Comparative study for the defluoridation of water by Coagulation

El-Oued is known for some diseases caused by fluoride concentration in drinkable water. To reduce it, we have chosen a sample with the highest content of fluoride among many sources in order to coagulate it with Al 2 (SO 4 ) 3 ·18H 2 O, Fe 2 (SO 4 ) 3 ·H 2 O and FeSO 4 . In order to get better reduction yield of fluoride, a study has been done on the influencing parameters (concentration, pH, temperature) to choose the best conditions. The remove of fluoride is favorable at low concentration of Al 2 (SO 4 ) 3 , at room temperature and normal acidity.


INTRODUCTION
The concentration of fluoride in groundwater depends on the geological characteristics, and chemical properties of rocks and climate of the region. Fluoride content in the groundwater of northern Algerian desert often exceeds the world Health Organization standards, which indicated that the consumption of high fluoride water for long periods causes health complications from discolored teeth to fluoride poisoning bone. When concentration between (0.5-1.5 mg / l), it gives good protection against tooth decay, and if it exceeds 1.5 mg / l, defect occurs in teeth enamel but at a concentration between 4 and 8 mg / l, it leads to the risk of fluorosis skeletal [1].
The water of El Oued is characterized by high concentrations of fluoride, associated with severely high and excessive total mineralization. This water is the only source of drinking. The hot and dry climate has forced people to consume a lot of water which leads to raise the daily consumption rate of fluoride, in addition the large consumption of dates and tea leads to the spread of fluorosis disease which is characterized by the yellowish of tooth enamel according to the classification of the national program of school health [2,3]. To prevent these diseases from happening or reduce them , many defluoridation techniques are used such as: membrane technologies, precipitation and adsorption. A comparative study of coagulation has been done with different sulfate salts of (Aluminum, iron (II) and iron (III) ) then determination of optimal conditions of factors affecting the reduction of fluoride in drinking water.

1. Preparation of curve witness fluoride
To determine the concentration of fluoride in Various samples, a potentiometer method was used (Rodier2005) [4]. Different standard concentration solutions were prepared from NaF salt in cups of plastic. Then their potential are measured by using specific fluoride pole (ISE15381/1) and a pH-meter model (pH211), using a solution of TISAB (9) . The graph E = f (log C F ) is presented in Figure 1.

Determination of fluoride concentration in some samples of the study area
The concentration of fluoride has been determined in some water sources of the study area in order to determine and treat the largest content of fluoride. The results are presented in Table 1. The selected sample (cold water of Shuhada) has a concentration of fluoride 2.61 mg / l.

Table1.
Fluoride concentration for some water in the study areas at T = 19.3 °C.

3. Determination of the predominant concentration of ions in the studied water
The study was done according to (Rodier2005) [4] on cold water of Shuhada as follows:

3. Total hardness
By complexity with EDTA (1) in the presence of Eriochrome BlackT at buffer solution of pH = 10.

3. 6. Calcium concentration
By complexity with EDTA (1) in the presence of murexide at a solution of pH = 12.

3. 7. Magnesium concentration
Calculated from the difference Total hardness and Calcium concentration. The results are presented in Table 2.

4. 1. Effect of cathion concentration
Based on the adsorption of F ˉ on both Al(OH) 3 and Fe(OH) 3 according to equilibriums (1), (2) , (3) and (4) [8-10]. 100 ml of Shuhada water was put in each cup of plastic then the pH and temperature T were measured, after that different amount of the same salt was added to each cup. After stirring for three minutes, they are left for a while then filtered, finally the amount of fluoride in the filtrate was measured.
The results were presented in Table 3.
International Letters of Chemistry, Physics and Astronomy Vol. 13 Table 3. Relation between the added cation and the residual fluoride.
We repeat the same steps of the previous experiment as mentioned in (2.4.1) by fixing the temperature and the added optimal concentration of each cation separately but changing the pH by buffer solutions. The results are presented in Table 4 and Figure 2.

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4. 3. Effect of temperature T
The same steps of the experiment are repeated as mentioned in (2.4.2) by fixing the concerned added salt and the optimal pH, but changing the temperature. The results were presented in Table 5 and Figure 3 [5].

RESULTS AND DISCUSSION
 According to the results of table 2 we observe that the high concentrations of (Ca 2+ , Mg 2+ , SO 4 2-, Clˉ) exceed the WHO (10) standards of water. This related to the geological characteristics and the structure of rocks .  According to the results of Table 3, defluoridation by the use of Al 2 (SO 4 ) 3 is the best. This can be explained by the adsorption of fluoride on the flocks of Al(OH) 3 (equilibrium 1

CONCLUSION
 According to this study on the water of some region of El-Oued, it appear that most of them Contain a high quantity of fluoride exceeds the standard value of (WHO) (10) with a high total hardness.  The present investigation indicates that reducing fluoride from water by using Al 2 (SO 4 ) 3 is economic and less harmful for health.  Through the study of factors affecting (concentration, pH, temperature) it is possible to choose the best conditions for a reduction process with Al 2 (SO 4 ) 3 by adding an amount at a concentration of 0.0024 g / l, pH = 8 and a temperature of 26.5 °C. methyl orange Ph.Ph (6) : phenolphthalein TA (7) : alkalimetric title. TAC (8) : The complete alkalimetric title. TISAB (9) : total ionic strength adjustment buffer WHO (10) : World Health Organization.