Manufacturing Process of Mercury

The way that mercury is extracted from its ores is still done pretty much the same way it used to over two thousand years ago when Aristotle first mentioned it. Cinnabar ore is crushed and heated to where it lets off the mercury in the form of a vapor. This mercury vapor is then cooled, condensed down and collected. Close to ninety five percent of the content of mercury in cinnabar ore can be recovered with this method. 

Mining and processing of cinnabar ores
Cinnabar ore can be found in concentrated deposits that are usually close to the surface. Around ninety percent of these deposits are so deep that they have the need of underground mining to be done with tunnels. The rest (ten percent) can be excavated from open pits.

Cinnabar ore is first taken out of the rocks that surround it with drills and through blasting with explosives as well as with the usage of powerful equipment and machinery. The ore is then taken out of the mine with conveyor belts or in trucks etc. Given that cinnabar ore is moderately concentrated, it can be processes right away without having to get rid of the waste material first. In order to process it, the ore is first crushed in cone crushers. A cone crusher is made out of an interior grinding cone that spirals on an eccentric vertical axis inside a fixed outside cone. As soon as the ore is provided to the top of the crusher, it is then pressed between both the cones and this causes it to break into smaller pieces. After the ores has been crushed it is then broken down to even smaller size pieces with the help of mills. Every mill is made up of a big cylindrical container that lies on the side and that rotates on a horizontal axis. The mill might also have short steel rods or steel balls in order to help with the grinding of the ore. This action obviously causes the ore to be crushed down to a fine powder which is then placed into a furnace so it can be heated. There are certain operations that use a multiple hearth furnace where the ore is mechanically moved down a perpendicular shaft from one ledge to the following one by rakes that are rotating slowly. There are also others that utilize rotary kiln and this process causes the ore to be plummeted down the length of a long cylinder that rotates and that is inclined a few degrees off horizontal level. No matter what process is chosen, heat is provided by burning a fuel in the lower part of the furnace or kiln. The then heated cinnabar will have a reaction with the oxygen in the air and will produce sulfur dioxide, and this will allow the mercury to come up as vapor. This process is what is more commonly known as roasting.

Once the roasting has been completed the condensing process takes place. As soon as the mercury vapor comes up and out of the furnace with the sulfur dioxide, water (vapor), along with other combustion products. A good quantity of fine dust from the powdered ore is in addition carried and needs to separated and obtained. The hot furnace exhaust then goes through a condenser that is water cooled. Once the exhaust starts to cool, the mercury is the first to condense into a liquid and leaves the other gases and vapors to be vented or processed more in order to reduce the amount of pollution in the air. Then the liquid mercury is collected. Given that mercury has a very high specific gravity, the impurities have a tendency of rising top and will usually form a dark film. These are then taken out through filtration and the liquid mercury is left which is around ninety nine point nine percent pure. The impurities are then lime treated so as to separate and obtain any of the mercury left in them which sometimes forms in compounds.

Once these two stages have been completed it is time for the refining process. Almost all commercial grade mercury is of 99.9 percent pure and this can be utilized straight from the roasting and condensing process. There are some occasions nonetheless, in which a higher purity of mercury is necessary for some very few applications and needs to be refined more. Obviously the superfine mercury has a different price to it. There are several refining methods in which a higher purity of mercury can be obtained. The mercury can sometimes be mechanically filtered again and some impurities can be taken out through oxidation with chemicals or air. There are also times in which the mercury is refined by means of an electrolytic process which consists of an electric current that is passed through a tank of liquid mercury to get rid of the impurities in it. However, there is one refining method that is more customary which consists of a triple distillation process. In this process the temperature of the liquid mercury is very carefully raised until the impurities evaporate or the mercury itself evaporates, which would leave the impurities behind. This process which is known as a distillation process is repeated three times and the purity of the mercury increases with each distillation.