The study of microstructure and phosphorus distribution in converter slag

An efficient slagging is a key process to improve the dephosphorization ability in converter operation. The microstructure analyses can provide the information of phosphorus distribution in various mineral phases to feature completely the dephosphorization process.Two kinds of converter slags were investigated in this study, including conventional slag with high basicity and dephosphorization slag with low basicity.The characteristics of high basicity converter slag have been reported widely.However,the investigations on the low basicity slag properties for dephosphorization in converter are less discussed in steelmaking slag system.This study focused on the microstructure and phosphorus-containing phases in converter slag.The slag composition and mineral phase were examined by the usual XRF chemical analysis and EPMA,XRD studies.The results indicated that the phosphorus-containing phase in high basicity slag was the dicalcium silicate(2CaO·SiO_2 or C_2S) phase,while phosphorus in low basicity slag was incorporated in CaFeSiO_4 structure.

INFLUENCE ON THE DISTRIBUTION OF PHOSPHORUS BY ADDING AL-CONTAINING COMPONENT IN SLUDGE MELTING PROCESS

The laboratory scale experiments for determining the influence on the distribution of phosphorus by.adding Al-containing component in melting furnace were conducted. It is found that the addition of Al-containing component in melting furnace increased the amount of phosphorus in slag phase. Thermodynamic analysis of the industrial sludge melting process with the addition of different Al-containing components was also carried out. The compositions of slag and the gas in three different zones in melting furnace were obtained. The results also demonstrate that increasing the mole ratio Al/P of charged materials is an effective way to fix more phosphorus in slap, which can help reduce the amount of H3PO4 precipitate from guy in the waste heat boiler later.

Vanadium extraction and dephosphorization from V-bearing hot metal with fluxes containing CaO

Extracting vanadium and removing phosphorus simultaneously by adding CaO containing materials to V-bearing hot metal were investigated under the condition of simulating the process of vanadium extraction with insufficiently supplying oxygen in converter. Through preliminary experiments, 3 h and 1375 °C were chosen as the optimum holding time and reaction temperature for formal experiments, respectively. The results of the formal experiments suggest that making basic slag can extract vanadium and remove phosphorus simultaneously. The vanadium extraction rate(ηV) and phosphorus removal rate(ηP) both increase with an increase in the basicity of the original slag materials and the Fe2O3 contents. The vanadium distribution ratio)(V L′is about an order of magnitude greater than the phosphorus distribution ratio),(P L′but the latter is more sensitive to slag basicity than the former. The phosphorus distribution ratio is beyond 6 when the basicity of the original slag materials is beyond 1, which indicates a much better performance of phosphorus removal compared to the phosphorus removal in the current process. Therefore, it is very feasible to properly raise slag basicity to remove phosphorus with consideration of the grade of vanadium slag. The relations between ηV and ηP, and between L′V and L′P are linear under the experimental conditions.

Flow structure and phosphorus adsorption in bed sediment at a 90° channel confluence

The distribution of the phosphorus（P） adsorption in a bed sediment at channel confluences is an important issue for understanding the transport of contaminants in channel networks. In this study, the flow structure and its effect on the P distribution in the bed sediment were investigated in a 90° confluence flume. It is shown that the P adsorption amount in the sediment varies significantly in different hydrodynamic zones. The P adsorption amount is high in the flow separation zone where the horizontal velocity of the flow is very small, and it is low in the maximum velocity zone where the flow velocity reaches a maximum. The low P adsorption amount is observed in the downstream portion of the distorted shear layer, while the P enrichment is found in the upstream portion, as is related to the significant downwelling flow in this zone. Thus, the flow structure, especially, the flow velocity, has a significant effect on the distribution of the P adsorption in the bed sediment at the channel confluences.

Effect of organic matter on phosphorus recovery from sewage sludge subjected to microwave hybrid pretreatment

Microwave（MW） hybrid processes are able to disrupt the flocculent structure of complex waste activated sludge,and help promote the recovery of phosphorus as struvite.In this study,to optimize struvite yield,（1） the characteristics of matter released in MW-hybrid treatments were compared,including MW,MW-acid,MW-alkali,MW-H2O2,and MW-H2O2- alkali.The results showed that selective release of carbon,nitrogen,phosphorus,Ca^2＋,and Mg^2＋ achieved by sludge pretreatment using MW-hybrid processes.MW-H2O2 is the recommended sludge pretreatment process for phosphorus recovery in the form of struvite.The ratio of Mg^2＋：NH4^＋-N：PO4^3--P was 1.2：2.9：1 in the supernatant.（2） To clarify the effects of organic matter on struvite recovery,the composition and molecular weight distribution of organic matters were analyzed.Low molecular weight COD was found to facilitate the removal rate of NH4^＋-N and PO4^3-P via crystallization,and the amorphous struvite crystals（〈1 kDa） from the filtered solutions had high purity.Therefore,the present study reveals the necessity of taking into consideration the interference effect of high molecular weight organic matters during struvite crystallization from sewage sludge.

Apatite Loss in Pothwar Loess Plain(Pakistan) Fits a Simple Linear Reservoir Model

Apatite is the dominant phosphorus(P) mineral in early stages of soil development, and its redistribution as labile forms under pedogenesis controls terrestrial bioavailability. Quantitative distribution of labile forms of P and apatite-P was examined in Pothwar Loess Plain, Pakistan where the degree of pedogenesis varied with relief. Four soil types, Typic Ustorthents(Rajar), Typic Calciustepts(Missa), Udic Calciustepts(Basal), and Udic Haplustalfs(Guliana), were sampled from three replicated locations at genetic horizon level. With the exception of total P value at surface, the mean total and apatite-P decreased towards the surface in Udic Haplustalfs and Udic Calciustepts where dicalcium and octacalcium phosphate increased toward surface. Iron(oxides and oxyhydroxides) adsorbed and occluded P forms were also in greater quantities in Udic Haplustalfs and increased toward the surface, whereas they were lowest and uniform in the Typic Ustorthents. Aluminum- and organic P correlated with soil organic matter. Apatite-P decreased exponentially with an increase in the sum of iron adsorbed and occluded P fractions, and fitted the equation M(x)= M0 [1- exp(-wx)] with r2= 0.996, where M(x)is the mean apatite-P concentration in solum, M0 is the apatite-P content in the loess sediments, x is the cumulative iron adsorbed and occluded P, and w is an empirical factor indicating the change rate of apatite-P in the loess. From the calculated apatite-P of 740 mg kg-1at the time of deposition, mean apatite-P loss was 60% in Udic Haplustalfs, 33% in Udic Calciustepts, 23% in Typic Calciustepts, and 8% in Typic Ustorthents. The transformation of soil P to labile forms was faster and deeper in level or slight depressions followed by gently sloping areas in wide plains, and was the least in the gullied land.