Advances in the characterization of industrial minerals
The use of minerals by man is as old as the human race. In fact the advancement of human civilization has been intimately associated with the exploitation of raw materials. It is not by chance that the distinction of the main historical eras is based on the type of raw materials used. Hence the passage from the Paleolithic and Neolithic Age to the Bronze Age is characterized by the introduction of basic metals, mainly copper, zinc and tin, to human activities and the Iron Age was marked by the introduction of iron. Since then the use of metals has increased and culminated in the industrial revolution in the mid-eighteenth century which marked the onset of the industrial age in the western world. However, during the past 50 years, although metals were equally important to western economies as they had been previously, the amount of metals extracted annually in western countries has decreased significantly and metal mining activity shifted mainly to third world countries (in Africa, South America, Asia) and Australia, due to economic and environmental constraints. At the same time the role of industrial minerals has become increasingly important for the western economies and today, in developed EU countries, the production of industrial minerals has surpassed by far the production of metals. In some EU countries, metal mining activities have stopped completely. The importance of industrial minerals is expected to increase further in the future.
Portland Cement and other Calcareous Hydraulic Binders: History, Production and Mineralogy
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Published:January 01, 2010
Abstract
Portland cement has become a cornerstone of modern society and the present-day cement and concrete industry is one of the largest consumers of industrial minerals. The historical evolution of early calcareous hydraulic binders into the present standard Portland cement is a typical example of a product-performance-optimization process driven by the gradual accumulation of empirical know-how and fundamental process understanding. The early observation that a hydraulic binder may be formed when impure limestone is burnt at temperatures above the decomposition temperature of limestone led to the development of a wide range of early hydraulic binders throughout the 18th and 19th centuries. Initially, burning at relatively low temperatures (1000– 11008C) of impure limestone resulted in the production of fast-setting natural cements and hydraulic limes. Eventually, over the course of the 19th and 20th centuries, sintering at increasingly higher burning temperatures of natural impure limestones and artificial mixes of ground limestone and clay was introduced to produce slow-setting natural cement and finally (proto-)Portland cement with superior strength development.
Today, the Portland cement-production process consists of an energy-intensive, high-temperature sintering phase (14508C) of the raw materials, followed by fast cooling and fine intergrinding of the clinker product with gypsum to produce the Portland cement. The mineralogy of the clinker phases is relatively complex. C3S and C2S show several high- and low-temperature polymorphs, whereas C3A and C4AF allow considerable compositional solid solution. The addition of water to Portland cement initiates a complex scheme of hydration reactions to form a hardened cement paste. The advent of novel analytical techniques prompted recent advances in the understanding of the structures of the hydration products and the hydration mechanism. Nevertheless many aspects of the hydration reactions remain unsolved. The necessary future developments towards less energy intensive, low-CO2 cements may take advantage of the historical knowledge acquired in the production of a wide range of alternative hydraulic binders.
