Recovery of silicon from sewage sludge for production of high-purity nano-SiO2

Generation of excess sewage sludge has already caused many environmental problems. A novel investigation for recovery of Si from the carbonized raw sewage sludge (RS) has been conducted in this study. Results show that early rupture (by OH−) of Si–O–Si bond in the networks of SiO44- tetrahedron is the key step for formation of RS-derived sodium silicate (Na2O·(SiO2)x·(H2O)y). SiO2 gel is formed through the silica colloidal–particles cohesion, which is partly affected by the bridging role of the hydrated Na+ (1070.7 eV). O1s peaks of the SiO2 can be decomposed into two components, i.e. Si–O bridging oxygen atoms (532.4 eV) and hydroxyl groups (O–H, 533.0 eV). Intensity of the O–H stretching vibration bands around 3450 cm−1 (residual Si–OH), which is inversely related to the condensation degree, decreases as sol pH increases. Properties of this high purity RS-SiO2 enable it to have the potential for numerous technological (environmental and biotechnology) applications. Reutilization of RS for production of SiO2 may provide an environmental benefits to communities by protecting water, soil and air.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Efficiency of raw sludge (RS) treatment is decreased by the presence of silicon compounds. ► How to recover silicon is of great interest. ► Early rupture of Si–O–Si bond was important for destabilizing SiO44- tetrahedron networks. ► High-purity SiO2 was synthesized from RS-derived sodium silicate (Na2O·(SiO2)x·(H2O)y). ► Production of SiO2 from RS is a sustainable technology.