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

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

E L S E V I E R Resources, Conservation and Recycling 19 (1997) 11 20

x, e s o u l ~ u ,

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Phosphate 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

The red mud wasted from the Guinean bauxite refinery was studied for phosphate removal from model aqueous solutions of potassium orthophosphate (OPh) and sodium tripolyphos- phate (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 The influence of acid to mud ratio, and contact time between them, on the extent

of phosphate removal has been studied The importance of the preliminary acid treatment of the red mud was established by parallel experiments using both raw and activated red mud The dose of red mud added to the aqueous solutions, the contact time between them and initial concentrations of phosphates in the solutions for the complete removal of phosphates have been determined Regression models describing the process for both types of phosphate solutions have been deduced Copyright © 1997 Elsevier Science B.V

Keywords: Red mud; Phosphate removal: Orthophosphate; Tripolyphosphate

1 Introduction

R e d m u d is f o r m e d as a w a s t e 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 Its m a i n c o n s t i t u e n t s are i r o n (giving the r e d c o l o u r ) , a l u m i n i u m , s o d i u m a n d silica,

a n d t h e i r 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 l o c a t i o n T h e 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

PII S0921-3449(96)01 1 58-5

12 B Koumanova et al / Resources, Conservation and Recycling 19 (1997) 11-20

quantities of wasted red mud is a serious ecological problem Many investigations for its application have been done Because of its high content of iron and aluminium, red mud has been studied as a coagulant for wastewater treatment Its possible utilization for phosphorous removal from pickle liquor has been studied by Fowlie and Shannon [1] Pilot-plant studies were carried out to assess the potential of a material derived from red mud [2] ARMS (alumized red mud solids) has been produced when red mud was slurried with sulphuric acid and the resulting solid product was heat dried It was capable of efficient phosphorus removal at a dose of 100-200 mg/1 Couillard has investigated the properties of a red mud as a coagulant and the physiological effects of its use as well [3-5] Weaver and Ritchie have compared lime-based materials and red mud for phosphorus removal from piggery wastewaters [6] According to the results, lime-based materials were more effective than red mud

Shiao and Akashi have used red mud activated with hydrochloric acid as an adsorbent for removal of phosphates from aqueous solutions [7] Zakharova et al have reported the production of mixed aluminium-iron coagulant from red mud and spent pickling liquor from iron smelting plants [8] Treatment with dilute hydrochloric acid increased the yield of usable ferric oxide, alumina and titanium dioxide The mixed coagulant has been used for municipal wastewater treatment Phosphorus movement through sands modified by red mud has also been studied [9,10]

40

30

20

10

E,%]

_-,&

x, [min]

Fig 1 The extent of PO~- removal at different contact times between raw red mud and the model

F',

B Koumanova et al./ Resources, Conservation and Re¢3'cling 19 (1997) 11 20

EX]

13

A

8@

6@

0

4@

2@

8

E g , i ]

Fig 2 The influence of the raw red mud dose on the PO 3 removal (O-OPh, A-TPPh)

In this paper the investigations on red mud wasted from Guinean bauxite and its utilization for phosphate removal from aqueous solutions are discussed

2 Experimental procedure

Red 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 Spectrometer Perkin Elmer 370, and M6ssbauer Spectrometer Model MS 1.7 Red mud contained 48.4% Fe203, 26.6% Al20~, 5.5% SiO2, 1.2% CaO, 0.9% MgO, 2.8% R203 (including TiO2), loss on ignition 14.6°/,, It was found that the iron was bonded as ~-Fe203 and Fe(OH)3

The red mud was preliminarily dried at 105°C for 2 h Then it was treated with concentrated sulphuric acid (ranging from 10-30 ml H2SO 4 per g red mud) The

14 B Koumanova et al / Resources, Conservation and Recycling 19 (1997) 1 1 - 2 0

Table 1

Extent o f PO ] at different acid to m u d ratios

F o r OPh-solutions (C o = 46 rag/l) For TPPh-solutions (Co = 28 mg/l)

Acid to m u d ratio, ml/g E, % Acid to m u d ratio, ml/g E, %

contact time was varied from 1 to 24 h at continuous mixing using a magnet stirrer The treated mud was separated from the acid suspension, washed with distilled water (to pH 7), dried at 105°C and ground to powder The liquid phase remaining after acid suspension separation was used for investigations on the clarification of turbid waters [11,12]

The model aqueous solutions with determined concentrations of potassium orthophosphate (OPh) or sodium tripolyphosphate (TPPh) were prepared The latter is known as a binding agent in synthetic detergent production thus being a source for water pollution

To a 50 ml water sample, with the preliminary concentration of PO43 deter- mined, a fixed quantity of red mud was added with stirring for a definite time The concentration 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 have been carried out at the following conditions

Table 2

Extent o f p h o s p h a t e removal at different contact times between concentrated H2SO 4 a n d red m u d OPh-solutions (C o = 50 mg/l) TPPh-solutions (C O = 50 mg/l)

B Koumanova et al./ Resources, Consert,ation and Recycling 19 (1997) 11 20 15

E~ ~Z3

190

80

60

40

20

c , Cmg/] ] Fig 3 The influence of the initial concentration on the PO] removal (~-OPh, ~ -TPPh),

initial PO] concentration in aqueous solutions up to 50 mg/1,

contact time 5 - 1 2 0 min,

a dose of red mud added to the aqueous sample, 10 g/l

The m a x i m u m extent of phosphate removal at the conditions mentioned above was achieved after 30 min and did not change for a longer time of contact (42% for OPh- and 47% for TPPh-solutions, respectively) The results are illustrated in Fig,

1

Changing the red m u d dose in a range of 1 40 g/l has shown that 30 g/l is sufficient for the complete removal of PO 3 - from TPPh-solution At the same time

a dose o f 40 g/1 red m u d was required to give 92% PO 3 removal from OPh-solu- tion (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

The activation of red m u d has been carried out with different acid amounts and different contact times The results showing the influence of the acid a m o u n t used for preliminary red mud treatment on the phosphate removal from aqueous model solutions are presented in Table 1 The greatest removal for both types o f solutions

at the studied conditions was observed when the acid to mud ratio was 20 ml acid per g red mud

Keeping this ratio constant the extent o f phosphate removal was investigated when the contact time between the acid and red mud was varied (Table 2) According to the results, the variation of both the acid quantity and the contact time between acid and red mud slightly influences the extent of pO34 removal The investigations were carried out when the initial PO43 concentration was varied from 20 to 240 mg/1 The results are shown in Fig 3 The extent of PO 3 - removal decreased with an increase of the initial concentration of the model solutions This effect is more pronounced in the case of OPh-solutions

It was established that the dose o f activated red m u d added to the PO43- solutions is important for the process F o r both types of solutions 100% PO43- removal was achieved when a dose o f 20 g/1 activated m u d was used (Fig 4) The importance o f the preliminary acid treatment of the red mud was established

by parallel experiments using both raw and activated red mud In Fig 5 the results are compared for OPh-solution, and in Fig 6 for TPPh-solution The quantity of

PO 3 - removed from OPh-solution when activated red mud was used was almost double (72% vs 42%) The time when maximum removal was obtained was halved

40

20

E,%

Ig/ll

Fig 4 The influence of the activated red mud dose on the P O ] - removal ( ~ - O P , A-TPPh)

B Koumanova et al / Resources, Conservation and Recycling 19 (1997) 11 20 17

8O

60 I' i!

min

Fig 5 Dependence between the mixing time of red mud and OPh-solution and PO 3 removal (•-raw red mud, ~-activated red mud)

(30 rain for raw mud and 15 min for activated red mud) The same tendency was more clearly illustrated with TPPs-solutions (30 min for raw mud and only 5 min for activated red mud)

It is known that orthophosphates and polyphosphates have different interactions with metals and sorptive surfaces Orthophosphates when reacted with metals give solid metal orthophosphates, they also take part in reactions of complexation and sorptive reactions on the surfaces Polyphosphates do not form compounds with the metals contained in the structure of red mud Spectroscopic investigations have proved that orthophosphate ion combines with two bonds from the geotite surface and two of its oxygen atoms replace hydroxy groups on the surface So, it is possible that P301o ions could combine with 4 or 6 bonds on the surface

4 Optimization of the process

The optimum conditions for phosphate removal using activated red mud have been determined by controlled experiments

Red mud treated for 2 h with concentrated H2SO 4 (20 ml concentrated H2SO 4 per g mud) has been used

B Koumanova et al./ Resources, Conservation and Recycling 19 (1997) 11-20

100 E,%

i

60

40

20

O ~ I , 1 , 1 , I , I , I ,

min

Fig 6 Dependence between the mixing time o f red m u d and model TPPh-solution a n d PO 3 - removal ( m - r a w red m u d , O-activated red mud)

The choice o f the variables was m a d e on the basis o f the previous experiments The influence of the following factors has been studied:

xl - - red m u d a m o u n t , g/l;

x2 - - contact time between red m u d and aqueous sample, min;

x3 - - initial phosphate concentration, rag/1

The values o f the variables are shown in Table 3 The o p t i m u m composition plan [14] has been used and the extent of phosphate removal has been used as an objective function

A second degree polynomial has been deduced after the elimination o f the insignificant 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~;

Table 3

Variables used

B Koumanova et al./ Resources, Conservation and Recycling 19 (1997) 11-20

Table 4

Statistical estimation of the mathematical models

19

F o r T P P h - s o l u t i o n s it is:

I ~ = 84.27 + 9 1 9 x , - 10.51x 3 -{- 3.36x2x 3 - 4.27x~ - 14.47x~ + 4.03x~

T h e s t a t i s t i c a l e s t i m a t i o n s o f t h e 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 a r e

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 t h e c a l c u l a t e d v a l u e f o r F is l o w e r t h a n ftabl at a level 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:

F o r O P h - s o l u t i o n s F o r T P P h - s o l u t i o n s

5 Conclusions

It has been found that red mud, wasted from Guinean bauxite, is, after treatment

with 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 h a s a slight e f f e c t o n t h e 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 r e d m u d is s u i t a b l e

f o r t h e r e m o v a l o f l o w P O ] - c o n c e n t r a t i o n s

References

[1] Fowlie, P.J.A and Shannon, E.E., 1973 Utilization of industrial wastes and waste byproducts for phosphorous 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 treatment 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 from 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 metallurgical 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 Water 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 application 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 red sludge, a residue of Bayer's process for alumina production in water treatment: II Determina- tion of the optimal conditions for water clarification Comp Ren Bulg Acad Sci., 48 (No 11-12) 55-57

[13] Unifitzirovannie metodi issledovanija kachestva vod, v I 'Metodi himicheskogo analiza vod', 1977, Moscow (in Russian)

[14] Vouchkov, I.V and Stojanov, S.K., 1986 Mathematical modelling and optimization of technolog- ical objects Technika, Sofia (in Bulgarian)