Study On Preparation Of A Hemihydrate Gypsum For Wall Materials By Phosphogypsum

Phosphogypsum is an industrial by-product from the processing of phosphoric acid by the phosphate rock, its main component is calcium sulfate dihydrate, and contains phosphoric acid, phosphate, fluoride, a small amount of radioactive material and fatty acids, organic amines and ketone impurities. In China, phosphogypsum production is variously estimated to be more than20million tons per year. The use of phosphogypsum is probably well below10%of output. The main reason is the presence of minor components having a negative impact on the performance of product. And the by-product is usually occupied considerable land areas exposed to weathering processes, causing serious environmental damage of soil, air, water. Currently, a great deal of researchers at home and abroad devoted themselves to the utilization of phosphogypsum. There are many important properties of phosphogypsum worthy of recognition, the main advantages is high content of calcium sulfate dihydrate. It is not only able to reduce the consumption of natural gypsum resources, but also dealt with such a large tonnage of emissions. The utilization of phosphogypsum has a great development space.In this paper, phosphogypsum was used as raw material for the preparation of a hemihydrate gypsum. Autoclaved and drying process is completed in a homemade autoclave by one step. By means of fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), as well as the macro-property measurements, the mechanical strength of a hemihydrate gypsum, crystal structures were tested. At the same time the autocled conditions,the ratio of raw materials for preparing a hemihydrate gypsum, the effect of impurities in phosphogypsum and the pre-treatment on the performance of a hemihydrate were also studied. The study includes the following aspects.(1) Further study of the raw material ratio and autoclaved condition on the properties of a hemihydrate phosphogypsum. A series of technological parameters, such as pre-treatment environment, sample water-cement ratio, medium crystal agent content were studied by single factor experiment and orthogonal experiment. The results show that the phosphogypsum added0.4water,1%pre-treatment agent and0.06%medium crystal agent has the best performance. The optimum autoclaved pressure is0.17MPa.The best compressive strength of a hemihydrate phosphogypsum is28.09MPa. Standard consistency water consumption is45%, the setting time of8min, conform to the standards of wall materials in China, but poor water resistance, gypsum can be used as interior wall materials. The result shows that CaO has the most significant influence on the performance of a hemihydrate phosphogypsum by orthogonal analysis.(2) Minor components effect. Different calcium sulfate dihydrate preparation of a hemihydrate gypsum performance and microstructure has a larger difference.By adding minor components in the phosphogypsum for preparing a hemihydrate gypsum, we found that the effect of acidic substances had the worst strength and extended setting time. Neutral and alkaline environment is conductive to the formation and growth of a hemihydrate when use lime neutralized phosphogypsum.(3) Microscopic analysis was carried out on a hemihydrate gypsum. The result shows that preparation of a hemihydrate gypsum by phosphogypsum is feasible, compared with β hemihydrate gypsum, a hemihydrate gypsum has larger crystals, more regular shape and better crystallinity.