Mission mining

More than 1,600 feet below ground level, at its Green River Basin

facility in the American state of Wyoming, Tata Chemicals mines

trona, a naturally occurring soft-rock mineral. It then processes this

mineral on terra firma to produce soda ash, among the most widely

used chemicals in the world. It’s an operation that is both basic and

sophisticated, combining the dramatic and the commonplace in an

environment where business success depends on know-how and

efficiency as much as on camaraderie and community. Photojournalist

Larry Brown, company employee by designation and shutterbug by

passion, takes an inside view of this remarkable enterprise.

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A group of miners emerge from the ‘cage’, a hoist that brings them down more than 1,600 feet to the mine floor in two-and-a-half minutes. Four-wheeled diesel vehicles, open at the top, provide transportation across the mine, which has a network of tunnels spread over 20 square miles. This is the starting point of the operation that Tata Chemicals North America runs in Green River.

A bore miner, a high-impact beast of a machine, drills into a ‘production face’ in one of the mine’s tunnels. Here is where the journey of the soft-rock mineral out of the mine begins, from the face to a ‘flexible conveyor train’. More than 4 million tonnes of trona are mined every year at this facility and then processed in a surface refining plant to produce about 2 million tonnes of soda ash.

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A continuous miner, less productive but more flexible than a bore miner, fetches the trona and deposits it in a shuttle car, from where it is transferred to a conveyor belt. The Green River facility sits on the ‘mile-high’ prairies of southwestern Wyoming, home to the largest reserves of trona ore in the world — 60 billion tonnes spread over 1,000 square miles, at depths of up to 1,800 feet.

A worker drives bolts into the roof of an area that is being prepared for further mining and drilling. This is to support the roof and make the place safe from falling rock. Mining is an inherently dangerous operation; roof bolting — first used in the 1930s and now the primary support system in underground mining — has reduced roof-fall accidents to a great extent.

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A conveyor system (on the right) carries the mined trona 11 miles to its furthest point, to what is called the bin, where the ore is deposited. This 1,200-horsepower conveyor system is 2 miles in length and is an integral part of the underground operations at the facility, which functions round the clock, seven days a week, 365 days per year. No time for breaks here.

The mined trona is deposited in the bin, which is a deep pit that holds the mineral until it is moved out to the surface. The bin holds about 1,200 tonnes of the ore at any given time. Most of the hard work, up to this point and beyond, is mechanised. Which explains how Tata Chemicals North America is able to run such a heavy-duty operation with fewer than 500 people.

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A worker oversees the mined trona being transported to the surface, and daylight, by a skip. All the mined ore goes to the surface through such skips, which receive the mineral from the bin — 22 tonnes of it every 90 seconds, 24 hours a day.

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Calciners — huge containers in which a substance is heated to a high temperature, but below its melting point — heat the precision-crushed trona to 165°C. This is done to get rid of unwanted gases and some other impurities from the ore; the heating process transforms it into crude sodium carbonate. Each calciner can process about 130 tonnes of trona in an hour.

Here’s where the surface operations get going. The trona ore that has been brought up from the mine by the skips is transported to the plant and crushed. The conversion of trona ore into soda ash happens through a multi-step purification process. The part seen above is where the ore is precision crushed to a specific size and screened to prepare it for processing.

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With shale and other contaminants removed from the liquid substance obtained in the purification process, the water used to dissolve the ore can now be removed. Evaporators, such as those seen here, boil the solution, leaving behind soda ash crystals. These crystals show up as a kind of slurry. Any remaining water is separated from the crystals in a centrifuge.

The calcined ore is dissolved in hot water to remove insoluble particles such as shale, which are sedimentary rocks formed by the deposition of successive layers of clay (the water is needed to dissolve the crude sodium carbonate). For all the heavy lifting involved in the mining of trona, surface operations like these are what turn the impure ore into soda ash.

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All of which explains why the folks on the surface say, with some justification and not always in jest, that turning trona into soda ash, rather than merely extracting it, is the really big deal at the Green River Basin facility. The reaction of mining colleagues — seen here during a break in the work down under — to such heresy is too colourful to print.

The monohydrate soda ash crystals, as they are now known, are dried in rotary steam tube dryers. What emerges is soda ash without any of the water used in the purification process. This part of the operation employs steam pressure of 400psi to heat the soda ash to 205°C, another component of a process that creates the purest — the whitest of white — soda ash.

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The finished soda ash product is screened and stockpiled before being loaded for shipment by truck and railcar (seen here). Nearly 100 tonnes of soda ash can be loaded in each rail shipment and 100 such shipments are sent rolling out five days a week. And there’s plenty more where that comes from, given that the Green River facility has about 600 million tonnes of trona reserves, enough to provide for 100 years of production at current levels of output.

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