CHARACTERIZATION AND POSSIBILITIES FOR UTILIZATION OF INDUSTRIAL WASTES FROM PROCESSING, BENEFICIATION OF MINERALS, AND SMELTING

Abstract

The aim of this study is the characterization of some of main inorganic wastes for Bulgaria as slag and ash from lignite - fired power plants, clinker and lead slag from the lead and zinc smelting industry, and fayalite waste from copper smelting production. The chemical and phase compositions and particle size distribution of the waste materials were determined using XRF, XRD and laser diffraction, respectively. Hot stage microscope was used to evaluate the thermal behaviour of the samples. SEM was used to study the microstructure of the sample. 
The studied wastes contain mainly oxides of silica, aluminium, calcium and iron which also are basic for the building ceramics. In addition, they are finely dispersed with particle sizes below 1 mm, so they can be used without crushing or milling. However, due to the various and complex mineralogical composition the samples are characterized with different thermal behaviour.
The fly ash contains high percentage of amorphous phase, together with plagioclase, magnesium ferrite, quartz and some gypsum. As a result, it is chartered with wide firing interval at about 1200°C and can be considered as a main raw material for new building ceramics.
The lead slag contains less aluminium and silica and main crystal phases from the melilite group. It easy forms liquid phase at lower temperatures, so that can be considered as an alternative flux. 
Finally, the waste from copper smelting production, which mainly contain fayalite and magnetite, melts at the highest temperature. It cannot be considered as a flux but can be used as a filler in ceramic batches or as raw material for geopolymers as well.
From the studied wastes only the bottom ash, due to the extremely high gypsum content, and the clinker slag, because of presence of high amount carbon and metal iron, are not appropriate for direct usage in ceramic industry.