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Kansas Geological Survey, Bulletin 199, pt. 1, originally published in 1970

Toxicant-Carrier Granules from Kansas Bentonite With a Volcanic Ash Additive

by Allison L. Hornbaker and William B. Hladik

Originally published in 1970 as part of Kansas Geological Survey Bulletin 199, pt. 1, p. 11-13. This is, in general, the original text as published. The information has not been updated. An Acrobat PDF version of the complete bulletin (5 MB) is also available.


Increased sorptivity and lower bulk density of toxicant-carrier granules result when volcanic ash (both raw and processed) is used as an additive to Phillips County bentonite. Preparation of the bentonite includes oven drying and fine grinding. Granules made from 100 percent bentonite have sorptivity (kerosene) of 16 percent and a bulk density of 52 pounds per cubic foot. Best results were obtained using 60 percent by volume processed ash as an additive, increasing sorptivity to 29.44 percent and lowering bulk density to 3l.8 pounds per cubic foot.


Toxicant-carrier granules made from clay are used in greater amounts each year, especially in the corn belt. Granules made exculsively from Kansas bentonite have a relatively low sorptive capacity but have other toxicant-granule interaction characteristics that appear to produce more effective field results when compared with other commercial carrier granules. The primary purpose of this study was to increase the sorptive capacity and lower the bulk density of the bentonite granules and still retain the desirable characteristics that produce the more effective results.

Because there is, in our opinion, no suitable standardized test that gives reproduceable results to determine free-flow sorptive capacity of clay carrier granules, we devised the following test procedure which, when followed carefully, will give a true indication of sorptive capacity for free-flow granules.

The apparatuses used in running this test were a warming oven, a dessicator, a balance (accurate to 0.1 g), a 10-ml burette (0.05 ml divisions), 12 250-ml glass beakers, and a stop watch. The sorptive capacity of a clay granule, calcined or oven-dried raw, is determined by adding kerosene (specific gravity 0.80 @ 23 °C) to a 10-g sample of the granules contained in a 250-ml glass beaker until at the end of a 3-minute test period, the granules are saturated but still free-flowing. At no time is a spatula or stirring rod used to mix the granules. Time, initial and end rate of introduction of kerosene, thorough mixing, and determination of endpoint are critical to obtain consistent results; therefore the procedure must be followed carefully. Experience will enable the tester to obtain consistent results. When possible, tests on granules with known sorptive capacity should be run before running tests on unknown material. At least four preliminary tests should be run on the sample to be tested in order to determine what the sample should look like at the three-minute end-point.

Procedure for conducting the test is as follows:

  1. Dry sample at 105 ± 5 °C for 3 hours. Mix and cool in a dessicator.
  2. Weigh 10 g of dried sample accurately on a triple-beam balance and transfer to 250-ml glass beaker.
  3. Read kerosene level on burette to nearest 0.01 ml by estimation and record.
  4. Timing:
    1. First minute: Start stop watch. Introduce one-half to three-fourths the required amount1 of kerosene to saturate granules during the first minute. Granules must be in continuous rapid motion while kerosene is being added. Mix thoroughly with a quick rotary wrist motion of the hand-held beaker. Caution: Do not swirl granules out of beaker. [1 As determined from preliminary tests referred to in paragraph above.]
    2. Second minute: Add kerosene in rapid drop-by-drop amounts, mixing with quick rotary motion until granules begin to appear wet but are still free-flowing. Care should be taken not to oversaturate.
    3. Third minute: Add kerosene slowly drop-by-drop, mixing thoroughly until granules tend to adhere to one another. Close visual inspection away from burette is necessary. The end-point is reached at 3 minutes after start of test when the free-flow is retarded by a tendency for the granules to agglomerate, and when a thin film of kerosene adheres to the edge of the beaker. The end-point is critical and should be the same each time a test is run for a particular class of material to assure uniform results. The end-point is exceeded when granules appear wet, are not free-flowing, and adhere to beaker and to each other to form 1/8-inch or larger masses.
  5. Read the burette and record.
  6. Run three samples and average amount of kerosene absorbed.

Sorptive capacity is calculated as follows: average ml of absorbed kerosene X specific gravity (0.8) X 10. The procedure for cleaning the equipment is:

  1. Rinse with NaOH solution.
  2. Rinse with distilled water.
  3. Rinse with isopropyl alcohol.

An alternate method is to flush equipment with acetone.

Phillips County bentonite calcined at 1200° F produces a granule with a 16-percent maximum sorptive capacity for free-flow and bulk density of 52 pounds per cubic foot. Because of the close association and genetic relationship between bentonite and volcanic ash, volcanic ash was selected as an additive to increase the sorptive capacity, at the same time retaining the desirable properties of the 100-percent bentonite granules already tested. Additional tests must be conducted in the laboratory and in the field to determine the reactive effect on toxicants and performance in the field.

Two types of Long Island bentonite samples were prepared for the test. One sample was slaked in water, thoroughly mixed and spraydried. The second was oven-dried and ground to -40 mesh. Both samples were then mixed with various proportions by volume of raw Calvert ash, bloated Calvert ash, and crushed, bloated Calvert ash. Water was added in measured amounts to the dry ash-bentonite mixes and blended with a wire beater to the point where the bentonite-ash mixture agglomerated into distinct granules or pellets. The material was then fired at 1200° F, crushed, and screened to obtain a 16-40-mesh-sized granule. Sorptive capacity and bulk density was determined for each sample (Table 1).

Table 1--Test results on bentonite granules with volcanic ash additives.

Mixture and proportions Sorptive
By volume, % By weight, g
Bentonite Calvert ash Bentonite Calvert ash H2O, cc†
SD* G* R* B* CB*
1 80     20   214.0 5.3 110 20.64 41.3
2 60     40   160.5 10.6 90 21.60 37.6
3 40     60   107.0 15.9 90 28.72 29.7
4 80   20     214.0 42.0 100 23.2 39.7
5 60   40     160.5 84.0 90 23.84 37.1
6 40   60     107.0 120.0 80 24.32 36.4
7 80       20 214.0 10.5 100 19.04 42.3
8 60       40 160.5 21.0 100 22.56 37.7
9 40       60 107.0 31.5 85 25.92 34.1
10 40   60     107.0 126.0 100 24.0 36.3
11   80   20   208.0 5.3 110 19.92 41.6
12   60   40   156.0 10.6 90 22.56 37.4
13   40   60   104.0 15.8 70 28.96 30.7
14   80 20     208.0 42.0 100 19.20 44.3
15   60 40     156.0 84.0 90 26.36 37.4
16   40 60     104.0 126.0 80 27.12 35.2
17   80     20 208.0 10.5 100 21.20 43.5
18   60     40 156.0 21.0 90 24.24 37.6
19   40     60 104.0 31.5 80 29.44 31.8
20   40 60     104.0 126.0 100 24.96 35.9
SD = spray dried; G = ground, oven-dried (-40 mesh); R = raw ; B = bloated ; CB = crushed & bloated.
† H2O added to bentonite-ash mixture (in g),

In summary, sorptive capacity of clay granules was increased from 16 percent for composite samples of calcined bentonite to 29.44 percent granules made from 40-percent bentonite and 60 percent by volume of crushed, bloated volcanic ash, pelletized and calcined. Bulk density decreased from 52 pounds per cubic foot to 31.8 pounds per cubic foot. A blend with 60 percent raw ash and 40 percent bentonite by volume produced granules with 27.12 percent sorptivity and bulk density of 35.2 pounds per cubic foot.

Raw ash as an additive to bentonite for the purpose of increasing sorptivity and descreasing bulk density produces slightly less benefit than processed ash; therefore, it should be more economical for the results achieved.

Kansas Geological Survey, Toxicant-Carrier Granules from Kansas Bentonite With a Volcanic Ash Additive
Placed on web Oct. 4, 2016; originally published in March 1970.
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