Characterization of filter dust in the glass container industry and definition of its influence on green glass melts

Abstract

Filter dust in the container glass industry is continuously and almost completely recycled in the original source tanks. However, problems sometimes occur, with this practice, in green glass furnaces, which can be put down to the fluctuating redox levels of the filter dust. The characterization of the dust shows that the determination of the levels of chemical oxygen demand and of sulphite content is insufficient to assess the redox effect in the glass melts. Therefore, melting experiments with green glass batches containing filter dust were carried out on a laboratory scale. Surprisingly, in all cases the experiments led to a light oxidation of the glasses by the filter dust. The reason for this is considered to be the sulphate content in the dust and possibly the oxidation of the sulphite to sulphate under laboratory conditions. Individual cases of reduction by filter dust, as observed in practice, could be possibly due to sulphide in the dust or to a high content of carbon in the glass cullet used. These could also be attributable to fluctuations in production conditions or to the amount of moisture in the old glass cullet.