I would like to ask about the process requirements for using phosphogypsum to produce building materials
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Hello everyone! I would like to ask you about phosphogypsum, which is produced using disk or rotary filter machines in the phosphate production process. If this phosphogypsum is used to manufacture building materials such as cement, gypsum bricks, and gypsum boards, should the crystalline water contained in the calcium sulfate within the phosphogypsum be removed by drying? What is the target moisture content? Additionally, I would like to ask what kind of drying equipment is generally used, and what would be the energy consumption or cost per ton of water removed? Thank you all for your advice. This post was last edited by yunanshu on 2008-3-6 14:58]
OP, phosphogypsum is used in the production of building materials such as cement, gypsum bricks, and gypsum boards. The key issue lies in the impact of residual phosphorus and fluorine on the properties of gypsum, and this problem must be resolved first. Currently, there are methods such as washing, neutralization, lime washing, flotation, and flash calcination. Among these, the washing method is well-developed; the gypsum produced through this method has relatively stable properties, and it is widely used abroad. However, the washing process is complex, requires significant investment, and involves high water and energy consumption. Moreover, the wastewater generated after washing must be treated before it can be discharged. This pretreatment process becomes competitive only when the annual utilization volume of phosphogypsum reaches 100,000 to 150,000 tons ； The neutralization method uses inexpensive lime to neutralize the acids in phosphogypsum, forming insoluble compounds with soluble P2O5 and turning these soluble substances into inert ones. This process is simple, requires low investment, and does not cause pollution; however, the properties of the phosphogypsum after treatment are inferior to those obtained using the washing method ； The lime wash method is a combination of the washing method and the lime neutralization method. Similar to the washing method, it can remove soluble impurities from phosphogypsum on one hand, and neutralize residual acids to form insoluble substances on the other hand; however, wastewater treatment using this method is rather difficult ； Flotation is primarily used to eliminate the impact of organic impurities on phosphogypsum; since the influence of soluble impurities must also be taken into account, this method is generally implemented in combination with other methods ； The production technology for treating phosphogypsum using the flash calcination method involves converting harmful substances into inert ones through high-temperature decomposition; the drawback is that a small amount of acidic harmful gases are generated during the calcination process.
Phosphogypsum treatment is an environmental protection project, and our company is also working on it. For phosphogypsum produced by the diwater method, preliminary pretreatment is required; washing is recommended, with fresh water along with the waste heat generated by other processes being used for heating. The filtrate obtained from filtration can be returned to the water usage units (mainly the phosphate system). The free water and some of the crystalline water in phosphogypsum are removed through a calcination system to produce hemihydrate gypsum. Methods of calcination include: stir-fry pots, rotary kilns, fluidized bed furnaces, and pneumatic calciners. The energy consumption is approximately as follows: Cement retarder – Coal: 30 Kg/t; Electricity: 24 kW/t. Building gypsum powder – Coal: 65 Kg/t; Electricity: 22 kW/t
3# It says it’s washed, but I think it would be more accurate to say it’s retreated with sizing.
Thank you very much! I still have a few questions: what kind of equipment is used for washing, how much water is required, and what is the state of the water before and after washing? Also, regarding what you mentioned regarding energy consumption – \"Cement retarder: coal, 30 Kg/t; electricity, 24 kilowatts per ton. Building gypsum powder: coal, 65 Kg/t; electricity, 22 kilowatts per ton\" – what does \"/t\" refer to in terms of weight? Does it refer to the weight of the cement retarder or the weight of the water that has been removed?
Washing actually involves adding phosphogypsum to water to form a slurry, as mentioned on the 4th floor. The equipment is relatively simple: the pulping tank is equipped with a stirrer, followed by filtration. I’m not sure if there are any other specialized devices, but this step is relatively simple; there’s no need to make it too complicated. The data provided to you is for reference only; “/t” refers to the finished product, namely cement retarder and gypsum powder.
Filtering cannot be used; pressure filtration is required to increase the production capacity.
To use phosphogypsum in the production of building materials, it must be roasted and calcined; the 1.5 mole of crystalline water in calcium sulfate dihydrate must be removed so that it becomes hemihydrate gypsum before it can be used. The theoretical amount of crystalline water in construction gypsum is 6.2, but depending on the quality of the material, the actual amount of crystalline water is generally kept between 4.6 and 5.9.