The heart of Rio Tinto Minerals' borates business is the open-pit mine in Boron, California, one of two world-class borate deposits on the planet. Company founders began mining borates in 1872. What began as an underground mine was transformed into an open pit mine in 1957.
The mule teams that hauled borates out of our original mines in Death Valley are long gone, but the symbol endures in the 20 Mule Team Borax® product brand. In the marketplace, this brand is the mark of superior product quality and consistency, supply reliability, technical support and service.
Mining and refining
Rio Tinto Minerals mines approximately three million tonnes of borate ore every year from the Boron mine. It produces nearly half of the world's supply of refined borate products.
The mine measures 2.8km wide, 3.2km long and is up to 230m deep. More than 80 different minerals are found at this geologically unique site, including the four boron based minerals in greatest demand by industry: tincal, kernite, ulexite and colemanite.
Our processing plants produce such products as borax pentahydrate, borax decahydrate, and boric acid. Our fusing plants also produce anhydrous borate products. Each of our sites is ISO 14001 certified.
Although mining and refining are age-old activities, Rio Tinto Minerals continually improves its practices to raise productivity, ensure the safety of our team, and minimise environmental impact. At each stage of the process, borate samples are tested at on-site laboratories, allowing for instant analysis and adjustments.
Mining borates relies primarily on a combination of drilling, blasting and shovelling to collect ore, which is then hauled to massive crushing machines and, from there, to refinery centres.
Drilling and blasting
Drilling is an important part of exploration, and the best way to sample the type and purity of ore beneath the ground. Information about the deposit's location and composition is fed into a computer to develop long-term mine plans. Drills are also used to dig blast holes.
Explosives are used to blast loose the sandstone at the top of the deposit called overburden, and to loosen the boron ore below it.
Shovelling and hauling
Once the ore and overburden are loosened, enormous shovels scoop up the rubble from the bottom of the mine and dump it into haul trucks that can carry 220 tonnes each.
Ore from the mine must be crushed before it is refined. Powerful crusher machines reduce the ore to 2.5cm long pieces, increasing the ore's surface area to make the refining process more efficient.
Ore is transported out of the mine and throughout the refinery via an extensive system of conveyors.
There are six primary steps to refine raw ore into refined borates. The bulk of this process was developed at the Boron Operations:
- Dissolving - Crushed ore is mixed with hot liquor - a combination of borates and water. The borates dissolve in the water. Insoluble rocks, sand and other solids are removed using screens.
- Settling - The saturated borate solution is pumped into large settling tanks called "thickeners". Because the rock and clay mixture is heavier, it settles to the bottom of the tank, leaving borates dissolved in water - or liquor - on top.
- Crystallising - The liquor is transported to tanks called "crystallisers" to be cooled. The drop in temperature forces the borates to crystallise, forming a slurry of borate crystals and water.
- Filtering - The slurry is poured over special fabric filters and washed to ensure purity. Water is drawn away by a vacuum beneath the filter.
- Drying - Damp borate crystals are then transferred to huge rotating dryers that use hot air to finish the crystal drying process.
- Conveying - Dry borates drop onto a conveyor belt to be transported for storage or packing and shipping.
Testing and storing
At each stage of the process, borate samples are taken for quality checks. On-site laboratories allow for instant analyses and adjustments.
Refined borates are stored in silos or the 18,000 tonne domes at Boron Operations. Total storage capacity at the site is more than 90,000 tonnes.
Rio Tinto Minerals' commitment to protecting the environment dates back to the early days of borates business Borax. Back in 1916, company officials helped write the language that was adopted by US Congress to establish the National Park Service.
Out of respect for California's Death Valley, leaders donated land holdings to the federal government and lobbied to have the area protected as a National Monument in 1933 and again as a National Park in 1994.
In 2010, Rio Tinto Minerals donated another 110 acres and associated mineral rights to the federal government in order to expand Death Valley National Park. The donation extends the perimeter of the Park, giving the park's nearly one million annual visitors even more of this spectacular wilderness to explore.
Mining and processing borates requires significant amounts of water, making recycling and management efforts a priority. Ongoing reduction efforts include using recycled water to control dust on haul roads at Boron. Water consumption has also been reduced by millions of gallons through better water recycling.
Boron Operations have recently lowered energy use and greenhouse gas emissions by more than five per cent per tonne of product through improvements in plant design and maintenance practices.
Rio Tinto Minerals has established procedures around the world to reduce, reuse, and recycle waste produced at our operations and our offices. The Boron site has been repeatedly honoured with the Solid Waste Reduction Awards from the California Integrated Waste Management Board.