Management of Ferro‐alloy wastes

Abstract

The ferro‐alloy industry in South Africa can be divided into two groups of processes, the first concerned with the mining and initial beneficiation of ores and the second with the production of various metallic products, ranging from pig iron to various ferro‐alloys and stainless steel. Waste production from these processes is considerable, with the majority of waste products in the form of solids, such as furnace slags, emission control dusts, flotation tailings and leach residues. Traditionally, these waste materials have been disposed of to landfill, usually in the form of large‐scale heaps or dams. It is only since recently that the management of ferro‐alloy wastes is starting to be governed by concerns about the long‐term environmental stability of such deposits, which is associated with the potential leachability of salts and heavy metal species contained therein. The concept of Clean Technology is beginning to influence process design options in the sector with the ultimate aim to reduce the load of material discarded as waste, and to improve the environmental acceptability of these wastes. This includes not only the installation of new process technology, but also process‐integrated recycling of waste materials and new downstream processes, which use waste products as raw materials. These new technologies notwithstanding, waste materials that ultimately arise from any given process will have to be managed in such a way so as to ensure minimal impact on the disposal environment. We argue in this paper that operator liability with respect to waste management practice can be assessed only with the aid of a comprehensive model of the physical and chemical processes, which affect leach resistance within waste deposits. The point of departure from other work in this field is our interest in conditions within the landfill (in chemical engineering terms) as these relate to technology choice and operating conditions within the process(es), which generated the waste. The development of such a model is discussed, and a methodology which combines laboratory waste characterisation with the model to provide a predictive tool for the assessment of leachate generation and mobility is proposed.