The Practice of Ore Dressing in Europe: A Description of Foreign Methods for the Mechanical ... by Wheaton Bradish Kunhardt

Author:Wheaton Bradish Kunhardt
Language: eng
Format: epub
Publisher: J. Wiley & Sons
Published: 1884-03-25T05:00:00+00:00

The two extremes in which concentration and grading are simultaneously performed are found on the one hand in the system of depositing all the suspended matter of the slime in a series of long ** strips,'* ** runs " or troughs, and pits, suitably termed a labyrinth^ and, on the other, in the development of continuous classification in pointed boxes and vats, or spitz-kasteUy to such an extent that the water overflowing from the last pointed vat contains no mineral that can be saved with profit. The first method, which is a survival of an old, primitive practice, still prevails in England, though abandoned in most continental mining regions. The second system has been introduced in several of the advanced mills—^and is probably nowhere put to better practice than at Ems—^but the majority of dressing works carry out a mixed system, sorting fine sands and meals in continuous classifiers, and leading the overflow from these into a labyrinth where the pulp settles.

The classification produced in pits or deep runs is fairly regular; the shallower the run, however, or the thinner the stream of slime flowing over the deposited sediment, the closer does the separation approach that made on buddies, but it follows a well defined law, and generally becomes very irregular and unsatisfactory. Such shallow current classification is now rarely seen in practice. The labor incurred in handling the

deposits of a large labyrinth, especially in the cold season, and the loss due to letting the settled material dry partially before it is mixed with water and washed, are very serious objections to the first mode of classifying and concentrating. The loss of float mineral from partial dr3ring, familiar as this must be, seems frequently to be regarded with insufficient appreciation,^ Its production is strikingly noticeable in every case where fine, dry or merely moist material is mixed with water and fed upon slime tables; fine mineral particles are then seen floating on the surface of the water, and being borne off by the current instead of caught upon the washing apparatus; in a few seconds they are carried into the waste launder or to large, final settling basins, where they form a scum, sometimes quite thick, on the water surface. This loss is inevitable, regardless of a high specific gravity of the mineral; to avoid its effects it should be a rule in wet slime dressing that when a finely comminuted ore has once been mixed with water, it must, if possible, never be com* pletely deposited from it until the moment of the final separation of its constituents upon some washing apparatus. Governed by this rule, the abandonment of labyrinths even for the partial accomplishment of a general slime classification is a necessary result; as a classifier the labyrinth fills no place in a modem dressing mill which newer, continuous working apparatus cannot occupy to better advantage.

Continuous classification is now most commonly performed by means of the spitzlutte and spitzkasten. The syphon V trough, which is the old form of spitzlutte designed by Rit-tinger, is frequently met with in Austrian dressing works.

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