Electrokinetic properties of unexpanded and expanded perlite samples in suspensions of various electrolytes and surfactants were studied as a function of ionic strength, pH and, type and concentration of electrolyte and surfactant. Electrokinetic properties of a series of unexpanded and expanded perlite samples have been investigated using the microelectrophoresis technique. From the experimental results, it was found that (i) zeta potential increased with increasing ionic strength for both perlite samples, (ii) zeta potential values of unexpanded and expanded perlite suspensions in CaCl 2 solutions in the studied pH range were higher than that in NaCl solutions and, perlite samples had no isoelectrical point, (iii) Ca 2+ ions were potential determining ions for both perlite samples and adsorbed specifically in Stern layer, (iv) Na, Cl -, SO 42- and PO 43- ions compressed the double layer as indifferent electrolytes, (v) the sign of the surface charge of both perlite samples increased with increasing N-cetyl-N,N,N-trimethylammoniumbromide (CTAB) and N-cetylpyridiniumchloride (CPC) concentration, and (vi) when zeta potential values of N-cetyl-N,N,N-trimethylammoniumbromide (CTAB) and N-cetylpyridiniumchloride (CPC) were positive in all studied pH range, those of other surfactants sodiumdodecylsulfate (SDS) and benzyltriethylammonium chloride (BTEAC) were negative. [All rights reserved Elsevier]

Sepiolite, a highly porous mineral, is becoming widely used as an alternative material in areas where sorptive, catalytic and rheological applications are required. High ion exchange capacity and high surface area and more importantly its relatively cheap price make it an attractive adsorbent. In this study, the adsorption of acid red 57 by natural mesoporous sepiolite has been examined in order to measure the ability of this mineral to remove coloured textile dyes from wastewater. For this purpose, a series of batch adsorption tests of acid red 57 from aqueous sepiolite solutions have been systematically investigated as a function of parameters such as pH, ionic strength and temperature. Adsorption equilibrium was reached within 1 h. The removal of acid red 57 decreases with pH from 3 to 9 and temperature from 25 to 55 degreeC, whereas it increases with ionic strength from 0 to 0.5 mol L-1. Adsorption isotherms of acid red on sepiolite were determined and correlated with common isotherm equations such as Langmuir and Freundlich models. It was found that the Langmuir model appears to fit the isotherm data better than the Freundlich model. The physical properties of this adsorbent were consistent with the parameters obtained from the isotherm equations. Approximately, 21.49% weight loss was observed. The surface area value of sepiolite was 342 m2 g-1 at 105 degreeC, and it increased to 357 m2 g-1 at 200degreeC. Further increase in temperature caused channel plugging and crystal structure deformation, as a result the surface area values showed a decrease with temperature. The data obtained from adsorption isotherms at different temperatures have been used to calculate some thermodynamic quantities such as the Gibbs energy, heat and entropy of adsorption. The thermodynamic data indicate that acid red 57 adsorption onto sepiolite is characterized by physical adsorption. The dimensionless separation factor (RL) have shown that sepiolite can be used for removal of acid red 57 from aqueous solutions. The sorption capacity of the sepiolite is comparable to the other available adsorbents, and it is quite cheaper. (C) 2004 Elsevier B.V. All rights reserved.

In this study, electrokinetic properties of unexpanded (UEP) and expanded (EP) perlite samples have been extensively investigated as a function of concentration of various electrolytes such as NaCl, KCl, LiCl, NaNO //3, NaCH//3COO, MgCl//2, CaCl//2, BaCl //2, Na//2CO//3, Na//2SO//4, AlCl//3, FeCl//3, CoCl//2, CuCl//2 and Pb(NO//3)//2. The zeta potential measurements have been performed to determine the isoelectric point (iep) and potential determining ions (pdi). Although pH strongly altered the zeta potential of perlite samples, perlite samples do not yield any isoelectric point in the pH ranges of 2-11. Both of the perlite samples remain negatively charged in the pH ranges studied. The expanded perlite has a more negatively charged surface than the unexpanded perlite. Monovalent cations or anions and divalent anions are indifferent electrolytes for both perlite samples whereas MgCl//2, CaCl //2, BaCl//2, CoCl//2, CuCl//2, Pb(NO //3)//2, AlCl//3 and FeCl//3 change the interface charge from negative to positive for the expanded perlite but the potential determining ions for unexpanded perlite are CaCl//2, BaCl//2, AlCl//3, and FeCl//3 metal ions.

Colemanite is one of the most important underground riches of Turkey, having approximately 60% of the world boron deposits, and it has a large portion in the deposits. When colemanite having a 2CaOmiddot3B 2O 3middot5H 2O formula is mined naturally, it contains various clay minerals. In this study, the dissolution of colemanite in aqueous oxalic acid solutions was investigated in a batch reactor employing the parameters of stirring speed, particle size, temperature and acid concentration. It was found that the dissolution rate increases with increasing temperature and decreasing particle size. The conversion rate increased until 250 mol m -3 with increasing acid concentration and then decreased with increasing acid concentration. No important effect of stirring speed was observed. The dissolution kinetics of colemanite was examined according to heterogeneous and homogeneous reaction models, and it was found that the dissolution rate was controlled by product layer (or ash layer) diffusion process. The activation energy of the process was determined to be 9.50 kcal mol -1. The experimental data were tested by graphical and statistical methods and it was found that the following model best fits the experimental data t=t *[1-3(1-X) 2/3 +2(1-X)]

The dissolution kinetics in SO2-saturated water of ulexite, a sodium calcium borate, have been studied. The effect of particle size, gas flow rate and temperature were determined. Ulexite dissolution rates increased with decrease in particle size, with increase in temperature and were not affected by the flow rate of SO2. The activation energy for the dissolution was calculated as 58-01 kJ mol-1.