MAGNESIA ISN’T JUST FOR SICK STOMACHS
Industrial mineral article by Harold Hough
Mention magnesia and most people think about milk of magnesia. However, this industrial mineral is so critical that many industries would be sick without a regular dose of magnesia (MgO).
Magnesia comes from magnesite (MgCO3), a naturally occurring compound of magnesium. Magnesite is converted into magnesia by heating, which releases carbon dioxide. Some of the major producers are China, Australia, Canada, and Israel. About 550,000 tonnes are produced in the United States.
Most magnesite is mined in open pit operations, although there are some saltwater and brine operations. How it is to be used determines how it is processed. When crude magnesite is heated to between 700°-1000°C, carbon dioxide is driven off to produce caustic-calcined magnesia (caustic magnesia). Caustic magnesia is able to absorb liquids and to absorb heavy metals, which makes it useful in water treatment. It is also used to stop the deterioration of inexpensive, high acid paper used in many books in libraries and archives.
When calcined magnesia is heated to between 1530°-2300°C, the result is an exceptionally stable and strong material – even at high temperatures. This is known as 'dead-burned' or 'sintered' magnesia, and it is mainly used as a refractory material.
When calcined or dead-burned magnesia is heated in excess of 2800°C in an electric arc furnace, electrofused magnesia is produced. It has higher strength, resistance to abrasion and chemical stability than dead-burned magnesia. It is used in the manufacture of premium grade refractory bricks used in the high wear hot spots of Basic Oxygen Furnaces, electric arc or similar furnaces where temperatures can approach 950°C.
The largest consumer of magnesia worldwide is the refractory industry, which consumed about 56% of the magnesia in the United States in 2004, the remaining 44% being used in agricultural, chemical, construction, environmental, and other industrial applications.
But magnesia is also important in construction. It is a raw material in making Portland cement in dry process plants. And, since it is fire resistance, moisture resistance, mold and mildew resistance, and strong, it can be used in wallboards.
The only magnesia mine in the United States is operated by Premier Magnesia in Gabbs, NV. Interestingly, it is one of the oldest continuously operating mines west of the Mississippi. The company’s MSHA number is 2.
The Gabbs, NV open pit operations began in 1929 and during World War Two was responsible for producing magnesium for aircraft. After the war, it began to focus on refractory bricks for steel production. Today, much of its finished products are used in environmental and livestock applications. The company also produces magnesia from salt water in Florida.
Nearly half of the US production of magnesia comes from Martin Marietta’s brine wells in Michigan.
Another critical magnesium compound extracted from brine is magnesium chloride, which is used by the mining industry as a dust control agent. Great Salt Lake Minerals in Utah produces several products including magnesium chloride. Most production work is done by the sun, with final processing of the potash and magnesium chloride in a refinery.
Production is simple: Lake brine is put into a pond and the water allowed to evaporate. As the water dries out, salt crystals form. When most of the salt crystallizes out, the remaining brine is moved to another pond and allowed to evaporate more until potassium sulfate crystallizes. After that, the remaining brine magnesium chloride.
The process of moving the brine to the production facility is unique. In the early 1990s, the company got state approval to set up evaporation ponds in the west shore of the lake's west arm north of the causeway. So little new water flows into that arm of the lake, that salt concentrations are much higher.
The problem was how to get brine from those ponds to the refinery. The solution was to dig an underwater trench across the floor of the lake's northwest arm, from the ponds to the tip of the southern Promontory Mountains. Concentrated brine from the evaporation ponds would flow downhill through that trench. The brine's density would prevent it from mixing with the lake water above. From Promontory Point it is pumped to the company's ponds near the refinery.
The brine takes 21 days to flow seven miles, and is a clever and inexpensive way to take advantage of the physics of salt water and the geography of Great Salt Lake.
For the last two years, the company has been improving and expanding its refinery to increase production, which now is 350,000 tons of potassium sulfate (potash), 600,000 tons of magnesium chloride, and 2 million tons of salt a year.