Coal waste: A Potential Source for the Alumina Enrichment

Vast quantities of coal waste have accumulated over the years and caused significant economic and environmental problems in Central Alborz Zirab-Mazandaran Region of Iran. For this reason, in this study we focused on alkaline leaching process to extract alumina from coal waste as an alumina source. The chemical composition of the coal waste from the central Alborz coal washing plant - Zirab - Mazandaran was confirmed by X-ray diffraction (XRD), UV/visible, potentiometry, X-ray fluorescence (XRF), inductively coupled plasma (ICP), atomic absorption spectrometry (AAS) thermogravimetry (TG) and differential scanning calorimetry (DSC). The XRD pattern analysis demonstrated that the tailings are formed from silica, muscovite, kaolinite, magnesium iron aluminosilicate (clinochlore), rutile and pyrite. In this work, alkaline leaching methods (NaOH) were tested and the extraction efficiency was 80%. The main problem of extracting alumina from coal and similar compounds has been the presence of free silica, which was completely removed with the help of chemical additives and heating and reduced to below 1%. The optimization of the process was done and all the important factors involved in increasing the efficiency of alumina extraction and increasing the purity of the product were investigated and discussed. One of the valuable achievements of this work is the complete recovery of the NaOH or sodium carbonate consumed in the process, which has reduced the cost of consumables.