Garnet is a high hardness, high density granular filter media.
It is normally used as the lower (final) filtration
layer of a multi-bed down flow filtration system. Called
Multi-Media or Mixed Media filtration, the high density small
grain size of Garnet solves a major filtration problem. In a
single media granular filter such as a sand filter, the material
will hydraulically classify during back wash
according to granual size, the smallest rinsing to the top.
When water flows downward through the sand, the fine particles
at the top of the bed do most of the straining of the
sediment. The solids form a cake on the surface with filtration
typically taking place in the top few inches. As
the cake forms, the filtration becomes finer and head loss
increases exponentially in time.
The ideal situation would be to have the large grains of
media at the top to trap the large solids and a uniformly
decreasing grain size in the direction of fluid flow with the
small grains at the bottom to do the final polishing. The
penetration of the solids through the entire bed allows
increased solids storage, longer filter runs and higher
filtration rates.
A properly designed multi-media system will maintain its
unique inverse void gradation and provide superior
performance even after long periods of use in backwash.
This stable condition of large grains above finer ones is
achieved by the use of materials of different sizes and
specific gravities. Garnet with its high specific gravity of
4.0 forms the lower fine grain layer, its 0.3 mm effective size
can filter down to the 10-20 micron range. Filter sand (e.s.
=0.5 mm) and Anthracite (e.s. = 0.9 mm) or Filter-Ag can
form the larger less dense layers.
Multi-Media filtration technology is applicable to both water
and waste water treatment. Custom designed filters with
varying filter bed configurations can be designed to meet
specific needs. For the majority of municipal and industrial
water supply applications, a filter bed composed of 55 percent
low-density material, 30 percent medium density material,
and 15 percent high-density material is recommended.
Garnet sized per requirements, is the ideal high density
material.
#8 Garnet at 150 lb./ft.3 is a good choice for support beds
when using other high density filtration media such as high
purity Corosex II or the new manganese dioxide oxidation
media such as Pyrolox.
Advantages:
lHigh specific gravity allows unique filter designs.
In combination with other filter media both higher
flow rates, higher loadings and better filtration can
be achieved.
High hardness reduces attrition and provides for years of
reliable service.
An excellent support bed for other high density media.
Physical Properties:
Color - Light tan to reddish purple
Type - Almandite
Crystal System - Cubic
Fracture - Sub-conchoidal
Hardness - 7.5 (Moh's Scale)
Specific Gravity - 4.0
Density - 120 - 150 lbs./cu. ft.
Free Silica - None
|
