Changes in the structure of red mud and black nickel mud after activation

Abstract

This paper deals with the evaluation of the structure of selected hazardous wastes from the production of metals, namely waste from the production of aluminium - red mud and waste from the production of nickel - black nickel mud. In environmental applications, red mud and black nickel mud are likely to be used after activation. The samples were activated using hydrochloric acid to study the structure properties before and after the treatment. Both of these wastes have suitable adsorption and catalytic properties that could be positively affected by the activation of their surfaces. The morphology of the samples was documented by scanning electron microscope, phase analysis was performed using diffraction techniques, and the content of elements was determined by EDX analysis. Also, FTIR analysis of the samples was performed. Activation increases the specific surface area of samples, which is beneficial in many environmental applications, such as in the adsorptive removal of pollutants. Treatment of samples changes the surface properties of the adsorbent, such as electrostatic, hydrophobic, and hydrophilic. The activation creates a new surface structure and thus affects its properties. EDX analysis confirmed the high content of Fe, Al, Si and Ti, which are responsible for good adsorption and catalytic properties. X-ray diffractograms have shown only slight changes in the structure of wastes after activation. The results of SEM confirmed the changes in the surface structure and the creation of new active centres necessary for the successful adsorption process. The FTIR analysis determined the changes in the structure of the samples mainly due to the thermal degradation of C=O and O-Si-O bonds.