Electrothermal process

Elemental phosphoms from the electrothermal process is a distilled product of high purity and yields phosphoric acid pure enough for most industrial uses without any further treatment. The main impurity is ca 20—100 ppm arsenic present in the phosphoms as the element and in the phosphoric acid as arsenious acid. To remove the arsenic, the phosphoric acid destined for food, pharmaceutical, and some industrial-grade appHcations is treated with excess hydrogen sulfide, filtered, and blown with air to strip out excess H2S. This treatment generally reduces the arsenic content of the phosphoric acid to less than 0.5 ppm. The small amount of filter cake is disposed of in approved chemical landfills. 

An improved approach from the point of view of thermal efficiency is the electrothermal process in which the mixture of zinc oxide and carbon, in the form of briquettes, are heated in a vertical shaft furnace using the electrical resistance of the briquettes to allow for internal electrical heating. The zinc vapour and CO(g) which are evolved are passed tluough a separate condenser, the carbon monoxide being subsequently oxidized in air. 

Electrothermal process for manufacturing P introduced by J. B. Readman (Edinburgh). 

Cowles An electrothermal process for making aluminum alloys. A mixture of bauxite, charcoal, and the metal forming the alloy (usually copper), was heated in an electric furnace and the molten alloy tapped from the base. The process cannot be used for making aluminum alone because in the absence of the other metal the product would be aluminum carbide. Invented by the Cowles brothers and operated in Cleveland, OH in 1884 and later in Stoke-on-Trent, England. The electrical efficiency was poor and the process was superseded by the Hall-Heroult process. 

Electrothermic process, for zinc, 26 577 Electrothermic zinc smelting, 26 612 Electrotransport technique, for purifying vanadium, 25 522... 

The older retort and electrothermic processes have largely been replaced because of environmental and economic reasons. 

Other processes include an electrothermic process, an electric-arc vaporizer process, and the slag fuming process. 

E. A. Fletcher, F. Macdonald, and D. Kunnerth, High temperature solar electrothermal processing II. Zinc from zinc oxide, Energy, 10 1255-1272 (1985). 

Zinc oxide is produced either by the French or by the American process. Both processes are pyrometallurgical techniques in which the metal in a vapor state reacts with oxygen, forming zinc oxide. The difference between the methods is in the raw material used for the synthesis. In the French process, pure metal is evaporated, and the final product is as pure as the metal used for its production. In the American process, zinc vapor is obtained directly from an ore by burning it as a mixture with coal or in an electrothermic process where electric current provides the heat. More recently, a new method, somewhat similar to the French process, was introduced by Nanophase Technologies Corporation who patented a physical vapor synthesis process in which zinc metal is vaporized. The vapor is rapidly cooled in the presence of oxygen, causing nucleation and condensation of nanoparticle size zinc oxide. The particles are non-porous and free of contamination. 

These processes are the retort process and the electrothermal process [116]. The third process is the methane-sulfur process. 

One advantage of the electrothermal process over the retort process is that large capacity reactors are possible because the heat is produced internally instead of having to be conducted through the walls [120]. 

Essentially all the energy is consumed in calcium carbide manufacture. In the electrothermal process, the reaction is carried out at temperatures in excess of 1850°C. If we ignore the lime (recovered), and convert other consumption/by-product figures to energy values, we obtain (per mol acetylene equivalent) ... 

Ferrochrome (UK, France), or ferrochromium (USA), is a master alloy of iron and chromium containing between 40 and 75 wt.% Cr and varying amounts of carbon and silicon. It is prepared industrially by three different electrothermal processes—the carbothermic, the silicothermic, or the aluminothermic reduction of chromite ore, which is used as the main source of chromium. In the carbothermic process, a charge of chromite ore mixed with lime as fluxing agent is reduced by metallurgical coke or coal as reductant in a three-phase submerged-arc furnace. The overall chemical reaction involved is as follows ... 

Preparation of fused zirconia. Production of electrofused or simply fused zirconia consists in removing silica from zircon by melting zircon sand with coke into an electric arc furnace at temperatures of around 2800 to 3000°C. During the electrothermal process, silica is reduced to volatile sihcon monoxide (SiO), which escapes the furnace and leaves molten zirconia. On rapid cooling, a granular material is produced that is screened and crushed. Usually, the monoclinic zirconia produced contains less than 0.2 wt.% sihca. 

In the meantime Willson returned to Canada. He there established carbide operations in Merriton, Ontario, and at Shawinigan Falls, Quebec He formed the International Marine Signal Co. to manufacture carbide-energized buoys, and applied himself to the use of the electric furnace for smelting phosphate ores in his remaining years (W). Willson died in 1915, by which time he had seen his invention produce 90,000 tons of calcium carbide annually by 1904 and 250,000 by 1910, from zero in 1892 ( ). He perhaps would have been amazed to have witnessed the growth in the chemical uses of acetylene equivalent to one million tons per year of calcium carbide by 1960, produced in continuous furnaces which were 30 feet in diameter by 15 feet tall, each rated at 30,000 kw ( ). Nor could he have foreseen his furnace eventually supplanted as a source of acetylene by yet another electrothermic process, the direct formation of acetylene in an electric arc used to crack hydrocarbons such as natural gas. 

The Kivcet Process (an acronym in Russian for oxygen flash cyclone electrothermal process), was developed by the Vniitsvetmet Institute in Kazakhstan in 1967 for the treatment of both copper and lead concentrates (Sychev et al, 1985). A 25 t/d pilot plant was built and operated for a number of years followed by a plant to treat 500 t/d of mixed copper-zinc concentrates at Glubokoe in 1970. That plant produced a copper matte and zinc rich slag for slag fuming in the electric furnace to recover zinc oxide. 

G. Ch. Yao, Preparation of Al-Si alloy by electrothermal process, (Sheng Yang, Northeast University Press, 1998), 12-16. 

---