Hydraulic and Particle Size Characteristics of Some Diatomite Filter Aids

Abstract

This study presents data pertaining to the hydraulic and particle size characteristics of commercial grades of diatomite used as filter aids. To achieve this, the specific study objectives were to: evaluate the reproducibility and relative simplicity of two ASTM methods for determining the grain size of soils when those methods are used to determine the particle size distribution of diatomite filter aids; determine the particle size distribution of different lots of commercial grades of diatomite filter aids; determine K3 values of different grades and of different lots of the same grade of diatomite (K3 is a constant for a given grade of diatomite at 20°C and is inversely proportional to its coefficient of permeability); and, determine whether a relationship exists between the K3 value and particle size distribution. The determination of the permeability of diatomite filter aids in this study was confined to the evaluation of K3 coefficients in the recently developed diatomite filtration equation. The ASTM Method for Grain Size Analysis of Soils‐Designation D422‐39 (Method 1) and ASTM Tentative Method for Grain Size Analysis of Soils ‐Designation D422‐61T (Method 2) were used in this study for determining particle size distribution.

Effect of ions in solution on the permeability of filter aids

“…When filter cake permeability studies are conducted under exactly similar conditions, reproducible permeability results are obtained (7). As a result of such studies, research personnel recommended use of a. specific test and apparatus to be used to determine the permeability of filter aids (3).…”

“…Considerable variation in the value for the same grade of filter aid can be expected (7). Such variation is to the changes in the processing and source of the filter aid and to variations in the water used to evaluate K^.…”

“…When a colloidal particle is suspended in 'water, a thin liquid layer called the fixed layer surrounds the colloid and moves through the water with the colloid. The electrical potential difference between the outer edge of the fixed layer and point of electroneutrality in the water surrounding the particle is referred to as the electrokinetic or zeta potential (7). 10, 12, 15, 16, 17, 18…”

Design requirements of precoat filters for water filtration

“…In of filters may be optimized (27,43). Other research has been concerned with the characteristics of different filter aids and grades (2, 26,35,49), the evaluation of the filtering properties of various suspended solids (3,15,37,44,61), and the use of polyelectrolytes and aluminum sulfate to improve the filtering characteristics of filter aids (16,17,20,52,56,60). Extensive laboratory studies have been made to determine the applicability of precoat filters for the removal of iron (2,35,43,50,70), various flocculant solids (37, 44), clays (3,20,60,61), and suspended solids from coagulated and settled surface waters (15), raw surface waters, softened waters (15,27), and trickling filter effluent (36).…”

Effect of ions in solution on the permeability of filter aids

“…When filter cake permeability studies are conducted under exactly similar conditions, reproducible permeability results are obtained (7). As a result of such studies, research personnel recommended use of a. specific test and apparatus to be used to determine the permeability of filter aids (3).…”