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452 A COmPREhEnSIVE GuIdE TO SOlAR EnERGy SySTEmS

(4) extraction, (5) beneficiation, (6) processing, and (7) reclamation [40]. Each step can be
different for each mine. Popular types of mines include surface and underground mining,
which have both been employed for thousands of years of mining activity. Solution, or “in
situ” mining, which uses acids to dissolve metals into solutions and then recover ores from
those solutions, is a relatively new process gaining popularity. Physical factors of the ore
deposits determine the type and size of a mine, such as nature, location, size, depth, and
grade [41]. Surface mining is the most popular because it entails the least amount of cost
to developers and can be done relatively inexpensively with heavy machinery and explo-
sives. underground mines are employed if the deposits are deep and concentrated enough
to warrant extensive operations such as the added planning and drilling. Other types of
mines include deep-sea mining and asteroid or outer space mining. Although they speak
to our need to find new deposits to feed our industries, they have not yet been employed.
Once ore is beneficiated and processed, it must be refined. There are two categories
for the process of refining ore: pyrometallurgical processing and hydrometallurgical pro-
cessing. Pyrometallurgical processing uses physical properties such as smelting and is
more widespread. hydrometallurgical processing uses chemical properties and relies on
leaching ores with strong acids and recovering concentrated materials by precipitation or
solvent extraction/electrowinning (SX/EW) [42]. Both processes use physics and chem-
istry to gain higher concentrations of ore throughout many steps that may or may not be
needed or economical depending on the nature of the deposit—specifically, the ore grade
and concentrations of other desirable by-products.
For pyrometallurigical processing, or smelting, the ore is simply heated in a furnace until
the metals physically separate. Electric or “flash” furnaces are used for lower material volumes
and higher by-product recovery rates [43]. Impurities can be further removed by blowing
gases into the molten form of the ore to achieve even higher concentrations. Since PV mod-
ules require extremely pure concentrations of materials, metals must be even further refined
“electrolytically,” or “electrorefined.” during “electrorefinement,” the concentrate is electri-
cally dissolved by a specific current into a specific electrolyte and accumulates on a cathode
in nearly pure concentrations [44]. Such material is referred to as “cathode grade” material.
For hydrometallurgical processing, several steps must be taken. The ore goes through
crushing, grinding, washing, filtering, sorting and sizing, gravity concentrating, leaching,
ion exchange, solvent extraction, electrowinning, and precipitation [45]. In other words,
the ore is put into solution and then refined through precipitation or SX/EW. Finally, it is
electrorefined to cathode grade. The leftover electrolyte often contains other economically
retrievable metals that can be further refined.

23.3.2 Aluminum

Al is second to Si as the most abundant metallic element on Earth; however, its commer-
cial industrial application is only about 100 years old because it is very reactive in nature
and difficult to separate from other materials. Today, Al is favored for its lightweight
malleability, ductility, resistance to corrosion and durability. It can be easily machined and
cast. Second to Fe, Al is the most widely used metal in the global economy, including areas