Hydrophobic Modification Of Phosphogypsum-based Materials By Polyorganosiloxane And Its Propertie

Phosphogypsum is a solid waste produced during the wet process of phosphoric acid production.Currently,the amount of phosphogypsum stored in China has exceeded800 million tons,with an additional 80 million tons added each year.The main component of phosphogypsum is calcium sulfate dihydrate,which contains soluble and insoluble impurities and radioactive substances.As an acidic solid waste,its utilization is difficult and the utilization rate is low.The accumulation of phosphogypsum not only occupies a large amount of land,but also causes serious pollution to the environment.Therefore,how to achieve high added value and resource utilization of phosphogypsum is an urgent problem to be solved.The semi-hydrated phosphogypsum produced after calcination and dehydration has cementitious activity and great potential in the field of building materials application.However,the poor water resistance of the hardened phosphogypsum limits its widespread use.Therefore,the preparation of hydrophobic phosphogypsum-based materials is of great significance for achieving efficient utilization of phosphogypsum.In this study,efficient and environmentally-friendly polyorganosiloxanes were used for hydrophobic modification of phosphogypsum.The relevant research contents are as follows:(1)Hydrophobic coatings of H-PDMS/PMHS/OTS hybrid nano-silica were prepared on the surface of phosphogypsum using sol-gel and immersion methods.The effects of the coatings on the surface wettability,self-cleaning performance,microstructure and surface chemical properties of the phosphogypsum were studied.The results showed that the contact angle of the hydrophobic coating PGH-3 immersed for 90 minutes could reach 144.1°,with an average roughness of 52.194μm.After 50 times of tape adhesion experiments and 100 times of wear experiments,the contact angle still remained above 120°,indicating good chemical stability and durability.(2)Long carbon chain/alkoxy polysiloxanes(PVD-L)were synthesized using the silica-hydrogen addition reaction and reticulated long carbon chain polysiloxanes(PVD-C)were prepared under organotin catalysis.The effects of the synthesis process of the intermediate product PVD-L and the internal mixing of PVD-C on the physical properties,surface wettability,pore structure and microstructure of phosphogypsumbased materials were investigated.The results showed that the hydrophobically modified phosphogypsum-based material had a water absorption of 6.6%,a softening coefficient of 0.82,a contact angle of 112.9° and a porosity of 37.86% when the PVDC was dosed at 1.5%.(3)An organic/inorganic composite hydrophobic phosphogypsum-based material was prepared by the synergistic effect of organic H-PDMS hydrophobic agent and inorganic silicate cement.The synergistic effect of water-hardened second skeleton and low surface energy siloxane on the physical properties,surface wettability,pore structure,and microstructure of phosphogypsum were studied.The results showed that the hydrophobic phosphogypsum-based material had a water absorption rate of 2.5%,a softening coefficient of 0.94 and a contact angle of 134° when the silicate cement was dosed at 10% and the H-PDMS hydrophobic agent was dosed at 1.5%,and the hydrophobic phosphogypsum-based material had a porosity of 43.67% when the HPDMS hydrophobic agent was dosed at 0.9%.