Levigation

Levigation

Levigation is the process of grinding an insoluble substance to a fine powder, while wet. The material is introduced into the mill together with water, in which the powdered substance remains suspended, and flows from the mill as a turbid liquid or thin paste, according to the amount of water employed. There is no loss of material as dust, nor injury or annoyance to the workmen. Further, any soluble impurities in the substance are dissolved, and the product thereby purified. 'the greatest ad vantage of this process is the facility it affords for the subsequent separation of the product into various grades of fineness, because of the slower subsidence of the finer particles from suspension. The turbid liquid, flows into the first of a series of tanks, and is allowed to stand for a certain time. The coarsest and heaviest particles quickly subside, leaving the finer material suspended in the water, which is drawn from above the sediment into the next tank. The liquid is passed from tank to tank, remaining in each longer than it remained in the preceding, since the finer and lighter the particles, the more time is necessary for their deposition. In some cases a dozen or more tanks may be used, and the process then becomes exceedingly slow, as very fine slimes or muds may require several weeks for the final settling.
But as a rule, from three to five days is sufficient. The term "levigation" ; is now often applied to mere sedimentation,
a substance being simply stirred up in water, without previous
wet-grinding, in order to separate the finer from the coarser particles, as above.

The above information on chemistry subjects is as they were
described in the past centuries