On the use of industrial scraps for the treatment of zinc hydrometallurgical wastes by self-propagating reactions

In this work the development of a technique is presented that consists of blending highly toxic solid waste from electrolytic zinc plants, i.e. paragoethite waste, with suitable amounts of aluminum, silicon, and ferric oxide, and igniting the resulting mixture so that a self-propagating front reaction rapidly travels through the mixture without requiring additional energy. Specifically, the possibility of substituting commercial additives, needed for guaranteeing the self-propagation of the reacting mixture, with industrial scraps is demonstrated. In fact, commercial ferric oxide can be replaced by steelmaking scraps containing about 85% of iron oxides, while electronic industry by-products, characterized by Si content equal or higher than 94 wt.%, can be used instead of the corresponding commercial reactant.Similarly to the results obtained when commercial additives were used, the main reaction product, representing 70-80 wt.% of the total mass of the original mixture and obtained when the paragoethite waste content in the starting mixture does not exceed 30 wt.%, is constituted by an alumino-silicate matrix which embodies heavy metals, such as Pb, Zn, and Cd. Leaching tests of this solid product demonstrate the fulfillment of the environmental regulations for heavy metals.