Fillers and Pigment

Fillers are a special type of pigment that serve to thicken the film, support its structure and

simply increase the volume of the paint. Fillers are usually made of cheap and inert materials,

such as diatomaceous earth, talc, barytes, lime, clay, etc.

Pigments are granular solids incorporated into the paint to contribute color, toughness, or simply

to reduce the cost of the paint. There are three classes : (1) natural mineral pigments, (2)

pigments made by burning natural minerals and (3) manufactured paints. Some pigments are

toxic, such as the lead pigments that are used in lead paint.

Fillers

1. Diatomite

Diatomite is also known as Kieselguhr, is a sediment derived from the siliceous skeletons of tiny

diatoms i.e. algae mostly living in fresh water lakes. The sediments are fine grained, highly

siliceous, and consist of amorphous opaline silica with only minor amounts of organic residue,

secondary minerals, and co-deposited nondiatomaceous or crystalline clastic debris. Diatomites

occur within Tertiary to Recent lacustrine and marine sedimentary facies. Although diatomite is

widespread throughout the world. Deposits that contain high purity, commercially versatile ore

are uncommon. Diatomites used in filter medium, water and lubricants but also as a light filler

and polishing abrasives.

Physical properties

It shows fine structure, low bulk density, high porosity, and high surface area. It shows mild

abrasiveness, high absorptive capacity, and high brightness. Low bulk density distinguishes

diatomite from all other fine-grained sediments. High brightness or whiteness is an additional

and distinctive attributes of nearly pure diatomites. Industrial use diatomite needs to contain

>60% amorphous silica.

The fundamental chemical composition and intricate structure of the diatomite give diatomite

commercial value and versatility in filtration and filler applications.

The general chemical composition of the diatomite occurred in Nevada(USA) and chemical

composition of Tanzanian diatomite(Kagera)

Constituents Nvada Tanzania__________

Silica(SiO2) 89.75 76.94

Alumina(Al2O3) 3.08 11.94 (both Alumina and Iron)

Iron oxide(Fe2O3) 1.33

Titanium Oxide(TiO2) 0.14 Trace

Phosphate(P2O5) 0.04 Trace

Lime(Cao) 0.41 Trace

Magnesium(MgO) 011 No

Sodium(NaO) 0.19 No

Potassium(K2O) 0.22 No

Ignition loss 4.70 4.00

Fluorite 1.35

________________________________________________________________________

Origin & Occurrence

Diatomite is a fine- grained siliceous sedimentary rocks or unlithified sediment or biogenic

origin. Diatomite thrives in divers environments including marine, brackish and

lacustrine/streams. It is chiefly composed of amorphous silica, present in the form of opaline

diatom skeletons imparts low density and high surface area to milled powders. The melting

point of diatomaceous silica ranges between 1400 and 1750 degree centigrade.

Occurrence in Tanzania

Better quality occurs in the valley of the Kagera river in the Kagera region and also lies near the

Nyankanasi river point. Thickness of the beds 0.2m to 1m shows light brown or grey color in wet

and it dry white in color. Impure diatomaceous earth have been reported from Mbeya, Rukwa

rift. Its silica percentage is ranges from 42 to 57wt% Sio2.

Other uses

Diatomite filler is used as a processing aid in rubber manufacture, and as a mild abrasive in

polishes and cleaners and agrochemicals.

Economics

Freight costs have a significant impact on the overall cost of products to the customer because

of their low density; as a result, transport cost per ton is high.

2. Barytes (BaSO4)

Barytes is one of the important industrial minerals. Its name was derived from the Greek word

barys meaning heavy, and so the mineral is also named as heavyspar. It is usually colourless

or white, often tinged with yellow, red and brown. It has streak, and vitrious to resinous and

sometimes pearly luster.Its hardness is 3-3.5 and specific gravity 4.5.

Uses

Some 77% worldwide is used as a weighting agent for drilling fluids in oil and gas exploration to

suppress high formation pressures and prevent blowouts. Other uses are in added-value

applications which include filler in paint and plastics, sound reduction in engine compartments,

coat of automobile finishes for smoothness and corrosion resistance, friction products for

automobiles and trucks, radiation-shielding cement, glass ceramics and medical applications.

Baryte is an important raw material for extraction of barium metal which does not occur in native

state.

Mode of occurrence and origin

Baryte occurs in a large number of depositional environments, and is deposited through a large

number of processes including biogenic, hydrothermal, and evaporation, among others. Baryte

commonly occurs in lead-zinc veins in limestones, in hot spring deposits, and with hematite ore.

China is the worlds largest producer of barytes with output around 0.9 million tonnes a year

followed by India, USA, Russia and Mexico.

Occurrence in Tanzania

Barite occurs as a gangue mineral in number of mineralized gold and base metal veins in the

western Rift zone of Tanzania in the Lupa gold, Musoma and Mpanda goldfields. Sedimentary

Baryte deposits occur in the Kigoma and Handeni areas.

3. Talk, soapstone and steatite (Mg 3 (Si4 O10) (OH)2

In loose form, it is the widely-used substance known as talcum powder. It occurs as foliated to

fibrous masses, its crystals being so rare as to be almost unknown. It has a perfect basal

cleavage, and the folia are non-elastic, although slightly flexible. It is the softest known mineral

and listed as 1 on the Mohs hardness scale. It can be easily scratched by a fingernail. It is also

sectile (can be cut with a knife). It has a specific gravity of 2.52.8, a clear or dusty luster, and is

translucent to opaque. Talc is not soluble in water, but it is slightly soluble in dilute mineral

acids. Its colour ranges from white to grey or green and it has a distinctly greasy feel. Its streak

is white.

Mode of occurrence and origin

Talk occurs commonly as lences and pockets in metamorphosed dolomite, crystalline schists or

gneisses and as large bodies in ultrabasic rocks. It is often associated with serpentine, chlorite,

asbestos. Actinolite, tourmaline and magnetite. It is formed as secondary mineral resulting from

hydrothermal alteration of magnesium bearing rocks.

4. Clays ( Bentonite and kaolin)

Bentonite

An impure clay, primarily montmorillonite. Two types of bentonite are generally identified. One is called

the swelling type or sodium bentonite, which has single water layer particles containing Na+ as the

exchangeable ion. The other has double water layer particles with Ca++ as the exchangeable ion. It is

called calcium bentonite or non-swelling type. The difference in bentonite and other clays lies in lattice

structure. The sheet of atoms in bentonite are much thinner and more easily separable in water. That is

why bentonite occupies more surface area than other clays. This property is known as dispersibility,

which is unique to swelling type of bentonite.

Uses

Bentonite has great water binding ability and consequently very low permeability to water. It has been

found, that the prmeability of the soil is reduced considerably when substituted by sodium bentonite.

Hence, this material is often employed in construction engineering ot make a porous medium water-tight.

It can be used alone or with some other grouting material.

Bentonites having low iron content, have been found to be good catalytic agents in petroleum refining.

The bentonites having Ca and / or Mg as exchangeable ions are good decolourizers. Bentonites can

absorb water to a greater extent than ordinary plastic clays. Fuller's earth, on the other hand, is non-

plastic or semi-plastic in character.

Drilling muds consist of water to which sodium bentonite and pulverized barytes are added. Such muds

are prepared mainly for deep drilling, like oil-well drilling. Bentonite imparts two properties :

It gives the fluid a viscosity several times that of water.

It seals the wall of the holes, thus preventing water loss.

Mode of occurrence and origin

Bentonite is found associated with lake and marine shales and sandstones and volcanic galss.

Bentonite is regarded to have been formed by the alteration of volcanic ash deposits, mostly in

upper Cretaceous formations. Fuller's earth represent a shaley facies of Tertiary rock.

Vermiculite (Mg,Fe++,Al)3(Al,Si)4O10(OH)24(H2O)

In commerce, vermiculite which expands more than 10 times the original volume is regarded of

good quality. With an expansion below 10 times the original volume, vermiculite is considered of

low grade.

Distribution in Tanzanaia

Bentonites occur in a deposit at Oldinyo Gelai in the noth-western part of the Arusha district. At

Minjingu greenish smectite bearing clays occur along with acidic volcanic rocks. Other places

like Sinya bentonite deposits occur at Kenyan-Tanzanian border at Lake Amboseli.

Pigments.

Natural pigments include various clays (ochers), titanium, lime, mica, and talcs.

OCHRE

Ochre is a natural earth containing silica and clay decorated by hydrous forms of iron oxide,

such as yellow-brown limonite or brown-yellow to green-yellow goethite, and traces of gypsum

or manganese carbonate (Umber).

Limonite is a general term used to describe all forms of hydrated iron oxide minerals (FeO(OH))

that occur as natural clay.

The amount of iron oxide (Fe2O3) in ochre is quite variable. It may be as low as about 20%,

going up to 70%. Depending upon the content of hydrated iron oxide, the color of ochre varies

from light yellow to golden to orange. Umber is a greenish brown containing some 45% Fe2O3

and 15% MnO2.

It is used for colour washes, distemper and oil paints. It is also used in making coloured paper.

Mode of occurrence and origin

Ochres occur as an alteration product of their iron minerals or by degradation of highly

ferruginous rocks in the form of weathered residual concentrations. They are ferric hydroxide

mixed with clay and other impurities. The minerals that are unstable under weathering

conditions suffer chemical decay, the soluble parts, like silica, may be removed and the

insoluble residues, mainly iron-oxides and other impurities may accumulate in the form of

ochres.

ilmenite, rutile

TiO2 is manufactured from the minerals ilmenite, rutile which are primarily sourced from

mineral sand deposits, but also can be processed from hard rock deposits.

Titanium dioxide (TiO2) is a white pigment that is a key ingredient of paints, paper and plastics.

For white products, TiO2 is the material of choice as it is the brightest and whitest commercially

available pigment.

Zircon is commonly tied up with titanium mineral deposits so most producers also sell quantities

of zircon. For few it is the primary focus, but for many miners it is a high-value, by-product

bonus.

Supply

In terms of mineral production, Australia and South Africa are leading producers. Since 2008/09,

new African sources have come online in Mozambique and Madagascar.

Rutile has almost double the TiO2 content at 92-95% TiO2 but is less abundant than ilmenite.

The biggest commercially active sources are in Australia and Sierra Leone.