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Journal of Coastal Development ISSN: 1410-5217 Volume 5, Number 3, June 2002 : 111-116 Accredited: 69/Dikti/Kep/2000

Original paper

IMPROVING PUBLIC QUALITY BY CHEMICAL TREATMENT

Diyono Ihsan, Istadi and Mohamed Djaeni*)

Department of Chemical Engineering, Diponegoro University Jl. Prof. Sudharto, Tembalang, Semarang, Indonesia, 50239 Telp/Fax. (024) 7460058

Received: May 6, 2002 ; Accepted: May 27, 2002

ABSTRACT

The public salt produced by salt farmers in Juwana, Pat,i Central Java, Indonesia with the NaCl content of about 92.86% (dry base) is still below the standard quality of industrial salt (98.5% of dry base). Improving public salt quality has become an important topic of discussion. This research look into the influences of chemical compound, namely (NaOH), sodium carbonate 2+, 2+ 2- (Na2CO3) and (BaCl2) to reduce pollutant (Ca Mg and SO4 ) in order to increase the percentage of NaCl content in public salt. The purification process was carried out in three series mixer. In this investigation, 100 ml of public salt solution is gradually treated by adding those compounds, which were varied from 0.50 to 3.50 gram with the step size of 0.50 gram. The results showed that the purity of NaCl could be enhanced up to 99.6% that was achieved by adding 2.00 gram o f NaOH, 1.50 gram of Na2CO3 and 2.50 gram of BaCl2. This purity is suitable to meet community and industrial demands.

Key words: Chemical treatment; precipitation; public salt

*) Correspondence: Telp. 024-7460058, Fax. 024-7460058

INTRODUCTION level salt concentration; the salt becomes crystallized gradually (Shreve, 1977). Salt products have been consumed by The crystallization process is human beings as an important food started at the level of 7.1° Be in terms of additive and as the raw material for indus- precipitation of calcium carbonate trial application. Salt has been produced (CaCO3) while still having a low level of from seawater that is easily available in salt (Anonymous, 1996). Therefore, the the world. Indonesia is one of the salt salt compound precipitated is calcium producer countries where the salt is produ- sulphate in the form of fine gypsum ced by salt industries and salt farmers. (CaSO4.2H2O). The range of calcium Particularly, salt in Indonesia is produced sulphate precipitation is wider than the by solar evaporation of seawater in the salt other salt compound crystallization, fields. The seawater evaporation rate especially for , so that the depends mainly on air humidity, wind decrease of fine gypsum plays a role as a velocity and solar heat . The evaporation part of NaCl crystallization. Accordingly, of sea water in the salt field causes a high the separation of gypsum crystal is difficult concentration of seawater and at a certain to carry out if it is done only through

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Journal of Coastal Development ISSN: 1410-5217 Volume 5, Number 3, June 2002 : 111-116 Accredited: 69/Dikti/Kep/2000

washing, due mainly to its existence CaCl2 + Na2CO3 ç CaCO3 + 2NaCl within the NaCl and the CaSO4 + Na2CO3 ç CaCO3 + Na2SO4 low of the gypsum in the water. Na2SO4 + BaCl2 ç BaSO4 + 2NaCl The precipitation of compound cannot be avoided due to the On the basis of the above reaction similarity in range of the NaCl salt it could be concluded that the pollutted ion crystallization, 26.2º Be, in the form of will be reduced by precipitation. Hence, MgSO4 and MgCl2. Particularly in the NaCl content will be increased by Indonesia, the salt produced by salt formation in reaction. farmers and known as public salt is about 70% of all national production. The low quality of the public salt produced cannot sufficiently meet the grade requirement of ATERIALS AND ETHODS the table salt and industrial salt type. M M Consequently, a purifying process of public salt is needed in order to achieve the The material used in the experiment was table and industrial salt grade quality. This public salt from Juwana, Pati, Central Java purifying process is conducted by Indonesia with an NaCl content of 92.86% decreasing the polluter compound and (dry base), participating agent, and reagent increasing the NaCl content. The salt analysis. The precipitant substances used purifying process can be carried out by were sodium hydroxide, sodium carbonate chemical treatment and gradual and barium chloride, while the chemical precipitation based on filtration process. materials used for the analysis were EDTA In this experimental work, the solution (0.1 N), AgNO3 solution (0.2 N), chemical treatment was conducted by the hydroxylamine solution (5%) and EBT and addition of chemical substances to the Murexide indicators, respectively. public salt in order to increase the NaCl The public salt was dissolved in content and to decrease the polluter the water, stirred to achieve the saturation compound especially for magnesium and condition and filtrated from the polluter. calcium salt. Monod (1991) expressed that 100 ml of the solution was poured into a the gram equivalent of both Na+ and Cl- measuring glass as a sample of within seawater is not proportional . It solution. The settler solution was then can be shown in the Pacific seawater that added gradually to the sample. Afterwards, has a gram equivalent of Na+ and Cl- of sodium hydroxide was added to the brine 480 and 560 respectively. This solution at varying weights and carefully phenomenon will make it necessary to add stirred. The sediment formed was filtrated a chemical treatment such as Na+ donor in and measured for its weight, while the order to increase NaCl level. The chemical filtrate will be continued to the next added as a Na+ donor is sodium hydroxide process (Monod, 1991). The addition of and sodium carbonate. The barium sodium carbonate at various weights was chloride compound is added to the implemented to this filtrate and then was 2- carefully stirred. The sediment formed was solution in order to cover the SO4 ion excess and to give more Cl- ion that will filtrated, dried and then measured for its settle the sulphate salt to the form of weight, while the filtrate will be continued to the next process. The last settling was barium sulphate (BaSO4). The of this implemented by adding barium chloride at treatment can be written as follows: various weights, followed by stirring. The sediment precipitated was then filtrated ç MgCl2 + 2NaOH Mg(OH)2 + 2NaCl and measured, while the filtrate was ç MgSO4 + 2NaOH Mg(OH)2 + Na2SO4 analysed as a product. Schematically, the

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Journal of Coastal Development ISSN: 1410-5217 Volume 5, Number 3, June 2002 : 111-116 Accredited: 69/Dikti/Kep/2000 purification of public salt is presented in The increase of the NaCl content the following figure. of salt produced using chemical treatment was due to the precipitation of material

Water Public Salt NaOH Na2CO3 impurities such as Mg (OH)2, CaCO3 and

BaSO4 on salt solution that were formed by chemical reaction between Ca2+, Mg2+ and 2 SO4 with NaOH, Na2CO3 and BaCl2. The Mixing Mixer Mixer precipitation process could occur since the Tank 1 2 solubility of these compound are lower than NaCl. Comprehensively, the effect of chemical treatment by adding NaOH, Sediment Sediment Na2CO3 and BaCl2 are described in the following sections. BaCl 2 Mixer The Effect of NaOH Addition Filtrate 3 Filtrate 2+ Sediment This step is aimed to reduce Mg in public salt by adding NaOH ranging from 0.50 to Figure 1. Schematic Diagram of Public 3.00 grams with the step size of 0.50 gram. Salt Purification This compound reacted with magnesium ion (Mg2+) and calcium ion (Ca2+) to The chemical analysis has been produce magnesium hydroxide (Mg(OH)2) conducted to the common seawater by and Ca(OH)2. The solubility of these volumetric titration for of Cl-, SO42-, Ca2+, compounds in the amount of 3.4x10-11 and Mg2+ to investigate their salt- and 5.5x10-6 are lower than NaCl compound concentration. solubility. The reaction NaOH with Mg2+ and Ca2+ is ionic reaction, as expressed in the following reactions.

ç RESULTS AND DISCUSSIONS MgCl2 + 2NaOH Mg(OH)2 + 2NaCl MgSO + 2NaOH ç Mg(OH) + Na SO 4 2 2 4 ç The composition of public salt and salt CaCl2 + NaOH Ca(OH)2 + 2NaCl produced by chemical treatment can be Hence, the formation of Ca(OH) written in Table 1. The NaCl content of the 2 and Mg(OH)2 is stoichiometrically equal to salt produced as a result of the experiment the amount of NaOH addition. In this step, work increased from 92.86% to 99.57 %. only Ca(OH)2 precipitated from the solution because of its lowest solubility as Table 1. Composition of public salt and presented in Table 2. The result is also salt product from chemical illustrated in Figure 2 in order to treatment understand the trend of Mg(OH)2 precipitation by adding the amount of Public salt Chemical NaOH. Referring to those results, the Component (% w/w) treatment addition of more than 2.00 gram of NaOH (% w/w) could not increase the amount of NaCl 92.86 99.57 precipitated Mg(OH)2. The precipitated CaSO 2.87 0.28 4 Mg(OH)2 even tended to be constant, 2+ MgSO4 1.26 0.065 which indicated that the amount of Mg MgCl2 3.02 0.083 concentration in the solution was equal to the solubility of Mg(OH)2. Based on

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Journal of Coastal Development ISSN: 1410-5217 Volume 5, Number 3, June 2002 : 111-116 Accredited: 69/Dikti/Kep/2000

Figure 2, it could be also concluded that The CaCO3 with the solubility of -9 the response of Mg(OH)2 precipitation was 4.8x10 is lower than Ca(OH)2 solubility exponential with the change of NaOH so that CaCO3 was easily removed from addition that indicated the process the solution by precipitation. The result precipitation is first order process. showed that the CaCO3 commenced to Meanwhile, the Ca(OH)2 could not be precipitate at the addition of 0.5 gram perfectly precipitated since its solubility is Na2CO3 as seen in Table 3. The result was higher than Mg(OH)2. This compound will also plotted in graph as seen in Figure 3. be removed using Na2CO3 addition as Based on that figure, the response of described in the next section. precipitated CaCO3 is exponential with the change of Na2CO3 addition In this case, the Table 2. The Addition of NaOH and the amount of precipitated CaCO3 was amount of precipitated Mg(OH)2 maximally achieved at the addition of 1.5

gram of Na2CO3. It indicated the balance NaOH Amount of precipitated 2+ of Ca in the solution equals to CaCO3 addition (g) Mg(OH)2 (g) 0.50 0.30 concentration. Excessive addition (more than 1.5 gram) could not increase the 1.00 0.70 2+ 1.50 0.85 amount of precipitated CaCO3 since Ca in solution is stoichiometrically equal to 2.00 0.94 1.5 gram of Na CO . Meanwhile, another 2.50 0.94 2 3 anion. namely SO 2- , could not precipitate 3.00 0.94 4 in the form of CaSO due to its higher 4 solubility. It would be perfectly precipitated in the form of BaSO4 by 1 adding BaCl2. 0,8 Table 3. Addition of Na CO and the 0,6 2 3 weight of precipitated CaCO3 gram 0,4 0,2 Na2CO3 Weight of precipitated 0 0,5 1 1,5 2 2,5 3 3,5 Addition (g) CaCO3 (g) PrecipitatedMg(OH)2 in Weight of NaOH addition (gram) 0.50 0.45 1.00 0.91 1.50 0.93

2.00 0.93 Figure 2. The effect of NaOH addition on 2.50 0.93 Mg(OH)2 precipitation 3.00 0.93

The Effect of Sodium Carbonate Addition 1

0,8 The objective of this step is to remove Ca2+ in the filtrate from the first treatment by 0,6 2+ adding Na2CO3. In this process, Ca is 0,4 2- CaCO3 (gram) CaCO3 combined with CO3 by forming CaCO3, Precipitated The as expressed as follows: 0,2 0 1 2 3 4 Weight of Na2CO3 addition (gram) CaCl2 + Na2CO3 ç CaCO3 + 2NaCl

CaSO4 + Na2CO3 ç CaCO3 + Na2SO4 Figure 3. The effect of the addition of Ca(OH)2 + Na2CO3 ç CaCO3 + NaOH Na2CO3 on CaCO3 precipitation

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Journal of Coastal Development ISSN: 1410-5217 Volume 5, Number 3, June 2002 : 111-116 Accredited: 69/Dikti/Kep/2000

The Effect of Barium Chloride Addition

2- 2,3 This method is objected to remove SO4 by adding BaCl2 to form BaSO4, as 1,8 expressed in the following equation. 1,3

(gram)

CaSO4 + Na2CO3 ç CaCO3 + Na2SO4 0,8

Na2SO4 + BaCl2 ç BaSO4 + 2NaCl

The Precipitated BaSO4 BaSO4 Precipitated The 0,3 0 1 2 3 4 The solubility of BaSO4 in the Weight of BaCl2 Addition (gram) amount of 9.2x10-11 is very low and it makes SO 2- precipitating from the 4 Figure 4. The effect of the addition of solution. The total of precipitated BaSO4 BaCl2 on BaSO4 precipitation equals to the amount of BaCl2 addition since the formation occur through ionic reaction. In this method, the amount of

BaCl2 was varied from 0.50 to 3.50 gram with the step size of 0.5 gram to obtain CONCLUSION optimal precipitation. The result was listed in Table 4 and it was then presented in The improvement of public salt quality can Figure 4. Refer to those results, the optimal be implemented by chemical treatment of BaSO4 precipitation is reached at adding with the addition of Sodium hydroxide, 2.50 gram of BaCl2. At this condition, the Sodium Carbonate and Barium Chloride in 2- concentration of SO4 in solution is similar three series mixer. It could remove the to BaSO4 solubility. When the addition of concentration of impure ion such as 2+ 2+ BaCl2 was increased more than 2.50 gram, Calcium (Ca ), Magnesium (Mg ) and 2- the amount of precipitated BaSO4 is sulphate (SO4 ) ions in brine solution constant. This is due to the amount of through ionic reaction. Hence, the method 2- SO4 in public salt solution is could also increase the purity of Sodium stoichiometrically equal to 2.50 gram of Chloride (NaCl) content from 92.86% to BaCl2. 99.57% (dry base) that is suitable to meet community and industrial demand. Table 4. Addition of BaCl2 and the weight of BaSO4 precipitate

BaCl2 addition Weight of precipitated EFERENCES (g) BaSO4 (g) R 0.50 0.55 1.00 1.10 Anonymous, 1985. SII Garam Konsumsi. 1.50 1.65 Departemen Perindustrian, Jakarta. 2.00 2.15 2.50 2.34 Anonymous, 1976. SII Garam Industri. 3.00 2.34 Departement Perindustrian, Jakarta

3.50 2.34 Anonymous, 1996. Laporan Penelitian Industri Garam, Balai Penelitian dan Pengembangan Industri,

Semarang.

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Austin, G.T., 1986. Shreve‘s Chemical Leddy, J.J., 1985. Salt, Chlor-Alkali and Process Industries, 5th Edition, Related Heavy Chemicals, in J.A. McGraw-Hill Book Inc., Kent (Editor), Riegel‘s Handbook Singapore. of Industrial Chemistry, 8th Edition, van Nostrand Reinhold Heinke, G.W. 1996. Water Supply, Co., New York Environmental Science and Engineering, 2nd Edition, Monod, J., 1991. Seawater and Brine Prentice-Hall Inc., New Jersey. Water Treatment Handbook, 6th Edition, Vol. 1, Lavoisier

Publishing, Paris. .

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