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Aqueous silver (i) adsorption on a low density moroccan silicate
Silver (I) adsorption
on a low density
silicate
Ann. Chim.
Sci. Mat, 1996,23,
pp.‘161-164
AQUEOUS SILVER (I) ADSORPTION ON A LOW DENSITY MOROCCAN SILICATE A. RIDHA,
Dipartement
de Chimie,
FacultC
H. ADERDOUR, H. ZINEDDINE, M.Z. M. EL MORABIT. A. NADIR1 des Sciences,
B.P. 4010,
B&i
M’hamed,
BENABDALLAH,
50003-Mekds,
Maroc.
Summarv~: This paper describes first the determination of the physico-chemical characteristics and the surface properties of a natural Moroccan low density silicate from the diatomites family. Then, the adsorption of aqueous Ag+ ions on this diatomite and the Langmuir model are studied.
Resume : Etude de l’adsorption de l’arrrent (I) en solution aqueuse sur un silicate nature1 marocain de faible densite. Cet article d&it dans une premiere partie la determination des caracteristiques physico-cbimiques et des proprietes de surface d’un silicate nature1 marocain de faible densite, appartenant a la famille des diatomites. L’etude d’adsorption des ions Ag’ aqueux sur ce mattriau et le trace de l’isotherme Langmuir font l’objet de sa seconde partie.
1. INTRODUCTION The adsorption phenomenon is widely used in water treatment processes [I to 41. As the at&&y of various kinds of soils for heavy metals is well known [S to ‘71,we have studied in this work the silver aqueous ions adsorption on a variety of diatomite abundant in the soils of the Rif mountain chain in the north of Morocco. This study is a preliminary step in the development of a process of silver removal from some kinds of liquid industrial waste waters. It includes in the first part the physico-chemical characterization and the surface properties determination of the chosen variety of diatomite (referred to in this paper as DR). The experimental results of the study of aqueous ions Ag” adsorption on DR are presented in the second part and the validity of the Langmuir adsorption model is then discussed.
Reprints : A. RIDHA, Faculte des Sciences ; BP 4010 ; B&i-M’hamed
; 50003 Meknes (MAROC)
162
A. Fiidha et al.
2. MATERIALS AND METHODS The chemical composition ,of DR has been determined by Atomic Absorption Spectrophotometry (PHILIPS PYE UNICAM PU9000) and X Fluorescence (PHILIPS PW14000). Its global specific area has been calculated according to liquid nitrogen adsorption measurements at 77 K (BET. method according to the norm NF X11-621). Its density and porosity have been determined by a mercury porosimeter (AUTOPORE II 9220). The adsorption study was undertaken using natural DR finely grinded without any treatment in the following experimental conditions : The suspensions obtained by addition of 0.2 g of DR to 1 1 of aqueous solutions of silver nitrate at different initial concentrations (Co = 5, 10, 50 and 100 mg/l) were continuously stirred at t = 25 “C during 7 hours. Their pH was adjusted to 4 by addition of HN03 0,5 N. Small aliquots of the suspensions were taken at regular time intervals, filtered on 0.45 pm membranes, acidified by HN03 1 % and their silver concentration was determined by Atomic Absorption Spectrophotometry. The equilibrium time determined was then used for the Langmuir isotherm drawing at pH = 4 with silver concentration tanging from 5 to 110 mg/l and a DR mass of 0.1 g for a 500 ml solution, All the chemicals used in this study were from BDI?’ and of (( Analar )) quality. 3. RESULTS AND DISCUSSIONS 3.1. Characterization of the diatomite The most important constituents and the physico-chemical characteristics of the studied variety of diatom&e are given in Tables 1 and 2. TABLE 1 : Chemical composition of the diatomite Constituent SiOa AI203
Fe203 Mgo CaO CaCO3 Na20 PbO K20
Loss at 1OOO’C
DR (% of weight) 68.00 4.87 0.80 0.83 3.47 6.78 5.79 0.13 0.76 15.56
According to the quantitative analysis of DR, silica is the principal component of this material whose adsorption capacity can thus be explained. Furthermore, the measured density of a DR sample dried during 24 hours at 100 “C in an oven shows that it is a low density natural silicate. The high value of the external specific area (> 10000 cmVml) of this diatomite should explain its important reactivity. The great porosity of DR and its specific area (B.E.T.) suggest that the silver fixation is possible on the surface grains as well as in their depth.
Silver
(I) adsorption
on a low density
silicate
163
TABLE 2 : Physico-chemical characteristics of the diatomite Parameters Mean pore radius (A) Specific surface area ( cm2/ml) Specific area (B.E.T.) (mVg) Open porosity (Oh) Apparent density (gkm3) Real density (gkm3)
Value 1745 12967 14.3 46 0.65 1.22
3.2. Adsorption study The adsorption capacity whose variations have been studied is X/m =(Co - C,) / m where C!, is the residual concentration (mg/l) of Ag’ ions and m is the mass (g) of DR dispersed in 1 1 of solution. The kinetic curves (figures 1.a & 1,b) show that the adsorption equilibrium is quickly reached with an initial concentration COof silver (I) equal to 5.08 mg/l (about 30 minutes). For higher values of Co, the equilibrium takes about 120 minutes to be reached. Hence, we have chosen to undertake the isotherm drawing experiments with a contact time equal to 3 hours.
FIGURE 1 : Effect of Ag (I) initial concentration COon the adsorption capacity and on the average fixation yield ([DR] = 0.2 g/l ; pH = 4 ; T = 25 “C). + Co = 5.08 mg/l
n
Co = 10.09 mg/l
A Co = 50.25 mg/l
x CO = 102.13 mg/l
After the tirst 10 minutes of the suspension stirring, more than 60 % of Ag is already eliminated from the aqueous solution : about 90 % for the smallest value of Co (5.08 mg/l) and 68 % for Co = 10.09 mg& Therefore, the tixation yield depends closely on Co value. When this concentration varies from 5 to 100 mg/l, the adsorbed metal quantity increases from 24.13 to 73.6 mg/g and the fixation yield decreases from 94 to 15 % Meanwhile, a total elimination of silver from a 100 mg/l solution is possible with a DR concentration equal to 20 fl.
A. Ridha et a/.
164
3.3. Lanemuir isotherm In the studied concentration interval (5 to 110 mg/l), the results concerning the adsorption equilibrium at pH = 4 (figure 2) are in good agreement with the Langmuir model [8], described by the linearized equation (1). The value of r (0.9962) suggests that there is a monomolecular layer of Ag (I) on the external surface of DR particles. The Langmuir constants b and K, representing respectively the adsorption capacity of DR and the equilibrium constant have been determined graphically and their values are b = 58.00 mg/g meaning that DR has a great affinity for Ag’ ions and K = 1,141 l/mg meaning probably a significant stability of the adsorption equilibrium at pH = 4. LC x/m
= &
+ 6.q
(1)
C, : Residual concentration of Ag’ ions at the equilibrium (mg/l) X/m : Adsorption capactiy (mg/g) K, b : Langmuir constants 0 i----t--i-+-t--+----c----+--i 0 10 20 JO 40 50 00 70 00 cr (mti ) FIGURE 2 : Langmuir adsorption isotherm. 4. CONCLUSION The diatomite variety studied in this work is a low density microporous silicate. Aqueous Ag’ cations can be completely removed from a solution where an appropriate amount of DR is dispersed. The silver fixation on DR surface is done according to the Langmuir model which means that there is a monomolecular layer formation. The high elimination yield observed at low initial concentrations of Ag is promising for a further use of DR as a low cost and efficient adsorbent in a treatment process aiming to eliminate silver from some kinds of industrial waste waters. The development of such a process is in progress in our laboratory. 5. REFERENCES [l] GAID (K.), CAVELIER (C.), MARTIN (G.), Wat. Res., 1982,& 7 [2] DUSART (O.), SOUARI (S.), MAZET (M.), Environ, Technol., 1990, u, 721. [3] DIPAK (R.), GREENLAW (P.N.), SHANE (R.S.), J. Environ. Sci. Health, 1993, A 28(l), 37. [4] LOW (K.S.), LEE (C.K.), TAi (C.H.), J. Environ. Sci. Health, 1994, A 29 (l), 171. [5] PANDAY (K.K.), PRASAD (G.), SINGH (V.N.), Water. air and soil poll., 1986,27, ,287. [6] SINGH (A.K.), SINGH (D.P.), SINGH (V.P.), Environ. Technol Lett., 1988,9, 1153. [73 MAJONE (M.), PETRANGELI PAPINI (M.), ROLLE (E.), Environ. Technol., 1993,u, [S] LANGMUIR
(I.), J. Am. Chem. Sot., 1915 , fl, 1139.
629.
on a low density
silicate
Ann. Chim.
Sci. Mat, 1996,23,
pp.‘161-164
AQUEOUS SILVER (I) ADSORPTION ON A LOW DENSITY MOROCCAN SILICATE A. RIDHA,
Dipartement
de Chimie,
FacultC
H. ADERDOUR, H. ZINEDDINE, M.Z. M. EL MORABIT. A. NADIR1 des Sciences,
B.P. 4010,
B&i
M’hamed,
BENABDALLAH,
50003-Mekds,
Maroc.
Summarv~: This paper describes first the determination of the physico-chemical characteristics and the surface properties of a natural Moroccan low density silicate from the diatomites family. Then, the adsorption of aqueous Ag+ ions on this diatomite and the Langmuir model are studied.
Resume : Etude de l’adsorption de l’arrrent (I) en solution aqueuse sur un silicate nature1 marocain de faible densite. Cet article d&it dans une premiere partie la determination des caracteristiques physico-cbimiques et des proprietes de surface d’un silicate nature1 marocain de faible densite, appartenant a la famille des diatomites. L’etude d’adsorption des ions Ag’ aqueux sur ce mattriau et le trace de l’isotherme Langmuir font l’objet de sa seconde partie.
1. INTRODUCTION The adsorption phenomenon is widely used in water treatment processes [I to 41. As the at&&y of various kinds of soils for heavy metals is well known [S to ‘71,we have studied in this work the silver aqueous ions adsorption on a variety of diatomite abundant in the soils of the Rif mountain chain in the north of Morocco. This study is a preliminary step in the development of a process of silver removal from some kinds of liquid industrial waste waters. It includes in the first part the physico-chemical characterization and the surface properties determination of the chosen variety of diatomite (referred to in this paper as DR). The experimental results of the study of aqueous ions Ag” adsorption on DR are presented in the second part and the validity of the Langmuir adsorption model is then discussed.
Reprints : A. RIDHA, Faculte des Sciences ; BP 4010 ; B&i-M’hamed
; 50003 Meknes (MAROC)
162
A. Fiidha et al.
2. MATERIALS AND METHODS The chemical composition ,of DR has been determined by Atomic Absorption Spectrophotometry (PHILIPS PYE UNICAM PU9000) and X Fluorescence (PHILIPS PW14000). Its global specific area has been calculated according to liquid nitrogen adsorption measurements at 77 K (BET. method according to the norm NF X11-621). Its density and porosity have been determined by a mercury porosimeter (AUTOPORE II 9220). The adsorption study was undertaken using natural DR finely grinded without any treatment in the following experimental conditions : The suspensions obtained by addition of 0.2 g of DR to 1 1 of aqueous solutions of silver nitrate at different initial concentrations (Co = 5, 10, 50 and 100 mg/l) were continuously stirred at t = 25 “C during 7 hours. Their pH was adjusted to 4 by addition of HN03 0,5 N. Small aliquots of the suspensions were taken at regular time intervals, filtered on 0.45 pm membranes, acidified by HN03 1 % and their silver concentration was determined by Atomic Absorption Spectrophotometry. The equilibrium time determined was then used for the Langmuir isotherm drawing at pH = 4 with silver concentration tanging from 5 to 110 mg/l and a DR mass of 0.1 g for a 500 ml solution, All the chemicals used in this study were from BDI?’ and of (( Analar )) quality. 3. RESULTS AND DISCUSSIONS 3.1. Characterization of the diatomite The most important constituents and the physico-chemical characteristics of the studied variety of diatom&e are given in Tables 1 and 2. TABLE 1 : Chemical composition of the diatomite Constituent SiOa AI203
Fe203 Mgo CaO CaCO3 Na20 PbO K20
Loss at 1OOO’C
DR (% of weight) 68.00 4.87 0.80 0.83 3.47 6.78 5.79 0.13 0.76 15.56
According to the quantitative analysis of DR, silica is the principal component of this material whose adsorption capacity can thus be explained. Furthermore, the measured density of a DR sample dried during 24 hours at 100 “C in an oven shows that it is a low density natural silicate. The high value of the external specific area (> 10000 cmVml) of this diatomite should explain its important reactivity. The great porosity of DR and its specific area (B.E.T.) suggest that the silver fixation is possible on the surface grains as well as in their depth.
Silver
(I) adsorption
on a low density
silicate
163
TABLE 2 : Physico-chemical characteristics of the diatomite Parameters Mean pore radius (A) Specific surface area ( cm2/ml) Specific area (B.E.T.) (mVg) Open porosity (Oh) Apparent density (gkm3) Real density (gkm3)
Value 1745 12967 14.3 46 0.65 1.22
3.2. Adsorption study The adsorption capacity whose variations have been studied is X/m =(Co - C,) / m where C!, is the residual concentration (mg/l) of Ag’ ions and m is the mass (g) of DR dispersed in 1 1 of solution. The kinetic curves (figures 1.a & 1,b) show that the adsorption equilibrium is quickly reached with an initial concentration COof silver (I) equal to 5.08 mg/l (about 30 minutes). For higher values of Co, the equilibrium takes about 120 minutes to be reached. Hence, we have chosen to undertake the isotherm drawing experiments with a contact time equal to 3 hours.
FIGURE 1 : Effect of Ag (I) initial concentration COon the adsorption capacity and on the average fixation yield ([DR] = 0.2 g/l ; pH = 4 ; T = 25 “C). + Co = 5.08 mg/l
n
Co = 10.09 mg/l
A Co = 50.25 mg/l
x CO = 102.13 mg/l
After the tirst 10 minutes of the suspension stirring, more than 60 % of Ag is already eliminated from the aqueous solution : about 90 % for the smallest value of Co (5.08 mg/l) and 68 % for Co = 10.09 mg& Therefore, the tixation yield depends closely on Co value. When this concentration varies from 5 to 100 mg/l, the adsorbed metal quantity increases from 24.13 to 73.6 mg/g and the fixation yield decreases from 94 to 15 % Meanwhile, a total elimination of silver from a 100 mg/l solution is possible with a DR concentration equal to 20 fl.
A. Ridha et a/.
164
3.3. Lanemuir isotherm In the studied concentration interval (5 to 110 mg/l), the results concerning the adsorption equilibrium at pH = 4 (figure 2) are in good agreement with the Langmuir model [8], described by the linearized equation (1). The value of r (0.9962) suggests that there is a monomolecular layer of Ag (I) on the external surface of DR particles. The Langmuir constants b and K, representing respectively the adsorption capacity of DR and the equilibrium constant have been determined graphically and their values are b = 58.00 mg/g meaning that DR has a great affinity for Ag’ ions and K = 1,141 l/mg meaning probably a significant stability of the adsorption equilibrium at pH = 4. LC x/m
= &
+ 6.q
(1)
C, : Residual concentration of Ag’ ions at the equilibrium (mg/l) X/m : Adsorption capactiy (mg/g) K, b : Langmuir constants 0 i----t--i-+-t--+----c----+--i 0 10 20 JO 40 50 00 70 00 cr (mti ) FIGURE 2 : Langmuir adsorption isotherm. 4. CONCLUSION The diatomite variety studied in this work is a low density microporous silicate. Aqueous Ag’ cations can be completely removed from a solution where an appropriate amount of DR is dispersed. The silver fixation on DR surface is done according to the Langmuir model which means that there is a monomolecular layer formation. The high elimination yield observed at low initial concentrations of Ag is promising for a further use of DR as a low cost and efficient adsorbent in a treatment process aiming to eliminate silver from some kinds of industrial waste waters. The development of such a process is in progress in our laboratory. 5. REFERENCES [l] GAID (K.), CAVELIER (C.), MARTIN (G.), Wat. Res., 1982,& 7 [2] DUSART (O.), SOUARI (S.), MAZET (M.), Environ, Technol., 1990, u, 721. [3] DIPAK (R.), GREENLAW (P.N.), SHANE (R.S.), J. Environ. Sci. Health, 1993, A 28(l), 37. [4] LOW (K.S.), LEE (C.K.), TAi (C.H.), J. Environ. Sci. Health, 1994, A 29 (l), 171. [5] PANDAY (K.K.), PRASAD (G.), SINGH (V.N.), Water. air and soil poll., 1986,27, ,287. [6] SINGH (A.K.), SINGH (D.P.), SINGH (V.P.), Environ. Technol Lett., 1988,9, 1153. [73 MAJONE (M.), PETRANGELI PAPINI (M.), ROLLE (E.), Environ. Technol., 1993,u, [S] LANGMUIR
(I.), J. Am. Chem. Sot., 1915 , fl, 1139.
629.