Green synthesis of water-glass from municipal solid waste incineration bottom ash

Water-glass is extensively used as a silica precursor in different chemical applications such as alkali activated binders and nano-silica. The current production of water-glass involves the fusion of sand with soda ash at temperatures above 1000 oC, which makes the production expensive and environmentally unfriendly. Therefore, it would be an interesting alternative to prepare water-glass by recycling silica from waste materials. One of such waste materials is the bottom ash from municipal solid waste incineration, which contains a silica content between 40 and 60%. However, bottom ash consists also of a complex combination of minerals, metals and salts. An acid treatment is, therefore, envisaged to remove many contaminants and release silica from silicate minerals. Subsequently, the silica was extracted from the remaining solid content by dissolution in a sodium hydroxide solution. Thus, this study shows it is possible to prepare water-glass using an environmental friendly method.