Phosphate removal from aqueous solutions using red mud wasted in bauxite Bayer's process

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The red mud wasted from the Guinean bauxite refinery was studied for phosphate removal from model aqueous solutions of potassium orthophosphate (OPh) and sodium tripolyphosphate (TPPh). The red mud has been treated with concentrated sulphuric acid. After filtration of the acid suspension, the activated mud was washed (pH 7), dried and ground to powder.

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Nội dung Text: Phosphate removal from aqueous solutions using red mud wasted in bauxite Bayer's process

x,e s o u l ~ u , ¢ommx, valalon ELSEVIER Resources, Conservationand Recycling19 (1997) 11 20 P hosphate removal from aqueous solutions using red mud wasted in bauxite Bayer's process B. Koumanova*, M. Drame, M. Popangelova University of Chemical Technology and Metallurgy, Department qf Chemical Engineering, 8 Kliment Ohridski Str., 1756 Sq[ia, Bulgaria Received 30 August 1995; revised 12 July 1996; accepted 3 August 1996 Abstract T he red mud wasted from the Guinean bauxite refinery was studied for phosphate removal f rom model aqueous solutions of potassium orthophosphate (OPh) and sodium tripolyphos- p hate (TPPh). The red mud has been treated with concentrated sulphuric acid. After f iltration of the acid suspension, the activated mud was washed (pH 7), dried and ground to p owder. The influence of acid to mud ratio, and contact time between them, on the extent o f phosphate removal has been studied. The importance of the preliminary acid treatment of t he red mud was established by parallel experiments using both raw and activated red mud. T he dose of red mud added to the aqueous solutions, the contact time between them and i nitial concentrations of phosphates in the solutions for the complete removal of phosphates h ave been determined. Regression models describing the process for both types of phosphate s olutions have been deduced. Copyright © 1997 Elsevier Science B.V. K eywords: R ed mud; Phosphate removal: Orthophosphate; Tripolyphosphate 1. Introduction R e d m u d is f o r m e d as a waste d u r i n g b a u x i t e refining k n o w n as B a y e r ' s process. I ts m a i n c o n s t i t u e n t s are iron (giving the red colour), a l u m i n i u m , s o d i u m a n d silica, a n d their a m o u n t s v a r y a c c o r d i n g to the b a u x i t e location. The d i s p o s a l o f large * Corresponding author. Tel: 4- 359 2 6254409; fax: + 359 2 685488: 0921-3449/97/$17.00 Copyright © 1997 Elsevier Science B.V. All rights reserved P II S 0921-3449(96)01 158-5
B. Koumanova et al. / Resources, Conservation and Recycling 19 (1997) 11-20 12 q uantities of wasted red mud is a serious ecological problem. Many investigations f or its application have been done. Because of its high content of iron and a luminium, red mud has been studied as a coagulant for wastewater treatment. I ts possible utilization for phosphorous removal from pickle liquor has been s tudied by Fowlie and Shannon [1]. Pilot-plant studies were carried out to assess the p otential of a material derived from red mud [2]. ARMS (alumized red mud solids) h as been produced when red mud was slurried with sulphuric acid and the resulting s olid product was heat dried. It was capable of efficient phosphorus removal at a d ose of 100-200 mg/1. Couillard has investigated the properties of a red mud as a c oagulant and the physiological effects of its use as well [3-5]. Weaver and Ritchie h ave compared lime-based materials and red mud for phosphorus removal from p iggery wastewaters [6]. According to the results, lime-based materials were more effective than red mud. S hiao and Akashi have used red mud activated with hydrochloric acid as an a dsorbent for removal of phosphates from aqueous solutions [7]. Zakharova et al. h ave reported the production of mixed aluminium-iron coagulant from red mud a nd spent pickling liquor from iron smelting plants [8]. Treatment with dilute h ydrochloric acid increased the yield of usable ferric oxide, alumina and titanium dioxide. The mixed coagulant has been used for municipal wastewater treatment. P hosphorus movement through sands modified by red mud has also been studied [9,10]. E,%] /° . ..._-,& 0" 40 30 20 10 [min] x, Fig. 1. The extent of PO~- removal at different contact times between raw red mud and the model s olution ( ~ - O P h , ~-TPPh).
B. Koumanova et al./ Resources, Conservation and Re¢3'cling 19 (1997) 11 20 13 F', E X] @9 1 , 7~ A 8@ 6@ 0 4@ 2@ 8 @ 18 £~' ,26 48 Eg,i] (O-OPh, A-TPPh). Fig. 2. The influence of the raw red mud dose on the PO 3 removal In this paper the investigations on red mud wasted from Guinean bauxite and its u tilization for phosphate removal from aqueous solutions are discussed. 2. Experimental procedure R ed mud was obtained from a bauxite ore refinery in Guinea. It was analyzed using Emission Spectral Analyser PGS-2 Q24 Carl Zeiss Jena, Atomic Absorption S pectrometer Perkin Elmer 370, and M6ssbauer Spectrometer Model MS 1.7. R ed mud contained 48.4% Fe203, 26.6% Al20~, 5.5% SiO2, 1.2% CaO, 0.9% M gO, 2.8% R203 (including TiO2), loss on ignition 14.6°/,,. It was found that the i ron was bonded as ~-Fe203 and Fe(OH)3. T he red mud was preliminarily dried at 105°C for 2 h. Then it was treated with c oncentrated sulphuric acid (ranging from 10-30 ml H2SO4 per g red mud). The
B . Koumanova et al. / Resources, Conservation and Recycling 19 (1997) 11-20 14 T able 1 E xtent of PO ] at different acid to m u d ratios F or OPh-solutions (C o = 46 rag/l) F or TPPh-solutions (Co = 28 mg/l) A cid to m u d ratio, ml/g E, % Acid to m u d ratio, ml/g E, % 10 73 l0 82 15 83 15 88 20 89 20 91 25 83 25 89 30 77 c ontact time was varied from 1 to 24 h at continuous mixing using a magnet stirrer. T he treated mud was separated from the acid suspension, washed with distilled w ater (to pH 7), dried at 105°C and ground to powder. The liquid phase remaining a fter acid suspension separation was used for investigations on the clarification of t urbid waters [11,12]. T he model aqueous solutions with determined concentrations of potassium o rthophosphate (OPh) or sodium tripolyphosphate (TPPh) were prepared. The l atter is known as a binding agent in synthetic detergent production thus being a source for water pollution. T o a 50 ml water sample, with the preliminary concentration of PO43 deter- m ined, a fixed quantity of red mud was added with stirring for a definite time. The c oncentration of PO 3 was controlled by standard spectrophotometric procedure [13]. Then the extent of phosphate removal was calculated. 3. Results and discussion 3.1. Experiments with raw red mud Previous experiments with non-treated red mud for the purpose of comparison h ave been carried out at the following conditions T able 2 E xtent of phosphate removal at different contact times between concentrated H 2SO 4 a nd red m u d O Ph-solutions (C o = 50 mg/l) T PPh-solutions (C O= 50 mg/l) C ontact time, h E, % Contact time, h E, % 93 l 94 1 3 90 3 95 6 90 6 96 10 95 10 90 24 95 24 96
15 B. Koumanova et al./ Resources, Consert,ation and Recycling 19 (1997) 11 20 E~ ~Z3 1 90 80 60 40 20 0 1 ] ] I ---- I -- ] 8 48 88 120 160 298 248 c, Cmg/]. ] Fig. 3. The influence of the initial concentration on the PO] removal(~-OPh, ~ -TPPh), i nitial PO] concentration in aqueous solutions up to 50 mg/1, c ontact time 5 - 1 2 0 min, a d ose of red mud added to the aqueous sample, 10 g/l. T he m a x i m u m extent of phosphate removal at the conditions mentioned above w as achieved after 30 min and did not change for a longer time of contact (42% for O Ph- and 47% for TPPh-solutions, respectively). The results are illustrated in Fig, 1. C hanging the red mud dose in a range of 1 40 g/l has shown that 30 g/l is s ufficient for the complete removal of PO 3- from TPPh-solution. At the same time a d ose of 40 g/1 red mud was required to give 92% PO 3 removal from OPh-solu- t ion (Fig. 2),
16 B . Koumanova et al. / Resources, Conservation and Recycling 19 (1997) 11-20 3.2. Experiments on the activation of red mud and its performance T he activation of red mud has been carried out with different acid amounts and d ifferent contact times. The results showing the influence of the acid amount used f or preliminary red mud treatment on the phosphate removal from aqueous model s olutions are presented in Table 1. The greatest removal for both types of solutions a t the studied conditions was observed when the acid to mud ratio was 20 ml acid p er g red mud. K eeping this ratio constant the extent of phosphate removal was investigated w hen the contact time between the acid and red mud was varied (Table 2). A ccording to the results, the variation of both the acid quantity and the contact t ime between acid and red mud slightly influences the extent of pO34 removal. T he investigations were carried out when the initial PO43 concentration was v aried from 20 to 240 mg/1. The results are shown in Fig. 3. The extent of PO 3 - r emoval decreased with an increase of the initial concentration of the model s olutions. This effect is more pronounced in the case of OPh-solutions. I t was established that the dose of activated red mud added to the PO43- s olutions is important for the process. For both types of solutions 100% PO43- r emoval was achieved when a dose of 20 g/1 activated mud was used (Fig. 4). T he importance of the preliminary acid treatment of the red mud was established b y parallel experiments using both raw and activated red mud. In Fig. 5 the results a re compared for OPh-solution, and in Fig. 6 for TPPh-solution. The quantity of P O 3- removed from OPh-solution when activated red mud was used was almost d ouble (72% vs. 42%). The time when maximum removal was obtained was halved E,% 4 0. 2 0. Ig/ll Fig. 4. The influence of the activated red mud dose on the P O ] - removal (~-OP, A-TPPh).
17 B. Koumanova et al. / Resources, Conservation and Recycling 19 (1997) 11 20 8O I'i! 60 40 ,,r . . . . 0, ' 0 20 40 60 80 100 120 140 min Fig. 5. Dependencebetween the mixing time of red mud and OPh-solution and PO3 removal(•-raw red mud, ~-activated red mud). (30 rain for raw mud and 15 min for activated red mud). The same tendency was m ore clearly illustrated with TPPs-solutions (30 min for raw mud and only 5 min f or activated red mud). I t is known that orthophosphates and polyphosphates have different interactions w ith metals and sorptive surfaces. Orthophosphates when reacted with metals give s olid metal orthophosphates, they also take part in reactions of complexation and s orptive reactions on the surfaces. Polyphosphates do not form compounds with the m etals contained in the structure of red mud. Spectroscopic investigations have p roved that orthophosphate ion combines with two bonds from the geotite surface a nd two of its oxygen atoms replace hydroxy groups on the surface. So, it is p ossible that P301o i ons could combine with 4 or 6 bonds on the surface. 4 . Optimization of the process T he optimum conditions for phosphate removal using activated red mud have b een determined by controlled experiments. R ed mud treated for 2 h with concentrated H 2SO 4 (20 m l concentrated H 2SO 4 p er g mud) has been used.
B. Koumanova et al./ Resources, Conservation and Recycling 19 (1997) 11-20 18 100 E,% i 60 40 20 O~ I , 1 , 1 , I , I , I , 0 20 40 60 80 100 120 140 min F ig. 6. Dependence between the mixing time of red m u d and model TPPh-solution and PO 3 - removal ( m - r a w red mud, O-activated red mud). T he choice of the variables was made on the basis of the previous experiments. T he influence of the following factors has been studied: x l - - red mud amount, g/l; x2 - - contact time between red m u d and aqueous sample, min; x3 - - initial phosphate concentration, rag/1. T he values of the variables are shown in Table 3. The optimum composition plan [14] has been used and the extent of phosphate removal has been used as an o bjective function. A s econd degree polynomial has been deduced after the elimination of the i nsignificant coefficients. F o r OPh-solutions it is: I~ = 78.79 + 8.76Xl -- 16.59x3 -- 2.46xlx 2 -- 16.74x 2 + 5.61x 2 + 1.81x~; T able 3 V ariables used V ariables Upper level Low level Base level R ed m u d amount, g/1 x I 20 0.5 10.25 C ontact time, min x 2 120 2 61 I nitial concentration of phosphates, mg/1 x 3 250 20 135
19 B. Koumanova et al./ Resources, Conservation and Recycling 19 (1997) 11-20 T able 4 Statistical estimation of the mathematical models s2 s ;~ F~l,~ F,~, (~ = 0.05) O Ph-solutions 3.0 4.95 1.63 3.3 T PPh-solutions 4.1 4.38 1.057 3.8 F o r T P P h - s o l u t i o n s it is: I ~= 84.27 + 9.19x, - 10.51x 3 -{- 3.36x2x 3 - 4.27x~ - 14.47x~ + 4.03x~. T h e statistical e s t i m a t i o n s o f the v a l u e s o b t a i n e d f r o m t h e r e g r e s s i o n m o d e l s are s h o w n in T a b l e 4. F o r b o t h m o d e l s the c a l c u l a t e d v a l u e for F is l o w e r t h a n f tabl at a l evel o f c o n f i d e n c e ~ = 0.05. T h e o p t i m u m c o n d i t i o n s are: For OPh-solutions For TPPh-solutions x , 13.3 g/l x I 19.5 g/1 .r~ 2 m i n x2 67 m i n .v3 20 m g / l x3 20 mg/1 5 . Conclusions It has been found that red mud, wasted from Guinean bauxite, is, after treatment w ith concentrated sulphuric acid, a highly effective reagent for the removal of p h o s p h a t e s f r o m a q u e o u s s o l u t i o n s . C o n t a c t t i m e has a slight effect o n the p r o c e s s w h e r e a s t h e d o s e o f m u d u s e d is m o r e significant. T h e a c t i v a t e d red m u d is s u i t a b l e for the removal of low PO]- concentrations. R eferences [1] Fowlie, P.J.A. and Shannon, E.E., 1973. Utilization of industrial wastes and waste byproducts for p hosphorous removal: an inventory and assessment. Ont. Min. Environ. Res. Rep., No. 6, pp. 102. [2] Shannon, E.E. and Verghese, K.I., 1976. Utilization of alumized red mud solids for phosphorus removal, J. WPCF, 48:1948 1954. [3] Couillard, D., 1982. Use of red mud, a residue of alumina production by the Bayer process in water t reatment. Sci. Total Environ., 25:181 191. [4] Couillard, D., 1983. Phosphorus removal from waters with the aid of effluents from aluminium-re- ducing industries. Eau du Quebec, 16:34 37. [5] Couillard, D. and Tyagi, R.D., 1986. Treatment of phosphorus (PO4) in wastewaters using residues f rom alkaline extraction of bauxite. Tribune du Cebedeau, 39:3 14. [6] Weaver, D.M. and Ritchie, G.S.P., 1987. The effectiveness of lime-based amendments and bauxite residues at removing phosphorus from piggery effluent. Environ. Poll., 46:163 175.
20 B . Koumanova et al. / Resources, Conservation and Recycling 19 (1997) 11-20 [7] Shiao, S.J. and Akashi, K., 1977. Phosphate removal from aqueous solution by activated red mud. J. WPCF, 49:280 285. [8] Zakharova, V.I., Nikolaev, I.V. and Lutsenko, G.N., 1985. Aluminium-iron coagulants from m etallurgical plant wastes. Soviet J. Water Chem. Technol., 7: 94-97. [9] Chowdhry, N.A., 1975. Sand and red mud filters: an alternative media for household effluents. W ater Poll. Control, 113: 17-18. [10] Kayaalp, M., Ho, G., Mathew, K. and Newman, P., 1988. Phosphorus movement through sands modified by red mud. Water (Australia), 15: 26-29. [11] Koumanova, B., Drame, M., Popangelova, M. and Stefanova, S., 1995. Use of Guinean red sludge, a residue of Bayer's process for alumina production in water treatment: I. Composition and possible a pplication for water clarification. Comp. Ren. Bulg. Acad. Sci., 48 (No. 9 10): 75-78. [12] Koumanova, B., Drame, M., Jontchev, Ch. and Popangelova, M., 1995. Application of Guinean r ed sludge, a residue of Bayer's process for alumina production in water treatment: II. Determina- t ion of the optimal conditions for water clarification. Comp. Ren. Bulg. Acad. Sci., 48 (No. 11-12) 5 5-57. [13] Unifitzirovannie metodi issledovanija kachestva vod, v. I 'Metodi himicheskogo analiza vod', 1977, M oscow (in Russian). [14] Vouchkov, I.V. and Stojanov, S.K., 1986. Mathematical modelling and optimization of technolog- ical objects. Technika, Sofia (in Bulgarian).