Mining & refining borates
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 minimize our environmental impact. At each stage of the process, borate samples are tested at onsite laboratories, allowing for instant analysis and adjustments.
Mining borates relies primarily on a combination of drilling, blasting and shoveling to collect ore, which is then hauled to massive crushing machines and, from there, to refinery centers.
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.
Rio Tinto Minerals uses explosives to blast loose the sandstone at the top of the deposit called overburden, and to loosen the boron ore below it.
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. Each shovel stands seven stories high and can lift 80 tons per load - the same weight of 40 average cars.
Haul trucks in the mine are tracked using GPS technology to ensure efficient and safe operations. The massive trucks measure 20 feet high, 40 feet long and drive on 12 foot high tires, and each can carry 240 tons of material. The $1 million trucks are so large that each has to be shipped in pieces and assembled at the mine.
Ore from the mine must be crushed before it is refined. Powerful crusher machines reduce the ore to one inch 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 more than 1 million tons of refined borates every year. The bulk of this process was developed at Rio Tinto Minerals' Boron Operations.
- Dissolving - In the first step of refining, 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.
- Crystallizing - The liquor is transported to tanks called "crystallizers" to be cooled. The drop in temperature forces the borates to crystallize, 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.
At each stage of the process, borate samples are taken for quality checks. Onsite laboratories allow for instant analyses and adjustments.
Refined borates are stored in 100 foot silos or the 20,000 tons domes at Boron Operations. Total storage capacity at the site is more than 100,000 tons.