Borates

How borates are formed
While boron is ubiquitous in the environment, substantial deposits of borates are relatively rare.

Borates are minerals formed when boron, a naturally occurring element, combines with oxygen and other elements. It takes vast amounts of borate minerals concentrated in one place to make a deposit worth mining. It also takes millions of years for the deposit to form.

The borate deposits at Rio Tinto Mineral's principle mine at Boron California, for instance, began life about 19 million years ago as a basin formed by several active lava flows across the landscape. Over several thousand years, water collected in the basin, forming a lake. Clay from surrounding rock formed an impermeable layer at the bottom of the lake. Hot springs rich in boron flowed into the lake, quickly cooling to form borax crystals. Then, another layer of clay washed in, effectively sandwiching the borax deposits in between two layers of clay.

About 16 to 18 million years ago, the lake dried up, leaving borax crystals embedded in the clay. Over time, the clay became covered by layers of sand, which bury the deposit more than 2,000 feet underground.

Tectonic movement, combined with years of erosion, eventually force the borax deposit upwards, to as close as 150 feet from the surface.

Mining borates
A combination of drilling, blasting and shovelling is used to mine borates. Drilling is an important part of exploration for deposits to mine. It is also used for digging blast holes. Explosives in blast holes loosen the sandstone covering the deposit (called the overburden), giving access to the ore beneath.

Once the ore and overburden are loosened, rubble is scooped from the bottom of the mine using huge shovels and dumped into haul trucks. Each shovel stands seven storeys tall and is able to lift 80 tonnes per load.

Haul trucks transport the mined ore to crushers, where the ore is crushed before refining. Crushers reduce the ore into one-inch pieces, increasing the ore's surface area to make the refining process more efficient. Crushed ore is transported out of the mine to the refinery via an extensive system of conveyors.

Refining borates
Rio Tinto Minerals uses six steps to transform raw ore into more than a million tonnes of refined borates every year:

1. Dissolving: Crushed ore is mixed with hot water to create "liquor" - a combination of borates and water. The borates dissolve in the water, while screens remove insoluble material such as rocks, sand and other solids.
2. Settling: The saturated borate solution is then pumped into large settling tanks called thickeners. As the rock and clay mixture is heavier, it settles in the bottom of the thickener, leaving borates dissolved in the liquor.
3. Crystallising: Liquor is transported to tanks called crystallisers, where the solution cools. The cooling forces the borates to crystallise, forming a slurry of borate crystals and water.
4. Filtering: The slurry is poured over special filters and washed to ensure its purity. Water from the filtering process is drawn away by a vacuum located beneath the filter.
5. Drying: The damp borate crystals are then transported to huge, rotating dryers where hot air is used to finish the crystal drying process.
6. Conveying: Dry borates then drop into a conveyor belt that transports the borates for storage, or packing and shipping. Refined borates are stored in 100-foot silos or 20,000 tonne domes.

Borate samples are taken at each stage of the process for quality testing. On-site laboratories allow instant analysis of samples and adjustments to the process.

Uses for borates
Borates are safe - posing no risk to people, animals or the environment under normal handling and use - and versatile - in many applications, there is no substitute for borates. The following are some key effects and uses of borates:

• In certain organisms, borates can inhibit metabolic processes. This makes them useful in controlling insects, bacteria and fungi in everything from construction timbers to cosmetics.
• Another key chemical effect of borates comes into play in laundry detergents and other cleaning products, where borates are important components in bleaching and stain removal.
• The chemical properties of borates serve to balance acidity and alkalinity in many applications. Detergents, fireworks and film processing solutions all rely on borates for a stable pH.
• Borates are able to bond with other particles to keep different ingredients dispersed evenly and are used to control viscosity in paints, adhesives and cosmetics.
• Borates modify the structure of glass to make it resistant to heat or chemical attack. In the same way, they facilitate the production of ultra-thin LCD screens, functional fibreglass and beautiful ceramic tiles and glazes.
• Borates interact with surfaces containing iron to form a coating which protects the metal from corrosion. They are important additives in products as diverse as antifreeze and aerosol cans.
• Combined with zinc, borates are used to retard flames and suppress smoke in polymers that coat electrical cables. Borates also act as a flame retardant in cellulose insulation.
• Borates absorb neutrons in applications ranging from nuclear containment shield to treatments for cancer.
• Plants need borax to grow, making borate an important agricultural micronutrient in the production of fertilisers and crop nutrient sprays.

Further information about our borate operations, please visit the Rio Tinto Minerals website.

For more information on our other products, see our corporate fact sheets.