RESUMO
In the present work, LaNi0.5Ti0.5O3 and La2NiTiO6 nanoparticles were synthesized by the modified Pechini method. LaNi0.5Ti0.5O3 was calcined at 1073 K for 17 h or 100 h, while La2NiTiO6 was calcined at 1273 K for 135 h. The double perovskite calcined at 1073 K for 17 h presented orthorhombic symmetry with Pbnm space group, mean particle size was 31.9 ± 1 nm, random ordering of Ni2+ and Ti4+ cations, Néel temperature close to 15 K, and magnetic moment of 1.29 µB. By increasing the calcination time, this material showed the same symmetry and space group, a mean particle size of 50.7 ± 2 nm, short-range ordering of Ni2+ and Ti4+ cations, Néel temperature around 12 K, and magnetic moment of 0.96 µB. La2NiTiO6 presented a monoclinic crystal structure, with P21/n space group, mean particle size of 80.0 ± 5 nm, rock salt ordering of Ni2+ and Ti4+, Néel temperature of approximately 23 K, and magnetic moment of 2.75 µB.
RESUMO
Fluoride can cause some diseases to humans when ingested in large quantities and for a long time. Due to this, it is necessary to remove or reduce the amount of fluoride in effluents before release into the water bodies. This work aimed to evaluate the ability of hydrocalumites synthesized by two different methodologies and calcined hydrocalumite in reducing the content of fluoride in aqueous solutions. The materials were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), N2 physisorption, thermogravimetric analysis (TGA), and differential thermal analysis (DTA). The removal capacity of fluoride ions ranged from 14.9 to 189.6 mg F- g-1. The removal mechanisms by hydrocalumites were ion exchange and adsorption at low concentrations, while at high concentrations were adsorption and precipitation of calcium fluoride. In relation to the use of calcined hydrocalumite, the removal mechanisms were ion exchange and reconstruction of structure (memory effect) in low concentrations. By the adsorption tests, it was observed that the results fit better the Langmuir isotherm model.
Assuntos
Poluentes Químicos da Água , Purificação da Água , Adsorção , Óxido de Alumínio , Cloreto de Cálcio , Fluoretos , Humanos , Concentração de Íons de Hidrogênio , Cinética , Soluções , ÁguaRESUMO
Hydrotalcite is a layered double hydroxide (LDH) consisting of brucite-like sheets of metal ions (Mg-Al). In this work, hydrotalcites were synthesized, and boron removal from oilfield wastewater was evaluated. LDHs were synthesized using the co-precipitation method. The calcined products (CLDHs) were obtained by heating at 500°C and characterized using X-ray diffraction, X-ray fluorescence, thermogravimetric analysis and the specific surface area (BET). The affinity of LDHs for borate ions was evaluated for calcined and uncalcined LDHs as a function of contact time, initial pH of the oilfield wastewater (pH â¼ 9) and the LDH surface area. The tests were conducted at room temperature (approximately 25ºC). The results indicated that 10 min were needed to reach a state of equilibrium during boron removal for calcined LDHs due to the high surface area (202.3 m(2) g(-1)) regardless of the initial pH of the oilfield wastewater, which resulted from the high buffering capacity of the LDHs. The adsorption capacity increased as the adsorbents levels increased for the range studied. After treatment of the oilfield wastewater containing 30 mg L(-1) of boron with Mg-Al-CO3-LDHs, the final concentration of boron was within the discharge limit set by current Brazilian environmental legislation, which is 5 mg L(-1). Pseudo-first-order and pseudo-second-order kinetic models were tested, and the latter was found to fit the experimental data better. Isotherms for boron adsorption by CLDHs were well described using the Langmuir and Freundlich equations.