Element-based optimization of waste ceramic materials and glasses recycling

Many waste ceramic materials and glasses (CerG) such as glass, concrete, pottery, porcelain, brick, and tiles are landfilled because they have been recognized to be less conducive to recycling. In this study, to enhance the recyclability of ceramic materials and glasses, a linear model to minimize natural resource consumption of CerG materials production is proposed. The model focuses on elementally based contents of substances in the CerG materials. The model demonstrates a case for major industrial ceramic materials consisting of eleven oxides: Al2O3, B2O3, CaO, Fe2O3, K2O, MgO, MnO, Na2O, P2O5, SiO2, and TiO2 in Japan. In addition to the ceramic materials and glasses within the eleven oxide systems, application of the same natural resources to by-products or waste materials such as ironmaking slag and sewage sludge molten ash, are included in this analysis. In the proposed model, for minimizing natural resource consumption to produce the target CerG, linear programming was employed to assess waste generation and new production of CerG, subject to supply and demand balance and elemental tolerance ranges of chemical compositions in CerG materials. Two discrepancies were found between the proposed model and the characteristics of materials or usages of materials. Therefore, in the case study, several kinds of CerG materials were not applicable in the analysis. Even though costs for recovered materials restrict economic feasibility for recycling waste CerG, economic aspects were not taken into consideration in the analysis. In addition, impurity contamination during recovery processes restricts recycling of CerG. If those two factors (which may restrict the current recycling systems) were ignored, around two-thirds of the current natural resource consumption for CerG could be reduced by promoting recycling in the case of Japan. Further, new recyclable paths could be found by those analyses such as ironmaking slag for flat glass, glass bottles, and glass wool; and sewage sludge molten slag for tiles.