329
Ind. Eng. Chern. Process Des. Dev. 1980, 79, 329-335
Investigations of the Rate of Sedimentation of Magnesium Hydroxide Obtained from Sea Water Bartill Petrlc" and Nedjeljka Petrlc Chemical Engineering Faculty, Split University, 58000 Splif, Yugoslavia
The influence of incomplete precipitationon the rate of sedimentation of magnesium hydroxide obtained from sea water, with the use of the flocculants, was studied. The study showed that incomplete precipitation of magnesium ions from sea water considerably affects the rate of sedimentation of magnesium hydroxide. The rate of sedimentation increased considerably and thus the capacity of the thickener was also increased. At a precipitation of 80 % , the c:apacity of the thickener increased by 86.5% in relation to complete precipitation. Calculations were made according to Kynch's theory. The above procedure leads to a substantial reduction in the content of calcium salt in the product, which can be explained by the law of adsorption, as set out by Paneth, Fajans, and Hahn.
Introduction In obtaining magnesium hydroxide from sea water, the rate of sedimentation of magnesium hydroxide often represents a bottleneck of production. The purpose of this study was to increase the rate of sedimentation of magnesium hydroxide, thus increasing the capacity of the thickener, to explain these phenomena, and to examine the effect of the increase in the rate of sedimentation on the purity of the product. With this in view, we carried out our study with the addition of Flocculant B (polyacrylamide) and set out to establish the optimal quantity of Flocculant B which must be added in order to attain the maximal sedimentation rate. The procedure of using the slag drawn from the production of copper as a flocculus has been described in the literature (Ionescu and Branisi, 1960). We tried using slag from highly carbonic Fe-Cr which was available as waste material. The results of these trials are presented in this paper. The main improvement of the process, Le., the increase in the rate of sedimentation of magnesium hydroxide and the increase in the capacity of the thickener, described in this paper, was achieved through the incomplete precipitation of magnesium hydroxide, i.e., precipitation with a nonstoichiometric quantity of calcium hydroxide, and this has so far not been described in literature. The effect of this improvement on the purity of the product was also examined. Experimental Section Materials. The sea water used for the precipitation of magnesium hydroxilde in this study had the following content of magnesium oxide and calcium oxide: MgO, 2.398 g/L and CaO, 0.592 g/L. In some of the series of trials the content of MgO and CaO in the sea water varied slightly from the given value. The value which was always taken into account was the real, Le., precise value. The composition of the lime used is listed in Table I. The slag from highly carbonic Fe-Cr was composed as follows: Cr203,8.214;; S O 2 ,29.91%; A1203,18.59%; FeO, 0196-4305/80/1119-0329$01.00/0
Table I SiO,, material
%
CaO, MgO, F e 2 0 3 , A Z O , , %
%
%
%
dolomite lime 0.076 57.55 42.27 0.064 0.042 lime from lime kiln 0.050 98.92 0.73 0.160 0.140 lime from acetylene 1.633 95.34 0.32 1.594 1.120 generator
2.53%; CaO, 1.82%; MgO, 39.06%. The solution of the slag from Fe-Cr was prepared as follows: 1.00 g of slag from Fe-Cr is dissolved in 20 mL of 8% sulfuric acid, 100 mL of distilled water is added, and the solution is then filtered. The procedure for the preparation of the slag solution was taken from the literature (Ionescu and Branisi, 1960). Flocculant B, which was used in these trials, is an anionic flocculant with 7% of active substance. The solution contained 0.05% active substance and was prepared by dissolving 1.00 g of Flocculant B in 139 mL of distilled water, with mixing and gentle heating. Experimental Procedure. The procedure for the pretreatment of the sea water was as follows. Sea water previously acidified to pH 3.8-4.0 was ventilated by countercurrent air in the desorption tower filled with Raschig rings (Gilpin et al., 1963). The completeness of the removal of C 0 2was tested by means of titration with NaOH. The precipitation of magnesium hydroxide was performed in the pretreated sea water. The procedure was as follows. Powdered lime (dolomite lime, lime taken from the lime kiln or lime from the acetylene generator) was added to 500 mL of pretreated sea water and the suspension was stirred with a magnetic stirrer for 30 min. Then, drop by drop, the appropriate quantity of either the solution of Flocculant B or the slag solution from Fe-Cr was added. The stirring was continued for 1 min and then the suspension was poured into a 1000-mL cylinder which had a tape marked in millimeters, and the deposition of the precipitate was then measured at given time intervals. The rate of sedimentation was tested at 20 "C. A large number
0 1980 American Chemical Society
330
Ind. Eng. Chem. Process Des. Dev., Vol. 19, No. 3, 1980 I
2LO
160 I
E
E N
1LO
120
100 ‘10 stoich o without f l o c c u l a n t b 2Uml f l o c c /Lit t 25ml d Wml -Ie lMmi - (
-,,-
100
80
EG 0
Lo
b
d‘ e
20
0
M
40
Eo t (min)
4oC
Figure 1. The dependence of the height of the precipitate (2)on the time of sedimentation ( t )in cases of complete precipitation, with the following additions of Flocculant B/L: a, without Flocculant B; b, 2.0 mL; c, 2.5 mL; d, 5.0 mL; e, 10.0 mL.
of measurements were carried out and could be reproduced fairly easily.
Results of the Study and Interpretation of the Results A study of the rate of sedimentation of magnesium hydroxide obtained from sea water through precipitation with dolomite lime, lime obtained from the lime kiln, or lime from the acetylene generator is presented in this paper, i.e., the dependence of the height of the precipitate (2) in time ( t ) and also the dependence of the density of the precipitate Mg(OHI2 on the time of sedimentation ( t ) . Figure 1 presents the dependence of the height of the precipitate (2) upon time ( t ) in measuring the rate of sedimentation when there is complete precipitation with dolomite lime with or without various additions of the flocculant Flocculant B. The following quantities of Flocculant B were added: 2.0, 2.5, 5.0, and 10.0 mL of Flocculant B/L of sea water; 1 mL of solution contains 7.14 X g of Flocculant B. It is clear that a large addition of Flocculant B/L (10 mL, i.e., 7.14 X g of Flocculant B/L) causes a higher rate of sedimentation, while the addition of 2.0,2.5, and 5.0 mL of Flocculant B/L of sea water shows similar curves of sedimentation rate. Without the addition of the flocculant (a) the rate of sedimentation is lower. Figure 2 presents the dependence of the height of the precipitate (2)on the time of sedimentation ( t )for complete precipitation with dolomite lime, without the addition of the flocculant or with the addition of 2.8 mL of slag solution from Fe-Cr. One milliliter of solution contains 8.3 X loT3g of slag. Tests are presented which were performed also with lime obtained from the lime kiln. The results of the study clearly show that by using slag from Fe-Cr no significant results were achieved in increasing the rate of sedimentation of magnesium hydroxide. Tests were also made using different quantities of slag, and they varied with the degree of “aging” of the slag.
I
I
I
I
0
LO
83
‘20
I
1
16C
202
I
2LO
t (mini
Figure 2. The dependence of the height of the precipitate (2) on the time of sedimentation ( t ) in cases of complete precipitation, with or without the addition of slag solution: 1, dolomite lime; 2, lime; a, 2.8 mL of slag solution; b, without slag solution. Table 11. The Dependence of the Rate of Sedimentation (in m m ) on the Degree of the Completeness of Precipitation time, min
0 5 10 15 20 25 30 35 40 45 50 55 60
degree of completeness of precipitation 50%
70%
75%
90%
171
171
16 14 13 12 11 11
65 42 35 32 30 29 27 26
171 65 47 41 37 35 32.5 31
171 87 61 51 47 44
29
41 40
100% 171 131 101 a3 71 64 59 55 51 50 49 48 47
However, the results were no more positive than those presented in Figure 2. In other tests we studied the rate of sedimentation when there is incomplete precipitation, i.e., when the quantity added is lower than the stoichiometrically required quantity of the precipitating agent. Table I1 presents the results of the study of the sedimentation rate without the addition of a flocculant for different degrees of completeness of precipitation, 5070, 7070,75%, 90%, and loo%, i.e., complete precipitation. Figure 3 presents the dependence of the density of the obtained precipitate of Mg(OH)*on time ( t )with the above quoted degrees of completeness of precipitation. The density of the precipitate was calculated from the measured values of the height of the precipitate (Z), the
Ind. Eng. Chem. Process Des. Dev., Vol. 19, No. 3, 1980 331
-I rn
With3ut flocculnn! a 50%stoich b ?3%-t~?5*1~-,~d 90%-!#-
60-
N
0
Gig -
e
3.0rnl F l o c c u l n n t - E l l i t
85% stoich b 90%-nc 95% -Id 100% -8,-
G
.
l00%-~~-
.? 40 I
Fa
30
C
I
b d a
01
= a 20
20
10 10
0
20
10
40
30
50
1
I
0
10
I
20
30
I
I
Lo
93
60 t (min)
Figure 3. The dependence of the density of Mg(OH)zon the time of sedimentation ( t ) without the addition of Flocculant B, with the following percentages (iatoichiometry) of completeness of precipitation: a, 50; b, 70%; c, 75%; d, 90%; e, 100%.
I
60 !( m i n )
Figure 5. The dependence of the density of Mg(OH)2on the time of sedimentation ( t ) ,with the addition of 3.0 mL of Flocculant B/L, with the following precentages (stoichiometry) of completeness of precipitation: a, 85%; b, 90%; c, 95%; d, 100%.
5 4 3 5 m l Flocculan!-Blllt a 85V0 stoich b 9 0 % -I,c 95% d ?oo~lo-#~-
-.-
b
LO
a
30
C
e d
20
10
I 0
M
10
M
50
10
60 t (rninl
10
20
30
LO
50 t (mlr)
50
Figure 4. The dependence of the density of Mg(OH)zon the time of sedimentation ( t ) ,with the addition of 3.5 mL of Flocculant B, with the following percentages (stoichiometry) of completeness of precipitation: a, 85%; b, 90%; c, 95%; d, 100%.
quantity of the precipitate of Mg(OH)2,and the dimensions of the cylinder in which the sedimentation occurs. It is seen from Tab1.e I1 and Figure 3 that when there is incomplete precipitation the rate of sedimentation is higher and the density of the precipitate of Mg(OH), is also higher; as the degr'ee of completeness of precipitation decreases, the rate of' sedimentation and the density of the precipitate increase. The above tests on the incompleteness of precipitation, as well as the tests presented in Figure 1,have led us to study the optimal addition of the flocculating agent Flocculant B, taking into consideration the degree of incompleteness of precipitation. Figures 4, 5, 6, and 7 present the density of the precipitate Mg(OH)2with the addition of 3.5, 3.0, 2.5, and 2.0 mL of Flocculant B a t various degrees of incompleteness of precipitation. By means of these tests we have been able to establish the optimal degree of iincomplete precipitation for a given addition of Flocculant B/L, i.e., that degree of incomplete precipitation at which the highest densities of the precipitate Mg(OH), are obtained. The results are presented
Figure 6. The dependence of the density of Mg(OH), on the time of sedimentation ( t ) ,with the addition of 2.5 mL of Flocculant B/L, with the following percentages (stoichiometry) of completeness of precipitation: a, 80%; b, 85%; c, 90%; d, 95%. 20mI Flocculant- B l l i t
0
I
a
70% s!o!ch
b
75%
c d e
80%
- .-
-I
85%-~~90%-,f-
I
I
I
I
I
332 Ind. Eng. Chem. Process Des. Dev., Vol. 19, No. 3, 1980 Table 111. The Dependence of the Optimal Degree of t h e Incomplete Precipitation for a Given Concentration of Flocculant B
F
a 2,5ml Flocculant- B l l i t b 2,Omi - -
50,
I
degree of completeness of precipitation, %
Flocculant B, mL/L
100
3.5 3.0 2.5 2.0 1.0 0.5
95 85 80 70 60
lot
I
a 3 5 m l Flocculont-Blllt b 30ml - , -
0
1
1
m
70
m
90
%stoich
Figure 9. The dependence of AZ on the percentage of the completeness of precipitation: a, 2.5 mL of Flocculant B/L; b, 2.0 mL of Flocculant B/L.
'Dm! Floccuionr- 3 5 05r: - -
0
2a: 10
!It
I
E
0
I
I
I
70
80
90
IC0
a
'la stoeh
Figure 8. The dependence of A 2 on the percentage of the completeness of precipitation: a, 3.5 mL of Flocculant B/L; b, 3.0 mL of Flocculant B/L.
in Table 111. Furthermore, the results of the study of the rate of sedimentation at different degrees of incomplete precipitation have made it possible for us to establish the , maximal rate of sedimentation for each addition of Flocculant B/L of sea water. Our investigation proceeded along the following lines. Considering that the initial concentrations of Mg(OH), vary for different degrees of incompleteness of precipitation, we made the concentration levels in the observed tests equal and observed the rate of sedimentation at given time intervals. As the basis for comparison, we took 100% precipitation with the parameters Zo, to, co, where Zo = initial height of the precipitate, to = initial time, and co = initial concentration. As the starting values of the parameters Z and t for incomplete precipitation, we took those at which c obtains the value of co, i.e., those obtained at equal concentrations. In this way we eliminated the effect of the different initial concentrations at different degrees of incomplete precipitation and only observed the effect of the degree of the incompleteness of precipitation on the rate of sedimentation for a given addition of Flocculant B/L. To arrive at equal concentrations, the following expression was used
zo -_
co -
2,
c1
where Z = height of precipitate and c = concentration. The tests were performed in cylinders of equal diameter. Starting from the above values of 2, i.e., those for which the concentrations at different degrees of incomplete precipitation were equalized, we determined AZ, i.e., the change in the height of the precipitate at time intervals of 20 min. Figures 8,9, and 10 present the recorded values of AZ. The figures show at which degrees of incomplete precipitation A 2 is the highest, i.e., at which the rate of sedimentation is the highest for a given addition of Floc-
0
50
50
70
80 '0
s'oich
Figure 10. The dependence of A 2 on the percentage of the completeness of precipitation: a, 1.0 mL of Flocculant B/L; b, 0.5 mL of Flocculant B/L.
culant B/L. It was thus possible, by measuring the rate of sedimentation in the test, to establish the optimal degree of incompleteness of precipitation for a given addition of Flocculant B/L or vice versa, the optimal additional of Flocculant B/L for a given degree of incomplete precipitation. Thus, by a simple procedure, we were, in fact, able to determine the isoelectric point for certain tests. Furthermore, the above figures clearly indicate that at the highest rates of sedimentation, Le., the highest AZ, for given additions of Flocculant B, the greatest densities of the Mg(OH)*precipitate are obtained (as shown in Figures 4, 5, 6, and 7). The above tests were carried out with dolomite lime. In using lime obtained from the lime kiln or lime from the acetylene generator, the highest rate of sedimentation for a given addition of Flocculant B/L of sea water, is obtained at the same degree of incompleteness of precipitation as for dolomite lime, which is additional evidence that the rate of sedimentation primarily depends on the degree of completeness of precipitation and not on Concentration. Figure 11 shows that, with the addition of 3.5 mL of Flocculant B / L the maximum is also a t 100% precipitation, as was to be expected. Furthermore, we studied the effect of the time of stirring after the addition of the flocculant. As seen in Figure 12, a shorter stirring time is more effective. Figure 13 shows the dependence of the concentration of the magnesium hydroxide suspension on temperature.
Ind. Eng. Chem. Process Des. Dev., Vol. 19, No. 3, 1980 3 5 Flocculant- B / l i t a dolomite lime b lime
- - =/
I
30
-
2 m l Flocculant
80'1. stolch.
- BI
333
lit
a
2C'C b 3SoC c 50°C
20-
10 -
I 0
I
a
90
Im % stoich
Figure 11. The dependence of A2 on the percentage of the completeness of precipitation, with the addition of 3.5 mL of Flocculant B/L: a, dolomite lime!; b, lime.
t
k30%stoich
35 ml Floculont-Bllit
stirring time a ? min b Smin c 15min
10
0
3
20
LO
50
w t (mini
Figure 13. The dependence of the density of Mg(OH)2on the time of sedimentation ( t )under various temperatures, at 80% precipitation and with an optimal addition of Flocculant B/L: a, 20 O C ; b, 35 O C ; c, 60 O C .
I
0
m
a
M t
(mm)
Figure 12. The dependence of the height of the precipitate (2)on the time of sedimentation ( t )when there is complete precipitation and an optimal addition of Flocculant B/L with different lengths of stirring time: a, 1 min; b, 5 min; c, 15 min.
Experiments were carried out at 80% precipitation with an addition of 2 mL, of Flocculant B/L i.e., under optimal conditions. It is clear that higher concentrations are obtained at higher temperatures. At 35 "C, the concentration of magnesium hydroxide is higher than a t 20 "C. At 60 " C there is a clear difference; Le., within 10 min a concentration of over !30 g/L is obtained. We carried out further tests in order to determine the effect of the initial concentration of magnesium hydroxide on the rate of sedimentation and on the concentration of the obtained suspension of magnesium hydroxide, and the effect of the degree of incompleteness of precipitation. Test a in Figure 14 was carried out at 80% precipitation and with the appropriate addition of Flocculant B/L, while test b was performled in such a way as to give the same quantity of magnesium hydroxide precipitate as test a; i.e., the initial concentration in both tests was the same. In test b, however, the precipitation was 10070, i.e., stoichiometric. In test b, sea water and distilled water were mixed in a 4:l ratio, so that the precipitation of magnesium in this case was 100% and the resulting quantity of pre-
20
l L o c
M
LO
60 t imin)
Figure 14. The dependence of the height of the precipitate (2)on the time of sedimentation ( t )when there is complete (b) and incomplete (a) precipitation.
cipitate was the same as in test a, where the precipitation was 80 % . There is a clear difference in the rate of sedimentation between tests a and b, and we can therefore conclude that the rate of sedimentation is considerably affected by the degree of completeness of precipitation. Furthermore, we studied the purity (ingredient content) of magnesium hydroxide obtained from sea water and dolomite, with particular reference to calcium salts.
334
Ind. Eng. Chem. Process Des. Dev., Vol. 19, No. 3, 1980
Table IV. Values of the Thickener for Different Degrees of Incomplete Precipitation and with Optimal Addition of the Flocculant B Flocculant B,
%
part 1
2
3
stoichiom. 80 85 95 100 80 85 ’95 100 80 85 95 100
CO * kg/m3 5.12 5.44 6.08 6.40 5.12 5.44 6.08 6.40 5.1 2 5.44 6.08 6.40
L/m’ 2.0 2.5 3.0 3.5 2.0 2.5 3.0 3.5 2.0 2.5 3.0 3.5
ell,
kg/m3 42.55 35.83 32.64 29.78 29.78 29.78 29.78 29.78 29.78 29.78 29.7 8 29.78
If, at 100% precipitation, we wash the precipitate with water of a hardness of 12.50-13.75 “E, the magnesium oxide obtained contains 0.90% CaO, while if we wash it with demineralized water, the precipitate then contains 0.61% CaO. At 95% precipitation magnesium oxide contains 0.46% CaO, while at 80% precipitation only 0.35% CaO, washed with demineralized water. Discussion In order to interpret our experimental results, which are presented in the tables and diagrams, we calculated the values of the thickener according to Kynch (Badger and Banchero, 1955; Kynch, 1952), using the following expressions LL -- x CL -- VL S 1 1 CL cu
CL =
co x zo
zi
~
zi
x
ZL
VL = tL
Zi is the intercept on the ordinate made by the tangent on the sedimentation rate curve within a given time t. The surface S was determined at the minimal value of the capacity (LL X CL)/S. Co is the concentration of the incoming suspension of magnesium hydroxide; C, is the concentration of the outgoing suspension of magnesium hydroxide; Lo is the volume of the incoming suspension; L, is the volume of the outgoing suspension; S is the surface of the thickener; and d is the diameter of the thickener. The values of the thickener were calculated for the specific conditions, i.e., for the different degrees of incomplete precipitation and with the optimal addition of the flocculant. Part 1 in Table IV shows that at a constant flow Lo = 3.60 m3/h, the final concentration of the suspension C,, after 60 min is considerably higher when the degree of completeness of precipitation is low. In part 2 of Table IV, taking the constant final concentration C, and a constant quantity of the obtained suspension, calculations were made to determine the range of the Lo flow as well as the dimensions of the thickener, its diameter, and surface. It is seen that when the degree of completeness of precipitation is lower, the flow increases, while the dimensions of the thickener are significantly reduced. Thus, at 80% precipitation the surface is reduced by 86.5% in relation to 100% precipitation. In part 3 of Table IV, taking the constant concentration C, and constant dimensions of the thickener, calculations
LO, m’B 3.60 3.60 3.60 3.60 4.50 4.23 3.79 3.60 8.40 5.84 4.15 3.60
Lo x c,,
(Lo x CO)/S,
kg/h
kg/mz h
s,mz
d, m
18.43 19.58 21.88 23.04 23.04 23.04 23.04 23.04 42.98 31.79 25.24 23.04
1.24 1.46 1.38 1.89 3.52 2.61 2.07 1.89 3.53 2.61 2.07 1.89
14.88 13.43 15.85 12.18 6.53 8.83 11.12 12.18 12.18 12.18 12.18 12.18
4.36 4.14 4.49 3.94 2.88 3.35 3.76 3.94 3.94 3.94 3.94 3.94
were made to determine the range of Lo and the quantity of the precipitate obtained. It is seen that the quantity of the magnesium hydroxide obtained is substantially increased at lower degrees of completeness of precipitation. The figure obtained at 100% precipitation is 23.04 kg/h, while that obtained at 80% precipitation is 42.98 kg/h, which represents a considerable increase in the thickener’s productive capacity. Furthermore, when there is incomplete precipitation the obtained product contains a considerably smaller quantity of calcium salts. The difference in CaO contents for complete and incomplete precipitation can be explained by the law of adsorption, as set out by Paneth, Fajans, and Hahn. According to this law the ions are efficiently adsorbed on ionic lattices if the ion forms a slightly soluble compound with the oppositely charged lattice ion (Kolthoff and Sandell, 1945). It derives from the above that magnesium ions will be adsorbed on magnesium hydroxide in preference to calcium ions, since magnesium hydroxide is less soluble than calcium hydroxide. Since magnesium ions are left behind in the solution when there is incomplete precipitation, these ions will be adsorbed on magnesium hydroxide, and thus magnesium hydroxide obtained through incomplete precipitation contains a considerably smaller quantity of calcium salts. The model of the particle would appear as follows. Stabilizing ions are calcium ions when precipitation is complete, magnesium ions when precipitation is incomplete, while counterions are OH ions. Flocculant B, as an anionic electrolyte, has distinctly flocculating characteristics. In our further analysis the following observations were made. Kynch’s theory (Kynch, 1952) provides for the possibility of the impact of electrochemical effects in a suspension, and this helps to explain our experimental results. Namely, the different concentration of ions in sea water and in the mixture of sea water and distilled water, i.e., for complete and incomplete precipitation, especially the different quantities of Mg ions, probably affect the behavior of the system in the process of sedimentation. Our experimental work clearly indicates that there is a difference in the rate of sedimentation between magnesium hydroxide obtained from sea water and that obtained from a mixture of sea water and distilled water. According to Stokes’ law, one would expect in a mixture of sea water and distilled water that the particles would fall more quickly, since 1
u=-x K
d2(Y’- 7) ‘ I r
d is the linear dimension of the particle, y’is the specific
Ind. Eng. Chem. Process Des. Dev., Vol. 19, No. 3, 1980 335
. o
Table V
CfllCJlCted results
Experlrrentol
- -
40-
20 -
~
0
~
0,s
1
15
25
2 TI
3
35
Flocculont-all
Figure 15. The dependence of the percentage of the completeness of precipitation on mL of Flocculant B/L: 0,calculated results; 0 , experimental results.
gravity of the particle, y is the specific gravity of the medium, p is the viscosity of the medium, and K is a constant. However, our experimental results indicate the contrary; Le., the sedimentation is clearly more rapid in sea water at 80% degree of completeness of precipitation in a mixture of sea water and distilled water having the same initial concentration of Mg(OH), at 100% precipitation. This kind of behavior of the system is probably due to the fact that when there is incomplete precipitation the stabilizing ions are mostly Mg ions and not Ca ions, and therefore changes in the density and size of the magnesium hydroxide particles may occur, which of course considerably affects the ratle of sedimentation because according to Stokes' Law the irate changes with the square diameter of the particle. Drawing from experimental data, Figure 15 presents the dependence of the added quantity of Flocculant B on the degree of completeness of precipitation under optimal conditions. The above-mentioned dependence is linear. For this dependence the following mathematical expression has been determined by means of the least square method and graphically: y = 12.88~+ 54.86, where y = % of the completeness of precipitation and x = mL of Flocculant B/L. The experimental results and the results from the mathematical dependence are in agreement. The required consumption of Flocculant B at various degrees of completeness of precipitation, expressed in terms of percentage (g of Flocculant B X 1OO/g of Mg(OH),), is given in Table V. A lower consumption of Flocculant B/g of Mg(OH)2is to be noted when there is incomplete precipitation. When precipitation is 8026, the consumption of the flocculant is 28.65% lower than the consumption of the flocculant when there is complete precipitation.
Conclusions By using slag from highly carbonic Fe-Cr as a flocculant we did not achieve satisfactory results in increasing the rate of sedimentation of magnesium hydroxide from sea FeSO,, etc.) does not water. This flocculant (A12(S04)3,
% of completeness
% of Flocculant
of precipitation
B/g of Mg( OH),
100 95 85 80 70 60
0.356 0.321 0.299 0.254 0.145 0.085
have distinct flocculating properties required for this purpose. Flocculant B has flocculating properties, and a significant increase in the rate of sedimentation can be achieved. With the application of incomplete precipitation in obtaining Mg(OH), from sea water, the sedimentation of the precipitate is considerably increased. The capacity of the thickener, calculated according to Kynch's theory, is increased by 86.590 at 80% precipitation, in relation to complete precipitation. The content of calcium salts in the product is considerably reduced when there is incomplete precipitation, and this can be explained by the adsorption law, as set out by Paneth, Fajans, and Hahn. We determined the mathematical expression of the dependence of the required quantity of the flocculant Flocculant B on the degree of completeness of precipitation under optimal conditions of sedimentation. When there is incomplete precipitation the required consumption of Flocculant B per unit of weight of the product Mg(OH), is lower in relation to complete precipitation. At 80% precipitation the consumption of the flocculant is 28.65% lower in relation to complete precipitation. Literature Cited Anderson, L. G. Mar. Techno/.,,SOC.J., 9, 17 (1975). Badger, W. L., Banchero, J. T., Introduction to Chemical Engineering", p 653, McGraw-Hill, New York, 1955. Braniski, Ai., FrucMer, S., Kathrein, A,, "Studii si cercetari de metalurgije, Acad. R.P.R.", 1960. Braniski, Ai., Kathrein, A., Ionescu, C. St., Fruchter, S., "Studii si cercetari de metalurgie, Acad. R.P.R.", 1961. Bunina, V. P., Dolgina, G. Z.,Ivanov, E. V., Ogneupory, UDK 666.762.64 (1974). Ford, W. F., Hayhurst, A., White, J., Trans. 6rif.Ceram. Soc.,80, 581 (1961). Foust, A. S.,Wenzel, L. A., Clump, C. W., Maus, L., Andersen, L. B., Principles of Unit Operation", p 465, Wiley, New York, 1960. Gaskell, T. F., Chem. Ind., 1149 (Oct 1971). Gilpin, W. C., Heasman, N., Refract. J.. 302 (July 1952). Giipin, W. C.. Ceram, F. J., Heasman, N., Refract. J., 214 (June 1963). Giipin, W. C., Ceram, F. I.,Refract. J., 68 (Mar 1969). Giipin, W. C., Spencer, D. R. F., Refract. J., 60 (Mar 1970). Gilpin, W. C., Heasman, N., Chem. I d . , 567 (July 1977). Ionescu, T., Branisi, A., The Patent Office, London, Patent specification 904891 (Jan 11, 1960). Ivanov, E. V., Doigina, G. Z.,Bunina, V. D., Ogneupory, No. 12, 4 (1973). Koithoff, I.M., Sandeii, E. B. "Textbook of Quantitative Inorganic Analysis", p 106, Macmillan, New York, 1945. Kriek, H. J. S.,Ford, W. F., White, J., Trans. 6 r . Ceram. SOC.,1 (Jan 1959). Kynch, G. J., Trans. Faraday SOC.,48, 166 (1952). Mascolo, G., Trans. Br. Ceram. Soc., 72, 251 (1973). Mutiuer, T., Timucin, M., J . Am. Ceram. Soc.. 58, 196 (1975). Nelson, J. W., Cutler, I.B., J . Am. Ceram. SOC.,41, 406 (1958). Pritish Chandra Sen, Ramakrishna Rao, M., Bhaskar Rao, H. V., Indian Ceram. Soc.. A5543d (Apr 1962). Shultz, R. L., J . Am. Ceram. SOC.,56, No. 1 (1973). Spencer, D. R. F., Coleman, D. S.,Mineral. Mag., 37, 839 (1970). Woodword, T., U S . Patent 2571 983 (Oct 16, 1951). Treffner, W. S.,J . Am. Ceram. Soc., 47, 401 (1964).
Received f o r reuiew December 29, 1976 Resubmitted April 13, 1978 Accepted February 26, 1980
