Precipitated silica, alkali silicates and zeolites from construction and demolition waste materials

Abstract

The construction and demolition industry generates a large volume of wastes, which are used in the same industry to elaborate new cementitious materials. However, the use of the mentioned wastes to prepare other type of silicate materials has been little reported. In the present work, silica, sodium silicate, potassium silicate, SAPO-34 zeolite and zeolite X, phillipsite, and sodalite were prepared using local sand waste, concrete, ceramic sanitary ware waste and building block. First, the wastes were characterized to know the elemental composition and mineralogical phases. Further alkaline fusion was carried out with NaOH and KOH, respectively. The products obtained in this step were neutralized with H2SO4 solution to form precipitated silica with high purity. For the zeolite experiments, SAPO-34 zeolite was synthesized using the precipitated silica, sodium aluminate, and H3PO4. Low Si/Al ratio zeolites were synthesized using the sodium silicate and like potassium silicate. The results of XRD technique show the formation of amorphous sodalite and phillipsite zeolites. Pure zeolite X was obtained only with the sodium silicate prepared from the ceramic ware waste; however, the use of an alternative aluminum source could be used with the other wastes to promote the formation of pure zeolites. With the non-conventional use of construction and demolition industry wastes, new technical opportunities were demonstrated herein to obtain functional materials promoting the circular economy and sustainable development.