Kinetics And Reaction Mechanism Study On Removing Phosphorus In Wastewater By Steel Slag

Currently,the categories of water pollutants are very complex,in addition to exceeded heavy metals,there are a lot of pesticides,fertilizers,detergents and other pollutants.Phosphorus is a typical pollutant in water.Excessive levels of phosphorus in water can lead to eutrophication of lakes and coastal waters that can cause blooms and red tides,severely hampering the development of water quality and fisheries.Artificial Wetland wastewater treatment system is an integrated ecosystem that has advantages of lower construction and operation costs,ease of maintenance,strong anti-hydraulic impact load capacity and so on.The total phosphorous removal rate of sanitary wastewater after flowing through wetland treatment system was above 90%that was well above 30%compared with the method of activated sludge.Slag is the inevitable product of the steelmaking process,the rational utilization of slag can protect the environment and preserve natural resources to achieve the aim of turning harm to advantages.Comprehensive utilization of slag had a solid start in China,but there are very f'ew research that take slag as the environmentally friendly materials in the environmental protection industry,especially when it seirve as an artificial wetland substrate.In this paper,the object of the study is BOS slag.We have discussed the impact that different reaction conditions on the phosphorous removal ability of slag and the kinetic constants.Through injecting sulfate and carbonate in a simulated wastewater to access to the real sewage effluent and use the way of extraction to reveal the reaction mechanism of removing phosphorous by slag.All the experimental steps would provide theoretical basis for the slag as an artificial wetland matrix material.The following conclusions:(1)The slag can obviously remove phosphate in simulated wastewater,when the slag(38.5-45 ?m)at a dose of 1 g/100 ml,the concentration of phosphate is 300 mg/L,and after reacting 24 hr at 20 ?,the removal rate of phosphorus was above 90%.(2)Two mechanisms to remove phosphorous in waste water by slag are adsorption and precipitation of Ca-P,respectively.When the concentration of phosphorus in wastewater was relatively low,the reaction process was based on adsorption.On the contrary,reaction was dominated by forming Ca-P-based precipitates when the wastewater was at a higher concentrations of phosphorus.The pH value of wastewater after the reaction was greater,the ration of removed phosphorous due to the precipitation of Ca-P was larger.(3)Initial concentration of phosphorus,the reaction temperature,the dosage of slag,the particle size of slag and the slag composition are factors that have significant influence on the removal ability of slag.The initial concentration of phosphorus,the reaction temperature,the amount of used.slag possessed evident effects on the precipitation of Ca-P;the particle size and composition affected adsorption process and precipitation of Ca-P.(4)The concentration of carbonate and sulfate in wastewater have an obvious impact on the ability of removing phosphorous.The dissolution of calcium on Slag was affected by carbonate,further affected the generation of Ca-P precipitates.The results reduced the removal rate.sulfate,iron ions,phosphate ions can form stable complexes improving the phosphorus removal rate to some extent.(5)The phosphorous removal process by slag confirm to the first-order kinetic.Different reaction conditions have considerable effects on kinetic constants of dephosphorous of slag.When the initial concentration decreased,the smaller the value of pH is,the reaction temperature raised and the amount of slag used in solution increased,the higher the kinetic constants are.