Such troilite must be separated from the ilmenite before reduction with hydrogen to produce oxygen, or else the plant must be designed to withstand and separate the sulfuric acid by-product. Thus, a very high grade ilmenite concentrate might be less desirable than a poorer grade concentrate that contains less troilite. Laboratory testing should search for contrasts in physical properties between mineral grains of the rock or soil that can facilitate separation of the desired mineral from the gangue. On Earth, an extreme case of the utility of large contrasts in physical properties is in placer gold mining, where enormous tonnages of gravel are washed and discarded to recover a tiny quantity of gold. The high density of the gold, and the availability of water to carry out easy density separations, makes this practical. More commonly, surface properties of the mineral grains are taken advantage of, as in froth flotation, where relative polarity of the mineral grains forms the basis of separation. Pilot Plant Test Once the laboratory testing has determined that a site has rock from which a mineral concentrate can be made, and that the concentrate can be treated chemically, a pilot plant test must be made. This test will include: (a) mining a large sample for a preliminary test, which will determine mining difficulty such as equipment wear, power costs, equipment sizes and operating costs. (b) Comminution tests, which will determine the types and sizes of equipment, and the required sizing of the product so that minerals can be separated from the gangue. (c) Mineral separation tests, which will determine the types of equipment, the modifications that must be made to the equipment, and the recovery, concentrate grade, middling grade and tailings losses. (d) Finally, once a satisfactory concentrate is produced, chemical separation of the desired element from the residue must be determined. All these steps must successfully completed to produce the desired product. The dangers of skimping on the pilot plant test are illustrated by the following case. A mining company was developing a mineral property south of Tucson, Arizona in the 1970s. The company chose not to sink a shaft, excavate a drift out to the mineralized area, and take a large mill test sample. Instead, they drilled some large holes from the surface into the mineralized area to make up a composite mill test sample. They then designed the mine and mill based on the tests on the drill samples. Only then, after building the mill, did they sink a production shaft and excavatea drift out to the mineralized area. They found that the mineralization was so broken up by faulting that it could not be mined. Thus, by skipping the step
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