Barite

Barite                  : BaSO4

Refractive Index   : 1.64-1.65
Specific Gravity   : 4.5
Mohs Hardness    : 3-3.5

The commercial significance of barite is related almost entirely to its high specific gravity. Most processed barite (90%) is used as a weighting agent in well drillling fluids. Its physical and chemical properties assume more importance for its filler applications and for its use as a source of barium.
Common mineral impurities in barite ores are quartz, carbonate minerals, sulfide minerals, and clay. Processing of barite depends upon ore purity and the nature of associated minerals. Drilling grades often require only crushing, grinding, screening, and milling. An intermediate washing step may be
employed to achieve required minimal specific gravity and BaSO4 content. Applications requiring high brightness and high chemical or mineralogical purity may necessitate flotation, bleaching with sulfuric acid, and wet grinding. 

Barite is also known as barytes and heavy spar. It is used as a source of bariuim in a number of barium compounds, including blanc fixe, a high-purity precipitated barium sulfate that is used in place of processed barite in certain demanding applications.

TYPES

Other than drilling fluid products, which account for most of production, barite is differentiated according to its chemical and filler uses.

 

Drilling grade

Barite for well drilling fluids is typically a 200 mesh product with specific gravity of at least 4.2 (i.e., >90% BaSO4 ). Color is not critical, but water-soluble alkaline earth metals are controlled so as not to interfere with drilling fluid rheology.

Glass grade 

Glass-grade barite is generally -30+140 mesh, with 96 to 98% BaSO4, <2.5% SiO2, and <0.15% Fe2O3. Iron and slica content may be further restricted for specific uses, and there may be limits on TiO2 and Al2O3.

Chemical grade

Barite for barium chemicals is -16mm+0.84mm (20 mesh) and contains at least 95% BaSO4, <1% SrSO4, <1% combined iron oxides, and no more than a trace of fluorine.

Filler grade

Filler uses for barite generally require high brightness, high purity, and fine particle size, usually -325 mesh or finer. Purity is typically highest quality filler grades are made by flotation, followed by wet grinding, bleaching with sulfuric acid, washing, drying, and milling.

Blanc fixe

Blanc fixe is precipitated barium sulfate for uses where higher brightness and purity and finer particle sizes are required than are generally available with barite. The precursor to blanc fixe is common to most barium compounds made from barite. Crushed barite is first roasted with coke in a rotary kiln at about 1200oC. This reduces the barium sulfate to barium sulfide in the form called black ash. The hot black ash is quenched in water and countercurrent leached to produce a barium sulfide solution. Blanc fixe is produced by treating this solution with sodium sulfate to precipitate ultrafine barium sulfate. This is then filtered, washed, milled, and dried.

Lithopone

Lithopone production starts with the same process used for blanc fixe, except that zinc sulfate is used in place of sodium sulfate. The intimate mixture of barium sulfate and zinc sulfide that precipitates is filtered, washed, dried, calcined, water quenched, wet ground, and dried. The result is a white mixture of barium sulfate, zinc sulfide, and zinc oxide. Lithopone was one of the first fine white pigments for industry but is now rarely used.

USES

Annual production of barite worldwide is approximately 5.4 million metric tons, dominated by China (33%), India (11%), and Morocco (8%). Ground barite for well drilling fluids accounts for 90% of all production. The balance is used in the manufacture of barium chemicals and glass and in filler applications.

Well drilling fluids 

Drilling fluids are designed to cool the drill bit, lubricate the drill stem, seal the walls of the well hole, remove cuttings, and confine high oil and gas pressures by the hydrostatic head of the fluid column. A high specific gravity fluid is required to maintain sufficient hydrostatic pressure to control hydrocarbon release and prevent gushers and fires. Barite is uniquely suited as the weighting agent because it is heavy, chemically inert, and nonabrasive. The deeper the hole the more barite is used, because hydrocarbon pressure rises strongly with depth below about 2100 meters. In most drilling
fluids barite is the major ingredient by weight percent.

Glass

In glassmaking barite saves fuel by reducing the heat-insulating froth on the melt surface. It also acts as an oxidizer and decolorizer, making the glass more workable. It reduces seeds and annealing time and improves glass toughness, brilliance, and clarity.

Coatings

Paints and primers represent the largest use for filler-grade barite. High-brightness micronized barite is used as an extender to provide the weight that customers equate with quality and because of its low binder demand, which allows high loadings. Blanc fixe is used where a finer particle size is needed for denser packing of the paint film, as in premium metal primers, and to provide resistance to corrosion by acids and alkalis. Despite their high brightness barite and blanc fixe have poor hiding and tinting strength because they are close to the refractive index of binders. They function instead as extenders and spacers, keeping the pigment particles separated and uniformly disseminated to optimize light scattering.

Polymers

Finely ground barite is used in rubber, where its weight, inertness, isometric particle shape, and low binder demand are advantageous. It has little effect on cure, hardness, stiffness, or aging. It is used in acid-resistant compounds, in white sidewalls for tires, and in floor mats. Blanc fixe fine enough to be semireinforcing is used to provide the same compound softness and resilience as barite but better tensile strength and tear resistance. Barite is used in PVC and polyurethane foam backings for carpeting and sheet flooring because of its ability to form dense coatings due to its high specific gravity and its ability to be used at high loadings.

Other uses

Because barium sulfate is insoluble and opaque to X-rays, blanc fixe meeeting pharmacopeia specifications is used as an indicator in medical X-ray photography. Natural barite is used in concrete for the construction of facilities handling nuclear materials because it absorbs gamma radiation.
Micronized white barite and blanc fixe are used as fillers and extenders, primarily to add weight, in bristolboard, playing cards, and heavy printing papers. Blanc fixe is used in the base coat of photographic papers to supply an inert substrate for the silver halide emulsion coat. Finely ground (-325 mesh) barite is used as an inert filler in brake linings and clutch plates.