Properties and possible ceramic uses of clays from lignite mine spoils of NW Spain

Clay spoils from lignite mines are studied to know their industrial possibilities. The clays come from a coal mining area in NW Spain. In relation to their mineralogical composition, clays can be classified into three main groups. Group 1 was characterized by the presence of kaolinite with an average value of 39%, illite with an average value of 28% and quartz with an average value of 30%. Group 2 was characterized to have the lowest content of kaolinite (30%), 12% of illite content, the highest quartz content (47%), an absence of dolomite and calcite. Group 3 shows the highest kaolinite content (72%), illite (10%) and lower quartz content (15%). The chemical and mineralogical composition allows the evaluation of the applicability of the clays studied. The heated samples were composed of bulky particles, predominantly of quartz and hematite, which are agglomerated in a vitreous matrix. An intermediate phase between spinel and hercynite was formed at 950 °C in the Groups 1 and 3, and remains in this series up to a temperature of 1150 °C. At higher temperatures other phases such as mullite was formed in Group 3 series together an abundant amorphous phase. Imported clays (ball-clays) from the UK and France by Spanish ceramic industry have similar characteristics, behaviour and uses that the clays from lignite deposits studied, (i.e. Groups 1 and 3).