Assessment of the recycling potential of stone processing plant wastes based on physicochemical features and market opportunities

The extraction of raw materials in many productive sectors has become problematic for the environment because of the negative impacts of the process and the inappropriate destination of the generated waste. Stone waste (SW) from the dimension stone industry has physical and chemical characteristics with great potential for use as an alternative raw material in several industrial activities. Its main constituents include silica, alumina, alkaline, and alkaline earth oxides, usually combined as calcite and dolomite in the crystalline phases. In this work, a case study was conducted with SW from a processing plant of dimension stones (also known as ornamental rocks) located in Viana do Castelo, Portugal. In this new methodology, the SW powder samples were characterised by X-ray fluorescence spectrometry, X-ray diffraction, differential thermal analysis, and thermogravimetry. Physical features, such as moisture content, specific surface area, particle size distribution, and true density were also determined. The pH and electrical conductivity of the SW as a suspension were also evaluated. The specific SW was analysed against the literature considering aspects related to environmental legislation and standards (waste classification), physical and chemical characteristics (potential), production data (quantity), recycling availability (viability), and market opportunities (applicability). This novel way in terms of the form and content of a paper is an intermediate approach between an original article and a state-of-art review. SW is normally considered inert but, owing to its high fineness (<200 μm), some potentially hazardous compounds can been leached. The state-of-the-art of SW applications suggests that this waste is promising raw materials for ceramics and cement, which eventually encapsulate contaminants in their structure. A critical discussion of the literature was conducted to reduce the knowledge gap about the most promising valorisation strategies for SW. New recycling proposals are also suggested.