Recovery and Enrichment of Phosphorus from the Nitric Acid Extract of Dephosphorization Slag

A method for the recovery and enrichment of the phosphate from dephosphorization slag was examined. First, the elution of aqueous phosphate from dephosphorization slag using aqueous HNO3 was examined using both the batch and flow methods. With the batch method, 82% of the dephosphorization slag could be dissolved within 30 min using 1.0 mol/L HNO3, indicating that the batch method could be used for mass processing to extract phosphorus in the bulk phase, but all components contained in the slag were unselectively dissolved. In contrast, by using 0.05 mol/L HNO3 via the flow method, 22% of the slag was dissolved in 100 min giving a more selective dissolution of phosphate from the slag compared with the batch method, which indicated that this method would be incompatible with mass processing for the purpose of extracting phosphorus in the bulk phase. In order to remove the Fe-species in the aqueous solution obtained by the batch method using 1.0 mol/L HNO3, which has been referred to as the “slag solution,” it was necessary to add calcium hydroxyapatite (CaHAp) to the slag solution. The optimal conditions for the removal of Fe-species using CaHAp were observed at a solution pH of ca. 1.5, which resulted in 100% removal of the Fe-species after 4 h. When the pH of the slag solution was adjusted to 7.0 after removing the Fe species, a pale pink solid sample was precipitated. The amounts of phosphate in the slag solution and in the pink solid were 3.5 and 42.0 mol%, respectively, indicating that the treatment suggested in the present study could be used for the recovery and enrichment of phosphate, that is, phosphorous, from dephosphorization slag

Hydrothermally Synthesized Ceria with a High Specific Surface Area for Catalytic Conversion of Ethanol to Ethylene

Morphological control can be used to improve the catalytic activity of cerium oxide (ceria, CeO2). In this study, ceria with a high specific surface area was synthesized via the hydrothermal reaction of ceric nitrate and was tested for the catalytic conversion of ethanol to ethylene. As a reference, ceria was also synthesized via a precipitation reaction of cerous nitrate using aqueous ammonia. The Japan reference catalyst JRC-CEO-1 also served as a reference. The specific surface area of the hydrothermally synthesized ceria was as high as that of JRC-CEO-1, but was much higher than that of either reference after calcination at 873 K. Thermogravimetric analysis and IR spectroscopy revealed that the cerias made by hydrothermal and precipitation reactions consisted of high-purity CeO2, whereas JRC-CEO-1 contained 1.5% decomposable functional groups (OH-, CO3 2-). For both ethanol conversion and ethylene selectivity in a catalytic dehydration reaction of ethanol, the activity of the hydrothermally developed ceria was higher than that for either reference. The reaction pathway for the dehydration reaction of ethanol over ceria showed that the specific surface area and the basicity of the Lewis basic sites of the ceria were influential properties. The high catalytic activity of the hydrothermally synthesized ceria was derived from its high specific surface area and high-purity CeO2

Recovery of Calcium Phosphates from Composted Chicken Manure

To recover phosphorus from composted chicken manure, a batch method with aqueous HNO3, HCl and H2SO4 was used to examine the elution behavior of the aqueous calcium and phosphate contained in the manure. Since the main components in manure are Ca2+ and K+ along with PO4 3- and those ions can be dissolved using an acidic eluate, it was expected that most of the aqueous Ca2+, K+ and PO4 3- could be obtained via the elution. Therefore, it seemed plausible that the removal of the aqueous K+ obtained by the elution of composted chicken manure would result in the formation of calcium phosphates. If calcium phosphates are formed, they can be used for phosphate rock, which also consists of various calcium phosphates. When using 0.1 mol/L HNO3, HCl or H2SO4, the elution behavior of the PO4 3- was not dependent on the acids. However, 0.1 mol/L H2SO4 was not sufficient for the elution of Ca2+, probably due to the precipitation of the calcium sulfate. The eluted amount of K+ using 0.1 mol/L HNO3 was lower than that using 0.1 mol/L of either HCl or H2SO4. Since the poor elution of K+ should enrich the concentrations of Ca2+ and PO4 3- in the acidic aqueous solution after the elution, it was suggested that aqueous HNO3 would be suitable as an eluate in the present system. After the elution of the composted chicken manure, when 0.1 mol/L HNO3 was used to adjust the solution pH of the acidic aqueous solution to greater than 6, Ca2+ and PO4 3- were precipitated, but K+ was not. The precipitate was calcium hydroxyapatite, one of the typical components of phosphate rock, which showed that composted chicken manure could be replaced phosphate rock as a new source of phosphorus

Recovery of the Phosphorus from the Nitric Acid Extract of Powder Collected in a Bag Filter during the Recycling of Used Fluorescence Tubes

During the recovery of phosphorus from the powder collected in a bag filter during the recycling of used fluorescence tubes (bag-powder), the batch method with aqueous HNO3 was used to examine the elution behavior of aqueous phosphate contained in the bag-powder. The main components of the bag-powder included Ca2+, PO4 3- and Y3+ along with Si4+, Sr2+ and lanthanide cations such as La3+ and Ce4+. Therefore, it seemed possible that, with the selective dissolution of Ca2+ and PO4 3- from the bag-powder, these lanthanide cations in the residue could be enriched. With the batch method, most of the phosphate in the bag-powder was dissolved within 0.2 min using 1.0 mol/L HNO3. The dissolution behavior of calcium cation was similar to that of the phosphate. In contrast, the dissolution of yttrium, the content of which was the highest among the lanthanide cations in the bag-powder, was increased with the dissolution times, reaching complete dissolution after 24 h. The Sr2+, La3+ and Si4+ in the bag-powder, however, did not dissolve under the same conditions. Although Ca2+, PO4 3- and Y3+ were the main components in the nitric acid extract, Y3+ was separated as YPO4 at pH = 4.0, while Ca2+ and PO4 3- were separated as calcium phosphates at pH= 7.0. These results revealed that the separation of calcium phosphates, YPO4 and some residue was possible, and resulted in the enrichment of lanthanide cations along with the recovery of phosphorus from the bag-powder. Using the present technique, 91% of the P in the bag-powder was recovered

Effects of Acid Treatment on the Acidic Properties and Catalytic Activity of MCM-41 for the Oxidative Dehydrogenation of Isobutane

Mesoporous silicas have shown promise as materials for solid catalysts or catalyst supports due to their unique characteristics. Metal-doped mesoporous silicas are known to be catalytically active in the oxidative dehydrogenation (ODH) of isobutane. However, heavy-metal-free mesoporous silicas have not been studied closely for their use as catalysts. In the present study, MCM-41 (#41 Mobil composition of matter) was acid-treated to enhance its catalytic activity, although pure MCM-41 was confirmed as catalytically inactive for the ODH of isobutane (isobutene yield = 0.9%). The pH of a slurry of as-synthesized MCM-41 was changed during acid treatment. A pH adjustment to 6.5 resulted in great improvement in catalytic activity (isobutene yield = 6.1%), but a pH adjustment to 4.5 resulted in insufficient improvement (isobutene yield = 4.5%). It was confirmed via XRD and N2 adsorption-desorption measurement that the pH adjustment to 4.5 degraded the ordered structure of MCM-41. This degradation would be a crucial factor that would render acid treatment less effective. In addition to the acid treatment, Al doping to MCM-41 was conducted. Al doping also greatly enhanced the acidity and catalytic activity of MCM-41

Effect of the template ion exchange behaviors of chromium into FSM-16 on the oxidative dehydrogenation of isobutane

The template ion exchange of chromium cations into FSM-16 (#16 Folded Sheets Mesoporous Materials) for 247 h resulted in a 2.89 wt% incorporation of those cations into the FSM-16, although only a 0.3 wt% incorporation had previously been reported. The XRD pattern of the resultant solid (Cr-FSM-16) showed that the hexagonal structure characteristic of FSM-16 remained after the 2.89 wt% incorporation of chromium cations. XPS could be used to detect the Cr3+ and Cr6+ species on the surface of Cr-FSM-16. A pre-edge peak that was due to a tetrahedrally coordinated Cr6+ species was confirmed in the XANES spectrum of the Cr-FSM-16, which showed that the coordination state around some Cr species was similar to that around the Si species in FSM-16. With the increase in the amount of chromium cations in FSM-16, its catalytic activity and stability during the oxidative dehydrogenation of isobutane were evidently improved

Oxidative Dehydrogenation of Isobutane to Isobutene on Metal-doped MCM-41 Catalysts

MCM-41 (#41 Mobil Composition of Matter) is a favorable material for heterogeneous reactions because of its unique porous structure. However, the catalytic activity of MCM-41 for the oxidative dehydrogenation (ODH) of isobutane to isobutene is known to be quite low. In the present study, a metal-doping method was employed to improve this catalytic activity. Doping of Cr, Co, Ni, or Mo into MCM-41 resulted in a great improvement in the catalytic activity. Since chromium-doped MCM-41 (Cr-MCM-41) showed the greatest catalytic activity among these catalysts, its redox property was further analyzed via XPS, XAFS and H2-TPR techniques. The XPS spectrum of Cr-MCM-41 suggested that it has Cr3+ and Cr6+ species on its surface. Also, a pre-edge peak due to Cr6+ species was confirmed in the XANES spectrum of Cr-MCM-41. In H2-TPR measurement, Cr-MCM-41 was more reducible than crystalline Cr2O3, which showed low catalytic activity for the ODH of isobutane. The reducible Cr6+ species on Cr-MCM-41 contributed to an improvement in the catalytic activity of MCM-41

The Catalytic Conversion of 1,2-Propandiol to Propanal on FSM-16 Molded by Wet-Treatment and Pressurization

The catalytic conversion of 1,2-propandiol to propanal is examined using FSM-16 particles (0.85－1.70 mm) molded by wet-treatment and pressurization. When FSM-16 was molded with 0.6 g of pressurization and supplied to the catalytic conversion of 1,2-propandiol at 673 K, this system resulted in a 94.8% conversion of 1,2-propandiol and 90.5% selectivity to propanal at 0.25 h on-stream, which was the maximum amount of activity. However, at 4.50 h on-stream, the activity decreased extremely to deactivation 19.9% conversion of 1,2-propandiol and 84.7% selectivity to propanal. In contrast, when FSM-16 molded with wet-treatment (0.15 g) was used for the conversion at 573 K, activity was greatly increased and stable 98.6% conversion of 1,2-propandiol and 56.2% selectivity to propanal at 0.25 h on-stream followed by 91.9% and 52.5%, respectively, at 4.50 h on-stream. The hexagonal structure of FSM-16 was suggested to have contributed to the suitable conversion of 1,2-propandiol to propanal

Acidic Properties of Various Silica Catalysts Doped with Chromium for the Oxidative Dehydrogenation of Isobutane to Isobutene

Although previous researchers have found that FSM-16 (#16 Folded Sheet Mesoporous material) doped with chromium and related Cr-doped silica catalysts has shown great activity for the oxidative dehydrogenation of isobutane to isobutene, information on the nature of these catalysts is insufficient. For this study, three types of Cr-doped silica catalysts were prepared by applying the template ion exchange method. CrOx/FSM-16 and CrOx/SiO2 were used as references. These catalysts were used for oxidative dehydrogenation, which was then characterized via various techniques. The most active catalyst was Cr-doped silica, which did not have the hexagonal structure that is characteristic of mesoporous FSM-16. Various characterizations showed that the catalytic activity of the Cr-species, stemmed from a weak acidic nature and a redox nature that originated from the combination of silicate and a Cr cation, as opposed to the hexagonal structure and strong acidic nature of FSM-16

Effects of Acidic Properties of FSM-16 on the Catalytic Conversion of 1,2-Propandiol in the Presence and Absence of Hydrogen

We have earlier showed how the catalytic conversion of 1,2-propandiol to propanal using FSM-16 (#16 folded sheets of mesoporous materials) when molded by wet treatment proceeded more favorably than when using FSM-16 molded by pressurization, while no comparison using other typical acidic catalysts and no examination of the acidic properties of FSM-16 was carried out. In the present study, the conversion using FSM-16 molded by wet treatment and pressurization was compared with that obtained by using typical acidic catalysts such as SiW12O40/SiO2 and MCM-41 (#41 of Mobil Composition of Matter) together with amorphous SiO2. Among these catalysts, FSM-16 molded by wet treatment showed the most suitable catalytic activity. In order to examine the effect of the molding procedure for FSM-16 on its structural and acidic properties, FSM-16 molded by both methods was examined using NH3-TPD, in situ FT-IR using NH3 as a probe molecule, and Hammett indicators together with XRD and TEM. According to Zaitsev's rule, the present conversion should afford acetone rather than propanal, which indicates that it would proceed via hydro cracking. Therefore, the conversion of 1,2-propandiol using FSM-16 was also examined in the presence and absence of hydrogen. Furthermore, hydration reactions of 1- and 2-propanol when using FMS-16 were examined. Based on the results obtained from this investigation, it was concluded that the conversion using a more acidic FSM-16 molded by wet treatment proceeded through dehydration rather than through hydro cracking