Exchange and discussion on \"Technologies, Equipment, and Applications for the Purification of Phosphogypsum\"

Current status of the resource utilization of phosphogypsum in China: With the rapid development of China’s phosphate fertilizer industry, the amount of phosphogypsum generated as a by-product has seen exponential growth. Improving the comprehensive utilization rate of phosphogypsum is not only an urgent issue that the phosphate fertilizer industry must address but also a priority that government agencies at all levels, research institutions, and related enterprises must tackle seriously. Phosphogypsum is a solid waste generated during the production of phosphate fertilizers and phosphoric acid; approximately (4.5–5) tons of phosphogypsum are produced for every 1 ton of phosphoric acid manufactured. The main component of phosphogypsum is calcium sulfate (CaSO4˙2H2O); it also contains small amounts of impurities such as partially unreacted phosphate rock, fluorides, phosphoric acid, organic matter, acid-insoluble substances, and iron-aluminum compounds. With the rapid development of high-concentration phosphate fertilizers and the phosphate industry in our country, the amount of phosphogypsum generated as a by-product has increased sharply. At present, the annual emission of phosphogypsum in our country amounts to around 50 million tons, and due to bottlenecks in recycling technologies, the cumulative stockpile has exceeded 200 million tons. In China, there are still no effective ways to utilize phosphogypsum; it is mostly stored, which not only takes up land but also wastes resources. The acidic and other harmful substances contained in it can easily pollute the surrounding environment. It is clear that phosphogypsum needs to be dealt with thoroughly; otherwise, it will have a negative impact on human health, the environment, social harmony, and land protection, while also causing immeasurable losses to the survival and development of enterprises. The harmless treatment of phosphogypsum waste has become a \"bottleneck\" issue affecting the production of phosphate fertilizer companies; improving the comprehensive utilization of phosphogypsum will be key to the sustainable development of the phosphate fertilizer industry. This article discusses in detail the problems existing in the comprehensive utilization of phosphogypsum and its resource-based applications, and puts forward several suggestions for the resource utilization of phosphogypsum. 2 Current status of the comprehensive utilization of phosphogypsum in China: According to incomplete statistics, the current level of comprehensive utilization of phosphogypsum in China is around 10,000 kt/year (that is, 10 million tons per year), which is lower than the utilization rate of desulfurization gypsum. Of this, approximately 2800 kt/a is produced as building gypsum, about 2500 kt/a as cement retarders, around 1600 kt/a as gypsum blocks and bricks, 1500 kt/a as a filling material, 1500 kt/a as a soil conditioner, and approximately 100 kt/a for the production of chemical products such as sulfuric acid and sulfuric anhydride. The main problems existing in the comprehensive utilization of phosphogypsum in our country at present are as follows. (1) Phosphogypsum contains many impurities, resulting in high utilization costs. Phosphogypsum contains acidic substances such as free phosphoric acid and sulfuric acid, which results in a low pH value and makes it prone to corroding production equipment. At the same time, phosphates, fluorides, and other substances contained in phosphogypsum have an adverse effect on the downstream processed products. Therefore, phosphogypsum must undergo processes such as purification and impurity removal before it can be utilized in subsequent steps. The use of phosphogypsum can cause secondary pollution; environmental protection facilities are necessary to meet **environmental standards, and the associated investment and operating costs are high. (2) Development is uneven among different regions, and the comprehensive utilization of phosphogypsum has remained at a low level for a long time. Affected by the distribution of regional resources and transportation distances, there are significant differences in the generation, storage, and comprehensive utilization of phosphogypsum across different regions. The discharge and storage of phosphogypsum mainly occur in regions where phosphate fertilizers are produced, such as Yunnan, Guizhou, Sichuan, Hubei, and Anhui. Meanwhile, the consumption of gypsum is primarily in areas with high production of building gypsum and cement, such as the economically developed provinces and cities in the eastern part of China. Due to the impact of the transportation radius, areas with high demand for gypsum face a supply shortage, while areas where emissions are concentrated are forced to store large quantities of it. (3) The standard system is incomplete. On the one hand, the lack of standards for phosphogypsum used in the production of various building materials hinders its application in different construction sectors. On the other hand, there are a lack of standards related to products derived from the comprehensive utilization of phosphogypsum; therefore, other similar standards have to be used as references. The low level of market acceptance makes it difficult to utilize phosphogypsum on a large scale. (4) China’s large output of natural gypsum limits the utilization of phosphogypsum. In 2010, China’s natural gypsum production was 45,000 kt, with the main production areas being Shandong, Hunan, Hubei, Jiangsu, and Anhui. The extensive extraction and use of natural gypsum not only damages the natural environment but also takes over the market from gypsum produced as an industrial by-product. Compared with the high overall utilization rates of industrial by-product gypsum in developed countries abroad, there is significant pressure to utilize phosphogypsum in China (for example, 35% in the United States and almost 100% in Japan). 3 Resource utilization of phosphogypsum 3.1 Use of phosphogypsum as a cement retarder At present, the main raw materials for cement retarders in China are natural gypsum and desulfurized gypsum. As cement production increases, the domestic demand for cement retarders is also growing. The increasing mining costs of natural gypsum deposits in our country, along with the decline in high-quality gypsum resources, have also created opportunities for using phosphogypsum as a cement retarder. Currently, the total amount of phosphogypsum used as a cement retarder in China is around 6 Mt per year. In 2012, China’s demand for cement retarders in cement production was approximately 90 Mt; even if all the production capacity for cement retarders made from phosphogypsum were utilized, it would still account for only about 7.4% of the total demand for such retarders. It is evident that phosphogypsum has great market prospects as a cement retarder. At present, the maximum scale for a single production line of cement retarding agents made from phosphogypsum in China is 800 kt/a. The biggest problem with using phosphogypsum as a cement retarder is that the impurities present in it can affect the setting time of cement, thereby reducing its strength. Therefore, appropriate purification and impurity removal treatments must be carried out on phosphogypsum, with the key being to remove acidic substances such as phosphorus and fluorine from it. The commonly used purification and impurity removal processes currently include washing and separation, neutralization, drying, and calcination. In the future, efforts should be made to improve the quality of phosphogypsum and reduce the production costs associated with its use as a cement retarder, in order to accelerate the substitution of phosphogypsum for natural gypsum and desulfurization gypsum as cement retarders. 3.2 Production of gypsum blocks and bricks from phosphogypsum Like natural dihydrate gypsum and desulfurized gypsum, phosphogypsum is primarily composed of CaSO4˙2H2O. It is technically feasible to use phosphogypsum to produce building materials such as gypsum blocks and gypsum bricks, and the strength, load-bearing capacity, and air permeability of these products are superior to those of traditional clay bricks and cement bricks. At present, the total production capacity for gypsum blocks made from phosphogypsum in China is approximately 5.0×106 m2 per year; the largest single-production line of this type belongs to Hefei Jinlong New Environmental Protection Building Materials Co., Ltd., with a capacity of 1.5×106 m2 per year ； The total production capacity of gypsum bricks made from phosphogypsum is approximately 2.0×109 units per year; the largest scale for a single production line is achieved by Guizhou Kailin (Group) Co., Ltd. It is necessary to further improve the standard system for the comprehensive utilization of industrial by-product gypsum, and to accelerate the development and revision of standards related to industrial by-product gypsum as well as its various applications. (4) In the future, great efforts should be made to promote the use of phosphogypsum as a cement retarder and in the production of new building materials such as gypsum board, gypsum blocks, and gypsum-based commercial mortars. Priority is given to encouraging projects that use phosphogypsum as the raw material exclusively: paper gypsum board production lines with a single-line capacity of 3.0×107 m2/year or more; projects for the construction or renovation of gypsum block production lines with a single-line capacity of 3.0×105 m2/year or more; projects for the construction or renovation of dry-mix gypsum building materials production lines such as plastering gypsum and bonding gypsum, with a single-line capacity of 100 kt/year or more; projects for the construction of high-strength gypsum powder production lines with a single-line capacity of 50 kt/year or more; and projects for the construction of building gypsum powder production lines with a single-line capacity of 1000 kt/year or more. (5) Develop a range of key common technologies, such as low-cost, high-performance, environmentally friendly phosphogypsum purification technologies; technologies for producing low-cost and high-performance cementing materials specifically for mine backfilling from low-quality phosphogypsum; and key technologies for improving soil using industrial by-product gypsum. (6) Actively pursue technological research on the chemical treatment of phosphogypsum, and promote the industrialization of advanced technologies such as using low-energy processes to produce sulfuric acid along with cement or calcium oxide from phosphogypsum, to produce calcium carbonate alongside sulfuric acid, and to produce potassium sulfate along with ammonium chloride or chlorinated NPK compound fertilizers. (7) The key to the comprehensive utilization of phosphogypsum lies in **policy support; financial, tax, and energy-related policies must be employed to enable enterprises to make a profit or at least break even from its comprehensive utilization. It is recommended that value-added tax on building materials and chemical products produced using phosphogypsum as raw material be exempted or refunded immediately upon collection. 5 Conclusion Due to differences in technology and living standards, the comprehensive utilization of phosphogypsum in our country is relatively underdeveloped. To date, the phosphogypsum emitted during the production of most current phosphate chemical enterprises has not been effectively utilized; it not only wastes resources and occupies land but also pollutes the environment, making its comprehensive development and utilization an urgent necessity. Phosphogypsum can be used to produce chemical products with high added value and large consumption volumes, such as building materials and fertilizers, thereby turning waste into treasure. Therefore, it is essential to strengthen research and development efforts aimed at the efficient utilization of phosphogypsum resources.

This post was last edited by gyt0731 on 2016-12-13 at 11:26 :) I have gathered technical standards related to the use of phosphogypsum (both domestically and internationally; please see the link: http://bbs.hcbbs.com/thread-1651393-1-1.html). I would like to ask if anyone has any additional information to add? From a technical standards perspective, the use of phosphogypsum in products such as gypsum boards, blocks, bricks, and powder has been going on for over 20 years, and to date its reputation remains mixed. It seems that there are quite a few psychological barriers and other issues associated with the use of phosphogypsum, which casts a somewhat ambiguous shadow over its use. Regarding the existing 300 million tons of phosphogypsum, along with an additional 80 million tons added each year, there are many reports online about positive technological developments and efforts to encourage its use. At the same time, there are also those who question the hazards of phosphogypsum and call for avoiding or abandoning its use. What are people’s opinions on this?