Humanity has extracted ores from the earth for thousands of years. However, very few minerals come directly from the ground in ready to use form. Raw minerals that require additional processing after mining are known as run-of-mine (ROM) ore. After extraction, underground mines sometimes break down this raw ore to help convey it to the surface, and this crushed product is also considered ROM. As most mined minerals occur in low concentrations, especially when it comes to rare earth minerals, further processing must occur before this ore can be sold for use--which is where mineral processing equipment plays a key role.
What is a Mineral?
You can find varying definitions for the word mineral, depending upon the context. The Merriam Webster dictionary defines it merely as “ore.” More intricate definitions deem a mineral as “a solid, homogeneous, crystalline, chemical element or compound that results from the inorganic processes of nature” or “a synthetic substance having the chemical composition and crystalline form and properties of a naturally occurring mineral.” Minerals can even include metals like iron, zinc, and other elements that occur naturally in the earth and are used to maintain health.
One legal definition from Black's Law Dictionary defines minerals as "any valuable inert or lifeless substance formed or deposited in its present position through natural agencies alone, and which is found either in or upon the soil of the earth or in the rocks beneath the soil." However, it then says that the meaning of the term is not definitive. There are limitations or augmentations to this definition depending on the situation in which it is used.
Perhaps the most apt definition comes from the Glossary of Geology, used by the US Geological Survey to determine minerals, which states that "a naturally occurring inorganic element or compound having an orderly internal structure and characteristic chemical composition, crystal form, and physical properties.” That said, mineral processing equipment can just as easily be used to process synthetic materials with similar chemical structures to those mined from the ground, as per one of the Merriam Webster definitions.
Each industry uses mineral processing equipment to break down material for specific applications. A certain amount of crossover exists, but methods and systems for concentrating valuable minerals from ores or other materials in which minerals occur differ somewhat depending on the desired end product and size of particulates needed.
Most Mined Minerals Worldwide
Though it uses a broader definition for describing mined minerals, the British Geological Survey (BGS) has published statistics on mineral production since 1913. While these vary over time due to changes in technology, certain mined materials are aggregates of several minerals.
The 2016 BGS analysis reveals the top five most mined minerals worldwide by weight as:
- Coal – 7.4 billion tons
- Iron – 4.6 billion tons
- Bauxite – 289 million tons
- Phosphate – 276 million tons
- Gypsum – 267.1 million tons
Coal is technically not a mineral but rather a rock made up of fossilized organic material that includes minerals, and processing involves mineral processing equipment. Coal processing requires sieving machines such as sieves or vibrating screens to process the raw coal and sort it by particle size, then crushing equipment, such as lump breakers.
Aluminum processing also uses crushing equipment like lump breakers or hammermills. Derived mainly from bauxite ore, a mineral-rich rock, it contains minerals like diaspore, boehmite, and gibbsite. Meanwhile, over 200 phosphate minerals occur naturally, used primarily in agriculture as fertilizers, and processing it can involve machinery such as air classifiers and vibrating screens that separate and remove carbonates.
Most Mined Materials in the US
According to the US Geological Survey, the top eight mineral commodities in the United States were worth $93.3 billion in 2019.
The eight most mined mineral commodities in the US by worth:
- Coal ($25.1 billion): Commonly contains minerals like illite clay, pyrite, quartz, and calcite.
- Crushed rock ($18.7 billion): Used primarily in the construction industry, depending on the rocks from which it comes, crushed rock contains minerals such as calcium carbonate, dolomite quartz, potassium feldspar, and sodium feldspar.
- Cement ($12.5 billion): Made primarily from limestone – containing the mineral calcite – and clay, it also uses gypsum to help it harden.
- Gold ($9.0 billion): Although also an element, the metal is also considered a mineral.
- Construction sand and gravel ($9.0 billion): Made mostly of quartz, the mineral silicon dioxide with small amounts of feldspar.
- Copper ($7.9 billion): The metal is considered both an element and mineral.
- Industrial sand and gravel ($5.7 billion): Similar to sand and gravel used in construction, it is purer, with higher silica content, and is used in the production of abrasives, ceramics, chemicals, electronics, filters, glass, paint, pigments and for other industrial uses.
- Iron ore ($5.4 billion): Mined iron is used primarily for steel.
Industries Requiring Mineral Processing Equipment
Various industries require machinery to process minerals for a plethora of applications. Regardless of the type of business, all mineral processing equipment essentially works towards the same goals: to concentrate the valuable minerals into usable proportions, separate them by particle size and further reduce the mineral particulates according to the purpose for which the material will be used.
Processing Industrial Minerals
Industrial minerals are categorized differently from metallic minerals, often referred to as non-metallic, and do not include fuels, water, or gemstones. The most widely used of these include sand, gravel, clays, limestone, diatomite, potash, pumice kaolin, silica, barite, bentonite, gypsum, and talc. These minerals are used in making countless products for both industrial and domestic purposes, including paint, glass, ceramics, paper, electronics, detergents, pesticides, medications, and detergents. Typical mineral processing machinery includes hammermills or other milling machines, air classifiers, sifters or sieves, lump breakers, and sometimes fine grinding machines.
Diatomite: A Crossover Between Industries
The same mineral can be used across multiple industries for vastly different purposes. Take diatomite, for example. It is also known as diatomaceous earth in its raw form; it is a mineral compound that occurs in deposits where diatoms – ancient algae-like plants – fossilized en masse. Its uses extend through agriculture, brewing, distilling, dietary supplement, food processing, and other industries, where it is used for insecticides, foods, medicines, rubber, skincare products, and paints, and filtering beer, whiskey, water, or fruit juice.
How diatomite is processed after mining depends upon the grade required (referred to as either filter-grade or food-grade). Used for filters and dynamite, filter-grade diatomite requires fewer processing steps, often contains up to 60% silica content, and is toxic to mammals. Food-grade diatomite entails additional processing to purify it, so typically has silica levels of less than 2%. Diatomite can range in particle size from under 3 μm to over 1 mm, but usually, particles occur in size between 10 to 200 μm.
Mineral processing equipment used to refine diatomite for industrial purposes usually starts with crushing the material into an aggregate, usually with a hammermill or other milling machine like air classifying mills, which minimizes the range in particulate size. A milling and drying process follows, which can entail the use of sifters or sieves to regulate particulate size, along with rotary airlocks, valves, and feeders to move the suspended particles along a hot stream of gases.
Rotary and flash dryers then dry the material – reaching temperatures between 150-800˚ F (70 to 430˚ C) until its moisture content reaches about 15%, usually from a moisture content between 40-60%. Exiting the dryer, these suspended particles then pass through a series of fans, cyclones, and separators to a baghouse, where operations then separate the material into variously sized particles, remove impurities and expel moisture from the powdery diatomite, which is then packaged in bulk for transport as a finished product.
Filter-grade diatomite utilizes additional stages. The mineral is calcined or sintered using gas or fuel oil, a process that heats it to 1200-2200˚ F (650-1200˚ C) in a machine called a rotary calciner. The diatomite powder reaches a point of incipient fusion, after which it goes through further milling and classification. After this, adjusting particle size further often involves the addition of sodium carbonate, a chemical refined from another mineral called trona. This increases particle size and allows a greater flow rate when filtering liquids.
While the process may be somewhat different depending on the mineral and end product, other minerals undergo similar processes using derivatives of the above equipment.
The mining industry uses equipment like hammermills or lump breakers for crushing minerals into useable proportions. Filtering equipment like vibrating screens is also used to divide waste material from that which is useable and equipment to help convey it, which could involve rotary feeders or valves.
Similarly, the construction industry needs to grind minerals down, sometimes to powder form as with cement. Cement is made primarily from limestone or other rocks containing the mineral calcium carbonate, combining it with silicon, aluminum, iron, and other minerals. As such, it is considered an aggregate, as are other minerals used in construction, such as sand, gravel, and crushed stone.
With pharmaceuticals or health supplements, minerals tend to need further reduction. For this, equipment like lump breakers breaks down clumps of minerals into granules used in capsules, or fine grinders reduce it into powder form so it can be pressed into tablets.
Many other types of enterprises require processed minerals for their products. Regardless of the industry, many of these also apply mineral processing equipment to concentrate, reduce, and purify the minerals they use. These include businesses in agriculture, food processing, steel, recycling, and other industries.
Mineral Processing Solutions by Prater Industries
Prater manufactures and customizes mineral processing equipment for use in just about any industry. The company offers a wide array of solutions for processing minerals that helps reduce particle size, feed, and meter, classify and separate materials, and design whole mineral processing systems.