The Pretreatment Study Of Comprehensive Utilization Of Poor Phosphorus Sludge

The production process of yellow phosphorus will inevitably produce a large amount of phosphorus sludge.The rich phosphorus sludge is used for extracting yellow phosphorus and the poor is not used properly because of the complex colloid structure.Most part of it is stored as hazardous wastes and used to produce phosphoric acid,which do harm to the surrounding environment.Extracting the yellow phosphorus from the poor phosphorus sludge and deeply treating the evaporated phosphorus residue can improve the utilization rate of phosphorus resource and get better economic and environmental benefits.In this thesis,the research object were poor phosphorus sludge with a phosphorus content of 10%~15% and evaporated phosphorus residue with less than 3% of phosphorus.Microwave and ultrasonic methods were used to preprocess the poor phosphorus sludge,and the influence of power,time,temperature on destruction of colloid in poor phosphorus sludge were analysed.A leaching experiment on evaporated phosphorus residue was carried out and the characteristics of residue were analyzed,then three methods of wet oxidation,air oxidation,cement were conducted to further treat the evaporated phosphorus residue so as to make it become the first kind of general industrial solid waste,at the same time,the effect of the dosage of oxidant,calcium hydroxide,cement,time and other factors on oxidation and precipitation of evaporated phosphorus residue was researched.The results showed:The result of pretreatment showed that the effect of microwave pretreatment on phosphorus mud was not obvious,namely,the colloidal structure of phosphorus mud was not destroyed obviously by the movement of the water molecules caused by electromagnetic field of microwave;The colloidal stability of poor phosphorus mud was broken by ultrasonic pretreatment,thus improved the phosphorus recovery.Its principle was that the shear force in the liquid produced by ultrasonic had effective damage to the colloid of phosphorus,and the best pretreatment conditions were: 40 ℃,20 min.The leaching tests showed that the metal elements in the leaching solution was up tothe maximum allowable emission concentration of the standard of "integrated wastewater discharge"(GB8978-1996),while the total phosphorus was 976.67 mg/L and phosphate was 413.26mg/L,so as it was class Ⅱgeneral industrial solid waste;There was still less than 3% of elemental phosphorus in the residual,which was in line with the "dangerous waste identification standard leaching toxicity identification" GB5085.4-2007 4.2inflammable dangerous solid waste,so it was dangerous solid waste.The results showed that(1)In the wet air oxidation experimentation,sodium hypochlorite was used to oxide the residue and the optimum oxidation conditions were as following: sodium hypochlorite dosage was 6g,reaction time was 30 min,the temperature was 60℃.Under the best conditions,the phosphorus in the sludge were basically all oxided,the main products were orthophosphate and phosphite.pH was the main determinant in the precipitation of Calcium hydroxide experiment,optimal pH was11.(2)Due to the massive phosphorus mud,evaporation residue phosphorus was not oxidized completely during the burning process,so that a large amount of phosphite and orthophosphate was existed in cinder solution.A large amount of water was needed for washing in the water washing experiment to make it meet the maximum allowable emission concentration of 0.5mg/L standard of phosphate(P)in "integrated wastewater discharge standard"(GB8978-1996).In the Calcium hydroxide precipitation experiment,when the dosage was 1.5g,solution pH was 12.2,phosphate concentration was still far more beyond 0.5mg/L standard.(3)The compositions of cement were calcium oxide,silicon dioxide,ferric oxide,oxide second aluminum,by which the phosphate were precipitated and the colloidal structure was formed by the way.When the phosphorus evaporation residue and cement ratio was 1:2 in quality,the orthophosphate in the leaching solution of the residue was completely precipitated,while the total phosphorus concentration was 476 mg/L.As the above,it was proved that the single method of deep treatment of the evaporated phosphorus residue could not reach the requirement of the first kind of general industrial solid waste.In summary,to make the phosphorus mud comprehensively utilized and improve the recovery rate of phosphorus and the economic efficiency and reduce the pollution to theenvironment,treatment process of the poor phosphorus sludge was: ultrasonic pretreatment→evaporating phosphorus→ air oxidationa one time washing→cement solidification,the wastewater of phosphorus produced by the treatment process was treated in the process air aeration→ coagulation sedimentation → fly ash adsorption.Eventually the poor phosphorus sludge can meet the requirements of the class I general industrial solid waste.