What Is Involved in Phosphate Mining?

Phosphate pollution refers to the pollution of the environment caused by phosphate produced in activities such as industrial production and daily life. Including pollution of waters and industrial radioactive pollution. ^[1-2]

China has vast water resources, but the sewage discharged by detergents has seriously polluted the water quality. Although the national environmental protection department has strengthened its management in recent years, and the media has also reported a lot about it, some people lack enough understanding of this and have disputes over how to prevent and control phosphate pollution. How much does phosphate in the detergent bring pollution damage to the environment? What are the measures to prevent phosphate pollution?

Detergents are daily necessities for people's lives. With the development of the economy, the production of detergents in China has reached in recent years. There are many types of detergents, such as washing powder, dishwashing detergents, toilet detergents, carpet detergents, metal detergents, and oily detergents that people often use.

Detergents are composed of surfactants and builders. The currently used builders are mainly phosphates, that is, sodium tripolyphosphate, whose content in detergents is generally between 20% and 40%.

As a detergent builder, it should have the following qualities: softening water performance, which can effectively combine calcium and magnesium ions in hard water, so that hard water can be fully softened; provide a certain alkaline and stable value to the detergent in general It is around; It has dispersion performance, that is, resistance to re-precipitation, which can prevent secondary re-contamination due to accumulation of dirt. Sodium tripolyphosphate has all these properties and is a good detergent builder. About 600 to 700 kt of sodium tripolyphosphate is used every year in China. ^[3]

Phosphate ore contains a certain amount of natural radioactive materials. The mining and processing of phosphate ore redistributes ²³⁸ U and its decay products to the products, by-products and waste of the phosphate industry, phosphate fertilizer for agriculture, and construction Both by-products and waste discharged into the environment form radiation sources. Due to the concealment and accumulation of radioactive pollution, its potential hazards should be more vigilant.

Radioactive pollution from phosphate mining and processing

1. Radioactivity of ore mining

In the ore dressing, the ore should be separated from tailings and clay slime. The radioactive content in the slime is similar to that in commercial ore, while the tailings is less. The fine rock dust discharged into the atmosphere during the drying and grinding process also contains certain radioactive materials. For example, a drying plant in a Florida plant in the United States processes an average of 217 × 10 ⁹ kg of wet ore each year, and emits about 250 MBq of ²³⁸ U and It is roughly equivalent to ²²⁶ Ra.

2. Radioactivity in wet production

In wet production, sulfuric acid is usually mixed with mineral powder. After treatment, the product is phosphoric acid and the by-product is phosphogypsum. Uranium and thorium in phosphate rock are mainly transferred into phosphoric acid, and radium is co-precipitated with phosphogypsum. Therefore, the content of uranium and thorium in some phosphate fertilizers produced by wet process is often significantly higher than that of ore, and phosphogypsum is used in building materials more carefully. In addition to non-radioactive fluorides, the atmospheric emissions of wet phosphorous chemical industry also contain a large amount of productive dust. Generally speaking, when the content of ²²⁶ Ra in the ore is 1500 Bq · kg ^-1 , 115 to 10 ⁶ Bq of ²²² Rn will be released per ton of phosphate ore. The wastewater of the wet process plant needs to be discharged after treatment. In the process wastewater with a pH of 1.5-2.0, the content of ²³⁸ U can reach tens of thousands of Bq · m ^-3 . Therefore, the proper treatment of process wastewater and sludge is very important to reduce its radioactive pollution to the environment.

3. Radioactivity in thermal production

The products produced by thermal method are yellow phosphorus, and the by-products are slag (calcium silicate slag) and iron phosphate. Yellow phosphorus itself is not very radioactive, and most of the radioactive material in the ore is concentrated in calcium silicate slag and iron phosphate. In addition, the melting process of ore causes ²¹⁰ Po and other volatile radioactive substances to be released to the atmosphere. The level of radioactive material in wastewater is generally low.

Radioactive contamination of phosphorus products

1. Radioactive effects in the use of by-products and waste residues

When the by-products and wastes of the phosphate fertilizer industry are reused, because they contain a lot of radioactive components, if used improperly, secondary pollution is likely to occur, leaving hidden dangers to the environment and public health.

Calcium silicate slag, a by-product of thermal method, is mostly used as ballast slag, filling material and concrete, but in addition to volatile ²¹⁰ Po during the melting process, the natural radioactive content of the ²³⁸ U series is as much as that of ore and slag. According to the survey, in a room built with 43% by weight slag cement board, the gamma absorbed dose rate in the air is significantly higher than the indoor average air absorbed dose rate.

2. Radioactivity in phosphate fertilizer

It is estimated that 0.45 tons of phosphate fertilizer is produced per ton of commercial ore, which contains approximately ²²⁸ U of 3 × 10 ⁵ Bq and ²²⁶ Ra of 2 × 10 ⁵ Bq and their decay products. Phosphate fertilizer applied to the soil will increase the radioactivity of the soil, but it will not be obvious for several years. Affected plants will also ingest some radioactive material, and additional doses received by people engaged in phosphate fertilizer production, transportation, storage, and use of a small number of people will increase. In addition, phosphate products are widely used as additives in feed, which will also increase the radioactive content of animal products such as milk.

Conduct a comprehensive investigation of the natural radioactive levels of phosphate ore in the province as soon as possible to facilitate reasonable deployment. If a certain proportion of high-radioactive phosphate is mixed with lower-level ones, it can effectively reduce the radioactivity levels in products, by-products and the three wastes, and also increase the average comprehensive grade of phosphate rock raw materials and the utilization rate of low-grade ore Prolonging the mining life and reducing the overall cost are beneficial to the sustainable development of the entire industry.

There must be radioactive content in the planning, environmental assessment, and completion acceptance of the phosphating enterprise construction. Periodic monitoring of radioactivity should be carried out with emphasis on the existing phosphate chemical plants, which is particularly necessary for major phosphate mining areas such as Kunming and Yuxi.

The comprehensive utilization of by-products and solid wastes, especially when phosphogypsum and various phosphorous slags are used in the manufacture of building materials, must be radioactively tested, reasonably limited in accordance with relevant standards, and secondary pollution must be strictly prevented.

Before the reclamation of the phosphate mine goaf, the radioactivity level survey should be conducted. If the level is too high, the reduced radioactivity level should be included in the plan according to the actual situation, and corresponding measures should be formulated to rationally adjust the plan to avoid blind restoration. Ken and the crowd settled.

Organize a special study on the radioactivity of phosphate industry at an appropriate time, and combine with the actual situation in Yunnan, formulate relevant local regulations and standards for the links that may generate radioactive pollution in the development and utilization of phosphate mineral resources, so as to prevent and control the radioactive pollution in phosphate industry Systematic, regular and legalized. ^[1]