THE ROLE OF SCIENCE
Scientists and inventors have long worked to develop and improve size-reduction processes and machines to solve the engineering challenges associated with grinding. Size reduction-used in every mineral-processing operation—has been a continuing field for scientific inquiry and this has contributed to more efficient size-reduction processes in a number of areas:
■ The design of better machines
■ Modeling and simulation techniques to optimize circuits
■ Control techniques to ensure that products meet tight specifications
■ Laboratory techniques to measure material and process characteristics
Although little is known about the people who invented manual — and water-powered querns, black powder, or the stamp mill, they must have been excellent scientists, because their inventions solved the problems of their times. By 1700, the value of science to technological innovations and improvements was starting to be recognized. At that time, apprenticeships (or their equivalents) were the main form of training. Although excellent for teaching current technological practices, these types of arrangements were less successful at encouraging the search for new ideas. And, in the mineral industry, new ideas were urgently required because the growing demand for metals and ores was leading to
■ Ore body depletion and loss (at the time, mining was done by following the veins that were exposed as mining proceeded, not by exploring ahead of mining using drill holes); deepening mines; and declines in metal grades
■ The need to concentrate minerals with fine grain sizes
■ Many accidents and deaths resulting from rock falls and poor access to deep mines
To alleviate a shortage of technically skilled workers who could better control and improve operations, and to protect the large revenues that governments received from mining operations, mining academies for advanced training began to be established. Universities had been offering advanced studies in philosophical and theological areas for hundreds of years, but engineering had been neglected. The rising interest in mining academies was a good indication that the link between prosperity and technical skill was being recognized.
Mining academies were established in Germany at Freiberg in 1766, Schemnitz in 1770, and Berlin in 1770; in Russia at St. Petersburg in 1773; and in Mexico City in 1791. These academies laid the foundations for the scientific advances in mineral engineering that occurred in the late 19th and early 20th centuries. The curriculum in these early academies mainly dealt with mineralogy, milling, and smelting.
The scientific culture moved easily into industry, although technology transfer must have seemed slow at times. The wry comment made by a distinguished smelting
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metallurgist who trained at Freiberg is pertinent: “[Up to 1860] the percentage recovery in the metal was practically altogether neglected, and smelters worked and were happy in a sort of metallurgical dreamland, trustingly hoping that whatever was right” (Sticht 1905).
By 1900, finer grinding was in great demand, particularly for the portland cement, cyanide, and flotation processes. The importance of science in improving processes was becoming very clear. Because breaking more particles or making a finer product requires more energy, the starting point for scientific improvements in grinding was to understand how the product size changed when more energy was used. A key question emerged: What is the size of mill required to grind ore to a required product size if the feed rate and grindability are known? Devising a good test for grindability has always been only part of the answer; the other part relates to accurately predicting the power required and then choosing the size of the mill that will absorb this power.
Peter von Rittinger and Friedrich Kick published two conflicting theories on this area of inquiry—the energy-size reduction relationship—during the last half of the 19th century, and these generated much debate and research. Missing from the original work and the later controversy was an accurate method of measuring the size and surface area of the dust particles that were inevitably generated and that formed most of the surface area. The controversy could not be resolved until new measurement techniques became available, and by the time these were developed, the question was of academic interest only because many other factors had come into play by then. But the controversy was useful, because it encouraged engineers to see the necessity of measuring process variables and to think about processes in quantitative terms. Research on the energy-size reduction link, which continued without pause, led to a third theory by Fred Bond in the mid-20th century. Bond’s theory became widely used for plant design.
By 1910, tumbling mills were coming into their own. The development of tumbling mills is discussed in Chapter 7, but we should mention a vital link here: The demand for these mills coincided with the rise of electrical power.
During the 20th century, electricity improved the technology of size reduction from fledgling machines and low-capacity processes to huge machines and immense-capacity processes, changing the mining industry dramatically by 1920. By 1990, the personal computer had become the easy-to-use means to make the necessary mathematical calculations to simulate the performance of size-reduction machinery and circuits, and modeling and simulation was becoming an essential tool for design and operation. By 2000, engineers were building motors so powerful that they no longer limited machine size, and scientists were developing blasting procedures using huge drills and new explosives that could shatter any quantity of rock in a single blast. The focus had changed from searching for power to ensuring that power was used as efficiently as possible.
Science was a crucial factor in all these impressive developments. Of course, in an inherently human feature of progress, not all changes proceeded smoothly. It was often difficult to create enthusiasm for change. In 1890, the great copper mining region in the United States known as the Lake Superior District was typical:
The real reason for want of progress in the concentration of ores in Lake Superior is that everyone is doing the same thing and no one is willing to take the first step to advance. Some of the mills are experimenting in a vague sort of way but all of the small mines expect to reap the benefit without cost of the experiments which the large mines ought to make and the large ones expect the largest ones to take the first step and find the paying improvement. (Benedict 1955)
This attitude changed in time. By 1915, for example, the potential value of ball mills was recognized at the Calumet and Hecla mine in Michigan’s Upper Peninsula when, even though the concept of ball millings was still unproven, 64 mills were installed in a new tailings retreatment plant. The plant operated successfully and produced large volumes of copper concentrate for years.
In the rest of this chapter, we introduce some of the scientists whose names have gone down in size-reduction history. Many others made significant contributions to the field, but we mention only a few here to give a flavor of how science and technology advanced in tandem to improve size-reduction processes and machines.