Steel vs Bamboo Part 2: Refining

In Part 1 we compared mining iron ore to the process of harvesting bamboo. In Part 2 we'll compare iron ore refining to the bamboo bike tube process.

Refining Iron Ore

Refining Iron Ore

After the iron ore, or taconite, has been mined, it needs to be crushed, separated, concentrated, mixed, pelletized, and shipped to blast furnaces and mills so it can be transformed into finished steel.

First, the crude taconite is delivered to crushers, where chunks as large as five feet are reduced to six inches or less. The crushed material is transferred to an ore storage building, then an apron feeder sends the ore to the concentrator building for grinding, separating, and concentrating.

The crude taconite is now roughly the size of a football. A series of conveyor belts continuously feed the ore into large primary grinding mills. Water is added at this point to transport it. When the ore is reduced to 3/4" or less, it moves out of the mill in a slurry solution.

Ore smaller than 1/4" is pumped in slurry solution to the wet cobber magnetic separator, which begins the process of separating the iron from the non-iron material. The magnetic iron ore is then laundered in two slurry surge tanks while the non-magnetics (silica/sand) go to the tailings disposal area.

Most of the material continues to be finely ground in one of five secondary ball mills, which are powered by electric motors ranging from 2,500 hp to 4,000 hp and are charged with 1-1/2" chrome grinding balls. Fine grinding is achieved using these smaller mills, bringing the ore to a similar grind as that found in face powder.

The screen undersize is then moved to hydroseparators, where silica is floated off the top. The hydroseparator underflow is pumped to the finisher magnetic separators. Once again, the magnetic separators grab the iron and discard the silica and sand. The concentrate from the separators is pumped to fine screening.

The oversize material is returned to the balls mills, while the undersize (with the most impurities removed) becomes the final concentrate. Waste from the circuit goes to the tailings basin and the final concentrate travels to thickeners located in the pellet plant. The underflow from the thickeners is pumped to a storage tank and then to disc filters for dewatering.

The product is called “filter cake”, and is now ready for mixing with the binding agent. Once the filter cake is complete, it travels onto a feeder belt and from there to a conveyor where bentonite, a bonding agent, is added. Bentonite is a clay from Wyoming used to help iron ore concentrate stick together when rolled into pellets. About 16 pounds of Bentonite are added to every ton of iron ore concentrate.

Small amounts of limestone (1%) are added and mixed with the concentrate. Limestone is added to meet the requirements of steel customers in the blast furnace process. The iron ore concentrate is now mixed and ready for the pelletizing process.

A pellet plant contains a series of balling drums where the iron ore concentrate is formed into soft pellets, in much the same manner that one rolls a snowball, to make a pellet about the size of a marble (between 1/4" and 1/2"). Pellets are screened to meet the size specification, with undersized or oversized pellets crushed and returned to the balling drums.

The soft pellets are then delivered to the roller feeder for final removal of the fines, which are also returned to the balling circuits. Now the soft pellets, correctly sized, are delivered to the traveling grate furnace for further drying and preheating. The grate is fired by natural gas.

From this point, the pellets are charged into the large rotary kiln where they are heat-hardened at 2,400 degrees Fahrenheit. The pellets are discharged into the revolving cooler and then moved to the pellet screening plant, onto the pellet loadout system. The whole process consumes energy in the form of electricity and natural gas.

The pellets are run through a final screening to remove those not meeting size specifications or those that are chipped or broken into fines. Pellets that meet the necessary standards are conveyed to the pellet stockpile, and are now ready for shipping by train to customers or to ore docks.

Now compare that to the bamboo refining process. A farmer removes any small branches and leaves (which are either mulched or used for fuel) and tempers the bamboo tubes by slowly heating a cooling them. The tempering process removes moisture and strengthens the bamboo.

Clearly a much less intrusive and more environmentally friendly process all around. And another reason why we've spent so much time and energy to bring you affordable bamboo bikes.

Stay tuned for Part 3, we'll compare the finishing processes including turning iron ore into steel and forming the tubes.