The electrode must become baked solid over its entire cross section (inside the charge) when it is fed downwards to compensate for its consumption in the furnace (which is a few centimeters per hour). The Söderberg electrodes are heated by the electric current and the furnace heat, then baked solid in the region of the contact clamps. These furnaces can be equipped with either pre-baked electrodes or Söderberg electrodes. Three electrodes are placed at the angles of an equilateral triangle with rounded corners. The floor and lower section of the furnace are water-cooled. The lower part is lined with hard blocks of strongly calcined carbon, and the upper part with firebrick. Thus, it locks up a certain percentage of the phosphorus.Īnother impurity is alumina - this increases the slag bulk but reduces the melting point.įurnace Construction, Components and Features Ī top view of a submerged-arc furnace for phosphorus production Furnace structure and individual components Ī submerge-arc furnace's shell or casing is fabricated from steel. Iron is considered an impurity and undesirable because it requires additional carbon and power for reduction. The resulting second liquid product is called ferrophosphorus. Iron oxide impurities are reduced and form iron phosphides. One such impurity-and the most important one-is iron oxide. This process also has intermediate reactions, and as such, the phosphate rock created has impurities. This main reaction produces a liquid calcium silicates slag, carbon monoxide gas and the desired product, phosphorus gas. The main internal reaction is described below:Ĭa 10(PO 4) 6F 2 + 15C + 9SiO 2 → 3P 2(g) + 9 + CaF 2 + 15CO(g) This is performed in a submerged-arc furnace at temperatures of between 11C. In this process, apatites (nearly always fluorapatite) are reduced in the presence of carbon ( coke) and silica (gravel). Large-scale production of phosphorus uses the Wöhler process.
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