Phosphate rock phosphorus production from

The volatile fluorides formed by this process are captured by water scrubbers (Section 10.4.3). However, about 58% of agricultural rock, or 50% of the total, ultimately goes into wet process phosphoric acid production (Section 10.4). Nonagricultural uses consume 13% of the total for elemental phosphorus production, from which both high-purity phosphoric acid and other phosphorus derivatives are made (Table 10.2). Nearly half of this, about 6% of the total, goes into the manufacture of phosphate builders for detergents, about a tenth into food and beverage additives, and the remainder into a multitude of small-scale applications. 

Shaft Furnaces The oldest and most important application of the shaft furnace is the blast furnace used for the production of pig iron. Another use is in the manufac ture of phosphorus from phosphate rock. Formerly hme was calcined exclusively in this type of furnace. Shaft furnaces are widely used also as gas producers. Chemicals are manufac tured in shaft furnaces from briquetted mixtures of the reacting components. 

By far the largest source of phosphorus is phosphate rock, with some use of phosphatic iron ore, from which phosphorus is obtained as a by-product from the slag. Phosphate rock consists of the insoluble tricalcium phosphate and other materials. For use as a fertilizer, phosphate must be converted to the water soluble form, phosphoric acid (H3PO4) which has three hydrogen atoms, all of which are replaceable by a metal. Tricalcium phosphate, is converted to soluble monocalcium phosphate and to superphosphate, A fertilizer factory, typically, a large installation, characterized by large silos produces year round, but peaks with the demands of the growing season. Phosphorus has many uses other than for fertilizer. 

The phosphate manufacturing and phosphate fertilizer industry includes the production of elemental phosphorus, various phosphorus-derived chemicals, phosphate fertilizer chemicals, and other nonfertilizer phosphate chemicals [1-30], Chemicals that are derived from phosphorus include phosphoric acid (dry process), phosphorus pentoxide, phosphorus penta-sulfide, phosphoms trichloride, phosphorus oxychloride, sodium tripolyphosphate, and calcium phosphates [8]. The nonfertilizer phosphate production part of the industry includes defluori-nated phosphate rock, defluorinated phosphoric acid, and sodium phosphate salts. The phosphate fertilizer segment of the industry produces the primary phosphorus nutrient source for the agricultural industry and for other applications of chemical fertilization. Many of these fertilizer products are toxic to aquatic life at certain levels of concentration, and many are also hazardous to human life and health when contact is made in a concentrated form. 

The manufacture of phosphorus-derived chemicals is almost entirely based on the production of elemental phosphorus from mined phosphate rock. Ferrophosphorus, widely used in the metallurgical industries, is a direct byproduct of the phosphorus production process. In the United States, over 85% of elemental phosphorus production is used to manufacture high-grade phosphoric acid by the furnace or dry process as opposed to the wet process that converts phosphate rock directly into low-grade phosphoric acid. The remainder of the elemental phosphorus is either marketed directly or converted into phosphoms chemicals. The furnace-grade phosphoric acid is marketed directly, mostly to the food and fertilizer industries. Finally, phosphoric acid is employed to manufacture sodium tripolyphosphate, which is used in detergents and for water treatment, and calcium phosphate, which is used in foods and animal feeds. 

In the specific case of wastewater generated from the condenser water bleedoff in the production of elemental phosphorus from phosphate rock in an electric furnace, Yapijakis [33] reported that the flow varies from 10 to 100 gpm (2.3-23 m /hour), depending on the particular installation. The most important contaminants in this waste are elemental phosphoms, which is colloidally dispersed and may ignite if allowed to dry out, and fluorine, which is also present in the furnace gases. The general characteristics of this type of wastewater (if no soda ash or ammonia were added to the condenser water) are given in Table 9. 

All phosphorus fertilizers come from wet process phosphoric acid or directly from phosphate rock. Normal superphosphate, triple or concentrated superphosphate, and ammonium phosphate are the three common types used. Normal or ordinary superphosphate (NSP or OSP) is mostly monocalcium phosphate and calcium sulfate. It is made from phosphate rock and sulfuric acid and is equated to a 20% P2O5 content. It led the market until 1964. The production of normal superphosphate is similar to that for the manufacture of wet process phosphoric acid (Chapter 2, Section 3) except that there is only partial neutralization. Normal superphosphate is no longer used to any great extent. The following reaction is one example of an equation that represents this process. 

There arc two main processes for the industrial production of phosphoric add, H3PO4. from phosphate rock (1) the wet process which involves tlie reaction of phosphate rock with H2SO4 to yield phosphoric acid and insoluble calcium sulfites, Several of the impurities present in the rock dissolve and remain with the product add. These are not important when the add is used for fertilizer manufacture. However, the impurities are deleterious to the manufacture of phosphorus chemicals. For a purer product, (2) the furnace process is used, wherein the phosphate rock is combined with coke and silica, producing elemental phosphorus as previously described. Oxidation of the phosphorus produces P2O5 which, when combined with H2O, yields H3PO4. 

The more modem process is based upon the previously described method for the production of elemental phosphorus from phosphate rock. Pure white phosphorus is oxidized to phosphorus pentoxide, which is then hydrated to form phosphoric acid. This method is particularly useful where a concentrated product of high purity is sought. 

Blast furnaces are used for the production of iron from ore and phosphorus from phosphate rock. 

Sources of Phosphates.—The most available and most exploited sources of phosphorus and its compounds at the present day are the phosphatic rocks, or phosphorites, which consist of tribasic calcium phosphate associated with calcium carbonate, alumina, magnesia, etc.1 Phosphates of alumina are also useful. The production of these secondary rocks from the older rocks has already been mentioned (p. 208). Although the apatites themselves, as pure minerals, contain a high proportion of phosphoric anhydride, they are difficult to decompose, and are admixed with other minerals of a still more refractory nature. 

A single, present-day phosphorus furnace produces from 60 to 160 tonnes of phosphorus per day, almost the same as the annual production figures of the early arc furnaces, and requires a power supply of about 90,000 kW for a single, 160 tonne/day furnace. Power consumption per tonne of phosphorus produced varies with the % calcium phosphate in the rock (% BPL level) and furnace size among other factors but ranges around 12,000-14,000 kWh/ tonne (Table 10.4). Hence, power is a major cost component of electric furnace phosphorus production. This realization has prompted a reexamination of fossil-fueled (petroleum coke-based) sources of heat for rotary kiln combustion to provide the energy of the endotherm of the reaction [15]. 

The industrial separation of N2 is discussed in Section 14.4. Mining of phosphate rock takes place on a vast scale (in 2001, 126Mt was mined worldwide), with the majority destined for the production of fertilizers (see Box 14.11) and animal feed supplements. Elemental phosphorus is extracted from phosphate rock (which approximates in composition to Ca3(P04)2) by heating with sand and coke in an electric furnace (equation 14.1) phosphorus vapour... 

Domestic supplies of vanadium are obtained from a deposit in Arkansas that is mined for vanadium alone from some deposits in the western states that yield coproduct uranium and vanadium and from slags derived from making elemental phosphorus from phosphate rock mined in Idaho. The vanadium-production potential of these deposits does not appear to be adequate to satisfy long-range domestic requirements. 

Various phosphates are produced from phosphoric acid which is made either by adding sulphuric acid to phosphate rock (wet process) or by burning phosphorus in air to give phosphorus pentoxide, which is then hydrated. Major uses of phosphoric acid are the production of phosphate and compound fertilizers, formation of sodium tripolyphosphate (which is used as a builder in detergents where it forms stable water-soluble complexes with calcium and magnesium ions) and the production of organic derivatives like triphenyl and tricresyl phosphate. These are used as plasticizers for synthetic polymers and plastics. 

For several years TVA produced calcium metaphosphate, Ca(POs)2, in a demonstration-scale plant. The process consisted of burning elemental phosphorus and reacting the resulting P2O5 vapor with phosphate rock. The molten product was tapped out of the ftirnace and -solidified on a watei cooled steel drum [17]. The resulting vitreous flakes were cooled further and crushed to pass a 10-mesh screen (about 1.6 mm). Development of a process for production of calcium metaphosphate involved three pilot plants and three demonstration-scale plants and a considerable amount of laboratory- and bench-scale work [IS]. The third demonstration-scale plant was technically successful and operated about 16 years, starting in 1949. A total of nearly 1 miflion tonnes was produced, including relatively small amounts from the first and second demonstration-scale plants. The process was economically competitive with TSP when both products were based on elemental phosphorus made by the electric-furnace process. 

Over 90% of the world s phosphate rock production is converted into orthophosphoric acid by the wet process (Chapter 5.2). Almost aU of this is used to make fertilisers and less than 5% is used to make other phosphorus compounds. Some of the latter are still made via the element itself, which is obtained directly from apatite by the electric furnace method (Chapter 4.1). Phosphate rock is sometimes used directly, in finely ground form as a fertiliser, or as an animal feed supplement, if the fluorine has been removed by prior heat treatment (Chapter 12.3). 

Vanadium is widespread in the earth s crust, twice as abundant as copper and ten times more than lead. Titanium minerals such as ihnenite often have a V-content of 0.1-0.3%. Vanadium is usually obtained as by-product from the extraction of iron from V-containing iron ores, uranium from V-containing carnotite and phosphorus from V-containing phosphate rocks. 

The only major bulk chemical not so far considered is phosphoric acid, which can be manufactured pure from phosphorus and in an impure form from phosphate rock. The latter process is the dominant one, the impure product being used mainly in the preparation of fertilizers. Phosphate rock is also the most common source of elemental phosphorus. It is extracted by open-cast mining. The thermal process for producing phosphoric acid from the element produces an acid which is about three times more expensive than that produced direct from phosphate rock using the so-called wet process. 

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