# A Novel Technosol Formulation for Sustainable Landfill Top Covers Using Non-Hazardous Wastes
## 3 Results and Discussion  
### Physico-Chemical Properties and Mineral Constituents of Waste Materials  
WFS showed an alkaline reaction (pH = 10.31) and low electrical conductivity (0.77 mS cm\({}^{-1}\)). It primarily consisted of quartz and clay minerals, with minor feldspars and calcite (Table 1). The clay separate (<2 \(\upmu\)m) was dominated by smectite with a well-ordered structure (Biscaye index = 0.79) with some mica, quartz, feldspars, and calcite. Smectite exhibited a basal spacing (001) of around 12.8 A in the air-dried state, indicating the presence of a single layer of water molecules in the interlayer space [33], and exchangeable monovalent cations. Upon ethylene glycol solvation, the basal spacing increased to 17 A (Figure 2a). \begin{table}
\begin{tabular}{l c c c} \hline \multicolumn{4}{c}{**Waste Material**} \\ \cline{2-4}
**Material Properties** & **Waste Foundry** & **Washing Aggregate** & **Composted** \\
**and Constituents** & **Sand (WFS)** & **Sludge (WAS)** & **Biosolids (CBS)** \\ \hline
**Physico-chemical parameters** & & & \\ \hline pH (in water) & 10.31 \(\pm\) 0.04 & 6.24 \(\pm\) 0.26 & 7.5 \(\pm\) 0.16 \\ Electrical cond. (mS cm\({}^{-1}\)) & 0.77 \(\pm\) 0.01 & 0.24 \(\pm\) 0.02 & 3.2 \(\pm\) 0.3 \\ \hline
**Mineral composition and organic matter content (wt \%)** & & & \\ \hline  & Quartz (65–70) & Clay minerals (7–80) & \\ Bulk sample & Clay minerals (20–25) & Quartz (15–20) & Organic \\  & Feldspars (<5) & Feldspars (<5) & matter (54) \\  & Calcite (<5) & Goethite (<5) & \\ \hline  & Smectite (75–80) & & \\  & Mica (5–10) & Kaolinite (70–75) & \\ Clay fraction & Quartz (<5) & Mica (20–25) & \\  & Feldspars (<5) & Smectite (<5) & \\  & Calcite (<5) & Quartz (<5) & \\ \hline
**Chemical composition** & & & \\ \hline  & Plant macronutrients (wt \%) & & \\ \hline  & N & - & - & 2.6 \\  & P & 0.008 & 0.037 & 4.2 \\  & K & 0.23 & 1.23 & 1.21 \\  & Ca & 0.35 & 0.07 & 6.7 \\  & Mg & 0.33 & 0.23 & 1.30 \\  & S & 0.04 & 0.04 & - \\ \hline  & & & \\ \hline  & & & \\ \hline  & & & \\ \hline  & & & \\ \hline \end{tabular}
\end{table} 
Table 1: Physical–chemical parameters and composition of the waste materials used as ingredients in Technosol formulation. Given that WFS is composed of relatively pure silica sand, chemical analyses showed negligible concentrations of Ca, Mg, and K, all consistently below 1.0 wt %. Moreover, total concentrations of potentially toxic elements remained consistently low (Table 1), and fell well below the regional screening levels established for industrial land use. A significant concern regarding the utilization of WFS is the potential leaching of elevated trace metal levels [34]. However, elemental analysis of leachate generated from this waste revealed minimal metal release, with measured concentrations (in mg L\({}^{-1}\)) remaining below 0.01 (Hg), 0.02 (Se), 0.05 (Cd and Sb), 0.1 (As, Cu, and Pb), 0.2 (Mo, Mn, and Zn), and 0.5 (Cr and Ni). Therefore, WFS exhibited a low leaching potential consistent with previous WFS applications [35]. Importantly, none of the measured trace elements exceeded toxicity thresholds for plant establishment [36]. In addition, the low sulphate (30 mg L\({}^{-1}\)) and chloride (<50 mg L\({}^{-1}\)) concentrations suggest the minimal presence of soluble salts, which can also be detrimental to plant establishment. WAS is made up of reddish yellow clays with a slightly acidic pH (6.24) and remarkably low electrical conductivity (0.24 mS cm\({}^{-1}\)). Clay minerals comprised between 75 and 80% of the bulk sample, while quartz, and, to a lesser extent, feldspars and goethite were present as accessory minerals (Figure 2b). The clay fraction was dominated by kaolinite, with minor amounts of mica and quartz. Additionally, XRD analysis of the clay separate revealed the presence of smectite with a basal spacing of 12.1 A in the air-dried state,  
Figure 2: Mineral composition of the waste materials determined from the X-ray powder diffraction patterns.