Principles of Material Treatment by Magnetic Means

Abstract

Magnetic phenomena have been known and exploited for many centuries. The earliest experiences with magnetism involved magnetite, the only material that occurs naturally in a magnetic state. Thales of Miletus stated that the magnetic interaction between lodestone, or magnetite, and iron was known for at least as long ago as 600 B.C. That magnetite can induce iron to acquire attractive powers , or to become magnetic, was mentioned by Socrates. Permanent and induced magnetism, therefore, represents one of man's earliest scientific discoveries. Practical significance of magnetic attraction as a precursory form of magnetic separation was recognized in 1792, when W. Fullarton obtained an English patent for separating iron ore by magnetic attraction [D1]. Since that time the science and engineering of magnetism and of magnetic separation have advanced rapidly and a large number of patents have been issued. While separation of inherently magnetic constituents was a natural early application of magnetism, Wetherill's separator, devised in 1895, was an innovation of significant proportions. It demonstrated that it was possible to separate two components, both of which were commonly considered to be non-magnetic. In the ensuing time various types of disk, drum and roll dry magnetic separators were developed although the spectrum of minerals treatable by these machines was limited to rather coarse and moderately strongly magnetic materials. Since the end of the nineteenth century there has been a steady expansion of both the equipment available and the range of ores to which magnetic separation is applicable. The development of permanent magnetic materials and improvement in their 1