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

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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Phosphate removal from aqueous solutions using red mud wasted in bauxite Bayers process x,e s o u l ~ u , ¢ommx, valalonELSEVIER Resources, Conservationand Recycling19 (1997) 11 20 P hosphate removal from aqueous solutions using red mud wasted in bauxite Bayers 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 1996Abstract T he red mud wasted from the Guinean bauxite refinery was studied for phosphate removalf rom model aqueous solutions of potassium orthophosphate (OPh) and sodium tripolyphos-p hate (TPPh). The red mud has been treated with concentrated sulphuric acid. Afterf iltration of the acid suspension, the activated mud was washed (pH 7), dried and ground top owder. The influence of acid to mud ratio, and contact time between them, on the extento f phosphate removal has been studied. The importance of the preliminary acid treatment oft 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 andi nitial concentrations of phosphates in the solutions for the complete removal of phosphatesh ave been determined. Regression models describing the process for both types of phosphates olutions have been deduced. Copyright © 1997 Elsevier Science B.V.K eywords: R ed mud; Phosphate removal: Orthophosphate; Tripolyphosphate1. 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 reservedP II S 0921-3449(96)01 158-5 B. Koumanova et al. / Resources, Conservation and Recycling 19 (1997) 11-2012q uantities of wasted red mud is a serious ecological problem. Many investigationsf or its application have been done. Because of its high content of iron anda luminium, red mud has been studied as a coagulant for wastewater treatment. I ts possible utilization for phosphorous removal from pickle liquor has beens tudied by Fowlie and Shannon [1]. Pilot-plant studies were carried out to assess thep 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 resultings olid product was heat dried. It was capable of efficient phosphorus removal at ad ose of 100-200 mg/1. Couillard has investigated the properties of a red mud as ac oagulant and the physiological effects of its use as well [3-5]. Weaver and Ritchieh ave compared lime-based materials and red mud for phosphorus removal fromp iggery wastewaters [6]. According to the results, lime-based materials were moreeffective than red mud. S hiao and Akashi have used red mud activated with hydrochloric acid as ana dsorbent for removal of phosphates from aqueous solutions [7]. Zakharova et al.h ave reported the production of mixed aluminium-iron coagulant from red muda nd spent pickling liquor from iron smelting plants [8]. Treatment with diluteh ydrochloric acid increased the yield of usable ferric oxide, alumina and titaniumdioxide. 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 models olution ( ~ - O P h , ~-TPPh). B. Koumanova et al./ Resources, Conservation and Re¢3cling 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 itsu 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 analyzedusing Emission Spectral Analyser PGS-2 Q24 Carl Zeiss Jena, Atomic AbsorptionS 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 f ...