Performance And Mechanism Of Phosphate Removal From Wastewater By Pyrite And Its Products By Heat Treatment

Pyrite, collected from Xinqiao ore of Anhui Tongling City as typical sample,was modified by heat treatment in the nitrogen atmosphere. The raw materials ofpyrite, its products by heat treatment and their adsorption products werecharacterized and analyzed by XRD, FE-SEM and XPS. The influence of factors forremoval low concentrations of phosphorus in solution by pyrite and its productswere investigated by the batch experiments, and the adsorption capacity ability ofreusing on the two materials were studied by the Column adsorption tests. Themechanism of phosphate removal by these two materials was demonstrated by bothbatch experiments and Column adsorption tests.The influence of particle size of pyrite, solid/liquid ratio, suspension pH, ionicstrength, temperature, sorption time on phosphate removal was investigated byconducting a series of batch sorption experiments to study low concentration ofphosphate removal by pyrite. In addition, the adsorption samples had beencharacterised by XPS and FE-SEM image. As the result of this study, the efficiencyof phosphate removal increased greater (9.3～90.7%,6.5～97.1%) by smallerparticle size (50～180mesh) of pyrite and by higher solid/liquid ratio (6.5～97.1%).Within in pH3～9.5, efficiency of phosphate removal was similar, in excess of95%. In the presence of nitrate anions, phosphate removal by pyrite was weakpromotion. Slight and large impacts were seen with chloride and sulfate,becarbonate anions, respectively. The temperature had a little effect on phosphateremoval. Kinetics showed the maximum removal efficiency by pyrite occurred aftercontact of16h. In the Column adsorption test with pyrite as filter, the adsorptioncapacity of the column was0.12mg/g when the effluent concentration was higherthan0.02mg P/L. The mechanism of uptake phosphate was in virtue ofchemisorption between phosphate and ferric ion released by pyrite oxidation.The optimal conditions of heat treatment on natural pyrite was:1%hydrochloric acid to remove carbonate composed in pyrite and surface oxide, andthe temperature and time of heat treatment were600℃and1h, respectively, undernitrogen atmosphere. Analyzed by XRD above product, pyrite transformed intopyrrhotite. Such product was used to study the adsorption of phosphate. It had littleinfluence on the factors of heat treatment time, the solid-liquid ratio, reaction temperature, etc. to removal phosphate by the products, which demonstrated thatthis sample had strong adaptability to water changes to some extent. The highestremoval phosphate efficiency was showed in the solution pH of5to6; in thepresence of bicarbonate anions, phosphate removal by product was stronglyinhibited; it reached equilibrium when the reaction time was6h. The adsorptioncapacity of the column was0.27mg/g by running the dynamic experiment with theproducts as filter for removal of low concentrations of phosphate.The mechanism of the low concentration of phosphate by the product of heattreatment on pyrite was: as the result of the surface oxidation of the product in theaerobic atmosphere, ferrous was transformed to ferric iron which could formFe(OH)3through hydrolysis reaction in the solution. Then it could be irreversiblybound to phosphate in the formation of FePO4, which deposited on the surface ofthe sample. When the two columns were exhausted, utilize solution containing0.1M hydrochloric acid and0.5M sodium to regenerate the colunms, and the resultwas available. All results showed from the experiments of removing phosphate inlow concentration by the product suggest that it has great economic value andenormous potential for application to wastewater.