Silicate-based substantially non-hydrated sorbent material comprising predominantly calcium silicate and/or calcium alumino-silicate has an atomic framework at least partially de-calcified in that a plurality of calcium atom sites in atomic framework are vacant. The activated material can be used as industrially useful sorbents for contaminant species such as metal ions, in the solidification of waste, in similar applications, and in the absorption of carbon dioxide which might otherwise be exhausted to atmosphere. The material has a further use as a precipitant of certain ionic species e.g. lead, leading to its removal from aqueous solution by precipitation.