Magnetic Ore Milling Work - 2

Magnetic Ore Milling Work - 2

 Long before this situation arose, it had been recognized by Eastern iron-masters that

sooner or later the deposits of high-grade ore would be exhausted, and, in consequence,

there would ensue a compelling necessity to fall back on the low-grade magnetic ores.

For many years it had been a much-discussed question how to make these ores available

for transporta- tion to distant furnaces. To pay railroad charges on ores carrying perhaps

80 to 90 per cent. of useless material would be prohibitive. Hence the elimination of the

worthless "gangue" by concentration of the iron particles associated with it, seemed to be

the only solution of the problem.

Many attempts had been made in by-gone days to concentrate the iron in such ores by

water processes, but with only a partial degree of success. The impossibility of obtaining

a uniform concentrate was a most serious objection, had there not indeed been other

difficulties which rendered this method commercially impracticable. It is quite natural,

therefore, that the idea of magnetic separation should have occurred to many inventors.

Thus we find numerous instances throughout the last century of experiments along this

line; and particularly in the last forty or fifty years, during which various attempts have

been made by others than Edison to perfect magnetic separation and bring it up to

something like commercial practice. At the time he took up the matter, however, no one

seems to have realized the full meaning of the tremendous problems involved.

From 1880 to 1885, while still very busy in the development of his electric-light system,

Edison found opportunity to plan crushing and separating machinery. His first patent on

the subject was applied for and issued early in 1880. He decided, after mature

deliberation, that the magnetic separation of low-grade ores on a colossal scale at a low

cost was the only practical way of supplying the furnaceman with a high quality of iron

ore. It was his opinion that it was cheaper to quarry and concentrate lean ore in a big way

than to attempt to mine, under adverse circumstances, limited bodies of high-grade ore.

He appreciated fully the serious nature of the gigantic questions involved; and his plans

were laid with a view to exercising the utmost economy in the design and operation of the

plant in which he contemplated the automatic handling of many thousands of tons of

material daily. It may be stated as broadly true that Edison engineered to handle immense

masses of stuff automatically, while his predecessors aimed chiefly at close separation.

Reduced to its barest, crudest terms, the proposition of magnetic separation is simplicity

itself. A piece of the ore (magnetite) may be reduced to powder and the ore particles

separated therefrom by the help of a simple hand magnet. To elucidate the basic principle

of Edison's method, let the crushed ore fall in a thin stream past such a magnet. The

magnetic particles are attracted out of the straight line of the falling stream, and being

heavy, gravitate inwardly and fall to one side of a partition placed below. The nonmagnetic

gangue descends in a straight line to the other side of the partition. Thus a

complete separation is effected.

Simple though the principle appears, it was in its application to vast masses of material

and in the solving of great engineering problems connected therewith that Edison's

originality made itself manifest in the concentrating works that he established in New

Jersey, early in the nineties. Not only did he develop thoroughly the refining of the

crushed ore, so that after it had passed the four hundred and eighty magnets in the mill,

the concentrates came out finally containing 91 to 93 per cent. of iron oxide, but he also

devised collateral machinery, methods and processes all fundamental in their nature.

These are too numerous to specify in detail, as they extended throughout the various

ramifications of the plant, but the principal ones are worthy of mention, such as:

The giant rolls (for crushing). Intermediate rolls. Three-high rolls.

Giant cranes (215 feet long span). Vertical dryer. Belt conveyors.

Air separation. Mechanical separation of phosphorus. Briquetting.

That Mr. Edison's work was appreciated at the time is made evident by the following

extract from an article describing the Edison plant, published in The Iron Age of October

28, 1897; in which, after mentioning his struggle with adverse conditions, it says: "There

is very little that is showy, from the popular point of view, in the gigantic work which

Mr. Edison has done during these years, but to those who are capable of grasping the

difficulties encountered, Mr. Edison appears in the new light of a brilliant constructing

engineer grappling with technical and commercial problems of the highest order. His

genius as an inventor is revealed in many details of the great concentrating plant.... But to

our mind, originality of the highest type as a constructor and designer appears in the bold

way in which he sweeps aside accepted practice in this particular field and attains results

not hitherto approached. He pursues methods in ore-dressing at which those who are

trained in the usual practice may well stand aghast. But considering the special features

of the problems to be solved, his methods will be accepted as those economically wise

and expedient."