Application of phosphogypsum in gypsum board

In the production of paper gypsum boards, the use of unpurified phosphogypsum is a crucial step in bonding the paper core, and poor bonding often occurs. A wet paper core that does not stick together and is prone to clogging the dryer is also a major factor contributing to poor bonding during drying ； If there is no adhesion when dry, it is considered waste; it is necessary to ensure adhesion between the wet and dry sheets for the sheet production line to function properly. However, phosphogypsum contains a large amount of free water, is highly acidic, and has a very complex composition of impurities; in particular, the presence of P2O5, F, organic substances, and alkalis reduces the setting and hardening capabilities of hemihydrate gypsum produced from phosphogypsum, thereby severely affecting its use in the production of paper-faced gypsum boards. Washing, neutralization, and classification are effective methods for purifying phosphogypsum, but the high purification costs (3–5 tons of water are required to purify 1 ton of phosphogypsum via washing) render it unusable in the gypsum board industry, while also causing severe secondary pollution. Some gypsum board manufacturers have conducted extensive research on the semi-hydrated phosphogypsum production process in an attempt to solve the problem of paper core adhesion, but with often unsatisfactory results. This post was last edited by fuhefei on 2008-3-16 10:32.]

The adhesion between the face mask paper and the core of the phosphogypsum board is the main problem, primarily due to the effects of water-soluble substances such as P2O5, F, Na2O, K2O, Cl-, and organic matter present in phosphogypsum; among these, P2O5, organic matter, and Cl- have the greatest impact. Of course, if the foaming process is good during the production of paper gypsum boards, the impact of these substances on their adhesiveness is significantly reduced. This is experience gained from our company’s production!

Modification methods of phosphogypsum for paper-based gypsum boards. The main measures of this modification technique involve adding alkaline calcium salts and acidic sulfates to adjust the pH value of the gypsum, thereby improving the adhesion between the gypsum slurry and the face paper. Modification process of phosphogypsum: Alkaline calcium salts are added to gypsum, followed by mixing, drying, and calcination to obtain mature gypsum with a pH value of 6.5–11.0. Then, acidic sulfates are added to a slurry composed of mature gypsum, water, and admixtures, in order to adjust the pH value of the slurry to 3.0–6.0. The alkaline calcium salts used for modifying phosphogypsum are calcium oxide, calcium hydroxide, and calcium carbonate. Acidic sulfates are aluminum sulfate, ammonium sulfate, and iron sulfate. Since sodium sulfate and magnesium sulfate are hygroscopic, even a small amount added can severely damage their adhesion to face masks, so they should not be used. Acidic sulfates are usually added in the form of an aqueous solution. To promote the setting of phosphogypsum slurry, potassium sulfate as a setting accelerator can be added.

**There are preferential policies for using phosphogypsum in gypsum board production, so many gypsum board factories use some phosphogypsum, though not in large quantities. To save costs, the phosphogypsum used is generally only calcined, without any washing processes such as water washing or alkali washing. If phosphogypsum is used to produce gypsum blocks or self-leveling gypsum, a washing process is necessary.

Washing with water is better; moreover, using some chemicals in conjunction can greatly improve the quality of the products produced. Our factory uses this method, and the results are excellent.

The cost of water washing is too high, making it uneconomical for most gypsum board manufacturers. Currently, in gypsum board production, the main reasonable process for using phosphogypsum is roasting it into powder, which is then used in combination with natural gypsum or desulfurized gypsum.

Shandong Anqiu Aobao Chemical Co., Ltd. has achieved considerable success in gypsum board technology; phone number: (0536) 4390162. Quality is also directly related to the color of phosphogypsum.

Could you provide a brief overview of Aoba’s properties? For example, its manufacturing process, its use in gypsum board, the amount used, and the impact it has on gypsum board, etc.

The comprehensive utilization of waste materials helps turn waste into valuable resources. In the process of producing 300,000 tons of potassium sulfate compound fertilizer per year, Shandong Aobao Chemical Group generates 300,000 tons of phosphogypsum, with an existing stock of 1 million tons. The accumulation of phosphogypsum within the factory not only leads to waste of resources but also causes environmental pollution. Therefore, the comprehensive utilization of phosphogypsum is an urgent task for our company. In 2004, Shandong Aobao Group and Shandong Taihe Group jointly established Weifang Aotai Gypsum Co., Ltd., leveraging their respective advantages in terms of resources, technology, and management. This company produces 300,000 tons of gypsum powder, 30 million square meters of gypsum board, 200,000 square meters of gypsum blocks, and 400,000 square meters of gypsum hollow panels per year. It is able to utilize 400,000 tons of waste materials each year, generating annual sales revenue of 180 million yuan and profits and taxes of 50 million yuan. The products possess properties such as light weight, thermal insulation, sound insulation, fire resistance, and moisture resistance, making them ideal new building materials with “breathing functions.” They offer good economic, environmental, and social benefits, enabling the group company to make significant progress in developing a circular economy.