ACTIVATED ALUMINA FOR REMOVING FLUORIDES FROM
DRINKING WATER FIGURE 1
G. J. FINK AND F. K. LINDSAY National Aluminate Corporation,Chicago, Ill.
vv
ITH the rapidly increasing numbers of communities reporting fluorine-bearing waters, the occurrence of fluorine toxicosis has taken on added significance and is now generally recognized as a serious public health problem. Many localities find it impossible to obtain satisfactory water supplies free from fluorine, and consequently the demand for a practicable method for removal of fluorine is urgent. Inasmuch as only a small percentage of the total municipal supply or eyen of that used by a single family is consumed for drinking and cooking purposes, a method for treating only this limited quantity would be satisfactory and in most instances probably preferable to treatment of the entire supply. Boruff (1) has reported results of fluoride-removal tests with an acti7-ated alumina which, although showing rather limited capacity, indicated the possibilities of this material. This paper is a report of tests with specially prepared activated alumina' supplied by the Aluminum Company of .4merica. I n all the studies involving preliminary tests of the effectiveness of rarious activated aluniinas on different types of waterq,
0
1
Patent applied for.
Results of tests demonstrating the effectiveness of a specially prepared activated alumina for removal of fluorides are given, and a small, handy, and economical unit for the use of this material in the home to treat drinking supplies is described. Two hundred and fifty gallons of water containing 5 p. p. m . of fluoride may be passed through this unit at a maximum rate of approximately 0.4 gallon per minute before the fluoride content of the effluent exceeds 1 p. p. m . The bed would then preferably be discarded, although it may be regenerated satisfactorily.
the fluoride-bearing waters were passed through a column of alumina 0.75 inch (1.9 cm.) in diameter and 12 inches (30.5 cm.) deep a t a rate of 20 cc. per minute. The weight of the contact material in each case was 1,'e pound (75.6 grams). After each 900 cc. of water passed through the test material, the fluoride content of the effluent mas determined and the test continued until the effluent showed a fluoride content approaching 0.5 p. p. m.
AFTER a comparison of several methods for determinaQ tion of fluoride, including a large number of tests on both synthetic and natural waters, the procedure described by Sanchis ( 3 ) was found convenient and satisfactory, and was adopted as the control method. -4comparison of results with this and with the method of Boruff and Abbott (2) on different waters is included in Table I. I n general, the latter method gave slightly lower results. I n preliminary tests to determine the comparative effects of different activated aluminas, use was made of natural waters from different sources and containing varying amounts of hardness and other salts, to each of which was added 5 p. p. ni. of fluoride as sodium fluoride. Further tests included the use of similar waters to which calcium fluoride, sodium silicofluoride, and barium silicofluoride had been added. T h e n the alumina with the highest capacity had been selected, natural fluoride-bearing waters with widely varying fluoride and other salt content were included. Results of typical tests are listed in Table I. I n tests 1,2, and 3,4.9 gallons of water had been passed through the alumina filter before the fluoride content of the effluent reached the figures indicated. The capacity of the alumina in test 4 was not exhausted. Sufficient quantities of the natural waters (tests 5 to 9) hare not been available to run the filters to exhaustion, but all the data indicate that the material is as effective on fluoride-bearing natural waters as on those to which sodium fluoride is added. I n no case was a zero test for fluorine obtained in the treated water; there was always a trace detectable even in the early effluents. In an effort to adapt this process to a unit which could be used in the household for treating the required quantities of water, various types of equipment TI ere tested with the result that a container which is being marketed as a household zeolite softener was selected as most convenient and 94 i
INDUSTRIAL A S D ENGISEEKIXG CHEhlISTRY
918
VOL. 78, NO. 8
I -
I
TABLEI. EFFECTOF TREATMENT Test
No. 1 2 3
4
5 8
7 8 9
Source of Sample Chicago t a p Chicago t a p Chicago t a p Chkago tap . h z . No. 1 .\riz. No. 2 Colo. N. Dak. W.Va.
++ NNaiPiFa aF + BaSiFs + Cap2
hnalysis of Influent Sanchis Boruff blgmethod method Cs(HCOI)! (HC0a)z CaSOi NaHC03 hfgS04 NaCl XarSOd F P P . p . m . P . p . m . P.p.m. P . p . m . P . P . ~ . P . P . ~P., p . m . P . D . m . P . p . m . 138 35 ,. 16 i 19 5.0 4.8 138 35 , 16 19 5.0 ... 138 35 ... 16 I 19 6 0 ... 135 35 , , .. 16 19 3 0 .. 14 .., 6 44; 242 !.0 5'9 .. 10 ... 6 754 1.5'2 ,0 16 ,. ... 6 .i 10 3 0 i.5 li .. . 873 . 149 171 4.0 3.7 124 5 ,. ilS . 2992 17 0.6 0.7
... ...
. .. .
;;
.
..
satisfactory (Figure 1). I t is built of vitreous enameled sheet metal, 12 inches deep and 8 inches in diameter, with an outlet near the bottom. For fluoride removal it is charged with a bed of activated alumina 6 inches deep retained between monel metal screens, the average charge weighing 9.75 pounds. The water is introduced a t the top and flows by gravity through the filter bed. Two hundred and fifty gallons of water containing 5 p. p. in. of fluoride may be passed through the unit a t a maximum rate of 0.4 gallon per minute before the fluoride content of the efluent reaches 1 p. p. m., a figure which seems to be considered generally as the maximum safe limit, Repeated tests have shown that, under conditions of normal operation, the bed does not act as an accumulator of organic growths, but on the contrary the bacterial count is materially decreased by the alumina treatment.
--.
7 -
PH
PH
8.0 8.0 8.0
i .5
8.0
7.5 I
1 . 5
8.1 z.7 8.7
1.6
8.1
...
...
t 6 7.6
...
Effluent-Sanchis Boruff method method F F P . p . m. P . p . m. 0.4 0.3 0.3 , 0.3 ... 0.3 .,, 0.5 0 3 0.5 0.5 0:4 0.6 0.5 0.3 0.3
maintained approximately constant is of particular interest and offers the possibility of obtaining higher efficiencies by acidifying the water t o be treated without attending difficulties. Boruff ( 1 ) reported the effects of linie treatment on fluoride removal on one water, and others have claimed that the presence of magnesium makes possible the removal of fluoride by softening. This latter question was investigated by comparing the effects of softening on various types of waters. Typical results are included in Table 111. Although in most cases an increased quantity of magnesium improved the fluoride remoral, there seems to be no rational relation between either calcium or magnesium content and fluoride reduction, and in no case were the results as satisfactory as those obtained by treatment with activated alumina.
*
STUDY of the problem of regeneration is be0 ing continued, but to date the application of regenerative treatments to the small household
TABLE 111. FLUORIDE REMOVAL BY SOFTENISG Fluoride u z t s does not appear feasible. Sodium chloride F Content exhibits practically no regenerating effect, and Test Source of Ca(H- >Ig(€€- Ca1IgNtt?. SofReSo. Sample COa): C o l i ? SO, SO, XaCl SO, Raw tened moved solutions acidified with hydrochloric acid and P . p . in. P . p . m. P.p . in. P . p . m. P . P . m. P . p . m. P.P. m. P . P. m. % hydrochloric acid solution (1 per cent) alone re1 Calif. + T a F 6!? .. .. 271 18.7 217 5 0 1.5 70 store only 90 per cent of the original capacity. JS ,. 14 6 448 242 8.0 8.0 ?;one 2 Iriz. S o . 1 3 I r i z . No. 1 + Complete regeneration is accomplished with an 1\IgSO,r 55 .. 14 31 448 242 8.0 5.0 38 6 Synthetic Ca 8 per cent solution of sodium hydroxide and with water li; .. 2.3 , .. .. . 44 5,0 3.5 30 an alkaline solution of sodium aluminate con5 T a p water SaF 13s :2.5 ,. 16 i 19 5 0 4.0 20 taining a total alkalinity equivalent to 8 per 6 T a p water + Ca hardnesi T cent sodium hydroxide. Incomplete investiga.,.,; .. 09 YaF -5:: 7 19 5 0 4.5 10 tions of the possible application of activated alui T a p water f MgSOd + XaF 138 35 ,, 193 7 19 5.0 2.2 56 mina in larger units, including central treating plants, indicate that such installations combined with regeneration may be feasible but no recomLiterature Cited mendations can be made until further results are available. I n the use of the household unit, although regenera(1) c. s.,lSD. c ~ 26, ~ 69-71 ~ ~(1934). , , (2) Boruff, C . S.,and Abbott, G. E., IND. EX. C H E M . , Anal. Ed., tion might be possible, the preferable procedure would be to 5, 236-8 (1933). replace the alumina after a definite period of use calculated (3) Sanchis, J. l f .Ibid., , 6 , 134-5 (1934). from the amount of water used and its average fluoride content. RECEIYED M a y 13, 1936. Presented before t h e Divisiori of Water. Sewage,
-
and Sanitation Chemistry a t the 91st Meeting of t h e American Chemical Society, Kansas City, Mo., d p r i l 13 t o 17, 1936. OF PH ON FLUORIDE REMov.LL TABLE 11. EFFECT
BY
ACTIYATED
-4LGXIS.t
+
1 T a p water 3-aF 2 Tapwater+NaF+NaOH 3 Tapwater+XaF+H?SOd
8 0 8.5 6.5
7.5
7.5 7.3
18.000 1i,l00 86,900
1011 95
205
The efficiency and capacity of the alumilia for fluoride removal is dependent upon the hydrogen-ion concentration of the water treated as shown by the typical data given in Table 11. Addition of alkalinity to the maters tested decreased the capacities. The fact that the pH of the effluent is almost immediately brought to a point near 7 . 5 and is
