Analysis of the Current Yellow Phosphorus Production Process and Its Problems

At present, both at home and abroad, industrial yellow phosphorus is produced by reducing phosphide with phosphate rock, silica and coke in an electric furnace at high temperature. The basic process is to mix phosphate rock, silica and coke (or high-quality anthracite) evenly according to the process ratio, and then put them into the electric furnace after mixing. They are heated to 1350 to 1450℃ in the electric furnace, and the following main chemical reactions occur:

Ca10F2(PO4)6+15C+6SiO2＝3P2+15CO +3Ca3Si2O7 +CaF2 （1）

6CaF2+ 7SiO2 = 3SiF4+2Ca3Si2O7 (2)

The elemental phosphorus generated by the reaction in the electric furnace is vaporous phosphorus (also known as phosphorus vapor P2). After the phosphorus vapor and gases such as CO generated in the process are filtered through the semi-molten layer and raw material layer in the electric furnace, they enter the three-stage or four-stage spray tower through the air duct for gas washing, cooling, condensation and precipitation of liquid yellow phosphorus, and are mixed together to form crude industrial yellow phosphorus. After refining, industrial yellow phosphorus is obtained, and the remaining high-concentration CO and other tail gases are sent to the yellow phosphorus tail gas tank for utilization.

At the same time, under the high-temperature reducing atmosphere in the electric furnace, the arsenate in the phosphate rock also undergoes a reduction reaction, and this type of reaction is relatively complete. The specific reaction is as follows:

2As2O3 + 3C → 4As + 3CO2↑ (3)

As2O3 + 3C → 2As + 3CO↑ (4)

As2O3 + 3CH4 → 4H3As + 3CO↑ (5)

Obviously, the furnace gas entering the duct contains not only phosphorus vapor, carbon monoxide and silicon tetrafluoride gas, but also elemental arsenic (vapor), gaseous arsine and a large amount of dust (including arsenic elemental precipitated by cooling and condensation of the raw material layer) and other impurities. The furnace gas temperature entering the first-stage spray tower is about 150~200℃. It is cooled or condensed by water spraying or condensing in the third-stage spray tower to convert the vaporous phosphorus into liquid phosphorus (P4). At the same time, the elemental arsenic vapor condenses into solid arsenic and forms a co-solvent with liquid yellow phosphorus to enter the crude industrial yellow phosphorus, and then undergoes multi-stage refining and impurity removal to obtain industrial yellow phosphorus. The refining process mainly removes a large amount of phosphorus mud formed by dust ash and hydrated silicon dioxide brought out by the furnace gas.

In recent years, China's yellow phosphorus production has made rapid progress, especially the major yellow phosphorus production enterprises in Hubei and Yunnan have made great contributions to promoting the reduction of product material consumption and energy consumption, as well as the reduction of pollutant emissions. In the development of China's yellow phosphorus industry, although there have been great improvements in technical equipment, resource utilization and environmental protection levels, the overall process technology remains at the level of the 1960s without major changes. And there are many problems. In particular, few people pay attention to improving product quality and grade by using process control in the production process. The following is an analysis of the characteristics of the migration and conversion of the main substances in the current yellow phosphorus production process .

At present, the main harmful element that affects the production and quality of yellow phosphorus is arsenic, because phosphorus and arsenic are elements of the same family, are mutually soluble and have similar properties, and are extremely difficult to separate. There are many technical developments and studies on the removal of arsenic from industrial yellow phosphorus at home and abroad, which are mainly divided into two categories: chemical method and physical method. Chemical methods include aqueous nitric acid oxidation, organic solvent extraction, etc., and physical methods include vacuum distillation, activated carbon adsorption, zone melting, electromagnetic purification, etc., which generally have high production costs and heavy secondary pollution, and most of the technologies are still in the laboratory stage. Obviously, economical and applicable yellow phosphorus impurity removal technology has gradually become an urgently needed technology for thermal yellow phosphorus and its downstream product manufacturers, especially the key arsenic removal technology. So far, there has been no relevant report on the technology of obtaining low-impurity or high-purity yellow phosphorus based on the process condition control of impurity transfer during the yellow phosphorus production process.

That is, the problems existing in the current yellow phosphorus production process are analyzed as follows :

（1）Low quality product

① The impurity content is high, and only ordinary industrial-grade products can be produced. It even directly affects the reaction activity of organic phosphorus synthesis, inhibiting the extension of the downstream phosphorus chemical industry chain; ② Further refining and purification are required to produce higher-grade products, and the refining cost is high.

（2）The amount of "three wastes" generated is large

① Wastewater - wastewater containing phosphorus and fluoride; ② Solid waste - phosphorus sludge (which contains a certain amount of phosphorus, but it is difficult to recover the phosphorus resources because it contains water and silica) and its phosphorus evaporation residue (which may be regarded as hazardous waste).

（3）Low comprehensive utilization rate of raw materials

① Fluorine resources are not utilized; ② Waste heat from phosphorus slag is not fully utilized.