CONTAMINATION OF QUARTZ BY IRON IN ENERGY-INTENSIVE GRINDING IN AIR AND LIQUIDS OF VARIOUS POLARITY

The influence of mill power and grinding environment on the contaminat ion of quartz by iron during vibration grinding was studied. It was fo und that the Fe content of ground powders increased with an increase i n specific grinding energy that was independent of the conditions of e nergy supply, that is whether it was supplied by varying the mill powe r or the grinding time. The specific contamination expressed as the ra tio of Fe content to newly created surface area depended upon the phys ical properties of the grinding environment. The influence of grinding conditions on the state of the iron in the products of grinder wear w as investigated by Mossbauer spectroscopy and by measuring the magneti c susceptibility of the ground powders. It was shown that the iron pro duced from grinder wear is present in two main forms: as a magneticall y ordered form identical with the basic material of the grinder and in a form of finely dispersed iron/iron compound showing superparamagnet ic behaviour. Based on the results obtained, the formation of a silica -supported iron or iron oxide catalyst was presumed. By this assumptio n, the catalytic decomposition of water and methanol that takes place during quartz at grinding by iron containing grinders can be explained .