Dewatering Flashcards
(23 cards)
The separation of pulp into two parts, one is
relatively solid-free and the other is relatively liquid-free, with respect to original pulp
Dewatering
- An operation that uses gravity to relatively dilute slimy pulp into a
thick pulp by allowing solid particles to settle. - Sedimentation is thus a time-dependent phenomenon and its rate
decreases with time.
Thickening
- process of removal of some liquid from compression zone due to
weight of clear liquid.
Exudation
agglomeration, clustering, coagulation or coalescence of fine
particles to form floccules or flocs in a liquid medium with the use of chemical reagents known as ____.
Flocculation
FLocculants
- Consist of a large cylindrical tank of 3 to 30 meters in diameter and
2.5 to 3 meters in depth with a very short conical bottom. - The feed is introduced continuously through a central semisubmerged feed well. clear water overflows into the top peripheral
launder. The settled solids are swept by a slowly revolving raking
mechanism
Thickeners
- Sludge swept by the rakes is directed towards the center to facilitate easy removal.
- Surface area must be large enough that the upward velocity of liquid is always lower than the settling velocity of the slowest-settling
particle which is to be recovered.
Thickeners
Surface area must be large enough that the upward velocity of liquid
is always lower than the settling velocity of the
slowest-settling particle which is to be recovered.
Thickeners
The degree of thickening produced is controlled by the
residence time of the particles and hence by the thickener depth.
Thickeners
THICKENERS
- The feed pulp containing about ____ to ____% solids is thickened to a pulp of ____ to ____ % solids.
- If it is desired to obtain clear liquid rather than the thick pulp, the
thickening operation is called ____ using a clarifier, similar
in design with a thickener
- 15%-30% solids —- 55-65% solids
- Clarification
The separation of finely divided solid particles from a fluid by driving the pulp to a membrane or septum (commonly called as the filter medium), porous to the fluid but impervious to the solid, through which the fluid called filtrate
passes.
Filtration
The volume of filtrate collected per unit time is termed as the ____
Rate of Filtration
As the filtration process proceeds, solid particles accumulate on the filter medium forming a packed bed of solids called ____.
Filter Cake
Type of Filters
____ are most frequently used in mineral beneficiation plants where the recovery of large amounts of solids is the requirement.
Cake Filters
Type of Filters
____ are used where higher flow rates and better washing and drying
are required.
Pressure Filters
Type of FIlters
____ are the most widely used filters in mineral beneficiation plants
and they are of either drum type or disc type.
Vacuum Filter
- The slurry that will be separated is injected into
the center of the press and each chamber of the press is
filled. - The liquid is strained through filter cloths by force using pressurized air or water.
Pressure Filter
- Consists of a cast cylinder
mounted horizontally and rotated
at a very low rpm. The cylinder
has a perforated surface over
which the filter medium is
wrapped tightly. The periphery of
the drum is divided into
compartments.
Rotary Vacuum drum Filters
As the drum rotates, the cake is
raised above the slurry level and
wash water is sprayed on the surface if required. On further rotation, the
cake is dried.
Rotary Vacuum Drum Filter
Consists of a number of circular discs mounted on a horizontal
tubular shaft and spaced by means of hubs. Filter medium
consists of cloth bags that cover over the sector and fastened to
the nipple.
The completed sector is joined to the central shaft by screwing
the nipple into the holes of the shaft.
Rotary Vacuum Disc Filter
- Utilize microporous ceramic sectors instead of conventional filter
cloth. - Filter cake is removed from the ceramic discs by scraper, eliminating
the need for compressed air for blow off. - The disc material is inert, resistant to almost all chemicals and slurry
temperatures, and has a long operational life
Ceramic Filter Disc
The____of concentrates prior to shipping is the last operation performed in the mineral processing plant.
It reduces the cost of transport and is usually aimed at reducing the moisture content to about 5% by weight. Dust losses are often a problem if the moisture content is lower.
Drying
–these consist of a relatively long cylindrical shell
mounted on rollers.
The shell is at a slight slope, so that material moves from the feed to discharge end under gravity
Rotary Thermal Dryer
– which uses hydraulic pressure at 100 bars to squeeze water from
the slurry that enters the annular space between the filter tube and an outer tube
Tube Press
