**9.1. Manufacturing of phosphorus**

The original procedure for the production of elemental phosphorus, as described by R. BOYLE in 1680, was based on the method of H. BRANDT [2],[3],[4]. The substance glowed in

**Fig. 1.** Phosphorus retort condensation arrangement (Albricht & Wilson) (a) and a French bone furnace (Four pour la calcination des os) (b) [7].

the dark1 and burst in flame into P4O10 when exposed to air [2],[5]. The procedure involved the distillation of large quantity of partly digested urine to the consistency of thick syrup. Fine white sand was added and the mixture was heated in a retort at first gently to remove the volatiles and then very intensely to produce phosphorus, which was distilled over and cooled under water. When the bone ash (M.M. COIGNET) was used as a raw material for the production of phosphorus, the process consisted of the treatment with sulfuric acid to pro‐ duce phosphoric acid, which was then concentrated and heated with coke in a retort to produce phosphorus according to the following equations [6],[7]:

$$\text{Ca}\_3\text{(PO}\_4\text{)}\_2 + 3\text{ H}\_2\text{SO}\_4 \rightarrow 3\text{ CaSO}\_4 + 2\text{ H}\_3\text{PO}\_4\tag{1}$$

$$\rm H\_3PO\_4 \rightarrow HPO\_3 + H\_2O \tag{2}$$

$$\text{14 HPO}\_3 + \text{I} \\ \text{2 C} \rightarrow \text{P}\_4 + \text{2 H}\_2 + \text{I} \\ \text{2 CO} \tag{3}$$

The drawing of the kiln for the calcination of bones2 is shown in **Fig. 1**(**b**).

<sup>1</sup> The name phosphorus (light-bearing) was often used by alchemists to name various light-bearing materials, which were devoid of the element, e.g. the Bologna phosphorus (luminescent barium sulfide), the Baldwin's phosphorus (luminescent calcium nitrate), etc. Probably the earliest prepared phosphorus salt was sodium ammonium hydrogen phosphate, which has been known since the ancient times [2].

<sup>2</sup> Bones became the source increasingly difficult to achieve. It is stated that the use of bones was so great in England during the eighties of 19th century that the battlefields on the continent of Europe were plundered to supply Great Britain's demand for phosphates [7].

The discovery of elemental (white) phosphorus3 was soon followed by the characterization of its combustion products, phosphorus pentaoxide,4 and in 1694, R. BOYLE prepared phosphor‐ ic acid by dissolving P2O5 in water. Phosphorus was found in plants by B. ALBINO in 1688, and the element was detected in human brain tissue by J.T. HENSING in 1719. In about 1770, phosphorus was recognized as an essential ingredient of animal bones and teeth by C.W. SHEELE, when he prepared the element from bone ash, carbon and sand. By 1779, the first phosphorus-containing mineral pyromorphyte (**Section 1.6.4**) was identified by J.T. HENSING [2].

The first organic phosphorus compound to be identified was probably lecithin, isolated from barin fat in 1811 by VAUQUELIN and characterized as a phosphorus-containing lipid by GOBLEY in 1850. The earliest laboratory synthesis of an organic phosphorus compound was reported by LASSAIGNE, who in 1820 obtained crude alkyl phosphates by the reaction of alcohols with phosphoric acid. The discovery of the first metal-phosphine complex by ROSE in 1847 was followed by CAHORS AND HOFFMANN who prepared the first organic complex with metalphosphorus bond. It can be considered as the beginning of the metallophosphorus chemis‐ try [2].

The following major classes of phosphorus compounds (**Fig. 2**) are recognized [2]:

**1. Oxyphosphorus compounds**, which contain covalent P-O linkages.

**Fig. 2.** The major division of oxyphosphorus compounds [2]:

the dark1

2

demand for phosphates [7].

calcination des os) (b) [7].

and burst in flame into P4O10 when exposed to air [2],[5]. The procedure involved

Ca PO 3 H SO 3 CaSO 2 H PO 3 4 24 ( )<sup>2</sup> +®+4 34 (1)

H PO HPO H O 34 3 2 ® + (2)

is shown in **Fig. 1**(**b**).

3 42 4 HPO 12 C P 2 H 12 CO + ®+ + (3)

the distillation of large quantity of partly digested urine to the consistency of thick syrup. Fine white sand was added and the mixture was heated in a retort at first gently to remove the volatiles and then very intensely to produce phosphorus, which was distilled over and cooled under water. When the bone ash (M.M. COIGNET) was used as a raw material for the production of phosphorus, the process consisted of the treatment with sulfuric acid to pro‐ duce phosphoric acid, which was then concentrated and heated with coke in a retort to

1 The name phosphorus (light-bearing) was often used by alchemists to name various light-bearing materials, which were devoid of the element, e.g. the Bologna phosphorus (luminescent barium sulfide), the Baldwin's phosphorus (luminescent calcium nitrate), etc. Probably the earliest prepared phosphorus salt was sodium ammonium hydrogen

 Bones became the source increasingly difficult to achieve. It is stated that the use of bones was so great in England during the eighties of 19th century that the battlefields on the continent of Europe were plundered to supply Great Britain's

**Fig. 1.** Phosphorus retort condensation arrangement (Albricht & Wilson) (a) and a French bone furnace (Four pour la

produce phosphorus according to the following equations [6],[7]:

418 Apatites and their Synthetic Analogues - Synthesis, Structure, Properties and Applications

The drawing of the kiln for the calcination of bones2

phosphate, which has been known since the ancient times [2].

<sup>3</sup> Three forms of phosphorus include (a) white phosphorus (the most reactive form) with at least two crystalline forms, (b) red phosphorus (discovered in 1847 by VON SCHROTTER) and (c) black phosphorus (discovered in 1914 by BRIDGEMAN) [5].

<sup>4</sup> Three forms of P4O10 are recognized [5]: (a) **H-form**, (b) **O-form** and (c) **O'-form**. The H-form is rhombohedral (R3C, *a* = 7.43 Å, *α* = 87.0° and *Z* = 2). In the hexagonal setting, *Z* = 6, *a* = 10.31 and *c* = 13.3 Å. The O-form is orthorhombic of the space group FDD2 and the cell parameters *a* =13.3, *b* = 8.14 and *c* = 5.26 Å and *Z* = 8. The O'-form is orthorhombic, the space group PNAM, *a* = 9.23, *b* = 7.18 and *c* = 4.94 Å and *Z* =2.


These compounds vary greatly in their abundance and importance. The compounds with the P-O linkages dominate the phosphorus chemistry. The most important types of oxyphospho‐ rus compounds are phosphates (salts with PO4 3− anion), phosphate esters (P-O-C linkage) and phosphoric compounds (P=O linkage) [2].

**Fig. 3.** Parker's electric furnace (a) [7] and the scheme of phosphorus furnace (b) [11].

The production of phosphorus by heating the mixture of silica, coke and phosphate rock was first proposed by AUBERTON and BOBLIQUE in 1867, and the use of electric furnace for the heating of the mixture was proposed in 1888 by the patents by J.B. READMAN [8] and T. PARKER and A.E. ROBINSON [9]. **Fig. 3**(**a**) shows Parker's electric furnace from his later patent in 1892 [10].

The basic method for the production of elemental phosphorus today (**Fig. 4**), except for engineering improvements, is essentially that of the method originated by READMAN. Lowergrade phosphate sand contaminated with clay is concentrated by washing to an average content of P2O5 in the range from 28 to 30%. Higher-grade sand with the content of P2O5 of 26 – 28% is used directly in the combination with washed sand. These fine phosphatic grains are compacted or "nodulized" and then sintered into fused agglomerates. The nodules are then mixed with silica and coke particles of similar size. Such mixture is called the "furnace burden". A typical furnace burden has the SiO2/CaO ratio of 0.8 to 1.2 and the P2O5/C ratio of 2.3 to 2.6 [6].

**Fig. 4.** The flow sheet for the electrothermal manufacture of elemental phosphorus [12].

Modern reduction plants for the manufacture of elemental phosphorus (**Fig. 4**) has three main units [12]:


**2. Carbophosphorus** (**organophosphorus**) **compounds**, which contain the P-C linkages including carbophosphanes (organophosphanes, P-C), carbophosphenes (organophos‐

**3. Azophosphorus compounds**, which contain the P-N linkages including azophosphanes (phosphazanes, P-N), azophosphenes (phosphazenes, P=M) and azophosphynes

**4. Metalophosphorus compounds**, which contain the P-metal linkages including metallo‐ phosphanes (P-M), metallophosphenes (P=M) and metallophosphynes (P≡M).

These compounds vary greatly in their abundance and importance. The compounds with the P-O linkages dominate the phosphorus chemistry. The most important types of oxyphospho‐

3− anion), phosphate esters (P-O-C linkage) and

phens, P=C) and carbophosphynes (organophosphynes, P≡C).

420 Apatites and their Synthetic Analogues - Synthesis, Structure, Properties and Applications

**Fig. 3.** Parker's electric furnace (a) [7] and the scheme of phosphorus furnace (b) [11].

The production of phosphorus by heating the mixture of silica, coke and phosphate rock was first proposed by AUBERTON and BOBLIQUE in 1867, and the use of electric furnace for the heating of the mixture was proposed in 1888 by the patents by J.B. READMAN [8] and T. PARKER and A.E. ROBINSON [9]. **Fig. 3**(**a**) shows Parker's electric furnace from his later patent in 1892 [10].

The basic method for the production of elemental phosphorus today (**Fig. 4**), except for engineering improvements, is essentially that of the method originated by READMAN. Lowergrade phosphate sand contaminated with clay is concentrated by washing to an average

(phosphazynes, P≡N).

rus compounds are phosphates (salts with PO4

phosphoric compounds (P=O linkage) [2].

The electric furnace for the reaction **Fig. 3**(**b**) is lined on the bottom and sides with thick carbon blocks, while the top is lined with refractory bricks. The furnace is heated by symmetrically positioned carbon electrodes. They go through almost airtight seal in the furnace roof into the reaction zone and are supported in a manner that enables them to move vertically depending on the power requirements of fluctuating furnace conditions. The temperature in the reaction zone ranges from 1400 to 1500°C. Under this condition, phosphorus vaporizes and rises with carbon monoxide and entrained dust through the space between the furnace burden particles. The mixture next passes through an electrostatic precipitator where the most of the dust is removed. The phosphorus vapor is then cooled, condensed and collected under water [6],[11], [12],[13].

The condensation of white phosphorus5 is carried out in two stages. In the first stage, the condensation tower water of 50 to 60°C is sprayed from the top to meet the phosphorus vapor

<sup>5</sup> Red phosphorus is produced in much less quantities than white phosphorus. The conversion of white phosphorus to red phosphorus is an exothermic reaction producing red phosphorus as a solid product. Since the conduction of heat from the reaction is difficult, the conversion is carried out semi-continuously in a ball mill at 350°C. White phosphorus is fed into the mill with such rate that the reaction temperature is kept constant [12].

being transported countercurrently from below, whereupon phosphorus condenses as a liquid. Solid phosphorus is formed in the second condensation tower, which uses water with the temperature of 10 to 25°C. CO gas is recovered for the use as a fuel in the sintering operation. The by-product calcium silicate is drawn off from the bottom of the furnace as molten liquid. Iron phosphide, "ferrophos" or ferrophosphorus (**Section 9.2.7**) formed from the iron impurities present in the phosphate ore is also drawn off as a melt [6],[12].

The mechanism of phosphate reduction is complex and there is no complete agreement among the exact path of each step in the reaction sequence. The overall reaction can be presented by the following equation [6]:

$$\text{Ca}\_3\text{(PO}\_4\text{)}\_2 + 3\text{ SiO}\_2 + 5\text{ C} \rightarrow 3\text{ CaSiO}\_3 + 5\text{ CO} + \text{P}\_2\tag{4}$$

Proposed mechanisms for the reactions are:

**1.** Phosphide mechanism [14]:

$$\text{5 C} \text{ Ca}\_3\text{(PO}\_4\text{)}\_2 + \text{40 C} \rightarrow \text{5 C} \text{ Ca}\_3\text{P}\_2 + \text{40 CO} \tag{5}$$

$$\text{23 Ca}\_3\text{(PO}\_4\text{)}\_2 + \text{5 Ca}\_3\text{P}\_2 \rightarrow \text{24 CaO} + \text{8 P}\_2\tag{6}$$

**2.** Acid displacement mechanism:

$$2\text{ Ca}\_3\text{(PO}\_4\text{)}\_2 + 6\text{ SiO}\_2 \rightarrow 6\text{ CaSiO}\_3 + \text{P}\_4\text{O}\_{10} \tag{7}$$

$$\text{P}\_4\text{O}\_{10} + 10\text{ C} \to 2\text{ P}\_2 + 10\text{ CO} \tag{8}$$

#### **3.** CO reduction mechanism:

$$\text{Ca}\_3\text{(PO}\_4\text{)}\_2 + 5\text{ CO} \rightarrow 3\text{ CaO} + 5\text{ CO}\_2 + \text{P}\_2\tag{9}$$

$$\text{5 CO}\_2 + \text{5 C} \to \text{10 CO} \tag{10}$$

The phosphide theory is generally considered as unlikely due to the thermodynamic reasons, but the acid displacement mechanism has considerable experimental support [6].
