Applied Clay Mineralogy Phần 9 ppt

LIGHTWEIGHT AGGREGATE Certain common clays are used to produce lightweight aggregate.. Clay and/or shale, which is a common clay, is used as the raw ma-terial to make lightweight aggrega

goethite, the firing temperature and degree of vitrification, the propor-tion of alumina, lime, and magnesia in the clay material, and the com-position of the fire-gases during burning ( Butterworth, 1953 ) The best white firing clays contain less than 1% Fe2O3 B tan-burning clays con-tain between 1% and 5% Fe2O3, and red-firing clays contain 5% or more Fe2O3.

Common clays occur in a variety of environments and in many differ-ent rocks across all time periods of the geologic record The source clay material can be glacial clay, soils, alluvium, loess, shale, weathered and fresh schist, slate, argillate, and underclays or seat earths.

2 LIGHTWEIGHT AGGREGATE

Certain common clays are used to produce lightweight aggregate The American Society for Testing Materials has published a standard spec-ification governing lightweight aggregates for concrete (Code No

C330-53 T, 1955) The unit weight of fine lightweight aggregate cannot exceed

70 lb/ft3 and the unit weight of coarse lightweight aggregate cannot exceed 55 lb/ft3.

Clay and/or shale, which is a common clay, is used as the raw ma-terial to make lightweight aggregate The raw mama-terial is crushed and fed into a rotary kiln or sintering machine The raw material is heated rapidly up to the range between incipient and complete fusion The bloating and vesiculation require the presence of substances that release gas after fusion has developed a molten jacket around the particles to prevent the escape of the gas The molten jacket must be viscous enough

to prevent the escape of the expanding gas Conley et al (1948) and

Riley (1951) have investigated the causes of bloating Several factors are important, most of which are based on chemical and mineralogical composition.

Shales and clays containing illites, chlorite, some montmorillonite, and mixed-layer clays are the most promising sources to make lightweight aggregate A close relationship exists between the chemical composition and the bloating characteristics of clay and shale Riley (1951) concluded that the viscosity of the melt produced by firing is determined essentially

by the bulk chemical composition based on SiO2, Al2O3, and the total of CaO, MgO, FeO, Fe2O3, K2O, and Na2O in which optimum viscosity of the molten jacket might be expected Fig 19 shows the limits of bloating established by Riley (1951) This was verified by Murray and Smith (1958) in their study of some Indiana shales Clays and shales of various

Applied Clay Mineralogy 144

geologic age and from many formations are used to make lightweight aggregate ( Cole and Zetterstrom, 1954 ; Greaves-Walker et al., 1951 ;

Mason, 1951 ; Plummer and Hladik, 1951 ; Burwell, 1954 ).

REFERENCES

Burwell, A.L (1954) Lightweight Aggregate from Certain Oklahoma Shales Oklahoma Geological Survey, Mineral Report 24, pp 1–20

Butterworth, B (1953) The Properties of Clay Building Materials in Ceramics—

A Symposium Green, A.T and Stewart, G.H., eds British Ceramic Society, London, England, pp 824–877

Cole, W.A and Zetterstrom, J.D (1954) Investigation of Lightweight Aggregates

of North and South Dakota US Bureau Mines, Report of Investigation 5065, 1043pp

Conley, J.E., Wilson, H., and Klinefelter, T.H (1948) Production of Lightweight Concrete Aggregates from Clays, Shales, Slates and Other Materials US Bu-reau of Mines, Report of Investigation 4401, 121pp

Greaves-Walker, A.F., et al (1951) The development of lightweight aggregate from Florida clays Eng Ind Exp Station Bull Ser., 116, 1–24

Holdridge, D.A (1953) The Colloidal and Rheological Properties of Clays in Ceramics—A Symposium Green, A.T and Stewart, G.H., eds British Ce-ramic Society, London, England, pp 60–93

Hyslop, J.F (1953) The Action of Heat on Clays in Ceramics—Symposium Green, A.T and Stewart, G.H., eds British Ceramic Society, pp 186–200 Mason, R.S (1951) Lightweight Aggregate Industry in Oregon GMI Short Pa-per 21, 23pp

Murray, H.H (1994) Common clay Chapter in Industrial Minerals and Rocks, 6th Edition Carr, D.D., ed Society for Mining, Metallurgy and Exploration, Littleton, CO, pp 247–248

Murray, H.H and Smith, J.M (1958) Lightweight Aggregate Potentialities of Some Indiana Shales Industrial Geological Survey, Report of Progress

12, 42pp

Norton, F.H (1948) Fundamental study of clay, VIII, a new theory for the plasticity of clay–water masses J Am Ceram Soc., 31, 236

Plummer, N and Hladik, W.B (1951) Manufacture of lightweight concrete aggregate from Kansas clays and shales State Geol Surv Kansas Bull., 91, 1–100

Ries, H (1927) Clays, Their Occurrence, Properties and Uses John Wiley and Sons, New York, 613pp

Riley, C.M (1951) Relation of chemical properties to the bloating of clays

J Am Ceram Soc., 34, 1–20

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Appendices A–D describe the test procedures for identifying and evaluation of kaolins, ball clays, bentonite, palygorskite–sepiolite, and common clays The following tests apply

to all the above-mentioned clays:

1 X-ray diffraction to determine the mineral content of the crude and degritted sample

2 Percent grit (+325 mesh)

3 pH

4 Particle size distribution of the degritted sample

The identification of the clay minerals and the non-clay minerals is necessary to determine the amount and type of clay and non-clay minerals present For example, generally the quartz and micas are concentrated in the grit (+325 mesh) portion of the clay Also, the grit is generally removed from the clay during processing so that the percent recovery of the portion which is 325 mesh can be calculated

The pH of the sample gives an indication of the presence of soluble salts, which may be deleterious to the final product Some kaolins have an alkaline pH which may indicate the presence of calcium and sodium salts which if they cannot be removed by processing will cause high viscosity for paper use and cause a lower temperature of vitrification in ceramic utilization Also, in the use of kaolins in paint there is a conductivity maximum and the presence of soluble salts may cause a conductivity which exceeds the specification

In ceramic kaolins and ball clays, the presence of montmorillonite can cause excess shrinkage, slow casting rate, and a short and low temperature vitrification range

In bentonites it is necessary to identify whether or not the clay is a sodium, calcium, or magnesium variety This can generally be identified by the c-axis d-spacing as sodium montmorillonite has a 12.2 A˚ spacing and calcium and magnesium montmorillonites have

a 14.2–14.8 A˚ d-spacing

In kaolins, ball clays, bentonites, and palygorskite–sepiolite clays, a high grit per-centage is detrimental In common clays depending on the type of structural clay product for which it is used, a higher grit percentage may be tolerated

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Appendix A

COMMONLY USED TESTS AND PROCEDURES FOR EVALUATING KAOLIN SAMPLES

Commonly used tests and procedures for evaluating kaolin samples are as follows:

1 Crude clay X-ray diffraction

2 Crude clay moisture

3 Percent grit (+325 mesh) (screen residue test)

4 Degritted X-ray diffraction

5 Crude clay pH

6 Crude clay brightness

7 Degritted clay brightness

8 Crude clay particle size

9 Crude clay Brookfield viscosity

10 Crude clay settling procedure

11 Leaching and brightness test

12 Magnetic separation

13 High shear (Hercules) viscosity

14 Processed clay Brookfield viscosity

15 Processed clay particle size

16 Processed clay brightness

17 Conductivity measurement

1 X-ray diffraction: Pulverize about 2 g of sample to 325 mesh Press the pulverized clay in the sample holder Follow operating procedures of the X-ray diffraction unit

2 Crude clay moisture

2a Apparatus

Balance sensitive to 0.1 g

Ceramic dish

Drying oven to operate at 105721C

2b Procedure

Weigh 200 grams (to the nearest 0.1 gram) of crude clay into a ceramic dish of known weight Place in an oven set at 1051731C and allow to dry overnight Remove from oven and weigh to the nearest 0.1 gram

2c Calculation

% moisture ¼ weight loss

initial weight of clay100

3 Percent grit: material coarser than 325 mesh

3a Apparatus

325 mesh (44 mm) US standard sieve

Ceramic dish

149

Balance sensitive to 0.1 g

Drying oven to operate at 105721C

Sodium hexametaphosphate

Soda ash

Small brush

Waring blender

3b Procedure

Dry approximately 200 g of crude clay overnight at 105 1C Mix 5 lb/ton equi-valent calgon and 1 lb/ton equiequi-valent soda ash in 500 ml water and mix on the Waring blender Add 100 g oven dried clay to the mixer cup and mix on low speed for 3 min.Sieve the slurry through a 325 mesh sieve If a crude particle size

is needed, collect screened slurry in a bucket Rinse screen until all clay has been washed through the sieve Closely observe residue remaining on sieve If a significant amount of unblunged clay remains, rinse residue back into Waring container with 500 ml water and mix an additional 3 min Screen the sample as above Place screen in oven until dry Brush residue from screen using small paintbrush into a tared ceramic bowl Weigh residue to the nearest 0.1 g and record After sample is degritted, the 325 mesh portion should be X-rayed to determine the mineral content of the degritted sample

4 Degritted x-ray diffraction: Pulverize about 2 g of sample to 325 mesh Press the pulverized clay in the sample holder Follow operating procedures of the X-ray diffraction unit

5 Crude clay pH test

5a Apparatus

pH meter

Balance sensitive to 0.1 g

250 ml beaker

Deionized water

Spatula

5b Procedure

Weigh 40 g of pulverized clay into a 250 ml beaker Add 160 ml of deionized water and stir well with a spatula until free of ‘‘lumps.’’ Measure pH

6 Crude clay brightness

6a Apparatus

Brightness meter

Ceramic dish

Drying oven to operate at 105721C

Brightness ring and press

Micro-pulverizer

Balance sensitive to 0.1 g

6b Procedure

Grind the sample to a fine powder (o100 mesh) in a pulverizer Degritted kaolin should be pulverized for 2 min Do not use the mortar and pestle Pack the sample in the brightness meter holder using 32.65 lb of pressure

7 Degritted clay brightness: Dry the degritted clay and follow the procedure described in item 6

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8 Crude clay particle size

8a Apparatus

Balance sensitive to 0.1 g

Waring blender and container

Deionized water

Plastic 250 ml bottle

250 ml flask

1000 ml beaker

8b Procedure

Using the sample from the crude residue test, determine the percent solids using

a 250 ml flask Determine dry clay content in the 250 ml flask Dilute percent solids to 7% using a 1000 ml beaker and mix for 3 min in a mixer Weigh 200 g slurry (14 g dry clay) into a 250 ml plastic bottle labeled with the sample iden-tification Submit sample for Sedigraph testing

8c Sedigraph procedure

8c.1 Sample preparation

Prepare a 7% by weight solution of clay in water totaling 200 g (For dry clay use

14 g in 186 ml of water; for slurry clay determine the percent solids and calculate the necessary amount of water to add to reach a 7% solution at 200 g of total weight.) Mix on medium speed for 8 min in Hamilton Beach blender Agitate for 2–3 min using Lightnin mixer and pour sample into the Sedigraph cup 8c.2 Sample analysis

Follow procedure provided by Sedigraph

8d Apparatus

Bouyoucos hydrometer

1 l graduated cylinder (2.5 in diameter) (a larger cylinder may be used, i.e

1205 ml soil sample cylinder)

Rubber stopper to fit graduated cylinder

Thermometer

Constant temperature water bath (19.41C) (a constant temperature room may

be used if a water bath is not available)

High-speed mixer (Hamilton Beach Model 936)

Table 1: Temperature correction values for hydrometer reading

Table 2: KNcorrection coefficients for variation in viscosity of suspending me-dium

Table 3: Maximum particle size equivalents

Table 4: KLcorrection coefficients for a given hydrometer number

8.1 Particle size test, hydrometer method

8.1a Apparatus

Bouyoucos hydrometer

1 l graduated cylinder (2.5 in diameter) (a larger cylinder can be used, i.e

1205 ml soil sample cylinder)

Rubber stopper to fit graduated cylinder

Thermometer

Constant temperature water bath (19.41C) (a constant temperature room may

be used if a water bath is not available)

High-speed mixer (Hamilton Beach Model 936)

Table 1: Temperature correction values for hydrometer reading

Table 2: KNcorrection coefficients for variation in viscosity of suspending medium

Table 3: Maximum particle size equivalents

Table 4: KLcorrection coefficients for a given hydrometer number

8.1b Procedure

Particle size distribution is checked by adding 700 ml of deionized water to

50 g of clay (if a larger cylinder is used, the test specimen should be increased accordingly) and agitating it in the Hamilton Beach Model 936 or other high-speed mixer for 8 min on medium speed Transfer sample to a 1 l grad-uated cylinder and dilute to the 1000 ml mark Stopper and shake the cylinder

to mix the sample and place it in a controlled temperature bath Gently immerse the hydrometer into the cylinder, allow it to stabilize, and take reading Re-cord the temperature as well This is made easier by using a stopper to suspend the thermometer in place (If testing more than one sample at a time, be sure

to wipe off both the hydrometer and thermometer before placing them into the next sample to avoid contamination.) Read the hydrometer to 0.2 g/l and the temperature to 0.2 1C at 1, 3, 10, 20, 60, 100, 200, 300, and 400 min settling time

8.1c Calculations

To find the correct grams per liter, add or subtract the appropriate amount shown in Table 1 to or from the actual hydrometer reading To find the percent

in suspension, divide each of the corrected grams per liter by the highest reading Use the following equation to determine the corrected particle diameter at each sampling time:

Dt¼DaKLKN

where:

Dt¼particle diameter in microns

Da¼maximum particle diameter in microns from Table 3

KL¼hydrometer correction coefficient from Table 4

KN¼correction coefficient from Table 2

8.1d Theory

To determine particle size with a Bouyoucos hydrometer, use is made of Stokes’ law The maximum diameter of particles in a suspension, based on Stokes’ law for assumed conditions, is expressed by the following equation:

Da¼

ffiffiffiffiffiffiffiffiffiffiffi 30nL p 980ðG  G0ÞT

where:

Da¼maximum particle diameter in millimeters (equivalent spherical diameter)

n ¼ coefficient of viscosity of suspending medium in poise (in this case, 671F ¼ 0.0102)

L ¼ distance in centimeters through which the particles settled (32.5 cm)

G ¼ specific gravity of clay particles (2.65 assumed for this formula)

G0¼time period, in minutes, of sedimentation

The above equation gives only the apparent diameter since it assumes that L is a constant In order to use Stokes’ law to determine the diameter of the particle, it

is necessary to know the distance through which the particle falls

Applied Clay Mineralogy 152

The correction coefficient, KL, for a given hydrometer is computed as follows:

KL¼

ffiffiffiffiffiffiffiffi

HR

p L where:

HR¼H1þ1

2 h 

volume of hydrometer bulb area of graduate

L ¼ distance in centimeters through which the particles settled (32.5 cm) Further:

H1¼distance from the top of the bulb to the reading

h ¼ length of the bulb

Variation in viscosity of water at temperatures other than 671F (19.41C) is accounted for by the use of the correction coefficient, KN, and is expressed by the equation:

KN¼

ffiffiffiffiffi

n1 n r

where:

n1¼viscosity coefficient at a given temperature

n ¼ (0.102) viscosity coefficient of water at 671F (19.41C)

Thus making the final equation for the ‘‘equivalent spherical particle diameter’’:

Dt¼DaKLKN