Circular economy in practice: Production of sustainable composites from waste

An element of the circular economy strategy is processing waste into useful products. This study aimed to produce materials incorporating hazardous waste contaminated with heavy metals. Sulfur polymer cement (SPC) modified with natural tung oil was used as the binder. Compared to Portland cement, sulfur-based binders not only reduce CO 2 emissions but also enable the utilization of sulfur waste, such as byproducts from the petrochemical industry. Samples were prepared using an SPC modified with different amounts of tung oil (2–8 wt % S) and two filler mixtures containing 6 and 12% waste (mixes A and B). The composites were tested for water absorption by immersion, compressive strength, and metal leaching toxicity (TCLP test and EN 12457-4). The water absorption of all samples was below 1.6 wt %. Worse results were observed for monoliths with higher waste content (mix B). The highest mechanical strength was observed for samples where the sulfur binder was modified with 4 wt % tung oil. The compressive strength of composites based on mixtures A and B was 8.0 and 11.5 MPa, respectively. Analysis of the samples showed an uneven coating of waste particles by the sulfur binder. The TCLP test indicated a potential risk of heavy metal leaching in an acidic environment (pH ca. 4). Conversely, the EN 12457-4 test demonstrated low heavy metal leaching for all mixture A composites.