Deep insight on mechanism and contribution of As(V) removal by thermal modification waste concrete powder

Recycling waste dolomite powder in cement paste: Early hydration process, microscale characteristics, and life-cycle assessment

Waste dolomite powder (WDP) is a byproduct obtained from dolomite quarries during the preparation of dolomite products. To study the re-utilisation of WDP, an eco-friendly cement-based material was prepared using WDP as a micro-aggregate. The effects of WDP on the early hydration process, microscale characteristics, and life-cycle assessment of cement paste are discussed in this study. The isothermal calorimetry results showed that the incorporating WDP in cement paste accelerated the early hydration process of cement according to the degree of reaction. In this case, the setting time of the cement pastes with WDP was shortened, and the early compressive strength was significantly improved. The results of X-ray diffraction and scanning electron microscopy analysis at early curing ages (1 and 3 d) showed changes in the peak intensity of ettringite and portlandite and a denser microstructure. Mercury intrusion porosimetry tests showed that the middle and large capillary pores were refined by the nucleation and filling effects of WDP. Based on environmental and economic evaluations, the utilisation of WDP reduced energy consumption, CO2 emissions, and economic costs. Compared to the sample without WDP, the energy consumption, CO2 emissions, and economic cost indices were 42 %, 42.69 %, and 39.4 % lower, respectively. Our results may provide valuable references for the re-utilisation of WDP in low-carbonation cement-based materials.

Reprocessed construction and demolition waste as an adsorbent: An appraisal

Construction and Demolition (C&D) waste is solid wastes generated from the construction, demolition, and renovation activities that constitute almost 30-40 % of globally generated solid wastes. Improper disposal and management of these materials can cause negative impacts on the environment, economy, and human health. Most research on C&D waste is limited to reduction, recycling, and reuse of the wastes. However, there is no systematic review dedicated entirely to the applicability of C&D wastes as adsorbent for waste management. This review presents the utilization of C&D wastes-based adsorbents for removing contaminants from environmental matrices covering triple edge benefits in the viewpoints of waste treatment, solid waste management, and disposal. The properties, the capability of C&D waste adsorbents on contaminant removal, and the influence of various factors on the adsorptive removal is detailed. Further, the mechanisms involved in contaminant removal by C&D waste are summarized. The review revealed that, chemisorption is the prominent mechanism of contaminant removal by most C&D wastes. Among the three types of C&D waste reviewed; concrete-based adsorbents were the most efficient for contaminant removal. Limited studies are avaiable in the literature on binary and multiple contaminant systems, reusability studies, and high dependence on solution pH, therefore further studies are warrated. As C&D waste contain trace concentration of heavy metals and contaminants, its leaching potential at different pH levels and adsorbate concentration need to be conducted, which has been hitherto neglected. Finally, the approaches, obstacles, and potential solutions to build an industrially and economically efficient C&D adsorbent are discussed.

Interactions of Cr3+, Ni2+, and Sr2+ with Crushed Concrete Fines

The underutilized cement-rich fine fraction of concrete-based demolition waste is a potential sorbent for aqueous metal ion contaminants. In this study, crushed concrete fines (CCF) were found to exclude 33.9 mg g−1 of Cr3+, 35.8 mg g−1 of Ni2+, and 7.16 mg g−1 of Sr2+ from ~1000 ppm single metal nitrate solutions (CCF:solution 25 mg cm−3) under static batch conditions at 20 °C after 3 weeks. The removal of Sr2+ followed a pseudo-second-order reaction (k2 = 3.1 × 10−4 g mg−1 min−1, R2 = 0.999), whereas a pseudo-first-order model described the removal of Cr3+ (k1 = 2.3 × 10−4 min−1, R2 = 0.998) and Ni2+ (k1 = 5.7 × 10−4 min−1, R2 = 0.991). In all cases, the principal mechanism of interaction was the alkali-mediated precipitation of solubility-limiting phases on the surface of the CCF. Four consecutive deionized water leaching procedures (CCF:water 0.1 g cm−3) liberated 0.53%, 0.88%, and 8.39% of the bound Cr3+, Ni2+, and Sr2+ species, respectively. These findings indicate that CCF are an effective sorbent for the immobilization and retention of aqueous Cr3+ and Ni2+ ions, although they are comparatively ineffectual in the removal and sustained exclusion of Sr2+ ions. As is commonly noted with Portland cement-based sorbents, slow removal kinetics, long equilibrium times, the associated release of Ca2+ ions, high pH, and the formation of loose floc may preclude these materials from conventional wastewater treatments. This notwithstanding, they are potentially suitable for incorporation into permeable reactive barriers for the containment of metal species in contaminated groundwaters, sediments, and soils.