Phosphorus Removal By Pulverized Oyster Shell

This work was concentrated on using oyster shell as based material to explore thepreparations of a durable, large surface area, high phosphorus removal efficiency andacollectable material. XRD, SEM, EDS and XRF techniques are used to characterizemicrostructures and compositions of the materials produced, and spectro-photometry usingammonium phospho-molybdate blue method was used to detect the phosphateconcentration in the wastewater. There were4different preparation methods were adoptedin this thesis.1) the sole use of oyster shell as raw materials;2) using clay minerals asbinder to produce collectable materials;3) Calcining and hydrothermal Modification ofoyster shells by using fumed silica technique;4) Unburned process with cement additioncombinations. The phosphorus removal efficiency, recovery and reuse properties of samplesprepared by different processes were discussed and provided as the basic data for making adurable material with lowest cost and high phosphate removal efficiency.Experimental results showed that oyster shell is rich in natural porous structure whichcould produce a large number of processed pore structure leading a strongly absorptionfeature. Pulverized oyster shell with a size less than100mesh and preheated at100-550℃can removal90%of phosphate in a wastewater with initial phosphate concentration of5mg/L. However, oyster shell powder has poor forming property and some binders must beadded to produce collectable materials. Clay mineral is a good binder and with30%dosagecan get a strength of18.56MPa when calcined at650℃. However, the phosphate removalefficiency of the material is low and can only achieve89.3%when contact with wasterwater with initial phosphate concentration of5mg/L for10days. Diatomite can alsoprovide good bind abilities and possess better phosphate remove abilities than clay with95.3%in8days, but still not efficient enough. The experimental data suggest that theoptimal conditions for material production by using48wt%of fumed silica and52wt%ofoyster shell are a calcination temperature of750℃, and a hydrothermal annealingtemperature:130℃for16h. Materials made under these conditions showed a95.1%phosphate removal after2days and a strength of10.96MPa. During the calcing process, thecalcium carbonate in oyster shell will react with SiO2in fumed silica and form hydrate calcium silicate after hydrothermal treatment, and that the hydrate calcium silicate reactswith phosphate ions in wastewaters to form hydroxylapatite precipitate.Compared to the above routes, unburned process is simpler and lower cost. Cementaddtive can supply efficient strength for the material. The best cement dosage is determinedto be10wt%and the corresponding strength is12.26MPa after curing for28days. Thematerial made from cement and oyster shell shows superior phosphate removal properties inmoderate or alkaline environment at elevated temperatures.By comprehensive analysis, material made from fumed silica following calcling andhydrothermal reaction posses the best phosphate removal properties and the longest servicelife time, while, the unburned technique has certain requirments of pH, environmentaltemperatures and others and can only suit for short term use though the process is verysimple and the cost is very low.