Removal And Mechanism Of Silicon And Phosphorus Impurities In Phosphogypsu

Phosphogypsum（PG）is a solid waste residue in the wet process of phosphoric acid,which is piled up in large quantities and causes environmental pollution.At present,the impurity occurrence and lattice morphology of PG are still technical bottlenecks to improve resource utilization.In this paper,PG was used as raw material to explore the existing forms of silicon and phosphorus in PG,and KH590 was used to modify and tributyl phosphate（TBP）was used to remove SiO₂.By controlling the phase change and growth of the crystal under normal pressure,the high-efficiency removal of silicon impurities and phosphorus is realized,and the removal mechanism of silicon and phosphorus is revealed.The main research results are as follows:（1）The removal process of SiO₂ from PG was studied.With the help of SEM,XRD and FTIR,the effects of solution p H,sulfuric acid concentration,KH590 dosage and reaction temperature on the removal of SiO₂ and the phase of PG were studied.Under the optimum parameters（20%H₂SO₄,1%KH590,70℃）for 60 min,and then treated with TBP,the SiO₂content in PG decreased from 5.17%to 0.08%,the removal rate was 98.5%,and the whiteness was 70.9%.The wettability of the removed impurities was analyzed by contact angle,and it was found that the contact angle increased significantly to 84.29°,which indicated that hydrophobic modification of SiO₂ surface by KH590 was the key to increase the removal rate.（2）The mechanism of silicon removal was revealed by cyclic experiments,FTIR and XPS,and the surface of SiO₂ was modified by condensation reaction with KH590as chain terminator.During heating and stirring,the siloxane group[–Si–OR–]of KH590 hydrolyzes to form functional silanol group[–Si–OH],and then dehydrates and condenses with–OH on the surface of SiO₂ to form SiO₂–O–Si–C bond.When a large number of hydrolyzed silanol-based monomers are grafted to form a dense hydrophobic layer,the hydrophobicity of SiO₂ surface is enhanced,and it is easier to be enriched in TBP oil phase and effectively separated from PG.（3）Taking desilicated gypsum as raw material,the effects of different reaction temperatures,solid-liquid ratio,H₂SO₄ concentration,Na Cl concentration and EDTA-2Na concentration on phosphorus leaching rate and crystal water content in PG were studied.The results show that at the concentration of 30%H₂SO₄,the leaching rate of phosphorus and the content of crystal water are 92.1%and 0.63%respectively.After adding 15%Na Cl into 5%H₂SO₄ for 120 min,the leaching rate of phosphorus is 91.3%,and the content of crystal water is 1.91%.However,crystal defects and long reaction time will increase phosphorus reabsorption.Therefore,EDTA-2Na is used as a complexing agent to control the crystal growth integrity,reduce the crystal size and particle aggregation,and weaken the phosphorus reabsorption.Adding 0.5%EDTA-2Na to react for 40 min,the phosphorus leaching rate was further increased to 97.5%.At the same time,the surface of AH product is clean and complete,with dispersed particles and whiteness of 92.5%.Through the phase analysis and micro-morphology analysis of the product,it is revealed that the mechanism of efficient phosphorus leaching is related to the dissolution-recrystallization process of PG.