ABSTRACT
Borax sludge is the waste produced by a trommel sieve in the borax production process and is used as an adsorbent for Cr(III) removal. The effects of various parameters, including pH, initial Cr(III) concentration and contact time were investigated for batch adsorption of Cr(III). The experimental results obtained were applied to different adsorption isotherms and kinetic models. The results indicated that the Temkin isotherm (R2 = 0.9749) was most suitable to explain the adsorption characteristics of borax sludge, and the removal of Cr(III) was achieved by a physisorption process. The overall kinetic data fitted the pseudo-second order rate model (R2 = 0.9990). According to thermodynamic studies, which were carried out at different temperatures, changes in enthalpy (ΔH) and entropy (ΔS) values for Cr(III) adsorption by borax sludge were determined to be 69.395 kJ/mol and 0.276 kJ/mol K, respectively. The study implied that borax sludge could be used as an alternative adsorbent in the adsorption of Cr(III) from aqueous solutions.
ABSTRACT
The hydrothermal synthesis of a mcallisterite (Mg2(B6O7(OH)6)2 · 9(H2O)) mineral at low temperatures was characterized. For this purpose, several reaction temperatures (0-70°C) and reaction times (30-240 min) were studied. Synthesized minerals were subjected to X-ray diffraction (XRD), fourier transform infrared (FT-IR), and Raman spectroscopies and scanning electron microscopy (SEM). Additionally, experimental analyses of boron trioxide (B2O3) content and reaction yields were performed. Furthermore, thermal gravimetry and differential thermal analysis (TG/DTA) were used for the determination of thermal dehydration kinetics. According to the XRD results, mcallisterite, which has a powder diffraction file (pdf) number of "01-070-1902," was formed under certain reaction parameters. Pure crystalline mcallisterite had diagnostic FT-IR and Raman vibration peaks and according to the SEM analysis, for the minerals which were synthesized at 60°C and 30 min of reaction time, particle size was between 398.30 and 700.06 nm. Its B2O3 content and reaction yield were 50.80 ± 1.12% and 85.80 ± 0.61%, respectively. Finally, average activation energies (conversion values (α) that were selected between 0.1 and 0.6) were calculated as 100.40 kJ/mol and 98.31 kJ/mol according to Ozawa and Kissinger-Akahira-Sunose (KAS) methods, respectively.
