1. Analysis of Current Situation of Phosphogypsum Utilization

China is a big country with phosphogypsum resources, and its phosphorus (fertilizer) chemical products are number one in the world. Agriculture is the foundation of the national economy and has ensured the rapid growth of phosphate fertilizers for more than 10 years. Driven by energy conservation and emission reduction environmental protection policies, the comprehensive utilization rate of phosphogypsum has increased year by year, but the utilization rate and utilization level are still low. In 2019, the utilization of phosphogypsum in my country was 30 million tons, a year-on-year decrease of 1 million tons, and the actual utilization rate was about 40%, a decrease of 3.22%.

2. Current Situation of Phosphogypsum Resource

In 2019, the various utilization methods of phosphogypsum in China mainly include: cement retarder, filling or road construction, external supply or joint operation, gypsum board, building gypsum, etc.

At present, in the application of phosphogypsum as a raw material for gypsum production, there are mainly the following methods:

(1) Phosphogypsum has a relatively complete extraction of phosphorus in the production process, and the residual phosphorus content is very low (less than 0.5%); or the phosphogypsum produced by slurry slag discharge (equivalent to water washing) process has high purity and low phosphorus content. The raw materials can be directly calcined by calcining equipment without any treatment.

(2) If the impurity content in phosphogypsum is high, the raw material of phosphogypsum can be used after washing and filtering. The soluble phosphorus compounds in the phosphogypsum are dissolved and filtered out mainly by washing with water. After filtration, the soluble phosphate in the phosphogypsum is greatly reduced, and the influence on the hydration and hardening performance of the phosphogypsum after subsequent calcination is reduced, to achieve the availability of phosphogypsum.

(3) The phosphogypsum raw material is neutralized with lime and then applied. This method mainly uses the strong alkaline properties of lime to remove the residual acid in the phosphogypsum to achieve the availability of the phosphogypsum.

(4) High temperature heat treatment----mainly use the characteristics of equipment and process to reduce the soluble phosphorus compounds in phosphogypsum with higher temperature and specific calcination method. It promotes the conversion of soluble substances to insoluble substances at a specific temperature section to reduce the content of soluble substances. Compared with other similar production lines for processing phosphogypsum, the flash calcined product has higher performance.

In practical applications, most of the impurity removal methods of phosphogypsum are a combination of various processes, such as water washing + neutralization, neutralization + flotation, neutralization + calcination, water washing + calcination, etc. The specific method to be adopted should be comprehensively analyzed and selected according to the characteristics of phosphogypsum itself.

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