This study is an application of the experimental design methodology for optimizing a potassium sulfate synthesis reaction. The latter is a two-stage reaction through an intermediate product (Schoenite: K 2 SO 4 .MgSO 4 Á6H 2 O). To determine optimal experimental conditions of the first stage, we have conducted a fractional factorial design and a central composite one. The optimal conditions of the second stage were determined only by means of a fractional factorial design. Several physico-chemical techniques were used to implement this study, namely potentiometry, complexometry, gravimetry and X-ray diffraction. This work has showed that this double decomposition reaction, when performed under the determined optimal conditions, gives good quality potassium sulfate (purity more than 95%) with a maximal yield.
This paper refers a method for the preparation of magnesium chloride hexahydrate (bischofite) from Sebkha el Melah of Zarzis Tunisian natural brine. It is a five-stage process essentially based on crystallization by isothermal evaporation and chemical precipitation. The two first steps were dedicated to the crystallization of sodium chloride and potassiummagnesium double salts, respectively. Then, the resulting liquor was desulfated using calcium chloride solution. After that another isothermal evaporation stage was implemented in order to eliminate potassium ions in the form of carnallite, KCl.MgCl2.6H2O. At the end of this step, the recovered solution primarily composed of magnesium and chloride ions was treated by dioxan in order to precipitate magnesium chloride as MgCl2.6H2O.C4H8O2. This compound dried at constant temperature of 100°C gave good quality magnesium chloride hexahydrate. Besides this salt, the various by-products obtained from the different treatment stages are also useful
a b s t r a c tThe discoloration of a textile dye derivative bromothymol blue (BTB) in aqueous solution with Fenton process (FP) has been studied. The performance of the FP depends on various operating parameters such as the initial concentration of hydrogen peroxide [H 2 O 2 ] 0 , the initial ferrous ion concentration [Fe 2+ ] 0 and the pH of the reaction medium. The optimal conditions of these variables, for the discoloration of BTB with FP, have been investigated by the use of Doehlert matrix. It has been demonstrated that under the optimal conditions ([H 2 O 2 ] 0 = 1.61 mM, [Fe 2+ ] 0 = 0.18 mM and pH = 2.85), FP leads to a maximum discoloration yield of BTB (67.58%± 4.39) after 1 h of treatment. These values were also experimentally validated. The obtained discoloration yield was 70.4%. After 6 h of BTB treatment in aqueous solution by FP, the color removal achievement was 91.54% and, the chemical oxygen demand (COD) removal reached 63%. Carboxylic acids and inorganic ions have been identified and followed during the mineralization of BTB with FP.
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