To discuss nonmetallic inclusion behaviors in a secondary refining process, cold model experiments on agglomeration, breakup, and transfer of fine particles are performed varying the operating factors such as an energy input rate, wettability, agitation practice, and the number of liquid phases. When the other operating conditions are the same, the agglomeration rate of the 1‐particle (isolated particle) with a hydrophobic property is larger than that with a hydrophilic one, and the transfer rate of the 2‐particle (cluster of 2 isolated particles) has the same tendency. The number of the 1‐particle with the hydrophobicity is estimated to increase at the transfer site of the particles from an open eye to a heavy liquid due to a bubble breakup, whereas the 1‐particle with the hydrophilicity shows an opposite trend because of less adhesion on the bubbles. The 1‐particle in the dual phase transfers from the open‐eye spot to a light liquid, although the value is not so much as that of the decrease in the agglomeration. A transfer condition of the inclusion composed of Al 2 O 3 or CaO ⋅ Al 2 O 3 is calculated when a particle contacts with a solid/liquid interface, and the CaO ⋅ Al 2 O 3 inclusion is estimated to be engulfed above 3.34 μm in diameter.

Liquid-liquid dispersion and mass transfer were investigated in mechanically stirred vessels without baffles by changing operation factors such as an impeller rotation speed, off-bottom clearance, volumetric liquid ratio, etc. The dispersion regime was categorized into five groups: the sedimentary liquid was kept at the vessel bottom (I), partially elevated without any collision (II), partially dispersed by colliding with the impeller bottom (III), both liquids were partially dispersed by collisions with impeller blades (III'), and the sedimentary liquid was completely dispersed (IV). The dispersion switched to I & RARR; II & RARR; III & RARR; IV with the increasing rotation speed and decreasing off-bottom clearance. The liquid-liquid mass transfer rate was significantly enhanced with the collision of the sedimentary liquid with the impeller bottom, and subsequently increased with the increasing rotation speed, volumetric liquid ratio, and vessel diameter and with the decreasing off-bottom clearance. A multiple regression analysis method was applied to determine the mass transfer rates of III and III'.

Si, Al, Cu, and Ag particles’ mixture which mainly composes pulverized silicon-based waste solar cells were individually separated by the batch flotation experiments with high recovery and content, and then a general flow chart of the sequential flotation procedure of n-component was postulated including 2-, 3-, and 4-components. The n-component mixture was separated to 1: n-1 or i: j (i + j = n) by a flotation procedure and n-1 times operation was necessary to divide into the individual component. The first flotation process to separate Al into the froth layer was carried out with a collector of SDS solution after dipping Si, Al, Cu, and Ag mixture into the SDS solution. Si was separated in the froth by the second flotation with a collector of a commercial neutral detergent after Al etching by HCl, and Si, Cu and Ag mixture dipped in the detergent. The Cu and Ag mixture was calcinated at 673 or 773 K and dipped into the detergent, and the third flotation with the collector of the detergent led to Cu in the froth and Ag in the sediment. The 4-component mixture was successfully separated into each component by the 3-consecutive flotation processes.

Radial directional solidification, in which a liquid is solidified toward the radial center, was explored as a technique for recycling kerf loss silicon powder into SOG-Si. The purification behavior of the metallic impurities Fe, Al, Ca, Mg, Ti, Mn, and Ni was examined experimentally and numerically. Specific resistivity after solidification achieved a range of 0.00029 to 0.00075 Ωm and an average value of 0.0005 Ωm. From the calculation of the concentration and specific resistivity profiles of each element in the silicon sludge, specific resistivity was estimated to be determined by Fe and Ca. The Fe and Al concentration profiles in three different directional solidification practices were computed under the same solidification time and distance conditions. In radial directional solidification, Fe purification was promoted most strongly close to the solid fraction of 0.8 and then rapidly diminished. This purification behavior depended on the lower instantaneous solidification rate in the radial direction at the position before the solid fraction of 0.8 and was followed rapidly by a higher solidification rate. Al purification in the radial directional solidification practice was slightly different from that in longitudinal solidification due to the small difference in the effective distribution coefficient in this calculation situation.

In this study, floatability rate of aluminum (Al) powders was analyzed for the purpose of separating valuable resources from residual materials in waste photovoltaic (PV) solar cells, and equations for flotation recovery were developed for various flotation types according to the rate-determining steps of the gas flowrate and feed rate. The flotation rate became a zero-order reaction at the rate-determining step of the gas flow rate and had the same form between a batch and continuous typed practices by substituting residence time with real time. Under the rate-determining step of the feed rate, the flotation rate was expressed by the linear combination of the first-order reaction of an even group material. The flotation recovery rate of Al powders was analyzed by the data of a batch floatability experiment and indicated by the linear expression of the first-order reaction of two groups due to the rate-determining step of the feed rate. The calculated separation recovery of n-cell type device increased as the number of cells increased and approached that of the batch and column types.

The effect of ultrasonic irradiation on direct maghemite (gamma-Fe2O3) preparation by a co-precipitation method with Fe3+ salt (Fe(NO3)(3)) and an excess amount of alkaline (KOH) solution without going through the conventional magnetite (Fe3O4) formation route was explored in comparison with impeller stirring. The preparation procedure for obtaining iron oxide nanoparticles was designed using the sequential processes of precipitation, decantation, drying and thermal dehydration, and ultrasonic irradiation or impeller stirring was done during the precipitation process. gamma-ferric oxyhydroxide (gamma-FeOOH) was partially formed in addition to alpha-ferric oxyhydroxide (alpha-FeOOH) and thermally dehydrated to gamma-Fe2O3 and hematite (alpha-Fe2O3) by ultrasonic-assisted co-precipitation of Fe3+ salt and the excess KOH solution, whereas only alpha-FeOOH and alpha-Fe2O3 were synthesized by impeller stirring. The difference between the products of the two methods was explained by the Lamer model associated with the nucleation and growth of FeOOH. Magnetization increased as the crystallite diameter decreased, which is estimated to facilitate partial formation of magnetic gamma-Fe2O3. Magnetization was enhanced by a lower ultrasonic frequency due to the stronger shock wave induced by the cavitation effect.

In this study, the effects of impeller rotation speed, off-bottom clearance, blade angle, types of solid and liquid, etc., on the suspension pattern of sedimentary particles and particle rise height in liquid were investigated with a hemispherical vessel without baffles under low particle concentration. The transition conditions of suspension pattern between regimes I and II, and regimes II and III, were observed visually, and their non-dimensional equations were expressed with an acceptable correlation by varying the above operation factors a great deal. Here, regime I is stagnation of particles on a vessel bottom, II is partial suspension, and III is complete suspension in liquid. The non-dimensional equation of the maximum particle rise height was also successfully obtained. The combination of the non-dimensional equations of transition and maximum particle rise height permitted us to determine the adequate solid/liquid mixing operation conditions without collision of particles with device parts.

Agglomeration, coalescence and flotation of non-metallic inclusions in steel melt are effective for obtaining "clean steel." In this study, the agglomeration and breakup behaviors of particles with a primary particle size distribution (hereinafter, polydisperse particles) in a liquid under impeller and gas stirring were compared by numerical calculations and model experiments. The particle-size-grouping (PSG) method in the numerical agglomeration model of particles was combined with a breakup term of agglomeration due to bubble bursting at the free surface. Polydisperse and monodisperse polymethylmethacrylate (PMMA) particles were used in the agglomeration experiments. The agglomeration rate of the polydisperse particles under impeller stirring was increased by an increasing energy input rate, whereas the agglomeration rate under gas stirring decreased under this condition due to the larger contribution of the breakup of agglomerated particles during bubble bursting in gas stirring. At the same energy input rate, agglomeration of polydisperse particles was larger under impeller stirring than under gas stirring. The agglomeration rate of polydisperse particles was larger than that of monodisperse particles under both impeller and gas stirring at the same energy input rate. The computational temporal changes in the total number of particles were in good agreement with the experimental results. This means that the difference in the agglomeration behaviors observed in impeller and gas stirring can be explained by the turbulent coagulation and subsequent agglomerated particle breakup in gas stirring. The computational temporal change in the number of each group approximately agreed with the experimental change in both impeller and gas stirring.

Zinc (Zn) removal by physically mixed particles of zero-valent iron (Fe) and iron sulfide (FeS) was investigated as one technology for Zn removal from waste groundwater. The effects of the Fe/FeS mass ratio, including a single Fe and FeS particles, and pH on changes in the concentrations of Zn, Fe, and S were examined by a batch test and column tests, and the mechanism of Zn elimination was discussed. Among all the mixing fractions of Fe and FeS, Zn was eliminated most effectively by 3Fe/7FeS (mass ratio of Fe/FeS = 3/7). The Zn removal rate decreased in the order of 3Fe/7FeS, FeS, and Fe, whereas the Fe concentration decreased in the order of Fe, FeS, and 3Fe/7FeS. The S concentration of FeS was larger than that of 3Fe/7FeS. The Zn removal rate by physically mixed 3Fe/7FeS particles was enhanced by a local cell reaction between the Fe and FeS particles. The electrons caused by Fe corrosion moved to the FeS surface and reduced the dissolved oxygen in the solution. Zn2+, Fe2+, and OH− ions in the solution were then coprecipitated on the particles as ZnFe2(OH)6 and oxidized to ZnFe2O4. Moreover, Zn2+ was sulfurized as ZnS by both the Fe/FeS mixture and the simple FeS particles. The Zn removal rate increased with increasing pH in the range from pH 3 to 7. From a kinetic analysis of Zn removal, the rate constant of anode (Fe)/cathode (FeS) reaction was almost the same as that of ZnS formation and slightly larger than that of Fe alone.

In order to explore the possibility of efficient chlorine removal from the poly (vinyl chloride) (PVC) containing waste plastics, simultaneous degradation and dechlorination of PVC at a relatively low temperature was investigated by changing the atmosphere gas and metal oxide as catalyst and/or adsorbent (catalyst/adsorbent). 5.0 g of PVC and various metallic oxides such as CaO, Fe3O4, SiO2, Al2O, Ca(OH)(2), MgO were used under the superheated steam and nitrogen atmosphere of 473 K. The degradation rate of the PVC sample was small and the chlorine conversion to inorganic chloride was not observed without catalyst/adsorbent in the presence of either superheated steam or nitrogen atmosphere. Under the superheated steam atmosphere, the CaO catalyst/adsorbent resulted in much larger rates of degradation and dechlorination than any other metal oxides such as Fe3O4, SiO2, Al2O, Ca(OH)(2), MgO compared with nitrogen atmosphere. The calcium compounds such as CaCl2, CaClOH and Ca(OH)(2) were formed in the sample by the combination of CaO catalyst/adsorbent and superheated steam. The rates of PVC degradation and chlorine conversion to inorganic chlorides were dramatically enhanced beyond the stoichiometric CaO amount for the CaCl2 formation reaction with PVC under the superheated steam atmosphere. (C) 2020 Elsevier Ltd. All rights reserved.

The alkali elution behavior of steelmaking slag in seawater was kinetically investigated and simulated under continuous flow in an open channel vessel with packed bed of steelmaking slag. Two types of steelmaking slags, viz. decarburization slag and dephosphorization slag, were used in this study. The alkali elution rate of decarburization slag was larger than that of dephosphorization slag due to larger free CaO content. The pH value for dephosphorization slag was almost the same as the seawater pH value in 3–4 days, whereas that for decarburization slag was stabilized in 3 days although the pH value was slightly larger than that of seawater. The capacity coefficients of alkali elution for dephosphorization and decarburization slags decreased together in an exponential manner with time. Based on a regression equation on the mass transfer capacity coefficient change with time, the alkali elution behavior was simulated and the calculated results agreed well with the experimental ones. The temporal pH change was predicted by changing slag surface area and seawater flow rate as a parameter. According to the simulation results for dephosphorization slag, the seawater pH value did not reach a high level in the ocean area.

The solid/liquid mass transfer rate of particles stagnation on vessel bottom and partial suspension in liquid was insufficiently known compared with that of completely suspended condition. In this study, the effect of suspension regime of sedimentary particles on the solid/liquid mass transfer rate in a mechanically stirred vessel without baffles was investigated. The solid/liquid mass transfer rate increased slightly with the increasing rotation speed at the stagnation regime; its rapid enhancement was found at the partially suspended regime, and the increasing rate became slow again at the complete suspension. Nondimensional equations for solid/liquid mass transfer rate of stagnation and completely suspended conditions were obtained with a good correlation. On the other hand, the suspended particle ratio under the partial suspension condition was estimated by the mass transfer rate of stagnation and completely suspended regimes and followed an S curve against the normalized rotation speed.

Steelmaking slag has been used in the coastal area for the purpose of the environmental improvement. Short-term alkali elution behavior induced by free CaO in the steelmaking slag was investigated by a batch and continuous vessel. In this study, long-term alkali elution experiments were done in an open channel vessel with a slag box to make clear the decreasing mechanism of the alkali elution from steelmaking slag into seawater. The experimental period was 44 d (1056 h). The pH values increased just in the beginning of the experiment, and then gradually decreased in about 100 min. They showed almost the same value as that of seawater in 1200 min. As the experimental time passed, the white deposits on the steelmaking slag layer, which were composed of Mg[OH](2) and CaCO3, spread to the lower slag zone in the slag box. The white deposit zone of larger slag size was more rapidly diffused downward than that of smaller one due to larger voidage in the slag layer. While carrying out the batch test with the used slag by the long-term experiment, the alkali elution rate of slag layer on the open channel flow was 0.03-0.11 times decreased compared with the unused slag, whereas that of the lower positioned slag layer was 0.10-0.38 times decreased. From these results, it was found that the alkali elution rate was reduced by the white deposit on the steelmaking slag.

In this study, we investigated the chemical composition of dissolved solids in the Ca River basin, North-Central Vietnam. Water samples were collected from August 2017 to July 2018 at three hydrological stations located in the main stream of the Ca River. Carbonate weathering was found as the dominant process controlling the water chemistry in that area. The average concentrations of dissolved solids generally decreased from upstream to downstream, resulting in low concentrations of the major ions in the downstream basin. Variations in the concentrations of major chemical ions and suspended solids at discharge were also investigated. Major chemical weathering products were found to behave chemostatically with increasing discharges upstream. However, dilution behaviors of solutes were shown in both midstream and downstream. Primary evidence shows that water storage in reservoirs impacts a variety of suspended solids and dissolved solids in the Ca River.

There are few study examples on the separation of metals by floating method. In this study, separation of silicon and aluminum, which are the main components of silicon-based solar cell module, was carried out by floating method in order to purify silicon from waste solar cell module. The selection of surfactant, control of electric charge, wettability of the solid particles, surface tensions, and bubble surface area are important for separation of solids by floating method. Sodium dodecyl sulfate (SDS) can increase the hydrophobicity of aluminum powder due to the difference of surface potentials between silicon and aluminum. SDS behaves as a collector of aluminum as well as a frothing agent to decrease the bubble size. At a SDS concentration of 2 g/L and sample dipping time of 10 min, 80.1 mass% of aluminum was floated and separated, and the sedimentary silicon reached a purity of 90.7% from a mixture of 50 mass% aluminum and 50 mass% silicon. Finally, at a pH value of 7.0, SDS concentration between 1.0 and 2.5 g/L and air flow rate of 2.5 L/min (STP) were suitable experimental conditions to purify silicon from a mixture of silicon and aluminum by flotation separation method.

It is important to remove nonmetallic inclusions from molten steel by agglomeration, coalescence and flotation1–5) for the purpose of obtaining clean steel. Many experimental and theoretical studies have been done on the agglomeration behavior of fine particles in liquid: agglomeration structure by using a fractal dimension,6–11) wettability of particles,12,13) heterogeneous agglomeration with a different surface electrification and size,14–18) particle collision frequency in turbulent flow,19,20) particle-size grouping.21) However, there are few studies on comparison of the particle agglomeration behavior among various mixing operations, although it is indispensable for the optimal mixing operation and design. In this study, experiments were conducted for three kinds of mixing operations: mechanical stirring by impeller (impeller mixing), gas blow mixing (gas mixing), and gas and liquid mixing by RH degasser (RH mixing) in order to compare the agglomeration rate of fine particles among three mixing operations. The theoretical model on the particle agglomeration coexisting with the breakage of particles was next developed and evaluated. There were some theoretical and experimental studies on the particle breakup by particles collision22,23) and fluid Comparison of Agglomeration Behavior of Fine Particles in Liquid among Various Mixing Operations

Chlorine removal from polyvinyl chloride (PVC) with the addition of catalysts, such as solid acid catalysts, and adsorbents, such as alkali and metal oxide, including a multiple one, was described using superheated steam and nitrogen as pyrolysis media in this research. The effect of the dechlorination temperature indicated that the treatment temperature was an important factor to control the carbonization and dechlorination ratio of PVC. The addition of a single metal oxide, such as TiO2, MgO, and CoO, showed better dechlorination ability compared to beta-zeolite and NaOH. CoO had a higher dechlorination ability than TiO2 and MgO. The metal-oxide-supported adsorbent of ZnO/CoO, MgO/CoO, and NiO/CoO systems was prepared by the impregnation method to increase decomposition and chlorine capture ability of the adsorbent during dechlorination. The ZnO/CoO adsorbent achieved the highest dechlorination ratio and especially increased the dechlorination ratio of PVC at ZnO >= 25 wt % under a superheated steam atmosphere compared to CoO alone. CoCl2 center dot 2H(2)O was observed in the X-ray diffraction pattern of 25ZnO/CoO and 50ZnO/CoO adsorbents after PVC dechlorination. The PVC dechlorination in a nitrogen atmosphere had the same results as superheated steam with no additive and CoO adsorbent at 473 K. However, the addition of 25ZnO/CoO adsorbent at 473 K had a lower dechlorination ability than superheated steam. It is supposed to result from the formation of CoCl2 center dot 2H(2)O in a superheated steam atmosphere. To obtain a similar dechlorination ratio and solid production yield to no additive, 25ZnO/CoO and 50ZnO/CoO adsorbents were able to decrease the pyrolysis temperature from 523 to 473 K.

HgCl2 that was homogenously dispersed over activated carbon was prepared by an HCl solution method (HgCl2(HCl)/AC), in the present study. The speciation of HgCl2(HCl)/AC in simulated flue gases was further investigated by a temperature-programmed decomposition desorption mass spectroscopy method, to clarify its transformation mechanism. It was found that HgCl2 sublimation occurred after Hg-H2O pretreatment, evidenced by the disappearance of the desorption peak of HgCl2 at 80 degrees C. After Hg-H2O pretreatment, new species of HgCl2 were formed, as confirmed by similar peak intensities of HgCl2 at mass numbers 270 and 272 at 335 degrees C. The SO2-H2O or H2S-H2O pretreatment helped stabilize the HgCl2 species supported over the AC, as evidenced by the weaker desorption peak of HgCl2 at around 80 degrees C. For the HgCl2(HCl)/AC pretreated with SO2-H2O, four desorption peaks of mercury were found, at 280, 335, 380 and 480 degrees C, indicating that new mercury compounds were formed during pretreatment or the TPDD process. The mercury desorbed at 280 degrees C was derived from a mercury complex of [HgCl](2)SO4 center dot center dot center dot A-C, while the mercury desorbed at 480 degrees C resulted from HgSO4. Some HgO species might be formed and stabilized over the AC during the TPDD process, corresponding to two mercury desorption peaks at 335 and 380 degrees C. After the pretreatment of HgCl2(HCl)/AC with H2S-H2O, some HgCl2 were transformed to HgS and HgO species, as evidenced by the mercury desorption peaks at 280, 305 and 380 degrees C.

In this study, copper (Cu) and aluminum (Al) particles derived from waste crystalline silicon solar cell modules were etched with mixed acid containing HNO3 and HCl, and the optimal mixing conditions were examined for the purpose of recovering silicon with high yield. The crushed particles of waste silicon solar cells were used after sieving between 450 and 600 μm particle size. The Cu etching rate decreased with the increasing HCl concentration in the region of HNO3/HCl ≧ 3.36, whereas it increased at HNO3/HCl < 3.36. The Al etching rate increased when HCl was added, although it was almost independent of the amount of HNO3. 99.6% silicon purity was achieved at the treatment time of 30 min. The rate-determining step of Cu and Al etchings was represented by the volume reaction model instead of the surface reaction model. The CuCl coating was observed on the residuals of Cu. The increasing HCl blocked the Cu etching, but the excess Cl− promoted the dissolution of CuCl due to complex formation, corresponding to the regions of HNO3/HCl ≧ 3.36 and HNO3/HCl < 3.36, respectively. In the region of HNO3/HCl < 3.36, the spontaneous complete etching time of Cu and Al was achieved with higher HNO3 concentration of 8.5–10 mol/L.