Assessment of waste hardened cement mortar utilization as an alternative sorbent to remove SO2 in flue gas.

Developing efficient low-cost absorbents has been recognized as a prerequisite for industrial application of wet flue gas desulfurization (WFGD). Herein, hardened cement mortar (HCM) particles developed from waste concrete blocks were used as an innovative absorbent for SO2. The results show that the SO2 in flue gas can be completely absorbed by the highly alkaline HCM slurry. Under optimum operating conditions, 0.8 g of SO2 was retained by per gram of HCM. Under acid conditions produced upon dissolving SO2 in water, the Ca-rich compounds in HCM particles can continuously release Ca2+ and OH- into the HCM slurry. The Ca2+ ions released can effectively combine with SO32-, resulting in the absorption of SO2 dissolved in water. The dissolution process of HCM particles is well described by the pseudo-second-order model. The desulphurization byproduct was characterized by X-Ray diffraction (XRD) analysis, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy and energy dispersive spectrometry (EDS). The results show that the desulphurization product mainly consists of gypsum. The technology developed provides a type of new material for removing SO2 in waste flue gas. It also offers an innovative solution for the disposal of waste concrete which is also a global environmental concern.

Fines isolated from waste concrete as a new material for the treatment of phosphorus wastewater.

Waste concrete is a key component of construction and demolition (C&D) waste produced in billions of tons. Exploring new technology for recycling waste concrete has become a global concern. Meanwhile, phosphorus (P) removal from wastewater consumes lots of natural minerals, leading to a heavy burden on the environment. In this study, the cement paste powder (HCPP) was used to remove phosphorus from wastewater. The results indicate that both HCPP and thermally modified HCPP (MHCPP) are effective phosphorus removal materials, with a maximum P-binding capacity of 3.9-mg P/g HCPP and 31.2-mg P/g MHCPP, respectively. The phosphorus removal mechanism of HCPP and MHCPP was also proposed: (1) Ca2+ and OH- can release from the surface of the HCPP or MHCPP to wastewater, forming a high-alkaline and Ca-rich solution; (2) hydrolysis of phosphorus species in the high-alkaline solution environment creates HPO42- species; (3) the HPO42- combines with Ca2+ and H2O, resulting in the formation of brushite; (4) the brushite precipitated from wastewater and adhered on the surface of the HCPP or the MHCPP particles. The study provides a new and low-cost material for treatment of phosphorus wastewater. Further, the study also offers a new approach for reusing of waste concrete fines.

The crystallization and structure features of barium-iron phosphate glasses.

The crystallization and structure features of xBaO·(90-x)(60P2O5-40Fe2O3)·10CaF2 glasses, where x=0, 5, 10, 15 and 20 mol%, are investigated in details by using X-ray diffraction analysis, Fourier transform infrared spectroscopy, Raman spectroscopy and differential thermal analysis. It is found that the major crystalline phase of barium iron phosphate glasses annealed between 650 °C and 850 °C is FePO4, and the crystallization is restrained by barium. The predominant infrared absorption band is attributed to the antisymmetric stretching vibrations of (PO3)(2-) in Q(1) units. Raman and Fourier transform infrared spectra reveal that the glasses' main structural networks are Q(1) and Q(0) tetrahedrons connected by P-O-P linkages. Moreover, the glass transition temperature increases with BaO content, which suggests that barium can strengthen the thermal stability of the iron phosphate glass.