Electrochemical Conversion of Construction and Demolition Waste (CDW) into Higher Value Co-Products Such as Calcium Hydroxide, Calcium Carbonate, and Silica for Closing the Materials and Carbon Cycle
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Construction and demolition waste (CDW) has a huge potential to reduce CO2 emissions directly and indirectly thereby paving the way towards sustainable development and circular economy. It can help to tackle the challenges of CO2 emissions reduction as well as waste management and control of air pollution arising from dust. Conventional methods for waste treatment and recovery are chemical (acids and bases) intensive and moreover recovery of chemicals is challenging whereas the electrochemical route can prove to be environmentally benign if the energy is harnessed from renewable sources. The research work demonstrates that the electrochemical conversion of CDW i.e., alkaline industrial waste to form calcium carbonate, calcium hydroxide and silica is a unique pathway in terms of sustainability and low-cost emission. The formation of calcium carbonate is thermodynamically downhill and stores CO2 permanently. These products can be utilized in construction industry and other industries thereby closing the materials and carbon cycle. The first part of the research delves into characterization of CDW using PSA, BET, XRD, TGA, and FTIR followed by electrochemical experiments. The process is environmentally friendly since it is governed by water splitting to create acidic and alkaline conditions for reactions. The performance of various electrodes is compared for the electrochemical leaching as well as conversion of CDW to desired products. Also, platinum electrodes are used to investigate its effect on various parameters including product yield. Additionally, the performance of the electrochemical system is evaluated by incorporating a stirring mechanism. Higher calcium dissolution and comparable faradaic efficiency with respect to published work is obtained. The electrochemical approach proves to be promising for leaching of elements and silica formation. Silica and calcium carbonate can be reused in the construction industry. Further studies can consider better reactor design and the effect of variable stirring speed, size of the stirrer, temperature and pulsing to increase the product and by-product formation.