MATERIALS AND METHODS

3.1. PARTICLES

CHAPTER 3

color to remove obvious impurities such as massive serpentine or large magnetite fragments, suspended in deionized water and sonicated to

release fibers. Separation involved diluting, stirring with a magnetic bar to collect magnetite and decanti ng to remove larger, heavier material. It was assumed that impurity brucite would dissolve away; the dissolution rate for brucite is about 1000-fold faster than that for chrysotile. The lack of excess magnesium in the processed

ore was taken as evidence that impurity brucite was not present.

Separation of magnetite fran chrysotile by sonication and stirring in water occurred within minutes. Simple grinding fails to separate the two minerals (Allen & Smith, 1975).

After gravity settling, suspensions were centrifuged to separate solids fran supernatant. Resulting solids were washed with deionized water and recentrifuged until the centrate reached a constant

conductivity. The paste was then dried in an oven at 70 C. The dried cake was placed in an alumina dish with a movable puck and crushed by oscillating for 30 seconds in a Spex Shatterbox. By this procedure about 50 grams of raw ore can be processed in one day, yielding about 30 g rams of fi be rs.

Sane initial consideration was given to making synthetic chrysotile, but physical characteristics of the resulting fibers (Yang, 1961) do not resemble those of the natural material found in Cal Hornia. Further, synthetic fibers may contai n rel atively high

1. hand sort

\tt

• ~ • 1 f

....

-

4. settle, centrifuge, wash a recentrifuge

2. suspend

a

sonicate

~ _~

5. dry

3. magnetic stir a decant

6. crush

Fig. 3.1. Chrysotile ore purification procedure.

Chemical canposition of the purified ore was determined by digestion in HF and aqua regia in a teflon banb (Bernas, 1967) usi ng the molybdate-bl ue method of St rickl and and Pa rsons for si 1 i ca (Fanning & Pilson, 1973) and atanic absorption spectrophotanetry (AAS) for cations. Na

2SiF

6 was used as a silica standard and Baker analytical standard (1 mg/ml in HN03) for magnesium. Results are listed in Table 3.1. Iron accounts for about 3.4 percent of the cation in the octahedral layer. A similar level is reported in a typical analysis by Union Carbide, also listed in Table 3.1. The more extensive analyses of Mumpton and Thanpson (1975) are shown as well.

In addition, the purified are contains about O.S percent magnetite, determined fran the amount of residue collected on the magnetic spin ba r in one fi ve-day, constant-pH expe riment.

The resulting chemical formula for the analyses done as part of this work is (Mg,Fe)3Si2.20S.1(OH)4' versus Mg 3Si 20S(OH)4 for pure serpentine. The magnesium to silica ratio in this work is lower than for the other reported analyses. Apparent molar ratios of magnesium plus i ron to sil ica are 1.36 in the current work, 1.S4 for the Uni on Carbide analysis and 1.S7 for Mumpton and Thanpson's analyses.

Analysis of centrate fran ore purification showed dissolved magnesium concentrations near 2 mg/L; this is much lower than the nearly 100 mg/L needed to account for the reported differences. Rather, the differences are assumed to be due to different purificati on and cleaning procedures, as well as raw-material differences.

Weight Pe rcent This

Uni on Ca rbi dea Thanpsonb

Component Work Mumpton &

MgO 39.70 41.9 42.41

Si02 45.44 42.8 41.40

A120

-

< 1 0.5 0.13

Fe20

3 4.62 4.0 5.02

CaO 0.18 0.11 0.26

NiO 0.03 0.33 0.03

Mn02 0.09

- -

K20 0.15

- -

Na20 NOc

- -

H20 & CO

2 9.8d

13.5 13.47

aAnalysis supplied by Union Carbide Corp., with ore.

bAverage of three reported analyses; reference: Mumpton and Thompson, 1975.

c None detected.

dEstimated by subtracti ng sum of other components from 100.

Quebec chrysoti1e was detennined by extraction with benzene and

cyclohexane to be from 0-50 ppm (Gibbs, 1971). The extract contained a peak at C

2, with a unimodal distribution about that point. It is not known if the organics are part of the crystal or are adsorbed on the surface. The organic material is thought to have its origin either: 1) fran circulating groundwater, 2) of magmatic origin, 3) of

sedimentary origin, or 4) fran distillation of pre-existing oil pools.

Percolation of surface water and sample contamination during

processing were considered unlikely. Speil and Leinweber (1969) also note that chrysotile contains natural organic impurities. They report that cyclohexane extraction of 11 U.S. and Canadian milled samples yielded fran 40-500 ppm organics.

3.1.1.3. Chrysotile Physical Characteristics

The surface area of the purified fibers, measured by si ng1 e-poi nt BET nit rogen adsorpti on usi ng a Quantasorb system

(Quantachrane Corporation), ranged fran 46.3 to 57.7 m2/g. A representative value is 48.5 m2/g; this is used in subsequent cal cul ati ons.

Figure 3.2 shows the distribution of fiber lengths in the purified ore; also shown are the overall distributions for samples taken fran the Feather river and fran Metropolitan's source-water reservoi rs

(McGuire et al., 1982; Bales et al., 1984). The natural-water samples have a flatter distribution, reflecting breakup of the larger fibers and disappearance of the smallest size particles. Techniques for

PURIFIED ORE 6//

---..;/

A't/

AI N

tI

*'

, p ,t

/

..c. ..

1.0

-

^0\C

--l

0.5

0.2

METROPOLITAN RESERVOIRS

0.1 0.5 2 5 10 20 40 60 80 90 95 98 99.5 99.9

Fraction

Stated Length

Fig. 3.2. Chrysotile size distribution; values for purified

ore from transmission electron microscopy analysis of 500

fibers; includes both single fibers and fiber bundles.

fran raw ore without intense gri ndi ng. Langer et al. (1978) report nearly the same size distribution for Calidria ore dispersed in one percent amyl acetate. Following milling for one minute, their size distribution was shifted down and to the right, with a slope nearer

that of the natural-water samples on Figure 3.2. Longer mill i ng shifted the size distribution further down and to the right.

Spurney at ale (1979) note that although use of wetti ng agents or organic solvents such as methyl alcohol, ethyl alcohol, isobutyl alcohol, etc. facilitates prepari ng chrysotile suspensions, these

organics may adsorb and change surface physical-chemical properties, making the resulting fibers unsuitable for representative biological experiments. These investigators used only double-distilled water to suspend fibers during the sample preparation. They state that surface properties in an aqueous suspension remained practically unchanged du ri ng fiber si ze-separati on experiments.

Langer et ale (1974) noted that gri ndi ng Quebec chrysotile ina Waring blender for 30 minutes produced irregular rather than straight fiber edges; some fibers exhibited a defonned and collapsed central capillary. Spex milling produced sane crushed fibers, but no

irregular edges were noted. Speil and Lei nweber (1969) show an electron micrograph of Spex-milled chrysotile in which none of the origi nal structure is evident. X-ray diffracti on confi nned that the fiber structure was destroyed. They suggest that structural changes we re caused by manenta ry 1 oca 1 i zed tempe ratu re su rges ; n a fi be r as it

absorbed the impact energy. They confi nned this by c011pari ng fibers that were ball milled wet versus dry. Wet milling precludes high localized temperatures. Langer et al. (1978) also note physical structural and surface damage as well as decreased hemolytic activity for fibers as milling time is increased.

The above considerations indicate that the short milling time (30 seconds) used in the present work had little effect on the size

distribution of fibers originally present in the are. Also,

sonication produces fibers with a size distribution similar to that achieved with an organic dispersing agent -- amyl acetate in the work by Langer et ale (1978). The purified ore exhibited

electron-diffraction patterns characteristic of chrysotile and revealed no damage due to processing. Figure 3.3 shows typical transmission electron micrographs of the purified ore and of fibers separated fran natural waters.

3.1.2. Brucite

Th ree different Mg(OH)2 mate ri a 1 s we re used. I niti al potentiometic surface-charge experiments were done with Mg(OH)2 powder reagent (MC/B Manufacturing Chemists), which is ~ 95 percent magnesium hydroxide. BET surface area, measured by single-point nitrogen

adsorption, is 45 m2

/g. The second and third were natural brucite (Mg(OH)2) from a mining area in Nevada and are tenned Lodi brucite and Gabb brucite, respectively. Both were obtained as rocks, through Wards Natural Science Establishment, Rochester, New York. The raw ore was broken and hand sorted to remove obvious impurities, then crushed with a mortar and pestle. Analyses by the same method as above for chrysotile indicated that the first material was about 48 percent

-..

...

^~- ^.

Fig •. 3.3. Electron micrographs of chrysotile fibers; a) from

chrysotile are, b) in California aqueduct sediment.

Mg(OH)2 and the second material was 100 percent Mg(OH)2' Surface areas were measured to be 0.67 and 1.96 m 2 /g respectively.

3. 1. 3 • A 1 LD11; num Ox ide

Adsorption experiments were carried out using "Aluminum Oxide e" (Alox), which is manufactured in Germany and was obtained fran Oegussa Corporation, Teterboro, New Jersey. It is reported to consist predanonantly of y-A1

2 0

3 (Kummert

Stumm, 1980). Prior to its use, the alLD11ina was washed once with 0.1 M NaOH and seven times with double-distilled water (Hohl & Stumm, 1976). The suspension was then centrifuged between washings, with sane loss of fine material in the centrate. The washed material was stored in distilled water for approximately one year prior to use. Stock suspensions for

experiments were made by drying a portion of the washed alumina at llO C, grinding lightly with a mortar and pestle to break large

aggregates, and transferri ng the requi red amount to 0.01 M NaCl solutions. Surface area of the washed material, measured by single-point BET nitrogen adsorption, is 82 m 2

/g. This is lower than the 100 m 2 /9 reported for the unt reated colloid and the 130 m 2

/g reported for the washed call oid by others (KurmJert

Stumm, 1980).

The lowe r val ue may refl ect both the removal of fi nes du ri ng washi

and failure to break aggregates before making surface-area

measu rements.

3.1.4. Silica Silica (Si0

2 ) was Min-U-Sil 30 obtained fran Pennsylvania Glass Sand Corporation, Berkeley Springs, West Virginia. The

manufacturer reports a silica content of 90.7 percent, a specific

(1976) and Young (1981); the latter noted 1 ittle difference in adsorption characteristics of cleaned versus uncleaned material.

5il ica was heated at 500 C for 24 hours to remove organic impurities.

It was then washed successively with 4 M HN0 3 and 4 M NaOH. Following each wash. silica was rinsed with double-distilled water until the pH of the supernatant was the same as the pH of the double-distilled water. Washed sil ica was dried overnight at 130 C. It was planned that many of the fines would be removed in the supernatants. The resulting particle size distribution (Figure 3.4) suggests that coarse material was lost. however.

3.2. OTHER MATERIALS AND CHEMICALS

Acid and base used for the constant-pH experiments was made from Dilut-it analytical concentrate (J.T. Baker). Other chemicals were reagent grade; solutions were filtered through 0.22 pm Millipore filters prior to use. Nitrogen gas was

~Matheson-grade."

containing less than 0.5 ppm CO 2 • Gas was further cleaned and humidified by bubbl ing successively through 5 M KOH and 0.5 M KOH and two vessels containing distilled water. Nitrogen-carbon dioxide mixtures were from Matheson, certified to be within one percent of the stated CO 2 content.

3.3. EXPERIMENTAL DESIGN

Insofar as possible, experiments were designed to model

conditions in water del ivered to Southern Cal ifornia through the east

____ Manufacturer

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