A method for the preparation of activated clays and cement additives from contaminated drill cuttings is provided. The substrate can be mixed with a mineral acid in a first reactor. The acidified substrate is then mixed with alkaline earth in a second reactor. The reactions are exothermic and provide heat to vaporize the contaminants, reaction products, and water. Recoverable constituents in the vapor can be condensed in a vapor collection system. The treated substrate can be heated and/or further reacted with acid, resulting in the formation of activated clays. For production of cement additives, the treated substrate can then be heated in a kiln and combined with cement clinker material for the preparation of cement and/or concrete.