The Grondal Process: Crushing and Wet Treatment of Iron Ore

Posted By Tom Cropper on 06 November 2014

Posted in The Vintage Machinery Almanac

This article was originally published in the April 1907 edition of “Electrochemical and Metallurgical Industry” magazine. The publication of this material aims to provide historical insight on The Grondal Process and its role in iron production. For an introduction to The Grondal Process, click here.

Any good type of commercial crusher may be used in the preliminary crushing of the ore. Usually either a Gates or Blake crusher is employed.

The broken ore is conveyed and distributed to the feed hoppers of the Grondal ball mills. The feeding arrangement consists of an ordinary roller-feeder driver at a uniform speed and so constructed as to admit of accurate adjustment of feed. The ball mill consists of a hollow cylinder, 4 feet in diameter and varying in width from 4 to 8 feet. It is reinforced with steel ribs and lined with manganese steel, or other steel alloy of good wearing quality. The mill is charged with about 2 tons of chilled cast-iron balls, of about 6 inches diameter.

Wet Treatment of Iron Ore

The ends are of cast iron, with suitable openings provided with a screen at the discharge end. The degree of fineness of the ore is regulated by varying the amount of water introduced into the mill.

It is found that working with ores of average hardness the consumption of iron, represented mainly by the wear on the balls, amounts to about 2 pounds per ton of ore treated.

Mills in The Grondal Process require from 20 to 25 hp. each; make from twenty-five to thirty revolutions per minute, and grind from 50 to 100 tons of ore per 24 hours, from T/i inch down to from 10 to 100-mesh in fineness.

In order to free the pulp from the bulk of the non-magnetic climes, it is often advisable to pass the pulp coming from the ball mill through a slime-box before charging it into the separator proper. The slime-box consists of a V-shaped box, the pulp entering at the top and a stream of water at the bottom. The slime boxes are usually built in pairs, and between each pair is placed an electromagnet with a hatchet-shaped pole piece. This electromagnet is of such strength as just not to lift any magnetic particles out of the water. The velocities of the pulp and clear water are so arranged that the heavier particles settle at the bottom, from whence they are drawn off to the separator in the next step of The Grondal Process. The function of the magnet is to arrest magnetic particles in the fine slimes which collect on the surface of the water immediately under the pole piece in masses, and from time to time drop to the bottom whence they are carried off with the main pulp to the separators.