# A Novel Technosol Formulation for Sustainable Landfill Top Covers Using Non-Hazardous Wastes
## 2 Materials and Methods  
### Selection and Characterization of Waste Materials  
Three distinct non-hazardous wastes were selected as input materials for designing a Technosol for landfill top covers: (a) waste foundry sand (WFS); (b) washing aggregate sludge (WAS); and (c) composted biosolids (CBS). These waste materials, recognized by the European Waste Catalogue under the codes 100906, 010408, and 190503, respectively, are abundantly generated and readily available worldwide [16; 17; 18]. WFS, a by-product of the metal casting industry, is widely used for creating sand molds and cores. Over time, the sand degrades and becomes unsuitable for further casting operations, leading to its disposal in landfills. WAS is a silty-clay waste generated during the washing and screening  
Figure 1: Simplified cross-section of a typical waste landfill (not to scale). This paper focuses on developing a waste-derived Technosol for the vegetative and the protective layers of the toposil cover.  
of aggregates for quality control in construction applications. This process produces a waste stream that requires proper management and disposal solutions. CBS originates from wastewater treatment processes. Composing stabilizes the organic components of the sewage sludge, transforming it into a nutrient-rich product that improves soil quality, improves water retention, and fosters plant growth.  
Prior to constructing the Technosol, a comprehensive characterization of the selected waste materials was performed to assess their compatibility and ensure compliance with regulatory requirements. This involved a detailed evaluation of their physical-chemical properties, mineralogical and chemical composition, and leachate quality. Potentiometric measurements of pH, Eh, and electrical conductivity were conducted on representative samples, by stirring 10 g of solid waste in 25 mL of deionized water for 5 min, followed by a standing period of 30 min. pH measurements were performed using a CRISON BASIC 20 pH meter with a glass electrode calibrated with pH 4 and 7 buffer solutions at 25 \({}^{\circ}\)C. Electrical conductivity measurements were made using a CRISON GLP 31 conductivity meter equipped with a glass electrode calibrated with two standard KCl solutions. Each procedure was repeated three times, and the average values were recorded.  
Mineralogical analysis was carried out by X-ray powder diffraction (XRD) to determine the bulk mineralogical composition and identify clay minerals in the fine fraction. The XRD patterns were obtained on a BRUKER D8-Advance diffractometer, using monochromatic Cu-K\(\alpha\) radiation operated at 40 kV and 30 mA, with a step size of 0.015\({}^{\circ}\) and a scan speed of 0.1 s per step. Two types of samples were prepared: (a) randomly oriented powder samples to determine the bulk mineralogical composition; and (b) oriented aggregate samples to identify clay minerals in the fine fraction (<2 \(\upmu\)m). The oriented aggregates were air-dried and solvated with ethylene glycol to accurately identify smectite. Semi-quantitative mineral abundances were determined using intensity factors derived from integrated peak area values of diagnostic reflections [19].  
Quantitative analysis of essential macronutrients and potentially toxic trace elements was achieved through inductively coupled plasma optical emission spectroscopy (ICP-OES) following a four-acid (HCIO\({}_{4}\)-HNO\({}_{3}\)-HCl-HF) digestion process. For accuracy and precision, rigorous quality control procedures were implemented, including reagent blanks, duplicate analysis, and certified reference materials (OREAS series). The analysis of reference materials exhibited deviations from certified concentrations of less than 10% (relative standard deviation, RSD), achieving remarkable precision better than 2% RSD for most elements.