Synthesis and thermodynamic properties of arsenate and sulfate-arsenate ettringite structure phases

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

Expanding the utilization strategy of waste concrete powder (WCP) is conducive to minimizing the environmental burden caused by construction & demolition wastes (C&DW). In this study, WCP prepared in the laboratory was thermally treated and used to remove As(V) from wastewater. Batch adsorption tests were implemented to explore the influence factors such as modification temperature (0-850 °C), pH (1.00-12.00), dosage (2-50 g/L), co-coexisting ions (SO₄^2-, NO₃^-, Cl^- and PO₄^3-) and temperature (25-45 °C). Various methods including spectroscopic tests, Rietveld refinement and sequential extraction process were employed to examine the mechanisms and their contribution to As(V) removal. Results show that the As(V) removal capacity of WCP was slightly enhanced after treatment at 200 °C, the pseudo-second-order kinetics model and Langmuir model could describe the adsorption process well. The maximum uptake capacity for As(V) calculated by Langmuir model at 25, 35 and 45 °C were 31.89, 25.56 and 17.42 mg/g respectively, and the removal rate reached a maximum of 95.37% (C₀ = 100 mg/L). Thermodynamically, the As(V) elimination was exothermic and spontaneous. The ettringite produced by rehydration of WCP proved to be essential for As(V) removal. Electrostatic attraction, precipitation, complexation and ion exchange were identified to be the main mechanisms of As(V) adsorption. This study confirmed the potential of WCP in removing As(V) from wastewater and provided a new insight into the removal mechanisms.