Effect of temperature on halloysite acid treatment for efficient chloroaniline removal from aqueous solutions

Monochloroanilines and dichloroanilines are important reagents or chemical intermediates in the production of dyes, pharmaceuticals, and agricultural chemicals. These toxic compounds have a large tendency to accumulate in the environment and a low natural biodegradability, so improved methods to remove or sequester them are needed. Halloysite is used as an efficient adsorbent to remove toxic compounds, such as aniline, from aqueous solutions. The purpose of this study was to evaluate whether acid-activated halloysites from the "Dunino" (Poland) strip mine could be effective in the removal of not just aniline but also of its chloro-substituted forms from aqueous solutions. The composition, structure, and morphology of activated halloysites were characterized using the following methods: wavelength dispersive X-ray fluorescence analysis (WDXRF), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), Fourier-transform infrared spectroscopy (FTIR), and N2 adsorption-desorption analysis. The acid-activated halloysites had an increased ability to remove aniline and chloroanilines from aqueous solutions as the acid activation temperature was increased. This suggests that the acid activation temperature is an important factor that influences the ability of acid activated halloysites to adsorb aromatic amines (anilines) from water. The efficiency of aniline and chloroaniline removal by halloysite activated at 80°C reached maximum levels, especially for the removal of aniline and 4-chloroaniline. The adsorption isotherm data were best described by the Langmuir adsorption model. The values of the Langmuir adsorption constants were calculated using the inverse liquid chromatography method.