12.6 Introduction

Almost all waste materials produced at a mining and milling operation can be divided into two classes. Mine waste is that product which is mined but which is not processed before being placed on a waste dump. Tailing is that product which is discarded after mining and processing to remove the economic products. Processing may range from simple mechanical sorting to crushing and grinding followed by physical or chemical processing. It contains all other constituents of the ore except majority of the extracted metal. It may also contain heavy metals and other substances at concentration levels that can be toxic to biota in the environment. The mechanical stability of the tailings mass is poor because of its small grain size and high water content. The ultimate purpose of a tailing impoundment is to contain fine-grained tailings. The long-term cost of tailings disposal depend in part on mechanical stability and environmental integrity.

Tailings were disposed off where convenient and most cost-effective, often in flowing water or directly into drainages. Definition of impending stability concerns are raised in part by the use of tailings material in tailings dams or embankments. to mitigate these concerns, such embankments often rely on a certain amount of controlled seepage to enhance stability, which in turn affects environmental performance. Products are removed from their original location, broken up and placed in piles in which the conditions of oxidation, seepage, leaching and erosion differ considerably from those at their original location. This increases the potential considerably for wind or water erosion of surface materials and their transport into the environment. The potential for oxidation and leaching is also increased with the result that dissolved contaminants may be carried away from the pile into the environment.

 

Design of tailing impoundments depends on the quantity and the individual characteristics of the tailings produced by mining and milling operation as well as the climatic, topographic, geologic, hydro-geologic and geotechnical characteristics of the disposal site, apart from regulatory requirements related to dam safety and to environmental performance.