Study On Crystallization Phosphorus Removal Based On Oyster Shell Powder

Phosphorus is an indispensable element in people’s activities and industrial production,and at the same time it is also a non-renewable resource.The domestic sewage contains a large amount of phosphorus,which can be recycled and used to meet the requirements of saving resources and protecting the ecological environment.In this paper,the phosphorus in water was recovered by HAP crystallization method,and the research mainly focus on the preparation and selection of high quality and high efficiency seed crystals by using oyster shell powder.Firstly,the feasibility of using raw oyster shell powder as seed crystal was studied.the effect of PH、 C（Ca）/c（P）and dosage of seed crystal on crystallization phosphorus removal was studied by using single factor analysis method.In this study I Set pH as 6,7,8,9;C（Ca）/c（P）as 1,2,3,5,10,dosage of seed crystal as 0g,0.5g,1.0g,2.0g,5.0g,10.0g,respectively.The results showed that raw oyster shell powder not a good HAP seed crystal,at the same environment,increasing the dosage of oyster shell powder couldn’t enhance the phosphorus removal efficiency continuously and stability.Using the method of calcination to further modify the oyster shell powder.The effects of calcination temperature and calcination time on the modification degree of the oyster shell powder were studied.Then do the experiment of phosphorus removal by crystallization using the modified oyster shell powder under different initial phosphorus concentration and pH conditions.and the product was analyzed by using of XRD.The calcination temperature was set at 500 ℃,600 ℃,700 ℃,750 ℃ and 800 ℃ respectively.The calcination time was set as 10 min,30min,1h,1.5h respectively.The results showed that the modified oyster shell powder（10g）was calcined Completely at the temperature of 800 ℃ for 30 min,and the modification could increase the release ability of Ca²⁺ of oyster shell powder.The efficiency of phosphorus removal of calcined oyster shell powder was up to 228.125mg/g,which was several times or even several times higher than that of other Phosphorus adsorbent material or other crystal seed;XRD analysis results show that the product contains a lot of calcium hydrogen phosphate and a small amount of hydroxyapatite.Using calcined oyster shell powder for further research.Slow-Release Ca²⁺ seed Crystals was prepared by PVA-embedded Oyster Shell Powder.The effects of PVA concentration,PVA + PEG dosage,PEG concentration and curing agent on the physical properties and slow release properties of seed crystals were studied by orthogonal experiment.The effect of slow release Ca²⁺ on phosphorus removal was investigated.And the mechanism of Ca²⁺ slowly release from seed crystal was explained by SEM analysis and the phenomena in the experiment.Set the PVA concentration as 8%,9%,10%,11%,the PEG concentration was 0%,0.4%,0.8%,1.2%,the PVA + PEG dosage was12 m L,12.5mL,13 mL,13.5ml,the curing agent was 4% boric acid,4% boric acid + 4% CaCl2.The results showed that the seed crystals could release Ca²⁺ for 20 days,and the effect of slow release and phosphorus removal was good.The optimum seeding formula was 12 m LPVA + PEG（PVA concentration was 8%,PEG concentration was 0.8%）The solution was embedded in 20 g of calcined oyster shell powder and made into 4% boric acid solution for 2 days.The crystallization products were analyzed by SEM and XRD analysis.The results show that there is a very obvious CaCO₃ diffraction peak in XRD.The results showed that the release of Ca²⁺ in the early release of Ca²⁺ was too fast.Subsequently,the efficiency of seed crystal recovery was calculated and the seed crystals were evaluated.It was found that the highest phosphorus recovery efficiency of the 16 seeds was 44.53 mg / g.This was a good Ca²⁺ sustained-release of phosphorus removal seed crystals,the seed production method worthy of popularization and application.