calcium carbonate. Identification of the calcium carbonate *Regional Institute of Technology, Jamshedpur. powder is under study. Since it is a synthetic sample it may bear the same crystalline para-meter as the sol particles. The pH of the sol samples prepared was found to be 8.9 ± .2. Measurement of Zeta potential (;) The electrophoretic mobilities were mea-sured by Zeta meter, using Type 11 UVA plexiglass electrophoretic cell and molybdenum cylindrical anode and platinum iridium strip cathode. The mobilities of different samples of sol particles were 1.17--.05 1.4 Sec - 1 Volt-1 cm-1. All measurements on electrokinetic potential were made within the period of three hours after the preparation of sol. Adsorption Experiment Adsorption of the small ions namely Cu++ and Co 	 in the same environment as that of the sol particles were carried on calcium carbonate powder at 30° -i-- 0.1°C. Since the measurement of electrophoretic mobilities of the sol particles were carried out at 27.5±2°C, the experimental conditions for the adsorption experiment may be taken to be similar as that for sol particles. The concentration range was varied from 10-7M to 10-2 M, hence to deter-mine accurately, the amount of Cu 4- + and Co+- in the lower concentration region, Atomic Adsorption Spectrophotometer was used. Solu-tions of higher concentration were diluted to bring them into the working range of the instrument. Results : In order to define the structure of the double layer at solid-solution interface, it would have been better to study the interaction of conventional mono, di and trivalent cations i.e. sodium, barium and lanthanum, since the coa-gulation concentration would effect the measure-ment of mobilities because of high conducting medium. 	 The variation of zeta potential with these ions except sodium is shown in Fig. 1. It seems that trivalent ions also reverse the charge of the sol particles whereas highly hydrolysable thorium ions do not. A possible explanation for such behaviour is given later. Consistent with the aim of the present work, hydrolysable metal ions, commonly used in flotation practice were selected, namely Com- , Ni+Te Cum-  and Zn-+. The variation of zeta potential in their presence are shown in Fig. 2. These results show a sensitisation pro-cess occurs at very low concentration. Since the sol is negatively charged, cationic surface active agents namely cetyle pyridinium bromide (C.P.B.) and dodecyl pyridi-nium bromide (D.P.B.) were selected to study their interaction with sol particles. Fig 3 gives the data. The surface active agents used below CMC are uni-univalent inorganic electrolyte viz. KCI, NaCI etc. This interaction should have shown similar trend as reported by Ottewill and Rastogi(1) on Agl solution interface. A similarity does occur i.e. concentration at which the first charge reversal occurs is about 104 lower than the monovalent ion indicating the process of adsorption to be sensitised. It is upto the region of zero zeta potential, the surface may be taken as becoming oleophilic. i.e. carbon like, hence may be amenable to make a definite contact angle with air bubble. Higher concentra- tion than 1 x10 -8 and 1.66 x10-8 M lead to the formation of second layer and the surface again becomes hydrophilic. Hence in this region any concentration of the collecting ions wiil be detrimental to flotation studies. Generally the flotation of calcite is done in acid medium. Sodium dodecyl sulphate (S.D.S.) was also included along with cationic surface active agent. The variation of zeta potential in its presence is shown in Figure-4. As reported earlier Cu--- and Co 	 were both found to reverse the charge on calcite particles at very low concentration. Three diffe- rent concentrations viz 8.7 x 10-5 M, 7.14 x 10-4 M and 1.428 x 10-4 M corresponding to the region of positive zeta potential were selected in order to have a comparative study of the concentration of Cu++ ion on sensitisation. The interaction of the sol particles having fixed 2l6 Cul  ion concentration was followed a function of S. D. S. concentration. Results are in Figure 4. It can be seen from Figure 4 that the Cu ion at a concentration 8.5 x10-5 M are very effective but the concentration of S.D.S. required to reduce c to zero is more than the other two cases of higher concentration of 	 ions. In such cases efficiency and the cost involved in the use of collecting ion should form the criteria for selecting the concentration of the activator. A comparative study of the effectiveness of Cu--  and Co- + ions was made using the same molar concentration and at the same pH. The results of the interaction with S. D. S. are included in Figure 5. It can be seen from that Cu-I4- is more effective than Co++ ions in acti-vating the surface. To proble this result further a direct adso-rption measurement of these ions were carried out on CaCO3 suspension. Adsorption curves are shown in Figure 6. It further confirms that the Cu 	 ions adsorbed more strongly than the Co - ions. Effect of pH The pH of the sol prepared remain within the range 8.9 ± 0.2. An attempt was made to study the effect of pH on surface charge. Since the carbonate is highly soluble in acid, it was difficult to reach below pH =7. Perusal of the Figure 7 indicates that the surface charge is slightly increased and it became constant at pH =10. Hence one can safely work with the sot around pH=10. Similar studies were made with fixed concentration of Co++ ions both in the negative and positive range of zeta potential. The variation of pH was studied in both cases. At concen- tration 8.5 x 10-6 M, the charge of the sol particles reverses at pH-9.7, while in other case there is a tendency to increase zeta potential but it became constant above pH =10. Charge reversal in first case may be attributed to increase the concentration of hydrolysis produc-tion on the surface. On the basis of information received from the foregoing experimental data, laboratory tests were performed for the flotation of CaCO3 and CO3 (PO4)2 under similar condition. These sus- pension were conditioned at 9 pH. The pH in both cases was changed from 9 to 5. Using S.D.S. as collector, flotation experiments were performed. It was found that carbonate floated very well but under the similar conditions phos-phate did not. Discussion : The changes in electrokinetic potential of the sol particles can be better interpreted if the structure of the double layer formed is known. The experimental conditions for the preparation of CaCO3 sol suggest that the structure of the double layer should be as shown in Figure 8 (a). Since the surface bears a negative charge the balancing charge will be comprised of uni-and di-valent cations persent in solution. Much talked zeta potential ( ) should not be taken to represent either the surface potential To or To-, the Stern potential. It is best defined as the fall of potential between the surface of shear and the bulk when the double layer is subjected either to mechanical or electrical stress. Since the particles are (-2 x 10-6 cm ) small assumed to be spherical and the changes in zeta potential values with and without the electrolyte remain in the range of -_ 25 my, these were calculated using Huckel2 equation namely 6 ..7z ?ll Where 	 = co-efficient of viscosity of the medium Electrophoretic mobility = Dielectric constant and no attempt was made to correct these values for elctrophoretic and relaxation effects. 217 In this study the changes in zeta potential have been measured in the presence of both long chain ions and small metal ions. The charge reversal occurs even in the presence of small ions. The changes in double layer structure are shown in Figure 8(b) and 8(c). Charge reversal may be assigned to adsorption of one or more of the species formed in processes enumerated below (3, 4, 5, 6) : (a) the free aquo cations or first hydro-lysis product (b) polynuclear complex of discrete composition (c) a surface polymer or precipitate of metal hydroxide at a certain concen-tration depending on pH. Collector to be used in these studies must have a well defined chemical composition and structure and of known purity. In this case charge reversal may be assigned to factor (a) because these act as a uni univalent electrolyte below C M C. The charge reversal in the case of hydroly-sable metal cation may be either due to factor (b) or (c). The scheme of charging in the surface according to mechanism (c) is given below : x OH— ......... M (OH)x  (n—x)± M(OH) x(n—x)+ --;--0H— ......... M(OH)x+1(11-x-1)— M(OH)n(n x)++M± 	 M (OH)x-1 	 4-H20 and for (b) the scheme is : Myn+ 	 x OH ...... My (OH) x (n") xi+  IVlyn 	 x OH ...... My (OH)x[x— (nxy)] —1  where n — no. of charge x = no. of hydroxyl ions y = no. of metal ions Since Cu++ and Co++ ions were used extensively in this study, the probable hydrolysis  products and polynuclear complexes of thes eions are given below : Cu = Cu(OH)±, Cu2(OH)22', Cu(OH)42 , Cu(OH)3  and Cu(OH)2 Co = Co(OH)+ Co(OH)2 and Co(OH) 3 At the interfacial region the situation is completely different from bulk. The inter-face is a region where the electric field is large and is of the order of 106 vcm —1  or more (7,8). The primary consequence of this field is to lower the dielectric constant of the interfacial medium. In aqueous media it is around 6. Therefore, the reaction occuring in the interface should be regarded different than occurring in the bulk. As such the surface precipitation (6) may occur at lower concentra-tion than required for bulk and may be regarded as a separate phase. In the present study, the charge reversal on CaCO3 particles may be due to the precipita- tion of hydrolysed species of hydrolysable metal ions namely Co++, Ni++, Cu++ and Zn++. As concentration of the above divalent ions are increased, the hydrolysed species of the ions increase and adsorbed at the Stern layer at calcite-water interface. When the concentration of these ions reached to a critical value ( see Figure 3 ) they are precipitated and reverse the charge of the sol particles. In the case of aluminium, first charge reversal is due to the precipitation of hydrolysed metal ions, but when their concentration is increased further the second reversal of charge occurs. This may be due to the dissolution of the surface precipitate. The third charge reversal may be ascribed due to the formation of poly-nuclear complex formed at higher concentration of A13+ ions and also at higher pH. In the case of lanthanum ions, possibility of polynuclear complex are remote, hence after second charge reversal the particles remain negatively charged. 218 „711E  E '0 0  a CJ cf ti es) ". 4-1 a=,  0 • 0 a " -ec cn tJl 11  — O Ei V P9         0 0 H) O 	 eo, 	 O 	 co 	 O A tti 1.4 1 tjuafoci P4a7 w 1 0 0 ny ip!fualod O N) O O krb 219 - Ve +ye -8 	 -7 	 -6  Log OA) Fig.3. Variation of Zeta Potential vrs Log (M) concentration. 0 	  C. P. 	 & 	 B '220 3o -4 101,11C STRENGTH OF 50L ti 2m1.4 CONCENTRATION OF SOL = .063g ?qt. pH OF SOL. = 8.9 t.2 • 1111111.16.ftikindflfialrffiadgfeita4:. UalfeafiCaSi4 AMON 0 0 +-• -cc 	 AL. 3.31 F.;),"▪ 1.3 atf.3d o4az . 	 ,...IRTOVA•12:11,1,0,1K 0 34) U- 5 17. OJ II 	 E 4. 0 MU U: 1014t1DPd 0402 04- • tr) c—) 221 0 -5 a. -5 	-4 EQ. COHC 0 Loy(14) I04tIC 	 mt.( p0 	 .2 It tC STRENGTH OF IN. — 2.  COUCE0TRAT1014 Of 110‘.. .065 seiit. Thorium ions present a different case, As reported earlier, excess of sodium carbonate was present in the bulk to stabilise the calcium carbonate sol. Th4+ ions being highly charged, are ineffective in producing the charge reversal on the sol particles. 	 It may be due to the solubility of the thorium hydroxide in excess of carbonate ions (9). This result further confirms the mechanism of charge reversal on sol particles discussed above. Fig 6 Adsorption o‘ Cu+ t and Cn++ on Co Cos powder.-4— cuf.4,—o—toso, .0 0 4 ye 20 p fig. 7 Variation of Leta Potential yrs pR —.0-- sot , 	 Sot +055440.51401 5o4 	 co 504 (i.42axto-5u). Interaction of S. D. S. with calcite sus-pension in presence of hydrolysable metal ions : The changes in the structure of the double layer in presence Cu++ and Co++ ions are shown in Figure 8 (b) and 8 (c), the later gives the change in double layer structure when the charge on the particle is reversed i.e. surface charge becomes positive. The action of these metal ions has been ascribed to activate the surface of calcite suspension. Fig. 8(d) gives the changes in the double layer with varying concentration of S. D. S. in presence of fixed concentration of activating ions. Figure (4) 8- (5) show a second charge reversal occurs at a certain concentration of S. D. S. depending on concen- tration of 	 and Co++ ions. This interaction immediately suggest that the surface become again hydrophobic because negative polar group point towards the surface and the tail in the solution. Effective concentration of S.D.S. for the coverage of the surface is 3.57 x Hence S.D.S. and other commercially available anionic surface active agents can be used as collecting ions. Important work on flotation of calcareous phosphate ore is already mentioned earlier (10, 11). With the exception of work done at Sala International, sodium oleate or oleic acid as collector, sulphuric acid and phosphoric acid as pH regulator and phosphorite depressant respectively has been used. The reported con-sumption of phosphoric acid is nearly 7 kg/ton. After removing calcite from the calcareous phos-phatic ore, sodium silicate was used to depress calcite while Serrana, Jacupirange, Brazil used Serrana starch. The collector used by Sala International was developed by an associate of the company. However these processes involved costly item for benefication of calcareous phos-phate ore. The beauty of this work lies in the fact that conventional Cu++ or Co++ act as activator for calcite and a common anionic sur-face active agent can be used as collector. The laboratory tests have shown that calcite can be floated at pH 5 after conditioning, while phos-phorite does not. 5 1 222 Na 4(01-) 2_ M(0)4" 	 SD x+0+ 5D Ct (ow)x.:11 0 H)171  xY- + S0 Na D 2 CciCo Co3-  dG  '1164 Co3  Co3  CO3-  SD SO ON 418 - - - - - - (002 1.4 (00 ÷ (n-)04)+ -x+) - 1,,i(08)(2:x)4) 	 C L Ay(o )){ mxy-x}+  _ c C 0 14 My x ° H f  WOO: coi- m(0x)2 	 Na d (C)  Co3     Ca Co 4G Fig.8. Structura of double layer ;  (a), Ca Co3 (negative) sol; (b) in presence of hydrolysable metal ions 	 negative charge .,(c) In presence of hydro- lysable ions with charge reversol and (d) in presence of hydrolysable metal ions and 5.0.S. .111••n n• •.....es. 223 Acknowledgement The authors are indebted to Prof. V. A. Altekar, Director, National Metallurgical Labo-ratory, Jamshedpur for providing facilities to carry out part of the work at N. M. L. Thanks are also due to Principal, R.I.T., Jamshedpur for his keen interest in the work. References 1. OTTEWILL, R. H. AND RASTOGI, M. C. Trans. Faraday Society, 56, 866 ( 1960 ). 2. OVERBEEK, J. Th. G. Adv. in Colloid Sc. Vol. 3,99 (1950). 3. ABRAMSON, M. B. JAYCOCK, M. J. AND OTTEWILL, R. H. J. Che. Soc. London 1964, 5034, 5051. 4. MATIJEVICE, ABRAMSON, M. B., SCHULZ, K. F. AND KERKER, M. J. Phys. Chem. 64, 1157, ( 1960 ). 5. MAT! DEVICE ABRAMSON, M. B. OTTEWILL, R, H., SCHULZ, K. F. AND KERKER M. J. J. Phy. Chem. 65. 1924 ( 1961 ). DISCUSSION T. N. Mishra, Directorate of Geology, Bihar, Question : State of Bihar has a sedimentary deposit of calcareous phosphate containing on ,7n average of 2% P 2 O , , 20% CaCO3 , 25 °A, Silica and micro constituents like Cu, Zn, The in traces. Can this material be beneficiated for commercial utilisation ? One of us (B.K.L. Das) is thankful to the Ministry of Education and Culture, Government of India for the award of J. R. F. and also to Principal, R. I. T., Jamshedpur for the award of Institute Junior Research Fellowship. 6. JAMES, R. 0. AND HEALY, T: W. J. Colloid Interface Sc. 40, 53 ( 1972 ). 7. ANDERSEN, T. N. AND BOCKRIS, J. 0. M. Electrochem. Acta. 9, 347 ( 1964 ). 8. GRAHAM E, D. C. J. Chem. Phy. 18, 903 ( 1950 ) 9. VOGEL A. I., Qua. (nor. Anal. Page 606 ( 1975 ) 10. Proc. of the Sympo on Adv. Sc. and Tech. of Mineral Beneficiation in India B. A. R. C. ( 1981 ) 11. Investigation report on the Beneficiation of Maldeota, Phosphate rock ( U. P.) N. M. L. Jamshedpur ( 1979 ). Author : I think the ore can be upgraded provided fundamental studies on nature of gangue minerals etc. are performed. Since calcite and silica both are activated under a particular condition by transition metal ions, the ore may be beneficiated with suitable collectors after determinig the prerequisite conditions. 224 

Simulated Model Studies on the Beneficiation of Calcareous Phosphate Ore

http://eprints.nmlindia.org/4409/1/215-224.PDF

Simulated Model Studies on the Beneficiation of Calcareous Phosphate Ore

Abstract

Similar works

Full text

Available Versions

eprints@NML